Water Filter

Method of making a water filter

Water Filter Abstract:
The specification discloses a double shell filter comprising an inner shell of bounded 80 to 400 U.S. mesh screen carbon particles and an outer shell of bonded 20 to 80 mesh screen carbon particles wherein the inner and outer particles are bonded internally to each other and the two shells are bonded together preferably by an ultra high molecular weight polymer binder having a melt index of less than about 1 gram per ten minutes as determined by ASTM D1238 at 190 degrees C. and 15 kilograms load.

Water Filter Claims:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making a carbon particle filter comprising:

providing a mold defining the exterior configuration of said filter;

mixing the carbon particles with a binder and filling it into said mold,

said binder comprising a low melt index polymeric material having a melt index of less than 1 gram per 10 minutes as determined by ASTM D 1238 at 190 degrees C. and 15 kilograms load, whereby said polymeric material will tackify at elevated temperatures without becoming sufficiently liquid to substantially wet the carbon particles in order that diminution of the effective carbon surface is eliminated; and

subjecting said carbon particles and said binder to heat and pressure to cause said carbon particles to bind to each other whereby a carbon particle filter can be obtained.

Water Filter Description:
BACKGROUND OF THE INVENTION

The present invention relates to water filters. Typically, such filters comprise a hollow core cylindrical block of bonded, activated charcoal. Water flows through the perimeter of the charcoal filter and into the center core from whence it flows to the user. Typically, some type of porous plastic sleeve is located in the core to keep the charcoal from flaking off into the water.

One problem with such filters is that if the charcoal particles are fine enough to do a proper filtering job, they inhibit water flow substantially. One prior artisan has attempted to overcome this by cutting longitudinal grooves in the outer peripheral surface of the filter. However, it is believed that this merely causes water to flow through the filter at the base of the groove and effectively or substantially eliminates water flowing through an outer layer of the filter.

Another problem with bonded charcoal particle filters is that the plastic binder used to bond the charcoal particles together tends to clog the pores of the activated charcoal. While such clogging does not completely eliminate the effectiveness of the activated charcoal, it does tend to reduce its efficiency.

U.S. Pat. No. 3,950,251 discloses a cylindrical filter element formed of a polymer bonded, compressed charcoal inner core with a porosity of about 10 microns and a second outer filter element sleeve made up of unbonded granular activated charcoal of 14 to 40 mesh particle size. A serious problem with such an arrangement is that the outer sleeve of unbonded charcoal has to be contained in a porous plastic container to keep the charcoal from spilling out of the filter during shipping and storage.

Also, water tends to "channel" through the unbonded outer charcoal without being filtered. On the other hand, bonding can substantially limit the effective surface area of the larger particles, in that the binder clogs the pores. The effective surface area of the larger particles is already less per unit of weight than that of the smaller inner particles, and the binder aggravates the problem.

SUMMARY OF THE INVENTION

In the present invention, a satisfactory degree of filtration without undue inhibition of water flow is achieved by providing a cylindrical filter having an inner bonded 80 to 400 U.S. Mesh screen carbon particle shell, most preferably 80 to 325 U.S. mesh screen, and an outer shell of bonded 20 to 80 U.S. mesh screen and preferably 20 to 60 U.S. mesh screen carbon particles, which is also bonded to the inner charcoal shell so as to create an integral package. This filter is made in accordance with a unique process whereby a separator sleeve is placed into a filter mold, a mixture of the smaller carbon particles and binder is placed on the inside of the separator sleeve and a mixture of the larger charcoal particles and binder is placed on the outside of the separator sleeve. The separator sleeve is then removed and the mass is sintered and pressed to create a unitary carbon filter having two different particle size, integrally bonded layers.

