Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
  • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
  • A61L15/42—Use of materials characterised by their function or physical properties
  • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents

Definitions

• the present invention relates to absorbent composites suitable for exposure to dielectric heating. More particularly, the present invention relates to an absorbent composite having a superabsorbent material and an energy receptive additive, the energy receptive additive heating up in the presence of microwave energy.
• fibrous web materials such as airformed webs of absorbent material
• a fibrous sheet of cellulosic or other suitable absorbent material which has been fiberized in a conventional fiberizer, or other shredding or comminuting device, to form discrete fibers.
• particles of superabsorbent material have been mixed with the fibers.
• the fibers and superabsorbent particles have then been entrained in an air stream and directed to a porous, foraminous forming surface upon which the fibers and superabsorbent particles have been deposited to form an absorbent fibrous web.
• binder materials have been added to the web structure.
• binder materials have included adhesives, powders, netting and binder fibers.
• the binder fibers have included one or more of the following types of fibers: homofilaments, heat- usible fibers, bicomponent fibers, meltblown polyethylene fibers, meltblown polypropylene fibers, and the like.
• Conventional systems for producing stabilized airlaid fibrous webs have mixed the binder fibers with absorbent fibers, and then deposited the mixed fibers onto a porous forming surface by using a vacuum system to draw the fibers onto the forming surface.
• These techniques can include: an airforming of a fibrous layer; and an exposing of the fibrous layer to dielectric energy during a distinctively short (e.g. , less than about 3 seconds) activation period to activate the binder-fibers to provide the stabilized airlaid layer.
• exposing a fibrous layer containing particles of conventional superabsorbent material to dielectric heating does have its disadvantages.
• One disadvantage is the susceptibility of conventional superabsorbent material to explode or pop (similar to popcorn) when exposed to dielectric heating.
• Another disadvantage is the susceptibility of conventional superabsorbent material to arcing when exposed to dielectric heating.
• the fibrous layer may ignite or no longer be suitable for incorporation into personal care products such as diapers, children's training pants, adult incontinence garments, medical garments, sanitary napkins, and the like.
• arcing in many methods of manufacture is viewed as undesirable for a variety of safety concerns.
• the present inventors have recognized the difficulties and problems inherent in incorporating conventional superabsorbent material into fibrous layers that are thereafter subjected to dielectric heating.
• the present inventors conducted intensive research toward the development of absorbent composites capable of being subjected to dielectric heating, in general, and microwave heating, in particular.
• the absorbent composites of the present invention are believed to minimize or eliminate the exploding or popping that often occurs when a particle of conventional superabsorbent material is exposed to dielectric heating.
• the absorbent composites of the present invention are believed to minimize or eliminate the amount of arcing that often occurs when a particle of conventional superabsorbent material is exposed to dielectric heating.
• the absorbent composites of the present invention may be incorporated into a fibrous layer that is thereafter subjected to dielectric heating. Any reduction or elimination of arcing would have a positive impact on the amount of waste that often occurs in the manufacture of absorbent bodies that are exposed to dielectric heating. Moreover, any reduction or elimination of arcing would increase the level of safety associated with manufacturing absorbent bodies that are subjected to dielectric heating.
• the absorbent composite includes a superabsorbent material and an energy receptive additive.
• the energy receptive additive has a dielectric loss tangent of at least about 0.15.
• the absorbent composite has a superabsorbent material and an energy receptive additive.
• the energy receptive additive has a dielectric constant of at least about 4.
• a microwave heatable absorbent composite includes a superabsorbent material and an energy receptive additive. The energy receptive additive is in intimate association with and covers the surface of the superabsorbent material. Moreover, the energy receptive additive heats up in the presence of microwave energy.
• FIG. 1 illustrates a representative fluidized bed coating apparatus.
• the absorbent composites of the present invention include a superabsorbent material covered with an energy receptive additive.
