WO2006020161A2 - Surface cross-linked superabsorbent polymer particles and methods of making them - Google Patents
Surface cross-linked superabsorbent polymer particles and methods of making them Download PDFInfo
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- WO2006020161A2 WO2006020161A2 PCT/US2005/025343 US2005025343W WO2006020161A2 WO 2006020161 A2 WO2006020161 A2 WO 2006020161A2 US 2005025343 W US2005025343 W US 2005025343W WO 2006020161 A2 WO2006020161 A2 WO 2006020161A2
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- 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
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F13/534—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having an inhomogeneous composition through the thickness of the pad
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/28—Treatment by wave energy or particle radiation
-
- 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
- A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
- A61F2013/530481—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials
- A61F2013/530708—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials characterized by the absorbency properties
- A61F2013/530737—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials characterized by the absorbency properties by the absorbent capacity
- A61F2013/530766—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium having superabsorbent materials, i.e. highly absorbent polymer gel materials characterized by the absorbency properties by the absorbent capacity by the cross-link factor
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
- C08J2333/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
Definitions
- the present invention relates to superabsorbent polymer particles with improved surface cross-linking and their use in absorbent articles.
- the invention relates to a process for making these superabsorbent polymer particles.
- SAPs Superabsorbent polymers
- SAPs are often applied in form of small particles, such as fibers or granules. They generally consist of a partially neutralized lightly cross- linked polymer network, which is hydrophilic and permits swelling of the network once submerged in water or an aqueous solution such as physiological saline. The cross-links between the polymer chains assure that the SAP does not dissolve in water.
- One commonly applied way to reduce gel blocking is to make the particles stiffer, which enables the SAP particles to retain their original shape thus creating or maintaining void spaces between the particles.
- a well-known method to increase stiffness is to cross-link the carboxyl groups exposed on the surface of the SAP particles. This method is com ⁇ monly referred to as surface cross-linking.
- the art refers e.g. to surface cross-linked and surfactant coated absorbent resin particles and a method of their preparation.
- the surface cross-linking agent can be a polyhydroxyl compound comprising at least two hydroxyl groups, which react with the carboxyl groups on the surface of the SAP particles.
- surface cross-linking is carried out at temperatures of 15O 0 C or above.
- the particles are preferably exposed to the elevated tem ⁇ peratures for at least 5 minutes but less than 60 minutes.
- Another known method for surface cross-linking absorbent resins uses the carboxyl groups of the polymer, which are comprised on the surface of the resin, react with a poly- hydric alcohol.
- the reaction can be accomplished at temperatures in the range of 90 0 C to 250°C.
- hydroxyalkylurea or hydroxyalkylamide can be used as cross-linking agent.
- the surface cross-linking reaction can be carried out at temperatures from about 90°C to about 17O 0 C for 60 to 180 minutes.
- a water-soluble peroxide radical initiator as surface cross-linking agent is also known.
- An aqueous solution containing the surface cross-linking agent is applied on the surface of the polymer.
- the surface cross-linking reaction is achieved by heating to a temperature such that the peroxide radical initiator is decomposed while the polymer is not decom ⁇ posed.
- the surface cross-linking reaction can be carried out under heat, wherein the temperature is preferably in the range of 60 0 C to 250 0 C.
- the surface cross-linking reaction can also be achieved by a photo-irradiation treatment, preferably using ultraviolet rays.
- the surface cross-linking agent is applied on the surface of the SAP particles. Therefore, the reaction preferably takes place on the surface of the SAP particles, which results in improved cross-linking on the surface of the particles while not substantially affecting the core of the particles. Hence, the SAP particles become stiffer and gel- blocking is reduced.
- a drawback of the commercial surface cross-linking process described above is, that it takes relatively long, commonly at least about 30 min.
- the more time is re ⁇ quired for the surface cross-linking process the more surface cross-linking agent will penetrate into the SAP particles, resulting in increased cross-linking inside the particles, which has a negative impact on the capacity of the SAP particles. Therefore, it is desir ⁇ able to have short process times for surface cross-linking.
- short process times are also desirable with respect to an overall economic SAP particle manufacturing process.
- SAPs known in the art are typically partially neutralized, e.g. with sodium hydroxide. However, neutralization has to be carefully balanced with the need for surface cross- linking:
- the surface cross-linking agents known in the art only react with free carboxyl groups comprised by the polymer chains but they are not able to react with a neutralized carboxyl groups. Thus, the carboxyl groups can either be applied for surface cross-linking or for neutralization, but the same carboxyl group cannot be applied to fulfill both tasks.
- Surface cross-linking agents known in the art do not react with chemical groups other than carboxyl groups, e.g. they do not react with aliphatic groups.
- the neutralization step is of ⁇ ten carried out in the very beginning of the process, before the monomers are polymerized and cross-linked to form the SAP.
- Such a process is named 'pre-neutralization process'.
- the SAP can be neutralized in the middle of polymerization or after polym ⁇ erization ('post-neutralization'). Furthermore, a combination of these alternatives is also possible.
- the present invention relates to superabsorbent polymer particles comprising polymer chain segments
- cross-links are present on the surface of the superabsorbent polymer par ⁇ ticles.
