EP1265571A1 - Procede de fabrication de structures absorbantes comprenant des preparations polymeres absorbantes et un agent de maintien de la permeabilite - Google Patents

Procede de fabrication de structures absorbantes comprenant des preparations polymeres absorbantes et un agent de maintien de la permeabilite

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Publication number
EP1265571A1
EP1265571A1 EP00912178A EP00912178A EP1265571A1 EP 1265571 A1 EP1265571 A1 EP 1265571A1 EP 00912178 A EP00912178 A EP 00912178A EP 00912178 A EP00912178 A EP 00912178A EP 1265571 A1 EP1265571 A1 EP 1265571A1
Authority
EP
European Patent Office
Prior art keywords
absorbent
absorbent polymer
maintenance agent
permeability
permeability maintenance
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00912178A
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German (de)
English (en)
Inventor
Arman Ashraf
Bryn Hird
Mardelle Elizabeth Jones
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Procter and Gamble Co
Original Assignee
Procter and Gamble Co
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Filing date
Publication date
Application filed by Procter and Gamble Co filed Critical Procter and Gamble Co
Publication of EP1265571A1 publication Critical patent/EP1265571A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F13/00—Bandages or dressings; Absorbent pads
    • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
    • A61F13/15577—Apparatus or processes for manufacturing
    • A61F13/15617—Making absorbent pads from fibres or pulverulent material with or without treatment of the fibres
    • A61F13/15658—Forming continuous, e.g. composite, fibrous webs, e.g. involving the application of pulverulent material on parts thereof

Definitions

  • TECHNICAL FIELD This application relates to a process of making absorbent structures containing absorbent particles, wherein the relatively high permeability of absorbent polymer compositions can be maintained even after mechanical stress has been applied to the polymer particles, as typically occurs during the manufacture of disposable absorbent articles.
  • This process involves addition of a permeability maintenance agent, such as fine powder(s) to the absorbent polymer compositions. This process is particularly useful for the manufacture absorbent structures for being used to absorb body fluids such as urine and menses.
  • a highly desired characteristic for such products is thinness. For example, thinner diapers are less bulky to wear, fit better under clothing, and are less noticeable. They are also more compact in the package, making the diapers easier for the consumer to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor, including less shelf space required in the store per diaper unit.
  • absorbent polymers are often made by initially polymerizing unsaturated carboxylic acids or derivatives thereof, such as acrylic acid, alkali metal (e.g., sodium and/or potassium) or ammonium salts of acrylic acid, alkyl acrylates, and the like in the presence of relatively small amounts of di- or poly-functional monomers such as N,N'-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol di(meth)acrylate, or t allylamine.
  • the di- or poly-functional monomer materials serve to lightly cross-link the polymer chains thereby rendering them water-insoluble, yet water- swellable.
  • These lightly crosslinked absorbent polymers contain a multiplicity of carboxyl groups attached to the polymer backbone.
  • Absorbent polymers can also be made by polymerizing unsaturated amines or derivatives thereof in the presence of relatively small amounts of di- or poly-functional monomers, in an analogous fashion.
  • absorbent polymers useful as absorbents in absorbent members and articles such as disposable diapers need to have adequately high sorption capacity, as well as adequately high gel strength. Sorption capacity needs to be sufficiently high to enable the absorbent polymer to absorb significant amounts of the aqueous body fluids encountered during use of the absorbent article.
  • Gel strength relates to the tendency of the swollen polymer particles to deform under an applied stress, and needs to be such that the particles do not deform and fill the capillary void spaces in the absorbent member or article to an unacceptable degree, thereby inhibiting the rate of fluid uptake or the fluid distribution by the member or article.
  • the permeability of a zone or layer comprising swollen absorbent polymer can be increased by increasing the crosslink density of the polymer gel, thereby increasing the gel strength.
  • this typically also reduces the absorbent capacity of the gel undesirably. See, for example, U.S. Patent 4,654,039 (Brandt et al.), issued March 31 , 1987 (reissued April 19, 1988 as U.S. Reissue Patent 32,649) and U.S. Patent 4,834,735 (Alemany et al.), issued May 30, 1989.
  • absorbent polymers can exhibit gel blocking under certain conditions. "Gel blocking” occurs when particles of the absorbent polymer deform so as to fill the capillary void spaces in the absorbent member or article to an unacceptable degree, thereby inhibiting the rate of fluid uptake or the distribution of fluid by the member/article. Once gel-blocking occurs, further fluid uptake or distribution takes place via a very slow diffusion process. In practical terms, this means that gel-blocking can substantially impede the distribution of fluids to relatively dry zones or regions in the absorbent member or article. Leakage from the absorbent article can take place well before the particles of absorbent polymer in the absorbent article are fully saturated or before the fluid can diffuse or wick past the "blocking" particles into the rest of the absorbent article. See U.S.
  • Patent 4,834,735 (Alemany et al), issued May 30, 1989
  • This gel blocking phenomenon has typically necessitated the use of a fibrous matrix in which are dispersed the particles of absorbent polymer.
  • This fibrous matrix keeps the particles of absorbent polymer separated from one another and provides a capillary structure that allows fluid to reach the absorbent polymer located in regions remote from the initial fluid discharge point. See U.S. Patent 4,834,735 (Alemany et al), issued May 30, 1989.
