Filter having chemical resistance, antistatic property and water vapor resistance, and process for producing the same

A water vapor resistant filter comprising a permeable molded material, nonwoven fabric or felt and a solid coating thereon,

• wherein the permeable molded material, nonwoven fabric or felt comprises polyimide fiber having a repeating unit represented by the following formula (I), and
• the permeable molded material, nonwoven fabric or felt is covered with a melting fluorine resin, a solvent-soluble cold setting fluorine resin or a fluorine elastomer:
• ##STR12## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR13## and R represents at least one divalent aromatic group selected from the group consisting of ##STR14##

A water vapor resistant antistatic filter comprising a permeable molded material, nonwoven fabric or felt and a solid coating thereon,

• wherein the permeable molded material, nonwoven fabric or felt comprises polyimide fiber having a repeating unit represented by the following formula (I), and
• the permeable molded material, nonwoven fabric or felt is covered with (i) an electroconductive material and (ii) a condensed polycyclic polynucleus aromatic resin, a solvent-soluble cold setting fluorine resin or a fluorine elastomer:
• ##STR15## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR16## and R represents at least one divalent aromatic group selected from the group consisting of ##STR17##

A process for producing a water vapor resistant filter, which comprises the steps of

• immersing a permeable molded material, nonwoven fabric or felt comprising a polyimide fiber having a repeating unit represented by the following formula (I) into an organic solution containing a condensed intermediate of a condensed polycyclic polynucleus aromatic resin in a concentration of from 20 to 60% by weight, and
• drying the immersed permeable molded material, nonwoven fabric or felt to thereby cover the permeable molded material, nonwoven fabric or felt with the condensed intermediate, and
• thermosetting the condensed intermediate covering the permeable molded material, nonwoven fabric or felt:
• ##STR18## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR19## and R represents at least one divalent aromatic group selected from the group consisting of ##STR20##

A process for producing a water vapor resistant filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with a dispersion of a melting fluorine resin fine powder dispersed in water or in an organic solvent or with a dispersion of a melting fluorine resin fine powder and a synthetic resin dispersed in water or in an organic solvent, and
• heating the coated permeable molded material, nonwoven fabric or felt at a temperature of from 260.degree. to 400.degree. C. to solidify the coating thereon:
• ##STR21## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR22## and R represents at least one divalent aromatic group selected from the group consisting of ##STR23##

A process for producing a water vapor resistant filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with a solution of a solvent-soluble cold setting fluorine resin, and
• drying the coated permeable molded material, nonwoven fabric or felt at room temperature or by heating to solidify the coating thereon:
• ##STR24## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR25## and R represents at least one divalent aromatic group selected from the group consisting of ##STR26##

A process for producing a water vapor resistant filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with a solution or latex of a fluorine elastomer, and
• heating the coated permeable molded material, nonwoven fabric or felt to solidify the coating thereon:
• ##STR27## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR28## and R represents at least one divalent aromatic group selected from the group consisting of ##STR29##

A process for producing a water vapor resistant antistatic filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with an electroconductive material and a condensed polycyclic polynucleus aromatic resin dispersed in an organic solvent, and
• heating the coated permeable molded material, nonwoven fabric or felt at a temperature of from 150.degree. to 300.degree. C. to solidify the coating thereon:
• ##STR30## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR31## and R represents at least one divalent aromatic group selected from the group consisting of ##STR32##

A process for producing a water vapor resistant antistatic filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with an electroconductive material and a solvent-soluble cold setting fluorine resin dispersed in an organic solvent, and
• drying the coated permeable molded material, nonwoven fabric or felt at room temperature or by heating to solidify the coating thereon:
• ##STR33## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR34## and R represents at least one divalent aromatic group selected from the group consisting of ##STR35##

A process for producing a water vapor resistant antistatic filter, which comprises the steps of

• coating a permeable molded material, nonwoven fabric or felt comprising polyimide fiber having a repeating unit represented by the following formula (I) with an electroconductive material and a fluorine elastomer dispersed in water or in an organic solvent, and
• drying the coated permeable molded material, nonwoven fabric or felt at room temperature or by heating to solidify the coating thereon:
• ##STR36## wherein n represents an integer of more than 1;
• X represents a tetravalent aromatic group selected from the group consisting of ##STR37## and R represents at least one divalent aromatic group selected from the group consisting of ##STR38##