BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to a multi-layered cartridge housing for a fluid purifier to inhibit fluid contamination.

2. Description of the Related Art: Various water purifiers have been proposed to purify water for laboratory use. With the increase in sophistication of scientific testing equipment, the need for purified water has increased along with an increase in the desired level of purity. Laboratory requirements for purified water include reagent grade water with a resistivity of up to 18.3 megohm-cm and a total organic content (TOC) of less than 10 parts per billion. In order to achieve the above standards of water purification, water purifiers typically have four or more tubes containing purification cartridges. In those systems, water enters a tube at the top and flows down through purification media and up to the top of the next canister on the outside of the cartridge. Such a flow path exposes the water to a substantial surface area both during and after passing through the filter media. Often the fluid must flow through the container and conduit several times before the desired level of purity is achieved. This increased exposure to the conduit increases the possibility that contaminants may enter the fluid purification system.

When using an ultra-pure water purification system, the filter cartridge is often constructed of a plastic material. Any coloring pigment in the plastic may be dissolved by the water in its ultra-pure form because in its ultra-pure deionized form, it becomes a solvent. Accordingly, it has been recognized that the water purifier components which come in contact with the purified water should be constructed of any material which substantially limits absorption of contaminants by the water.

Chomka et al., in U.S. Pat. No. 5,397,468, have found that the various components of a water purification device may be constructed of polyethylene or another thermoplastic material that limits solvent absorption which causes contamination. However, this typically results in a cartridge housing which is susceptible to biological (i.e. bacterial) formation because the plastic

materials suggested by Chomka are clear or translucent in their natural state. As a result, if the filter is left unused for a period of time, light may cause bacteria to grow and the filter media to deteriorate. Accordingly, the present invention provides a filter cartridge which minimizes the release of extractable constituents and inhibits the growth of bacteria.

SUMMARY OF THE INVENTION The present invention provides a filter cartridge that includes a housing having an inlet, an outlet, and containing filter media. The cartridge housing has a first layer formed of a pure plastic material that does not react with the filter fluid, and a second layer of pigmented material that is typically a plastic material that includes additives to obscure the transmission of light through the housing so that bacteriological formation is inhibited. Calcium cabonate may also be added to the layer. Additionally, glass fibers may be added to the second layer to increase structural strength. In a preferred aspect of the present invention, the first layer may be selected from the group consisting of a pure polypropylene, a polyvinylidene fluoride material, polypropylene, Teflon® resin or another fluorinated thermoplastic material. In another aspect of the invention, a third layer of a gas impermeable membrane is provided so that gases are prevented from entering the filter media. For example, some types of filter media is adversely affected by exposure to carbon dioxide, and the like.

In another aspect of the invention the filter cartridge is formed of three layers such that the pure plastic layer is the inner-most (wetted) layer and the gas impermeable and the pigmented layers are positioned outside the inner layer. Preferably, the gas impermeable layer is disposed adjacent the inner layer, and the pigmented layer is the outermost layer. Pigment may be supplied on the external layer so that a design or product insignia will not interfere with the quality of the filtered water.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood by the forgoing description and the accompanying drawings in which:

FIG. 1 is a typical laboratory water purification system with disposable cartridges and non-disposable housing;

FIG. 2 is a filter cartridge with an integral housing;

FIG. 3 is a cross-section of a housing having two layers; and,

FIG. 4 is a cross-section of a housing having three layers.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for an improved water purification filter cartridge housing by selecting materials which are in contact with the water to minimize the release of extractable constituents, and also providing for the prevention of bacterial growth in filter media within the housing. The present invention may be utilized in a water purification system with a housing that contains disposable cartridges as illustrated in FIG. 1. Additionally, the present invention is illustrated in a cartridge with an integral housing unit in FIG. 2. In one type of water purification filler assembly illustrated in FIG. 1 , a water purification system filter assembly 20 includes housings 22 in which are disposed separate disposable cartridges 24. The cartridges 24 contain an appropriate water purification media, such as ion exchange resins or activated carbon, and are designed to separate the feed water from the product water. The flow through the media is either radially inward or outward as shown. The separate non-disposable housing 22 is designed to be able to withstand the water pressure of fluid flowing through the filter assembly. The illustrated housing consists of a bowl-shaped bottom secured with threads suggested at 26 to a flow manifold 28 that incorporates a feed inlet and the product outlet. The preferred flow through the filter is indicated by arrows 29.

The material selected for the housing can have a substantial effect on the quality of the final product. Often a plastic material is selected for the housing material because of its light weight and its relatively low cost. Typically, the plastic which is used contains a pigment or a colorant. Cartridge housings also may use additives such as calcium carbonate, talc; additionally glass fibers, and the like may be used to increase the structural strength of the cartridges. Because the water is deionized during the purification process, and deionized water acts as a solvent, impurities in the purified fluid may result from pigments or other additives which can be dissolved from the cartridge housing. Accordingly, the wetted surfaces, that is, the surfaces that contact the fluid, must be chosen to minimize the dissolution of colorants and other additives in the plastic housing.

