DESCRIPTION METHOD FOR PRODUCING POLYMER ELECTROLYTE MEMBRANE TECHNICAL FIELD [1] The present invention relates to a method for producing a polymer electrolyte membrane. BACKGROUND ART [2] A fuel cell is a kind of electric power supply capable of generating electric energy by electrochemically oxidizing a fuel such as hydrogen or methanol, and an intense interest has been shown towards the fuel cell, as a clean energy supply source, recently. Particularly, it is expected that a polymer electrolyte fuel cell is widely used as a distributed power generation facility of comparatively small scale, and a power generator of mobile bodies such as automobile and marine vessel, because of such low standard operation temperature as about 100°C and high energy density. Also, an intense interest has been shown towards the polymer electrolyte fuel cell as a power supply of portable mobile equipment and a portable device, and it is expected to install the polymer electrolyte fuel cell in a cellular phone and a personal computer in place of a secondary cell such as nickel-hydrogen cell or lithium ion cell. [3] In the fuel cell, anode and cathode in which the reaction capable of generating electricity occurs, and a polymer electrolyte membrane being used as a proton conductor between the anode and the cathode usually constitute a membrane electrode assembly (hereinafter sometimes abbreviated to MEA) and a cell comprising separators and MEA sandwiched between the separators is formed as a unit. The polymer electrolyte membrane is mainly composed of the polymer electrolyte material. The polymer electrolyte material is also used for a binder of an electrocatalyst layer or the like. [4] As a polymer electrolyte material, aromatic polyetherether ketone, aromatic polyetherketone and aromatic polyethersulfone have been actively investigated in point of heat resistance and chemical stability. [5] Also, in the sulfonated compound (for example, patent documents 1 and 2) of an aromatic polyetherketone (hereinafter, sometimes abbreviated to PES) (examples thereof include VICTREX PEEK-HT, manufactured by VICTREX PLC) , there was a problem that ' because its crystallinity is high, a polymer having the composition of low density of a sulfonic acid group becomes insoluble in a solvent, resulting in poor processability because of a remained crystal moiety. To the contrary, when the density of the sulfonic acid group is increased so as to enhance processability, the polymer is not crystalline and drastically swells in water, and therefore, purification of the polymer becomes very difficult and production of the polymer was not easy. [6] As a method of controlling an amount of the sulfonic acid group, an example, in which a monomer having a sulfonic acid group introduced is polymerized to form sulfonated aromatic polyethersulfone in which an amount of a sulfonic acid group is controlled, is reported in an aromatic polyethersulfone type (for example, patent document 3 ) . However, also in this method, a problem that a membrane prepared at elevated temperature and at high humidity swells is not solved, and this tendency is remarkable particularly in a fuel solution such as methanol or in composition in which a sulfonic, acid group density is high, and in such a polymer electrolyte membrane which is inferior in resistance to hot water and resistance to hot methanol, it was difficult to adequately inhibit fuel crossover such as methanol or the like and to impart mechanical strength for' enduring cycling of swelling and drying. [7] As described above, the polymer electrolyte material according to prior art is insufficient as measures for improving economic efficiency, processability, proton conductivity, fuel crossover, mechanical strength and therefore long-term durability, and there has never been obtained an industrially useful polymer electrolyte material for a fuel cell. [8] As an invention to solve these problems, in patent document 4, there is proposed a method in which a polymer having a crystallization power is converted to a solution by introduction of a protective group (hydrolytic group for imparting solubility) , a film is formed from the solution, and then deprotection (hydrolysis) is carried out, and it is said that by evaluating mechanical characteristics and improving a relation between a chemical structure and resistance to hot water, resistance to hot methanol and processability, an electrolyte membrane, which is excellent in proton conductivity, fuel barrier properties, mechanical strength, resistance to hot water, resistance to hot methanol, processability and chemical stability, can be provided. However, further improvement has been desired. [9] Further, in patent document 5, there is proposed an electrolyte membrane which is excellent in conductivity and durabilityby reinforcingwithaporous film. However, in patent document 5, since an assembled membrane in which a fluorine-type electrolyte membrane is packed in a fluorine-type fine porous membrane is disclosed, and an exchange capacity of the electrolyte membrane used in an example is 1.25 meq/g, proton conductivity as an assembled polymer electrolyte membrane was insufficient, and moreover since a constituent polymer is a fluorine-type, a hydrogen gas easily permeates through the membrane and therefore durability in an open circuit state in operating a fuel cell using the electrolyte membrane was insufficient. Patent Document [10] Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 6-93114 Patent Document 2: Published Japanese Translation No. 2004-528683 of the PCT Application Patent Document 3: U.S. Patent Application No. 2002/0091225 Patent Document 4: Japanese Unexamined Patent Publication (Kokai) No.2006-261103 Patent Document 5: Japanese Unexamined Patent Publication (Kokai) No.2007-257884 DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [11] Further improvement in performance of a durability test (dry-wet cycle test) , in whicha cycle of wetting of an electrolyte membrane accompanied by generating of electricity and drying in an open circuit condition is carried out, has been desired. Moreover, it is necessary to achieve a high level of proton conductivity and a high level of durability simultaneously in order to use in fuel cell applications which are operated at a high temperature higher than 80°C and under low humidity conditions having a relative humidity of 60% or less such as an automobile application. Particularly, in recent years, since requirements for performance of a fuel cell increase with the advance of fuel cell technology, and higher ionic conductivity is desired in an electrolyte membrane, a situation where an electrolyte polymer having a density of an ionic group of 2 mmol/g or more is desirable occurs. [12] Here, an electrolyte polymer having a density of an ionic group of 2 mmol/g or more is often synthesized by desalting and polycondensation, and when the polymer is isolated and purified, a polymerization solution is charged into a large amount of water to perform purification by precipitation in order to remove salt of by-product, and after drying the precipitate, the precipitate is redissolved to form a coating