### (12) 

# United States Patent Rangachari et ai.

(54) NON-IONIC PLASTICIZERADDITIVES FOR WOOD PULPSANDABSORBENT CORES
(75) Inventors: Krishnakumar Rangachari, Savannah; Kays Chinai, St. Simons Island, both of GA (US)
(73) Assignee: Rayonier Products and Financial Services Company, Ferandina Beach, FL (US) 

### ( *) Notice: Subject to any disclaimer, the term ofthis patent is extended or adjusted under 35 U.S.c. 154(b) by 0 days.
(21) Appl. No.: 09/642,862 (22) Filed: Aug. 21, 2000

Related U.S. Application Data
(63) Continuation-in-partofapplicationNo. 09/408,047, filed on Sep. 29, 1999. 

### (51) Int. CI?

...................................................... A61F 13/15 (52) U.S. CI.

.......................... 604/375; 264/116; 264/122; 264/518; 162/158 (58) Field of Search

..................................... 264/518, 115, 264/116, 122; 162/158; 604/375
(56) References Cited

2,249,118 3,554,862 

### U.S. PATENT DOCUMENTS

7/1941 De Witt

. 1/1971 Hervey et al.

....................... 162/158

## 111111 1111111111111111111111111111111111111111111111111111111111111 US006310268Bl
(10) 

## Patent No.: 

# US 6,310,268 

# Bl Oct. 30, 2001 (45) 

## Date ofPatent:

3,677,886 3,809,604 4,144,122 4,303,471 4,432,833 4,583,980 4,610,678 5,516,569 5,547,541 5,641,561 5,695,486 5,776,308 5,837,627 5,858,172 5,866,242 5,916,670 5,935,880 7/1972 Forssblad et al.

..................... 162/72 5/1974 Estes et al.

.... .......... ... ... ... ... 162/100 3/1979 Emanuelsson et al.

............. 162/158 12/1981 Kemi

.................................... 162/158 2/1984 Breese

.................................. 162/158 4/1986 Schneider et al.

....... ... ... ... ... 604/359 9/1986 Weisman et al.

.................... 604/368 5/1996 Veith et al.

............................ 428/68 8/1996 Hansen et al.

......................... 162/12 6/1997 Hanson et al.

....................... 442/417 12/1997 Broughton et al.

.................. 604/374 7/1998 Sears et al.

.......................... 162/158 11/1998 Halabisky et al.

................... 442/385 1/1999 Sears et al.

.......................... 162/158 2/1999 Tan et al.

............................. 428/219 6/1999 Tan et al.

............................. 428/219 8/1999 Wang et al.

........................... 442/65 

### FOREIGN PATENT DOCUMENTS

WO 99/24667 WO 00/36215 A1 5/1999 CWO).

6/2000 CWO). 

### Primary Examiner-Mary Lynn Theisen 

### (74) Attorney, Agent, or Firm-Rockey, Milnamow & 

### Katz, Ltd. (57) ABSTRACT
Softwoodpulp sheets, soft absorbent cores, and methodsfor making the soft woodpulp sheets or soft absorbent coresby addition ofnon-ionic plasticizers before, during or after the pulp or core manufacturing process are disclosed. Preferred non-ionic plasticizers are ethers or esters such as triacetin, citrates or glycol derivatives.

34 Claims, No Drawings

## US 6,310,268 Bl 1 NON-IONIC PLASTICIZERADDITIVES FOR

WOOD PULPSAND ABSORBENT CORES

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/408,047 filed Sep. 29, 1999.

FIELD OF THE INVENTION

This invention is directed to soft wood pulp sheets, soft absorbentcores, and methodsfor makingthe softwoodpulp sheets or soft absorbent cores by addition of non-ionic plasticizers before, during or after the pulp or core manufacturing process. Preferred non-ionicplasticizers are ethers

or esters such as triacetin, citrates or glycol derivatives.

BACKGROUND OF THE INVENTION
A wide variety of absorbent structures for use in disposable absorbent articles are known in the art. Common commercial absorbent articles include diapers, adult incontinenceproducts, catamenials and bandages. Theseproducts
are provided with various functional components for receiving, absorbing and retaining fluids.

Disposable absorbent articles, such as diapers, feminine hygiene products, adult incontinence devices and the like have found widespread acceptance. To function efficiently, such absorbent articles must quickly absorb body fluids, distribute those fluids within and throughout the absorbent article and be capable of retaining those body fluids with sufficientenergyto drythe surfacewhenplacedunderloads. Inaddition,the absorbent article needbesufficiently soft and flexible so as to comfortably conform to body surfaces and provide close fit for lower leakage. 

## 2 distribution offluid to the absorbent core while minimizing spread of the fluid in this layer.

The absorbent core is typically formulated of a cellulosic wood fiber matrix or pulp, which pulp is capable of absorbS inglargequantitiesoffluid.Absorbentcorescanbedesigned in avarietyofwaysto enhancefluid absorption andretention properties. By way of example, the fluid retention characteristics of absorbent cores can be greatly enhanced by disposing superabsorbent materials amongst fibers of the 10 wood pulp. Superabsorbent materials are well known in the art as substantially water-insoluble, absorbent polymeric compositionsthat are capable ofabsorbing large amounts of fluid in relation to their weight and forming hydrogelsupon such absorption. Absorbentarticles containing blends or 15 mixtures ofpulp and superabsorbents are known in the art. The distribution of superabsorbents within an absorbent

core can be uniform or non-uniform. By way of example, that portion of an absorbent core proximate to the backing layer (farthest away from the wearer) can be formulated to 20 contain higher levels of superabsorbent than those portions ofthe coreproximate the facing or acquisitionlayer. Byway offurther example, thatportionofthe core closestto the site of fluid entry (e.g., acquisition zone) can be formulated to transport (wick) fluid into surrounding portions ofthe core 25 (e.g., storage zone). As consumer demand for less expensive and less bulky disposable absorbentproductsincreases,manufacturerscontinue to seekeffective ways to reduce size and cost without
30 sacrificing the quality of the fluid transport properties or structural integrity of the products during use. Preferably, the disposable products should be soft, thin and absorbent. Unfortunately, when softness and thinness characteristics