- the present invention further relates to a method of surface cross-linking superabsorbent polymer particles which comprises the steps of
- a) providing superabsorbent polymer particles comprising polymer chain segments, b) adding a surface cross-linking composition comprising cross-linking molecules having at least two C C double bonds and further comprising radical former molecules, c) exposing the superabsorbent polymer particles and the surface cross-linking composi ⁇ tion to electromagnetic irradiation capable of activating the radical former, whereby the cross-linking molecules and the radical former molecules react with at least some of the polymer chain segments comprised at surfaces of the superabsorbent polymer particles to form covalent cross-links between the polymer chain segments, wherein the cross-links comprise the reaction product of the cross-linking molecule and wherein the cross-links further comprise the reaction product of the radical former molecules.
- the present invention relates to absorbent products comprising the superabsor ⁇ bent polymer particles of the present invention.
- Figure 1 is a top plan view of a disposable diaper, with the upper layers partially cut away.
- Figure 2 is a cross-sectional view of the disposable diaper shown in Figure 1
- the SAPs according to the present invention comprise a homopolymer of partially neu ⁇ tralized ⁇ , ⁇ -unsaturated carboxylic acid or a copolymer of partially neutralized ⁇ , ⁇ - unsaturated carboxylic acid copolymerized with a monomer copolymerizable therewith. Furthermore, the homo-polymer or copolymer comprised by the SAP comprises aliphatic groups, wherein at least some of the aliphatic groups are at least partially exposed on the surface of the superabsorbent polymer particles
- SAPs are available in a variety of chemical forms, including substituted and unsubsti- tuted natural and synthetic polymers, such as carboxymethyl starch, carboxymethyl cellu ⁇ lose, and hydroxypropyl cellulose; nonionic types such as polyvinyl alcohol, and polyvi ⁇ nyl ethers; cationic types such as polyvinyl pyridine, polyvinyl morpholinione, and N, N- dimethylaminoethyl or N,N-diethylaminopropyl acrylates and methacrylates, and the re ⁇ spective quaternary salts thereof.
- SAPs useful herein have a multiplicity of anionic, functional groups, such as sulfonic acid, and more typically carboxyl groups.
- polymers suitable for use herein include those, which are prepared from po- lymerizable, unsaturated, acid-containing monomers.
- such monomers include the olefinically unsaturated acids and anhydrides that contain at least one carbon-to-carbon olefinic double bond. More specifically, these monomers can be selected from olefini ⁇ cally unsaturated carboxylic acids and acid anhydrides, olefinically unsaturated sulfonic acids, and mixtures thereof. Some non-acid monomers can also be included, usually in minor amounts, in preparing SAPs.
- non-acid monomers can include, for example, the water-soluble or water- dispersible esters of the acid-containing monomers, as well as monomers that contain no carboxylic or sulfonic acid groups at all.
- Optional non-acid monomers can thus include monomers containing the following types of functional groups: carboxylic acid or sulfo ⁇ nic acid esters, hydroxyl groups, amide-groups, amino groups, nitrile groups, quaternary ammonium salt groups, aryl groups (e.g., phenyl groups, such as those derived from sty- rene monomer).
- aryl groups e.g., phenyl groups, such as those derived from sty- rene monomer.
- Olefinically unsaturated carboxylic acid and carboxylic acid anhydride monomers in ⁇ clude the acrylic acids typified by acrylic acid itself, methacrylic acid, ethacrylic acid, ⁇ - chloroacrylic acid, ⁇ cyanoacrylic acid, ⁇ -methylacrylic acid (crotonic acid), ⁇ - phenylacrylic acid, ⁇ -acryloxypropionic acid, sorbic acid, ⁇ -chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, ⁇ -sterylacrylic acid, itaconic acid, citroconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricar- boxyethylene and maleic acid anhydride.
- acrylic acids typified by acrylic acid itself, methacrylic acid, ethacrylic acid, ⁇ - chloroacrylic acid, ⁇ cyanoacrylic acid, ⁇ -methylacrylic acid
- Olefinically unsaturated sulfonic acid monomers include aliphatic or aromatic vinyl sul ⁇ fonic acids such as vinylsulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid and styrene sulfonic acid; acrylic and methacrylic sulfonic acid such as sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3- methacryloxypropyl sulfonic acid and 2-acrylamide-2-methylpropane sulfonic acid.
- vinylsulfonic acid allyl sulfonic acid, vinyl toluene sulfonic acid and styrene sulfonic acid
- acrylic and methacrylic sulfonic acid such as sulfoethyl acrylate, sulfo
- Preferred SAPs according to the present invention contain carboxyl groups.
- These poly ⁇ mers comprise hydrolyzed starch-acrylonitrile graft copolymers, partially neutralized hy- drolyzed starch-acrylonitrile graft copolymers, starch-acrylic acid graft copolymers, par ⁇ tially neutralized starch-acrylic acid graft copolymers, saponified vinyl acetate-acrylic ester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers, slightly network crosslinked polymers of any of the foregoing copolymers, partially neutralized poly- acrylic acid, and slightly network crosslinked polymers of partially neutralized poly- acrylic acid, partially neutralized polymethacrylic acid, and slightly network crosslinked polymers of partially neutralized polymethacrylic acid.
- polymers can be used ei ⁇ ther solely or in the form of a mixture of two or more different polymers, that when used as mixtures, individually do not have to be partially neutralized, whereas the resulting copolymer has to be.
- 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.
- SAPs comprise partially neutralized, slightly network crosslinked, polyacrylic acid (i.e. poly (sodium acrylate/acrylic acid)).
- SAPs are at least 50%, more preferably at least 70%, even more preferably at least 75% and even more preferably from 75% to 95% neutralized.
