US 8,523,971 B2 · Multilayer nanofiber filter

Abstract

A method of making a multilayer filter and the multilayer filter made by the method. The method includes generally two steps. The first step is to coat a layer of nanofibers on a single side or both sides of a substrate medium to obtain a composite filter medium, and the second step is to fold the composite filter medium in a serpentine fashion to form a multilayer filter. The second step may alternatively be accomplished by stacking up a number of sheets of the composite filter medium to form a multilayer filter having a structure of two layers of nanofibers being sandwiched between two layers of said substrate medium. The resulting multilayer filter produced by either method contains at least one structural unit which has two layers of nanofibers being sandwiched between two layers of the substrate medium.

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Drawings

Claims33

Dependent claims

A method of making a multilayer filter, comprising the steps of:

(a) coating a layer of nanofibers on a single side or on both sides of a substrate layer to obtain a composite filter medium;
and
(b) folding the composite filter medium into a serpentine-shaped arrangement to form a multilayer filter wherein the composite filter medium is folded into a plurality of nanofiber layers arranged in a sequential arrangement having alternating essentially perpendicular segments and essentially parallel segments with respect to airflow;
wherein the essentially perpendicular segments are larger than the essentially parallel segments;
wherein when airflow is applied, air passes through the plurality of nanofiber layers;
and
wherein in the multilayer filter pressure drop is reduced by at least 20% when compared with a filter having nanofibers deposited in a single layer while attaining a filtration efficiency within 10% of the filter having the nanofibers deposited in a single layer.

4 more elements

A multilayer filter having a top layer and a bottom layer and comprising:

(i) a plurality of layers of a substrate layer;
and
(ii) a plurality of layers of nanofibers,
the top layer and bottom layer each being a layer of the nanofibers and between the top layer and bottom layer there being at least one unit, or a plurality of units, each comprising one or more layers of the nanofibers sandwiched between two layers of the substrate layer;
wherein the substrate layer is made of coarse fibers having an average diameter in the range of between 1 and 30 microns, a basis weight in the range of between 10 and 600 gsm, a pressure drop of less than 2 Pa under 5 cms−1 face velocity, and a filtration efficiency of less than 3% for a particle size ranging from 0.05 to 0.5 microns;
wherein the layer of nanofibers has an average diameter within the range of between 0.1 and 0.4 microns, a basis weight of less than 0.3 gsm, and a thickness of less than 10 microns;
and
wherein the nanofibers maintain a pressure drop that is reduced by at least 20% when compared with a filter having nanofibers deposited in a single layer while attaining a filtration efficiency within 10% of the filter having the nanofibers deposited in a single layer.

5 more elements

Dependencies are inferred from the claim text.

Description5,320 words

Summary411 words

#Nanofibers ranging from 10 nm to 1000 nm have been used in filtration medium to capture submicron particles below 1000 nm. The ability of nanofibers to capture particles is believed to be due to combination of interception of submicron particles by the fibers as well as the Brownian motion or “random walk” of submicron particles, both of which facilitate the particles to be captured by the large surface/mass ratio of the nanofibers.

#Conventional filtration media may have a layer of nanofibers with a size distribution in a range of 100 to 300 nm laid on a substrate layer of the medium, as depicted in FIG. 1A. Further increase of capture capability may be obtained by increasing the nanofiber surface area such as by reducing the fiber diameter and/or by increasing the packing density of the nanofibers, as measured in terms of grams of nanofibers per square meter. However, since the nanofibers do not possess structural rigidity, when more fibers are laid, the additional nanofibers often compress to form a dense (i.e. low porosity or void space) and thick layer that substantially increase the pressure drop across the medium. This lowers the permeability of the filtration medium to airflow, and resulted in undesirable breathability to the filtration medium.

#Consequently, it is desirable to develop an improved nanofiber filtration medium that has a high filtration efficiency but low pressure drop. It is also desirable to develop a method of making the nanofiber filtration medium having these improved properties.

Brief description of the drawings30 figures

#FIG. 1A depicts a prior art filtration medium with a nanofiber layer on a substrate layer having 0.12 grams per square meter of nanofibers.

#FIG. 1B depicts the filtration medium of the present invention having the substrate layer sandwiched between the nanofiber layers having 0.12 grams per square meter of nanofibers on each side.

#FIG. 2A depicts a prior art filtration medium of FIG. 1A having 0.24 grams per square meter of nanofibers.

Detailed description4,214 words

#Reference will now be made in detail to a particular embodiment of the invention, examples of which are also provided in the following description. Exemplary embodiments of the invention are described in detail, although it will be apparent to those skilled in the relevant art that some features that are not particularly important to an understanding of the invention may not be shown for the sake of clarity.

#Furthermore, it should be understood that the invention is not limited to the precise embodiments described below, and that various changes and modifications thereof may be effected by one skilled in the art without departing from the spirit or scope of the invention. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. In addition, improvements and modifications which may become apparent to persons of ordinary skill in the art after reading this disclosure, the drawings, and the appended claims are deemed within the spirit and scope of the present invention

#A filtration medium may include one substrate layer and at least one nanofiber layers coated on at least one side of said substrate layer to form a bi-layer laminate unit, as depicted in FIG. 1A. In another arrangement, a filtration medium may also include at least one substrate layer, and at least two nanofiber layers. The substrate layer may be sandwiched between the nanofiber layers in a series to form an alternating tri-layer laminate unit, as depicted in FIG. 1B. The nanofiber layers and the substrate layer may adhere to one another to form a well-bonded laminate structure. The term “well-bonded laminate structure” means a multilayer filtration medium in which none of the layers are substantially corrugated. Using layers with small thickness may facilitate the formation of a well-bonded laminate structure.

Facts

Application

12/775,465Filed 6 May 2010 · us provisional application

Priority

7 May 2009

Published

US 2010/0307119 A19 Dec 2010

Granted

3 Sep 2013

Term ends

27 Jun 2031

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment, including 417 days of adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification26 codes

B01D 39/1623
The material being fibrous: of synthetic origin
B01D 39/2017
Glass or glassy material: the material being filamentary or fibrous
B01D 39/2055
Of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires: carbonaceous material
B01D 39/2065
Carbonaceous material: the material being fibrous

Timeline

7 May 2009Priority claimedParent application 61/176,115
6 May 2010Application filedUS 12/775,465
29 Aug 2010Assigned to The Hong Kong Polytechnic Universityassignment of assignor's interest
9 Dec 2010PublishedUS 2010/0307119 A1
3 Sep 2013GrantedUS 8,523,971 B2
7 Nov 2014Assigned to Avalon Nanofiber Limitedassignment of assignor's interest
12 Oct 2026TodayWithin its term
27 Jun 2031Term endsEstimated, includes 417 days of adjustment

Multilayer nanofiber filter

Life of this patent

Multilayer nanofiber filter

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims33

Description5,320 words

Classification26 codes

Life of this patent

Drawings

Description5,320 words