• superabsorbent material of the present invention A wide variety of materials can be suitably employed as the superabsorbent material of the present invention. It is desired, however, to employ superabsorbent material in particle form capable of absorbing large quantities of fluids, such as water, urine or other bodily fluid, and of retaining such absorbed fluids under moderate pressures. It is even more desired to use relatively inexpensive and readily obtainable superabsorbent materials.
• particle By “particle,” “particles,” “particulate,” “particulates,” and the like, it is meant that a material is generally in the form of discrete units. The particles can include granules, pulverulents, powders, or spheres.
• the particles can have any desired shape such as, for example, cubic, rod-like, polyhedral, spherical or semi-spherical, rounded or semi-rounded, angular, irregular, etc. Shapes having a large greatest dimension/smallest dimension ratio, like needles, flakes and fibers, are also contemplated for use herein.
• the use of "particle” or “particulate” may also describe an agglomeration including more than one particle, particulate, or the like.
• superabsorbent material As used herein, “superabsorbent material,” “superabsorbent materials” and the like are intended to refer to a water-swellable, water-insoluble organic or inorganic material capable, under the most favorable conditions, of absorbing at least about 10 times its weight and, desirably, at least about 15 times its weight in an aqueous solution containing 0.9 weight percent of sodium chloride.
• Such materials include, but are not limited to, hydrogel-forming polymers which are alkali metal salts of: poly(acrylic acid); poly (methacry lie acid); copolymers of acrylic and methacrylic acid with acrylamide, vinyl alcohol, acrylic esters, vinyl pyrrolidone, vinyl sulfonic acids, vinyl acetate, vinyl morpholinone and vinyl ethers; hydrolyzed acrylonitrile grafted starch; acrylic acid grafted starch; maleic anhydride copolymers with ethylene, isobutylene, styrene, and vinyl ethers; polysaccharides such as carboxymethyl starch, carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(acrylamides); poly(vinyl pyrrolidone); poly (vinyl morpholinone); poly (vinyl pyridine); and copolymers, and mixtures of any of the above and the like.
• hydrogel-forming polymers which are alkali metal
• the hydrogel-forming polymers are desirably lightly cross-linked to render them substantially water-insoluble. Cross-linking may be achieved by irradiation or by covalent, ionic, van der Waals attractions, or hydrogen bonding interactions, for example.
• a desirable superabsorbent material is a lightly cross- linked hydrocolloid. Specifically, a more desirable superabsorbent material is a partially neutralized polyacrylate salt.
• Superabsorbent material employed in the present invention suitably should be able to absorb a liquid under an applied load.
• AUL Absorbency Under Load
• the AUL value is expressed as the amount (in grams) of an approximately 0.9 weight percent saline (sodium chloride) solution absorbed by about 0.160 grams of superabsorbent material when the superabsorbent material is under a load.
• Common loads include those of about 0.29 pound per square inch, 0.57 pound per square inch, and about 0.90 pound per square inch.
• Superabsorbent materials suitable for use herein desirably are stiff- geling superabsorbent materials having an AUL value under a load of about 0.29 pound per square inch of at least about 7; alternatively, at least about 9; alternatively, at least about 15; alternatively, at least about 20; alternatively, at least about 24; and, finally, alternatively, at least about 27 g/g.
• the gel stiffness or shear modulus of a superabsorbent material is further described in U.S. Patent No. 5, 147,343 to Kellenberger and/or U.S. Patent No.
• the superabsorbent material is in the form of particles which, in the unswollen state, have maximum cross-sectional diameters ranging between about 50 and about 1,000 microns; desirably, between about 100 and about 800 microns; more desirably between about 200 and about 650 microns; and most desirably, between about 300 and about 600 microns, as determined by sieve analysis according to American Society for Testing Materials Test Method D-1921. It is understood that the particles of superabsorbent material may include solid particles, porous particles, or may be agglomerated particles including many smaller particles falling within the described size ranges.
• the absorbent composites of the present invention also include an energy receptive additive.
• the energy receptive additive is in intimate association with and covering the surface of the superabsorbent material.
• Suitable energy receptive additives may be in particulate, liquid or semi-liquid form and are capable of becoming excited when subjected to dielectric heating.