- Network crosslinking renders the polymer substantially water-insoluble and, in part, determines the absorptive capacity of the hydrogel-forming absorbent polymers. Processes for network crosslinking these polymers and typical network crosslinking agents are described in greater detail in U.S. Patent 4,076,663.
- a suitable method for polymerizing the ⁇ , ⁇ -unsaturated carboxylic acid monomers is aqueous solution polymerization, which is well known in the art.
- An aqueous solution comprising ⁇ , ⁇ -unsaturated carboxylic acid monomers and polymerization initiator is subjected to a polymerization reaction.
- the aqueous solution may also comprise further monomers, which are co-polymerizable with the ⁇ , ⁇ -unsaturated carboxylic acid mono ⁇ mers.
- At least the ⁇ , ⁇ -unsaturated carboxylic acid has to be partially neutralized, either prior to polymerization of the monomers, during polymerization or post polymerization.
- the monomers are at least 50 %, more preferably at least 70%, even more preferably at least 75% and even more preferably from 75% to 95% neutralized.
- the monomers in aqueous solution are polymerized by standard free radical techniques, commonly by using a photoinitiator for activation, such as ultraviolet (UV) light. Alter ⁇ natively, a redox initiator may be used. In this case, however, increased temperatures are necessary.
- the water-absorbent resin will preferably be lightly cross-linked to render it water- insoluble.
- the desired cross-linked structure may be obtained by the co-polymerization of the selected water-soluble monomer and a cross-linking agent possessing at least two polymerizable double bonds in the molecular unit.
- the cross-linking agent is present in an amount effective to cross-link the water-soluble polymer.
- the preferred amount of cross-linking agent is determined by the desired degree of absorption capacity and the desired strength to retain the absorbed fluid, that is, the desired absorption under load.
- the cross-linking agent is used in amounts ranging from 0.0005 to 5 parts by weight per 100 parts by weight of monomers (including ⁇ , ⁇ -unsaturated carboxylic acid monomers and possible comonomers) used. If an amount over 5 parts by weight of cross- linking agent per 100 parts is used, the resulting polymer has a too high cross-linking density and exhibits reduced absorption capacity and increased strength to retain the ab ⁇ sorbed fluid. If the cross-linking agent is used in an amount less than 0.0005 parts by weight per 100 parts, the polymer has a too low cross-linking density and when contacted with the fluid to be absorbed becomes rather sticky, water-soluble and exhibits a low ab ⁇ sorption performance, particularly under load. The cross-linking agent will typically be soluble in the aqueous solution.
- cross-linking agent Alternatively to co-polymerizing the cross-linking agent with the monomers, it is also possible to cross-link the polymer chains in a separate process step after polymerization.
- the viscous SAPs are de ⁇ hydrated (i.e. dried) to obtain dry SAPs.
- the dehydration step can be performed by heat ⁇ ing the viscous SAPs to a temperature of about 120°C for about 1 or 2 hours in a forced- air oven or by heating the viscous SAPs overnight at a temperature of about 60°C.
- the content of residual water in the dehydrated SAP after drying predominantly depends on dyring time and temperature and can range from 0.5% by weight of dry SAP up to 50% by weight of dry SAP.
- the content of residual water in the dehydrated SAP after drying is 0.5% - 45% by weight of dry SAP, more preferably 0.5% - 30%, even more preferred 0.5% - 15% and most preferred 0.5% - 5%.
- the SAPs can be transferred into particles of numerous shapes.
- the term "particles" re ⁇ fers to granules, fibers, flakes, spheres, powders, platelets and other shapes and forms known to persons skilled in the art of SAPs.
- the particles can be in the form of gran ⁇ ules or beads, having a particle size of about 10 to 1000 ⁇ m, preferably about 100 to 1000 ⁇ m.
- the SAPs can be in the shape of fibers, i.e. elongated, acicular SAP particles.
- the SAP fibers have a minor dimension (i.e.
- the diameter of the fiber of less than about lmm, usually less than about 500 ⁇ m, and preferably less than 250 ⁇ m down to 50 ⁇ m.
- the length of the fibers is preferably about 3 mm to about 100 mm.
- the fibers can also be in the form of a long filament that can be woven.
- the dehydrated SAP particles undergo a surface cross- linking process step.
- surface describes the outer-facing boundaries of the par ⁇ ticle.
- exposed internal surfaces may also belong to the surface.
- surface cross-linked SAP particle refers to an SAP particle having its molecu ⁇ lar chains present in the vicinity of the particle surface cross-linked by a compound re ⁇ ferred to as surface cross-linker.
- the surface cross-linker is applied to the surface of the particle.
- the level of cross-links in the vicinity of the surface of the SAP particle is generally higher than the level of cross-links in the inte ⁇ rior of the SAP particle.
- thermally activatable surface cross-linkers are thermally activatable surface cross-linkers.
- thermally activatable surface cross-linkers refers to surface cross-linkers, which only react upon exposure to increased temperatures, typically around 150 °C.
- Thermally activatable surface cross-linkers known in the prior art are e.g. di- or polyfunc- tional agents that are capable of building additional cross-links between the polymer chains of the SAPs.
- Other thermally activatable surface cross-linkers include, e.g., di- or polyhydric alcohols, or derivatives thereof, capable of forming di- or polyhydric alcohols. Representatives of such agents are alkylene carbonates, ketales, .and di- or polyglycidly- ethers.
- (poly)glycidyl ethers, haloepoxy compounds, polyaldehydes, polyoles and polyamines are also well known thermally activatable surface cross-linkers.