solution for membrane formation from a solution. However, the present inventors found out the problem that in this purification, since an electrolyte polymer having a density of an ionic group of 2.0 mmol/g or more is dissolved in water, or purification and isolation of the polymer by a conventional purification by precipitation is very difficult because of extremely large swelling. MEANS FOR SOLVING THE PROBLEMS [13] Thus, the present inventors first made earnest investigations concerning a method in which an electrolyte polymer having a density of an ionic group of 2 mmol/g or more can be industrially purified, and consequently they have noted an unprecedented method of removing a part of a salt component produced during polycondensation from a polymerization solution of the electrolyte polymer directly by centrifugal separation, thereby preparing a coating solution. [14] The present invention employs the following means in order to solve such problems. That is, a method for producing a polymer electrolytemembrane of the present invention comprises the steps of removing a part of a salt component produced during polycondensation from a polymerization solution of a polymer electrolyte having a density of an ionic group of 2 mmol/g or more directly by centrifugal separation, thereby preparing a coating solution; applying the coating solution on a substrate by casting; removing a part of a solvent from the coating solution to form a film-shaped material on the substrate; and bringing the f ilm-shapedmaterial on the substrate into contact with water and/or an aqueous acidic solution to remove the salt component produced during the polycondensation. EFFECTS OF THE INVENTION [15] In accordance with the present invention, it becomes possible to industrially purify an electrolyte polymer having a density of an ionic group of 2 mmol/g or more, and therefore an electrolyte membrane having a density of an ionic group of 2 mmol/g or more can be obtained. Further, an assembled polymer electrolyte membrane using the electrolyte polymer can realize a fuel cell having excellent electric generation performance at a high temperature and under low humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS [16] Fig. 1 is a view showing structures of electrolyte polymers to which a crown ether is not added, and added. Fig. 2 is a view showing a radial distribution function and a coordination number between sulfur atoms in a sulfonic acid group. Fig. 3 is a schematic view of a constitution of a continuous application systemby casting for producing an assembled polymer electrolyte membrane. Fig. 4 is a schematic view of a constitution of a continuous application system by casting for producing an assembled polymer electrolyte membrane. Fig. 5 is a schematic view of a constitution of a continuous application systemby casting for producing an assembled polymer electrolyte membrane. Fig. 6 is a schematic view of a constitution of a continuous application system by casting for producing an assembled polymer electrolyte membrane. BEST MODE FOR CARRYING OUT THE INVENTION [17] Hereinafter, preferable embodiments of the present invention will be described. [18] The method for producing a polymer electrolyte membrane of the present invention comprises the step of removing a part of a salt component produced during polycondensation from a polymerization solution of a polymer electrolyte having a density of an ionic group' of 2 mmol/g or more directly by centrifugal separation, thereby preparing a coating solution. [19] In the polycondensation of the present invention, a method commonly used in polymer synthesis can be used, and is not particularly limited. For example, a method in which an alkali metal is substituted for a diol end of a monomer containing diol, the resulting compound is reacted with a monomer having dihalide end to desalt and polymerize, or a reaction, in which an acid produced in polymerizing a monomer containing diamine with a monomer containing dicarboxylic chloride is neutralized with an alkali metal to produce a salt component indirectly, can be employed. These methods are suitable particularly for a polymerization system in which salt produced as a by-product is hardly dissolved in a polymerization solvent and precipitated assolid. Further, these methods can also be preferably employed for removal of salt produced as a by-product in a coupling reaction between dihalide and Zn salt other than the polycondensation. Moreover, they are also effective for a system in which an additive or a remaining monomer, insoluble in a polymerization solvent, is present. [20] Herein, the term "direct" means that a method, in which a polymer is brought into contact with a large amount of a solvent in which by-product salt is soluble and a polymer is insoluble, such as water, methanol, acetone, toluene or hexane to precipitate the polymer in water or the solvent, is not adopted, and a polymerization solution is subjected to centrifugal separation as-is to separate a produced insoluble by-product salt and the like into a solid fraction and a liquid fraction. In this time, the polymerization solution may be diluted with a solvent, in which the polymer electrolyte is soluble, and it is preferred to adjust the viscosity of the polymerization solution in consideration of the efficiency of centrifugal separation operation. [21] Next, a polymer electrolyte having a density of an ionic group of 2 mmol/g or more will be described. The ionic group is not particularly limited as long as it is an atomic group having negative charge, but the ionic group is preferably a group having a proton exchange capability. As the functional group, a sulfonic acid group, a sulfoneimide group, a sulfuric acid group, a phosphonic acid group, a phosphoric acid group, and a carboxylic acid group are preferably used. Such an ionic group includes the case where the functional groups are in the form of a salt. Examples of the cation, which forms the salt, include any metal cation, and NR4+ (R is any organic group) . In the case of a metal cation, its valence is not specifically limited and any metal cation can be used. Preferable specific examples of the metal ion include ions of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Mn, Al, Fe, Co, Ni, Cu, Zn, Zr, Mo, W, Pt, Rh, Ru, Ir, and Pd. Among these, Li, Na, K, Ca, Sr, and Ba are more preferable, particularly, Na and K, which are inexpensive, do not adversely affect the solubility, and are easily capable of proton substitution, are more preferably used. Further, ester may be substituted for the ionic group in addition to metal salts. [22] Two or more kinds of these ionic groups can be contained in the polymer electrolyte material, and there may be cases where a combination of these ionic groups is more preferable. This combination is appropriately determined depending on a structure of a polymer. Among these ionic groups, it is more preferable to have at least a sulfonic acid group, a sulfoneimide group, and a sulfuric acid group in view of high proton conductivity, and it is most preferable to have at least a sulfonic acid group in view of resistance to hydrolysis. [23] In recent