Process of producing a filter element of composite fibers

Claim 2

A process for producing polyolefin/polyester composite fibers, comprising the steps of: spinning a polyester core and a polyolefin sheath to achieve resulting composite fibers; stretching the resulting composite fibers to twice or more the original length at a temperature higher than the secondary transition point of said polyester by 20° C. or more and lower than the melting point of said polyolefin to achieve resulting composite fibers; and annealing the resulting composite fibers at a temperature higher than the secondary transition point of said polyester by 20° C. or more and lower than the melting point of said polyolefin for 30 second or more, to obtain composite fibers having a low apparent Young's modulus of 210 Kg/mm 2 or less.

Claim 3

A process for producing polyolefin/polyester composite fibers according to claim 1, wherein said polyolefin is selected from the group consisting of high density polyethylene, low density polyethylene and crystalline polypropylene.

Claim 4

A process for producing polyolefin/polyester composite fibers according to claim 1, wherein said polyester is selected from those having a melting point of 200° C. or higher and ethylene terephthalate units occupying 50% by weight or more of the molecule and being of fiber grade.

Claim 5

A process for producing a filter element, which comprises: winding up on a winding core polyolefin sheath/polyester core composite fibers that have previously undergone stretching to at least twice their original length at a temperature at least 20° C. higher than the second transition point of the polyester and lower than the melting point of the polyolefin, and annealing for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester, such that the fibers have an apparent Young's modulus of 210 Kg/mm 2 or less; winding while heating said composite fibers to the melt-adhesion temperature of the sheath component of said composite fibers to adjust the void content thereof to a desired one; cooling the resulting material; taking out said winding core; and obtaining a dense filter having low porosity.

Claim 6

A process for producing a filter element, which comprises: winding up on a winding core polyolefin sheath/polyester core composite fibers that have previously undergone stretching to at least twice their original length at a temperature at least 20° C. higher than the second transition point of the polyester and lower than the melting point of the polyolefin, and annealing for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester, such that the fibers have an apparent Young's modulus of 210 Kg/mm 2 or less; winding while heating said composite fibers to the melt-adhesion temperature of the sheath component of said composite fibers to adjust the void content thereof to a desired one; cooling the resulting material; taking out said winding core; and obtaining a dense filter having low porosity.

Claim 7

A process for producing polyolefin/polyester composite fibers, comprising the steps of: spinning a fiber comprising a polyester core and a polyolefin sheath to achieve a resultant spun fiber; stretching the resultant spun fiber under stretching conditions which lead to increasing the resultant spun fiber from an original length to a length that is at least twice the original length at a stretching temperature that is lower than a melting point of the polyolefin and at least 20° C. higher than a secondary transition point of the polyester to provide a resultant stretched fiber; annealing the resultant stretched fiber for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester; and obtaining a resultant composite fiber having an apparent Young's modulus of 210 Kg/mm 2 or less.

Claim 8

A process for producing polyolefin/polyester composite fibers, comprising the steps of: spinning a fiber comprising a polyester core and a polyolefin sheath to achieve a resultant spun fiber; stretching the resultant spun fiber under stretching conditions which lead to increasing the resultant spun fiber from an original length to a length that is at least twice the original length at a stretching temperature that is lower than a melting point of the polyolefin and at least 20° C. higher than a secondary transition point of the polyester to provide a resultant stretched fiber; annealing the resultant stretched fiber for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester; and obtaining a resultant composite fiber having an apparent Young's modulus of 210 Kg/mm 2 or less.

Claim 9

A process for producing a hard, homogenous filter element, comprising the steps of: winding on a winding element composite fibers comprising a polyolefin sheath component and a polyester core component produced according to a process comprising the steps of: spinning a fiber comprising a polyester core and a polyolefin sheath to achieve a resultant spun fiber; stretching the resultant spun fiber under stretching conditions which lead to increasing the resultant spun fiber from an original length to a length that is at least twice the original length at a stretching temperature that is lower than a melting point of the polyolefin and at least 20° C. higher than a secondary transition point of the polyester to provide a resultant stretched fiber; annealing the resultant stretched fiber for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester; and obtaining a resultant composite fiber having an apparent Young's modulus of 210 Kg/mm 2 or less; winding while heating the fibers to the melt-adhesion temperature of the sheath component of the composite fibers to adjust the void content thereof and to obtain a resulting material; cooling the resulting material; and removing the winding element.

Claim 10

A process for producing a hard, homogenous filter element, comprising the steps of: winding on a winding element composite fibers comprising a polyolefin sheath component and a polyester core component produced according to a process comprising the steps of: spinning a fiber comprising a polyester core and a polyolefin sheath to achieve a resultant spun fiber; stretching the resultant spun fiber under stretching conditions which lead to increasing the resultant spun fiber from an original length to a length that is at least twice the original length at a stretching temperature that is lower than a melting point of the polyolefin and at least 20° C. higher than a secondary transition point of the polyester to provide a resultant stretched fiber; annealing the resultant stretched fiber for at least 30 seconds at a temperature lower than the melting point of the polyolefin and at least 20° C. higher than the secondary transition point of polyester; and obtaining a resultant composite fiber having an apparent Young's modulus of 210 Kg/mm 2 or less; winding while heating the fibers to the melt-adhesion temperature of the sheath component of the composite fibers to adjust the void content thereof and to obtain a resulting material; cooling the resulting material; and removing the winding element.

Claim 11

A process for producing a hard, homogenous filter element, according to claim 6, wherein the filter element has low porosity.

Claim 12

A process for producing a hard, homogenous filter element, according to claim 6, wherein the filter element has an upper limit service temperature of 140° C.