  • dispersing the absorbent polymer in a fibrous matrix at relatively low concentrations in order to minimize or avoid gel blocking can significantly increase the bulkiness of the absorbent article or lower the overall fluid storage capacity of thinner absorbent structures. Using low concentrations of absorbent polymers limits somewhat the real advantage of these materials, i.e. their ability to absorb and retain large quantities of body fluids per given volume.
  • the permeability/flow conductivity of a material can be defined in terms of its Saline Flow Conductivity (SFC).
  • SFC is a measure of the ability of a material to transport saline fluids, such as the ability of a layer comprising swollen absorbent polymer to transport body fluids.
  • an air-laid web of pulp fibers (e.g., having a density of 0.15 g/cc) will exhibit an SFC value of about 200 x 10 cm sec/g.
  • Absorbent polymers with relatively high permeabilities can be made by increasing the level of crosslinking which increases the strength of the swollen gel, but this typically also reduces the absorbent capacity of the gel undesirably, as described above.
  • Surface crossiinking of absorbent polymer particles is often employed to increase the surface modulus of the particle in the swollen state, while maintaining a relatively high sorption capacity.
  • a surface crosslinked particle has a "core-shell" structure with an exterior shell that has a higher crosslink density than the interior core of the particle.
  • the interior of the core-shell particle typically has a lower crosslink density, and the shell typically has a higher crosslink density than a homogeneously crosslinked particle with the same capacity.
  • Absorbent polymer compositions comprised of surface-crosslinked particles are typically more permeable to fluid in the swollen state than analogous homogeneous absorbent polymer compositions with similar capacities. Without being bound by theory, it is believed that the increase in modulus of the surface layer affords increased resistance to deformation under an applied load, and hence increased porosity and permeability. The gradation in crossiinking from surface to interior can vary, both in depth and profile.
  • Suitable methods for surface crossiinking include those where (i) a di- or poly-functional reagent(s) capable of reacting with existing functional groups within the absorbent polymer is applied to the surface of the absorbent polymer; (ii) a di- or poly-functional reagent that is capable of reacting with other added reagents and possibly existing functional groups within the absorbent polymer such as to increase the level of crossiinking at the surface is applied to the surface (e.g., the addition of monomer plus crosslinker and the initiation of a second polymerization reaction); (iii) no additional polyfunctional reagents are added, but additional reaction(s) is induced amongst existing components within the absorbent polymer either during or after the primary polymerization process such as to generate a higher level of crossiinking at or near the surface (e.g., suspension polymerization processes wherein the crosslinker is inherently present at higher levels near the surface); and (iv)
  • suitable di- or polyfunctional crossiinking reagents include di/poly-haloalkanes, di/poly-epoxides, di/poly- acid chlorides, di/poly-tosyl alkanes, di/poly-aldehydes, di/poly-acids, and the like.
  • GB-A-2.082.614 (Richman) describes the addition (either under wet or dry conditions) of between 1 and 75% of an extender material such as cellulose derivatives, or inorganic materials like clay or minerals.
  • the objective of this development is an increase of absorbent capacity.
  • a further known approach for improving the liquid handling performance of absorbent polymers is the addition of inorganic material during the formation of the polymer or the cross-linking thereof, which can be used to reduce gel blocking.
  • An approach along these lines is described in US-A-4.500.670 (McKinley), wherein structures are described which have between 1 and 99% of an inorganic powder added, which provides an increase of gel strength from less than about 0.1 psi to 2.1 psi (at 40 % inorganic powder).
  • Such gel strengths are typically characteristic of materials
  • Absorbent polymer particles can be substantially affected during processing in the manufacture of absorbent articles. Abrasion of the surface and/or breaking of the individual particles tends to occur, resulting in the generation of smaller particles. Without being bound by theory, it is believed that the relatively small particles produced during the damaging process tend to fill the voids between the larger particles, thereby reducing the permeability of the system. Furthermore, in surface-crosslinked materials, it is believed that damage to the polymer particles exposes the inner material which has a relatively low degree of crossiinking. In the swollen state, this inner material has relatively low gel strength, and tends to deform to fill residual void spaces within the gel bed. Thus, damage to the absorbent polymer particles can substantially reduce the permeability of the material and/or the rate of fluid absorption.
  • the present invention is a process of making an absorbent structure wherein
  • absorbent polymer particles which having an SFC value of more than 5 x 10 cm sec/g, are mixed with a Permeability Maintenance Agent, preferably a particulate one, and then combined with a carrier, which can be fibrous, or a porous web, such as a fibrous web or a foam.
