Liquid purification or separation – Processes – Separating
Reexamination Certificate
2002-04-22
2004-02-10
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Separating
C055S485000, C055S488000, C055S489000, C210S323100, C210S488000, C210S489000
Reexamination Certificate
active
06689278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a filter for removing an aqueous fluid and entities, such as bacteria, existing in such aqueous fluid, from a nonaqueous fluid.
2. Description of the Related Art
A number of patents are directed toward the combination of a hydrophobic filter and a hydrophilic filter for removing air or other gas from an intravenous fluid before such intravenous fluid reaches a patient. See, e.g., U.S. Pat. Nos. 4,013,072; 4,031,891; 4,116,646; 4,262,668; 4,278,084; 4,515,606; 4,525,182; 4,571,244; 4,615,694; 5,126,054; 5,308,333; 5,439,587; and 5,536,413.
None of the preceding patents, however, applies to a device which filters the fluid first through the hydrophobic filter and then through the hydrophilic filter or vice-versa. In each case, the intravenous liquid comes into contact with a hydrophobic filter through which gas from the liquid may escape and then the intravenous liquid passes through a hydrophilic filter.
Three patents do, though, apply to devices which transmit fluid through both a hydrophobic filter and a hydrophilic filter, viz., U.S. Pat. Nos. 4,026,792; 4,459,139; and 4,938,389.
U.S. Pat. No. 4,026,792 of George Otto Orth, Jr. applies to a “method of treating waste water containing particulate matter, liquid oils and fats to remove the same. . . .” The disclosure indicates that this waste water is first forced through a hydrophobic filter by centrifugal force. “Fats, oil and oily particulate matter are adsorbed by the hydrophobic filter . . . . The remaining waste water then moves radially into the hydrophilic filter . . . which removes the remaining particulate matter. As indicated in column 3 of U.S. Pat. No. 4,459,139, “The key characteristic of the hydrophobic filter membrane is, of course, that it will allow air or other gas to pass therethrough but will block the passage of water or other aqueous liquids. . . . [But] . . . a hydrophobic filter membrane has its own water-breakthrough point, i.e., the amount of pressure differential across the membrane required to drive water through it.” For the method of U.S. Pat. No. 4,026,792 to function as intended, the centrifugal force must, therefore, be sufficiently large that the pressure differential at least equals the water-breakthrough point.
In U.S. Pat. No. 4,459,139 of Charles E. vonReis and Karlis Vizulis, itself, a device is claimed “having a hydrophilic filter in overlying relationship to [a] . . . hydrophobic filter on the inlet chamber side of the hydrophobic filter such that any fluid flow from the inlet chamber to the outlet chamber can only be by passage of the fluid first through the hydrophilic filter and then through the hydrophobic filter. . . . ” Both the hydrophobic filter and the hydrophilic filter have a pore size rating in air of less than 0.5 microns and, preferably, of approximately 0.2 microns; each then “. . . blocks bacteria from passing. . . . ” These filters, furthermore, preclude liquid from reaching a suction pump used to aspirate liquid from a patient. The fact that a significant pressure differential is created across the combined filters is evident from the following excerpts:
In columns 2 and 3, it is stated that “[i]n operation the aspirator pulls a vacuum (i.e. a negative pressure) . . . to aspirate fluid from the patient. . . . ”
The vonReis patent, in column 4, further observes, “The hydrophobic filter used in the practice of the present invention should preferably have a water-breakthrough point of at least about 10 psi, and ideally above the maximum pressure differential which can be expected, i.e. about 14 psi for the aspirating system described.”
Columns 1 and 2 of the vonReis patent contain a declaration that, “[i]t is well known that a hydrophilic filter allows the passage of air therethrough until it is saturated with liquid but blocks or at least substantially restricts the passage of air when it does become saturated with liquid. Where the pressure differential across the hydrophilic filter does not exceed the bubble point of the filter (i.e. the pressure required to force air through the filter when it is saturated with liquid), the passage of air is completely blocked when it becomes saturated. But even where the pressure differential does exceed the bubble point, the hydrophilic filter when saturated will nevertheless substantially restrict the passage of air.”
And, again in column 4 of the vonReis patent, one reads, “ . . . in a preferred embodiment the hydrophilic filter membrane used had a bubble point of from about 7 to 10 psi and as it reached saturation the blockage of air was about 80%. . . . ”.
U.S. Pat. No. 4,525,182 of Donald B. Rising and Richard G. Naegeli, Jr., in fact, asserts, “The typical small pore size of the wetted [hydrophilic] filter prevents gas from passing through said filter at the usual operating pressures.” Moreover, using almost identical language, U.S. Pat. No. 5,439,587 of Ralph J. Stankowski, Michael C. Heath, and Douglas A. Boucher asserts, “The typical small pore size of the hydrophilic filter prevents gas from passing through the filter at the usual operating pressures.”
The third patent concerning a device which transmits fluid through both a hydrophobic filter and a hydrophilic filter, i.e., U.S. Pat. No. 4,938,389 of Scott R. Rossi and Jeffrey P. Gilbard, claims a reservoir for storing sterile liquids connected to a dispensing tip with a flow passage across which a filter assembly is sealed. The filter assembly comprises “a hydrophilic filter and a hydrophobic filter arranged in fluid communication serially along said flow passage so that said hydrophilic filter is nearer to said reservoir than said hydrophobic filter, said hydrophobic filter and said hydrophilic filter each having pores sufficiently small to act as a microbial filters.”
“In preferred embodiments of the invention, the filter assembly has the hydrophobic and hydrophilic filters separated, e.g., by a support ring. A more preferred embodiment has a filter structure whereby there are a plurality of support rings between, and on opposite sides of, the filters to provide structural support and filter separation.”
Since the examples of the Rossi patent utilized an “eye drop solution” as the sterile liquid, since solutions for rinsing a person's eyes are generally aqueous saline solutions, and since the Rossi patent was not limited to nonaqueous solutions, it is apparent that a significant pressure differential would have to be created across the hydrophobic filter, i.e., the water-breakthrough point would have to be reached, in order to permit the solution to pass through the hydrophobic filter.
It should be noted that none of the preceding patents were intended to remove water from another liquid.
Additionally, lines 11 through 12 in column 3 of U.S. Pat. No. 5,126,054 clarify that the “[l]iquiphobic layer 18 is superimposed on liquiphilic layer 16. . . . ” Similarly, U.S. Pat. No. 5,536,413 implies that there is no space between the liquiphobic and the liquiphilic layers of the gas venting element of that patent when it states that “ . . . the layers of the gas venting element may be individually prepared and bonded together by various means known to those skilled in the art.”
Moreover, none of the filter material in the preceding patents combines hydrophilic and hydrophobic characteristics on the molecular level. U.S. Pat. No. 4,031,891 of Thurman S. Jess does state, “While the invention has been described above as using three different filter elements, namely a hydrophilic filter element to cover the central window opening . . . and separate hydrophobic filter elements covering the opposing window openings . . . , it will be understood by those skilled in the art that use can also be made of a continuous sleeve of filter material, the ends of which have been rendered hydrophobic in nature and the central portion of which has been rendered hydrophilic in nature.” It is, however, apparent that the hydrophilic and the hydrophobic segm
Fehr Thompson E.
Kim John
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