JP2018183997A - Ion exchange membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion exchange membrane which has high air permeability while having such a laminated structure that a base material film and a porous resin film are joined to each together, and accordingly effectively suppresses high electric resistance by lamination of a base materiel sheet.SOLUTION: There is provided an ion exchange membrane in which a gap part of a porous base material film is filled with the ion exchange membrane, where the porous base material film has such a structure that at least two layers of porous olefin-based resin layers are laminated with a bond strength of 100 gf/cm or more and less than 700 gf/cm, and has air permeability of 500 sec/100 ml or less in terms of 100 μm.SELECTED DRAWING: None

Description

  The present invention has a porous olefin-based resin film through which a large number of fine pores penetrate as a base material, and an ion exchange membrane having a structure in which ion exchange resin is filled in the pores of the film, and It relates to a method of manufacturing the same.

  Ion exchange membranes are used as membranes for electrodialysis used in salt production and desalting processes in the food sector, electrolyte membranes for fuel cells, and for acid recovery from acids containing metal ions generated in the steel industry. It is used industrially in many fields such as diffusion dialysis membranes. Such an ion-exchange membrane has a structure in which a base film having a function as a reinforcing material is provided in an ion-exchange resin as a core material, thereby providing a certain membrane strength and membrane shape stability. Has been granted. If there is no core material, the ion exchange resin has a large number of ion exchange groups. Therefore, when immersed in an aqueous electrolyte solution, the ion exchange resin easily swells, and the ion exchange membrane undergoes a decrease in strength and a form change.

  Conventionally, it is known to use a porous thermoplastic resin film as the base film, and it is actually used. In such an ion exchange membrane based on a porous film, pores in the porous film as a substrate are filled with an ion exchange resin. As a result, the electric resistance of the membrane (hereinafter referred to as membrane resistance) Has the advantage of low). For example, Patent Document 1 discloses a cation exchange membrane for salt production containing a porous stretched polyethylene film (Hypore made by Asahi Kasei Corporation, Cetilla made by Tonen Chemical Nasu Co., Ltd.) as a base film.

  By the way, the use of the ion exchange membrane is various, and the scale of implementation is also different. Therefore, the size of the ion exchange membrane is also different, and depending on the size, the strength, dimensional stability, and morphological stability, etc. It is necessary to increase. For this reason, it is necessary to increase the thickness of the porous substrate film in the ion exchange membrane. Since this porous film is provided with a large number of pores, it is lower in strength than a film without such pores, and since there is no waist, it can be made thicker. This is because the strength of the ion exchange membrane is increased, and dimensional stability and form stability are improved.

  However, commercially available porous films have a limited thickness, and most have a thickness of about several tens of μm. This is because if a porous film having an appropriate thickness is produced according to the use and size of the ion exchange membrane, the production becomes a small amount and the industrial merit is impaired.

  Therefore, a commercially available porous film with a limited thickness is laminated, and an ion exchange membrane is produced using this laminated film as a base film. Lamination means becomes a problem.

For example, Patent Document 2 discloses an ion exchange membrane that includes a porous film obtained by laminating two porous resin sheets and bonded by thermal fusion at a temperature equal to or higher than the melting point as a base film. Since bonding is performed by thermal fusion at a temperature equal to or higher than the melting point, there is a problem that pores formed in the porous film are blocked. That is, such a base film has high air permeability, and an ion exchange membrane formed using the base film has high electrical resistance. Therefore, in Patent Document 2, a fibrous resin sheet (specifically, a fibril-like sheet) is used as the porous resin sheet to be laminated, and the porosity (porosity) is increased to increase the pores due to heat fusion. The increase in the air permeability and the high electrical resistance of the ion exchange membrane resulting from the blockage of the ion are suppressed.
However, when a fibrous film is used as the base film, the porosity becomes too large, and naturally the mechanical strength cannot be reduced, and the thickness of the base film must be increased more than necessary. Cause problems. Therefore, this means cannot use a general olefin resin, and for this reason, Patent Document 2 uses a polytetrafluoroethylene, which results in a very high cost. End up.

Further, in Patent Document 3, the applicant of the present invention filled the monomer composition for forming an ion exchange resin into the voids of a plurality of stacked porous resin sheets (laminated sheets) without bonding, There has been proposed a method for producing an ion exchange membrane by polymerizing the monomer composition in this state to obtain an ion exchange resin.
In this method, the porous resin sheets are not directly joined to each other but are joined by the ion exchange resin filled in the voids (pores). The problem of pore clogging can be completely avoided, the high electrical resistance of the ion exchange membrane can be reliably prevented, and an expensive special resin such as polytetrafluoroethylene is used as the material of the porous resin sheet There is no need to use this, and the cost advantage is great. However, in this method, since the porous resin sheets are not joined to each other, there is a problem that interfacial peeling is likely to occur between the porous resin sheets, and further improvement is necessary.

JP 2009-96923 A JP 2008-4500 A JP2012-21099A

  Accordingly, an object of the present invention is to provide an ion in which the base film is a porous resin film bonded to each other, but has a low air permeability, and therefore, the high electrical resistance due to the lamination of the base sheet is effectively suppressed. An object of the present invention is to provide an exchange membrane and a manufacturing method thereof.

