Patent Description:
Tubular fiber filters are widely available for filtration. Examples include a nonwoven fiber sheet wrapped around a central core or a melt spun fiber filter for a water filter cartridge. However, these filters have diameters generally larger than one inch and/or have inadequate filtration efficiencies and flow rate performance for microfiltration of particle sizes from <NUM> microns to about <NUM> microns. <CIT> and <CIT> describe examples of porous fiber filters having high porosity values. There is a need for improved tubular porous fiber filters with relatively small diameters that provide strength and improved filtration properties.

The invention is defined by the appendant independent claims. The present disclosure addresses this unmet need and provides tubular porous fiber filters with relatively small diameters that provide strength and improved filtration properties. These tubular porous fiber filters are self-supporting, strong, and efficient at filtering small micron size particles from liquid or air. These filters can be made from bicomponent fibers or combinations of bicomponent fibers and monocomponent fibers.

The present disclosure provides small diameter tubular porous fiber filters. In this application, "small diameter" means a tubular filter having an outer diameter (OD) less than about <NUM> inch (<NUM>). In a specific example, the OD may be slightly larger than ½ inch (e.g., about <NUM> to about <NUM>). In a specific example, the OD may be equal to or less than about ½ inch (<NUM>). In another example, the OD may be equal to or less than ¼ inch (<NUM>). In another example, the OD may be equal to or less than <NUM>/<NUM> inch (<NUM>). In a further example, the tubular porous fiber filter has an OD of between about <NUM> to less than about <NUM>.

The inner diameter (ID) of the tubular porous fibers may be any appropriate value that is less than the OD. For example, in different embodiments, the inner diameter (ID) of the tubular porous fiber filters may be equal to or greater than about <NUM> (but less than the OD). In a specific example, the ID may be greater than <NUM>. In another example, the ID may be equal to or greater than <NUM>. In a further example, the ID may be equal to or greater than <NUM>. In a further example, the ID may be equal to or greater than <NUM>. In a further example, the ID may be equal to or greater than <NUM>. In a further example, the ID may be equal to or greater than <NUM>.

The inner diameter is situated concentrically in relationship to the outer diameter. The distance between the outer edge of the inner diameter space and the outer diameter of the tube is the same at any point. This leads to a generally consistent wall thickness throughout the tubular filter. The wall thickness of the tubular porous fiber filter may range from about mm to about <NUM>. In a specific example, the wall thickness may be equal to or greater than <NUM>. In another example, the wall thickness may be equal to or greater than <NUM>. In a further example, the wall thickness may be equal to or greater than <NUM>. In a further example, the wall thickness may be equal to or greater than <NUM>.

The tubular porous fiber filter of the present disclosure is homogenous with a seamless structure.

The tubular porous fiber filter of the present disclosure is self-supporting.

The tubular porous fiber filter of the present disclosure may have a tensile strength great than about <NUM> PSI along the long axis of the filter using the ASTM D638 method.

The tubular porous fiber filter of the present disclosure may be strong with a burst strength of at least about <NUM> pounds per square inch (PSI). In one specific example, the burst strength may be at least <NUM> PSI. In another example, the burst strength may be at least <NUM> PSI. In a further example, the burst strength may be at least <NUM> PSI.

The tubular porous fiber filter of the present disclosure may have a strength that allows it to be back washed at pressures greater than about <NUM> PSI. In another example, the tubular porous fiber filter may have a strength that allows it to be back washed at pressures greater than <NUM> PSI. In a further example, the tubular porous fiber filter may have a strength that allows it to be back washed at pressures or greater than <NUM> PSI.

In various embodiments, the tubular porous fiber filters of the present disclosure do not contain a binding agent. Additionally, the fibers in the filters may be thermally fused together at spaced apart locations.

In different embodiments, the fibers in the tubular porous fiber filter of the present disclosure have an average diameter less than about <NUM> microns. In a specific example, the fibers have an average diameter of less than about <NUM> microns. In another example, the fibers have an average diameter of less than about <NUM> microns. In a further example, the fibers have an average diameter of less than about <NUM> microns. In an even further example, the fibers have an average diameter of or less than about <NUM> microns. However, the average fiber diameter is generally greater than <NUM> microns, greater than <NUM> microns, or greater than <NUM> microns.

The tubular porous fiber filter of the present disclosure may comprise fibers with different diameters, and the different diameter fibers may have different ratios (not in accordance with the invention). For example, the filter may contain more than one kind of fiber. One fiber may have a diameter of <NUM> microns while another fiber may have a diameter of <NUM> microns. Further, these two kinds of fibers may be present at various ratios (weight %). Non limiting examples of various ratios include but are not limited to <NUM>% to <NUM>%, <NUM>% to <NUM>%, <NUM>% to <NUM>%, or <NUM>% to <NUM>%.

