WO2008138386A1

WO2008138386A1 - Absorbent articles comprising acidic cellulosic fibers and/or acidic superabsorbing material, and benzoic acid, hydroxy benzoic acid and esters thereof

Info

Publication number: WO2008138386A1
Application number: PCT/EP2007/004408
Authority: WO
Inventors: Jan WÄSTLUND-KARLSSON
Original assignee: Sca Hygiene Products Ab
Priority date: 2007-05-16
Filing date: 2007-05-16
Publication date: 2008-11-20

Abstract

The present invention relates to an absorbent article, such as a diaper, panty diaper, sanitary napkin or incontinence device comprising a liquid-permeable topsheet, a backsheet and an absorbent core enclosed between said liquid-permeable topsheet and said backsheet, wherein said absorbent core comprises (a) acidic cellulosic fibers having a pH value of 5.5 or less and/or an acidic superabsorbent material made from a synthetic polymer comprising polymerized ethylenically unsaturated acid group- containing monomers, said superabsorbent material having a pH value of 5.5 or less, and (b) - at- least-one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof ; under the proviso that in absorbent articles comprising said acidic superabsorbent material and benzoic acid in combination the acidic superabsorbent material has a pH of 5.0 or less; the corresponding acidic cellulosic material and superabsorbent material and their use for odour control. It was noted that acidic cellulosic material or acidic superabsorbent material when used in combination with at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof reduce the formation of malodours in absorbent articles to a surprising extent.

Description

Absorbent articles comprising acidic cellulosic fibers and/or acidic superabsorbing material, and benzoic acid, hydroxy benzoic acid and esters thereof

The present invention relates to an absorbent article such as a diaper, panty diaper, sanitary napkin or incontinence device comprising an effective odour control system. The present invention relates in particular to such absorbent articles wherein acidic superabsorbers and/or acidic cellulosic fibers, such as acidic fluff pulp, and at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof interact favourably to reduce malodours such as ammonia.

TECHNICAL BACKGROUND

One important area of development in the area of absorbent articles of the above-mentioned type is the control of odorous compounds forming typically after the release of body fluids, especially over a long period of time. These compounds include fatty acids, ammonia, amines, sulphur- containing compounds and ketones and aldehydes . They are present as natural ingredients of body fluids or result from degradation processes of natural ingredients such as urea, which is broken down by microorganisms or bacteria occurring in the urogenital flora to ammonia.

Various approaches exist to suppress the formation of unpleasant odours in absorbent articles.

WO 01/80913 Al and WO 01/80915 Al relate to disposable absorbent articles like sanitary napkins and panty liners which comprise an antibacterial cationic polysaccharide, such as chitosan materials, to counteract the formation of unpleasant odours in absorbent articles. Furthermore, the documents describe that the disposable absorbent article comprises an acidic pH buffering means. Many examples of acids and the corresponding acid salts are listed as suitable pH buffering means. It is furthermore taught in WO 01/80913 Al that cationic saccharides and acidic pH buffering means are preferably mixed within the fibers of the absorbent core. There is, however, no disclosure of the combination of acidic cellulosic fibers or an acidic superabsorbent material and benzoic acid as antibacterial in this document.

WO 00/35504 relates to a process for producing an acidic superabsorbent polysaccharide, wherein the polysaccharide -is - crosslinked and the pH of the polysaccharides is adjusted to values of from 3.5 to 5.5 in order to provide odour control . Moreover, this document describes that an acidifying agent may be incorporated, such as organic acids, e.g. benzoic acid. Furthermore, conventional absorbent materials, such as cellulose pulp may also be incorporated into the absorbent article. This document is however silent on the use of acidic cellulosic fibers or an acidic synthetic superabsorbent material, such as polyacrylates, in combination with benzoic acid.

GB 1 456 200 relates to a deodorant composition having an antibacterial effect which may also be used for distribution in cellulose wadding or absorbent material such as paper tissue or cotton towel for use as a sanitary towel . Said composition comprises an antibacterial and an anti-oxidant . The antibacterial is taken from the list consisting of hexachlorophene , dichlorophenol , trichlorophenol , tetrachlorophenol , di (trichlorohydroxyphenyl) ether, a p- hydroxybenzoic acid ester, and the like. Suitable antioxidants may be butylated hydroxyanisole, butylated hydroxyl toluene, α-tocopherol , ascorbic acid, 2,6-di-t- butylhydroquinone and propyl gallate. The combination of an acidic absorbent material, such as acidic cellulosic fibers or an acidic superabsoirbent material with p-hydroxybenzoic acid esters is however not disclosed.

DE 102 56569 Al deals with water-absorbing porous foams based on crosslinked polymerisates containing at least one odour- control agent selected from (a) anhydride group-containing compounds, (b) acid group-containing compounds, (c) cyclodextrines, (d) bactericides and (e) surface active agents. It is not explicitly disclosed in this document to combine the odour-control agents according to the above items (b) and (d) .

US 2JD05/0154133. Al relates .to a__polymer_mixture, with odour control including (a) a hydrogel-forming polymer capable of absorbing aqueous fluids and prepared by polymerizing an olefinically unsaturated carboxylic acid or a derivative thereof, and (b) a copolymer of C2-C8 olefin or styrene with an anhydride in a molar ratio between the C2-C8 olefin or styrene and the anhydride in a range of from 3:1 to 1:3. It is mentioned in this document that odour control is good when acidic hydrogels are used in hygiene articles. Furthermore, it is mentioned that antimicrobials substances may be added to the polymer mixture, for instance, quaternary ammonium compounds, phenols, amides, acids and nitro compounds. However, the document does not disclose acidic superabsorbent materials in combination with benzoic acid as antibacterial .

US 2004/0213892 Al discloses a highly swellable absorption medium with a reduced cracking tendency in a moist environment. The highly swellable absorption medium comprises (a) a natural polymer modified with acidic groups or a synthetic polymer containing at least partially neutralized acid groups, (b) at least one nitrogen-containing nonionic surfactant coating agent, (c) further treated with a Lewis acid. It is mentioned that the Lewis acid can be selected from various antibacterials , for instance, organic acids or metal ions such as zinc. In the polymer component (a) the degree of neutralization of the acidic monomer component can vary, but is preferably in the range of 25 mol% to 85 mol% and thus encompasses a wide pH range. Therefore acidic fibers or acidic superabsorbents in combination containing benzoic acid are not disclosed in this document.

The superabsorbent article disclosed in WO 01/32226 Al, which has odour control and microbial control, comprises a top layer, a liquid impervious back layer and a liquid absorbing intermediate layer containing (a) a surface-crosslinked, partially neutralized, acidic hydrophilic polymer, characterized by comprising (b) an alkali-neutralizing agent which- is evenly -distributed- in said absorbent intermediate layer. The term "acidic hydrophilic polymer" is said to be not acidic itself and has a pH above 5 and a degree of neutralization of at least 50 %. The alkali-neutralizing agents include organic di- or polycarboxylic acids, benzoic acid, phosphoric acid and other organic acids. That is, the combination of benzoic acid with acidic absorbing materials (pH 5 or below) is not disclosed in this document.

In the absorbent article of EP 1 358 894 Al the absorbent body includes a water absorbent, predominantly open-celled crosslinked acid-functional addition polymer foam comprising at least one odour control means selected from (a) compounds containing anhydride groups, (b) compounds containing acidic groups, (c) cyclodextrins, (d) biocides, (e) surfactants having a HLB value of less than 11, (f) odour absorbing agents, (g) microorganisms, (h) pH buffering systems, and (i) chelating agents. In this document a distinction is made between "polymer foam" and "superabsorbent particles" . The ^xvsuperabsorbent particles" are disclosed only in connection with a specific embodiment wherein the hydrogel foam layer is an acquisition layer and the distribution and/or storage layer is made of a mixture of cellulosic fluff pulp mixed with superabsorbent particles. Furthermore, this document does not explicitly disclose the combination of the odour control means according to item (a) , (b) or (h) , which all seem to lead to acidic pH values, with biocides according to item (d) .