are improved through the use of additives known in the art, 35 absorbency is sacrificed. Therefore, there is a need in the industry for manufacturing processes which produce a soft and thin material while maintaining the desired level of absorbency. While the design of individual absorbent articles varies depending upon use, there are certain elements or components common to such articles. The absorbent article contains aliquidpervioustop sheetorfacinglayer, whichfacing layer is designed to be in contact with a body surface. The facing layer is made of a material that allows for the unimpeded transfer of fluid from the body into the core of the article. The facing layer should not absorb fluid per se 45 and, thus, should remain dry. The article further contains a liquid impervious back sheet or backing layer disposed on the outer surface ofthe article and which layer is designed Absorbent materials, such as absorbent cores may be
40 made from pulp in the form of sheets orboard. The pulp is defiberized in order to manufacture an absorbent material. Therefore, additiveswhichimprove the characteristicsofthe absorbentendproductmaybe added 1)to thepulp, 2) during the manufacture ofpulp board, or 3) during manufacture of the absorbent core. Conventionally, for the manufacture of absorbent materials, softness is achieved by the addition of debonders to the pulp, since the softness of a pulp product is greatly influenced by the degree to which the constituent wood pulp is debonded, i.e., the extent to which hydrogen to prevent the leakage of fluid out of the article. 50 bonds within the wood pulp are broken. For example. debonderis addedto thepulpwhile thepulp isinthe holding chests, prior to deposition of the pulp slurry on the Fourdrinier wire. The result is softer pulps or pulp products, Disposedbetweenthe facing layer andbacking layeris an absorbentmemberreferredto in the art as an absorbentcore. The function of the absorbent core is to absorb and retain body fluids entering the absorbent article through the facing layer. Because the origin of body fluids is localized, it is necessary to provide a means for distributing fluid through- 55 outthe dimensions ofthe absorbent core to make full use of which typically have decreased hydrogen bonding. Wood pulp softness can be expressed in terms of properties such as Mullen strength (the strengthofpulp or apulp product, measured in kilopascals (kPa), defined in greater detail below), and Kamas energy (the energy required to convert a given amount of pulp or pulp product to a fluff all the available absorbentmaterial. This is typically accomplished either by providing a distribution member disposed between the facing layer and absorbent core and/or altering the composition of the absorbent core per se. 60 material, measured in watt hours per kilogram (Wh/kg), defined in greater detail below). Lower values of Mullen strength and Kamas energy correlate to softer, increasingly debonded, pulp. Fluid can be distributed to differentportions ofthe absorbent core by means of a transfer or acquisition layer disposed between the facing layer and core. Because of the proximityofsuch an acquisition layerto the bodysurface of the wearer, the acquisition layer should not be formed from 65 material that retains large amounts offluid. The purpose of the acquisition layer is to provide for rapid transfer and Many industrial pulp applications involve the conversion of pulp to fluff pulp by mechanical means. The efficient mechanical fluffing ofwoodpulp requires a pulp (stiff) that will debond to a desirable degree with minimum energy

## US 6,310,268 

## Bl 

## 3 input and little mechanical fiber damage. Such pulp must have the proper bulk and degree of inter-fiber bonding. A hard pulp sheet will increase the energy needed to create fluffpulp and will therefore lead to increased fiber damage, while an unduly softpulp sheetwill lead to pull-out oflarge 5 pieces ofpulp, causing poor fluffing.

Currently, cationic compounds are used in the manufacture ofwood pulp products such as sanitary papers to yield 

## 4 tensile strength ofthe core. Thus, use ofthe above steps to produce soft absorbent cores results in substantial increases in the cost of the core.

For example, soft absorbent materials are disclosed in U.S. Pat. Nos. 5,866,242 and 5,916,670. However, the processesdisclosedthereinmaybeexpensive, so itwouldbe desirable to use an additive which would provide a lower cost alternative, ifsuch additive could be used to treatpulps to provide beneficial properties to pulp, and thereafter to a product which has a soft hand feel. This is accomplished through the lubricating nature of the substantive softening molecule; less extensive inter-fiber bonding leading to greater bulk and the plasticizing effect of these additives. 10 absorbentcoresformed from treatedpulps,without decreasing absorbency.

There are several cationic chemical materials known for

use to softenpulp to produce afluffordebondedpulp. These cationicmaterials are quaternary ammonium compounds, as disclosedinU.S. Pat. Nos. 3,554,862; 3,677,886; 3,809,604; 4,144,122 and 4,432,833 among others. There continues to be a need in the art, therefore, for a material that satisfies the absorbency, strength and softness requirements needed for use as absorbent core in disposable 15 absorbent articles and which simultaneously provides time and cost savings to both the pulp manufacturer and the manufacturer ofthe absorbent article. Nonionic agents are also used to a limited extent to debond pulp in the paper industry (BEROCELL587, available from EkaNobel)buteventheycause adverse affects on absorbency. It is believed that this effect is due to the presence of long hydrophobic side chains. Accordingly, it wouldbe desirable to provide amethod of treating pulp sheets to form fluff pulp with improved soft20 nesswithout sacrificing the absorbentpropertiesofthe pulp.

Water-soluble polyhydroxy alcohols have been disclosed

as softening agents in U.S. Pat. No. 2,249,118. Non-ionic 25 compounds such as fatty acid esters in combination with cationic retention agents have been disclosed in U.S. Pat. No. 4,303,471 to obtain good disintegration properties for pulp.

However, pulp softening and debonding, when accom- 30 plishedbythe conventionaltreatmentsdescribed above,will result in a material that is less absorbent.

As an alternative to the use ofadditives, materials maybe specifically engineered to obtained the desired characteristics. In addition to blending pulp with superabsorbent 35 material, a variety of other means for improving the characteristics ofpulp have been described. SUMMARY OF THE INVENTION One aspect of the invention is an absorbent core comprising from 0.1% to 10% of at least one non-ionic plasticizer. The plasticizer may be a citrate or triacetin; the core may have a suppleness of greater than about 0.7 g-l; a density offrom about0.25g/ccto about0.5g/cc; and abasis weight of from about 200 g/m2 to about 550 g/m2.

