WO2007024445A1

WO2007024445A1 - Hvac meltblown nanoweb filter media

Info

Publication number: WO2007024445A1
Application number: PCT/US2006/030407
Authority: WO
Inventors: David Thomas Healey; Donna Latham
Original assignee: Hollingsworth & Vose Company
Priority date: 2005-08-19
Filing date: 2006-08-03
Publication date: 2007-03-01

Abstract

An HVAC filter media is provided having an improved filtration efficiency and a high MERV rating, as well as methods for making the same. In one exemplary embodiment, an HVAC filter media is formed from a coarse nonwoven web having a fine fiber web mated thereto. The resulting filter media preferably has a MERV rating of at least about 7.

Description

HVAC MELTBLOWN NANOWEB FILTER MEDIA

FIELD OF THE INVENTION The present invention relates to filter media for use in the HVAC market, and in particular to HVAC filter media having an improved efficiency.

BACKGROUND OF THE INVENTION

MERV (Minimum Efficiency Reporting Value) ratings are used by the HVAC (Heating, Ventilating and Air Conditioning) industry to describe a filter's ability to remove particulates from the air. The MERV rating is derived from the efficiency of the filter versus particles in various size ranges. A higher MERV rating means better filtration and greater performance.

There are currently two common types of HVAC filters used in commercial and residential markets. The first type is a carded nonwoven, which relies solely on mechanical filtration. These filters can be made from several different materials, including various polymers, cotton, rayon, acrylics, etc. The materials are, however, limited to having a minimum fiber size of about 7 μ. As a result, current carded nonwoven HVAC filters can only achieve a MERV rating, at a usable pressure drop, of about 7.

The second type of HVAC filters commonly used in commercial and residential markets relies on electrostatic charge to obtain higher filtration efficiencies. This class of filters typically consists of meltblowns, spunbonds, carded electret nonwovens, fibrillated films, etc. Many of these products can achieve an initial MERV rating, with a usable pressure drop, of up to about 12. One drawback is, however, that the filters tend to lose electrostatic charge during the life of the filter, thereby decreasing the efficiency of the filter.

Accordingly, there remains a need for HVAC Filter media having an improved filtration efficiency and a high MERV rating. There also remain a need for methods for making such filters.

SUMMARY OF THE INVENTION

The present invention generally provides filter media having an improved filtration efficiency and a high MERV rating, as well as methods for making the same. In one exemplary embodiment, an HVAC filter media is provided formed from a coarse nonwoven web, such as a carded nonwoven web, having a fine fiber web mated thereto. The coarse nonwoven web and the fine fiber can each be formed from a variety of materials, and the filter media can include any number of layers of each web. The resulting filter media preferably has a MERV rating of at least about 7, and more preferably about 8. The MERV rating is preferably independent of any electrostatic charge, and in particular the HVAC filter media can be substantially free from electrostatic charge and still have a MERV rating of at least about 7, and more preferably about 8.

In one exemplary embodiment, the coarse nonwoven web can be formed from fibers having an average cross-sectional area of at least about 20 μ², and more preferably at least about 78.5 μ², and the fine fiber web can be formed from fibers having an average cross-sectional area less than about 12.5 μ², and more preferably in the range of about 0.2 μ² to 1.8 μ², and most preferably about 0.5 μ². Where the coarse nonwoven web and fine fiber web are formed from cylindrical fibers, the coarse nonwoven web can be formed from fibers having an average diameter of at least about 5 μ, and more preferably at least about 10 μ, and the fine fiber web can be formed from fibers having an average diameter of less than about 5 μ, and more preferably in the range of about 0.5 μ to 1.5 μ, and most preferably about 0.8 μ.

In another exemplary embodiment, the coarse nonwoven web can have a basis weight in the range of about 20 gsm to 200 gsm, and/or an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O. The fine fiber can have a basis weight in the range of about 0.5 gsm to 30 gsm, and/or an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O. The fine fiber web can also be mated to the coarse nonwoven web using a variety of techniques. In one exemplary embodiment, the fine fiber web can be a meltblown fine fiber web that is meltblown directly onto at least one surface of the coarse nonwoven web. The fine fiber web can be formed from, for example, polypropylene meltblown fibers. In other embodiments, the fine fiber can be adhesively bonded to or laminated onto the coarse nonwoven web.

