Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With subsequent cutting – grooving – breaking – or comminuting
Reexamination Certificate
1999-08-05
2001-09-25
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With subsequent cutting, grooving, breaking, or comminuting
C119S173000, C502S080000, C502S400000
Reexamination Certificate
active
06294118
ABSTRACT:
DESCRIPTION
The invention concerns a process for production of sorbents based on cellulose-containing material and at least one smectitic clay mineral for absorption of liquid. These sorbents are suitable to absorb any liquids; they are particularly suited as litter for domestic animals, for which reason the subsequent comments refer to this area of application.
Keeping of domestic animals, especially in a city environment, is increasingly connected with the use of litter. This has the task of absorbing liquids released by the animal. It is also supposed to remove the semisolid, moist animal excrements and excretions and thus reduce odor development. Good litters are also supposed to absorb the discharge or released liquid with formation of a compact clump, which can be simply and thriftily removed. An optimal litter should therefore have high absorption capacity and fully absorb the liquid discharged by the animals within the charge without wetting the bottom of the litter box.
The litters found on the market are organic substances, like straw, sawdust, wood chips, bark, shredded paper, cellulose fibers, agricultural residues, etc.; these are used alone or in mixtures with inorganic material. The drawback of organic litters is the frequently nonexisting or insufficient clump formation and its consistency, as well as their tendency toward bacterial decomposition, especially in cooperation with moisture.
A sorbent, especially a litter for domestic animals based on swellable smectitic clay minerals, is known from U.S. Pat. No. 5,000,115, which can additionally contain sand or cellulose-containing materials, like wood shavings or chips and ground paper. The components are mixed dry without compaction.
A process to produce litters for domestic animals is known from U.S. Pat. No. 4,341,180, according to which water-containing wastepaper residues are dewatered to a water content of about 32 to 40%, pressed, pelletized and dried after addition of sodium bicarbonate as deodorant. The paper residues can contain about 10 to 50% ordinary paper fillers, like kaolin. The described fillers are not swellable, for which reason the litter do not form clumps during absorption of liquids.
A litter and method for its production are known from DE-A-41 01 243, according to which cellulose, cellulose derivatives and/or cellulose-containing materials of agricultural or industrial origin, as well as wood wastes, like sawdust, with a particle size of up to 1 mm are mixed or agitated with ballast agents and thickeners, like bentonite, in the presence of water, the mixture is dewatered without compaction to a residual water content of no more than 10 wt % and the remaining residue ground to a particle size above 1 mm. The ballast agent is added in an amount so that the bulk density of the litter after drying lies above about 500 kg/m
3
. The higher bulk density relative to the organic litters is mentioned as advantageous.
A litter based on cellulose-containing material as wet substance and a capillary-active, small-grained material, like ground limestone, wood flour, ground clay, bentonite or ground pumice is known from DE-A-38 16 225. Recovered paper stock as wet substance with a moisture content of 50 to 60% and ground pumice with a moisture content of less than 30% are preferably mixed and then dried. During use of a mixture of wood flour and cellulose fibers compaction occurs in a screw compactor. However, compaction is left out during the use of inorganic capillary-active substances. The litter is crumbly and has a high percentage of fine-dust material. During addition of liquids it does not form clumps.
A method for production of sorbents based on smectite to absorb liquids is known from DE-A-4 338 362, in which (a) a smectite with a water content of less than 6 wt %; (b) a mass of fibrous cellulose and organic pigments occurring during processing of papermaking effluents; and (c) anhydrous calcium sulfate or calcium sulfate hemihydrate are mixed, compacted and pulverized; the amount ratio between (a), (b) and (c) is chosen so that the water content of the granular material is less than 20 wt %. During compaction pieces are formed with a broad particle size distribution, which are then ground, during which a relatively large amount of fine-dust material is formed.
A method is known from EP-B-0 663 793 (DE-A-43 27 159) for production of sorbents based on smectites and cellulose-containing materials with low bulk density, in which a moist mixture of smectite and ground wood material or another cellulose-containing material of plant origin, i.e., cellulose-containing primary raw material, is treated during internal shear with subsequent extrusion and then dried and granulated. During granulation a relatively high percentage of finely divided material is formed.
A method to produce a clump-forming litter is disclosed In U.S. Pat. No. 5,456,284, in which a smectitic clay is mixed before or after extrusion with a small percentage of a water-soluble adhesive or binder, for example CMC.
Sorbents based on clay mineral particles with a particle size from 710 &mgr;m to 4 mm are known from EP-A-0 087 001, which represent compacted masses of particles of less than 2 mm. The clay mineral particles are joined together by water-soluble or water-dispersible substances, like cellulose derivatives, e.g., carboxymethylcellulose, or starches. Use of a cellulose-containing material not swellable in water is not described.
Finally, a method is known from DE-A-43 11 488 (EP-A-0 619 140) for production of sorbents based on cellulose fibers, ground wood material and clay minerals, in which a finely divided cellulose-containing material with an average fiber length of 0.4 to 3 mm and residual moisture of 5 to 15 wt % and/or a ground wood material with an average fiber length of 0.05 to 2.0 mm and a residual moisture of 10 to 20 wt % and a smectitic clay mineral in finely divided form with an average particle size of 0.1 to 1.0 mm, a residual moisture content of 5 to 15 wt % and a smectite content of at least 50 wt % are homogeneously mixed and the compacted mixture ground. Compaction occurs by means of pressing rolls (briquetting rolls or press granulation rolls). A relatively high percentage of finely divided material is formed during size reduction.
It has now been found relative to the prior art just described that the properties of sorbents, especially litters, can be substantially improved if the components, essentially smectitic clay material(s) and finely divided cellulose-containing materials are compacted under high pressure at a precisely set water content, making sure that the percentage of finely divided material is kept as low as possible.
The invention therefore concerns a method for production of sorbents based on cellulose-containing material and at least one swellable smectitic clay mineral, which form clumps on absorption of liquid; the method is characterized by the fact that
(a) the cellulose-containing material and the smectitic clay material are thoroughly mixed in finely divided form, the total water content of the components being mixed lying between about 25 and 40 wt % or being adjusted to this range by adding water,
(b) the mixture is compacted using a die press and
(c) the compacted molded articles leaving the die press are cut essentially across the direction of emergence and dried.
Cellulose-containing material is understood according to the invention to be a material that virtually does not swell in water and therefore has no binder properties either, in contrast to the cellulose derivatives described in EP-A-0 087 001.
The sorbents produced according to the process of the invention are relatively light so that they can be better transported and handled by consumers. For example, a litter box can be easily filled and emptied. The sorbents so produced also exhibit excellent clump formation, in which the clumps to be disposed of have reduced weight; they do not form dust and have excellent absorption capacity. It is presumed, without being wedded to this theory, that the advantageous properties
Haubensak Otto
Huber Werner
Sellmayr Petra
Cox Scott R.
Sud-Chemie AG
Tentoni Leo B.
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