- the cross-linking is based on a reaction between the functional groups comprised by the polymer, for example, an esterification reaction between a carboxyl group (comprised by the polymer) and a hydroxyl group (comprised by the surface cross-linker).
- an esterification reaction between a carboxyl group comprised by the polymer
- a hydroxyl group comprised by the surface cross-linker
- the method of the present invention is applied for surface cross-linking of SAP particles.
- the polymer chains comprised by the SAP particles commonly already have been cross-linked by a cross-linker known in the art, comprising at least two polymerizable double bonds in the molecule unit.
- the cross-linking of different polymer chain segments of the present invention is not intended to bond different SAP particles to each other.
- the method of the present invention does not lead to any appreciable inter- particulate bonds between different SAP particles but only results in intra-particulate di ⁇ rect covalent bonds within an SAP particle. If present, such interparticulate direct cova ⁇ lent bonds would hence require additional inter-particulate cross-linking materials.
- polymer chain segment refers to the part of the polymer chains between two neighboring, existing cross-links or to the part of the polymer chains between sites, where the polymer chain is branched.
- Preferred cross-linking molecules of the present invention are polyfunctional allyl and acryl compounds, such as triallyl cyanurate, triallyl isocyanurate, trimethylpropane tricry- late or other triacrylate esters, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, butanediol diacrylate, pentaerythritol tetraacrylate, tetra allylorthosilicate, di- pentaerythritol pentaacyralate, di-pentaerythritol hexaacyralate, ethyleneglycol diacry ⁇ late, ethyleneglycol dimethacrylate, tetra allyloxy ethane, diallyl phthalate, diethylene- glycol diacrylate, allylmethacrylate, triallylamine, 1,1,1-trimethylolpropane triacrylate, triallyl citrate,
- the cross-linking molecules are selected from the group consisting of squalene, N,N' methylenebisacrylamide, icosa-pentaenic acid, or sorbic acid.
- the most preferred cross-linking molecule of the present invention is triallyl cyanurate.
- the radiation activatable radical former molecules are able to form radicals upon elec ⁇ tromagnetic radiation.
- the radical former molecules can belong to two dif ⁇ ferent types of radical former: a) Radical former molecules undergoing photo- fragmentation upon irradiation and b) radical former molecules undergoing photo- reduction upon irradiation.
- the reaction mechanism of both types is described in detail below. According to the present invention, it is not preferred to mix radical former mole ⁇ cules of type a) with radical former molecules of type b).
- Radical former molecules of type a) can be selected from the group consisting of dialkyl peroxy-dicarbonates, benzilketales, di-tert-butyl peroxide, di-benzoyl peroxide, bis- (aroyloxyl) peroxides such as bis-(4-methoxy) di-benzoyl peroxide, or bis-(4-methyl) di- benzoyl peroxide, or bis-(4-chlor) di-benzoyl peroxide, 2,4,6-tri-methyl di-benzoyl per ⁇ oxide, 3-benzoyl benzoic acid, 1,3-dibenzoyl propane, di-benzoyl disulphide, S-phenyl thiobenzoates, acylphosphine oxides, benzoylphosphineoxides, aryl-aryl-sulphides, di- benzoyl methanes, phenylazo-di-phenyl sulphone, substituted dialkyl
- Radical formers of type b) can be selected from the group consisting of of acetophenone, benzophenone, anthraquinone, xanthone, thioxanthone, camphorquinone, terephthalophe- none, benzil, fluorenone, ⁇ -ketocoumarin as well as acetophenone-, benzophenone-, an ⁇ thraquinone-, xanthone-, thioxanthone-, camphorquinone-, terephthalophenone-, benzil-, fluorenone-, ⁇ -ketocoumarin-derivatives.
- Suitable acetophenone derivatives or benzo ⁇ phenone derivatives also comprise reaction products, such as condensation products of acetophenone derivatives or benzophenone derivatives, comprising at least two acetophenone or benzophenone groups.
- reaction products such as condensation products of acetophenone derivatives or benzophenone derivatives, comprising at least two acetophenone or benzophenone groups.
- derivates are chosen to enable or further enhance water-solubility of the radical for ⁇ mer molecule.
- the radical former molecules of type b) comprise a first group selected from the group consisting of methyl, benzyl, aryl, preferably phenyl and substituted phenyl, and a second group selected from the group consisting of an aryl, an alkyl of 1 to 4 car ⁇ bon atoms, cyclopropyl, cyclopentyl, cyclohexyl, ⁇ , ⁇ -dialkoxyalkyl, and ⁇ -hydroxyalkyl and wherein the first group is covalently bound to the second group via an additional car- bonyl group.
- Radical former molecules having a relatively high molecular weight often tend to form more stable radicals, as the charge of the radical can be distributed better within the radical. Without wishing to be bound be theory, it is be ⁇ lieved that if the radical were very unstable, it more likely reacts to recombine to the radi ⁇ cal former molecule.
- preferred radical former molecules according to the present invention will comprise aromatic groups, such as arenes. This also leads to more stable radicals as the unpaired electron can be distributed throughout the aromatic group.
- radical former molecules of the present invention are acetophe- none- or benzophenone-derivatives.
- Suitable acetophenone derivatives or benzophenone derivatives are described, for exam ⁇ ple, in European Patent Application EP-A-O 346 734; European Patent Application EP- A-O 377 199; European Patent Application EP-A-O 246 848; German Patent Application DE-A-4 037 079 and German Patent Application DE-A-3 844 444.
