Production method of porous medium

A production method of a porous medium comprising a non-water-absorptive support and a porous layer provided on the support, the method comprising:

• applying Water-based Composition A comprising inorganic microparticles of an average primary particle diameter of less than or equal to 30 nm, a hydrophilic binder and water onto the support to form a layer,
• drying the layer to form the porous layer, and
• applying Water-based Composition B onto the dried porous layer,
• wherein the Water-based Composition A further comprises a compound represented by formula (1) having a molecular weight of less than or equal to 200,
• wherein R1, R2 and R3 each represent a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an aryl group, an acyl group, a heteroaryl group, a heterocyclic group, —NR4R5, or —OR6;
• R4, R5 and R6 each represent a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an aryl group, an acyl group, a heteroaryl group, a heterocyclic group, an amino group or a cyano group further, R1 and R2, R1 and R3, and R1 and R4 may be joined together to form a ring;
• and X represents an oxygen atom or NH,
• wherein the Water-based Composition B comprises a component which forms coagulants in the Water-based Composition A or increases viscosity of Water-based Composition A, when the component is added in the Water-based Composition A, and the Water-based Composition A does not comprise a component which forms coagulants in the Water-based Composition A or increases viscosity of Water-based Composition A, when the component is added in the Water-based Composition A.