Since the material composition of the housing may adversely affect the quality of the filtered water, the housing 22 includes a pure plastic layer 32 which is in contact with the wetted surfaces, and is chosen to minimize the release of extractable constituents, such as pigments. Any inert plastic, low extractable, material can be used to form layer 32. Materials such as pure

polyethylene, polypropylene, and polyvinylidene fluoride (PVDF), Teflon® resin or another fluorinated thermoplastic material, nylon, and the like, are preferred choices. "Pure" is intended to include inert, low extractable materials without pigments or fillers, and any material which does not react adversely to the deionized water. The use of a pure plastic material for the cartridge housing, such as polypropylene, however, has several disadvantages. The pure plastic material is typically clear, or at least translucent, and allows the passage of light through the filter housing to the filter media. This light may stimulate bacteriological growth in the water purification media and have an adverse affect on the quality of the water produced. Additionally, a clear or translucent cartridge housing in the water purification media is undesirably visible to the user. Finally, over a period of time the pure plastic materials typically allow the passage of gases from the atmosphere into the filter media. This action can also adversely effect the performance of the filter media. For example, carbon dioxide, always present in the atmosphere, will reduce the capacity of ion exchange resins. The present invention has the advantages of a pure plastic wetted surface, and overcomes the above mentioned problems by providing the cartridge housing to minimize the above disadvantages.

As illustrated in FIG. 1, the housing of the present invention is constructed having multiple layers. The inner layer 32 is in contact with the water is selected for purity, while the outer layer 34 is selected to block passage of light and/or gases. As noted above, the outer layer may be formed from a colored resin and/or include additives for structural strength. Moreover, if there is a separate outer layer, the tubes may be opaque or include a colored design to prevent light from reaching the filter media material and without the possibility of contaminating the filtered water.

Figure 2 is another illustration of the multilayered cartridge housing of the present invention incorporated in a filter cartridge unit 50. As illustrated, the filter cartridge unit includes a top plate 52, a bottom plate 54 and a cylindrical tube 56 in which fluid filter media 58 is disposed. The cylindrical tube includes a first layer 62 which is formed from a pure plastic material, such as polypropylene, or other material which does not react adversely to the deionized water. A second layer 64 is provided which may be formed from a pigmented material, and may further include gas impermeable additives.

If a cartridge has an integral housing, as suggested in FIG. 2, a representative example of a method for constructing the cartridge housing having two layers includes forming the cylinder

by co-extrusion, in which the multiple layers of materials are extruded together. A cartridge assembly is disclosed in co-pending U.S. Patent Application Serial No. 08/598,818, entitled Water Purification Cartridge Assembly with Unidirectional Flow Through Filter Media, filed concurrently with this application, on February 9, 1996, and is incoφorated herein by reference. FIG. 3 illustrates a cross section of a cartridge housing having an inner layer 62 formed from a pure plastic material and an outer layer 64 that contains fillers, and/or pigments and/or a gas impermeable additives.

The layer components may be molded. For example, the housing, illustrated in FIG 1 , may be formed first by thermoforming or molding the outer layer, inserting the outer layer into an injection mold cavity and then injection molding the inner layer onto the outer layer. As the mold cools, the inner layer will fuse with the outer layer.

Finally, as an alternative embodiment, shown in a cross-sectional view of a filter cartridge housing in FIG. 4, three layers may be provided in housing 70, an inner layer 72, an intermediate layer 74, and an outer layer 76. The inner layer may be formed from any type of inert plastic material which is non-reactive to the fluid passing within the filter. Preferably the material is a pure plastic, such as polypropylene or PVDF. The intermediate layer may be formed from a gas impermeable membrane layer so that gas may be prevented from contacting and possibly deteriorating the filter media. This may be a metallic layer. Finally, the outer layer 76 may be plastic that includes a colorant, or another additive, as desired to modify the visual appearance of the cartridge and prevent passage of light through to the purification media.

When the cylinder is formed as by, for example, molding, the outer layer may be molded and then a coating may be provided on the outer layer to retard gas transfer. A metallic film may be used to retard gas transfer and may be applied, for example, by plating, spraying, vapor deposition techniques, and the like, which are well known to those skilled in the art. The outer layer (with the metallic coating) is then inserted into an injection mold cavity and the inner layer is injection molded onto the inside surface of the outer layer.

In operation, a fluid flows through the cartridge housing under pressure. The housing should be constructed to withstand the expected pressure of the fluid flowing through the filter apparatus. In the present invention, the strength of the filter cartridge may be primarily due to one of the layers, with the other layer(s) providing the useful properties of protection from contamination due to gas permeation into the filter fluid and/or light passing with the cartridge. Alternatively, the strength of the filter cartridge may be borne by any two or all three of the

layers. In a preferred embodiment, the pure plastic inner layer is substantially thicker than the pigmented plastic outer layer, and both cooperate in the structural stability of the cartridge. Accordingly, there is disclosed a multiple layer construction for water purification housing cartridges. The layers are selected to meet specific chemical and physical requirements. The multiple layer construction is selected to maximize the chemical compatability with deionized water and minimize the contamination by constituents. The outer layer(s) is/are selected to minimize passage of light and gases. Finally, the tube may be coextruded in which the multiple layers are extruded together in tubular form. Alternatively, the multiple layer molding of components may also be desirable. In this manner, the outer layer is molded and then the inner layer is injection molded about the inner surface of the outer layer.

Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims. What is claimed is: