Liquid purification or separation – Filter – Material
Reexamination Certificate
2001-11-28
2004-07-13
Walker, W. L. (Department: 1723)
Liquid purification or separation
Filter
Material
C210S502100, C210S503000, C536S030000, C536S031000, C536S056000, C536S062000
Reexamination Certificate
active
06761272
ABSTRACT:
The invention relates to filters consisting of filter paper or paper-type non-woven material. Said filters partially or wholly consist of fibrous material containing cellulose.
Filter paper is a type of paper produced from cellulose, plastic fibers or glass fibers and used for the filtration in households, technical applications and for analyses. Paper-type nonwoven materials are composite materials consisting of fibrous material containing cellulose. Filter bags, for example, or filter cartridges produced by winding or folding are manufactured from filter paper or paper-like nonwoven materials. The filters so produced are disposed of after they have been used once. In connection with filters used as one-way, disposable articles it is deemed desirable that such filters are biodegradable for reasons of environmental protection. This, however, is achieved only if the filters exclusively consist of cellulose.
Filters generally serve for separating solid particles from gases or liquids. Especially in connection with the filtration of aqueous media, however, it is frequently deemed desirable that certain ions can be jointly separated as well, either in order to achieve an additional purification effect or to obtain an enrichment in the filter paper. This relates in particular to toxic heavy metals as well as to hardening constituents in drinking water, as well as to the concentration of metal traces in larger water samples for the purpose of simpler analytical detection.
No fibers for filter materials have become known heretofore that have an adequate capacity for absorbing hardening constituents in order to effect a noticeable enhancement in the production of beverages in the presence of the usual degrees of water hardness, on the one hand, and which are capable of binding heavy metals with adequate strength so as to effect a notable flavor enhancement with the possible low concentrations on the other. Commercially available systems for improving the quality of drinking water, therefore, comprise a cartridge filled with ion exchangers as their core component. However, such cartridges are known to pose problems due to the multiplication of germs if there is no flow-through in the water system, and they load the environment because such cartridges can be recycled only incompletely.
The invention was based on the problem of providing filters consisting of filter paper or paper-type nonwoven material that are characterized by a high filtration capacity and are additionally capable of absorbing and binding undesirable foreign or attendant substances in the filter medium such as, for example hardening constituents or heavy metals. Furthermore, the problem of the invention is to provide suitable methods for producing the filters.
The problem is solved according to the invention by the features specified in claim
1
. The features relating to the proposed methods for producing the filters are the objects of claims
2
to
13
.
The filters made of filter paper or paper-like nonwoven material partially or wholly consist of fibrous material containing cellulose. The properties of the filters are substantially enhanced by a special treatment of the material containing cellulose, either prior to or after the manufacture of the filter paper. According to the invention, the treatment is carried out in such a manner that the material containing cellulose is at least partially carbamided with urea up to a nitrogen content of 1 to 4% by mass bonded in amino-methane acid ester groups (carbamide groups), and phosphorylated with phosphoric acid or ammonium phosphate up to a phosphorus content of 3 to 8% by mass. In addition to high filtration capacity, the filter produced from cellulose-containing material so modified additionally possess the special properties of binding hardening constituents as well as toxic heavy metals, which impair the flavor. An enhanced swelling property of the cellulose fibers is obtained by such a treatment, and a broader field of application is obtained in that way for the filters, which can be preferably employed for the separation of mechanical impurities from liquids and gases. In the case of aqueous solutions that need to be filtrated, the filters possess the advantageous property of exchanging the cations of ion-forming impurities for sodium or ammonium aluminum ions. Absorbed are in particular polyvalent cations (hardening constituents, heavy metals etc.) but also cationic tensides, quaternary organic ammonium compounds etc. Other fields of application include dust removal, water technology, in particular in water pipelines, and the use of the filters as air, coffee, smoke or dust filters.
From the treated cellulose fibers it is possible to produce in the manner known per se filter paper or paper-type nonwoven material either made exclusively of cellulose fibers or in mixture with other suitable starting materials for such filters such as, for example plastics or glass fibers.
It is then possible to produce from the filter paper or the paper-like nonwoven material different types of filters such as, for example filter bags or cartridge filters. The filters are used as one-way filters, as a rule. Filters exclusively consisting of cellulose and/or the modified cellulose-containing material as defined by the invention offer the advantage that they are completely biodegradable.
All fibers with a high cellulose content that are suitable for the manufacture of paper such as, for example cotton linters, sulfate and sulfite celluloses from various timbers, and fibers recycled from old paper can be used as cellulose fibers. The following possibilities are available with respect to the phosphorylation and carbamidation reaction:
Treatment of the entire cellulose-containing starting material prior to the manufacture of the filter paper or paper-containing nonwoven material;
treatment of a partial amount of the required cellulose starting material prior to the manufacture of the filter paper or paper-like nonwoven material, and subsequent mixing of said partial amount with untreated cellulose-containing fiber material; and
manufacture of the filter paper or paper-like nonwoven material in the manner known per se, and subsequently treatment of the web of filter paper or paper-like nonwoven material by phosphorylation and carbamidation.
Different degrees of phosphorylation and carbamidation can be adjusted for the nitrogen and phosphorus contents within the specified range limits depending on the purpose of application of the filters.
The phosphorylation and carbamidation of the cellulose-containing starting material for the production of the filter paper or the paper-type nonwoven material is carried out under the following conditions:
It is important that the cellulose-containing fiber material is brought into a particularly reactive form prior to the phosphorylation and carbamidation reaction. Such a so-called activation is carried out by adjusting the moisture content of the cellulose-containing material by adding water to it in an amount of at least 30% by mass of the cellulose-containing material. The cellulose-containing starting material usually already has a water content of from 5 to 25%. In order to achieve the desired activation it is necessary that the cellulose-containing fiber material is subjected to the action of water over a longer period of time. The duration is substantially dependent upon the already existing moisture content of the material and amounts to at lest half an hour.
The reaction partners phosphoric acid or ammonium phosphate and urea have to be admixed to the cellulose-containing material in such a way that said reaction partners are present in the material with uniform distribution after the mixing process has been completed. In addition to the aforementioned activation, attention has to be paid in particular to a uniform distribution of the reaction partners in the cellulose-containing fiber material.
It is not absolutely necessary to maintain a defined sequence for adding the reaction partners.
The activation can be advantageously combined with
Knieling Michael
Lange Bckehard
Pieschel Friedemann
Collard & Roe P.C.
Helmut Körber
Menon Krishnan S.
Walker W. L.
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