- the radical former molecule of this type comprises a labile bond, and is hereinafter gen ⁇ erally depicted as R a -R b .
- the labile bond breaks, whereby two radicals (R 3 " and R b ') are formed according to Formula 1.
- This homolytic cleavage may result in two identical radicals, if the labile bond com ⁇ prised by the radical former molecule (so-called precursor molecule) divides the mole ⁇ cule into two identical parts.
- the homolytic cleavage may result in two dif ⁇ ferent radicals.
- R. R b ⁇ R - + R, b The radicals, which have been formed, can now react with an aliphatic C-H group com ⁇ prised by a polymer chain segment of the SAP particle forming a carbon-centered radical at this polymer chain segment according to Formula 2.
- the carbon-centered radical within the polymer chain segment formed in the reaction of Formula 2 can react with the radical formed in Formula 3.
- the reaction product of this reaction is a polymer chain segment, which has the reaction products of the radical for ⁇ mer molecule and the cross-linking molecule bound thereto according to Formula 4.
- the net reaction is depicted in Formula 7:
- radical former molecule may again form radicals upon electromagnetic irradiation, or
- Radical former molecules undergoing photo-reduction upon irradiation comprise car- bonyl groups.
- such radical former molecules are ketones.
- the radical former molecules of this type Upon electromagnetic irradiation, preferably upon irradiation by UV light, the radical former molecules of this type are transferred in an "excited state" (triplet state) according to Formula 8. Hence, they are not yet transformed into a radical, but are much more reac ⁇ tive than before they were irradiated.
- the radical former molecule in its excited state reacts with an aliphatic C- H group comprised by a polymer chain segment and abstracts a hydrogen radical, thereby forming a carbon-centered radical at this polymer chain segment and a ketyl radical ac ⁇ cording to Formula 9:
- the carbon-centered radical within the polymer chain segment formed in the reaction of Formula 8 can now react with the radical formed in Formula 10.
- the reaction product of this reaction is a polymer chain segment, which has the reaction products of the radical former molecule and the cross-linking molecule bound thereto according to Formula 11.
- the net reaction is depicted in Formula 14:
- radical former molecules undergoing photo-reduction upon irradiation are preferred over radical former molecules undergoing photo- fragmentation.
- radical former molecules undergoing photo- fragmentation are applied, only a part of the radical former molecule is comprised by the cross-link between the polymer chain segments, whereas for radical former molecules undergoing photo-reduction, the complete radical former molecule in its reduced form (with a carbonyl group being reduced to a hydroxyl group) is comprised by the cross-link between the polymer chain segments.
- reaction prod ⁇ uct comprised by the cross-link between polymer chain segments is only a part of the ini ⁇ tial radical former molecule - typically one half of the initial molecule.
- the reaction product com ⁇ prised by the cross-link between polymer chain segments is the complete radical former molecule in its reduced form (with a carbonyl group being reduced to a hydroxyl group).
- the cross-links between polymer chain segments according to the present invention are mainly present on the surface of the SAP particles, although a few of those cross-links may also be formed inside the SAP particles. This is because a small amount of the sur ⁇ face cross-linking composition may penetrate inside the SAP particles after the composi ⁇ tion has been applied onto the SAP particle surfaces.
- these cross-links between polymer chain segments inside the SAP particles are not an objective of the present in ⁇ vention but only may take place unavoidably to a very small degree.
- more than two polymer chain segments can be cross-linked to each other, following the reaction mechanism described above.
- the rate determining step of a radically initiated cross-linking reaction in the absence the cross-linking molecule is the so-called recombination of two carbon centered radicals, forming a direct covalent bond between two polymer chain segments.
- This recombination follows a kinetic law of a sec ⁇ ond order reaction, i.e. the reaction rate of such combination reaction is proportional to the product of the concentrations of the two combining carbon centered radical species.
- the two carbon centered radicals need to hit each other during their short lifetime, despite their distance and possible sterical obstructions due to the rigidity of the polymer chains to be connected.
- a cross-linking molecule is added according to the present invention, it is believed, that the reaction between the cross-linking molecule or its reaction product - i.e. the radical formed according to Formula 3 for type a) radical formers, respectively, the radical formed according to Formula 11 for type b) radical formers - and the carbon centered radical in the polymer chain, forming a covalent bond, follows a kinetic law of pseudo-first order, i.e. the reaction rate is believed to be only proportional to the concen ⁇ tration of the carbon centered radical, since the concentration of the second reaction part ⁇ ner, i.e. the cross-linking molecule respectively its reaction product, is so high that it can be regarded as constant throughout the reaction.
- Reactions of pseudo-first order kinetics are known to be kinetically favored versus reactions of second order kinetics, i.e. they have a higher reaction speed, in particular if the reactive species, in this case the interme ⁇ diate carbon centered radical in the polymer chain, are low in concentration.
- the overall process can be run at a higher line speed due to the presence of the surface cross-linker and its kinetically favorable influence on the rate-determining step of the overall reaction.
- Oxygen is known as a radical- scavenger that readily reacts with carbon-centered radicals. If the desired reaction of the carbon-centered radicals is accelerated, as it is believed in the case of the present inven ⁇ tion, without wanting to be bound by theory, the unwanted side reaction with oxygen can be at least partly circumvented. Hence, the necessary process measures to suppress pres ⁇ ence of oxygen during the reaction do not need to be exerted as rigorously, which may facilitate processing and decrease capital cost.
- UV-light is used with a wave-length of 220-380 run, selected on the selected radical former molecule(s).