<FIG> illustrates one example of a tubular porous fiber filter <NUM> that has a fiber orientation along a length <NUM> of the filter <NUM>. In this example, the fibers are generally aligned along the length and extend in the length direction. For example, the fibers are oriented generally in parallel along a long axis of the filter. As otherwise described herein, the fibers may be bicomponent fibers.

The tubular porous fiber filter <NUM> of the present disclosure may have a gradient structure (not in accordance with the invention). One example is illustrated by <FIG>. In the example shown by <FIG>, the filter <NUM> may have a smaller pore size at the external surface <NUM> than at the internal surface <NUM>. This is shown schematically by denser or smaller diameter fibers at the external surface. For example, pore sizes along the external surface <NUM> may be about <NUM> to about <NUM> microns. Pore sizes along the internal surface <NUM> may be about <NUM>% or <NUM>% or <NUM>% or <NUM>% larger. In the example shown by <FIG>, the filter may have a smaller pore size at the internal surface <NUM> than at the external surface <NUM>. This is shown schematically by denser or smaller diameter fibers at the internal surface. For example, pore sizes along the internal surface <NUM> may be about <NUM> to about <NUM> microns. Pore sizes along the external surface <NUM> may be about <NUM>% or <NUM>% or <NUM>% or <NUM>% larger. In liquid filtration applications, when surface filtration property is preferred, the liquid flow would be in the direction from the smaller pore size surface to the larger pore size surface. This is illustrated by <FIG>.

All fibers have the same fiber density or diameter throughout the structure. This is schematically illustrated by <FIG>. This may be referred to as a homogeneous fiber distribution.

In <FIG>, flow <NUM> moves from the outside of the filter to the inside of the filter. Flow <NUM> exits one of the ends of the filter via way of the internal surface <NUM>. This may be referred to as outside-inside filtration or "pressure differential" filtration. This could be achieved by adding positive pressure from outside or pulling vacuum from inside. When deep filtration property is preferred, the liquid flow would be in the direction from the larger pore size surface to the smaller pore size surface. This is illustrated by <FIG>. In <FIG>, flow <NUM> moves from the inside of the filter to the outside of the filter. Flow <NUM> enters at one of the ends <NUM> of the filter and exits via way of the external surface <NUM>. This may be referred to as inside-outside filtration or "cross flow" filtration. This disclosed design will provide the tubular filter with improved filtration efficiency and longevity. The pore size differences between the smaller and larger surface could be, <NUM>, <NUM>, <NUM> or <NUM>%. For example, the pore size of internal surface and external surface could vary from <NUM> to <NUM> microns independently, or from <NUM> to <NUM> microns independently.

The fibers in tubular porous fiber filters of the present disclosure can be bicomponent fibers or combinations of bicomponent fiber and monocomponent fibers.

In one embodiment, the fiber used to make the tubular porous fiber filters of the present disclosure is a bicomponent fiber. These bicomponent fibers include, but are not limited to, polyethylene/polypropylene (PE/PP), polyethylene/polyethylene terephthalate (PE/PET), polypropylene/polyethylene terephthalate (PP/PET), polyethylene terephthalate polypropylene/ (PET/PP), co-polyethylene terephthalate/polyethylene terephthalate (co-PET/PET), polyethylene terephthalate /Nylon (PET/Nylon), Nylon/polyethylene terephthalate (Nylon/PET), ethylene vinyl alcohol/polyethylene terephthalate (EVOH/PET), Nylon/Nylon, EVOH/Nylon, and PET/polybutylene terephthalate (PET/PBT). Bicomponent fibers may have different cross-sectional structures, such as core/sheath, side-by-side, tipped, islands in the sea, and segmented pie. The bicomponent fibers can also have different shapes, such as round, trilobal, and cross shaped structures.

The bicomponent fibers have a core/sheath structure. The sheath has a higher melting point than the core. In an alternate example which does not form part of the present invention, the core may have a higher melting point than the sheath.

The tubular porous fiber filters of the present disclosure have a structure in which the fibers in the filter are predominantly oriented along the long axis of the tubular filter.

The tubular porous fiber filters of the present disclosure have a structure in which the void space in the filter is less than about <NUM>%. In other examples, the void space may be less than about <NUM>%, less than about <NUM>% or less than about <NUM>% based on the following calculation. Void Volume or Porosity (%) = [<NUM> - (Bulk Density) / (Material or Fiber Density)] x <NUM> Where: <MAT> <MAT>.