  • a mechanical stress is applied to the polymer particles, whereby the effect of this mechanical stress on the permeability should be less for the blend of the polymer particles with the Permeability Maintenance Agent, compared to the effect of the mechanical stress on an analogous material without the Permeability Maintenance Agent
  • 7 3 7 3 is at least 5 x 10 cm sec/g greater, preferably at least 10 x 10 cm sec/g greater, and
  • the absorbent polymer particles material exhibits an SFC value of at least 20 x 10 cm sec/g greater than the reduction in SFC for the absorbent polymer particle/Permeability Maintenance Agent blend
  • the absorbent polymer particles material exhibits an SFC value of at least 20 x 10 cm sec/g greater than the reduction in SFC for the absorbent polymer particle/Permeability Maintenance Agent blend
  • the absorbent polymer particles can have a particle size distribution such that at least 30% by weight has a particle size of more than 300 ⁇ m
  • Preferred Permeability Maintenance Agents are silica, preferably fumed silica
  • the Permeability Maintenance Agent can have an average particle size of no more than 10 ⁇ tn, preferably no more than 1 ⁇ m or even less than 0 1 ⁇ m
  • the Permeability Maintenance Agent can be added at a level of not more than 3 0%, preferably not more than 1 0 %, and more preferably of not more than 0 8%, and even more preferably of not more than 0 6% based on the total weight of said absorbent polymer particles, and said Permeability Maintenance Agent, and at a level of at least 0 2%, preferably more than 0 4%
  • the process can include the step of transporting and or storing said absorbent polymer particles/Permeability Maintenance Agent blend prior to or after said mixing step
  • the mixing step can be dry mixing of dry absorbent polymer particles and dry Permeability Maintenance Agent
  • the combination step can be dry mixing of the absorbent polymer particles/Permeability Maintenance Agent blend with a carrier, such as an airlaying process
  • the absorbent structure made according to the present invention preferably comprises at least 40%, more preferably at least 60%, even more preferably at least 80% absorbent polymer particles, and most preferably more than 90 % based on the total weight of said absorbent polymer particles, said carrier, and said Permeability
  • the present invention also relates to an absorbent structure comprising a absorbent polymer particles/Permeability Maintenance Agent blend having an SFC reduction in a damaging test of less than 10% relative to the SFC of the AAP without Permeability Maintenance Agent prior to damaging.
  • body fluids includes urine, blood, menses and vaginal discharges.
  • synthetic urine solution refers to an aqueous solution prepared by dissolving 2.0 g KCI, 2.0 g Na2SC>4, 0.85 g NH4H2PO4, 0.15 g (NH4)2HP ⁇ 4, 0.25 g CaCl2-2H2 ⁇ , and 0.50 g MgCl2-6H2 ⁇ in distilled water to yield one liter of solution.
  • absorbent polymer refers to a polymer which has a Gel Volume (GV) of at least 10 g/g.
  • the term "absorbent core” refers to the component of the absorbent article that is primarily responsible for fluid handling properties of the article, including acquiring, transporting, distributing and storing body fluids. As such, the absorbent core typically does not include the topsheet or backsheet of the absorbent article.
  • the term "absorbent member” refers to the components of the absorbent core that typically provide one or more fluid handling properties, e.g., fluid acquisition, fluid distribution, fluid transportation, fluid storage, etc.
  • the absorbent member can comprise the entire absorbent core or only a portion of the absorbent core, i.e., the absorbent core can comprise one or more absorbent members.
  • the improved absorbent polymer compositions described herein are particularly useful in absorbent members whose primary function is the storage of aqueous body fluids. However, these compositions may also be present in other absorbent members.
  • the term “comprising” means various components, members, steps and the like can be conjointly employed according to the present invention. Accordingly, the term “comprising” encompasses the more restrictive terms “consisting essentially of and “consisting of,” these latter, more restrictive terms having their standard meaning as understood in the art
  • the present invention relates, to a process of making absorbent structures wherein absorbent polymer compositions are used, and in particular compositions that exhibit high absorbency of synthetic urine solution under an applied load as well as high permeability to fluid in the swollen state, after the polymer composition has been exposed to mechanical stress such as during the manufacturing process of the absorbent structure
  • the absorbent polymer compositions include a variety of water-insoluble, but water-swellable polymers These are typically lightly crosslinked polymers which contain a multiplicity of acid functional groups such as carboxylic acid groups
  • acid polymers suitable for use herein include those which are prepared from polyme ⁇ zable, acid-containing monomers, or monomers containing functional groups which can be converted to acid groups after polymerization
  • Such monomers include olefinically unsaturated carboxylic acids and anhydrides, and mixtures thereof
  • the acid polymers can also comprise polymers that are not prepared from olefinically unsaturated monomers
  • polysaccha ⁇ de-based polymers such as carboxymethyl starch and carboxymethyl cellulose
  • poly(am ⁇ no acid) based polymers such as poly(aspart ⁇ c acid)
  • poly(am ⁇ no acid) absorbent polymers see, for example, U S Patent 5,247,068, issued September 21 , 1993 to Donachy et al , which is incorporated herein by reference
  • non-acid monomers can also be included, usually in minor amounts, in preparing the absorbent polymers herein
  • Such non-acid monomers can include, for example, monomers containing the following types of functional groups carboxylate or sulfonate esters, hydroxyl groups, amide-groups, ammo groups, nitnle groups, quaternary ammonium salt groups, and aryl groups (e g , phenyl groups, such as those derived from styrene monomer)
  • Other optional non-acid monomers include unsaturated hydrocarbons such as ethylene, propylene, 1-butene, butadiene, and isoprene
  • Olefinically unsaturated carboxylic acid and anhydride monomers include the acrylic acids typified by acrylic acid itself, methacrylic acid, ⁇ -chloroacrylic acid, a- cyanoacrylic acid, ⁇ -methylacrylic acid (crotonic acid), -phenytacrylic acid, ⁇ - acryloxypropionic acid, sorbic acid, ⁇ -chlorosorbic acid, angelic acid, cinnamic acid, p- chlorocinnamic acid, ⁇ -stearylacrylic acid, itaconic acid, citroconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, thcarboxyethylene, and maleic anhydride.
