Patent Application
20070269643
The fibers used in the filter medium of the present invention are core-sheath fibers, preferably spunbond polyester, produced with an antimicrobial additive in the sheath polymer. The fibers are prepared by spinning together two polymers to produce a bicomponent fiber. Each fiber is composed of an inner “core” polymer with an outer “sheath” polymer. In the present invention, an antimicrobial agent is added to the sheath polymer before extrusion.
The term “core-sheath” is art recognized and refers to fibers containing at least two different component polymers that are arranged to occupy distinct sections across the cross-section of each of the fibers along the entire or substantially entire length of the fiber. In a preferred embodiment, the core-sheath fibers generally contain at least two component polymers having different melting points, and the lowest melting component polymer forms at least a portion of the peripheral surface of each of the filaments. The component polymers are generally selected to have a melting point difference between the highest melting component polymer and the lowest melting component polymer of at least about 5° C., more preferably at least about 10° C., most preferably at least about 30° C., such that the lowest melting polymer can be melted or rendered tacky without melting the higher melting component polymers of the filaments. This difference in melting points is advantageously used to bond the fibers to each other via the softened/melted sheath component(s). When a nonwoven web containing the core-sheath fibers is heated to a temperature equal to or higher than the melting point of the lowest melting component polymer but below the melting point of the highest melting component polymer, the melted peripheral portions of the filaments form interfiber bonds, especially at the cross-over contact points, throughout the web while the high melting polymer portions of the filaments maintain the physical and dimensional integrity of the web.
The sheath portion of a fiber is bonded to one or more adjacent core fibers, forming an interconnected three-dimensional array of core fibers interspersed and connected by the sheath material. The sheath material connects the core fibers together, such that the carded nonwoven filter media is porous. This bonding is generally accomplished by melting the sheath material about the core fiber. At points of contact, the melted sheath material solidifies upon cooling, thereby forming the interconnected three-dimensional porous filter media.
The nonwoven web formed from the core-sheath fibers is bonded using any effective bonding means that heats the web to a temperature sufficiently high enough to melt the lowest melting component polymer but below the melting point of the higher melting structural component polymers of the web, thereby causing the filaments to form interfiber bonds, especially at cross-over contact points, throughout the web. For example, a through-air bonding, oven bonding, or infrared bonding process that effects interfiber bonds without applying significant compacting pressure can be used. Particularly useful is a through-air bonding process which effects interfiber bonds by thoroughly and evenly heating the web with a penetrating flow of forced, heated air.
The core-sheath fibers are produced from a wide variety of thermoplastic polymers that are known to form fibers. As indicated above, the core-sheath fibers contain at least two component polymers having different melting points. Examples of suitable polyolefins include polyethylene, e.g., high density polyethylene, low density polyethylene and linear low density polyethylene; polypropylene, e.g., isotactic polypropylene, syndiotactic polypropylene, and blends of isotactic polypropylene and atactic polypropylene; polybutene, e.g., poly(1-butene) and poly(2-butene); polypentene, e.g., poly(1-pentene), poly(2-pentene), poly(3-methyl-1-pentene) and poly(4-methyl-1-pentene); copolymers thereof, e.g., ethylene-propylene copolymers; and blends thereof. Polymers suitable for the second component of the fiber include polyolefins; polyamides, e.g., nylon 6, nylon 6/6, nylon 10, nylon 12 and the like; polyesters, e.g., polyethylene terephthalate, polybutylene terephthalate and the like; polycarbonates; polystyrenes; thermoplastic elastomers, e.g., ethylene-propylene rubbers, styrenic block copolymers, copolyester elastomers and polyamide elastomers and the like; fluoropolymers, e.g., polytetrafluoroethylene and polytrifluorochloroethylene; vinyl polymers, e.g., polyvinyl chloride; polyurethanes; and blends and copolymers thereof. In a preferred embodiment, the polymers used are spunbond polyester fibers.
Particularly useful core-sheath fiber pairs include polyolefin-polyamide, e.g., polyethylene-nylon 6, polyethylene-nylon 6/6, polypropylene-nylon 6, polypropylene-nylon 6/6, polyethylene-a copolymer of nylon 6 and nylon 6/6, and polypropylene-a copolymer of nylon 6 and nylon 6/6; polyolefin-polyester, e.g., polyethylene-polyethylene terephthalate, polypropylene-polyethylene terephthalate, polyethylene-polybutylene terephthalate and polypropylene-polybutylene terephthalate; and polyolefin-polyolefin, e.g., polyethylene-polypropylene and polyethylene-polybutylene, and most preferably spunbond polyesters.
The term “spunbond fibers” as used herein indicates small diameter filaments that are formed by extruding one or more molten thermoplastic polymers as fibers from a plurality of capillaries of a spinneret. The extruded fibers are cooled while being drawn by an eductive or other well-known drawing mechanism to form spunbond fibers. The drawn spunbond fibers are then deposited or laid onto a forming surface in a random manner to form a loosely entangled and uniform fiber web. The laid fiber web is then subjected to a bonding process, such as thermobonding or by needlepunching, to impart physical integrity and dimensional stability. Typically, spunbond fibers have an average diameter of at least about 10 microns. Exemplary processes for producing spunbond nonwoven webs are well known. Spunbonded webs are characterized by a relatively high strength/weight ratio, high porosity, have abrasion resistance properties and are typically non-uniform in such properties as basis weight and coverage.
Spunbonded polymeric nonwoven webs can be produced by extruding polymer through a die to form a multiplicity of continuous thermoplastic polymer strands as the polymer exits holes in the die in a generally downward direction onto a moving surface where the extruded strands are collected in a randomly distributed fashion. The randomly distributed strands are subsequently bonded together by to provide sufficient integrity in a resulting nonwoven web of continuous fibers.