• suitable energy receptive additives absorb microwave energy efficiently, converting it to heat.
• the energy receptive additive extends over at least about 10 percent of the surface of the material being covered; alternatively, over at least about 20 percent of the surface of the material being covered; alternatively, over at least about 30 percent of the surface of the material being covered; alternatively, over at least about 40 percent of the surface of the material being covered; alternatively, over at least about 50 percent of the surface of the material being covered; alternatively, over at least about 60 percent of the surface of the material being covered; alternatively, over at least about 70 percent of the surface of the material being covered; alternatively, over at least about 80 percent of the surface of the material being covered; and finally, alternatively, over at least about 90 percent of the surface of the material being covered.
• the term "surface” and its plural generally refer herein to the outer or the topmost boundary of an object.
• the phrase "intimate association" and other similar terms are intended to encompass configurations including the following: those where at least a portion of an energy receptive additive is in contact with a portion of the surface of at least one particle of superabsorbent material; and/or those where at least a portion of an energy receptive additive is in contact with a portion of another energy receptive additive such as in, for example, a layered or mixed configuration.
• a suitable energy receptive additive absorbs energy at the desired frequency (typically between about 0.01 to about 300 GHz) very rapidly, in the range of fractions of a second; alternatively, less than about a quarter of a second; alternatively, less than about a half of a second; and at most about one second.
• a suitable energy receptive additive should have a dielectric loss factor that is relatively high.
• the dielectric loss factor is a measure of how receptive to high frequency energy a material is.
• the measured value of ⁇ ' is most often referred to as the dielectric constant, while the measurement of ⁇ " is denoted as the dielectric loss factor.
• a suitable measuring system can include an HP8720D Dielectric Probe and a model HP8714C Network Analyzer, both available from Agilent Technologies, a business having offices located in Brookfield, Wisconsin, U.S.A. Substantially equivalent devices may also be employed.
• ⁇ " is always positive; however, a value of less than zero is occasionally observed when ⁇ " is near zero due to the measurement error of the analyzer.
• the dielectric loss tangent is defined as the calculated ratio of ⁇ "/ ⁇ '. This dielectric loss tangent (tan ⁇ ) results as the vector sum of the orthogonal real( ⁇ ')and imaginary ( ⁇ ") parts of the complex relative permittivity ( ⁇ r )of a sample.
• Energy receptive additives useful in the present invention typically have a dielectric constant ⁇ measured in the frequency range of about 900 to about 3,000 MHz ⁇ of at least about 4; alternatively, at least 4; alternatively, at least about 8; alternatively, at least 8; alternatively, at least about 15; or alternatively, at least 15.
• the energy receptive additives suitable for use in the present invention have a dielectric loss tangent — measured in the frequency range of about 900 to about 3,000 MHz - of at least about 0.15; alternatively, at least 0.15; alternatively, at least about 0.25; alternatively, at least 0.25; alternatively, at least about 0.5; or alternatively, at least 0.5. It should be noted that the dielectric constant and dielectric loss tangent are dimensionless.
• Examples of materials that may be suitable energy receptive additives, followed by their dielectric constants are: titanium dioxide (110), hydrogen peroxide at 0 °C (84.2), water at 20 °C (80.4), methyl alcohol at -80 °C (56.6), glycerol at 25 °C (42.5), titanium oxide (40-50), glycol at 25 °C (37), sorbitol at 80 °C (33.5), ethanol at 25 °C (24.3), propanol at 80 °C (20.1), ferrous sulfate at 14 °C (14.2), ferrous oxide at 15.5 °C (14.2), calcium superphosphate (14-15), zircon (12), graphite or high density carbon black (12-15), calcium oxide granules (11.8), barium sulfate at 15.5 °C (11.4), ruby (11.3), silver chloride (11.2), silicon (11-12), hydrogenated castor oil at 27 °C (10.3), magnesium oxide (9.7), alumina (9.3-11.5), anhydr
• Other examples include, but are not limited to, various mixed valent oxides such as magnetite (Fe 3 O4), nickel oxide (NiO) and such; ferrite, tin oxide, carbon, carbon black and graphite; sulfide semiconductors such as FeS 2 , CuFeS 2 ; silicon carbide; various metal powders such as aluminum, iron and the like; various hydrated salts and other salts, such as calcium chloride dihydrate; diatomaceous earth; adipic acids; aliphatic polyesters, e.g.