  According to the present invention, in the ion exchange membrane in which the void portion of the porous substrate film is filled with the ion exchange resin, the porous substrate film has at least two porous olefin-based resin layers of 100 gf / cm. As described above, there is provided an ion exchange membrane characterized in that it has a laminated structure with a bonding strength of less than 700 gf / cm, and has an air permeability of 100 μm thickness conversion of 500 sec / 100 ml or less. The

According to the invention,
Providing at least two porous olefin-based resin films;
A step of producing a porous substrate film having a laminated structure by superposing the plurality of porous olefin-based resin films, heating to a temperature of -20 ° C. or higher and lower than the melting point, and stretching and molding;
A step of immersing the porous substrate film in a polymerizable composition for forming an ion exchange resin to produce an ion exchange membrane precursor in which voids of the film are filled with the polymerizable composition;
Polymerizing the polymerizable composition in the ion exchange membrane precursor;
A process for producing an ion exchange membrane characterized by comprising:

In the production method of the present invention,
(1) Each of the plurality of porous olefin-based resin films has a porosity of 20 to 60%,
Is preferred, and
(2) As the polymerizable composition for forming the ion exchange resin, a composition containing a monomer having an ion exchange group is used, and the ion exchange resin is formed by the polymerization.
Or
(3) As the polymerizable composition for forming the ion exchange resin, a composition containing a monomer having a functional group capable of introducing an ion exchange group is used, and the ion exchange group is introduced after the polymerization. ,
The following means can be adopted.

In the ion exchange membrane of the present invention, a substrate film having a laminated structure in which at least two porous olefin resin films are superposed is used. The bonding strength of the porous olefin-based resin film layer is as high as 100 gf / cm or more, and while having such a high laminated structure, its air permeability is extremely low as 500 sec / 100 ml or less in terms of 100 μm thickness. . That is, such low air permeability means that this laminated structure is not formed by joining porous olefin-based resin films by thermal fusion, and clogging of pores in the film. Is effectively avoided.
Therefore, in the ion exchange membrane of the present invention, the strength is improved by the laminated structure of the base film with high bonding strength, and furthermore, blockage of pores in the base film due to the lamination is effectively avoided. The increase in electrical resistance due to the lamination is effectively suppressed.

  In the present invention, the above laminated structure of the base film, that is, a laminated structure exhibiting a high bonding strength while having a low air permeability, has a temperature close to the melting point (melting point − This is realized by performing stretch molding at a temperature of 20 ° C. or higher and lower than the melting point. That is, at the interface of the porous olefin resin films facing each other, the long chain molecules of the olefin resin are entangled by the stretching operation, and as a result, the porous olefin resin film is laminated with the above high bonding strength. Will be. In addition, the laminated film thus obtained has a characteristic that the burst strength is improved as compared with a single-layer porous film having the same thickness. In addition, since the stretching operation is at a temperature close to the melting point, but below the melting point, unlike the joining by heat fusion, clogging of fine pores in the porous olefin resin is effectively avoided, and thus low permeability. It is possible to secure the mood.

In such the present invention, the greatest advantage is that an unstretched porous olefin-based resin film having a limited thickness that is easy to manufacture and obtain is used, and this is laminated by the stretching operation by the above-described method. Is set to an appropriate number and the thickness can be increased to obtain a high-strength base film. That is, a single layer thick porous film equivalent to the base film used in the present invention can be produced by a known method. However, depending on the intended strength, it is not feasible to produce a porous film having such a thickness each time. That is, because the use is remarkably limited, mass production on an industrial basis cannot be performed, and it is not profitable to produce in small quantities.
However, in the present invention, a porous olefin resin film having a limited thickness that is easy to manufacture and obtain is used, and this is laminated, and the bonding strength is high and the thickness is high without increasing the air permeability. Since a porous laminated film can be produced, an ion exchange membrane can be produced using this as a base film. That is, even if the base film has a thickness that is not suitable for mass production due to limited use, it can be easily produced using a film having a thickness that is easy to manufacture and obtain. Very useful.

It is a schematic sectional drawing of the porous base film used for preparation of the ion exchange membrane of this invention.

<Porous substrate film>
A description will be given with reference to FIG. The porous substrate film used in the present invention (shown as 1 as a whole) has a laminated structure in which two porous olefin resin layers 3 and 3 are laminated. This stacking interface is indicated by 5.
In addition, although it has a two-layer structure in FIG. 1, the number of layers is not limited to two, and each layer is formed of a porous olefin resin and can be stretched in a superposed state. As long as it is, the number of layers may be three or more. That is, the number of laminated layers can be set to an appropriate number according to the strength or thickness required for the porous substrate film 1.

  The porous olefin-based resin layer 3 has a large number of fine pores (the reference numerals are omitted) penetrating from the front surface to the back surface. For example, when used as a base film for an ion exchange membrane, the average pore diameter of the pores (observed on the front or back surface) is 0.01 to 2.0 μm, particularly 0 so that appropriate exchange membrane characteristics can be obtained. It is set to about .015 to 0.4 μm.

  Further, in the present invention, the volume ratio occupied by the pores having such a size, that is, the porosity is preferably in the range of 20 to 65%, particularly 30 to 60%. That is, when the porosity is excessively large, for example, when the resin layer 3 is formed of a fibrous material such as a non-woven sheet, the strength of the layer 3 is considerably reduced, and the effect of improving the strength by lamination is obtained. There is a risk that it may be damaged and the dimensional stability may also be lost. Moreover, when this porosity is too low, when manufacturing an ion exchange membrane using this base film 1, it will become high electrical resistance and there exists a possibility that an ion exchange membrane characteristic may be impaired.

  Furthermore, the thickness of the porous olefin resin layer 3 is about 20 to 150 μm.