US 2003/0135172 Al relates to a method of preparing a storage layer for body fluids and an absorbent article comprising the same. The storage layer is made by (a) forming a sprayable blend comprising one or more superabsorbent-forming monomers, superabsorbent polymer particles, water, and one or more initiators, (b) applying said sprayable blend to a fibrous web, and (c) polymerizing this blend. It is mentioned that the blend formed in step (a) contains at least one odour- control- agent, which- ean—be- selected-from -zeolites, -Silica, _ carbon, chelants, antimicrobial agents, perfuming ingredients, masking agents and mixtures thereof. The antimicrobial agent includes quaternary ammonium, phenolic, amide, acid and nitro compounds and mixtures thereof.

WO 02/094329 Al is concerned with odour control containing absorbent materials. The superabsorbent polymer particles are based on monomers having carboxylic acid groups, but are said to contain a neutralization degree of at least 50 mol%, which is not in the acidic range.

That is, both latter mentioned documents do also not disclose acidic cellulosic fibers or an acidic superabsorbing material in combination with benzoic acid.

It is one technical object of the present invention to satisfy the ongoing demand in the art for improved odour control .

It is one further technical object to provide an absorbent article having an efficient odour control system. It is one further technical object of the present invention to considerably reduce or eliminate ammonia formation in absorbent articles.

Further objects will become apparent from the following description of the invention.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to an absorbent article, such as a diaper, panty diaper, panty liner, sanitary napkin or incontinence device, comprising a top sheet, a back sheet and an absorbent -core enclosed-between said top sheet_ and said_ back sheet, wherein said absorbent core comprises (a) acidic cellulosic fibers having a pH value of 5.5 or less and/or an acidic superabsorbent material made from a synthetic polymer comprising polymerized ethylenically unsaturated acid group- containing monomers, said superabsorbent material having a pH value of 5.5 or less, and

(b) at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof; under the proviso that in absorbent articles comprising said acidic superabsorbent material and benzoic acid in combination the acidic superabsorbent material has a pH of 5.0 or less.

The present inventors have found that acidic cellulosic fibers or acidic superabsorbent polymers in combination with benzoic acid, hydroxybenzoic acid esters thereof interact favourably in the suppression of unpleasant odours.

Without wishing to be bound by theory, the mechanism underlying the odour reduction of the present invention is assumed to be as follows. It was found that the ammonia which causes the malodour in absorbent products, such as incontinence products is formed in the following way: Bacteria + urea → NH3

In the present invention, benzoic acid, hydroxybenzoic acid or an ester thereof acts as a material with a function of suppressing bacterial growth while the acidic cellulosic fibers or acidic superabsorbent materials provide an acidic environment that also reduces bacterial growth. Moreover, the acidic cellulosic fibers or acidic superabsorbent may also remove the ammonia (NH3) actually formed.

The aim of the present invention is to develop an absorbent article where the amount of unwanted bacteria, such as ammonia-producing bacteria -does _not__increase_ during _use_ and therefore ammonia produced by these bacteria is removed.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the specification and claims, the use of "comprising" is intended to cover also the more restricting meanings "essentially consisting of" and "consisting of".

As "absorbent article" we understand articles capable of absorbing body fluids such as urine, watery feces, female secretion or menstrual fluids. These absorbent articles include, but are not limited to diapers, panty diapers, panty liners, sanitary napkins or incontinence device (as used for instance for adults) .

Such absorbent articles have a liquid-pervious top sheet, which during use is facing the wearer's body. They further comprise a (preferably liquid-impervious) back sheet, for instance a plastic film, a plastic-coated nonwoven or hydrophobic nonwoven and an absorbent core enclosed between the liquid-pervious top sheet and the back sheet. A suitable top sheet may be manufactured from a wide range of materials such as woven and nonwoven materials (e.g. a nonwoven web of fibers) , polymerical materials such as apertured plastic films, e.g. an apertured formed thermoplastic film and hydroformed thermoplastic films; porous foams; reticulated foams; reticulated thermoplastic films; and thermoplastic grims . Suitable woven and nonwoven materials can be comprised of natural fibers (e.g. wood or cotton fibers) , synthetic fibers (e.g. polymeric fibers such as polyesthers, polypropylene or polyethylene fibers) or from a combination of natural and synthetic fibers. When the top sheet comprises a nonwoven web, the web may be manufactured by a wide number of known techniques. For example, the web may be spun-bonded, carded, wet-laid, melt-blown, hydroentangled, combinations of the above or the like. In accordance with the invention, it is preferred to make use of apertured plastic films, (e.g. thermoplastic films) or nonwoven materials based on synthetic fibers, e.g. those made from polyethylene or polypropylene homo- or copolymers or polymer compositions based thereon.

Optionally, at least one further layer exists between the absorbent core and the top sheet and may be made from hydrophobic and hydrophilic web or foam materials. As "web material" we understand coherent flat fiber-based structures of a paper tissue, woven or nonwoven type. The nonwoven material may have the same features as described above for top sheets.

Specifically, the at least one further layer may contribute to fluid management, for instance in the form of at least one acquisition/distribution layer. Such structures are taught for instance by US 5,558,655, EP 0 640 330 Al, EP 0 631 768 Al or WO 95/01147. "Foam materials" are also well-known in the art and for instance described in EP 0 878 481 Al or EP 1 217 978 Al in the name of the present applicant.

The absorbent core may be partially or totally surrounded by a core wrap. It comprises an absorbent material that is generally compressible, conformable, non- irritating to the wearer's skin and capable of absorbing and retaining liquids such as urine and other body exudates.

ACIDIC CELLULOSIC FIBERS

In one embodiment the absorbent core comprises acidic cellulosic fibers, in particular acidic fluff _pulp fibers, having a pH value of 5.5 or less.

The term "cellulosic fibers" also referred to as "CF" relates to fibers from wood, woody plants and certain non-woody plants and cellulose-based recycled and regenerated fibers. Woody plants include for instance deciduous (hardwood) and coniferous (softwood) trees. Non-woody plants include for instance cotton, flax, esparto, grass, milkweed, straw, jute hemp and bagasse. The cellulosic fibers are preferably "pulp fibers" .

The term "pulp fibers" includes chemical pulp and mechanical pulp fibers .

According to DIN 6730, "chemical pulp" is a fibrous material obtained from plant raw materials from which most non- cellulose components have been removed by chemical pulping without substantial mechanical post-treatment . In case of chemical pulping processes such as the sulfite or sulfate (Kraft) process, primarily the lignin components and the hemi-cellulose components are dissolved from the wood to varying degrees depending on the field of application of the chemical pulp. The result is a fibrous material consisting primarily of cellulose.

"Mechanical pulp" is the general term for fibrous materials made of wood entirely or almost entirely by mechanical means, optionally at increased temperatures. Mechanical pulp is subdivided into the purely mechanical pulps (groundwood pulp and refiner mechanical pulp) as well as mechanical pulps subjected to chemical pretreatment : chemo-mechanical pulp (CMP) , such as chemo-thermomechanical pulp (CTMP) .