  • acrylic acids typified by acrylic acid itself, methacrylic acid, ⁇ -chloroacrylic acid, a- cyanoacrylic acid, ⁇ -methylacrylic acid (crotonic acid), -phenytacrylic acid, ⁇
  • Preferred absorbent polymers contain carboxyl groups. These polymers include hydrolyzed starch-acrylonit le graft copolymers, partially neutralized hydrolyzed starch- acrylonitrile graft copolymers, starch-acrylic acid graft copolymers, partially neutralized starch-acrylic acid graft copolymers, hydrolyzed vinyl acetate-acrylic ester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers, slightly network crosslinked polymers of any of the foregoing copolymers, polyacrylic acid, and slightly network crosslinked polymers of polyacrylic acid. These polymers can be used either solely or in the form of a mixture of two or more different polymers. Examples of these polymer materials are disclosed in U.S. Patent 3,661 ,875, U.S. Patent 4,076,663, U.S. Patent 4,093,776, U.S. Patent 4,666,983, and U.S. Patent 4,734,478.
  • Most preferred polymer materials for use in making the absorbent polymers are slightly network crosslinked polymers partially neutralized polyacrylic acids and starch derivatives thereof.
  • the absorbent polymers comprise from about 50-95, preferably about 75% neutralized, slightly network crosslinked, polyacrylic acid (i.e., poly (sodium acrylate/acrylic acid)).
  • Network crossiinking renders the polymer substantially water- insoluble and, in part, determines the absorptive capacity and extractable polymer content characteristics of the absorbent polymers. Processes for network crossiinking these polymers and typical network crossiinking agents are described in greater detail in U.S. Patent 4,076,663.
  • absorbent polymer is preferably of one type (i.e., homogeneous), mixtures of absorbent polymers can also be used in the present invention.
  • mixtures of starch-acrylic acid graft copolymers and slightly network crosslinked polymers of polyacrylic acid can be used in the present invention.
  • absorbent structures as made according to the present invention there can be used one and the same polymer type or composition throughout the total structure, or there can be different types or compositions in different parts of the structure.
  • a material or composition can have the same concentration throughout the structure, or can be at varying concentrations distributed therethrough.
  • the particle size and particle size distribution - such as can be determined by conventional sieving or optical methods - is of lesser importance.
  • the present invention is not limited by this constraint. Even further, in order to enhance the permeability properties, it can be advantageous to have more than 30% of the particles having a particle size of more than about 300 ⁇ m.
  • particle size distributions are determined according to the method described in the Test Methods section of US-A- 5.419.956 (Roe et al).
  • the absorbent polymers useful in the present invention can be formed by any polymerization and/or crossiinking techniques. Typical processes for producing these polymers are described in U.S. Reissue Patent 32,649 (Brandt et al.), issued April 19, 1988, U.S. Patent 4,666,983 (Tsubakimoto et al.), issued May 19, 1987, and U.S. Patent 4,625,001 (Tsubakimoto et al.), issued November 25, 1986, all of which are incorporated by reference.
  • Polymerization methods to prepare absorbent polymers useful in the present invention can include free radical, ring-opening, condensation, anionic, cationic, or irradiation techniques.
  • the polymer may be prepared in the neutralized, partially neutralized, or un-neutralized form, even though the desired product is un-neutralized.
  • the absorbent polymer may be prepared using a homogeneous solution polymerization process, or by multi-phase polymerization techniques such as inverse emulsion or suspension polymerization procedures.
  • Crossiinking can be effected during polymerization by incorporation of suitable crossiinking monomers.
  • the polymers can be crosslinked after polymerization by reaction with a suitable reactive crossiinking agents.
  • Surface crossiinking of the initially formed polymers is a preferred process for obtaining absorbent polymers having relatively high PUP capacity, porosity and permeability. Without being bound by theory, it is believed that surface crossiinking increases the resistance to deformation of the surfaces of swollen absorbent polymer particles, thus reducing the degree of contact between neighboring polymer particles when the swollen particles are deformed under an external pressure.
  • Surface crosslinked absorbent polymers have a higher level of crossiinking in the vicinity of the surface than in the interior.
  • surface describes the outer-facing boundaries of the particle.
  • porous absorbent polymers e.g., porous particles, etc.
  • exposed internal boundaries can also be included.
  • a higher level of crossiinking at the surface it is meant that the level of functional crosslinks for the absorbent polymer in the vicinity of the surface is generally higher than the level of functional crosslinks for the polymer in the interior.
  • the gradation in crossiinking from surface to interior can vary, both in depth and profile.