Examples of the olefin resin forming the porous olefin resin layer 3 include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, and 4-methyl-1-pentene. , Homopolymers or copolymers of α-olefins such as 5-methyl-1-heptene, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-olefin copolymers Typical examples include chlorine-containing olefin resins such as coalescence.
The olefin resin also includes a fluorine resin such as polytetrafluoroethylene, but such a fluorine-containing resin is difficult to form non-fibrous pores. Non-fluorinated olefinic resins, particularly high, medium or low density polyethylenes are preferred as exemplified above because bonding is also difficult (probably because the molecules are difficult to expand and contract), and the intrinsic viscosity [η ] Is most suitable for high-density polyethylene having a value exceeding 1.5 dl / g.

  The porous olefin-based resin layers 3 and 3 described above need to be stretched, and the stretching direction agrees with the winding direction of the film (the length direction of the film or the direction of discharging the raw material resin during film formation. Although it may be abbreviated as “MD” and its vertical direction (which agrees with the width direction of the film; hereinafter, abbreviated as “TD”), it may be either uniaxial or biaxial stretching. It is preferably stretched at a stretch ratio of at least 1.2 times, particularly 1.4 times or more in the MD direction, and at a stretch ratio of at least 1.2 times, particularly 1.5 times or more in the TD direction. The film is preferably stretched, and the total stretching ratio is preferably 10 times or less. This is because if the draw ratio is small, the bonding strength described later will be low.

  The porous base film 1 having a laminated structure composed of the above-described porous olefin resin layers 3 and 3 is, for example, an additive for pore formation (paraffin or Using a resin composition containing an inorganic powder, etc., a film having a predetermined thickness is formed by extrusion molding or the like, and then the additive contained in the film is removed by extraction with an organic solvent, dissolution with an acid or alkali, etc. After that, a predetermined number (two in FIG. 1) of the obtained unstretched porous olefin resin film is overlaid and stretched.

In the above, the stretching operation is performed in a state where a predetermined number of unstretched porous olefin resin films are overlapped, and stretched at a predetermined stretching ratio in a uniaxial direction or a biaxial direction using a roll, a tenter, or the like. In addition to this, it is preferable to perform heat setting such as heat fixation or heat relaxation in order to improve heat shrinkage resistance.
Further, heat treatment such as stretching and heat setting or heat relaxation is naturally performed at a temperature lower than the melting point, but in the present invention, it is necessary to perform in a temperature region close to the melting point, in particular, a melting point of −20 ° C. or more, In particular, it is preferable to carry out in the temperature range of -15 ° C to -1 ° C in order to obtain good bonding strength. The reason why good bonding strength can be obtained by selecting the temperature is not clear, but is considered as follows. That is, by overlapping in a state close to the melting point in this way, molecules of the olefin resin enter the inside of the interface at the interface 5 of the porous olefin resin film. Subsequently, the olefin resin molecules are stretched by the stretching operation, and entanglement occurs. Subsequent cooling fixes this entanglement, and the porous olefin resin films are bonded to each other with high bonding strength to form the porous base film 1 having a laminated structure composed of the porous olefin resin layers 3 and 3 described above. Will be.
The film thickness of the porous substrate film 1 is not particularly limited, but is usually 40 to 250 μm. From the viewpoint of freely obtaining a thick ion exchange membrane, it is preferably 80 to 250 μm.

In the porous base film 1 formed as described above, the bonding strength of the porous olefin resin layers 3 and 3 is extremely high as 100 gf / cm or more and less than 700 gf / cm, particularly 150 to 550 gf / cm. In this patent, the unit of gf / cm is used, but when the SI unit system is used, conversion is performed with gf / cm = 0.008 N / cm.
Surprisingly, when the bonding strength is in the range of 100 gf / cm or more and less than 700 gf / cm, good burst strength and membrane resistance per unit thickness can be obtained. Although it is not clear that a good burst strength per unit thickness and membrane resistance can be obtained when the bonding strength is in the above range, it is considered as follows. The porous olefin resin film is kept low in air permeability by being superposed and stretched at a temperature close to the melting point without pressing (pressing) the porous olefin resin film in a direction perpendicular to the surface. I can do it. Further, when the stretching is performed, the molecular entanglement at the interface portion described above is generated, so that the pore diameter of the interface portion becomes denser than that of the film surface portion, thereby improving the membrane breaking strength per unit thickness. As a result, it is considered that better burst strength and membrane resistance can be obtained as compared with a microporous membrane laminated by pressing in a direction perpendicular to the surface. In addition, when the porous olefin resin layers 3 and 3 are laminated and joined, the fine pores formed in the porous olefin resin film are not blocked because they are not heated above the melting point. Therefore, the air permeability of the base film 1 is low, and the air permeability in terms of 100 μm is 500 sec / 100 ml or less, particularly in the range of 100 to 300 sec / 100 ml.

<Ion exchange membrane>
The ion exchange membrane of the present invention has a structure in which the void portion (that is, pores that are not closed) of the porous base film 1 formed as described above is filled with an ion exchange resin, The laminated structure of the porous substrate film 1 provides high strength, and further, the deterioration of the film characteristics resulting from high electrical resistance due to lamination is effectively avoided.

Ion exchange resins;
The ion exchange resin filled in the pores of the porous substrate film 1 may be a known one, for example, an ion exchange group that allows the hydrocarbon-based or fluorine-based resin to exhibit an ion-exchange ability, specifically Are those into which a cation exchange group or an anion exchange group has been introduced.