A method for forming an HVAC filter media is also provided and can include forming a coarse nonwoven web, such as a carded nonwoven web, and mating a fine fiber web to at least one surface of the coarse nonwoven web to form a filter media having a MERV rating of at least about 7, and more preferably about 8. The coarse nonwoven web is preferably formed from fibers having an average cross-sectional area of at least about 20 μ², and more preferably at least about 78.5 μ², and the fine fiber web can be formed from fibers having an average cross-sectional area less than about 12.5 μ², and more preferably in the range of about 0.2 μ² to 1.8 μ², and most preferably about 0.5 μ². Where the coarse nonwoven web and fine fiber web are formed from cylindrical fibers, the coarse nonwoven web can be formed from fibers having an average diameter of at least about 5 μ, and more preferably at least about 10 μ, and the fine fiber web can be formed from fibers having an average diameter of less than about 5 μ, and more preferably in the range of about 0.5 μ to 1.5 μ, and most preferably about 0.8 μ.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. IA is photomicrograph at IOOX of a fine meltblown fiber disposed on a carded nonwoven web;

FIG. IB is photomicrograph at 750X of the filter media shown in FIG. IA;

FIG. 1C is a chart showing the fiber diameter distribution of the filter media shown in FIGS. IA and IB; FIG. 2 A is a photomicrograph at IOOX of a carded nonwoven web;

FIG. 2B is a photomicrograph at 750X of the carded nonwoven web shown in FIG. 2A;

FIG. 2C shows the fiber diameter distributions of a carded nonwoven web; and

FIG. 3 is a chart illustrating the efficiency of Samples 1A-3B and Controls A-C tested at various particle size ranges.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides filter media having improved filtration efficiency and a high MERV rating, and to methods for making the same. In one exemplary embodiment, the filter media can include a coarse nonwoven web having a fine fiber disposed thereon. The resulting filter media preferably has a MERV rating of at least about 7, and more preferably about 8. The MERV rating can be independent of any electrostatic charge, and in particular the HVAC filter media can be substantially free from electrostatic charge and still have a MERV rating of at least about 7, and more preferably about 8. The filter media is particularly useful in the HVAC market, however a person skilled in the art will appreciate that it can be adapted for a variety of other filtration uses.

The coarse nonwoven web used to form the HVAC filter media can be formed from any number of layers, and it can be formed from a variety of materials having various properties. In an exemplary embodiment, the coarse nonwoven web is formed from fibers having an average cross-sectional area that is at least about 20 μ², and more preferably at least about 78.5 μ². Where the fibers used to form the coarse nonwoven web are cylindrical fibers, a cross-sectional area of about 20 μ² equates to a fiber diameter of about 5 μ, and a cross-sectional area of about 78.5 μ² equates to a fiber diameter of about 10 μ. The fibers can also have a basis weight that is in the range of about 20 gsm to 500 gsm. The exemplary coarse nonwoven web, when formed, can have an air permeability that is in the range of about 100 CFM/ft² to 3000 CFM/ft² as measured at 0.5" H₂O. A mixture of various fiber types can be also used and combined together during the carding process. Exemplary fibers used to form the coarse nonwoven web include, by way of non-limiting example, meltblown materials, spunbond materials, wet laid materials, fluff pulp materials, etc. In one exemplary embodiment, the coarse nonwoven web can be a carded nonwoven web formed from a mixture of a biocomponent fiber, such as a 4 denier, 51 mm bi component 180 C melt point fiber, and staple fibers, such as a 6 denier, 2" polyethylene terephthalate staple fiber and a 0.9 denier 2" polyethylene terephthalate staple fiber. In other embodiments, the coarse nonwoven web can be in the form of a fibrillated film, a spunbond, or a web formed from fluff pulp processes.

The filter media also include a fine fiber web that is mated to one or more surfaces of one or more layers of a coarse nonwoven web used to form the filter media The fine fiber web can be formed from a variety of materials and processes, and it can have a variety of properties. In an exemplary embodiment, the fine fiber web is formed from fibers having an average cross-sectional area that is less then about 12.5 μ², and more preferably that is in the range of about 0.2 μ² to 1.8 μ², and most preferably that is about 0.5 μ². Where the fibers used to form the fine fiber web are cylindrical fibers, a cross-sectional area of about 12.5 μ² equates to a fiber diameter of about 5 μ, and a cross-sectional area in the range of about 0.2 μ² to 1.8 μ² equates to a fiber diameter in the range of about 0.5 μ to 1.5 μ, and a cross-sectional area of about 0.5 μ² equates to a fiber diameter of about 0.8 μ. The fibers can also have a basis weight that is in the range of about 0.5 gsm to 30 gsm. The exemplary fine fiber web, when formed, can have an air permeability that is in the range of about 100 CFM/ft² to 3000 CFM/ft² as measured at 0.5" H₂O. One exemplary material used to form the fine fiber web is polypropylene, such as a 400 Melt Flow Index Polypropylene available from Ashland Chemical.