The starting pulps which may be used in the present invention may relate to primary fibrous materials (raw pulps) or to secondary fibrous materials, whereby a secondary_ fibrous material is defined as a fibrous raw material recovered from a recycling process. The primary fibrous materials may relate both to a chemically digested pulp and to mechanical pulp such as thermorefiner mechanical pulp (TMP) , chemothermorefiner mechanical pulp (CTMP) or high temperature chemithermomechanical pulp (HTCTMP) . Synthetic cellulose- containing fibers can also be used. Preference is nevertheless given to the use of pulp from plant material, particularly wood-forming plants. Fibers of softwood (usually originating from conifers) , hardwood (usually originating from deciduous trees) or from cotton linters can be used for example. Fibers from esparto (alfa) grass, bagasse (cereal straw, rice straw, bamboo, hemp) , kemp fibers, flax and other woody and cellulosic fiber sources can also be used as raw materials. The corresponding fiber source is chosen in accordance with the desired properties of the absorbent core, such as softness and absorption capacity in a manner known in the art. With regard to the softness of the products, the use of chemical raw pulps is also preferred, whereby it is possible to use completely bleached, partially bleached and unbleached fibers. The chemical raw pulps suitable according to the invention include, inter alia, sulfite pulps, kraft pulps (sulfate process) , soda pulps (cooking with sodium hydroxide) , pulps from high-pressure cooking with organic solvents (e.g. Organosolv, Organocell, Acetosolv, Alcell) and pulps from modified processes (e.g. ASAM, Stora or Sivola process) . Among the kraft pulps, it is possible to use those which were obtained in continuous cooking systems (MCC (modified continuous cooking) , EMCC (extended modified continuous cooking) and ITC (isothermal cooking) . The products of discontinuous kraft processes (e.g. RDH (rapid displacement heating) , Superbatch and Enerbatch) are also suitable as a starting product. The sulfite processes include the acidic sulfite/bisulfite processes, bisulfite process, "neutral sulfite semi-chemical pulping" (NSSC) process and alkaline sulfite processes such as processes in which in addition to-aqueous- alkali, sulfite and/or_anthraquinone- in combination with organic solvents such as methanol were used for cooking, e.g. the so-called ASAM process (alkali sulfite anthraquinone methanol) . The major difference between the acidic and neutral or alkaline sulfite processes is the higher degree of delignification in acidic cooking processes (lower kappa numbers) . The NSSC process provides semi- chemical pulps which are advantageously defibered in downstream mechanical fibrillation before they are used according to the invention for the purpose of oxidation. The sulfite and kraft pulps considerably differ in terms of their fibrous material properties. The individual fiber strengths of sulfite pulps are usually much lower than those of kraft pulps. The mean pore width of the swollen fibers is also greater in sulfite pulps and the density of the cell wall is lower compared to sulfate pulps, which simultaneously means that the cell -wall volume is greater in sulfite pulps. For this reason, there are also obvious differences regarding water absorption and swelling behavior of the cellulosic fibrous materials, which must also be taken into consideration when selecting a material for the absorbent core. For the purpose of the present invention, general cellulosic fibers, in particular pulp fibers as described above are also referred to as "standard CF" or "non-acidic CF".

The cellulosic fibers to be used in the absorbent core are preferably fluff pulp fibers. The term "fluff pulp fibers" as used herein is well known in the art of making paper and absorbent products. It refers to a variant of "standard CF" as described above which is characterized by its fluffy state which can be achieved by comminuting standard chemical (e.g. Kraft or sulfite), mechanical (e.g. groundwood pulp and refiner mechanical pulp) or chemomechanical pulp (CMP) , such as TMP, CTMP or HTCTMP. Preferably chemical or _chemomechanical pulp, optionally in a bleached form is used for the preparation of fluff pulp. Fluff pulp may comprise mainly, preferably exclusively, softwood fibers which impart the necessary softness for use in absorbent products. Suitable wood pulp fibers for manufacturing fluff pulp are e.g. Southern Softwood Kraft and Northern Softwood Sulphite. There are various grades of fluff pulps, such as debonded, also called treated, fluff pulps which are softer than regular fluff. Main producers of fluff pulp are Weyerhaeuser Co. and Georgia Pacific Corp. in the U.S. and Finland-based Stora Enso Oy. For the purpose of the present invention, general fluff pulp as described above is also referred to as "standard fluff pulp" or "non-acidic fluff pulp". In the following, "fluff pulp" and "fluff CF" will be used as synonyma .

The pH value of standard CF, including standard fluff pulp varies significantly, e.g. depending on the production method. Generally, standard (fluff) CF have a pH of from above 5.5 to 6.5, preferably around 6. Unlike standard (fluff) CF, the acidic (fluff) CF for use in the present invention have a pH of 5.5 or less. For removing bacteria, a pH value of 5.0 or less is advantageous. The pH value of the acidic (fluff) CF is preferably 2.0 to 5.0, more preferably 2.5 to 4.5, still more preferably 3.0 to 4.0 and most preferably 3.2 to 3.6. The pH of CF can be measured using the standard test Tappi T 509-02.

The acidic (fluff) CF may also be admixed with standard (fluff) CF and/or superabsorbent polymer material (SAP) . The superabsorbent material may be acidic or non-acidic or a mixture thereof . Regarding the understanding of the term "superabsorbant" and suitable materials reference is made to the later description of "acidic superabsorbent materials" .

If superabsorbant material is admixed to the acidic cellulosic fibers the total amount of the superabsorbent material may be 10 to 70 weight%, based on the weight of the core (excluding the_ compound selected from_the group, consisting of benzoic acid, hydroxybenzoic acid and esters thereof) .

In addition to the above materials, i.e. acidic (fluff) CF and optionally non-acidic (fluff) CF and superabsorbent material, the absorbent core may comprise, in admixture, other absorbent materials. Any other absorbent material that is generally compressible, conformable, non-irritating to the wearer' s skin and capable of absorbing and retaining liquids such as urine and other body exudates can be used. Examples of other absorbent materials to be incorporated in the absorbent core include a wide variety of liquid-absorbent materials commonly used in disposable diapers and other absorbent articles such as creped cellulose wadding; melt blown polymers, including co-form,- chemically stiffened, modified or cross-linked cellulosic fibers; tissue, including tissue wraps and tissue laminates, absorbent foams, absorbent sponges, absorbent gelling materials, or any other known absorbent materials or combinations of materials.

As indicated before, the absorbent core in the absorbent article of the invention may also contain fibers others than acidic CF. These other fibers are preferably also capable of absorbing body liquid as is the case for hydrophilic fibers. Most preferably the fibers are other cellulosic fibers such as standard fluff pulp, cotton, cotton linters, rayon, cellulose acetate and the like. The standard fluff pulp can be of the above-described mechanical or chemical type, the chemical pulp being preferred.

In the corresponding absorbent core and, if applicable, each layer thereof, the total amount of cellulosic fibers, i.e. acidic (fluff) CF or a mixture of acidic and non-acidic (fluff) CF, is preferably 90 to 30 wt.-%, more preferably 80 to 35 wt.-%, in particular 70 to 40 wt.-%, for instance 70 to 50 wt.-%, based on the weight of the absorbent core (without the_ at least one compound selected- from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof) . The term " (fluff) CF" is used as abbreviation for "non-fluffed cellulosic fibers such as non- fluffed pulp and/or fluff cellulosic fibers, i.e. fluff pulp"

If used in admixture, the weight ratio of acidic (fluff) CF and non-acidic (fluff) CF is not particularly restricted

(e.g. 5/95 to 95/5, 10/90 to 90/10, 20/80 to 80/20) . Accordingly, weight ratios of acidic (fluff) CF/non-acidic

(fluff) CF of 100/0 to 50/50 (e.g. 95/5 to 60/40, 90/10 to 70/30) can be preferably selected depending on the properties to be achieved.

METHOD OF PRODUCING THE ACIDIC (FLUFF) CELLULOSIC FIBERS, AND ACIDIFYING AGENT

There are no specific restrictions as to the method of producing the acidic (fluff) cellulosic fibers for use in the present invention. According to a preferred embodiment, the acidic (fluff) CF are obtained by treating standard CF with an acidifying agent. If an acidifying agent is used the same differs structurally from benzoic acid or hydroxybenzoic acid. The acidifying agents for use in the present invention are not specifically limited in kind, as long as they do not disintegrate or decompose the standard fluff pulp being treated. One example is SO2 -water. Preferably the acidifying agent is a suitable acid, e.g. a weak, acid or a salt thereof. The use of halogen-free non-oxidizing acids is preferred. Suitable acids are those which when incorporated in the standard (fluff) CF will not release any substances which may be harmful or acrid to skin. It should be noted that the skin in the region which comes into contact with absorbent articles is very sensitive, in infants and adults, alike. Hence, the acid used as an acidifying agent is preferably one that is approved of or admitted for use in food and/or . cosmetics .