Examples of the hydrocarbon resins include styrene resins and acrylic resins, and examples of the fluorine-based materials include perfluorocarbon resins.
The ion exchange group is a functional group that can be negatively or positively charged in an aqueous solution. In the case of a cation exchange group, examples thereof include a sulfonic acid group, a carboxylic acid group, and a phosphonic acid group. A sulfonic acid group which is a strongly acidic group is preferred. In the case of an anion exchange group, examples thereof include primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, and quaternary pyridinium groups. Groups and quaternary pyridinium groups are preferred.

  The ion exchange resin having an ion exchange group as described above has an appropriate ion exchange capacity (for example, depending on the porosity of the porous base film 1 described above and the amount of ion exchange groups introduced into the ion exchange resin (for example, , About 0.1 to 4.0 meq / g) in the ion exchange membrane.

<Manufacture of ion exchange membrane>
In the present invention, the ion exchange membrane having the porous base film 1 described above prepares a polymerizable composition for forming an ion exchange resin (preparation of a polymerizable composition), and in such a polymerizable composition In addition, the porous base film 1 is dipped to fill the pores in the film 1 with the polymerizable composition (filling the polymerizable composition), and then the polymerizability filled in the pores. It is produced by polymerizing the composition and, if necessary, introducing ion exchange groups into the polymer (ion exchange resin precursor) obtained in the polymerization step (ion exchange group introduction step).

1. Preparation of polymerizable composition;
The polymerizable composition for forming an ion exchange group is a monomer having an ion exchange group or a monomer having an ion exchange group (hereinafter referred to as a functional group for introducing an exchange group). These monomers are sometimes referred to as “basic monomer components”), contain a crosslinking monomer and a polymerization initiator, and are prepared by mixing these components.

  The monomer having a functional group for introducing an exchange group and the monomer having an ion exchange group may be those conventionally used for producing an ion exchange resin.

Examples of the monomer having a functional group for introducing a cation exchange group include styrene, vinyl toluene, vinyl xylene, α-methyl styrene, vinyl naphthalene, α-halogenated styrenes and the like.
Examples of the monomer having a functional group for introducing an anion exchange group include styrene, bromobutyl styrene, vinyl toluene, chloromethyl styrene, vinyl pyridine, vinyl imidazole, α-methyl styrene, vinyl naphthalene and the like.

Examples of the monomer having a cation exchange group include sulfonic acid monomers such as α-halogenated vinyl sulfonic acid, styrene sulfonic acid, and vinyl sulfonic acid, and carboxylic acid monomers such as methacrylic acid, acrylic acid, and maleic anhydride. Examples thereof include monomers, phosphonic acid monomers such as vinyl phosphoric acid, salts and esters thereof, and the like.
Examples of the monomer having an anion exchange group include amine monomers such as vinylbenzyltrimethylamine, [4- (4-vinylphenyl) -methyl] -trimethylamine, and vinylbenzyltriethylamine, vinylpyridine, vinylimidazole, and the like. And nitrogen-containing heterocyclic monomers, salts and esters thereof.

  In addition, when a monomer having an ion exchange group is used as the monomer as described above, a target ion exchange membrane can be obtained at the stage where the polymerization step described later is completed. When a monomer having a functional group for use is used, a target ion exchange membrane can be obtained by carrying out an ion exchange group introduction step after the polymerization step.

The crosslinkable monomer is used to densify the ion exchange resin and enhance swelling suppression, membrane strength, etc., and is not particularly limited. For example, divinylbenzene, divinylsulfone , Divinyl compounds such as butadiene, chloroprene, divinylbiphenyl, trivinylbenzenes, divinylnaphthalene, diallylamine, and divinylpyridine.
Such a crosslinkable monomer is generally preferably 0.1 to 50 parts by weight, more preferably 1 to 40 parts by weight with respect to 100 parts by weight of the basic monomer component described above.

  Furthermore, in addition to the above-mentioned monomer having a functional group for introducing an exchange group, a monomer having an ion exchange group, and a crosslinkable monomer, other copolymerizable with these monomers as required. These monomers may be added. Examples of such other monomers include styrene, acrylonitrile, methylstyrene, acrolein, methyl vinyl ketone, and vinyl biphenyl.

As the polymerization initiator, conventionally known polymerization initiators are used without particular limitation. Specifically, octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxylaurate, t- Organic peroxides such as hexyl peroxybenzoate and di-t-butyl peroxide are used.
Such a polymerization initiator is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the basic monomer component.

In order to adjust the viscosity, a matrix resin can be blended with the polymerizable composition containing the above-described various components as necessary.
Examples of such matrix resins include, for example, saturated aliphatic hydrocarbon polymers such as ethylene-propylene copolymers and polybutylene, styrene polymers such as styrene-butadiene copolymers, polyvinyl chloride, and various kinds thereof. Styrene monomers such as vinyltoluene, vinylxylene, chlorostyrene, chloromethylstyrene, α-methylstyrene, α-halogenated styrene, α, β, β'-trihalogenated styrene, ethylene, butylene, etc. Or a conjugated diolefin such as butadiene or isoprene) can be used.
These matrix resins are used in such an amount that the polymerizable composition has a viscosity that can be quickly filled and held in the pores of the porous substrate film 1 without causing dripping or the like.

2. Filling the polymerizable composition;
Filling into the pores of the porous substrate film 1 is performed, for example, by immersing the film 1 in a tank filled with the polymerizable composition described above. By this immersion, an ion exchange membrane precursor in which the polymerizable composition is filled in the pores of the porous substrate film 1 is obtained.
Of course, the polymerizable composition can be filled by spray coating or the like instead of dipping.