• the present invention is not limited to the use of only one energy receptive additive, but could also include mixtures of two or more energy receptive additives.
• the energy receptive additive may be in particulate form; consequently, it is understood that the particles of energy receptive additive may include solid particles, porous particles, or may be an agglomeration of more than one particle of energy receptive additive.
• One skilled in the art would readily appreciate the possibility of treating the surface of a particle of energy receptive additive to enhance its ability to efficiently absorb microwave energy. Suitable surface treatments include scoring, etching, and the like.
• the energy receptive additive may also be in the form of a liquid or semi-liquid.
• a solution, dispersion or emulsion of one or more effective energy receptive additives may be formulated.
• a liquid or semi-liquid formulation may be deposited on the surface of superabsorbent material in the form of finely atomized droplets or by any of a variety of other known methods including spraying or blowing in the form of steam, and the like. When so deposited, at least a portion of the energy receptive additive would come into intimate association with and cover at least a portion of the surface of a particle of superabsorbent material.
• the intimate association of an energy receptive additive with a superabsorbent material may be achieved with the optional use of an association agent.
• the association agent usually includes substances that can be applied in liquid or semi-liquid form to either the superabsorbent material or the energy receptive additive.
• the term "applied” as used herein is intended to include situations where: at least a portion of the surface of a particle of superabsorbent material has an effective amount of association agent on it to facilitate adherence, via mechanical and/or chemical bonding, of at least a portion of the surface of the superabsorbent material to at least a portion of an energy receptive additive; at least a portion of an energy receptive additive has an effective amount of association agent on it to facilitate adherence, via mechanical and/or chemical bonding, of at least a portion of the energy receptive additive to a portion of the surface of a particle of superabsorbent material; and/or at least a portion of an energy receptive additive has an effective amount of association agent on it to facilitate adherence, via mechanical and/or chemical bonding, of at least a portion of an energy receptive additive to a portion of another energy receptive additive.
• the association agent is applied to the selected material in an amount of from about 99: 1 to about 1:99, by
• association agent can be made by one skilled in the art and will typically depend upon the chemical composition of the materials to be maintained in intimate association with one another. Desirably, the association agent is suitable for use in applications involving human contact. Thus, the association agent should be non-toxic and non- irritating to humans.
• An association agent suitable for use in the present invention is typically prepared by the formation of a liquid or semi-liquid capable of being generally uniformly atomized. In particular, a solution, dispersion or emulsion including at least one of the association agents identified herein may be prepared.
• association agent is described herein as being applied as finely atomized droplets, it may be applied to the selected material by any other method such as by spraying in liquid or semi-liquid form, spraying and blowing in the form of steam, and the like.
• association agent Several types of association agent are capable of being employed in the present invention.
• Illustrative association agents suitable for use in various embodiments of the present invention include, for example: water; volatile organic solvents such as alcohols; aqueous solutions of film-forming materials such as dried milk, lactose, soluble soy protein, and casein; synthetic adhesives such as polyvinyl alcohol; and mixtures thereof.
• the presence of water in the association agent is particularly effective in predisposing the superabsorbent material to wetting.
• the absorbent composites of the present invention are believed to be suitable for use in a variety of disposable absorbent articles including, but not limited to: health care related products including ostomy products, surgical drapes, gowns, and sterilization wraps; personal care absorbent products such as feminine hygiene products, diapers, training pants, incontinence products and the like; as well as facial tissues.
• the absorbent composites may be used in a manner similar to that in which conventional superabsorbents have been used: for example, in laminates, in relatively high density cores (i.e. , compacted cores, calendered cores, densified cores, etc.), or in relatively low density cores (i.e. , not compacted, for example, airlaid cores).