- the UV-light may be used in combination with an electron-beam, and also in combination with an IR-light.
- the surface cross-linking composition is applied in amounts of less than 25% by weight of SAP particle, preferably in amounts of less than 15%, more preferably in amounts of less than 5%, even more preferably in amounts from 0.1% to 5% and most preferably in amounts from 0.1% to 1.5%.
- the ratio of the cross-linking molecule to the radical former molecule is preferably in the range of 0.2 to 5, even more preferred between 0.33 and 3 and mostly preferred in the range of 1 to 3, with said ratios being molar ratios.
- the surface cross-linking composition may be sprayed onto the SAP particles by means of a fluidized-bed spraying chamber. Simultaneously IR-irradiation may be applied to accomplish drying and simultaneously UV-light may be applied to accomplish cross- linking in the fluidized-bed.
- drying and cross-linking may take place in two steps in series, which could be carried out in any order.
- any con ⁇ ventional drying equipment can be used in the drying step.
- little or no drying is required, e.g. in cases, where only a small amount of the surface cross-linking composition is applied dissolved in small amounts of solution.
- the radiation activatable radical former molecules may upon activation by irradiation react with aliphatic C-H bond comprised by a nearby polymer chain segment, abstracting a hydrogen radical and leaving a carbon centered radical.
- the radiation activatable radical former molecules may upon radiation also react with car- boxyl groups comprised by the polymer chain segments.
- the cross-linking process of the pre ⁇ sent invention is not restricted to the carboxyl groups but also comprises the numerous aliphatic groups within the polymer chains of the SAP.
- the number of available reaction sites for the surface cross-linking process of the SAP particles is strongly increased. Therefore, it is possible to achieve a far more homogenous, uniform surface cross-linking compared to the surface cross-linking known from the art.
- the percentage of the reaction product of the radia ⁇ tion activatable radical former molecules and the cross-linking molecules on the surface of the SAP particles will preferably be higher than the percentage of said reaction product inside the SAP particles.
- the UV irradiation for the surface cross-linking can preferably be carried out in a conven ⁇ tional manner with UV lamps having a power between 50 W and 2 kW, more preferably between 200 W and 700 W, and even more preferred between 400 W and 600 W.
- Irradia ⁇ tion time is preferably between 0.1 sec. and 30 min., more preferably between 0.1 sec. and 15 min, even more preferably between 0.1 sec. and 5 min and most preferably be ⁇ tween 0.1 sec. and 2 min.
- Commercially available mercury pressure UV-lamps can be used. The choice of the lamp depends on the absorption spectrum of the radical former molecules used. Lamps having a higher power generally permit more rapid cross-linking.
- the distance between the UV-lamp(s) and the SAP which is to be cross-linked preferably varies between 5 cm and 15 cm.
- the surface cross-linking according to the present invention is much quicker.
- Prior art surface cross-linking reac ⁇ tions carried out under increased temperatures commonly take up to 45 minutes. This time consuming process step renders the manufacturing process of SAP particles less economic than desirable.
- the cross-linking process according to the pre ⁇ sent invention can be carried out very quickly and hence, strongly adds to a much more efficient and economic overall manufacturing process.
- the surface cross-linking reaction proceeds quickly, the molecules com ⁇ prised by the surface cross-linking composition applied on the surface of the SAP parti ⁇ cles have less time to penetrate inside the SAP particles.
- the surface cross- linking process is mainly restricted to the surface of the SAP particles and avoids unde- sired further cross-linking reactions inside the SAP particles.
- the ⁇ , ⁇ - unsaturated carboxylic acid monomers are often neutralized prior to the polymerization step (pre-neutralization).
- Compounds, which are useful to neutralize the acid groups of the monomers are typically those, which will sufficiently neutralize the acid groups without having a detrimental effect on the polymerization process.
- Such compounds in ⁇ clude alkali metal hydroxides, alkali metal carbonates and bicarbonates.
- the material used for neutralization of the monomers is sodium or potassium hydroxide or carbonate.
- the neutralizing compound is preferably added to an aqueous solution com ⁇ prising the ⁇ , ⁇ -unsaturated carboxylic acid monomers (pre-neutralization).
- the carboxyl groups comprised by the ⁇ , ⁇ -unsaturated carboxylic acid monomers are at least partially neutralized. Consequently, -after the polymerization step- also the carboxyl groups comprised by the ⁇ , ⁇ -unsaturated carboxylic acid of the polymer are at least par ⁇ tially neutralized.
- neutralization results in sodium acry- late, which dissociates in water into negatively charged acylate monomers and positively charged sodium ions. If the final SAP particles are in the swollen state, after they absorbed aqueous solution, the sodium ions are freely movable within the SAP particles. In absorbent articles, such as diapers or training pants, the SAP particles typically absorb urine.
- urine comprises a relatively high amount of salt, which at least partly is pre ⁇ sent in dissociated form.
- the dissociated salts comprised by the urine make absorption of liquid into the SAP particles more difficult, as the liquid has to be absorbed against an osmotic pressure caused by the ions of the dissociated salts.
- the freely movable sodium ions within the SAP particles strongly facilitate the absorption of liquid into the particles, because they reduce the osmotic pressure. Therefore, a high degree of neutralization can largely increase the capacity of the SAP particles and the speed of liquid absorption.
- the surface cross-linkers known in the art react with the carboxyl groups of the polymer. Hence, the degree of neutralization has to be balanced with the need to surface cross-link, because both process steps make use of the carboxyl groups.