3. polymerization;
As described above, the ion exchange membrane precursor in which the polymerizable composition is filled in the pores of the porous substrate film 1 is heated and polymerized in a polymerization apparatus such as a heating oven.
When a monomer having an ion exchange group is used as the basic monomer component, the intended ion exchange membrane can be obtained by completing this step. When a monomer having a functional group for introducing an exchange group is used as a basic component, it is necessary to introduce an ion exchange group after completion of this step.

In this polymerization step, generally, a method is adopted in which an ion exchange membrane precursor filled with a polymerizable composition is sandwiched between films of polyester or the like and heated from room temperature under pressure. The pressurization is generally performed at a pressure of about 0.1 to 1.0 MPa by pressurization with an inert gas such as nitrogen or a roll. By this pressurization, polymerization is performed in a state in which an excess polymerizable composition present at the outer interface of the film 1 is pushed into the pores of the film, thereby effectively preventing the occurrence of resin accumulation and the like. be able to.
Further, the polymerization conditions depend on the type of polymerization initiator, the type of monomer, and the like, and may be appropriately selected and determined from known conditions.

The polymerization temperature may be a temperature lower than the melting point of the olefin resin forming the porous substrate film 1 and is generally in the range of about 40 to 130 ° C. in the case of a polyethylene film.
The polymerization time varies depending on the polymerization temperature and the like, but is generally about 3 to 20 hours.

4). Ion exchange group introduction;
As described above, when a monomer having an ion exchange group is used as a basic monomer component in the polymerization composition, an ion exchange resin is formed by the above polymerization process. However, when a monomer having a functional group for introducing an exchange group is used as a basic monomer component, the resin obtained in the above polymerization step has an ion exchange group. Therefore, it is necessary to introduce ion exchange groups after the polymerization step.

The introduction of the ion exchange group is carried out by a method known per se. For example, in the case of producing a cation exchange membrane, it is carried out by a treatment such as sulfonation, chlorosulfonation, phosphoniumation, hydrolysis, and the like. When producing an exchange membrane, it is carried out by a process such as amination or alkylation.
The ion exchange membrane of the present invention obtained as described above has a characteristic that it has a high burst strength even if the membrane resistance is the same. Generally, the film resistance in terms of thickness of 1 cm indicates 50 to 300 Ω · cm ² / cm, and the burst strength in terms of thickness of 1 cm is 30 to 70 MPa / cm.

The ion exchange membrane thus formed is appropriately cut into an appropriate size and used or sold.
Such an ion exchange membrane has a high strength depending on the number of laminated porous base film 1, and the blockage of pores of the film 1 is effectively avoided, and the base film 1 exhibits high air permeability. Therefore, since the ion exchange resin filled in the pores has a portion that is effectively continuous from the front surface to the back surface of the base film 1, its electric resistance is low, and high electric power by lamination Resistance is suppressed and ion exchange characteristics are also good.

The invention is illustrated by the following experimental example.
Various characteristics of the porous substrate film and the ion exchange membrane were measured by the following methods.

1. Film thickness of porous substrate film Using a micro thickness gauge (type KBN (trademark), terminal diameter Φ5 mm, measuring pressure 62.47 kPa) manufactured by Toyo Seiki, measurement is performed at an ambient temperature of 23 ± 2 ° C.

2. Membrane melting point of porous substrate film Measured by using DSC-220C manufactured by Seiko Denshi Kogyo Co., Ltd. A porous substrate film was punched into a circle with a diameter of 5 mm, and several sheets were stacked to give 3 mg, which was used as a measurement sample. This was spread on an aluminum open sample pan having a diameter of 5 mm, and a clamping cover was placed thereon and fixed in the aluminum pan with a sample sealer. Under a nitrogen atmosphere, the temperature was increased from 30 ° C. to 180 ° C. at a rate of temperature increase of 10 ° C./min, and the temperature at which the melting endotherm curve was maximized was taken as the film melting point. When there were a plurality of melting curve peaks, the temperature of the peak with the largest peak area was taken as the film melting point.

3. Bonding strength of porous substrate film A sample with a part of the bonding surface peeled off in advance at a width of 15 mm and a length of 150 mm at 25 ° C. and 65% relative humidity was prepared, and a tensile tester (Autograph AGS manufactured by Shimadzu Corporation) was prepared. -X) was set in the T state at a chuck distance of 75 mm, and the bonding force was measured at a speed of 500 mm / min. The bonding strength was determined from the measured bonding force by the following formula.
Bonding strength (gf / cm) = bonding force (gf) / sample width (cm)

4). The air permeability of the porous base film was measured using a Gurley type air permeability meter according to JIS P-8117. In this specification, the air resistance is expressed as air permeability. Based on this measured value, it is converted to a thickness of 100 μm to obtain the air permeability.
Air permeability (sec / 100 ml) = Measured air permeability (sec / 100 ml) × 100 (μm) / film thickness (μm)

5. Porosity of porous substrate film A rectangular sample of Xcm × Ycm was cut out and calculated by the following equation (1).
Porosity (%) = {1− (10000 × M / ρ) / (X × Y × T)} × 100 (1)
(1) In the formula, T: sample thickness (μm), M: sample weight (g),
ρ: Resin density (g / cm ³ )

6). The average pore diameter of the porous base film was measured by a half dry method in accordance with ASTM-F316-86.

7). Intrinsic viscosity [η]
[η] was measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020.