The fine fiber can be mated to at least one surface of the coarse nonwoven web using a variety of techniques. By way of non-limiting example, the fine fiber can be laid, air laid, carded, dry laid, wet laid, spun bond, meltblown, or laminated onto the coarse nonwoven web. Other mechanical, chemical, or radiation bonding techniques can also be used to mate the fine fiber to the nonwoven web. In an exemplary embodiment, the fine fiber is meltblown directly onto one or more surfaces of one or more layers of a coarse nonwoven web to form a high efficiency HVAC filter media. The resulting filter media preferably has a basis weight that is in the range of about 20.5 GSM to 530 GSM, and an air permeability that is in the range of about 50 CFM/ft² to 1500 CFM/ft² as measured at 0.5" H₂O. The resulting filter media also preferably has a high efficiency, such that the MERV rating of the filter media is at least about 7, and more preferably about 8, with little or no increase in pressure drop across the media. The high MERV rating is believed to be due to the use of the fine fiber .web, rather than the presence of any electrostatic charge, as will be discussed in more detail below. Thus, the filter media can be substantially free from electrostatic charge, or it can optionally include an electrostatic charge to further enhance the filtration efficiency and MERV rating. FIGS. IA and IB illustrate a photomicrograph of a fine fiber meltblown web deposited onto a carded nonwoven web. FIG. 1C is a chart showing the fiber diameter distribution of the fine fiber meltblown web of the filter media shown in FIGS. IA and IB. FIGS. 2 A an 2B illustrate a photomicrograph of the carded nonwoven web without the fine fiber meltblown web disposed thereon. FIG. 2C is a chart showing the fiber diameter distribution of the carded nonwoven web of the filter media shown in FIGS. 2A and 2B.

The following non-limiting examples serve to further illustrate one exemplary embodiment of the invention. All fiber sizes in the samples refer to the average diameter of the fibers.

Sample IA

Sample IA is prepared by forming a carded nonwoven web from 28.8% of a 4 denier (20 μ) fiber, 48% of a 6 denier (24.6 μ) fiber, and 19.2% of a 0.9 denier (9.5 μ) fiber. 4% of a 0.8 μ polypropylene meltblown fiber is then meltblown directly onto one side of the carded nonwoven web to form the filter media. The resulting filter media has a basis weight of 73 gsm, a thickness of 74 mils, and an air permeability of 360 CFM/ft² at 0.5" H₂O.

Sample IB

Sample IB is prepared using the same process and materials described above with respect to Sample IA. The filter media is then condition by soaking the filter media in isopropyl alcohol to remove any electrostatic charge before testing. The resulting filter media has a basis weight of 73 gsm, a thickness of 74 mils, and an air permeability of 360 CFM/ft² at 0.5" H₂O.

Sample 2A

Sample 2A is prepared by forming a carded nonwoven web from 28.8% of a 4 denier (20μ) fiber, 48% of a 6 denier (24.6 μ) fiber, and 19.2% of a 0.9 denier (9.5 μ) fiber. 4% of a 0.8 μ polypropylene meltblown fiber is then meltblown directly onto one side of the carded nonwoven web to form the filter media The resulting filter media has a basis weight of 73 gsm, a thickness of 74 mils, and an air permeability of 360 CFM/ft² at 0.5" H₂O.

Sample 2B

Sample 2B is prepared using the same process and materials described above with respect to Sample 2A. The filter media is then condition by soaking the filter media in isopropyl alcohol to remove any electrostatic charge before testing. The resulting filter media has a basis weight of 73 gsm, a thickness of 74 mils, and an air permeability of 360 CFM/ft² at 0.5" H₂O.

Sample 3A

Sample 3 A is prepared by forming a carded nonwoven web from 48.8% of a 4 denier (20 μ) fiber, and 48.8% of a 15 denier (39 μ) fiber. 2.4% of a 0.8 μ polypropylene meltblown fiber is then meltblown directly onto one side of the carded nonwoven web to form the filter media. The resulting filter media has a basis weight of 128 gsm, a thickness of 77 mils, and an air permeability of 340 CFM/ft² at 0.5" H₂O.

Sample 3B

Sample 3B is prepared using the same process and materials described above with respect to Sample 3 A. The filter media is then condition by soaking the filter media in isopropyl alcohol to remove any electrostatic charge before testing. The resulting filter media has a basis weight of 128 gsm, a thickness of 77 mils, and an air permeability of 340 CFM/ft² at 0.5" H₂O. Control A

Control A is prepared by forming a carded nonwoven web from 60% of a 4 denier (20 μ) fiber, 20% of a 6 denier (24.6 μ) fiber, and 20% of a 0.9 denier (9.5 μ) fiber. The resulting filter media has a basis weight of 155 gsm, a thickness of 160 mils, and an air permeability of 406 CFM/ft² at 0.5" H₂O.

Control B

Control B is prepared by forming a carded nonwoven web from 60% of a 4 denier (20 μ) fiber, 20% of a 6 denier (24.6 μ) fiber, and 20% of a 0.9 denier (9.5 μ) fiber. The resulting filter media has a basis weight of 160 gsm, a thickness of 72 mils, and an air permeability of 331 CFM/ft² at 0.5" H₂O.