• Absorbent articles having stabilized absorbent structures which include the absorbent composites discussed herein are disclosed in U.S. Application Serial No. , entitled "Absorbent Article
• an absorbent composite of the present invention may be exposed to microwave energy while minimizing or eliminating the arcing commonly associated with the microwave heating of a particle of superabsorbent material that does not have an energy receptive additive covering its surface.
• energy receptive additives suitable for use in the present invention absorb energy, such as radio frequency (RF) or microwave energy, more rapidly than the superabsorbent material and thus heat faster than the superabsorbent material.
• RF radio frequency
• the energy receptive additive By heating faster than the superabsorbent material, the energy receptive additive will activate any adjacent binder fibers thereby stabilizing the airlaid web.
• the absorbent composites of the present invention would therefore allow for the activation of binder fibers to form stabilized structures at higher speeds, shorter heating times, and lower energy levels.
• Energy receptive additives can be receptive to various specific spectra of energy. Just as a black item will absorb more energy and become warmer than the same item colored white when subjected to the same amount of solar energy, energy receptive additives will absorb energy at their specific wavelength, directed at them.
• One method of providing energy to an energy receptive additive is via dielectric heating (e.g. , RF or microwave heating).
• Dielectric heating is the term applied to the generation of heat in non-conducting materials by their losses when subject to an alternating electric field of high frequency.
• the frequencies necessarily range from about 0.01 to about 300 GHz (billion cycles/sec).
• Heating of non-conductors by this method is extremely rapid.
• This form of heating is applied by placing the non-conducting material between two electrodes, across which the high-frequency voltage is applied.
• This arrangement in effect constitutes an electric capacitor, with the load acting as the dielectric. Although ideally a capacitor has no losses, losses do occur in practice and sufficient heat is generated at high frequencies to make this a viable form of heating.
• the frequency used in dielectric heating is a function of the power desired and the size of the work material. Practical values of voltages applied to the electrodes are about 2000 to about 5000 volts/in of thickness of the work material.
• the source of power is by electronic oscillators that are capable of generating the very high frequencies desired.
• the basic requirement for dielectric heating is the establishment of a high-frequency alternating electric field within the material or load to be heated. Once the electric field has been established, the second requirement involves dielectric loss properties of the material to be heated.
• the dielectric loss of a given material occurs as a result of electrical polarization effects in the material itself and may be through dipolar molecular rotation and ionic conduction. The higher the dielectric loss of a material, the more receptive to the high frequency energy it is.
• RF heating occurs at about 27 MHz and heats by providing about half the total power delivered as ionic conduction to the molecules within the workpiece, with the remainder of the power delivered as dipolar molecular rotation.
• Microwave heating is dielectric heating at still higher frequencies.
• the predominate frequencies used in industrial microwave heating are 915 and 2450 MHz, although other frequencies may be used and particular energy receptive additives may be found to be receptive at only particular frequencies.
• Microwave heating is about 10 to about 100 times higher in frequency than the usual dielectric heating, resulting in a lower voltage requirement if the dielectric loss is constant, although the dielectric loss is generally higher at microwave frequencies.
• the absorbent composites of the present invention may be prepared in a manner similar to fluidized bed coating processes.
• at least one particle of an energy receptive additive is suspended in a fluidized bed coating apparatus that creates a strong upward current or stream of fluidizing gas, usually air, typically at an inlet temperature approximating that of room temperature.
• the strong upward current or stream of fluidizing gas moves the energy receptive additive upward until the energy receptive additive passes out of the upward stream and passes downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the energy receptive additive may re-enter the upward-moving stream of fluidizing gas.
• the energy receptive additive While in the upward-moving stream, the energy receptive additive passes through a zone where an association agent is applied to the energy receptive additive. After the association agent is applied to the energy receptive additive, at least one particle of superabsorbent material is introduced into the apparatus.