Preferably the acidifying agent is selected from optionally hydroxyl-substituted mono- and polycarboxylic acids, their salts, and mixtures thereof. The mono- or polycarboxylic acid may be aliphatic or aromatic. The salt is preferably an alkali metal (e.g. K or Na) or earth alkaline metal salt (e.g. Ca or Mg) . If used in salt form, the acidifying agent, preferably the optionally hydroxyl-substituted mono- and polycarboxylic acid is only partially neutralized to provide acidic solutions in water.

The optionally hydroxyl-substituted monocarboxylic acid is preferably selected from saturated or unsaturated, linear or branched aliphatic carboxylic acids which preferably have from 1 to 18 carbon atoms, more preferably 2 to 8 carbon atoms, in particular 2 to 4 carbon atoms. The acid may be substituted by one, two or more hydroxy groups. Examples of this monocarboxylic acid include formic acid, acetic acid or propionic acid or lactic acid.

The optionally hydroxyl-substituted polycarboxylic acid (e.g. diacid or triacid) may also be substited by one, two or more hydroxy groups. The organic (poly) acid may be an unsaturated (e.g. mono- or diunsaturated) or saturated, linear or branched aliphatic carboxylic acid preferably having from 2 to 18 carbon atoms, more preferably 3 to 8 carbon atoms, e.g. 4 to 6 carbons atoms. Examples thereof include oxalic acid, malic acid, maleic acid, malonic acid, succinic acid, tartaric acid, citric acid or sorbic acid.

The use of optionally hydroxyl-substituted polyacids, their salts and mixtures thereof is preferred. These polyacids are preferably employed in a partially neutralized state and thus capable to act as buffer. The degree of neutralization preferably ranges from 15 to 95% of the carboxyl groups and is jnqre preferably 30_ to 90%, e.g. 50_to _80%. _Such partially neutralized polycarboxylic acids can also be provided by mixing polyacid and the corresponding salt in the necessary molar ratio.

Generally it is preferred to select among the above mono- and polyacids weak acids, in particular those having a pK value of at least 1,5, more preferably at least 2, even more preferably at least 3, e.g. 4 to 5 (for polyacids the pKl value) measured in water at 25°C.

Most preferably, the acidifying agent is selected from aqueous solutions of citric acid, oxalic acid, lactic acid, malic acid, malonic acid, maleic acid, succinic acid, tartaric acid, sorbic acid, formic acid, salts thereof, and mixtures thereof. The most preferred acidifying agent for use in the present invention is citric acid and its salts.

The acidic CF, in particular the acidic fluff CF can be obtained by treating standard (fluff) CF with a solution of the acidifying agent. The same is preferably used in a concentration of 0.5 to 10 weight-% and preferably furnishes a pH of about 2 to 6 , in particular 3 to 5. Desirably, the concentration of acidifying agent is selected such that the weight ratio of acidifying agent (s) to dry CF is about 1 to 20%, in particular 3 to 10%. The solution used for the treatment is preferably aqueous although volatile organic solvents may also be used as this facilitates the drying of the (fluff) CF.

The treatment of the standard (fluff) CF with the solution of the acidifying agent is achieved by combining standard (fluff) CF with the solution of the acidifying agent (e.g. by preparing a slurry, dipping or spraying) followed by the preferred steps of mixing and/or drying the mixture, followed by an optional fiberization step to break apart possibly aggregated fibers . Said drying may be achieved by letting the treated fibers .stand at ambient .air or. preferably- by heating, for instance to 50 to 95°C. Suitable heating conditions are also disclosed in US 6,852,904 (col. 5, lines 30 to 53). The treatment is preferably done by the pulp manufacturer since this obviates the additional step of treating standard fluff pulp by the manufacturer of the absorbent article.

As to suitable acidic (fluff) cellulosic fibers, reference can also be made to US 6,852,904 B2.

ACIDIC SUPERABSORBENT MATERIAL

In a further embodiment the absorbent core comprises an acidic superabsorbent material .

The term "superabsorbent material" is well known in the art and designates water- swellable, water-insoluble materials capable of absorbing the multiple of their own weight in body fluids. Alternatively to the term "superabsorbent material" the term "absorbent gelling material (AGM)" can be used. Preferably, the superabsorbent material is capable of absorbing at least about 10 times its weight, preferably at least about 15 times its weight, in particular at least about 20 times its weight in an aqueous solution containing 0.9 wt. -% of sodium chloride (under usual measuring conditions where the superabsorbent surface is freely accessible to the liquid to be absorbed) . The superabsorbent material is in particular capable of retaining these amounts (at least 10 times, preferably at least 15 times, in particular at least 20 times its weight) of saline solution after centrifugation. To determine this fluid retention capacity of the superabsorbent material in saline after centrifugation, the standard test EDANA WSP 241.2 can be used.

The superabsorbent material may be in any form suitable for use in absorbent articles including particles, fibers, flakes, spheres and the like, the particle form being preferred.

Acidic SAPs are based on homo- or copolymers comprising at least one polymerizable unit (monomer) having an acidic group (e.g. a carboxylic acid group or a sulfonic acid group) such as methacrylic acid, acrylic acid, maleic acid, vinylsulfonic acid. The corresponding polymers include, but are not limited to poly (meth) acrylic acids, ethylene maleic anhydride copolymers, polymers and copolymers of vinylsulfonic acids, polyacrylates, acrylic acid grafted starch and isobutylene maleic anhydride copolymers. These polymers are preferably crosslinked to render the materials substantially water insoluble. According to one preferred embodiment of the present invention, the superabsorbent material is a crosslinked homo- or copolymer comprising (meth) acrylic acid units, for instance of the type disclosed in EP 0 391 108 A2.

The superabsorbent polymer can be based on:

(αl) 0.1 wt. % to 99.999 wt.%, preferably 20 wt . % to 98.99 wt.%, and more preferably 30 wt.% to 98.95 wt.% of polymerized, ethylenically unsaturated, acidic group- containing monomers or salts thereof, or polymerized, ethylenically unsaturated monomers containing a protonated or a quaternary nitrogen, or mixtures thereof, wherein mixtures comprising at least ethylenically unsaturated, acidic groups- containing monomers, preferably acrylic acid, are particularly preferred;

(α2) 0 wt. % to 70 wt. %, preferably 1 wt . % to 60 wt.%, and more preferably 1 wt.% to 40 wt.% of polymerized, ethylenically unsaturated monomers which can be co- polymerized with (αl) ;

(α3) 0.001 wt.% to 10 wt.%, preferably 0.01 wt.% to 7 wt.%, and more preferably 0.05 wt.% to 5 wt.% of one or more cross- linkers;

(α4) 0 wt.% to 30 wt.%, preferably 1 wt.% to 20 wt.%, and more preferably 5 wt.% to 10 wt.% of water-soluble polymers; and

(α5) 0 wt.% to 20 wt.%, preferably 0.01 wt.% to 7 wt.%, and more preferably 0.05 wt.% to 5 wt.% of one or more auxiliaries, wherein the sum of the component weights (αl) to (α5) amounts to 100 wt.%.