- the surface cross-linking composition comprises ra ⁇ diation activatable radical former molecules, which -once activated e.g. by UV radiation- are able to react with the aliphatic groups comprised by the polymer. Therefore, it is pos ⁇ sible to neutralize the monomers to a larger degree without significantly diminishing the possibility of later surface cross-linking.
- the carboxyl groups comprised by the ⁇ , ⁇ - unsaturated carboxylic acid monomers are preferably at least 50 %, more preferably at least 70%, even more preferably at least 75% and even more preferably between 75% and 95% neutralized.
- the carboxyl groups comprised by the ⁇ , ⁇ -unsarurated car ⁇ boxylic acid of the polymer are at least 50 %, more preferably at least 70%, even more preferably at least 75% and even more preferably between 75% and 95% neutralized.
- a still further advantage of the present invention is the reduction of undesired side- reactions during the surface cross-linking process.
- Surface cross-linking known from the prior art requires increased temperatures, commonly around or above 150°. At these tem ⁇ peratures, not only the surface cross-linking reaction is achieved, but also a number of other reactions take place, e.g. anhydride-formation within the polymer or dimer cleavage of dimers previously formed by the acrylic acid monomers. These side-reactions are highly undesired, because they result in SAP particles with decreases capacity.
- the surface cross-linking process according to the present invention does not necessar ⁇ ily need increased temperatures but can also be carried out at moderate temperatures us ⁇ ing electromagnetic radiation, such as UV radiation, those side-reactions are considerably reduced.
- the surface cross-linking reaction can pref ⁇ erably be accomplished at temperatures of less than 100°C, preferably at temperatures less than 80 °C, more preferably at temperatures less than 50 °C, even more preferably at temperatures less than 40 °C, most preferably at temperatures between 20 0 C and 40°C.
- drying of the SAP is typically carried out at temperatures above 100 0 C.
- the SAP particles At elevated temperatures around or above 150°C commonly applied in the surface cross- linking process known from the prior art, the SAP particles sometimes change their color from white to yellowish. As according to the surface cross-linking process of the present invention, it is possible to carry out the surface cross-linking process under moderate temperatures, the problem of color degradation of the SAP particles is strongly reduced.
- the surface cross-linking composition may comprise only one type of cross-linking molecules, or may, alternatively, comprise two or more chemically different cross-linking molecules.
- the surface cross-linking compo ⁇ sition may comprise only one type of radiation activatable radical former molecule, or may, alternatively, comprise two or more chemically different radiation activatable radi ⁇ cal former molecules.
- surface cross-linking composition of the present invention can be applied together with one or more thermally activatable surface cross-linkers, e.g. 1,4- butandiol.
- the SAP particles further have to comprise carboxyl groups wherein at least some of the carboxyl groups are at least partially exposed on the outer surface of the SAP particles and wherein the thermally activated surface cross- linker is covalently bound to at least a part of the carboxyl groups at least partially ex ⁇ posed on the surface of said SAP particles.
- the surface cross-linking composition of the present invention is used together with a thermally activatable surface cross-linker, both UV radiation and increased tem ⁇ peratures (above 140°C) are necessary for the surface cross-linking process.
- the surface of the resulting SAP particles will further comprise the reaction product of the thermally activatable surface cross-linker.
- the surface cross-linking composition is preferably used in a liquid solution, more pref ⁇ erably in an aqueous solution.
- the surface cross- linking composition has to be distributed evenly on the SAP particle prior to or during UV radiation. Therefore, the surface cross-linker is preferably applied by spraying onto the SAP particles.
- the method of the present invention may further comprise an optional washing step to wash off unreacted molecules comprised by the surface cross-linking composition or to wash off molecules formed by side reactions.
- absorbent article refers to devices that absorb and contain liquid, and more specifically, refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body.
- absorbent articles include but are not limited to diapers, adult incontinent briefs, diaper holders and liners, sanitary napkins and the like.
- Preferred absorbent articles of the present invention are diapers.
- diaper refers to an absorbent article generally worn by infants and incontinent persons about the lower torso.
- Disposable is used herein to describe articles that are generally not intended to be laun ⁇ dered or otherwise restored or reused i.e., they are intended to be discarded after a single use and, preferably, to be recycled, composted or otherwise disposed of in an environ ⁇ mentally compatible manner.
- FIG 1 is a plan view of a diaper 20 as a preferred embodiment of an absorbent article according to the present invention.
- the diaper is shown in its flat out, uncontracted state (i.e., without elastic induced contraction). Portions of the structure are cut away to more clearly show the underlying structure of the diaper 20. The portion of the diaper 20 that contacts a wearer is facing the viewer.
- the chassis 22 of the diaper 20 in Figure 1 com ⁇ prises the main body of the diaper 20.
- the chassis 22 comprises an outer covering includ ⁇ ing a liquid pervious topsheet 24 and/or a liquid impervious backsheet 26.
- the chassis 22 may also include most or all of the absorbent core 28 encased between the topsheet 24 and the backsheet 26.
- the chassis 22 preferably further includes side panels 30, leg cuffs 32 with elastic members 33 and a waist feature 34.
- the leg cuffs 32 and the waist feature 34 typically comprise elastic members.
- One end portion of the diaper is configured as the front waist region 36 of the diaper 20.
- the opposite end portion is configured as the rear waist region 38 of the diaper 20.
- the intermediate portion of the diaper is configured as the crotch region 37, which extends longitudinally between the front and rear waist re ⁇ gions.
- the crotch region 37 is that portion of the diaper 20 which, when the diaper is worn, is generally positioned between the wearer's legs.
