Abstract:
The instant invention is directed towards a method of preparing a clumping animal litter comprising a combination of a high molecular weight polymer, a gum, and cellulosic components. The invention particularly relates to a method of preparing a clumping animal litter that comprises a homogenous mixture of anionic polyacylamide, a guar gum, grist and optionally cellulosic fines in combination with one or more sources of cellulosic material, thereby providing a litter with enhanced absorption, clumping size and hardness.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/962,797, filed on Dec. 21, 2007, and entitled “METHOD OF PRODUCING CLUMPING ANIMAL LITTER COMPOSITION AND THE COMPOSITION” which is a divisional of U.S. patent application Ser. No. 11/049,140, filed Feb. 1, 2005 and entitled “CLUMPING ANIMAL LITTER COMPOSITION AND METHOD OF PRODUCING THE SAME”, now U.S. Pat. No. 7,331,309, issued Feb. 19, 2008, the contents of each of which are incorporated in their entirety herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a clumping animal litter comprising a homogenous mixture of a polymer, a gum and cellulosic components and methods of preparation thereof; particularly, an animal litter which comprises a homogenous mixture of anionic polyacylamide, guar gum, a grist and optionally cellulosic fines in combination, thereby providing a litter with enhanced absorption, clumping size and hardness. 
       BACKGROUND OF THE INVENTION 
       [0003]    Methods and compositions are known that utilize absorbent materials in litter boxes and animal cages in an effort to efficiently and effectively collect animal urine and/or feces. Currently, there are generally two types of consists of an absorbent particulate material, which acts to absorb animal dross until the material reaches a saturation point, at which time the litter must be replaced. Unfortunately, without chemical additives, until the saturation point is reached the soiled absorbent material can grow mold and/or emit an objectionable odor requiring frequent replacement with fresh litter. 
         [0004]    Clumping types of litter are currently the most popular litter on the market. In this type, the portion of the wetted granular litter forms a solid agglomerate, or clump, usually within a short period of time. This clump can then be easily removed while the rest of the granular litter remains. 
         [0005]    Clay is currently the most commonly used absorbent material in both clumping and non-clumping types of animal litter, as it is able to absorb a substantial amount of liquid. However, due to the costs associated with mining and shipping of clays, litters made from this material tend to be more expensive and environmentally destructive than that produced from organic wood-based sources such as sawdust, waste paper, pulp, husks, wood pellets and the like. Furthermore, clays contain silica, a known carcinogen. Thus, the use of silica containing compounds raises health concerns for both the animal involved and the person changing the litter. Moreover, clumps of clay do not readily break down in water and may clog household plumping. 
         [0006]    U.S. Pat. No. 5,927,049 to the present inventors (herein incorporated by reference in its entirety) has effectively solved these problems utilizing a simple and elegant procedure for the creation of a non-clumping, all-natural litter that is biodegradable, odor controlling, dustless, smooth throughout continued handling and capable of absorbing 5 times more fluid than clay. In particular, this invention exploits the odor neutralizing properties inherent in southern yellow pine, which eliminate volatile odors (e.g. mercaptan, amines, skatole gases) emitted from animal waste without the need for additional artificial additives. 
         [0007]    While much of the prior art discloses the use of organic wood-based sources as a preferred or alternative embodiment, until the advent of the aforementioned method to the instant inventors few manufactures have been able to create a wood-based particulate litter that is economical to produce. These wood-based animal litters are expensive to fabricate, as they are often difficult to manufacture. Wood-based litters typically require multiple applications of aqueous additives (e.g. biocides, deodorizers, pesticides and the like), followed by a drying step in order to create litters with the desired properties. 
         [0008]    Thus, what is lacking in the prior art is a clumping animal litter with superior absorbance and enhanced clumping properties that remains intact under mechanical stress, yet economical to produce and inhibits mold growth. Ideality the animal litter composition would use industrial or agricultural byproducts, thereby providing an economical and environmental friendly litter that is able to readily disperse when disposed into the household plumbing system. 
       DESCRIPTION OF THE PRIOR ART 
       [0009]    Recently a variety of methods and procedures have been described in the prior art for preparing animal litters utilizing superabsorbent polymers in combination with both inorganic and organic substrates and mixtures of both. Many patents have been directed toward a clumping litter that forms agglomerates quickly and with sufficient mechanical integrity and size so as to permit easy removal of animal waste in a solid mass. 