years, simplification of a water control system is thought to be important for the full-scale popularization of a fuel cell for automobiles or a fuel cell for household use, and power generation is carried out at a high temperature higher than 80°C and under low humidity conditions having a relative humidity of 60% or less. Accordingly, the electrolyte membrane needs to have a density of an ionic group of 2 mmol/g or more. [24] Herein, the density of an ionic group refers to the number of mols of an ionic group introduced in 1 g of a dried polymer electrolyte material, and as the value of the density increases, an amount of the ionic group is large. For example, when the ionic group is a sulfonic acid group, the density (mmol/g) of an ionic group can be represented by a value of the density of the sulfonic acid group. Particularly in the present invention, an electrolyte membrane having a density of an ionic group of 2.0 mmol/g or more can be industrially produced. The density of the ionic group can be measured by capillary electrophoresis, elemental analysis or acid-base titration. Among these methods, it is preferable that the density is calculated from a S/C ratio using a capillary electrophoresis method or an elemental analysis method because of ease of the measurement. However, it is also possible to determine the ion-exchange capacity by an acid-base titration method. The density of an ionic group of the present invention uses a value measured by the capillary electrophoresis method, but there is little difference between this value and values measured by other methods, and the values of other methods can be employed. Details of the capillary electrophoresis method will be described in EXAMPLES. The polymer electrolyte membrane of the present invention, as described later, includes anaspect of an assembled polymer electrolyte membrane comprising an electrolyte having a density of an ionic group of 2 mmol/g or more and a porous film, and in this case, the density of the ionic group is determined based on the total amount of the assembled polymer electrolyte membrane. [25] Further, an example in which the density is calculated from a S/C ratio using an elemental analysis method will be shown below. [26] A sample of an electrolyte membrane as a specimen was immersed in pure water of 25°C for 24 hours, and dried in a vacuum at 40°C for 24 hours, and then elemental analysis was carried out. Analysis of carbon, hydrogen and nitrogen was carried out by a full automatic elemental analysis apparatus varioEL, analysis of sulfur was carried out by a flask combustion method and titration with barium acetate, and analysis of: fluorine was carried out by flask combustion and ion chromatogram methods. Density (mmol/g) of sulfonic acid group per unit gram was calculated from a composition ratio of a polymer. [27] Further, the procedure of the acid-base titration is shown for reference. The measurement is carried out three or more times and the" obtained values are averaged. (1) A sample is ground by a mill and screened through a net sieve #50 and the particles passed through the net sieve are used as a measuring sample. (2) A sample tube (with a cap) is weighed with a precision balance. (3) About 0.1 g of the sample obtained in (1) is put in the sample tube and dried in a vacuum at 40°C for 16 hours. (4) The sample tube containing the sample is weighed to determine a dry weight of the sample. (5) Sodium chloride is dissolved in a 30 wt% aqueous solution of methanol to prepare a saturated saline. (6) 25 mL of the saturated saline obtained in (5) is added to the sample, followed by ion exchange while stirring for 24 hours. (7) Hydrochloric acid produced is titrated using a 0. 02 mol/L aqueous solution of sodium hydrate. As an indicator, two drops of a commercially available phenolphthalein solution for titration (0.1% by volume) are added and it is judged as the end point when the solution shows a reddish purple color. (8) The density of the sulfonic acid group is determined by the following equation. Density of sulfonic acid group (mmol/g) = [Concentration (mmol/ml) of aqueous sodium hydroxide solution x amount (ml) added dropwise]/Dry weight (g) of sample Other components, for example, inactive polymers, or organic or inorganic compounds which do not have electric conductivity or ionic conductivity, may be contained in the electrolyte having an ionic group of the present invention within a scope which does not impair the object of the present invention. [28] Examples of a method for introducing the ionic group include a method of using a monomer having an ionic group and polymerizing it, and a method of introducing an ionic group by a polymer reaction. The present invention uses a polymerization solution of a polymer electrolyte having a density of an ionic group of 2 mmol/g or more, and it is preferred to use a monomer having an ionic group as a raw material in order to stably attain a polymer having a density of an ionic group of 2 mmol/g or more. The ionic group, as described above, includes a metal salt, and the metal salt of an ionic group is preferable because it can reduce detachment and decomposition of the ionic group in a polymerization step, and in the step of removing a part of a solvent to form a film-shaped material on the substrate, the film-shaped material is thermally stable during drying the solvent, and corrosion of the film-shaped material due to acid can be reduced, and therefore cost of production facilities can be reduced. [29] When a monomer having the metal salt of an ionic group is used, it is preferred to include a step of desalting and polycondensingby adding a cyclicmetal scavenger and/or glycols . The monomer having the metal salt of an ionic group is preferably introduced in a polymer chain in order to obtain the polymer electrolyte having a density of an ionic group of 2 mmol/g or more, but the monomer having the metal salt of an ionic group is often solid and hardly dissolved in an organic solvent. If a polycondensation reaction is carried out with the metal salt in a solid state, the density of a sulfonic acid group of the resulting polymer tends to be lower than a stoichiometric value . [30] The present inventors found that by adding a cyclic metal scavenger and/or glycols to perform polycondensation, (1) solubility of a monomer, which contains a metal salt of an ionic group, in a polymerization solvent can be increased, and a molecular weight of a polymer electrolyte, having a density of an ionic group of 2 mmol/g or more, can be increased, and (2) it becomes possible to suppress the thermal decomposition of an ionic group due to heating during polymerization and partial "gelation due to aggregation of a metal salt end of an ionic group. [31] The cyclic metal.scavenger of the present invention is not particularly limited as long as it forms chelate complex with a metal cation or has a structure which subsumes a metal cation. As the cyclic metal scavenger, for example, porphyrin, phthalocyanine, corrole, chlorin, cyclodextrin, crown ethers, thiacrown ethers formed by substituting S or NH for o of the crown ether, and azacrown ethers are preferably used. Crown