- the waist regions 36 and 38 may include a fastening system comprising fastening mem ⁇ bers 40 preferably attached to the rear waist region 38 and a landing zone 42 attached to the front waist region 36.
- the diaper 20 has a longitudinal axis 100 and a transverse axis 110.
- the periphery of the diaper 20 is defined by the outer edges of the diaper 20 in which the longitudinal edges 44 run generally parallel to the longitudinal axis 100 of the diaper 20 and the end edges 46 run generally parallel to the transverse axis 110 of the diaper 20.
- the diaper may also include other features as are known in the art including front and rear ear panels, waist cap features, elastics and the like to provide better fit, containment and aesthetic characteristics.
- the absorbent core 28 may comprise any absorbent material that is generally compressi ⁇ ble, conformable, non-irritating to the wearer's skin, and capable of absorbing and retain ⁇ ing liquids such as urine and other certain body exudates.
- the absorbent core 28 may comprise a wide variety of liquid-absorbent materials commonly used in disposable dia ⁇ pers and other absorbent articles such as comminute wood pulp, which is generally re ⁇ ferred to as air felt.
- absorbent materials examples include creped cellu ⁇ lose wadding; melt blown polymers, including co-form; chemically stiffened, modified or cross-linked cellulosic fibers; tissue, including tissue wraps and tissue laminates, absor ⁇ bent foams, absorbent sponges, absorbent gelling materials, or any other known absorbent material or combinations of materials.
- the absorbent core may further comprise minor amounts (typically less than 10%) of non-liquid absorbent materials, such as adhesives, waxes, oils and the like.
- SAP particles of the present invention can be applied as absorbent mate ⁇ rials.
- the SAP particles of the present invention preferably are present in amounts of at least 50% by weight of the whole absorbent core, more preferably at lest 60%, even more preferably at least 75% and still even more preferably at least 90% by weight of the whole absorbent core.
- Figure 2 shows a cross-sectional view of Figure 1 taken in the transverse axis 110.
- Figure 2 illustrates a preferred embodiment of the different zones comprised by the ab ⁇ sorbent cores.
- the fluid acquisition zone 50 comprises an upper acquisition layer 52 and a lower acquisition layer 54, while the fluid storage zone underneath the fluid acquisition zone comprises a storage layer 60, which is wrapped by an upper core wrap layer 56 and a lower core wrap layer 58.
- the upper acquisition layer comprises a nonwoven fabric whereas the lower acquisition layer preferably comprises a mixture of chemically stiff ⁇ ened, twisted and curled fibers, high surface area fibers and thermoplastic binding fibers.
- both acquisition layers are provided from a non-woven material, which is preferably hydrophilic.
- the acquisition layer preferably is in direct contact with the storage layer.
- the core wrap material comprises a top layer and a bottom layer, which layers may be sealed together along their edges, e.g. by adhesive.
- the top layer and the bottom layer can be provided from a non- woven material.
- the top layer and the bottom layer may be provided from two or more separate sheets of materials or they may be alternatively provided from a unitary sheet of material. Such a unitary sheet of material may be wrapped around the storage layer, e.g. in a C-fold.
- the storage layer the present invention typically comprises SAP particles mixed with fi ⁇ brous materials. Other materials as suitable for the absorbent core may also be comprised.
Abstract
Description
Claims
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AU2005274865A AU2005274865A1 (en) | 2004-07-20 | 2005-07-15 | Surface cross-linked superabsorbent polymer particles and methods of making them |
CA002573442A CA2573442A1 (en) | 2004-07-20 | 2005-07-15 | Surface cross-linked superabsorbent polymer particles and methods of making them |
JP2007522607A JP2008506528A (en) | 2004-07-20 | 2005-07-15 | Surface-crosslinked superabsorbent polymer particles and method for producing the same |
BRPI0513537-0A BRPI0513537A (en) | 2004-07-20 | 2005-07-15 | surface-absorbing superabsorbent polymer particles and methods for their manufacture |
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- 2004-07-20 AT AT04017071T patent/ATE484298T1/en not_active IP Right Cessation
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- 2005-07-15 CN CNA2005800214777A patent/CN101076358A/en active Pending
- 2005-07-15 WO PCT/US2005/025343 patent/WO2006020161A2/en active Application Filing
- 2005-07-15 KR KR1020077001267A patent/KR20070039050A/en not_active Application Discontinuation
- 2005-07-15 AU AU2005274865A patent/AU2005274865A1/en not_active Abandoned
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WO2006020161A3 (en) | 2006-06-01 |
JP2008506528A (en) | 2008-03-06 |
CN101076358A (en) | 2007-11-21 |
IN2006DE07971A (en) | 2007-04-27 |
EP1629854A1 (en) | 2006-03-01 |
US20060020053A1 (en) | 2006-01-26 |
ZA200700147B (en) | 2008-05-28 |
US7588777B2 (en) | 2009-09-15 |
KR20070039050A (en) | 2007-04-11 |
AU2005274865A1 (en) | 2006-02-23 |
BRPI0513537A (en) | 2008-05-06 |
EP1629854B1 (en) | 2010-10-13 |
AR054672A1 (en) | 2007-07-11 |
DE602004029569D1 (en) | 2010-11-25 |
US7871640B2 (en) | 2011-01-18 |
US20090299315A1 (en) | 2009-12-03 |
ATE484298T1 (en) | 2010-10-15 |
CA2573442A1 (en) | 2006-02-23 |
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