Another aspect of the invention is an absorbent core comprising:

from about 30weight percent to about 90 weight percent

of cellulosic fibers; and, from about 0.1 weightpercent to about 10weightpercent

of at least one non-ionic plasticizer; wherein said core has a suppleness of greater than about

0.7 g-\ a density offrom about 0.25 g/cc to about 0.5 glcc and abasisweightoffrom about 200glm2 to about 550 g/m2. Examples ofsuitable plasticizers are esters orethers. The One particular desirable character is the stiffness of the absorbent core. Asthe disposable hygiene productsindustry
moves towards ultrathin products, stiffness ofthe absorbent
corehasbecome acriticalissue.Theuseofmercerizedfibers to reduce the stiffness (orimprove the softness) ofabsorbent
cores has been disclosed in U.S. Pat. No. 5,866,242. However these fibers arc expensive when compared to nonmercerized fibers. 40 ethersorestersmaybe glycolderivatives, and the estersmay alsobe citrates. Suitable glycolethersinclude alkylethersof low molecular weight glycols or aryl ethers oflow molecular weight glycols. Suitable glycol esters include formic esters of low molecular weight glycols, ethanoic esters of Debonding agents such as quaternary ammonium compounds can be used to produce soft pulp sheets and absorbent cores. However, as previously mentioned, the use of debonders result in a substantial negative impact on absorbency. 45 low molecular weight glycols or propanoic esters of low molecular weight glycols. A preferred ester is triacetin. Preferred citrates are of the formula

50 There have beennumerous attemptsby the manufacturers of absorbent materials to produce core materials which arc highly absorbent, strong, and soft U.S. Pat. No. 4,610,678 discloses an air-laid material containing hydrophilic fibers and superabsorbent material,wherein the material is air-laid 55 wherein Rl, R2 and R3 are each independently alkyl groups, and in a dry state and compacted without the use of any added binding agents. Such material, however, has low integrity and suffers from shake-out orloss ofsubstantial amounts of superabsorbent material. U.S. Pat. No. 5,516,569 discloses that superabsorbent material shake-out can be reduced in 60 air-laid absorbentsbyaddingsignificant amountsofwaterto material during the air-laying process. The resultant material, however, is stiff of low density and has a high watercontent (>about 15 weightpercent). The high stiffness

can be reduced using embossing which requires an addi- 65 tional processing step in the manufacturing process, but embossing hasbeen shown to have a negative impact onthe R4 is selected from the group consisting of hydrogen, alkyl groups and _C(O)R5, wherein R5 is an alkyl group. The plasticizer may be triacetin. Cellulosic fibers used to make the cores may be derived from at least one type of pulp sheet, or from a mixture of at least two types of pulp sheets. The core may further comprise from about 9.99 weight percent to about 60 weight percent of superabsorbent polymer. When the

core contains superabsorbent polymer, the core may have a normalized wicking energy greater than about 2,300 ergs/g.

## US 6,310,268 

## Bl 5 Another aspect of the invention is a method for manufacturing asoftenedabsorbentmaterialfrom cellulosicfibers comprising the steps of:

a) defiberizing cellulosic fibers to form defiberized cellulosic fibers; b) blending said defiberized cellulosic fibers with superabsorbent material to form a blended material; c) depositing said blended material onto a carrier layer

under vacuum to form a layered absorbent web; and d) compressing said web to form an absorbent material, 

## 6 glycols.Apreferred esteristriacetin. One ormore non-ionic plasticizers may be added, as combinations of non-ionic plasticizers may increase the efficacy of the desired result.

The term "citrate" as used herein refers to compounds of 5 general formula I,

Formula I

10
wherein an effective softening amount of at least one

non-ionic plasticizer is added to at least one of said cellulosic fibers, said defiberized cellulosic fibers, said blended material, said web and said absorbent 15 material. wherein Rl, R2 and R3 are each independently alkyl groups (each may be different, or all may be the same), and R4 is selectedfrom the groupconsistingofhydrogen, alkylgroups and _C(O)R5, wherein R5 is an alkyl group. The absorbent material may be an absorbent core. If the plasticizer is anti-microbial, the softened absorbent wood pulp product is an anti-microbial, softened, absorbent wood pulp product. If the plasticizer is odor-preventing, the soft- 20 ened absorbent wood pulp product is an odor-preventing, softened absorbent wood pulp product. The term "alkyl" as used herein alone or in combination refers to C1-C12 straight or branched, saturated or unsaturated (alkenyl, alkynyl, allyl) chain radicals derived from saturated hydrocarbons by the removal of one hydrogen atom. Representative examples of alkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, isobutyl, and tert-butyl among others. Suitable plasticizers are as defined above. The cellulosic fibers used to make the cores may be derived from at least
onetype ofpulp sheet,orfrom amixture ofatleasttwo types 25 ofpulp sheets. The term "aryl" as used herein alone or in combination refers to a carbocyclic aromatic group having about 6 to 12 carbon atoms such as phenyl, naphthyl, indenyl, indanyl, azulenyl, fluorenyl and anthracenyl. Another aspect of the invention is a wood pulp sheet comprising:

from about 90 weight percent to about 99.9 weight

percent of cellulosic fibers; and, from about 0.1 weightpercent to about 10weightpercent

of at least one citrate, wherein said sheet has a defiberization energy offrom about 35 to about 60 Whlkg. Suitable citrates are as defined above. Presentlypreferred woodpulp sheets have a wicking energy greater than about 40,000 ergs/g, and more preferably greater than about 60,000 ergs/g.

Another aspect ofthe invention is a method for softening wood pulp sheets comprising the step of adding to said sheets an effective wood pulp sheet softening amount of at least one citrate of the formula

wherein R\ R2 and R3 are each independently alkyl groups, and

R4 is selected from the group consisting of hydrogen,

alkyl groups and _C(O)R5, wherein R5 is an alkyl group. Suitable citrates are as defined above.

DETAILED DESCRIPTION OF IRE INVENTION

Definitions The term "non-ionic plasticizer" as used herein refers to compoundssuch as estersorethers. The ethersorestersmay be glycol derivatives, and the esters may also be citrates. Suitable glycol ethers include alkyl ethers oflowmolecular weight glycols or aryl ethers of low molecular weight glycols. Suitable glycol esters include formic esters oflow molecular weight glycols, ethanoic esters oflow molecular weight glycols orpropanoic esters oflow molecularweight The term "woodpulp" asusedhereinrefers to acellulosic material obtained from wood produced according to apulp30 ing process including but not limited to sulfite, kraft and thermomechanical pulping processes, and in which lignin and other cellulose pulp impurities may be removed in whole or in part by a process which includes but is not limited to an oxidation or other bleaching process, wherein cellulosichydroxyl groupsnaturallypresentinthe cellulosic 35 materialhave notbeenchemicallysubstitutedorderivatized. Cellulose ether and acetate end-use derivative products are not considered wood pulp.