Control C Control C is prepared by forming a carded nonwoven web from 60% of a 4 denier (20 μ) fiber, 20% of a 6 denier (24.6 μ) fiber, and 20% of a 0.9 denier (9.5 μ) fiber. The resulting filter media has a basis weight of 145 gsm, a thickness of 90 mils, and an air permeability of 370 CFM/ft² at 0.5" H₂O.

The efficiency of Samples IA, IB, 2A, 2B, 3A, 3B, Control A, Control B, and Control C are each tested at various particle size ranges. Table 1 shows the test results for each filter media.

Table 1

FIG. 1 is a chart showing the efficiency as tested at various particle size ranges for each of the samples and the controls. As shown, Samples 1A-3B have a much higher efficiency at each of the particle size ranges tested than Controls A-C. As a result, Controls A-C have a MERV rating of 7, whereas Samples 1 A-3B have an increased MERV rating of MERV 8. The fine fiber is thus effective to produce a high efficiency HVAC filter media that does not rely on electrostatic charge to obtain a high MERV rating. One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

What is claimed is:

Claims

CLAIMS:

1. An HVAC filter media, comprising: a carded nonwoven web formed from fibers having an average cross-sectional area of at least about 20 μ²; and a fine fiber web mated to the carded nonwoven web, the fine fiber web being formed from fibers having an average cross-sectional area less than about 12.5 μ²; wherein the HVAC filter media has a MERV rating of at least about 7.

2. The HVAC filter media of claim 1 , wherein the MERV rating is at least about 8.

3. The HVAC filter media of claim 1 , wherein the fine fiber web comprises a meltblown fine fiber web that is meltblown directly onto at least one surface of the carded nonwoven web .

4. The HVAC filter media of claim 1 , wherein the fine fiber web is formed from fibers having an average cross-sectional area in the range of about 0.2 μ² to 1.8 μ².

5. The HVAC filter media of claim 1, wherein the fine fiber web is formed from fibers having an average cross-sectional area of about 0.5 μ².

6. The HVAC filter media of claim 1 , wherein the carded nonwoven web is formed from fibers having an average cross-sectional area of at least about 78.5 μ².

7. The HVAC filter media of claim 1 , wherein the carded nonwoven web has a basis weight in the range of about 20 gsm to 200 gsm.

8. The HVAC filter media of claim 1 , wherein the fine fiber web has a basis weight in the range of about 0.5 gsm to 30 gsm.

9. The HVAC filter media of claim 1, wherein the carded nonwoven web has an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O.

10. The HVAC filter media of claim 1 , wherein the fine fiber web has an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O.

11. The HVAC filter media of claim 1 , wherein the fine fiber web is formed from polypropylene meltblown fibers.

12. The HVAC filter media of claim 1 , wherein the HVAC filter media is substantially free from electrostatic charge.

13. A method for forming an HVAC filter media, comprising: forming a carded nonwoven web formed from fibers having a cross-sectional area of at least about 20 μ²; and mating a fine fiber web formed from fibers having a cross-sectional area less than about 12.5 μ² to at least one surface of the carded nonwoven web to form a filter media having a MERV rating of at least about 7.

14. The method of claim 13, wherein the MERV rating is at least about 8.

15. The method of claim 13, wherein the HVAC filter media is substantially free from electrostatic charge.

16. The method of claim 13, wherein the fine fiber web is meltblown onto at least one surface of the carded nonwoven web.

17. The method of claim 13, wherein the fine fiber web is laminated onto at least one surface of the carded nonwoven web.

18. The method of claim 13, wherein the carded nonwoven web is formed from a mixture of fib ers .

19. The method of claim 13, wherein the fine fiber web is formed from fibers having an average cross-sectional area in the range of about 0.2 μ² to 1.8 μ².

20. The method of claim 13, wherein the fine fiber web is formed from fibers having an average cross-sectional area of about 0.5 μ².

21. The method of claim 13, wherein the carded nonwoven web is formed from fibers having an average cross-sectional area of at least about 78.5 μ².

22. The method of claim 13, wherein the carded nonwoven web has a basis weight in the range of about 20 gsm to 200 gsm.

23. The method of claim 13, wherein the fine fiber web has a basis weight in the range of about 0.5 gsm to 30 gsm.

24. The method of claim 13, wherein the carded nonwoven web has an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O.

25. The method of claim 13, wherein the fine fiber web has an air permeability in the range of about 100 CFM/ft² to 3000 CFM/ft² when measured at 0.5" H₂O.

26. The method of claim 13, wherein the fine fiber web is formed from polypropylene meltblown fibers.