• a strong upward current or stream of fluidizing gas usually air, optionally at an elevated inlet temperature (i.e. , a temperature typically above room temperature), moves the energy receptive additive and the superabsorbent material upward until the energy receptive additive and the superabsorbent material pass out of the upward stream and pass downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the energy receptive additive and the superabsorbent material may re-enter the upward-moving stream of fluidizing gas until an absorbent composite is formed.
• the energy receptive additive would come into intimate association with the superabsorbent material to form an absorbent composite.
• the absorbent composite so formed would include at least one particle of superabsorbent material covered with at least a first layer of at least one particle of energy receptive additive.
• the energy receptive additive of the first layer would be in intimate association with and covering the surface of the superabsorbent material.
• the absorbent composites of the present invention may also be prepared by another embodiment of the process described herein.
• At least one particle of a superabsorbent material is suspended in a fluidized bed coating apparatus that creates a strong upward current or stream of fluidizing gas, usually air, typically at an inlet temperature approximating that of room temperature.
• the strong upward current or stream of fluidizing gas moves the superabsorbent material upward until the superabsorbent material passes out of the upward stream and passes downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the superabsorbent material may re-enter the upward-moving stream of fluidizing gas. While in the upward-moving stream, the superabsorbent material passes through a zone where an association agent is applied to the superabsorbent material.
• At least one particle of energy receptive additive is introduced into the apparatus.
• a strong upward current or stream of fluidizing gas usually air, optionally at an elevated inlet temperature, moves the energy receptive additive and the superabsorbent material upward until the energy receptive additive and the superabsorbent material pass out of the upward stream and pass downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the energy receptive additive and the superabsorbent material may re-enter the upward-moving stream of fluidizing gas until an absorbent composite is formed.
• the association agent it is applied that the energy receptive additive would come into intimate association with the superabsorbent material to form an absorbent composite.
• the absorbent composite so formed would include at least one particle of superabsorbent material covered with at least a first layer of at least one particle of energy receptive additive.
• the energy receptive additive of the first layer would be in intimate association with and covering the surface of the superabsorbent material.
• the absorbent composites of the present invention may also be prepared by still another embodiment of the process described herein.
• at least one particle of energy receptive additive and at least one particle of superabsorbent material are suspended in a fluidized bed coating apparatus that creates a strong upward current or stream of fluidizing gas, usually air, typically at an inlet temperature approximating that of room temperature.
• the strong upward current or stream of fluidizing gas moves both the energy receptive additive and the superabsorbent material upward until the energy receptive additive and the superabsorbent material pass out of the upward stream and pass downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the energy receptive additive and the superabsorbent material may re-enter the upward- moving stream of fluidizing gas. While in the upward-moving stream, the energy receptive additive and the superabsorbent material pass through a zone where an association agent is applied to both the energy receptive additive and superabsorbent material. After the association agent is applied, the strong upward-moving stream of fluidizing gas, usually air, optionally at an elevated inlet temperature, moves the energy receptive additive and the superabsorbent material upward until the energy receptive additive and the superabsorbent material pass out of the upward stream and pass downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the strong upward-moving stream of fluidizing gas usually air, optionally at an elevated inlet temperature
• the energy receptive additive and the superabsorbent material may re-enter the upward- moving stream of fluidizing gas until an absorbent composite is formed.
• the energy receptive additive would come into intimate association with the superabsorbent material to form an absorbent composite.
• the absorbent composite so formed would include at least one particle of superabsorbent material covered with at least a first layer of at least one particle of energy receptive additive.
• the energy receptive additive of the first layer would be in intimate association with and covering the surface of the superabsorbent material.
• the absorbent composites of the present invention may also be prepared by yet another embodiment of the process described herein.
• at least one particle of a superabsorbent material is suspended in a fluidized bed coating apparatus that creates a strong upward current or stream of fluidizing gas, usually air, typically at an inlet temperature approximating that of room temperature.
• the strong upward current or stream of fluidizing gas moves the superabsorbent material upward until the superabsorbent material passes out of the upward stream and passes downward in a fluidized condition countercurrent to the upward stream of fluidizing gas.
• the superabsorbent material may re-enter the upward-moving stream of fluidizing gas.