Preferred monoethylenically unsaturated acidic groups- containing monomers (αl) are acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, α-methylacrylic acid (crotonic acid) , α-phenylacrylic acid, β-acryloxypropionic acid, sorbinic acid, α-chlorosorbinic acid, 2 ' -methylisocrotonic acid, cinnamic acid, p- chlorocinnamic acid, β-stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxythylene and maleic acid anhydride, wherein acrylic acid and methacrylic acid are particularly preferred. Besides these carboxylate group-containing monomers, further monoethylenically unsaturated acidic group-containing monomers (αl) can be ethylenically unsaturated sulfonic acid monomers or ethylenically unsaturated phosphonic acid monomers .

Reference is made to paragraphs [0032] and [0033] of US 2007/0015860 Al, respectively, wherein various examples for ethylenically unsaturated sulfonic acid monomers and ethylenically unsaturated phosphonic acid monomers, respectively, are described.

According to the present invention it is preferred that the polymer- comprises at least_50 wt .%, preferably at least _ 70 wt. %, and more preferably at least 90 wt . % carboxylate group-containing monomers. According to the present invention it is particularly preferred that the polymer comprises at least 50 wt.%, preferably at least 70 wt . % acrylic acid, which is preferably neutralized to at least 20 mol%, and more preferably to at least 50 mol%.

Referring to the ethylenically unsaturated monomers (αl) containing a protonated nitrogen and containing a quaternated nitrogen, respectively, reference is made to paragraphs [0035] and [0036] of US 2007/0015860 Al, wherein various examples of these compounds are mentioned.

Monoethylenically unsaturated monomers (α2) which can be co- polymerized with (αl) include acrylamides and (meth) acrylamides .

Preferred (meth) acrylamides besides acrylamide and meth- acrylamide include alkyl -substituted (meth) acrylamides or aminoalkyl-substituted derivatives of (meth) acrylamide such as N-methylol (meth) acrylamide,

N,N-diamethylamino (meth) acrylamide, dimethyl (meth) acrylamide or diethyl (meth) acrylamide . Possible vinylamides are for example N-vinylamides, N-vinylformamides, N-vinylacetamides , N-vinyl -N-methylacetamides , N-vinyl -N-methylformamides , vinylpyrrolidone . Among these monomers, acrylamide is particularly preferred.

Moreover, monoethylenically unsaturated monomers (α2) which are copolymerizable with (αl) are preferably water- dispersible monomers. Water-dispersible monomers are preferably acrylic acid esters and methacrylic acid esters, such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate or butyl (meth) acrylate, as well as vinylacetate, styrene, and isobutylene.

-Cross-linkers (α3) according -to- the -present--invention can-be compounds which have at least two ethylenically unsaturated groups in one molecule (cross-linker class I) , compounds which have at least two functional groups which can react with functional groups of the monomers (αl) or (β2) in a condensation reaction (=condensation cross-linkers) , in an addition reaction or a ring-opening reaction (cross-linker class II) , compounds which have at least one ethylenically unsaturated group and at least one functional group which can react with functional groups of the monomers (αl) or (α2) in a condensation reaction, an addition reaction or a ring- opening reaction (cross-linker class III) , or polyvalent metal cations (cross-linker class IV) .

Referring to the kinds of crosslinking of the polymer using compounds of the crosslinker classes I to IV, reference is made to paragraph [0040] of US 2007/0015860 Al. Suitable compounds or mixtures thereof belonging to the crosslinker classes I to IV are mentioned in paragraphs [0041] to [0049] of US 2007/0015860 Al.

Water-soluble polymers (α4) such as those comprising partially or fully saponified polyvinyl alcohol, polyvinylpyrrolidone, starches or starch derivatives, polyglycols or polyacrylic acids can preferably be polymerized into the superabsorbent polymer particles. The molecular weight of these polymers is not critical, as long as they are water-soluble. Preferred water-soluble polymers can be starches or starch derivatives or polyvinyl alcohol . The water-soluble polymers, preferably synthetic like polyvinyl alcohol, can also serve as graft basis for the monomers to be polymerized.

As auxiliary (α5) , suspension agents, organic or inorganic particles such as for example odor binders, in particular zeolites or cyclodextrins , skin care substances, surface- active agents, or antioxidants are preferably included with the polymer particles . _

If benzoic acid ester, hydroxybenzoic acid or an ester thereof is added to the absorbent article, the acidic superabsorber has preferably a pH value of 3.0 to 5.5, more preferably 3.5 to 5.3 and most preferably 4.1 to 5.2. In absorbent articles containing benzoic acid, the acidic superabsorber has preferably a pH value of 3.0 to less than 5.0, more preferably 3.5 to 4.95 and most preferably 4.1 to 4.9

Thereby, the pH is measured using the standard test EDANA WSP 200.2.

Unlike standard SAPs having a pH which lies e.g. in a range of 5.8 or more, the acidic SAPs to be used in the present invention has a lower pH, with the preferred ranges as defined in the preceding paragraph.

There are two ways of manufacturing acidic SAP. One way is to add an acid, e.g. citric acid, to a standard SAP, thereby reducing the pH. The other method is to maintain a low degree of neutralisation. A standard SAP has a high percentage (typically at least 70%) of the acidic groups neutralised under formation of alkali metal salts. In contrast thereto, acidic SAPs manufactured according to this method have a lower degree of neutralisation, typically 15 to 60%. The degree of neutralisation and pH strongly correlate which implies that the acidity of the SAP can be controlled by the degree of neutralisation.

In view of the above, it is also preferred that the absorbent core comprising the acidic superabsorbent has a pH value of 3.0 to 5.7, more preferably 3.5 to 5.5, in particular 4.1 to 5.4 after wetting with synthetic urine. In further embodiments the preferred upper pH value of the core is 5.0 or less, 4.95 or 4.9.

The pH of the absorbent core can be measured very precisely with the test method described in the examples.

The absorbent core may have more than one layer and then preferably comprises

• at least one layer comprising a mixture of cellulosic (fluff) fibers and acidic superabsorbent material and optionally non-acidic superabsorbent material, or

• at least one layer comprising a mixture of acidic cellulosic (fluff) fibers and optionally superabsorbent material.

As non-acidic superabsorbent material (also designated in the present specification as standard superabsorbent material) we understand superabsorbent materials of the above described type showing a pH of e.g 5.8 or more. Non-acidic SAPs comprising polymerizable units with acidic groups preferably have a neutralization degree of at least 70%.

In the absorbent core and, if applicable, each layer thereof, the total amount of superabsorbent material (of acidic and optionally non-acidic type) is preferably 10 to 70 wt.-%, more preferably 20 to 65 wt.-%, in particular 30 to 60 wt.-%, for instance 30 to 50 wt.-%, based on the weight of absorbent core (excluding the at least one compound selected from the group consisting of benzoic acid, salts thereof and p- hydroxybenzoic acid esters) .

The weight ratio of acidic SAP/non-acidic SAP. is not particularly restricted (e.g. 5/95 to 95/5, 10/90 to 90/10, 20/80 to 80/20), even though it would appear that higher amounts of acidic SAP seem to enhance the effect of the present invention. Accordingly, weight ratios of acidic SAP/non-acidic SAP of 100/0 to 50/50 (e.g. 95/5 to 60/40, 90/10 to 70/30) can be preferably selected depending on the properties to be achieved.

The acidic superabsorbent material may be optionally admixed with any other absorbent material that is generally compressible, conformable, non-irritating to the wearer's skin and capable of absorbing and retaining liquids such as urine and other body exudates .

Examples for other absorbent materials include a wide variety of liquid-absorbent materials commonly used in disposable diapers and other absorbent articles such as comminuted wood pulp, which is generally referred to as air felt or fluff, as well as creped cellulose wadding; melt blown polymers, including co-form; chemically stiffened, modified or cross- linked cellulosic fibers; tissue, including tissue wraps and tissue laminates, absorbent foams, absorbent sponges, non- acidic superabsorbent polymers (such as superabsorbent fibers) , or any other known absorbent materials or combinations of materials.