ethers are suitable from the viewpoint of polymerization stability or ease of removal, and among these, 12-crown-4 (1,4,7,10-tetraoxacyclododecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane), and 18-crown-6 (1,4,7,10,13,16-Hexaoxacyclooctadecane) are suitably used, and 18-crown-6 is optimal because of low cost. These may be used singly, or may be used as amixture of two or more thereof. Further, amounts of these additives are appropriately determined experimentally and are not particularly limited, but these amounts are preferably the molar number or less of a metal salt of an ionic group in a monomer used. [32] As the glycols, polyhydricalcohols suchas ethylene glycol, diethylene glycol, triethylene glycol and glycerin; and polyglycols typified by polyalkyl glycol such as polyethylene glycol and polypropylene glycol are preferably used. Among these, polyalkyl glycol is preferable, and polyethylene glycol is more preferable. A molecular weight of polyglycols is preferably 4000 or less which does not interfere with properties of an electrolyte polymer, and more preferably 600 or less, at which polyglycols are liquid at room temperature from the viewpoint of affinity for a solvent. [33] If the above-mentioned cyclic metal scavenger and/or glycols are added during polycondensation, this achieves the above effects, and it is preferable from the following effects to comprise the step of adding the cyclic metal scavenger and/or glycols prior to the step applying the coating solution onto a substrate by casting. [34] The reason for this is that in the production process of the polymer electrolyte membrane containing a metal salt of an ionic group, if the cyclic metal scavenger and/or glycols is added, this inhibits aggregation between metal salts of an ionic group to make free metal salt soluble in a solvent, and therefore this addition achieves an effect in the step of applying a coating solution onto a substrate by casting, and it becomes possible to provide a polymer electrolyte membrane with high quality and high durability in which electric generation performance under low humidity conditions is improved. That is, since not only the addition during polycondensation but also the addition at the subsequent step have the above effect, it is preferred to add the cyclic metal scavenger and/or glycols at other step as long as it is performed before the step of applying a coating solution onto a substrate by casting. [35] Further, the cyclic metal scavenger and/or glycols is preferably removed before the final stage of the electrolyte membrane from the viewpoint of improving mechanical strength and water resistance, and it is preferred to comprise the step of removing the cyclic metal scavenger and/or glycols after the step of removing a part of the solvent to form a film-shaped material on the substrate. A method of removing them is not particularly limited, but this removing operation is preferably carried out at the step of contact with water and/or an aqueous acidic solution from the viewpoint of improving productivity. [36] With respect to the effect of adding the cyclic metal scavenger and/or glycols, the present inventors made an assumption that the added cyclic metal scavenger exerts an interaction on a metal cation coupled with the ionic group, and an added molecule cuts in between ionic group/metal cation/ionic group to develop the effect of addition. That is, it is assumed that the cyclic metal scavenger and glycols are coordinated to the metal cation coupled with the ionic group, and act as protective agents of the ionic group to cause thermal decomposition during polymerization or during solvent-drying after application by casting to hardly occur, and its steric hindrance inhibits aggregation between ionic groups, the solubility of a monomer having a metal salt of the ionic group in a polymerization solvent is improved, and production of aggregate at a production step of an electrolyte membrane can be reduced. [37] As the reason of the assumption, calculation results by computational science are shown below. [38] The present inventors investigated a microstructure of a polymer electrolyte membrane containing potassium sulfonate having added crown ether which is one of a cyclic metal scavenger by molecule simulation. Molecule simulation is a technique which is successing in obtaining reliable findings concerning atomic-level detail structure and movement of liquid, polymer and protein models, which cannot be investigated by experiments, by outstanding improvement in a computational speed of computer and development of methodology in recent years. [39] The present inventors calculated, first, molecular orbitals at a B3LYP/6-31G (d, p) level and evaluated interactional energy between K+ and crown ether (18-crown-6). A method of molecular orbitals is a method which resolves Schrodinger equation numerically to evaluate an electron state of molecules . As a result of calculation, interactional energy between K+ and crown ether was 77 kcal/mol and it was found that a bond therebetween is very strong compared with a hydrogen bond (about 5 kcal/mol) . This result shows that crown ether can be suitably used as a K+ scavenger. [40] Next, the present inventors investigated amicrostructure of an electrolyte polymer to which crown ether was added using a molecular dynamics method. The molecular dynamics method is a technique which sequentially resolves equations of motion of a molecular group system for all constituent molecules to determine an orbital of each molecule. [41] In this calculation, calculation of molecular dynamics was executed using a polymer model shown in a structural formula (1). An asterisk in the structural formula indicates to be continued. (Chem 1) [43] As composition of a system, 4 molecules of a polymer shown in the structural formula (1) were arranged, and 410 molecules of a NMP molecule were arranged so that a concentration of a polymer solution is 20 weight % (crown ether not added model). Moreover, an additional model, in which 24 molecules of crown ethers (18-crown-6) were arranged so as to be equal in mole to a sulfonic acid group in a polymer, was made (crown ether added model). [44] With respect to calculation conditions, temperature was controlled so as to be 25°C by use of a Nose-Hoover method [M. Tuckerman, B.J. Berne and G. J. Martyna, J. Chem. Phys.97, 1990 (1992) ] ] , and pressure was controlled so as to be 1 atm by use of a Parrinello-Rahmanmethod [M. Parrinello and A. Rahman, J. Appl. Phys., 52, 7182(1981)] using an oblique cell. Further, calculations of vdW interaction and electrostatic interaction in a real space were performed assumed that a cut off radius rc = 10 angstroms, and calculation of electrostatic interaction in a reciprocal space was performed assumed that a cut off radius a = 0.21 angstroms-1 and |n|2 max = 50 by use of a Ewald method. [45] With respect to potential parameters used in molecular dynamics calculation, equilibrium positions of a bonding length and bonding angle of a polymer, dihedral angle force-field parameter, charge, and vdW parameter of K+ were optimized by use of molecular orbital calculation. Further, as