8). Ion exchange capacity and water content of the ion exchange membrane The ion exchange membrane is immersed in a 1 mol / l-HCl aqueous solution for 10 hours or more.
Thereafter, in the case of a cation exchange membrane, the counter ion of the ion exchange group is replaced with sodium ion from sodium ion with 1 mol / l-NaCl aqueous solution, and the liberated hydrogen ion is subjected to potentiometric titration using an aqueous sodium hydroxide solution ( COMMITITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) (Amol). On the other hand, in the case of an anion exchange membrane, a counter ion is substituted from a chloride ion to a nitrate ion with a 1 mol / l-NaNO ₃ aqueous solution, and the free chloride ion is converted into a potentiometric titrator (COMMITITE-900) using an aqueous silver nitrate solution. Quantified by Hiranuma Sangyo Co., Ltd. (Amol).
Next, the same ion exchange membrane was immersed in a 1 mol / l-NaCl aqueous solution for 4 hours or more, and sufficiently washed with ion exchange water. Thereafter, the moisture on the surface was wiped off with a tissue paper, and the mass (Wg) of the film when wet was measured. Furthermore, it dried under reduced pressure at 60 degreeC for 5 hours, and measured the weight (Dg) at the time of drying. Based on the measured values, the ion exchange capacity and water content of the ion exchange membrane were determined by the following equations.
Ion exchange capacity = A × 1000 / D [meq / g-dry mass]
Moisture content = 100 × (WD) / D [%]

9. Ion Exchange Membrane Thickness After immersing the ion exchange membrane in a 0.5 mol / L-NaCl solution for 4 hours or more, the surface of the membrane was wiped off with tissue paper, and the micrometer MED-25PJ (Mitutoyo Co., Ltd.) ).

10. Burst strength per unit thickness of ion exchange membrane:
The ion exchange membrane was immersed in a 0.5 mol / L-NaCl aqueous solution for 4 hours or more and washed thoroughly with ion exchange water. Next, the burst strength was measured according to JIS-P8112 by using a Murren burst tester (manufactured by Toyo Seiki) without drying the membrane. The burst strength per unit thickness was calculated from the measured value obtained and the thickness of the ion exchange membrane according to the following formula.
Burst strength per unit thickness (MPa / cm) = measured burst strength (MPa) / film thickness (cm)

11. Membrane resistance per unit thickness of ion exchange membrane An ion exchange membrane is sandwiched in a two-chamber cell having a platinum black electrode, 0.5 mol / L-NaCl aqueous solution is filled on both sides of the ion exchange membrane, and an AC bridge (frequency 1000 cycles / Second), the resistance between the electrodes at 25 ° C. was measured, and the membrane resistance was determined from the difference between the resistance between the electrodes and the resistance between the electrodes when no ion exchange membrane was installed. In addition, the ion exchange membrane used for the said measurement used what was previously equilibrated in 0.5 mol / L NaCl aqueous solution.
The membrane resistance per unit thickness was calculated from the obtained membrane resistance and the thickness of the ion exchange membrane by the following formula.
Film resistance per unit thickness (Ω · cm ² / cm) = film resistance (Ω · cm ² ) / film thickness (cm)

<Production Example 1>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with rolls heated from both sides, and a thickness of 195 μm Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes are stacked and stretched in the MD direction at 120 ° C. by 1.4 times, then 1.9 times in the TD direction at 120 ° C., and finally heat treated at 131 ° C. to obtain a laminated porous substrate. A film was obtained. Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 2>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with rolls heated from both sides, and a thickness of 170 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes are stacked and stretched in the MD direction at 120 ° C. by 1.4 times, then 1.9 times in the TD direction at 120 ° C., and finally heat treated at 129 ° C. to form a laminated porous substrate. A film was obtained. Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 3>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 190 μm Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to obtain a single layer porous substrate film. Table 1 shows the physical properties of the obtained porous substrate film.

<Production Example 4>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 210 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded article, then stretched 1.9 times in the TD direction at 120 ° C., and finally heat treated at 132 ° C. to obtain a single layer porous substrate film. Table 1 shows the physical properties of the obtained porous substrate film.

<Production Example 5>
Two single-layer porous substrate films prepared in Production Example 4 were stacked and hot-pressed at 120 ° C. and a pressure of 8.2 kg / cm ² for 5 minutes. Table 1 shows the physical properties of the obtained porous substrate film.

<Production Example 6>
Two single-layer porous substrate films prepared in Production Example 4 were stacked and hot-pressed at 135 ° C. and a pressure of 8.2 kg / cm ² for 5 minutes. Table 1 shows the physical properties of the obtained porous substrate film.

<Production Example 7>
A laminated porous substrate film was obtained in the same manner as in Production Example 1 except that the stretching temperature was 137 ° C and the final heat treatment temperature was 140 ° C. When the peel strength of the obtained laminated porous substrate film was measured, the laminated film was not peeled and the film was broken. The physical properties are shown in Table 1.