The term "softenedpulps" refers to fibrous end-use wood pulps (for example, fluff pulps) that have some chemical 40 agent (softener) added to soften the pulp, preferably by reducing interfiber bonding (addition ofthe softener results in a soft pulp sheet). The chemical agents (softeners) are commercial products added to fluff pulps during sheet forming which make the pulp sheet softer and easier to fluff
45 or defiber. The force with which pulp fibers bond is measured indirectly by measuring Mullen strength or the force (or energy) expended to debond or fluff a given pulp sheet.

Asusedherein, the term "cellulosicfibers" refersto those fibers which are conventionally employed to form aweb for
50 use, for example, in absorbent articles. A wide variety of pulped cellulosic fibers, derived from wood and non-wood sources, canbeused. Cellulosicfibers that canbeusedin the presentinvention are wellknownin the art andincludewood pulp, cotton, flax and peat moss. Wood pulp is preferred. 55 Cellulose acetate fibers are not included in this definition. Pulps and cores of the present invention are cellulose acetate-free. Pulps can be obtained from mechanical or chemi-mechanical, sulfite, kraft, pulping reject materials, organic solvent pulps, etc. Both softwood and hardwood
60 species are useful. Softwood pulps are preferred. It is not necessary to treat cellulosic fibers with chemical debonding agents, cross-linking agents and the like for use in the present invention. Wood pulp is most commonly employed because of its availability and price. Therefore, cellulosic
65 fibers derivedprimarily from woodpulp are mostpreferred. Suitable wood pulp fibers for use with the invention can be obtained from well-known chemicalprocesses. The pulp

## US 6,310,268 

## Bl 7 fibers may also be processedby chemical methods, thermomechanical methods, chemithermomechanical methods, or combinations thereof. The preferred pulp fiber is produced 

## 8 required to produce rupture of a material under certain experimental conditions. Mullen strength is determined on some of the products presented in the examples using a methodbasedonTAPPIT807.A

### TMI MonitorBurst 1000is used to measure the hydrostatic pressure required to rupture
a pulp sheet. Mullen strength is recorded as kPa at rupture.

The term "Kamas energy" as used herein refers to the energy required to convert a given amount ofpulp or pulp product to a fluff material measured in watt hours per kilogram (Wh/kg). A Kamas lab hammer mill Model H-OI-C was used to defiberize some of the products presented in the examples. Strips ofpulp sheets 5 cm wide and having a basis weight of 640 gsm were fed into the hammermill, using, 4200 rpm motor speed, 50% feeder speed, and an 8 mm screen. The energy required to defiberbychemical methods, either sulfate or sulfite. The preferred starting material is prepared from long-fiber coniferous 5 woodspecies such as southernpine, Douglasfir, spruce, and hemlock. Other chemical pulps made from short or long fibered wood species, ground wood fibers, recycled or secondary wood pulp fibers, and bleached and unbleached wood pulp fibers can be used. Short wood fibers are pro- 10 duced from hardwood species, such as eucalyptus, using known chemicalprocesses or from any wood species using mechanical or chemithermomechanical methods. Details of the production ofwoodpulp fibers are well-known to those skilled in the art. 15 ize the pump sheet is recorded, and reported as Wh/kg of fluff, the energy of defiberization. The term "wood pulp sheet" as used herein refers to cellulosic fiber sheets formed using the wet-laid process. The sheetstypicallyhave abasisweightofbetween200 and 800gsm anddensitybetween0.3 to 1.0g/cc. Thepulp sheets
are subsequentlydefibered in a hammermill to convert them into fluff pulp before being used in an absorbent product. Wood pulp sheets can be differentiated from tissue paper or paper sheets by their basis weights. Typically, tissue paper has abasisweightoffrom about5 to about50gsmandpaper sheets have basis weights of from about 47 to about 103 gsm. Therefore, these materials have lower basis weights than wood pulp sheets. The Gurley stiffness values of the absorbent materials
were measured using a Gurley stiffness tester (Model No 4171E), manufactured by Gurley Precision Instruments of 20 Troy, N.Y. The instrument measures the externally applied momentrequired to produce agivendeflection ofatest strip of specific dimensions fixed at one end and having a concentrated load applied to the other end. The results are obtained in "Gurley stiffness" values in units ofmilligrams. 25 Itshouldbe notedthatthe higherthe stiffnessofthe material, the less flexible and hence the less soft it is.

The term "absorbent core" as used herein refers to a cellulosic wood fiber matrix orpulp, which pulp is capable ofabsorbinglarge quantities offluid. Absorbentcorescanbe 30 designedin avarietyofwaysto enhance fluid absorption and retention properties. By way ofexample, the fluid retention characteristics of absorbent cores can be greatly enhanced bydisposing superabsorbent materials amongst fibers ofthe woodpulp. The absorbent core maybe used to manufacture 35
consumer products such as diapers, feminine hygiene products or incontinence products.

Superabsorbent materials are well-known to those skilled in the art as substantially water-insoluble, absorbent polymeric compositions that are capable of absorbing large 40 amounts of fluid in relation to their weight and forming hydrogels upon such absorption. The Methods One aspect of this invention is a method for obtaining a softened absorbent coreby adding aplasticizer as a softener to the process stream at any convenient point in the air-laid manufacturing process. The process stream contains wood pulp as well as other additives. Production of an absorbent material by air-laying means is well known in the art. Briefly, cellulosic fibers (e.g., pulp) are processed using a hammermill to individualize the fibers. The individualized fibers are blended with SAP granules in a blending system and pneumatically conveyed into a series offorming heads. The blending and distribution ofabsorbent materials can be controlled separately for each forming head. Controlled air circulation and winged agitators in each chamber produce uniform mixture and distribution ofpulp and SAP. The SAP
can be thoroughly and homogeneously blended throughout the web or contained only in specific stratabydistributingit to selected forming heads. Fibers (and SAP) from each forming chamber arc deposited by vacuum onto a carrier layer, thus forming a layered absorbent web. The web is subsequently compressed using calenders to achieve desirable density. The deified web is wound into a roll using conventional winding equipment. A forming wire can be covered with tissue paper to reduce the loss of material as the carrierlayer. Thetissuepaperlayercanberemovedprior to calendering or incorporated into the formed material.

Moreover, an absorbent core having improved properties may be obtained by post-manufacturing application of additive, by applying the additive to the core which results from the air-laid process described above.