• the superabsorbent material While in the upward-moving stream, the superabsorbent material passes through a zone where an energy receptive additive, in liquid or semi-liquid form, is deposited on and covers the surface of the superabsorbent material.
• the energy receptive additive and the superabsorbent material may re-enter the upward-moving stream of fluidizing gas until an absorbent composite is formed.
• the absorbent composite so formed would include at least one particle of superabsorbent material covered with an energy receptive additive.
• the energy receptive additive would be in intimate association with and covering the surface of the superabsorbent material.
• a fluidized bed coating apparatus similar to that illustrated in FIG. 1 may be utilized to form the absorbent composites of the present invention.
• a generally vertically-mounted, generally cylindrical chamber (221) is open at chamber proximal end (222) and closed at chamber distal end (223).
• the chamber (221) is optionally provided with an inner chamber (224) that has a diameter less than that of the chamber.
• the inner chamber (224) is open at both inner chamber proximal end (225) and inner chamber distal end (226).
• the chamber proximal end (222) is fitted with a plate (227) that has a porous area (228) that generally matches the diameter of the inner chamber (224).
• the inner chamber (224) is positioned a distance above the plate (227) and is generally aligned along the vertical axis of the chamber (221).
• an upward current or stream (229) of fluidizing gas usually air, typically at an inlet temperature approximating that of room temperature, such as from a valve (230) from a source of compressed gas (231).
• the upward-moving stream (229) of fluidizing gas generally flows through the inner chamber (224) by entering through the inner chamber proximal end (225) and exiting through the inner chamber distal end (226).
• at least one particle of energy receptive additive (233) is introduced into the chamber (221).
• the upward-moving stream (229) of fluidizing gas is adjusted so as to provide a fluid-like flow to the energy receptive additive (233).
• the upward-moving stream (229) of gas moves the energy receptive additive (233) upward until the energy receptive additive passes out of the upward stream and passes downward in a fluidized condition countercurrent to the upward-moving stream of fluidizing gas.
• the energy receptive additive (233) may re-enter the upward-moving stream (229) of fluidizing gas. While in the upward-moving stream, the energy receptive additive passes through a zone where an association agent (235) is applied to the energy receptive additive (233).
• This zone is generally located in the vicinity of a sprayer means (234) positioned near the center of the plate (227).
• a sprayer means 234.
• the association agent is applied to the energy receptive additive (233)
• at least one particle of superabsorbent material (232) is introduced into the chamber (221).
• the upward-moving stream (229) of gas is adjusted so as to provide a fluid-like flow to the superabsorbent material (232) and the energy receptive additive (233).
• the inlet temperature of the upward-moving stream (229) of fluidizing gas is optionally elevated to a temperature in excess of room temperature.
• the cyclic flow of the superabsorbent material (232) and the energy receptive additive (233) would generally be allowed to continue in the chamber (221) until the energy receptive additive comes into intimate association with the superabsorbent material to form an absorbent composite.
• the absorbent composite is then recovered or removed from the chamber (221).
• the absorbent composite so formed would include at least one particle of superabsorbent material covered with at least a first layer of at least one particle of energy receptive additive.
• the energy receptive additive of the first layer would be in intimate association with and covering the surface of the superabsorbent material.
• a fluidized bed coating process is relatively mild in its effect on the superabsorbent material being brought into intimate association with the energy receptive additive and would therefore be less damaging to the microstructure of the superabsorbent material as compared to other processes.
• the absorbent composites of the present invention may also be formed using a variety of other processes incorporating, for example, a V-shell blender or other apparatus that is relatively mild in its effect on the superabsorbent material.
• the absorbent composite of the present invention may remain in the apparatus and subject to the strong upward current or stream of fluidizing gas at an elevated temperature until the moisture content of the absorbent composite is less than that which would support the growth of microorganisms.
• the moisture content of the absorbent composites should be about 15 percent or less by weight; desirably, about 10 percent or less by weight; more desirably, about 5 percent or less by weight; and most desirably, about 3 percent or less by weight.
