Abstract: A cylindrical filter which is easily produced and has a high withstand strength, a high filtration accuracy and a long filtration life; a microfine fiber web and a non-woven fabric suitable to a production of such a cylindrical filter; and processes for producing such web, non-woven fabric and cylindrical filter, are provided, the web consisting of microfine mixed fibers spun according to melt-blown process, the mixed fibers consisting of high melting point microfine fibers and low melting point microfine fibers having a melting temperature difference of 10° c. or more, the low melting point microfine fibers being contained in a quantity of 10 to 90% by weight in the mixed fibers; the non-woven fabric being obtained by heat-treating the web; and the cylindrical filter being obtained by winding up the web or the nonwoven fabric, followed by heat-treatment.

Abstract: A precision cartridge filter having an average filter diameter of 10 .mu.m or less is produced by preparing a web composed of conjugate microfine fibers by a conjugate melt-blowing process, wherein the conjugate microfine fibers have a lower melting point component, a higher melting point component, and a melting point difference between the lower melting point component and higher melting point component of 20.degree. C. or more; followed by heating and molding the web at a temperature greater than or equal to the melting point of said lower melting point component, but less than the melting point of said higher melting point component.