In another aspect of the invention, the carbon particles are bonded together by means of a very low melt index polymer, which becomes tacky without becoming sufficiently liquid to substantially wet the carbon particle surface. Deleterious diminution of the effective carbon surface area is minimized. Further, this unique polymer binder, not heretofore suggested for use as such, facilitates binding layered masses of carbon particles, e.g. a two layer system, in that heating sufficiently to tackify and bond the innermost layer of particles can be achieved without wetting thoroughly the outer layer of particles.

These and other objects, advantages and features of the present invention will be more fully understood and appreciated by reference to the written specification and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of a charcoal filter made in accordance with the preferred embodiment of this invention; and

FIG. 2 is a perspective partially broken view showing the apparatus for making the filter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment, the filter 1 of the present invention comprises an inner porous plastic cylinder 10, an inner bonded carbon sleeve 20 around cylinder 10, an outer bonded carbon sleeve 30, a bottom end cap 40 and a top end cap 50 (FIG. 1). The outer charcoal layer 30 is covered by fabric 60 and fabric scrim 61, which are held in place by plastic net wrap 70.

Inner plastic sleeve 10 is a conventional porous plastic sleeve which allows water to flow readily through its cylindrical wall. It is threaded at one end 11 whereby the filter assembly 1 can be threaded onto a threaded member in a suitable filter housing. It has an outer diameter such that it fits snugly within inner carbon layer 20. It is from 3/4 to 11/4 inch in diameter, and most preferably about 1 inch.

Inner carbon layer or sleeve 20 comprises 80 to 400 mesh U.S. Series screen powdered carbon, and most preferably 80 to 325 mesh powdered carbon. Activated carbons are produced and identified according to their mesh size. In an 80 to 325 mesh carbon, the particles are of a size such that 90 to 95 percent of the carbon will pass through an 80 mesh screen but remain on a 325 mesh screen. In contrast, 75 to 85 percent of an 80 to 400 mesh carbon will remain on a 325 mesh screen. All screen numbers used herein refer to U.S. Sieve series screens.

In many charcoals, screen size definition is somewhat difficult due to the presence of "fines." Such fines are extremely fine particles which will pass through any practical screen. These may comprise as much as 20% by weight of the charcoal and are disregarded by the charcoal producers themselves in grading their charcoals. The screen grading referred to herein also disregards the presence of fines.

The preferred binder in accordance with the present invention comprises a polymeric material with a very low melt index (melt flow rate) which becomes tacky at elevated temperatures without becoming sufficiently liquid to significantly wet the carbon particle surface. The melt flow rate or melt index as determined by ASTM D1238 or DIN 53735 at 190 degrees C. and 15 kilograms. Load should be less than about 1 gram/10 minutes, more preferably less than 0.5 grams/10 minutes and most preferably less than 0.1 gram/10 minutes. A most preferred binder is an ultra high molecular weight, high density polyethylene. The high molecular weight gives rise to the restricted flow properties of the melted material which is so important to this aspect of the invention. An example of a commercially available ultra high molecular weight, high density polyethylene is Hostalen.RTM. GUR-212. It has a density of 0.935 grams per cubic centimeter and a melt index of less than 0.1 grams per ten minutes as determined by DIN 53735 at 190/15. Such polyethylenes have a molecular weight of from about 4 to about 6 million. They have a vicat softening point of approximately 74 degrees centigrade and a crystalline melting range of 135 to 138 degrees C.

The temperature at which the most preferred binder becomes sufficiently tacky to adhere to the carbon particles may vary depending on the specific polymer used. With the high molecular weight, high density polyethylene, we find that the binder and carbon particles can be processed at a temperature of from about 175 degrees C. to about 205 degrees C. for about 2 hours.

The percentage of the preferred binder used to bind the inner layer is from about 17 to about 25 percent, and most preferably about 20 percent by weight based on the combined weight of the carbon and binder. For the outer layer, from about 20 to about 30 percent by weight binder is used in the binder/carbon composition, and most preferably about 25 percent. One must use enough binder to hold the carbon particles together, but avoid using so much as to block the surface pores of the carbon particles.