• a second energy receptive additive to an absorbent composite.
• the second energy receptive additive, as well as any subsequent additional energy receptive additive, would be added in generally the same manner as would a first receptive additive according to at least one of the process embodiments described herein.
• absorbent composites having more than two energy receptive additives it is also within the present invention to form absorbent composites having more than two energy receptive additives. Consequently, it is within the scope of the present invention to form absorbent composites having a single energy receptive additive or absorbent composites having two or more energy receptive additives in a variety of multi-layered or multi-mixture configurations with each energy receptive additive-containing layer or mixture including one or more energy receptive additives.
• Various embodiments of the process described herein may operate at inlet temperatures ranging from about room temperature to about 72 °C.
• the inlet temperature may, however, range considerably higher than about 72 °C so long as the bed temperature in the apparatus does not exceed a temperature that would cause decomposition of the absorbent composite or any material included in the absorbent composite.
• the selection of a particular inlet temperature would depend on the superabsorbent material, the energy receptive additive and the optional association agent, and may be readily selected by one skilled in the art.
• an absorbent composite of the present invention has a weight ratio, based on the total weight of the superabsorbent material and the energy receptive additive in the absorbent composite, of superabsorbent material to energy receptive additive of from about 99: 1 to about 1:99; alternatively, from about 45:55 to about 95:5; alternatively, from about 60:40 to about 80:20; and finally, alternatively, from about 65:35 to about 70:30.
• This Example illustrates an alternate method of preparing the absorbent composites disclosed herein.
• DRYTECH 2035 superabsorbent available from Dow Chemical Company, Midland, Michigan, U.S.A., was sieved to 300-600 micron particle size using standard sieves.
• India Ink a source of carbon black, available in solution form from Speedball Art Products Company, 2226 Speedball Road., Statesville, North Carolina, U.S.A. The solids content of the India Ink was determined separately to be about 21 percent.
• an energy receptive additive in the form of the India Ink solution, was mixed 1: 1 with DRYTECH 2035 superabsorbent. The mixing occurred in a weighing dish using a spatula. The weighing dish and its contents were thereafter placed in an oven and dried at about 105 °C for approximately 1 hour.
• the absorbent composite so formed contained approximately 83 percent (by weight) superabsorbent and approximately 17 percent (by weight) energy receptive additive.
• This Example illustrates still another method of preparing the absorbent composites disclosed herein.
• DRYTECH 2035 superabsorbent available from Dow Chemical Company, Midland, Michigan, U.S.A., was sieved to 300-600 micron particle size using standard sieves.
• a source of graphite in the form of a graphite stick item No. 970A-BP, available from General Pencil Company, Inc., Jersey City, New Jersey.
• Graphite an energy receptive additive, was obtained by grinding the graphite stick in a mortar and pestle. The ground graphite was sieved such that particles of graphite having a size of less than 150 microns were utilized in this example.
• the ground graphite particles were mixed 4: 1 with DRYTECH 2035 superabsorbent. The mixing occurred by placing the mixture in a sealed bottle and shaking vigorously by hand for a few minutes. A small amount of association agent (e.g. , water) may also be utilized.
• association agent e.g. , water
• Example 3 This Example illustrates yet another method of preparing the absorbent composites disclosed herein.
• DRYTECH 2035 superabsorbent available from Dow Chemical Company, Midland, Michigan, U.S.A., was sieved to 300-600 micron particle size using standard sieves.
• Also utilized in this example was a source of graphite in the form of a graphite stick, item No. 970A-BP, available from General Pencil Company, Inc. , Jersey City, New Jersey.
• Graphite an energy receptive additive, was obtained by grinding the graphite stick in a mortar and pestle.
• the ground graphite was sieved such that particles of graphite having a size of 150-300 microns were utilized in this example.
• the ground graphite particles were mixed 4: 1 with DRYTECH 2035 superabsorbent. The mixing occurred by placing the mixture in a sealed bottle and shaking vigorously by hand for a few minutes.
• a small amount of association agent e.g. , water may also be utilized.

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