Anotheraspect ofthisinventionrelatesto the treatmentof wood pulp sheets useful for making a fluff pulp preferably for absorbency intensive applications. Surprisingly, this method oftreating wood pulp sheets with a softening agent to soften the pulp does not adversely effecting the absorbency of the material. The wood pulp sheet is treated by applying to the wood pulp sheet a sufficient amount of a The terms "superabsorbent polymer" or "SAP" as used herein refer to a polymeric material that is capable of absorbinglarge quantities offluidbyforming ahydratedgel. 45 The superabsorbent polymers also can retain significant amounts ofwaterundermoderatepressures. Superabsorbent polymers generally fall into three classes, namely, starch graft copolymers, cross-linked carboxymethylcellulose derivatives, and modified hydrophilic polyacrylates. 50 Examples of such absorbent polymers are hydrolyzed starch-acrylonitrile graft copolymer; a neutralized starchacrylic acid graft copolymer, a saponified acrylic acid estervinyl acetate copolymer, a hydrolyzed acrylonitrile copolymer or acrylamide copolymer, a modified cross-linked 55 polyvinyl alcohol, a neutralized self-cross-linking polyacrylic acid, a cross-linked polyacrylate salt, carboxylated cellulose, and a neutralized cross-linked isobutylene-maleic anhydride copolymer. An absorbent material ofthe present invention can contain any SAPknown in the art. The SAP 60
canbe in the form ofparticulate matter, flakes, fibers andthe like. Exemplary particulate forms include granules, pulverizedparticles, spheres, aggregates and agglomerates. Exemplary and preferred SAPs include salts ofcrosslinked polyacrylic acid such as sodium polyacrylate. 65 material comprising the softening agent.

The term "Mullen strength" as used herein refers to the hydrostatic pressure, typically measured in kilopascals, Various types ofwoodpulp sheetswere testedto measure the effect that the softening agents ofthe present invention

## US 6,310,268 

## Bl 

## 9 had onproperties including Mullen strength, Kamas energy, absorption time and fluid retention. Itwasfound that citrate esters reduce Kamas energy, reduce Mullen strength, and have a negligible effect on both absorption time and fluid retention properties ofpulp sheets.

Whenthe invention ispracticedindustrially, the softening agents are best applied to wood pulp sheets in an aqueous solutionwhichcanbe madeup in aholding tank orprepared continuouslywith an in-line staticmixer. Inthe manufacture ofabsorbentpulp sheets, these agents canbe addedto afiber slurry at the machine chest, fan pump or headbox. Theycan also be applied by spray application to a wet pulp sheet or
can be applied via a "dip and nip" procedure in which an evacuatedbut not completely driedpulp sheetisdipped into
a solution containing the agent and subsequently pressed. Additionally, softening agents of the invention may be sprayed, rolled or printed onto one or both sides of a pulp sheet.

The woodpulp used in the sheets treated by the methods of the present invention can also be pretreated prior to use with the present invention. This pretreatment may include physical treatment, such as subjecting the fibers to steam, or chemical treatment, for example, cross-linking the cellulose fibers using any ofa variety ofcross-linking agents such as dimethyl dihydroxyethylene urea. Cross-linking the fibers, for example, increases their resiliency, and thereby can improve their absorbency. The fibers may also be twisted or crimped, as desired.

Although not to be construed as a limitation, examples of pretreating fibers include the application offire retardantsto the fibers, such as by spraying the fibers with fire-retardant chemicals. Specific fire-retardant chemicals include, byway of example, sodium borate/boric acid, urea, and ureal phosphates. In addition, the fibers may be pre-treated with surfactantsorother liquids, such aswaterorsolvents,which modify the surface of the fibers. These are known as softened or debonded fibers. Other pre-treatments include exposure to antimicrobials, pigments and densification or softening agents. Fibers pre-treated with other chemicals, such as thermoplastic and thermosetting resins also may be used.

Wood pulp sheets may be treated for softening by sprayingthe softeneronthe sheet as it is rolledupuponformation in the papermaking process, or by spraying the softener as the rolled sheets ofpulp are unrolled for further processing. Sheets so treated, when utilized to make an absorbent core, results in a softer absorbent core which retains capacity for liquid retention.
The Additives

Plasticizers such as tributyl citrate have been used in combination with terpolymers to form binder compositions to make soft absorbentwebswhich are capable ofdispersing in an aqueous environment into unrecognizable pieces in U.S. Pat. No. 5,935,880. These binder compositions of the

,880 patent are used by those skilled in the art as additives 

## 10 citric acid esters have been used for odor-prevention in sanitary hygiene products as disclosed in U.S. Pat. No. 4,583,980. In the '980 patent, a high concentration of additive (12.5-37.5%) is utilized to create an additive layer 5 in the product. By contrast, the present invention utilizes much lower concentrations.

10 Triacetinhasbeenused as asolventfor abondingmedium such as cellulose acetate to form a strengthened web containingpulpedcellulosicfibers as disclosedinU.S. Pat. Nos. 5,837,627 and 5,695,486. However, when these materials
are strengthened using a combination of cellulose acetate and triacetin, absorbencydecreases. Inthepresentinvention, cellulose acetate is not contemplated to be within the definition of cellulosic fibers.

Triacetinwasfirst recognizedto provide softeningin pulp 15 in U.S. Pat. Nos. 5,776,308 and 5,858,172. These patents also disclosed other non-ionic compounds such as alkyl ethers, aryl ethers, formic, ethanoic and propanoic esters of low molecular weight glycols (such as propylene glycol diacetate and 2-phenoxyethanol) for softening wood pulp. 20 However, the citrate esters ofthe present invention have not beendisclosedfor suchpurposes. Moreover, the use ofthese non-ionic compounds as additives in the manufacture of absorbent cores has not previously been disclosed.

Examples ofsuitable plasticizers are esters or ethers. The 25 ethersorestersmaybe glycolderivatives, and the estersmay also be citrates or triacetin. Suitable glycol ethers include alkyl ethers oflow molecular weight glycols or aryl ethers of low molecular weight glycols. Suitable glycol esters include formic esters of low molecular weight glycols,
30 ethanoic esters of low molecular weight glycols or propanoic esters oflow molecular weight glycols.

Examples of suitable citrate esters include trimethyl citrate, acetyl trimethyl citrate, triethyl citrate, tri-n-butyl citrate, acetyltriethylcitrate, acetyltri-n-butylcitrate, acetyl 35 tri-n-hexyl citrate, n-butyryl tri-n-hexyl citrate, acetyl tri-n- (hexyl/octyl/decyl) citrate and acetyl tri-n-(octyl/decyl) citrate and combinations thereof among others.