  • Suitable methods for surface crossiinking include those where (i) a di- or poly-functional reagent(s) capable of reacting with existing functional groups within the absorbent polymer is applied to the surface of the absorbent polymer; (ii) a di- or poly-functional reagent that is capable of reacting with other added reagents and possibly existing functional groups within the absorbent polymer such as to increase the level of crossiinking at the surface is applied to the surface (e.g., the addition of monomer plus crosslinker and the initiation of a second polymerization reaction); (iii) no additional polyfunctional reagents are added, but additional reaction(s) is induced amongst existing components within the absorbent polymer either during or after the primary polymerization process such as to generate a higher level of crossiinking at or near the surface (e.g., suspension polymerization processes wherein the crosslinker is inherently present at higher levels near the surface); and (iv)
  • Patent 4,734,478 (Tsubakimoto), issued March 29, 1988; U.S. Patent 5,164,459 (Kimura et al.), issued November 17, 1992; published German patent application 4,020,780 (Dahmen), published August 29, 1991 ; and published European patent application 509,708 (Gartner), published October 21 , 1992; all of which are incorporated herein by reference.
  • An essential element for processes according to the present invention is an agent which is added to the absorbent polymers to allow that such materials experience a smaller decrease in permeability upon exposure to mechanical stress than do analogous materials without such agent.
  • modern processes aim at producing absorbent structures with high ratios of absorbent polymers relative to the carrier means - concentrations of 60% of absorbent polymer in a matrix of 40% fibrous materials are not unusual any more. At the same time, such processes aim at producing at higher and higher production speeds.
  • Such usage rate increases are often achieved by using conventional equipment - such as for transporting, metering or positioning of the material - which originally was designed for much lower usage rates, often 50%, or even 20% of the rates currently employed.
  • a conventional approach is to increase the flow rates of the material - or the transport speed or velocity - through the system. Often, this results in increase of the mechanical stress which is exerted on the materials due to increased abrasion, collision with walls, etc..
  • the current invention uses an additive to the absorbent polymer in order to reduce their susceptibility of the absorbent polymer to a reduction in performance caused by mechanical stress, in particular with regard to the permeability of such materials, as evaluated by the "Saline Flow Conductivity" (SFC).
  • SFC Seline Flow Conductivity
  • Such an additive is referred to herein as a Permeability Maintenance Agent.
  • An essential element for the present invention is the addition of a particulate material to the absorbent polymer.
  • a particulate material such as - without any limitation - silica, silicon dioxide, amorphous silica, alumina, titanium dioxide, clays, or other non-absorbent polymer particles, such as can be produced by grinding, emulsion polymerization, precipitation polymerization techniques, or any combination of the foregoing materials.
  • the size of the particulate material can be determined by conventional particle size analysis methods, such as sieving or optical analysis, and is typically no more than 10 ⁇ m, and often less than about 1.0 ⁇ m or even less than 0.1 ⁇ m.
  • the powder used herein comprises fine amorphous fumed silica, such as that in the form of a product referred to as Cab-O-Sil L- 90, manufactured by Cabot Corporation, Tuscola, IL.
  • the fine powder may be added in concentrations up to about 3%, preferably not more than 1.0%, more preferably not more than 0.8%, and most preferably not more than 0.6 %, whilst at least 0.2%, preferably 0.4% should be added, all percentages being based on the total mixture of absorbent polymer and fine powder.
  • the process of the current invention includes mixing or blending the fine powder with the absorbent polymer particles so as to achieve a homogeneous blend of the two materials.
  • the materials may be blended or mixed in the dry state, or in the form of a slurry or suspension.
  • the materials are blended in the dry state.
  • preferred blending processes aim for a homogeneous distribution of the materials.
  • the blending process should further be as gentle as possible so as to minimize the extent of abrasion and/or breakage of the absorbent polymer particles. Mixing may be done in a continuous process, or in a batchwise fashion.
  • Preferred suitable equipment for such a gentle process is generally known to to one skilled in the art, such as ploughshare mixer as available from Gebr. L ⁇ dige grabau GmbH, Germany, under the designation KM as continuous mixer, or FM as batch mixer, or as continuous mixer from Schugi BV, Netherlands, or as batch mixer from
  • absorbent structures Methods of forming absorbent structures wherein particulate absorbent materials is held in a fixed position by means of a carrier are well known in the art.
  • the absorbent structure should be porous to allow liquid transport, and the carrier should be a fibrous material or a porous substrate, such as a fibrous or foam web.
  • the polymer material can then be added to this carrier, and can be mechanically trapped by the carrier, such as is the case with conventional cellulose batts comprising fluff and particulate absorbent materials, or with a porous web enveloping the materials.
  • the polymer material can be attached to the carrier by an attachment means, such as adhesives, or chemical agents, which can bond the particles to the substrate, either permanently, such as by covalent chemical bonding, or temporarily which refers in this context to a bonding mechanism, such as hydrogen bonding, which loses its bond strength upon wetting, such as during use.
  • an attachment means such as adhesives, or chemical agents, which can bond the particles to the substrate, either permanently, such as by covalent chemical bonding, or temporarily which refers in this context to a bonding mechanism, such as hydrogen bonding, which loses its bond strength upon wetting, such as during use.
  • the fixation is achieved by containing the particulate material between layers of such a carrier, these can be bonded to each other such as by the above referred adhesives or covalent bonding means, or by compression, or crimping, preferably in a particular pattern so as to create pockets with the particulate absorbent material therein.
  • the carrier comprises fibers
  • these can be natural, preferably cellulosic fibers, or man-made fibers, such as viscose/rayon fibers, or synthetic polymer fibers, which can comprise polyethylene, polypropylene, polyester or polyamine, which can be made of pure monomers, or can be co-polymers.
  • Bi- or multi-component fibers can be used.