         [0010]    For example, U.S. Pat. No. 5,609,123 to Luke et al describes a pet litter composition comprising a particulate substrate with a low absorptive capacity, preferably a non-swelling clay, having bonded onto its surface fine particulate particles coated with a superabsorbent polymeric material and another particulate “clumping particle” to promote clumping. The superabsorbent polymer is an anionic polymer, preferably formed from a blend of carboxylic acid monomers, e.g. (meth)acrylic acid from 10 to 100 % weight and (meth) acrylamide monomers from 0 to 90% weight. Unlike the high molecular weight, water soluble, anionic polymer utilized in the present invention, the superabsorbent polymer of Luke et al is a water insoluble, cross-linked polymeric material. Additionally, the manufacturing process of Luke et al requires that the surface of the substrate particle be sprayed first with a specific amount of liquid and allowed to absorb into the substrate particles, before application of the superabsorbent polymer and clumping particle blend. Too much liquid can cause undesirable swelling that can interfere with the beneficial performance of the superabsorbent polymer and clumping particles. 
         [0011]    U.S. Pat. No. 6,148,768 to Ochi et al describes a pet litter for disposal of animal wastes, which comprise granular bodies containing fiber and a superabsorbent polymer skin layer. The granular body is composed of a core containing the fiber and a skin layer, which covers the core. The skin layer preferably contains an anti-powdering agent and superabsorbent polymer, such as a cross-linked polyacrylic acid. The patent fails to teach or suggest the use of a gum or gum derivatives on the granular body. 
         [0012]    U.S. Pat. No. 4,157,696 to Carlberg describes an animal waste absorbent and deodorizing composition for use as an animal litter. The composition comprises pellets made from fly ash and cellulose fibers that form channels from the surface of the pellet to the interior of the pellet to permit capillary action to draw the dross into the interior of the pellet to deodorize and dehydrate the waste. Various pelletizing aids may be used, such as the synthetic polymer formed from sodium acrylate and acrylamide. 
         [0013]    U.S. Pat. No. 6,662,749 to Wiedenhaft et al discloses an animal litter comprising a cellulosic substrate coated with an inner coating composed of an absorbent polyacrylate or acrylate copolymers and a second outer coating of guar gum, the binding agent used to form the aggregate. The particularly preferred polyacrylate is sold under the name Spinks 211 (H.C. Spinks Clay Company, Inc. located in Paris, Tenn.) . However, unlike the instant invention, this animal litter requires the stepwise addition of an inner coating of an absorbent polymer onto the substrate with an outer coating of guar. Thus, the inner coating of polymer can only exhibit its absorbent properties when the liquid penetrates the outer coating of guar gum, which can disrupt the formation of the aggregate. 
         [0014]    None of abovementioned prior art teach or suggest the use of a homogenous mixture of an absorbent polymer, a gum, grist and optionally cellulosic fines, to provide a clumping litter with improved clumping ability and absorbency. Thus, there remains a continuing need in the art for a clumping litter that forms a mechanically stable and absorbent agglomerate that is easy to manufacture. 
       DEFINITIONS 
       [0015]    The term “anionic polyacrylamides”, as used in the present specification and claims, is intended to mean a group of water soluble, high charge density, high molecular weight macromolecules with a molecular weight of at least 5,000,000 to 30,000,000; preferably at least about 10,000,000. 
         [0016]    The term “grist” as used in the instant specification and claims is intended to mean the milled cellulosic material produced prior the formation of the pellet during the pelletization process. The grist can be comprised of one or more sources of softwoods, e.g. pine, cedar, fir, spruce and combinations thereof, since these materials have been found to innately contain odor-neutralizing and microbial resistant properties. Moreover, the grist can be obtained in any form such as wood chips, husks, hulls, shavings or sawdust, straw and combinations thereof, preferably from materials reclaimed from outside processes (i.e. lumber yard). 
         [0017]    The terms “cellulosic fines” and “densified wood saw dust”, are both used interchangeably in the instant specification and claims and are intended to mean the byproducts produced during the pelletization process or the superfluous cellulosic material generated during the manufacture of lumber or paper products which pass through at least one 10 to 30 mesh (U.S. Standard) screen. The cellulosic fines can include, among other things, small pellet pieces and any grist that did not form into proper pellets. 
         [0018]    The term “near instantaneous” as used in the instant specification and claims, is intended to mean a period of time of less than 2 minutes. 
         [0019]    The term “clump hardness” as used in the instant specification and claims, refers to the adhesiveness created by the homogenous mixture which allows the clump to remain substantially intact after being dropped from a height of one foot 5 minutes after formation of the clump. 