The binder must be utilized in powder form so that it can be uniformly mixed and dispersed with the carbon particles. The use of the preferred embodiment polymer binder allows one to bind the carbon particles together in both layers without excessively wetting the carbon particles when melted and thereby effectively occluding much of the surface area of the carbon particles. The preferability of using an ultra high molecular weight, low melt index polymeric material to a conventional polymeric binder is established by reference to Table I, containing examples 1 through 18, below. As can be seen by reference to Table I, the percentage of available carbon is 50 to 100 percent greater or more than when conventional polymer binders are used.

Of course, as regards that aspect of the present invention which broadly involves using carbon particles of two different size ranges, conventional binders can be employed. These are typically polyethylenes having much higher melt indexes. The percentage of binder used tends to run higher in these formulations, e.g., as high as 35 percent. Such binders are usually polyethylene or polyethylene copolymer materials having molecular weights substantially lower than 4 to 6 million.

The process for making the assembly comprising inner sleeve 10, inner carbon cylinder 20 and outer carbon cylinder 30 involves the use of a hinged cylindrical shaped molding cup 100 having an upwardly projecting central dowel 110 (FIG. 2). A separator sleeve 120 is placed in mold 100 and is located in a groove 111 in the bottom 101 of mold cup 100. Separator sleeve 120 is approximately 1/8 of an inch thick and can be made of paper, glass, metal or any other like material.

Once separator sleeve 120 is in place, the inner layer carbon is blended with binder and loaded into the space between inner sleeve 10 and separator 120. A special funnel having a mass flow hopper is used in order to keep the carbon particles from separating during the filling operation. Such funnels have sides sloped at 80 degrees, rather than the usual 60 degrees.

Hinged half 100a of mold cup 100 is closed on half 100b and the two halves clamped together by suitable clamping means (not shown). (It is not essential that mold 100 be hinged, and in production it will not be hinged). Then, the outer layer carbon is blended with binder and loaded into the space between separator sleeve 120 and the outer cylindrical wall of mold cup 100.

With all of the carbon and binder blend in place, separator sleeve 120 is removed from mold cup 100. Mold cup 100 and its contents are then heated to from about 175 to about 205 degrees centigrade. Simultaneously, the carbon/binder blends are subjected to from about 30 to about 120 p.s.i. pressure via pressure piston 130 which is lowered into mold cup 100 and which includes a central clearance opening 131 for inner dowel 110.

Compression piston 130 has approximately the diameter of inner charcoal cylinder 20. This is because compression is required primarily for the smaller inner carbon particles and binder. If piston 130 were the diameter of both layers 20 and 30 combined, inner layer 20 would not compress adequately. While some of the outer charcoal particles and binder get forced up around the outside of piston 130 during compression, the "sleeve" thus formed is trimmed off during the later trim operation.

The carbon/binder layers are then allowed to cool and the composite structure is removed from mold 100. The binder creates an integrated structure in which the inner carbon layer 20 is bonded to itself, outer carbon layer 30 is bonded to itself, and both layers are bonded to each other, thereby creating a unitized structure.

This composite is then trimmed at both ends to create smooth, firm ends. Porous plastic sleeve 10 is inserted into the inner cylinder in inner layer 20 left by dowel 110. The composite filter is then dipped into melted polyproplene in a slush mold to form bottom cap 40 (FIG. 1). Top cap 50 is formed in the same way, except that the top cap slush mold includes a threaded member onto which the threaded end 11 of inner plastic sleeve 10 is threaded so that polyproplene forms around the top end 11 of sleeve 10 and does not get into it and block it as is the case with bottom cap 40.

The resulting composite is then wrapped with a layer of nonwoven scrim 61 and a somewhat thicker nonwoven fabric having an effective porosity of 25-35 microns and a thickness of about 1/8 of an inch. These layers are held in place by a final plastic net 70 which is wrapped around fabric 60 as is conventional.