The fibers present in the absorbent core are preferably also capable of absorbing body liquid as is the case for hydrophilic fibers. Most preferably the fibers are cellulosic fibers such as wood pulp fluff, cotton, cotton linters, rayon, cellulose acetate and the like, the use of cellulosic fluff pulp being preferred. The cellulosic fluff pulp can be of mechanical or chemical type as described above, the chemical pulp being preferred.

COMPOUND SELECTED FROM THE GROUP CONSISTING OF BENZOIC ACID, HYDROXYBENZOIC ACID AND ESTERS THEREOF

Very low amounts of a compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof (in the following referred to as "benzoic compound") cooperate already with acidic (fluff) CF or acidic superabsorbent material in a very efficient odour control. A preferred lower weight limit of the benzoic compound seems to be at least 10^"^g per g dry acidic (fluff) CF-or -dry acidic superabsorbent material . Herein the term "dry" used in relation to acidic (fluff) CF is to be understood such that no water has been added to the acidic (fluff) CF and that the only water present in the acidic (fluff) CF is the unavoidable residual water from manufacturing. For the purpose of the present application, an acidic (fluff) CF or an absorbent core is preferably regarded as "dry" after a circular test sample thereof having a thickness of 5 to 6 mm, a diameter of 5 cm and which has been compressed to a bulk of about 8-10 cm^/g has been kept for at least one week at ambient temperature {e.g. 20⁰C) and a specific relative humidity, e.g. 50 % RH. The term "dry" used in relation to acidic superabsorbent material is to be understood such that no water has been added to the acidic SAP and that the only water present in the acidic SAP is the unavoidable residual water from manufacturing.

More preferably, the benzoic compound is present in amounts of at least 10^~4 g, even more preferably at least 5 x 10"⁴g, even more preferably at least 10^~^g, e.g. at least 2 x 10^~3g per g dry acidic (fluff) CF or dry acidic superabsorbent material. According to one further embodiment, the amount of the benzoic compound may be at least 10^~2g per g dry acidic (fluff) CF or dry acidic superabsorbent material. There is no specific upper limit, even though for economic reasons, a point may be reached where it may no longer be useful to further increase the content of the benzoic compound, for instance to values of 0,1 or 1 g per g acidic (fluff) CF or acidic superabsorbent material, if this is not accompanied by an enhanced odour suppression.

In terms of the total weight of the absorbent core, the benzoic compound is preferably present in an amount of at least 0.001 wt.-%, more preferably at least 0.01 wt.-%, even more preferably at least 0.05 wt.-%, even more preferably at least 0.1 wt.-%, e.g. at least 0.5 wt.-%, based on the total dry weight of the entire absorbent core. _There is.no specific upper limit, even though for economic reasons, a point may be reached (e.g. at 2, 5 or 10 wt.%) where it may no longer be useful to further increase the content of the benzoic compound, if this is not accompanied by an enhanced odour suppression.

As indicated above, the "benzoic compound" is a compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof. Preferably use is made of benzoic acid.

Benzoic acid is generally known in the art to be an effective antibacterial substance. Benzoic acid is used, for instance, as a food preservative. Benzoic acid inhibits the growth of bacteria. It is either added directly or it is created from reactions with its sodium, potassium or calcium salt, or the like. The antibacterial action starts with the absorption of benzoic acid into the bacterial cell. If the intracellular pH changes to 5 or lower the anaerobic fermentation of glucose through phosphofructokinase is decreased by 95%.

Benzoic or hydroxybenzoic acid esters used in the present invention are aliphatic or aromatic esters, wherein the ester unit has preferably not more than 8 carbon atoms, more preferably of not more than 6 carbon atoms. Still more preferred are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, phenyl esters and the like. They are, however, not restricted to these substances . More preferred are p- hydroxybenzoic acid esters, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, phenyl esters and the like.

TECHNIQUE OF INCORPORATION THE (HYDROXY) BENZOIC ACID/ESTER COMPOUND INTO THE ABSORBENT CORE

The present invention is also not subjected to any limitations regarding the technique of incorporating the benzoic compound into the absorbent core . Dipping into and spraying a solution of benzoic compound are preferred but the benzoic compound could also be applied to the absorbent core as granules or powder.

For instance, it is conceivable to treat the fibers/material [acidic (fluff) CF, acidic superabsorbent material or a combination thereof, optionally in admixture with non-acidic (fluff) CF and/or non-acidic superabsorbent material] present in the absorbent core with a solution of the benzoic compound before, during or after formation of the absorbent core from said absorbent materials, and, if applicable, before, during or after admixture with other absorbent materials.

According to one preferred embodiment, acidic (fluff) cellulosic fibers, optionally in admixture with non-acidic (fluff) CF are treated as such, i.e. in the absence of other absorbent materials, with a solution of the benzoic compound. One very effective and preferred treatment technique involves applying the solution of benzoic compound to a sheet of cellulosic fibers (e.g. by spraying the solution onto the sheet, dipping the sheet into the solution, etc.) . If fluff pulp is to be treated the benzoic compound solution can be applied prior to or after the comminuting step leading to the fluffy state.

Alternatively, standard (fluff) CF are treated simultaneously (e.g. by spraying, preparing a slurry, or dipping) with acidifying agent and benzoic compound. Then, the above- mentioned solution containing the acidifying agent also includes the benzoic compound. The benzoic compound is preferably contained in amounts leading to the above- disclosed contents. Regarding other treatment conditions, reference can be made to the above description of manufacturing acidic (fluff) CF.

-According - to- one further- embodiment-, -a solution of- the - benzoic compound is sprayed onto the acidic superabsorbent . This is an especially preferred and effective embodiment since it avoids the extra step of spraying the benzoic compound solution when manufacturing the absorbent article.

One technique of achieving incorporation of the benzoic compound also involves treating an already formed absorbent core comprising acidic (fluff) CF, acidic superabsorbent material or a combination thereof, optionally in admixture with non-acidic (fluff) CF and/or non-acidic superabsorbent material with a solution of the benzoic compound, in particular the benzoic acid solution.

According to the above spraying techniques, the solution of the benzoic compound, in particular benzoic acid is sprayed on one or both sides of the absorbent core, or one of both sides of the individual layers constituting the same.

The solvent used for the solution of benzoic compound can be water, a preferably volatile organic solvent such as ethanol or a mixture of water and a water-miscible organic solvent such as ethanol. Preferably, the benzoic compound solvent is present in the solution in a relatively high concentration, preferably 1 to 30 wt.-%. The use of concentrated solutions ensures that the absorption capacity of the superabsorbent material is not impaired more than necessary.

The backsheet typically prevents the exudates absorbed by the absorbent layer and contained within the article from soiling other external articles that may contact the absorbent article, such as bed sheets and undergarments. In preferred embodiments, the backsheet is substantially impervious to liquids (e.g., urine) and comprises a laminate of a nonwoven and a thin plastic film such as a thermoplastic film having a thickness of about 0.012 mm to about 0.051 mm. Suitable backsheet films include those manufactured by Tredegar Industries Inc_^ of Terre Haute, Ind. and sold-under the trade names X15306, X10962, and X10964. Other suitable backsheet materials may include breathable materials that permit vapors to escape from the absorbent article while still preventing exudates from passing through the backsheet. Exemplary breathable materials may include materials such as woven webs, nonwoven webs, composite materials such as film-coated nonwoven webs, and microporous films. Since there is always a trade-off between breathability and liquid-impermeability it can be desired to provide backsheets showing a certain, relatively minor liquid-permeability but very high breathability values.

The above elements of an absorbent article can be assembled, optionally together with other typical elements of absorbent articles in a manner known in the art .