In the filter media, an antimicrobial agent will be present in each sheath strand rather than combining strands of core polymer with strands of antimicrobial. Generally, the filter media of the present invention is comprised of a majority of the core-sheath fibers with the sheath portion containing an antimicrobial agent. The remaining fibers of the filter media can be any other suitable fiber for the media. Preferably, the filter media is comprised of at least 75% of such core-sheath fibers, more preferably at least 90%, and most preferably all the fibers of the filter medium are such core-sheath fibers with the sheath portion containing an antimicrobial agent. The antimicrobial agent prevents a wide array of mold/fungus/bacteria from growing on the finished media. The finished media is intended for use in the pool/spa filter market or other end uses where the product's properties make it fit for use. Different levels of antimicrobial loading and varied total concentration percentage of antimicrobial in the sheath, assuming antimicrobial properties are maintained, can be used depending on the particular application. Generally, it is preferred that the amount of antimicrobial contained in the sheath ranges from 0.1 to 7.0 wt %, and more preferably from 0.5 to 5.0 wt % based on the weight of the total fiber.
In a preferred embodiment, a polymer chip pre-loaded with antimicrobial will be used. Americhem and Sanitized® are commercially available possible antimicrobial polymer suppliers. The Sanitized® products involve an antimicrobial additive based on a natural active substance in the form of silver-ions encapsulated in a patented ceramic material. Sanitized® MB PET 20-53, for example, imparts a reliable effect against a large number of microbes such as bacteria and fungi. The silver-ions inhibit the intracellular enzyme induction and block the oxygen transfer function of lower forms of life. Thus, microbes are inactivated and can no longer proliferate. The Americhem antimicrobial product performs the same function but is made up of different chemical compounds and provides antimicrobial protection by other chemical/physical means.
In general, the anti-microbial/anti-fungal additives can be inorganic compounds using such metals as copper, zinc, tin, and silver. The best results are obtained using a silver additive dispersed in a polymer such as polyethylene (PE), PET, or polybutylene terephthalate (PBT) carrier, but could be added directly to a melt of a sheath thermoplastic without an intermediate carrier.
The term “pool” as used herein, is intended to include swimming pools of various sizes, wading pools, spas, hot tubs, Jacuzzi, and the like. The term “pools” as used herein includes not only ordinary swimming pools but also whirlpools installed in sports clubs, Kurhaus (spa houses) and healthcare facilities, as well as various kinds of health promoting hot tubs and spas. For example, a spa can be considered a small pool used for bathing or hydrotherapy in which water is heated and circulated. A typical spa has a volume of less than about 1,500 gallons. The spa can include hydrotherapy jet circulation, hot water/cold water mineral baths, air induction bubbles, or combinations thereof. Other common terminology for spas includes hydrotherapy pools, therapeutic pools, whirlpools, hot spas, hydrotherapy spas, or hot tubs.
Generally, the water in the pool is not drained, cleaned or refilled for each individual bather. Thus, it often is desirable to have a reliable water purification system for the pool. The water in a pool can be purified, for example, by adding chlorine to kill microorganisms that thrive in the warm water. The pool water is typically filtered as it is circulated. Typically, the water is “prefiltered” by a coarse filter prior to entry into the purification system (usually sand or diatomaceous earth filters). These coarse filters can be polymeric or metallic screens which trap dirt and debris from the water before it enters the purification system. In the present invention, the purification system comprises the filter medium of the present invention.
More specifically, where the pool is a hot tub or the like, the prefilter is the sole filter and is used to removed debris, insects, oils, bacteria and biofilm from the water. Generally, most hot tubs and the like do not have a secondary water purification system. Therefore, these filters or cartridges perform the task of filtering the pool water and need to be cleaned on a regular basis. Providing a filter using the filter medium of the present invention would greatly improve the sanitation aspects of such a pool or hot tub.
According to a preferred configuration of the present invention, a bi-component fiber is formed of a sheath component and a core component using polyethylene terephthalate (PET) (or some other thermoplastic polymer) in the core, making up between 20 to 80% of the fiber by weight. The sheath is also PET, or some other suitable thermoplastic polymer, making up between 80 to 20% of the fiber by weight including, as a dispersed solid, an additive which is an anti-microbial compound, to gain the efficiency of the additive on the surface and not wasting the additive in the core.
In the more generalized case as mentioned above, the sheath may be quite thin. However, preferably the sheath is more than 25% of the total fiber cross-section. It has been found that one of the best methods for retaining the anti-microbial qualities in the fiber and in fabrics is to use sheath thicknesses which are properly related to the size of the anti-microbial additive particles. When the particles are larger or smaller, the thickness of the sheath is adjusted accordingly in order to make sure the microbial agent is firmly held in place, and not worked away.
The bi-component anti-microbial/anti-fungal synthetic fiber size would preferably range from 0.5 dTex to 30.0 dTex and could be produced as a cut staple fiber in lengths from 1.0 mm to 180 mm, or in a continuous filament.
Additives which can be incorporated include one or more of UV stabilizers at fire retardant additives; pigments; hydrophilic additives; hydrophobic additives; and/or anti-stain additives.
The bi-component fiber may be formed by the use of pellets of the two different polymers or a direct polymer stream from the reactor of which the fiber is to be formed. An anti-microbial additive is preferably incorporated into the sheath polymer prior to the final extruding of the fiber. In the prior art, this was mostly done as a treatment after extruding.
Having thus described the invention in detail, it will be understood that such detail need not be strictly adhered to, but that additional changes, and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the following claims.