Addition of the plasticizers of the present invention shouldnotdecreasethe relative liquid absorptionrate ofsaid 40 absorbent material by more than 5%. Compounds are preferably added neat, though it should be noted that application ofa softening agent to wood pulp is not limited to neat application, and can also include application in solution, as an emulsion, as a suspension or a 45 dispersion. One or more of the additives described above may be utilized. Plasticizers may act synergistically with each other. Moreover, other additives which maybe used in conjunction with the non-ionic plasticizers of the present invention include absorbent capacity enhancing materials 50 such as superabsorbent polymers, zeolites and activated carbon, brighteners such as titanium dioxide, and odor absorbents such as sodium bicarbonate, EDTA, zeolites, activated carbon and borates. Solvents can also reduce the dusting caused by the additives or the pulp itself because 55 more ofthe fines are attached andboundto the matrixbythe bonding medium.
in the wet laid process, for manufacturing absorbent materials having basis weights below 125. For the present invention, absorbent cores are manufactured by an air-laid 60 process, which is utilized to make materials having much higher basis weights. The effective softening amount ofthe additives described above will depend upon the system to be treated. Factors which will influence how much ofthe additive is necessary include the type ofwoodpulp utilized, particularprocessing conditions, which other additives are present, which particular additive is selected and the desired properties ofthe resultant absorbent core. Citric acid has been disclosed as a binder useful in combination with a densifying agent to bind particles to fibers in U.S. Pat. Nos. 5,641,561 and 5,547,541. However, 65 citric acidisnot aplasticizer, as it is acarboxylic acid, while art recognized plasticizers are esters or ethers.Additionally, Test Procedures & Definitions Inthe tests describedhereinafter, industry-employedstandard test procedures have beenused. Ifany deviations from

## US 6,310,268 Bl 11 standard test procedure have been made, such deviations have been identified. 

## 12 A decrease in stiffness was observed as the amount of triacetin treated pulp is increased. A control air-laid absorbent core had a stiffness of 980 mg, while the absorbent
coreswith 100% triacetintreatedpulpshad a stiffness of780 For purposes of evaluating the products obtained and described by the present disclosure as well as the invention herein, several tests were used to characterize the desirable fibrous wood pulp end-use performance improvements resulting from use ofthe presently disclosed softening agent treatment, and to describe some ofthe analytical properties 5 mg. Table 1 summarizes this trend. Suppleness values are derived from the stiffness values, obtained as described above. Suppleness and stiffness are inversely proportional, and a higher suppleness value is
more desirable for an absorbent material. To obtain a value of the pulp products. A summary of these tests and definitions follows:

"Pulp 1" is an untreated southern pine kraft pulp sold by

Rainier Inc. for use in applications requiring high absorbency. 10 for suppleness, stiffness is dividedby one thousand, and the resulting number is inverted.

"Pulp 2" is a southern pine kraft pulp which has been

treated with softener triacetin ofthe present invention. 15 "Pulp 3" is a southern pine kraft pulp which has been

treated with softener triethyl citrate of the present invention. "Pulp 4" is a cold caustic treated, mercerized fiber available from Rayonier Inc. "Pulp 5" is a southern pine kraft pulp available from

Rayonier Inc. which has been treated with a cationic (quaternary ammonium salt) debonder. To measure the absorbentcapacity andrate ofabsorbency ofabsorbent materials, a radial wicking test wasperformed
on Gravimetric Absorbency Test equipment. Maximum capacity is first measured, and then the time to reach 25%, 50% and 75% of saturation is recorded. Radial wicking results provided in Table 2 showed no negative impact on absorbency properties by including triacetin treated pulps, since the absorbentpropertiesofCoreA (no addedtriacetin) 20 were comparable to Core D (having 100% of 1% triacetin treated pulp). Therefore this example shows that at a 1 % triacetin charge, the stiffness of absorbent cores can be reduced by 20%. "Pulp 6" is a southern pine kraft pulp which has been

treated with softener tri-n-butyl citrate of the present 25 invention. Several experiments were conducted to demonstrate the effects of triacetin on the aforementioned debonding and absorbencypropertiesofwoodpulp, and on absorbentcores made therefrom. 30

The absorbentcoreswere generatedusingthe bench scale dry forming system. The bench-scale dry-forming system (BSDFS) is used to produce 12-inch diameter absorbent
cores. This system allows the user to vary the number of layers, amount ofsuperabsorbentpolymer (SAP), pulp type 35 and content,basisweight and density ofthe absorbentcores formed. The BSDFS can be used to produce multi-layered air-laid handsheets and mimics a large-scale air-laid pilot plant. The system comprises of a KAMAS CELLTM to defiberize the pulp, a 100-mesh, 12" forming wire in a 40
vacuum forming head, a SAP dosing system, compaction roll for initial densification of web and a heated press for final densification and bonding. The absorbent cores used herein comprised four layers: a bottom layer of tissue, followedbytwo layersofpulp and SAP, and afinal top layer 45 ofpulp.The tissue utilizedwasTissue Grade 3008, available from Cellu Tissue Corporation ofEast Hartford, Connecticut. The SAPutilized wasinthe form ofparticles soldunder the designation No. 7440, available from Stockhausen GmbH of Krefeld, Germany. 50

Gurley stiffness was measured using 3.5"x1" strips. Radial wicking tests were carried out on 2" circular pads using aGravimetricAbsorbencyTestSystem(GATS) instrument. EXAMPLE 1

Triacetin (available from Eastmann Chemical Co.) was applied to severalpulp sheets ofPulp 1by spraying directly 55

on the sheets (1% oven-dried charge). Pulp sheets thus treated were referred to as Pulp 2. The treated Pulp 2 and 60 non-treated Pulp 1 were combined at different ratios (0, 33%,66% and 100%) to make air-laid absorbent cores. The
cores contained 55% SAP. These coreswere tested to obtain 1 TABLE 1

Corel Pulp 2 (%)/Pulp 1 (%) Stiffness (mg) Suppleness (l/g)

A 01100 983 1.02 B 33/66 954 1.05 C 66/33 768 1.30 0 10010 784 1.28**~** basis weight for each sample was 520 gsm, density 0.3 glee.