The present invention also extends to the above-described acidic cellulosic fibers and acidic superabsorbent material and their use for odour control, preferably in those areas where bacterial control is an issue, including absorbent articles as claimed as well as wipes, such as wipes for the feminine hygiene, baby wipes, medical wipes and wipes for cleaning bathroom equipment, e.g. toilets; bandages; underpads ; absorbent drapes; underpants etc. Their use for odour-control in absorbent articles of the above-described type is preferred.

The following examples and comparative examples illustrate the present invention.

EXAMPLES

TEST METHODS

A) pH of absorbent core

The pH of the absorbent core can be measured very precisely with the following method involving the preparation of a test absorbent core and pH measurement using the same.

Method 2: Preparation of absorbent cores for test

Absorbent cores were punched out of an absorbent core produced in a pilot plant or in a factory. A standard method of mat forming a core was used in the production of the core in the pilot plant. The absorbent core consisted either

• of a homogenous mixture of acidic (fluffed) pulp and optionally other absorbent material such as non-acidic fluff, acidic or non-acidic superabsorbent material; or

• of a homogenous mixture of acidic superabsorbent material and optionally other absorbent material such as non-acidic or acidic (fluffed) pulp, or non-acidic superabsorber .

The absorbent core was compressed to a bulk of about 8-10 cm^/g. The size of the punched cores was 5 cm in diameter. The weight of the punched cores depends on the composition of the pulp core (i.e. depending on what product is to be tested; e.g. core of example 1 containing acidic pulp + standard SAP + benzoic acid with a total weight of 2.2 g; core of example 2 containing acidic superabsorbent material + standard pulp+ benzoic acid with a total weight of 1.6 g)

Method 2: Measurement of pH in an absorbent core

An absorbent core having a diameter of approximately 50 mm was prepared according to Method 1. A predetermined amount of Test liquid 1 was added to the absorbent core. The amount is selected such that it is not fully absorbed by the absorbent core and accordingly, upon squeezing liquid out of the core sample, sufficient liquid is available for pH measurement. This amount can vary to a certain extent without major influence on the-pH measured.- For core- samples consisting of materials selected from (acidic or non-acidic) pulp, acidic superabsorber (SAP) and standard SAP the following empirical formula has proven useful :

Amount of test liquid 1 = [ (amount of pulp in g) x 6 ml] + [(amount of acidic SAP in g) x 20 ml] + [(amount of standard SAP in g) x 25 ml]

For a reliable pH measurement of the cores of examples 1 and 2, respectively, one could thus use approximately 22.7 ml (Example 1) and 15.2 ml (Example 2) . After adding a suitable amount of test liquid 1, the absorbent core was left to swell for 30 minutes. Thereafter, pH was measured on the liquid squeezed out of the samples using a surface electrode, Flat- bottomed, type Single Pore Flat, Hamilton. The results of three tests were averaged for the measurement .

Test liquid 1 (referred to in Method 2) :

Synthetic urine containing the following substances: KCl, NaCl, MgSO₄, KH₂PO₄, Na₂HPO₄, NH₂CONH₂. The pH in this composition is 6.0 + 0.5. EXAMPLE 1

Circular test absorbent cores having a weight of about 2.2 g and a diameter of 5.0 cm were punched out of an absorbent core produced in a pilot plant. A standard method of mat forming a core was used in the production of the core in the pilot plant. The absorbent core consisted of 0.5 g standard superabsorber (SXM9155 available from Degussa) and 1.7 g acidic fluff pulp. The fluff pulp used was Weyerhaeuser acidic fluff pulp, which is commercially available from Weyerhaeuser under the material description TR118 and manufactured by treating ECF Kraft pulp based on 100% US Southern pine wood with 4% citric acid and 1% citrate as an additive. It has a pH of 3.4 ± 0.2. The pH of the acidic fluff pulp was measured in accordance with the standard Tappi T 509-02. More specifically, the above pH value is the 5 minutes pulp sheet pH based on Tappi method T 509-02. The absorbent core was compressed to a bulk of about 8-10 cm^/g.

To the absorbent core 3.2 ml of a 0.34 wt.-% aqueous solution of benzoic acid (available from VWR International) was added by either dripping the solution onto the surface (on one side) or dipping one side of the core into the solution. This led to a concentration of about 0.5 wt.-% benzoic acid in terms of dry absorbent core (untreated) . Then, the absorbent body was allowed to absorb 24.5 ml synthetic urine according to Method 3 as described below and allowed to incubate at 35°C.

6h and 8h, respectively, after the absorption of synthetic urine the amount of ammonia developed was measured.

Five measurements were averaged as mean value. The results are shown in Table 1. Method 3: Measurement of ammonia inhibition in absorbent cores

Absorbent cores were prepared in accordance with Method 1. Test liquid 2 was prepared. Bacteria suspension of Proteus mirabilis was cultivated in nutrient broth 30⁰C overnight. The graft cultures were diluted and the bacterial count was determined. The final culture contained approximately 10^ organisms per ml of test liquid. The absorbent core was placed in a plastic jar and the Test liquid 2 was added to the absorbent core, whereafter the container was incubated at 35°C, 6 and 8 hours respectively, whereafter samples were taken from the containers using a hand pump and a so called Drager-tube . -The ammonia content was obtained- as a colour change on a scale graded in ppm or volume percent.

Test liquid 2:

Sterile synthetic urine to which has been added a growth medium for micro-organisms. The synthetic urine contains mono- and divalent cations and anions and urea and has been prepared in accordance with the information in Geigy, Scientific Tables, VoI 2, 8th ed. 1981 p. 53. The growth medium for the micro-organisms is based on information of Hook- and FSA-media for entero-bacteria. The pH in this mixture is 6.6.

COMPARATIVE EXAMPLE 1

An absorbent core was formed in the same manner as in Example 1, with the sole exception that a treatment with a solution of benzoic acid was not carried out and a different but similar standard SAP (EK-X EN52 from Nippon/Ecotec) was used. COMPARATIVE EXAMPLE 2

An absorbent body was formed in the same manner as in Example 1 with the difference that the acidic fluff pulp was replaced by a standard fluff pulp (NB 416 from Weyerhaeuser) .

The results in terms of ammonia formation of Example 1 and Comparative Examples 1 and 2 are shown in the following Table 1.

Table 1 : Acidic pulp and benzoic acid ammonia formation (ppm) sample description benzoic acid per dry 6h 8h pulp core (in wt

Example acidic pulp¹, 0.5 230 780

1 standard SAP and benzoic acid

Comp. acidic pulp¹ and 0 740 1700 Ex. 1 standard SAP

Comp. pulp² , standard 0.5 690 1500 Ex. 2 SAP and benzoic acid

¹ acidic pulp (Weyerhaeuser TR118)

2 standard pulp (Weyerhaeuser NB 416)

EXAMPLE 2

Circular test absorbent cores having a weight of 1.6 g and a diameter of 5 cm were punched out of an absorbent product . The absorbent core consisted of fluff pulp and superabsorbent material. The fluff pulp used was 1.2 g Weyerhaeuser pulp NB416 and the superabsorbent 0.4 g BASF M7125 (pH 4.9 ± 0.2, commercially available) .

To the absorbent core 2.4 ml of a 0.34 wt.-% solution of benzoic acid (available from VWR International) was added by either dripping the solution onto the surface (on one side) or dipping one side of the core into the solution. This led to a concentration of about 0.5 wt.-% benzoic acid in terms of dry absorbent core (about 1.25 x 10^~3 g per g acidic superabsorber) . Then, the absorbent body was allowed to absorb 13.0 ml synthetic urine according to Method 3 as described above and was incubated at 35°C.

The measurement of ammonia inhibition was carried in the same manner as for Example 1.

Five measurements were averaged as mean value. The results are shown in Table 2.

COMPARATIVE EXAMPLE 3

An absorbent body was formed and evaluated in the same manner as in Example 2 with the sole difference that a treatment with the solution of benzoic acid was not carried out .

The result in terms of ammonia formation of Comparative Example 3 is shown in Table 2.