a vdW parameter of SO3- portion, parameters described in a literature [W.R. Cannon, B.M. Pettitt, J.A. McCammon, J. Phys. Chem., 98,6225(1994)] were employed. As other parameters, general-purpose parameter AMBER [W.D. Cornell, P. Cieplak, C.I. Bayly, I.R. Gould, K.M. Merz Jr, D.M. Ferguson, D.C. Spellmeyer, T. Fox, J.W. Caldwell and P.A. Kollman, J. Am. Chem. Soc., 117, 5179 (1995)] and DREIDING [S.L. Mayo, B.D. Olafson, W.A. Goddard III, J. Phys. Chem., 94, 8897 (1990)] were employed. [46] Structures of a crown ether not added model and a crown ether added model, which are determined by use of molecular dynamics calculations, are shown in Fig. 1. Aleft side indicates the crown ether not added model and a right side indicates the crown ether added model. A white sphere represents S (sulfonic acid group) , a dark gray sphere represents K+, and a gray rod represents anelectrolytepolymer, a light gray sphere represents crown ether, and a gray rod represents NMP. From Fig. 1, it was found that in an article not having added crown ether, the sulfonic acid groups are intensely aggregated with K+ interposed therebetween, and in an article having added crown ether, crown ether cut in between sulfonic acid group/K+/sulfondc acid group. [47] In order to estimate the effect of inhibiting aggregation between sulfonic acid groups quantitatively, a radial distribution function and coordination number between sulfur atoms in a sulfonic acid group were calculated. Herein, the radial distribution function g(r) is an average number of particles multiplied by a normalized constant, as shown in equation (1) . Herein, the average number of particles represents an average of the number of particles existing in a region which centers on a certain particle i and has a radius r±Ar. Further, the coordination number is a value obtained by integrating the average number of particles up to a certain distance. [48] [Nume 1] [49] Calculation results are shown in Fig. 2. A figure on a left side is a graph in which a vertical axis is the radial distribution function g (r) and a horizontal axis is r (angstrom), and a figure on a right side is a graph in which a vertical axis is the coordination number CN and a horizontal axis is r (angstrom) . Solid line indicates a crown ether not added model, and broken line indicates a crown ether added model. From Fig. 2, it was found that the coordination number of an article not having added crown ether is about 0.8 at a position of the first peak of the radial distribution function. This indicates that another sulfonic acid group exists at a high probability of about 80% in a first coordination zone of the sulfonic acid group. On the other hand, it was found that the coordination number between sulfonic acid groups of an article having added crown ether is about 0.2 and has much less coordination number than the article not having added crown ether. [50] The results of the above molecule simulation suggests an assumption that by adding the cyclic metal scavenger or glycols exerting a strong interaction on a metal cation coupled with the ionic group, an added molecule cuts in between ionic group/metal cation/ionic group to inhibit aggregation. Further, from the viewpoint of inhibiting aggregation of the ionic group, it is preferred to add an aggregation inhibitor so that a coordination number between sulfonic acid groups is 0.4 or less in a first coordination zone. [51] When the aggregation of the ionic group is thus inhibited, since a polymer in which a hydrophilic portion and a hydrophobic portion are even is obtained, and the membrane becomes less in strain and large in elongation, a membrane which has high durability in applications of the electrolyte membrane where a cycle of swelling/shrinkage is repeated. [52] Further, when a free metal salt is contained in a polymer electrolyte solution in addition to the metal salt of an ionic group, a metal cation composing the metal salt is coupled with the cyclic metal scavenger and/or glycols and the metal salt can be soluble in a solvent. In addition, when a monomer and an oligomer containing the metal salt of an ionic group are insoluble in a solvent, the monomer and the oligomer can be soluble in a solvent by adding the cyclic metal scavenger and/or glycols. [53] Next, the centrifugal separation of the present invention is a method of applying a centrifugal force to a sample by use of a centrifuge, and separating liquid (polymer electrolyte solution) and solid (by-product salt, basic compounds, remaining monomers) by virtue of difference in specific gravity, and publicly known methods can be applied. Heretofore, centrifugal separation has been applied to recovery of polymers purified by precipitation or recovery of regenerated ion-exchange resin, for example, but in the present invention, the centrifugal separation is adopted to precipitate unnecessary solid such as salt as a by-product and recover a polymerization solution. It is preferred to adjust the viscosity of the polymerization solution from the viewpoint of increasing efficiency of salt removal. When centrifugal separation is performed, the concentration of the polymerization solution is preferably 10 Pa-s or less, more preferably 5 Pa-s or less, and furthermore preferably 1 Pa-s or less. When the viscosity is 10 Pa-s or less, a centrifugal effect is high, and centrifugal separation can be performed in a short time using an industrial centrifuge. The centrifugal force can be appropriately determined experimentally according to a difference in specific gravity between a by-product salt and a polymer solution, viscosity of the polymerization solution, a solid content, and apparatuses to be used. A centrifugal force is 5000 G or more, preferably 10000 G or more, and more preferably 20000 G or more, and an apparatus which can be continuously operated at times other than removal of a precipitate is industrially suitable. [54] It is also effective that for the purpose of enhancing the efficiency of a centrifugal separation step, a polymerization solution is left standing prior to the centrifugal separation step to precipitate coarse by-product salt and use a supernatant, and it is also preferred to perform a two stage centrifugal separation in which a part of coarse by-product salt is precipitated by a centrifugal force of 5000 G or less. [55] The present invention may comprise the step of filtration by a filter in combination with the centrifugal separation step. The filtration by a filter is an operation of passing a mixture (polymerization solution) of liquid (polymer electrolyte solution) and solid (by-product salt, basic compounds, remaining monomers, etc.) through a porous body (filteringmaterial) which has many fine holes (pores) to separate solid particles having a larger diameter than that of the hole from liquid. Publicly known methods can be applied to the filtration by a filter, and conditions of filtering can be appropriately determined depending on a size of salt desired to be removed from the polymerization solution or viscosity of the polymerization solution, and publicly known methods, such as natural filtration, centrifugal filtration, filtering