<Production Example 8>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of finely divided silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 90 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes are stacked and stretched 1.1 times in the MD direction at 120 ° C., then stretched 1.1 times in the TD direction at 120 ° C., and finally heat treated at 130 ° C. to form a laminated porous substrate. A film was obtained. Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 9>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight finely divided silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 290 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two of the microporous membranes were stacked and stretched in the MD direction twice at 120 ° C., then stretched twice in the TD direction at 120 ° C., and finally heat treated at 132 ° C. to obtain a laminated porous substrate film. . Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 10>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 460 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes are stacked and stretched 2.5 times in the MD direction at 120 ° C., then stretched 2.5 times in the TD direction at 120 ° C., and finally heat treated at 133 ° C. to form a laminated porous substrate. A film was obtained. Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 11>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 660 μm Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes were stacked and stretched 3 times in the MD direction at 120 ° C., then stretched 3 times in the TD direction at 120 ° C., and finally heat treated at 134 ° C. to obtain a laminated porous substrate film. . Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Production Example 12>
Ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 7.0 dl / g 19.2% by weight, high-density polyethylene 12.8% by weight having an intrinsic viscosity [η] of 2.8 dl / g, dioctyl phthalate (D
OP) 48% by weight and 20% by weight of fine silica were mixed and granulated, then melt kneaded by a twin screw extruder equipped with a T-die at the tip, extruded, rolled with a roll heated from both sides, and a thickness of 850 μm. Molded into a sheet. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes are stacked and stretched 3.4 times in the MD direction at 120 ° C., then stretched 3.4 times in the TD direction at 120 ° C., and finally heat treated at 136 ° C. to form a laminated porous substrate. A film was obtained. Table 1 shows the physical properties of the obtained laminated porous substrate film.

<Example 1>
Each component was mixed according to the following formulation to prepare a polymerizable composition.
Styrene 73.5 parts by mass p-chloromethylstyrene 16.5 parts by mass Acrylonitrile 10.0 parts by mass Tributyl acetylcitrate 2.5 parts by mass Styrene oxide 2.9 parts by mass Kayabutyl D
(Di-t-butyl peroxide, manufactured by Kayaku Akzo Corporation) 1.9 parts by mass The composition of this polymerizable composition is shown in Table 2.
500 g of this polymerizable composition is put into a 1000 ml glass container, and the porous substrate film produced in Production Example 1 is immersed therein as a substrate sheet, and the polymer composition is filled in the voids of the film. did.
The porous base film filled with the above polymer composition was taken out, and both sides of the porous base film were coated with a polyester film having a thickness of 100 μm as a release material, and then at 120 ° C. under nitrogen pressure of 0.4 MPa. Polymerization was carried out by heating for 6.8 hours.

The obtained film was immersed in a 1: 1 (weight ratio) mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 60 minutes. Thereafter, the membrane was immersed in 90% sulfuric acid, 60% sulfuric acid and ion-exchanged water successively, further immersed in a 4 mol / L-NaOH aqueous solution for 12 hours, and washed with water to obtain a sulfonic acid cation exchange membrane. Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Examples 2 and 3>
A cation exchange membrane of the present invention was prepared in the same manner as in Example 1 using the base sheet and the polymerizable composition shown in Table 2. Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Example 4>
Each component was mixed according to the following formulation to prepare a polymerizable composition.
p-Chloromethylstyrene 86.0 parts by weight Divinylbenzene (purity 57%) 14.0 parts by weight Styrene oxide 4.0 parts by weight Kayabutyl D
(Di-t-butyl peroxide, manufactured by Kayaku Akzo Co., Ltd.) 4.0 parts by mass The composition of this polymerizable composition is shown in Table 2.
500 g of this polymerizable composition was placed in a 1000 ml glass container, and the porous substrate film produced in Production Example 1 was immersed therein as a substrate sheet, and the polymer composition was filled in the voids of the sheet. .
The porous base film filled with the polymer composition was taken out, covered on both sides of the porous base film using a 100 μm thick polyester film as a release material, and then at 80 ° C. under nitrogen pressure of 0.4 MPa. Polymerization was carried out for 5 hours and then at 90 ° C. for 2 hours.

The obtained film was immersed in a mixture of 15 parts by weight of 30% trimethylamine aqueous solution, 52.5 parts by weight of water and 22.5 parts by weight of acetone at 30 ° C. for 16 hours to form a quaternary ammonium type anion exchange membrane. Obtained. The results of evaluating the properties of the obtained anion exchange membrane are shown in Table 3.

<Examples 5, 6, and 7>
A cation exchange membrane of the present invention was prepared in the same manner as in Example 1 using the base sheet and the polymerizable composition shown in Table 2. Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Comparative Example 1>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the single-layer porous substrate film of Production Example 3 was used instead of the laminated porous substrate film of Production Example 1. Table 2 shows the composition of the polymerizable composition used in the preparation of the cation exchange membrane, and Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Comparative example 2>
An anion exchange membrane was prepared in the same manner as in Example 4 except that the single-layer porous substrate film of Production Example 3 was used instead of the laminated porous substrate film of Production Example 1. The composition of the polymerizable composition used for the production of this anion exchange membrane is shown in Table 2, and the results of evaluating the properties of the obtained anion exchange membrane are shown in Table 3.

<Comparative Example 3>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the single-layer porous substrate film of Production Example 4 was used instead of the laminated porous substrate film of Production Example 1. Table 2 shows the composition of the polymerizable composition used in the preparation of the cation exchange membrane, and Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Comparative example 4>
A cation exchange membrane was prepared in the same manner as in Example 2 using the laminated porous substrate film prepared in Production Example 5 instead of the laminated porous substrate film of Production Example 1, but concentrated sulfuric acid and chloro When the sulfonation was carried out with a mixture of sulfonic acids, the laminated porous substrate films were peeled off, and a desired cation exchange membrane could not be obtained.

<Comparative Example 5>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the laminated porous substrate film prepared in Production Example 6 was used instead of the laminated porous substrate film of Production Example 1. Table 2 shows the composition of the polymerizable composition used in the preparation of the cation exchange membrane, and Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Comparative Example 6>
Instead of the laminated porous substrate film of Production Example 1, two single-layer porous substrate films prepared in Production Example 4 were used as a substrate sheet by overlapping them, and a cation exchange membrane was prepared in the same manner as in Example 2. Although produced, when the sulfonation was carried out with a mixture of concentrated sulfuric acid and chlorosulfonic acid, the laminated porous substrate films were peeled off, and the desired cation exchange membrane could not be obtained.