  • Such fibers can be individualized, such as when using fluff pulp, or can be preformed into a web, such as tissues, or non-woven, or woven materials.
  • foamed structures, or apertured films can be used as a carrier, provided these have appropriate liquid handling properties, especially an adequate permeability.
  • a preferred execution for the present invention relates to combining cellulose fluff fibers with particulate absorbent polymer and Permeability Maintenance Agent blend, such as disclosed and described in US-A-5.017.324 (Kaiser); US-A-4.770.344 (Kaiser); EP-A-0.439.012 (Pieper); US-A-5.494.622 (Heath); EP-AO.292.623 (Angstadt); US-A- 4.755.178 (Insley); US-A-5.879.751 (Bogdanski), US-A-4.927.582 (Bryson); all of which are incorporated herein by reference.
  • the absorbent material is acquired in large quantities from the material supplier, and is then transported to the production line of the absorbent article, where it is metered into the absorbent structures there formed. From an economic point of view, it is often desirable to have the means for the transport to the lines and on the lines with minimal dimensions for the respective throughput.
  • particulate absorbent is fed through a piping system, with an air pressure differential as driving means.
  • the mechanical stress on the material can be significant, such as by interaction with walls of the transporting means or control member (like valves, or metering units), but also by interaction between the particles themselves. In particular at high transport rates, the resulting average particle speed can reach significant values. This mechanical stress can have negative impact on the performance properties of the material as discussed separately in more detail G. Effect of Permeability Maintenance Agent
  • the Permeability Maintenance Agent reduces the friction between the particles and either walls or other particles, and thus actually minimizes the damaging stress for the particles, which otherwise could result in break-up of the particle, or - especially for materials which have a particular surface cross-linked shell - damage or abrasion of this treated shell, and hence reduced efficiency.
  • Performance Under Pressure (PUP) Measurement of the Demand Wettability or Gravimetric Absorbence can provide information on the ability of a high concentration zone or layer of the absorbent polymer to absorb body fluids under usage pressures. See, for example, U.S. Patent 5,562,646 (Goldman et al.) issued October 8, 1996 and U.S. Patent 5,599,335 (Goldman et al.) issued Feb. 4, 1997 where Demand Wettability or Gravimetric Absorbence is referred to as Performance Under Pressure (PUP).
  • PUP Performance Under Pressure
  • a requisite property of absorbent polymers of the present invention is their relatively high permeability to fluid. In an absorbent member or article, this directly affects the ability of a material, such as a layer comprising swollen absorbent polymer, to transport body fluids away from the acquisition region at an acceptable rate.
  • Permeability/flow conductivity can be defined in terms of Saline Flow Conductivity (SFC), which is a measure of the ability of a material to transport saline fluid.
  • an absorbent polymer is deemed to have requisite permeability properties if its SFC value is at least about 50 x 10 ⁇ 7 crr ⁇ 3 sec/g.
  • a method for measuring saline flow conductivity is described in U.S. Patent 5,562,646 (Goldman et al.) issued October 8, 1996.
  • the test determines the amount of synthetic urine solution absorbed by absorbent polymers that are laterally confined in a piston/cylinder assembly under a confining pressure of 0.7 psi.
  • Saline Flow Conductivity A measure of permeability and an indication of porosity is provided by the saline flow conductivity of the gel bed as described in U.S. Patent No. 5,562,646, (Goldman et al.) issued Oct. 8, 1996.
  • Example 1 S Approximately 10 grams of the absorbent polymer composition (Sample 1 S) are placed in an 8 oz blending jar designed to be used with an Osterizer blender (Model # 855-08K). The mixture is blended on low speed at approximately 1200 rpm for 1 minute to complete damaging of the absorbent polymer/silica blend (Sample 1 SD).
  • Example 1 SD Capacity Measurements
  • PUP capacities are measured as described in the Test Methods section of U.S. Patent 5,599,335. Approximately 0.9 grams of the unsieved damaged absorbent polymer composition are transferred to a PUP cylinder, and gently spread out over the entire area of the screen comprising the base of the cylinder. The PUP capacity is determined under a confining pressure of 0.7 psi with the amount of fluid absorbed measured at frequent intervals for a period of 1 hour. Selected PUP capacity data are listed in Table 1 below.
  • Saline Flow Conductivity is measured as described in the Test Methods section of U.S. Patent 5,562,646. Approximately 0.9 grams of the absorbent polymer composition are transferred to a cylinder designed for Saline Flow Conductivity measurement cylinder, and gently spread out over the entire area of the screen comprising the base of the cylinder. The measured saline flow conductivity values are listed in Table 1 below:
  • SFC values are x 10 "7 cm 3 -sec/g. A comparison of the SFC values indicates that the permeability of the damaged absorbent polymer - silica blend (Sample 1 SD) is substantially greater than that of the damaged control sample without silica (Sample 1 D) under analogous test conditions.
  • absorbent polymer/silica blend about 10 grams of absorbent polymer (Sample 1 from Example 1 ) are weighed into a 25 ml (8 dram) glass vial with external dimensions of approximately 9.5 cm in height x 2.5 cm diameter (available from VWR. Co., West Chester, PA; Catalog No. 6601 1-165). About 0.05 g Sipernat D-17 (hydrophobic precipitated silica, Degussa Corporation, Ridgefield Park, NJ) are added to the absorbent polymer and mixed thoroughly using a Vortex Mixer (manufactured by Scientific industries Inc., Bohemia, NY; Model No. G-560; available from VWR. Co., West Chester, PA) or equivalent mixer, for approximately 1 minute (Sample 2S).