under a reduced pressure, and pressure-filtering, can be employed, and a filtering object liquid may be heated. A filter is not particularly limited, and it can be appropriately selected from a metal mesh, a cellulose-type filter, a glass fiber filter, a membrane filter, a filter fabric and a filter plate according to an amount of the polymerization solution to be treated or a filtration system. Further, when the centrifugal separation is combined with the filtration by a filter, a solid fraction (by-product salt, basic compounds, remaining monomers, etc.) in the polymerization solution can be removed more efficiently than the filtration by a filter alone. [56] Further, it is also useful to condense the polymerization solution by distillation under a reduced pressure or ultrafiltration in order to adjust the viscosity and the solid content to a level suitable for application prior to an application step. Particularly when viscosity adjustment of the polymerization solution is carried out in order to increase the efficiency of centrifugal separation and filtration by a filter, it is preferred to condense the polymerization solution. Further, coatability may be improved by condensation of the polymerization solution. Publicly known methods can be usually applied to the condensation, and a condensing apparatus, which includes a mixing machine and can prevent the generation of a coating due to evaporation of a solvent, can be more preferably used. It is preferable from the viewpoint of productivity and environmental protection to reuse the solvent recovered by condensation. [57] Next, the step of applying a coating solution obtained by separating the polymerization raw solution into solid and liquid directly through centrifugal separation onto a substrate by casting, and removing a part of the solvent to forma film-shaped material on the substrate will be described. [58] The solvent used in the present invention can be appropriately selected experimentally according to polymerization conditions or composition of an electrolyte polymer, and as the solvent, an aprotic polar solvent such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, or hexamethylphosphonetriamide; an ester-type solvent such as y-butyrolactone or butyl acetate; a carbonate-type solvent such as ethylene carbonate or propylene carbonate; or an alkylene glycol monoalkyl ether such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether is suitably used, and these may be used alone, or may be used as a mixture of two or more thereof. Further, in order to adjust the viscosity of the electrolyte solution, an alcohol-type solvent such as methanol or isopropanol; a ketone-type solvent such as acetone or methyl ethyl ketone; an ester-type solvent such as ethyl acetate, butyl acetate, or ethyl lactate; a hydrocarbon-type solvent such as hexane, or cyclohexane; an aromatic hydrocarbon-type solvent such as benzene, toluene, or xylene; a halogenated hydrocarbon-type solvent such as chloroform, dichloromethane, 1,2-dichloroethane, dichloromethane, perchloroethylene, chlorobenzene, or dichlorobenzene; an ether-type solvent such as diethyl ether, tetrahydrofuran, or 1,4-dioxane; a nitrile-type solvent such as acetonitrile; a nitrated hydrocarbon-type solvent such as nitromethane or nitroethane; or a low boiling point solvent such as water can be used as a mixture thereof. [59] Examples of usable polymer electrolyte in the present invention include aromatic hydrocarbon-type polymers having an ionic group such as ionic group-containing polyphenylene oxide, ionic group-containingpolyetherketone, ionic group-containing polyetherether ketone, ionic group-containingpolyethersulfone, ionic group-containing polyetherether sulfone, ionic group-containing polyether phosphine oxide, ionic group-containing polyetherether phosphine oxide, ionic group-containing poly(phenylene sulfide), ionic group-containing polyamide, ionic group-containing polyimide, ionic group-containing polyetherimide, ionic group-containing polyimidazole, ionic group-containing polyoxazole and ionic group-containing polyphenylene. Herein, the ionic group is as described above. [60] Amethodof synthesizing these polymers is not particularly limited as long as the method can satisfy the above-mentioned characteristics and requirements. Such a method is described in, for example, Journal of Membrane Science, 197, 2002, p. 231-242. The present invention is a method which is limited to desalting/polycondensation among polymerization methods, and is the most effective if it is applied in the presence of basic compounds. [61] Preferable polymerization conditions on a polymerization method are as follows. The polymerization can be carried out at a temperature within a range from 0 to 350°C, but the temperature is preferably 50 to 250°C. When the temperature is lower than 0°C, the reaction may not tend to proceed adequately, and when the temperature is higher than 350°C, decomposition of the polymer may tend to be initiated. The reaction is preferably carried out in a solvent. Examples of usable solvent include aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphonetriamide, but the usable solvent is not limited to these solvents and may be any solvent which can be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents can be used alone or in combination. [62] Examples of the basic compound include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, but the basic compound can be used without being limited to these compounds as long as it can convert aromatic diols into an active phenoxide structure. [63] As an inorganic salt to be eliminated, that is, a reaction end of a monomer, a combination of a monovalent alkali metal and halogen is preferably used. Specifically, the combination of Li, Na, K or Rb and F, CI, Br or I is used. In consideration of cost and a cyclic metal scavenger, the combination of Na or K and F or CI is particularly preferably used. The eliminated inorganic salt maybe coupled with a basic compound or a decomposed product of the basic compound. The decomposed product of the basic compound may interfere with a polymerization reaction, and a cyclic metal compound has the effect of inhibiting this interference. [64] In the polycondensation, water is sometimes produced as by-product. In this case, water can also be removed out of the system in the form of an azeotrope by making toluene or the like coexist irrespective of a polymerization solvent in the reaction system. As the method of removing water out of the system, an absorbent such as molecular sieve can be used. [65] An azeotropic agent used for removing reaction water or water introduced during the reaction is generally any inert compound which does not substantially interfere with polymerization, is azeotropically distilled with water and boiled at a temperature of about 25 to about 250°C. Common azeotropic agent is such as benzene, toluene, xylene, chlorobenzene, methylene chloride, dichlorobenzene, and trichlorobenzene. Naturally, it is useful to select such azeotropic agent that its boiling point is lower than that of a dipolar solvent used. Generally, the azeotropic agent is used, but it