COMPARATIVE EXAMPLE 4

An absorbent body was formed and evaluated in the same manner as in Example 2 with the sole difference that Degussa SXM 9405 (standard superabsorber) was used instead of BASF M7125 (acidic superabsorber) .

The result in terms of ammonia formation of Comparative Example 4 is shown in Table 2. COMPARATIVE EXAMPLE 5

An absorbent body was formed and evaluated in the same manner as in Comparative Example 3 with the sole difference that Degussa SXM 9405 (standard superabsorber) was used instead of BASF M7125 (acidic superabsorber) .

The result in terms of ammonia formation of Comparative Example 5 is shown in Table 2.

¹ Acidic superabsorber (BASF M7125)

² Standard superabsorber (Degussa SXM9405)

Claims

C L A I M S

1. Absorbent article, such as a diaper, parity diaper, sanitary napkin or incontinence device comprising a liquid- permeable topsheet, a backsheet and an absorbent core enclosed between said liquid-permeable topsheet and said backsheet, wherein said absorbent core comprises

(a) acidic cellulosic fibers having a pH value of 5.5 or less and/or an acidic superabsorbent material made from a synthetic polymer comprising polymerized ethylenically unsaturated acid group-containing monomers, said superabsorbent material having a pH value of 5.5 or less, and -(b) -at least one compound selected from the -group consisting of benzoic acid, hydroxybenzoic acid and esters thereof; under the proviso that in absorbent articles comprising said acidic superabsorbent material and benzoic acid in combination the acidic superabsorbent material has a pH of 5.0 or less.

2. Absorbent article according to Claim 1, wherein the acidic cellulosic fibers comprised in the absorbent core are obtainable by acidifying cellulosic fibers with an acidifying agent .

3. Absorbent article according to Claim 2, wherein the acidifying agent is an organic acid (other than benzoic acid and hydroxybenzoic acid) having a pK value of at least 1.5

(measured in water at 25°C) .

4. Absorbent article according to Claim 2 or 3 , wherein the acidifying agent is selected from aqueous solutions of citric acid, oxalic acid, lactic acid, malic acid, malonic acid, maleic acid, succinic acid, tartraric acid, sorbic acid, formic acid, salts thereof, and mixtures thereof.

5. Absorbent article according to any one of Claims 1 to 4 , wherein the acidic cellulosic fiber has a pH value of 5.0 or less .

6. Absorbent article according to any one of Claims 1 to 5 , wherein the acidic cellulosic fiber has a pH value of 2.0 to 5.0, preferably from 2.5 to 4.5, more preferably from 3.0 to 4.0, still more preferably from 3.2 to 3.6.

7. Absorbent article according to any one of Claims 1 to 6 , wherein the absorbent core comprises a mixture of acidic and non-acidic cellulosic fibers.

8.- Absorbent- article accord-ing to -any one of Claims- 1- to- 7, wherein the total amount of acidic and non-acidic cellulosic fibers in the absorbent core is 90 to 30 wt.-%, preferably 80 to 35 wt.-%, more preferably 70 to 40 wt.-%, based on the weight of the core (without the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof) .

9. Absorbent article according to Claim 8, wherein the weight ratio of acidic and non-acidic cellulosic fibers is 100/0 to 50/50, preferably 95/5 to 60/40, more preferably 90/10 to 70/30.

10. Absorbent article according to any one of Claims 1 to 8 , wherein the absorbent core comprises a mixture of acidic cellulosic fibers and non-acidic superabsorbent material.

11. Absorbent article according to Claim 10, wherein the total amount of the superabsorbant material in the absorbent core is 10 to 70 wt.-%, based on the weight of the core (excluding the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof) .

12. Absorbent article according to any one of Claims 1 to 11, wherein said cellulosic fibers are fluff pulp fibers.

13. Absorbent article according to Claim 1, wherein the absorbent article comprises a benzoic acid ester, hydroxybenzoic acid or an ester thereof and the acidic superabsorbent material has a pH value of 3.0 to 5.5, preferably 3.5 to 5.3 and more preferably 4.1 to 5.2.

14. Absorbent article according to Claim 1, wherein the absorbent article comprises benzoic acid and the acidic superabsorbent material has a pH value of 3.0 to less than 5.0, preferably 3.5 to 4.95 and more preferably 4.1 to 4.9.

15. Absorbent article according to any of Claims 1, 13 and 14, wherein the absorbent core comprises a mixture of acidic and non-acidic superabsorbent material .

16. Absorbent article according to any one of Claims 1 and 13 to 15, wherein the total amount of superabsorbent material (of acidic and optionally non-acidic type) in the absorbent core is 10 to 70 wt.-%, preferably 20 to 65 wt.-%, more preferably 30 to 60 wt.-%, based on the weight of the absorbent core (excluding the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof) .

17. Absorbent article according to Claim 15 or 16, wherein the weight ratio of acidic and non-acidic superabsorbent material is 100/0 to 50/50, preferably 95/5 to 60/40, more preferably 90/10 to 70/30.

18. Absorbent article according to any one of Claims 1 and 13 to 17, wherein the superabsorbent material is in the form of particles.

19. Absorbent article according to any one of Claims 1 and 13 to 18, wherein the acidic superabsorbent material is a crosslinked homo- or copolymer comprising (meth) acrylic acid units .

20. Absorbent article according to any one of Claims 1 and 13 to 19, wherein the superabsorbing material is admixed with any other absorbent material .

21. Absorbent article according to any one of Claims 1 to

20, wherein the amount of the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof is at least 10^"^g per g of the acidic cellulosic fiber and/or the^" acidic superabsorbent material- -

22. Absorbent article according to any one of Claims 1 to

21, being obtainable by treating the absorbent core with a solution of the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof .

23. Acidic cellulosic fibers having a pH of 5.5 or less characterized in that they comprise at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof.

24. Acidic cellulosic fibers according to Claim 23 obtainable by treating cellulosic fibers with an acidifying agent and the at least one compound selected from the group consisting of benzoic acid, hydroxybenzoic acid and esters thereof .

25. Acidic cellulosic fibers according to Claim 24, wherein said acidifying agent is selected among organic acids other than benzoic acid or hydroxybenzoic acid.

26. Acidic cellulosic fibers according to Claim 24 or 25, wherein said acidifying agent is present in an amount of 1 to 20 wt. -% based on the dry weight of the untreated fibers.

27. Acidic cellulosic fibers according to Claims 23 to 26, wherein the cellulosic fibers are fluff pulp fibers.

28. Acidic superabsorbent material made from a synthetic polymer comprising polymerized ethylenically unsaturated acid group-containing monomers, said superabsorbent material having a pH value of 5.0 or less and comprising benzoic acid.

29. Acidic superabsorbant material according to Claim 28 wherein the -acidic-superabsorbant -material—has a pH value- of - 3.0 to less than 5, preferably 3.5 to 4.95 and more preferably 4.1 to 4.9.

30. Acidic superabsorbent material made from a synthetic polymer comprising polymerized ethylenically unsaturated acid group-containing monomers, said superabsorbent material having a pH value of 5.5 or less and at least one compound selected from the group consisting of benzoic acid esters, hydroxybenzoic acid and esters thereof.

31. Acidic superabsorbant material according to Claim 30 wherein the acidic superabsorbant material has a pH value of 3.0 to 5.5, preferably 3.5 to 5.3 and more preferably 4.1 to 5.2.

32. Acidic superabsorbent material according to any of Claims 28 to 31, wherein the acidic superabsorbent material is a crosslinked homo- or copolymer comprising (meth) acrylic acid units .

33. Use of the acidic cellulosic fibers according to any one of Claims 23 to 27 for odor-control.

34. Use of the acidic superabsorbent materials according to any one of Claims 28 to 32 for odor-control.

35. Use according to Claim 33 or 34 for odor-control in absorbent articles.