  • Vortex Mixer manufactured by Scientific industries Inc., Bohemia, NY; Model No. G-560; available from VWR. Co., West Chester, PA
  • Example 2S Approximately 10 grams of the absorbent polymer composition (Sample 2S) are placed in an 8 oz blending jar designed to be used with an Osterizer blender (Model # 855-08K). The mixture is blended on low speed at approximately 1200 rpm for 1 minute to complete damaging of the absorbent polymer/silica blend ( Sample 2SD).
  • PUP capacities are measured as described in the Test Methods section of U.S. Patent 5,599,335. Approximately 0.9 grams of the unsieved damaged absorbent polymer composition are transferred to a PUP cylinder, and gently spread out over the entire area of the screen comprising the base of the cylinder. PUP capacities are determined under confining pressures of 0.7 with the amount of fluid absorbed measured at frequent intervals for a period of 1 hour. PUP capacity data are listed in Table 2 below. (iv) Permeability Measurement
  • Saline Flow Conductivity is measured as described in U.S. Patent No. 5,562,646. Approximately 0.9 grams of the unsieved absorbent polymer composition are transferred to a cylinder designed for Saline Flow Conductivity measurement (SFC), and gently no ⁇
  • a comparison of the SFC values indicates that the permeability of the absorbent polymer - silica blend (Sample 2SD) is substantially greater than that of the damaged control sample (Sample 1 D) under the analogous test conditions
  • a comparison of the PUP capacities indicates that the damaged absorbent polymer - silica blend (Sample 2SD) has a similar PUP capacity to the damaged absorbent polymer control (Sample 1 D) under the test conditions described
  • Example 1 from Example 1
  • a ceramic Mill Jar with external dimensions of approximately 14 6 cm in diameter x 17 cm height
  • About 2 45 grams Cab-O-Sil L- 90 amorphous fumed silica (Lot # 1J193, Cabot Corporation, Tuscola, IL) are added to the absorbent polymer in the Mill Jar and the jar is securely capped
  • the absorbent polymer-silica blend is thoroughly mixed by rotating the Mill Jar using a roller type Jar Mill (U S Stoneware, available from VWR Co , West Chester, PA, Catalog No 48900-000) at 90 rpm for 4 5 hours (Sample 3S)
  • Damaging Approximately 10 grams of the absorbent polymer composition (Sample 3S) are placed in an 8 oz blending jar designed to be used with an Ostenzer blender (Model # 855-08K) The mixture is blended on low speed at approximately 1200 rpm for 1
  • PUP capacities are measured as described in the Test Methods section of U.S. Patent 5,599,335. Approximately 0.9 grams of the unsieved damaged absorbent polymer composition are transferred to a PUP cylinder and gently spread out over the entire area of the screen comprising the base of the cylinder. The PUP capacity is determined under a confining pressure of 0.7 psi with the amount of fluid absorbed measured at frequent intervals for a period of 1 hour. Selected PUP capacity data are listed in Table 3 below. (iv) Permeability Measurement
  • Saline Flow Conductivity is measured as described in U.S. Patent No. 5,562,646. Approximately 0.9 grams of the absorbent polymer composition are transferred to a cylinder designed for Saline Flow Conductivity measurement (SFC), and gently spread out over the entire area of the screen comprising the base of the cylinder. The measured SFC values are listed in Table 3 below: Table 3:
  • a comparison of the SFC values indicates that the permeability of the damaged absorbent polymer - silica blend (Sample 3SD) is substantially greater than that of the damaged control sample without silica (Sample 1 D) under analogous test conditions.
  • absorbent polymer - silica blend 25.0 grams of absorbent polymer (Sample 1 from Example 1) are weighed into a 150 ml glass beaker with an internal diameter of approximately 52 mm.
  • Nos. 8070-05 and 8085-03 is set up to stir the absorbent polymer with the flat side of the blade across the bottom of the beaker.
  • About 1.43 grams of colloidal silica (35% solids, MA-ST colloidal silica in methanol, Nissan Chemical Industry, lot number 70673) and 1.5 grams of distilled water are thoroughly mixed in a 1 dram glass vial.
  • the silica suspension is then added dropwise to the absorbent polymer over a period of about 30 seconds while the mixture is stirred at approximately 170 rpm, to yield an absorbent polymer-silica agglomerate.
  • the agglomerate is mixed gently with spatula to ensure uniform mixing and is dried in a vented oven at 65°C for 1 hour (Sample 4S).
  • Patent 5,599,335. Approximately 0.9 grams of the unsieved absorbent polymer composition are transferred to a PUP cylinder and gently spread out over the entire area of the screen comprising the base of the cylinder. The PUP capacity is determined under a confining pressure of 0.7 psi with the amount of fluid absorbed measured at frequent intervals for a period of 1 hour. Selected PUP capacity data are listed in Table 4 below. (iv) Permeability Measurement
  • a comparison of the SFC values indicates that the permeability of the damaged absorbent polymer - silica blend (Sample 4SD) is substantially greater than that of the damaged control sample without silica (Sample 1 D) under the analogous test conditions.