is not always necessary when a high reaction temperature, for example, a temperature of 200°C or higher, is employed, particularly when a reaction mixture is continuously sprayed with an inert gas, and when an inside of a reaction system is maintained at a reduced pressure to lower a boiling point of a solvent. Generally, the reaction is desirably performed in a state of oxygen-free in an inert atmosphere. [66] When a condensation reaction is carried out in a solvent, the monomer is preferably charged so as to adjust the concentration of the resulting polymer within a range from 5 to 50% by weight. When the concentration is less than 5% by weight, the polymerization degree tends to hardly increase. On the other hand, when the concentration is more than 50% by weight, viscosity of the reaction system increases too much and a post-treatment of a reaction product tends to be difficult. [67] When solubility of the resulting polymer is in sufficient, an appropriate hydrolytic group for imparting solubility may be introduced, as required, and after polymerization, the hydrolytic group for imparting solubility may be removed by hydrolysis. [68] The hydrolytic group for imparting solubility of the present invention is a substituent temporarily introduced in order to facilitate membrane formation from a solution or filtration on the assumption that the substituent is introduced in a polymer hardly soluble in a solvent and is removed through hydrolysis in the following steps in the case where the hydrolytic group for imparting solubility is not introduced. The hydrolytic group for imparting solubility can be appropriately selected experimentally in consideration of reactivity, yield, stability of a state in which the hydrolytic group for imparting solubility is contained, and production cost. The stage, at which the hydrolytic group for imparting solubility is introduced in the polymerization reaction, may be a monomer, an oligomer or a polymer, and can be appropriately selected. [69] Specific examples of the hydrolytic group for imparting solubility include a method in which a site to ultimately become ketone is modified to an acetal site or a ketal site as a hydrolytic group for imparting solubility, and this site is modified to a ketone site by hydrolysis after membrane formation from solution. There is a method in which the ketone site is modified to a heteroatom analog of an acetal site or a ketal site, for example, thioacetal or thioketal. There are also methods in which sulfonic acid is modified to a soluble ester derivative, and in which a t-butyl group is introduced into an aromatic ring and de-t-butylated with an acid. [70] Since the hydrolytic group for imparting solubility improves the solubility in a common solvent and reduces crystallinity, aliphatic groups are used as a hydrolytic group for imparting solubility in that steric hindrance is large, and particularly aliphatic groups including a cyclic moiety are preferably used. [71] The position of the functional group, at which the hydrolytic group for imparting solubility is introduced, is more preferably a main chain of the polymer. When the hydrolytic group for imparting solubility is introduced in the main chain, a difference between the state at the time of introduction of the hydrolytic group for imparting solubility and the state after changing the hydrolytic group for imparting solubility to a stable group by hydrolysis is large, and packing of the polymer chain tends to be stronger, and the solubility of the polymer changes from soluble in a solvent to insoluble in a solvent, resulting in an increase in mechanical strength. As usedherein, the functional group, which is present in the main chain of the polymer, is defined as a functional group in which a polymer chain is cleaved when the functional group is eliminated. For example, this means that if a ketone group of aromatic polyetherketone is eliminated, benzene rings are isolated from one another. [72] This introduction of the hydrolytic group for imparting solubility is particularly effective for an application to a polymer having a property capable of crystallizing (crystallization power). The presence or absence of the . crystallinity of these polymers, and states of a crystal phase and an amorphous phase can be evaluated by a peak derived from a crystal in a wide X-ray diffraction (XRD), or by a crystallization peak in a differential scanning calorimetry (DSC). When the electrolyte membrane has a crystallization power, an electrolyte membrane in which changes in dimension (swelling) in hot water or hot methanol are small, that is, an electrolyte membrane which is excellent in resistance to hot water and resistance to hot methanol can be attained. When the changes in dimension are small, the membrane is hardly damaged during being used as an electrolyte membrane, and since peeling of the membrane from an electrocatalyst layer by swelling hardly occurs, electric generation performance is good. [73] The polymer electrolyte having a density of an ionic group of 2 mmol/g or more of the present invention preferably has a property capable of crystallizing (crystallization power) from the viewpoint of suppressing swelling due to water or a methanol aqueous solution or maintaining mechanical strength in wetting, and copolymerization of a monomer having a hydrolytic group for imparting solubility is particularly preferable in producing the above polymer electrolyte. [74] In the case of a polymer electrolyte, in which a hydrolytic group for imparting solubility is introduced for the purpose of improving solubility, it is particularly effective to comprise the step of the present invention of removing a part of a salt component produced during polycondensation from a polymerization solution directly by centrifugal separation, thereby preparing a coating solution. For example, if a purification step of performing precipitation in water without carrying out the above-mentionedpurif ication based on the direct centrifugal separation of the polymerization solution is employed, there was a problem that a part of the hydrolytic group for imparting solubility is hydrolyzed to cause the occurrence of a gel-like substance. Further, there may be cases where in the step of redissolving a polymer in a solvent to form a coating solution after isolating the polymer, the hydrolytic group for imparting solubility becomes insufficient and a part of the hydrolytic group for imparting solubility is not completely dissolved to deteriorate a rate of filtration by a filter significantly, an extraneous material resulting from a gel-like substance having slipped through the filter is produced at the time of membrane formation, and vertical streaks are produced, and an incidence of a defective piece increases. Further, even though the membrane looks a good item, the electrolyte membrane has an uneven structure like a sea-isle structure due to a gel-like substance having slipped through the filter, and this often causes tensile elongation or tearing strength to deteriorate, or often causes a membrane to be cloudy and damages quality. Even in the drying step, since the gel-like substance contains