       SUMMARY OF THE INVENTION 
       [0020]    In order to overcome the problems encountered by the prior art, the instantly disclosed invention is directed toward a clumping animal litter composition and a process of manufacturing the same. The litter is formed from cellulosic material that can be obtained from one or more sources of softwoods by any pelletizing process known in the art, for example the aforementioned method taught in U.S. Pat. No. 5,927,049 to the present inventors. During the formation of the pellets, the pellets are then moved across a sifting screen such that some of the cellulosic fines that separate from the pellets can be recycled as part of an mixture which includes an absorbent polymer (i.e. anionic polyacrylamide), dry powdered gum and grist. Alternatively, other sources of cellulosic fines generated from other manufacturing processes (e.g. lumber mill) can be used in the mixture. 
         [0021]    It has been discovered by the present inventors that high molecular weight anionic polyacrylamides impart properties desirable in a clumping litter (i.e. faster clumping speed and clump hardness) as compared with lower molecular weight copolymers of acrylamide and acrylic acid (also known as acrylate), commonly used in the prior art. These high molecular weight macromolecules are known for their excellent absorptive capacity for aqueous media (e.g. typically upwards of 400× the weight of the polymer) with minimal tackiness. 
         [0022]    Suitable absorbent polymers for use in the present invention include anionic polyacrylamides, a group of high charge density, water soluble, high molecular weight macromolecules produced through the polymerization of acrylamide and an anionically charged co-monomer, formed by any polymerization method known in the art. Some examples of anionically charged co-monomers include, sodium acrylate, potassium acrylate and other salts of acrylic acid and derivatives thereof known in the art. 
         [0023]    The preferred anionic polyacrylamide is supplied under the designation CLEAROUT P6400 (manufactured by Chemtall Inc., GA, USA). CLEAROUT P6400 is a fine white powder with an approximate bulk density of 0.8 and viscosities of; 1800 cps @ concentration of 5.0 g/L; 700 cps @ concentration of 2.5 g/L; 300 cps @ 1.0 g/L, (as measured by a Brookfield viscometer at 25° C.). The intrinsic viscosity (IV) is about 22 dL/g. The dissolution time of the polymer in DI water @ 5 g/L, 25° C. is 60 minutes. The polymer has range of anionically charged co-monomers of about 20 to 40 mole %. 
         [0024]    Examples of suitable gums or gum derivatives for use in the instant invention include guar gum. Particularly preferred guar gums include hydroxypropyl guar, carboxymethyl guar, carboxymethyl hydroxypropyl guar, and combinations and/or derivatives thereof known in the art. Other suitable gums include xanthan gum, locust bean gum and the like. 
         [0025]    Accordingly, it is a principle objective of the instant invention to provide a clumping litter and process for the formation thereof providing a homogenous admixure of anionic polyacrylamide polymer, gum, grist and optionally, cellulosic fines, thereby providing a clumping litter with both enhanced absorption and clumping properties. 
         [0026]    An additional objective of the invention is to produce a clump that is of sufficient hardness as to be readily removed by automated litter boxes, while able to readily disperse when introduced into the household plumbing system. 
         [0027]    A further objective of the instant invention is to provide a manufacturing process whereby the litter produced makes use of the superfluous cellulosic fines created during the pelletization process that were heretofore unused, thereby providing a more economical and environmentally friendly product. 
         [0028]    Another objective of the present invention is to provide an animal litter composition that has inherent odor controlling properties. 
         [0029]    It is still a further objective of the invention to provide an animal litter composition and method of manufacture that employs industrial or agricultural byproducts, thereby providing an environmentally desirable litter. 
         [0030]    Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objectives and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         [0031]      FIG. 1  is a schematic representation of a method for producing animal litter according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    An illustrative, but non-limiting, example of a method that simultaneously manufactures both a non-clumping type organic fiber pellets and a clumping type organic for use as animal litter is illustrated in the schematic view  10  of  FIG. 1 . As described herein, the clumping type process depends upon the by-products generated during the manufacture of the non-clumping litter, however, the grist and cellulosic fines could be obtained from other independent sources which produce grist and suitably sized cellulosic fines, i.e. lumber yards. It is noted that other conventional pelletizing apparatus and methods may be utilized. 
         [0033]    A preferred source of the cellulosic component, preferably, albeit not limited to, shavings of yellow pine wood  12  are delivered to a receiving depot  14  where it is off-loaded and placed into a kiln  16 . Once in the kiln  16 , the wood  12  is subjected to a temperature of about 120° F. to 200° F., at low consistent humidity, for a period of time, until the desired moisture level is achieved. The kiln  16  causes the wood  12  to reach uniform moisture content, preferably less than 8%. After the wood  12  has been cured, the material is transferred to a hammer mill  18  and ground into grist  20 . The grist  20  is collected in a first surge chamber  22 . The initial curing results in dimensional variances, produced by shrinkage during drying, and are eradicated during the grinding process. This results in a grist  20  that is uniform, evenly compressible, and conducive to holding a fixed shape. Additionally, the uniform nature of the grist  20  ensures that the pellets formed therefrom will bond well together. 