  • Example 5 The following example demonstrates the effect of the addition of silica on permeability of absorbent polymer prior to versus after being exposed to mechanical stress or damaging.
  • Example 1 Approximately 5 grams of the absorbent polymer composition (Sample 1 from Example 1) are placed in an 8 oz blending jar designed to be used with an Osterizer blender (Model # 855-08K). The absorbent polymer is damaged on low speed at approximately 1200 rpm for 1 minute to yield the damaged absorbent polymer Sample
  • PUP capacities are measured as described in the Test Methods section of U.S. Patent 5,599,335. Approximately 0.9 grams of the unsieved damaged absorbent polymer composition are transferred to a PUP cylinder, and gently spread out over the entire area of the screen comprising the base of the cylinder. PUP capacities are determined under confining pressures of 0.7 with the amount of fluid absorbed measured at frequent intervals for a period of 1 hour. PUP capacity data are listed in Table 5 below.
  • Saline Flow Conductivity is measured as described in U.S. Patent No. 5,562,646. Approximately 0.9 grams of the unsieved absorbent polymer composition are transferred to a cylinder designed for Saline Flow Conductivity measurement (SFC), and gently spread out over the entire area of the screen comprising the base of the cylinder. The measured saline flow conductivity values are listed in Table 5 below:
  • a comparison of the SFC values indicates that the permeability of the absorbent polymer - silica blend (Sample 2SD) whereas the silica is added prior to damaging is substantially greater than that of the polymer - silica blend (Sample 5SD) where the silica is added after damaging under the analogous test conditions.

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Abstract

L'invention concerne un procédé de fabrication d'une structure absorbante, qui consiste à prévoir des particules de polymère absorbantes, à mélanger lesdites particules et un agent de maintien de la perméabilité, de manière qu'un mélange soit formé, et à prévoir un support sélectionné, tel que des fibres, des substrats poreux, comme des nappes de fibres ou des mousses. Ledit procédé consiste également à prévoir un moyen permettant de combiner ledit mélange de particules de polymère absorbantes/agent de maintien de la perméabilité et ledit support, de manière qu'une structure absorbante soit formée, une contrainte mécanique étant exercée sur ledit mélange. Le procédé consiste encore à mélanger lesdites particules de polymère absorbantes et ledit agent de maintien de la perméabilité avant la combinaison, la valeur de conductivité de flux salin SFC du mélange particules de polymère absorbantes/agent de maintien de la perméabilité étant ainsi réduite, de manière qu'elle soit inférieure à celle des particules de polymère absorbantes sans l'agent de maintient de la perméabilité, alors que ladite contrainte mécanique est exercée.
EP00912178A 2000-03-06 2000-03-06 Procede de fabrication de structures absorbantes comprenant des preparations polymeres absorbantes et un agent de maintien de la permeabilite Withdrawn EP1265571A1 (fr)

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AU2003274077A1 (en) 2002-10-25 2004-05-13 Stockhausen Gmbh Two-stage mixing method for producing an absorbent polymer
MX251840B (es) 2003-02-10 2007-11-26 Nippon Catalytic Chem Ind Agente particulado que absorbe agua.
US8247491B2 (en) 2003-02-10 2012-08-21 Nippon Shokubai Co., Ltd. Water-absorbent resin composition and its production process
US7179851B2 (en) 2003-09-05 2007-02-20 Kimberly-Clark Worldwide, Inc. Damage-resistant superabsorbent materials
EP1677845B2 (fr) 2003-09-19 2016-06-22 Nippon Shokubai Co., Ltd. Composant hydrophile et procédé de fabrication associé
MXPA06004345A (es) 2003-11-07 2006-06-27 Nippon Catalytic Chem Ind Composicion de resina absorbente de agua en particulas y su proceso de produccion.
TWI353360B (en) 2005-04-07 2011-12-01 Nippon Catalytic Chem Ind Production process of polyacrylic acid (salt) wate
WO2006134085A1 (fr) * 2005-06-14 2006-12-21 Basf Aktiengesellschaft Polymeres formant des hydrogels, presentant une permeabilite amelioree et une capacite d'absorption elevee
TW200720347A (en) 2005-09-30 2007-06-01 Nippon Catalytic Chem Ind Water-absorbent agent composition and method for manufacturing the same
JP5367364B2 (ja) 2005-09-30 2013-12-11 株式会社日本触媒 吸水性樹脂を主成分として含む吸水剤およびその製造方法
TWI394789B (zh) 2005-12-22 2013-05-01 Nippon Catalytic Chem Ind 吸水性樹脂組成物及其製造方法、吸收性物品
EP1837348B9 (fr) 2006-03-24 2020-01-08 Nippon Shokubai Co.,Ltd. Résine absorbant l'eau et son procédé de fabrication
EP2484439B1 (fr) 2009-09-29 2022-12-14 Nippon Shokubai Co., Ltd. Absorbant particulaire d'eau et son procédé de fabrication
CN104582833A (zh) 2012-08-30 2015-04-29 株式会社日本触媒 颗粒状吸水剂及其制造方法

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US4500670B1 (en) * 1983-11-22 1994-12-27 Dow Chemical Co Composite mixtures for improving gel strength of water absorbent gels
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