<Comparative Example 7>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the laminated porous substrate film of Production Example 7 was used instead of the laminated porous substrate film of Production Example 1. Table 2 shows the composition of the polymerizable composition used in the preparation of the cation exchange membrane, and Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

<Comparative Example 8>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the laminated porous substrate film of Production Example 8 was used instead of the laminated porous substrate film of Production Example 1, but concentrated sulfuric acid and chloro When the sulfonation was carried out with a mixture of sulfonic acids, the laminated porous substrate films were peeled off, and a desired cation exchange membrane could not be obtained.

<Comparative Example 9>
A cation exchange membrane was prepared in the same manner as in Example 2 except that the laminated porous substrate film of Production Example 12 was used instead of the laminated porous substrate film of Production Example 1. Table 2 shows the composition of the polymerizable composition used in the preparation of the cation exchange membrane, and Table 3 shows the results of evaluating the characteristics of the obtained cation exchange membrane.

1: Porous base film 3: Porous olefin resin layer

Accordingly, an object of the present invention is to provide an ion in which the base film is a porous resin film bonded to each other, but has a low air permeability, and therefore, the high electrical resistance due to the lamination of the base sheet is effectively suppressed. It is to provide an exchange membrane .

According to the present invention, in the ion exchange membrane in which the void portion of the porous base film is filled with an ion exchange resin,
The porous substrate film has a structure in which at least two porous olefin resin layers are laminated with a bonding strength of 100 gf / cm or more and less than 700 gf / cm, and the film of the porous substrate film The thickness is 40 to 250 μm and the air permeability in terms of 100 μm thickness is 500 sec / 100 ml or less ,
The ion exchange membrane has an ion exchange membrane characterized by having a membrane resistance in terms of thickness of 1 cm of 50 to 300 Ω · cm ² / cm and a burst strength in terms of thickness of 1 cm of 30 to 70 MPa / cm. Is done.

The ion exchange membrane of the present invention is
Providing at least two porous olefin-based resin films;
A step of producing the porous substrate film having a laminated structure by superposing the plurality of porous olefin-based resin films, heating to a temperature of -20 ° C. or higher and lower than the melting point, and stretching and molding;
A step of immersing the porous substrate film in a polymerizable composition for forming an ion exchange resin to produce an ion exchange membrane precursor in which voids of the film are filled with the polymerizable composition;
Polymerizing the polymerizable composition in the ion exchange membrane precursor;
Manufactured by a method comprising:

In the above manufacturing method ,
(1) Each of the plurality of porous olefin-based resin films has a porosity of 20 to 60%,
Is preferred, and
(2) As the polymerizable composition for forming the ion exchange resin, a composition containing a monomer having an ion exchange group is used, and the ion exchange resin is formed by the polymerization.
Or
(3) As the polymerizable composition for forming the ion exchange resin, a composition containing a monomer having a functional group capable of introducing an ion exchange group is used, and the ion exchange group is introduced after the polymerization. ,
The following means can be adopted.

In the above, the stretching operation is performed in a state where a predetermined number of unstretched porous olefin resin films are overlapped, and stretched at a predetermined stretching ratio in a uniaxial direction or a biaxial direction using a roll, a tenter, or the like. In addition to this, it is preferable to perform heat setting such as heat fixation or heat relaxation in order to improve heat shrinkage resistance.
Further, heat treatment such as stretching and heat setting or heat relaxation is naturally performed at a temperature lower than the melting point, but in the present invention, it is necessary to perform in a temperature region close to the melting point, in particular, a melting point of −20 ° C. or more, In particular, it is preferable to carry out in the temperature range of -15 ° C to -1 ° C in order to obtain good bonding strength. The reason why good bonding strength can be obtained by selecting the temperature is not clear, but is considered as follows. That is, by overlapping in a state close to the melting point in this way, molecules of the olefin resin enter the inside of the interface at the interface 5 of the porous olefin resin film. Subsequently, the olefin resin molecules are stretched by the stretching operation, and entanglement occurs. Subsequent cooling fixes this entanglement, and the porous olefin resin films are bonded to each other with high bonding strength to form the porous base film 1 having a laminated structure composed of the porous olefin resin layers 3 and 3 described above. Will be.
The film thickness of the porous substrate film 1 of the present invention is in the range of 40 to 250 μm, but from the viewpoint of freely obtaining a thick ion exchange membrane, it is preferably 80 to 250 μm.

The introduction of the ion exchange group is carried out by a method known per se. For example, in the case of producing a cation exchange membrane, it is carried out by a treatment such as sulfonation, chlorosulfonation, phosphoniumation, hydrolysis, and the like. When producing an exchange membrane, it is carried out by a process such as amination or alkylation.
The ion exchange membrane of the present invention obtained as described above has a characteristic that it has a high burst strength even when the membrane resistance is the same, and the membrane resistance in terms of thickness of 1 cm is 50 to 300 Ω · cm ² / cm. The burst strength in terms of 1 cm thickness is 30 to 70 MPa / cm.

Claims (1)

  In the ion exchange membrane in which the void portion of the porous substrate film is filled with an ion exchange resin, the porous substrate film has at least two porous olefin-based resin layers of 100 gf / cm or more and less than 700 gf / cm. An ion exchange membrane characterized by having a laminated structure with a bonding strength of 100 μm and an air permeability of 100 μm thickness or less of 500 sec / 100 ml.