The void space in the tubular porous fiber filter is less than about <NUM>%. In other examples, the void space may be less than about <NUM>%, less than about <NUM>%, or less than about <NUM>% based on the mercury intrusion test (ASTM D4404).

The tubular porous fiber filters of the present disclosure can filter out particles <NUM> microns in size at an efficiency greater than <NUM>%. In a specific example, the filtration level may be greater than <NUM>%. In an even further example, the filtration level may be greater than <NUM>%.

In other examples, the tubular porous fiber filters of the present disclosure can filter out particles that are about <NUM> microns in size at the above efficiency rates. In further examples, the tubular porous fiber filters of the present disclosure can filter out particles <NUM> microns in size at the above efficiency rates. In even further examples, the tubular porous fiber filters of the present disclosure can filter out particles that are <NUM> micron in size at the above efficiency rates. In even further examples, the tubular porous fiber filters of the present disclosure can filter out particles that are <NUM> micron in size at the above efficiency rates.

The tubular porous fiber filters of the present disclosure may have a flow rate for water at least <NUM> gallons per square foot, per day (GFD; equal to <NUM> liters per square meter) at a pressure of <NUM> kPa (<NUM> PSI); at least <NUM> GFD at a pressure of <NUM> PSI; or at least <NUM> GFD at a pressure of <NUM> PSI. The tubular porous fiber filters of the present disclosure can be used in positive pressure filtration. Filtration options include cross flow filtration, or negative pressure based filtration, such as vacuum based filtration.

In one embodiment, the tubular porous fiber filters of the present disclosure can be used in filtration applications in which liquids flow from inside the tube to the outside of the tube. In another embodiment, the tubular porous fiber filters of the present disclosure can be used in filtration applications in which liquids flow from outside the tube to inside the tube.

The disclosed tubular porous fiber filters may be produced by polymer extrusion. Neat polymer is extruded through a die in which a known number of holes are present at known spacing and known diameter. Hot air at a fixed temperature and fixed velocity causes the extension of the extruded polymer fibers. Examples of the process air temperature vary between <NUM> to <NUM>, and air velocity between <NUM> and <NUM> m3/h (<NUM> and <NUM> cfm). The fibers are collected on a belt moving at fixed and known velocity. The extruded polymer fibers are shaped through a die of fixed dimensions, without the use of lubricants or other process aids. The porous fiber filters are cut to desired lengths. For example, the lengths of the filters can be <NUM> to <NUM> inches, <NUM> to <NUM> inches or <NUM> to <NUM> inches (<NUM> inch is <NUM>). Of course, it should be understood that other lengths may be used and are considered within the scope of this disclosure.

The tubular porous fiber filters of the present disclosure can be further coated with polymeric membranes. The coating membranes and process of coating polymeric membrane onto the tubular porous fiber filters of present disclosure are described in <CIT>and <CIT>. The polymeric membrane coating could be at the internal surface, the external surface, or at both the internal and the external surfaces of the tubular fiber filters.

The tubular porous fiber filters of the present disclosure can be used in bioprocesses. Nonlimiting examples include downstream processes in biopharmaceutical manufacturing; food processing, such as milk, wine or juice processing; water filtration, such as waste water treatment, oil production, and swimming pool filtration.

The tubular porous fiber filters of the present disclosure can be used as pre-filters for current membrane-based ultrafiltration, nanofiltration, and reverse-osmosis (RO) devices for reducing fouling of the membrane.

The following examples will serve to further illustrate the present disclosure without, at the same time, however, constituting any limitation thereof. On the contrary, it is to be clearly understood that resort may be had to various embodiments, modifications and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the scope of the disclosure.

Porous tubular fiber filters were made from bicomponent polyethylene terephthalate (PET)/polypropylene (PP) fiber. PET was the sheath of each fiber with PP at the core. The weight percentage (wt. %) of PET was <NUM>% and the wt. % of PP was <NUM>% in the bicomponent fibers. Filters were made as described above.

Claim 1:
A self-supporting seamless tubular porous fiber filter, the filter comprising bicomponent fibers, wherein the bicomponent fibers are oriented generally in parallel along a long axis of the filter,
wherein a void space in the filter is less than <NUM>%,
wherein the bicomponent fibers have a core/sheath structure, and the sheath has a higher melting temperature than the core, and
wherein the filter comprises fibers having a generally homogeneous fiber distribution such that all fibers have the same fibre density or diameter throughout the filter.