an extremely large amount of water, a drying time is lengthened to reduce productivity. [75] Since the hydrolytic group for imparting solubility is aimed at improving the solubility in a polymerization solvent, it is preferred to eliminate the hydrolytic group for imparting solubility by hydrolysis after the steps of forming a coating solution and applying the coating solution onto a substrate by casting. Apart of the hydrolytic group for imparting solubility can also be removed by heating at the time of drying a solvent, but in the present invention, since the step of bringing the film-shaped material on the substrate into contact with water and/or an aqueous acidic solution to remove a salt component produced during polycondensation is essential, it is preferred from the viewpoint of productivity to hydrolyze the hydrolytic group for imparting solubility simultaneously in this step to remove it. [76] As a polymer electrolyte having a density of an ionic group of 2 mmol/g or more, which is used in the method for producing an electrolyte membrane of the present invention, an aromatic hydrocarbon electrolyte containing the hydrolytic group for imparting solubility is preferably used for the above reason in considering ultimate performance of an electrolyte membrane, and an aromatic polyetherketone-type electrolyte is particularly preferable. Since the aromatic polyetherketone-type has good packing of an aromatic, ring and high structural regularity, it can form an electrolyte membrane having excellent water resistance even when the resulting density of an ionic group is 2 mmol/g or more. From the viewpoint of structural regularity, a residual ratio of a hydrolytic group for imparting solubility in the resulting electrolyte membrane is preferably 20% by mole or less with respect to a repeating unit of a polymer unit, and more preferably 10% by mole or less. [77] In the present invention, it is determined whether the structural regularity of the resulting electrolyte membrane is high or low by a full width (Hz) at half maximum of a peak of 133 ppm which is a main peak of aromatic. When this value is smaller (peak is sharp), it is determined that the electrolyte membrane has higher structural regularity, and the full width at half maximum is preferably 8 00 Hz or less, and more preferably 700 Hz or less. If the full width at half maximum is 800 Hz or less, it can be determined that stacking of aromatic is good and durability can be improved. Particularly, the method for producing an electrolyte membrane of the present invention is suitable for the production of an electrolyte membrane in which a half width (Hz) of 133 ppm is 800 Hz or less and the density of an ionic group is high. The structural regularity of the electrolyte membrane prepared by the method for producing an electrolyte membrane of the present invention can be evaluated by solid 13C DD/MAS NMR. Details of this will be described in EXAMPLES [78] As a substrate used in the present invention, publicly known material can be used, and examples of the substrate includes an endless belt or a drum made of metal such as stainless steel; a film composed of a polymer such as polyethylene terephthalate, polyimide or polysulfone; glass; and a release paper. In the case of metal, the surface is subjected to mirror finish, and in the case of a polymer film, a coated surface is subjected to a corona discharge treatment or a peeling treatment, and when a continuous application is carried out in the form of a roll, a backside of a coated surface can be subjected to a peeling treatment to prevent the electrolyte membrane from adhering to a backside of a coated substrate after taking-up the membrane. In the case of a film substrate, its thickness is not particularly limited, but it is preferably 30 to 200 μm from the viewpoint of handling. [79] As a method of applying a coating solution by casting, coating techniques such as knife coating, direct roll coating, gravure coating, spray coating, brush application, dip coating, die coating, vacuum die coating, curtain coating, flow coating, spin coating, reverse coating and screen printing can be employed. [80] A thickness of the electrolyte membrane prepared in the present invention is not particularly limited, but usually, an electrolyte membrane having a thickness of 3 to 500 μm is suitably used. An electrolyte membrane having a thickness of 3 μm or more is preferable for achieving film strength to stand up to practical use, and an electrolyte membrane having a thickness of 500 μm or less is preferable for reducing film resistance, that is, for improving electric generation performance. More preferable range of the membrane thickness is 5 to 200 μm, and furthermore preferable range is 8 to 200 μm. This membrane thickness can be controlled by various methods according to application methods. For example, when the coating solution is applied by a comma coater or a direct coater, the membrane thickness can be controlled by a solution concentration or a thickness of a solution applied onto a substrate, and when a slit die coater is used, the membrane thickness can be controlled by a discharge pressure, a nozzle clearance or a gap between a nozzle and a substrate. [81] In the method for producing an electrolyte membrane of the present invention, as a method of removing a part of a solvent to forma film-shaped material on a substrate, a method of heating a coated film applied on a substrate by casting to evaporate a solvent is preferable. As an evaporating method, publicly known methods, such as heating of a substrate, hot air and an infrared heater, can be selected. [82] A drying time and a drying temperature of the coated film can be appropriately determined experimentally, but it is preferred to dry the coated film at least to such an extent that if the coated film is peeled from a substrate, the film becomes self-supported. [83] Next, the step of bringing the film-shaped material on the substrate into contact with water and/or an aqueous acidic solution to remove the salt component produced during the polycondensation will be described. [84] In the present invention, it is essential to remove salt which cannot be removed by centrifugal separation by bringing the film-shaped material into contact with water and/or an aqueous acidic solution. When the salt is present, durability of the electrolyte membrane tends to be deteriorated starting from a salt portion. For example, when the concentration of a salt component contained in a film-shaped material before the membrane is brought into contact with water and/or an aqueous acidic solution is denoted by C3% by weight, and the concentration of a salt component after bringing the film-shaped material on the substrate into contact with water and/or an aqueous acidic solution is denoted by C4% by weight, it is preferred that C3 < 5, and C4/C3 < 0.3. When the C3 is less than 5% by weight, not only removal of salt in the step of bringing the film-shaped material into contact with water and/or an aqueous acidic solution can be performed with efficiency, but also defects such as voids resulting from the trace^of escaped salt can be reduced, and if C4/C3