         [0034]    The grist  20  is stored in the first surge chamber  22 , until a portion of it is conveyed via a transfer feeder  24  to a conditioning chamber  26  to later form pellets  30 . While the other portion of the grist  20 ″ is transferred to a low shear mixer  50  for addition with gum, absorbent polymer and optionally cellulosic fines. The portion of the grist  20  that is transferred to the conditioning chamber  26  is sprayed with an aqueous solution, preferably steam, for approximately 3-4 seconds to form a grist  20  having uniform moisture content. 
         [0035]    After being exposed to the aqueous solution, the moistened grist  20 ′ flows into a pellet mill  28 , where the moistened grist  20 ′ is processed into a uniform pellet  30 . During the pelletization process, the moistened grist  20 ′ is exposed to increased pressure and temperature for a short period of time. More specifically, the moistened grist  20 ′ is pressurized at about 60 Kpsi for approximately 4 to 10 seconds in the temperature range of about 180° F. to about 250° F. 
         [0036]    The pellets  30  are then transferred to a cooler  32  where the pellet temperature drops to ambient temperature. This cooling step advantageously allows the pellets  30  to coalesce before further processing. 
         [0037]    Once the pellets  30  have cooled, the pellets  30  pass through a shaker  34  having at least one sifting screen  36 , (e.g. a 10-mesh screen), to remove any materials that did not form into a proper pellet. As the pellets  30  move across at least one sifting screen  36 , the cellulosic fines  30 ′ are separated from the pellets  30  for later addition as part of a mixture that is combined with the grist  20 ″ in the low shear mixer  50 . Optionally, a portion or all of the cellulosic fines  30 ′ can be returned to the feeder  24  and mixed with grist  20  exiting from the first surge chamber  22 . In this way, the returned fine particles  30 ′ are combined with fresh grist  20  to form additional pellets  30 . 
         [0038]    Pellets  30  exiting the shaker construction  34  are collected in a second surge chamber  38 , in preparation for bagging. From the second surge chamber  40 , pellets are deposited into bags  42 . The bags  42  travel on a bag conveyor  44  though a heat sealer  46  that closes the bags. The sealed bags  42 ′ are then transported to remote location for sale and use as a non-clumping animal litter. 
         [0039]    Into the low shear mixer  50  is added at least one dry powdered gum, preferably a guar gum or guar gum derivative, at a concentration of about 5.0 % to 20.0% (wt/wt), preferably at about 10% (wt/wt) based on the weight of the mixture; a dry powder of the anionic polyacrylamide polymer at a concentration of about 0.1% to about 1.0% (wt/wt), preferably at about 0.3% (wt/wt), based on the weight of the mixture; a grist at a concentration of about 100% to 30% and recycled cellulosic fines 30′ at about 0% to 70%, preferably about 30% (wt/wt), based on the weight of the mixture; such that the total percentage adds up to about 110%. The mixture can optionally contain any desired additive discussed below. After addition of the aforementioned components, the mixer  50  is run for a predetermined amount of time, at least 10 minutes, under conditions well known to those skilled in the art, in order to provide a uniform mixture. The clumping litter mixture exiting the mixer  50  is collected in a third surge chamber  52 , in preparation for bagging. From the third surge chamber  52 , the mixture is released into a bagger unit  54 , wherein the mixture is deposited into bags  42 . The bags  42  travel on a bag conveyor  44 ′ through a heat sealer  46 ′ that closes the bags. The sealed bags  42 ″ are then transported to remote locations for sale and use as animal litter. Although illustrated herein as two separate conveyors and sealers, it is contemplated that the same conveyor and/or sealer can be used in the manufacture of both the clumping and non-clumping litter. 
         [0040]    Without limiting the scope of the present invention, suitable low shear mixers include drum mixers, cement mixers, auger mixers, vibrating bed mixer or other means of mixing known in the art. These can be batch or continuous feed mixers. 
         [0041]    It is contemplated by the instant invention to provide at least one additive during the mixing step described above, at about 0% to about 20% of the weight of the mixture. Non-limiting examples of additives include, but are not limited to oils or extracts of fragrances, antimicrobial agents, deodorants, disinfectants, colorants (i.e. pigments, dyes, lakes), and combinations thereof. Other suitable additives include oxidizers, such as sodium perborate and/or calcium peroxide, to neutralize the volatile odors (i.e. mercaptan, amines, skatole gases) emitted from the waste. Addition of at least one of the aforementioned additives during the formation of the pellet would produce pellets that comprise the characteristics of the additive throughout, e.g. color, fragrance, etc. 
         [0042]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and drawings/figures. 
         [0043]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.