TABLE 2

Effect of using various ratios of Pulp 1 and triacetin treated Pulp 2 on

radial wicking properties of absorbent cores (Density"" 0.30 glee)
Average

Amount of 1 % triacetin pulp: 0%, Core A

Maximum Capacity (gig) 20.4 T25 (s) 12.5**T~W** n6 T75 (s) 246.1 Amount of 1 % triacetin pulp: 33%, Core B

Maximum Capacity (gig) 21.1 T25 (s) 14.0**T~W ~.5**  T75 (s) 255.6 Amount of 1 % triacetin pulp: 66%, Core C

Maximum Capacity (gig) 21.6**T~W D~**  T50 (s) 82.8 T75 (s) 240.4 Amount of 1 % triacetin pulp: 100%, Core 0

Maximum Capacity (gig) T25 (s) T50 (s) T75 (s)

EXAMPLE 2 20.4 D.9 81.4 233.3

a stiffness value on a Gurley Precision Electronic Bending A second group ofexperiments involved determining the Resistance Tester. The stiffness value indicates the softness 65 effect ofdensity on softnessofair-laid absorbentcores. Each of the material, with a lower stiffness value indicating a core contained 55% SAP. Air-laid absorbent cores were
more soft material. generatedfrom four differentpulp grades, and tested accord-

## US 6,310,268 Bl 

## 13 ing to the following procedure. Typically, absorbent cores made in the lab have adensity ofapproximately 0.3 glcc. To achieve greater density, a fiat press was used to lower thickness, thereby increasing density. Pressed samples were tested for stiffness. The fiat presswas also used to compress radialwicking samplesfrom the coresto around0.39 glcc to simulate production run densities. As indicated in Table 3, density resultedin an increase in stiffnessfor allthe samples studied. Overall the cores containing triacetin treated pulps had a significantly lower stiffness when compared to the samples ofPulp 1. Itwas also observed that this decrease in stiffness is maintained irrespective of the density.

TABLE 3

Stiffness vs Density
Density Stiffness Suppleness Sample' % Treatment (glcc) (mg) (l/g) Pulp 1 none 0.327 888 1.13 0.375 1043 0.96 0.431 1201 0.83 Pulp 4 none 0.296 496 2.02 0.341 498 2.01 0.356 574 1.74 Pulp 5 0.25% debonder 0.301 522 1.92 0.393 593 1.69 0.42 695 1.44 Pulp 22 3% triacetin 0.293 482 2.07 0.368 552 1.81 0.429 630 1.59**,~** basis weight of 520 gsm**2~** 3% charge of triacetin on oven-dried pulp

EXAMPLE 3 

## 14 densified to adensity of0.18 (g/cc). After spraying aknown quantity oftriacetin (in this case 2.5% based on oven-dried pulp in the core), the core was allowed to sit in a temperature-controlled room for 2 hours.Afterthis, the core 5 was densified to a density of0.3 glcc and the stiffness was measured.

The result from this experiment is shown in Table 5, which illustrates that spraying triacetin directly on an air10 laid absorbent core also results in a reduction in stiffness.

TABLE 5

Effects of Spraying Plasticizer on Formed Absorbent Core

15 Sample Stiffness(mg) Suppleness (l/g)

20 Core made from Pulp 1, no triacetin Core made from Pulp 1 with 2.5% triacetin added to core 888 492

EXAMPLE 5 1.13 2.03

To determine the softeningeffectsofcitrate esters,triethyl
25 citratewas applied to Pulp 1 at a 3% oven-driedcharge. The treated pulp (Pulp 3) was then utilized to generate air-laid absorbent cores. These cores were tested for stiffness according to the procedure described in Example 1. The results (Table 6) show that triethyl citrate (obtained from
30 Morfiex Inc. of Greensboro, Ga.) behaves very similar to triacetin in reducing the stiffness ofthe absorbent core.

TABLE 6 Theeffectofvaryingthe amountoftriacetin appliedto the 35 Effect of Citrate Added to Pulp on Absorbent Core Produced Therefrom pulp was tested by applying varying amounts oftriacetin to Pulp 1 pulp sheets. The amount of triacetin charged on oven-driedpulpwasvariedfrom 0, 1%, 1.5%,2.0,3.0%,5% and 10%.Air-laid absorbent cores were made then made by using these treated pulp sheets. Each core contained 55% SAP. Stiffness ofthese sheets was then tested according to the procedure described in Example 1. Sample' Stiffness(mg) Suppleness (l/g)

Core made from Pulp 1, no triethyl 888 1.13 citrate
40 Core made from Pulp 3, 3% triethyl citrate added to pulp 401 2.49

Core made from Pulp 2, 3.1% 481 2.08 triacetin added to pulp Increasing the amount of triacetin charge resulted in an overall decrease in stiffness. This trend canbe seen in Table**,~** each sample contained 55% SAP, had a basis weight of 520 gsm and a 4, which illustrates that nearly a 50% reduction in stiffness 45 density of 0.3 glcc
was obtained.

TABLE 4

Effects ofAmount ofTriacetin in Pulp on Stiffness ofAbsorbent Core'

% Triacetin Stiffness (mg) Suppleness (l/g)

0 888 1.13 1 785 1.27 1.5 543 1.84 2.0 440 2.27 3.1 481 2.08 5 475 2.11 10 430 2.33**,~** basis weight of 520 gsm and density of 0.30 g/cc

EXAMPLE 4
In this example, triacetin was sprayed directly onto an absorbentcoremadeusingthe BSDFSdescribedpreviously. The absorbent core was made using untreated Pulp 1. Each
corecontained55% SAP, andhadabasisweightof520gsm. The sprayingwithtriacetinwasdone after the core hadbeen EXAMPLE 6

To compare the softening ability of citrate esters to 50 triacetininpulp, the following experimentswereperformed. The citrate esters were obtained from Morfwex, Inc of Greensboro, N.C.

To apply the additive to the pulp, 12-inchsquare sheetsof 55 Pulp 1 at a basis weight of 640 gsm were weighed and a calculatedmassofplasticizerwassprayedevenly across one side ofthe sheet. Each pulp sheet was placed in a separate bag and allowed to sit overnight. Next, Kamas energy was determined for each sample, in order to characterize the
60 amount of energy required to break a sheet.
The results are provided in Table 7 (low charge of plasticizer) and Table 8 (higher charge of plasticizer). All three of the tested plasticizers reduced Kamas energy by
65 about 35% when compared to the untreated Pulp 1, from 60 to 38 Whlkg. The leftover half ofeach pulp sheet from the Kamas energy test was used in the Mullen strength test.

## US 6,310,268 Bl 15

TABLE 7

Plasticizer Kamas Energy Sample (%) (Wh/kg)
Pulp 1 00.0 59.76 Pulp 2 0.27 53.35 Pulp 2 0.52 47.00 Pulp 2 0.74 38.36 Pulp 1 0.00 59.76 Pulp 3 0.26 47.22 Pulp 3 0.55 44.35 Pulp 3 0.74 39.12 Pulp 1 0.00 59.76 Pulp 6 0.27 47.09 Pulp 6 0.48 40.07 Pulp 6 0.71 41.47 Pulp 6 0.99 39.10 Pulp 5, 0.25% 44.48 debonder

TABLE 8

Plasticizer Kamas Energy Sample (%) (Wh/kg) Pulp 1 00.0 59.76 Pulp 2 1.03 39.18 Pulp 2 2.00 38.89 Pulp 2 3.00 35.44 Pulp 1 0.00 59.76 Pulp 3 1.00 39.92 Pulp 3 2.02 36.97 Pulp 3 3.00 34.90 Pulp 1 0.00 59.76 Pulp 6 2.01 36.97 Pulp 6 2.94 36.78 Pulp 5, 0.5% 31.14 debonder

EXAMPLE 7 Mullen Strength (kPa)

1091.73 896.30 832.80 848.20 1091.73 920.60 845.00 840.80 1091.73 909.60 924.70 871.60 907.70

Mullen Strength (kPa)

1091.73 757.17 792.03 706.83 1091.73 834.50 762.43 785.43 1091.73 860.80 825.37 

## 16
to overcome the negative suction force in order to absorb fluid. The positive force results from the capillary pressure of the fiber. As the absorbent material picks up fluid, the positive pressure decreases. A point is reached when the 5 positive force necessaryto counter-balance the suctionforce insufficient. This point is referred to as equilibrium absorbencyandrepresentsthe cessationofabsorption. Thehydrostatic pressure is systematically increased from 3 mm to 45
cm of water, and the equilibrium absorbency at the 40 cm 10 hydrostatic tension value is measured. At a hydrostatic tension value of about 3 mm ofwater, the fiber network is completely saturated with the test fluid. At the hydrostatic tension value of about 40 cm of water the maximum retention is measured. The confiningloadonthe samplewas 15 0.05 psi, to ensure contactbetweenthe sample and test cell. A schematic illustration of an instrument used to obtain measurements for this characterization is described in u.S. Pat. No. 5,916,670. The instrumentcomprises afluid source as well as an adjustable sample compartment. The fluid
20 source comprises aconstant-level fluid reservoirinconjunction with a supply reservoir. The entire fluid reservoir componentisplaced on abalance to allowfor determination ofthe mass ofthe fluid lost or gained by the fluid reservoir. The fluid source is connected via a tube to the adjustable
25 sample compartment. The adjustable single port compartment (available from M-K Systems of Danvers, Mass.) comprises a solid support on which is placed a filter paper (Whatman#5) and a sample ofabsorbentmaterial. The solid support mechanism together with the filter and sample are 30 attached to a device which allows for raising and lowering ofthe sample height relative to the height ofthe fluid in the fluid reservoir. When the level ofthe sample in the sample compartment is the same as the level of the constant level fluid reservoir, there is no hydrostatic pressure head applied
35 to the sample. As the sample level is raised above the level offluid in the constantlevelreservoir, anegative hydrostatic pressure headis appliedto the sample. The magnitude ofthe hydrostaticpressure head is equal to the difference inheight between the sample and the fluid reservoir as measured in The procedure for measuring stiffness and suppleness described in Example 1 was utilized to compare pulps treated in accordance with the present invention to commercially available pulps. Each sample had a basis weight of 320 gsm and contained no SAP. Table 9 illustrates that the
cores made with the plasticizer treated pulps had a significantly lower stiffness when compared to the untreated 45 sample. Also the core made with the debonded pulp had comparable stiffness to the cores made with plasticized pulps. 40 centimeters. Following the procedure described above, the various samplesofabsorptivematerialwereplacedin the instrument and fluid absorption was measured over a range of hydrostaticpressures. Each samplehad abasisweight of320gsm and contained no SAP. The equilibrium absorbency at the highest negative hydrostatic headwasreported as Retention in 

### gig in Table 10.

TABLE 9
Pulp 1 Pulp 5

% Treatment none 0.25% debonder Density (glee) 0.28 0.31 Stiffness (mg) 732 291 Suppleness (g-l) 1.4 3.4

EXAMPLE 8 50 Pulp 2

3% triacetin 0.27 345

2.9 55 The cores made with the debonded pulp had a significantly lower retention when compared to the untreated and plasticized samples. Therefore the cores made with plasticized pulps have a significantly lower stiffness without any negative impact on absorbent properties, unlike the cores made with the debonded pulps.

TABLE 10
Pulp 1 Pulp 5 Pulp 2 Pulp 3

% Treatment None 0.25% 3% 3% Triethyl Various absorptivematerialsofthe presentinventionwere examined to determine their ability to absorb fluids against

a negative hydrostatic pressure gradient, utilizing the following procedure. 60 Density (glee) Retention (gig) 0.17 3.93 Debonder 0.18 1.94 Triacetin Citrate 0.17 0.15 3.56 3.76

Absorbency ofthe sample is measured at negative hydrostatic pressure, i.e., negative hydrostatic head. The negative 65 hydrostatic pressure exerts a suction force on the sample. The absorbent material needs to have enoughpositive force EXAMPLE 9 Wickingpropertiesofthe materialwere measuredusing a GATS system manufactured by M/K Systems of Danvers,

## US 6,310,268 Bl 17 Mass. to determine the valuesfor 45° wicking. The setup of the test is described in detail in U.S. Pat. No. 5,916,670, hereby incorporated by reference. A 45° wicking test cell is attached to the absorption measurementdevice. The test cell essentially consists ofa circular fluid supplyunit for the test sample and 45° ramps. The fluid supply unit has a rectangular trough and liquid level is maintained at the constant height by the measuring unit.

To perform the test, a sample ofthe absorbent material to 5

10 

## 18 than the cores formed using debonded pulps.

TABLE 12
Pulp 1 Pulp 5 Pulp 5 Pulp 2 Pulp 3

% Treatment None 0.25% 0.5% 3% 3% Triethyl Debonder Debonder Triacetin citrate Density 0.18 0.20 0.19 0.20 0.20 (glee) T25 (s) 4.1 7.5 6.3 4.4 3.2 T50 (s) 9.7 17.5 15.7 10.6 10.2 T75 (s) 17.7 29.1 29.0 18.5 18.4

EXAMPLE 11
To compare the use oftriacetin ofthepresentinventionto conventional additives which combine triacetin and cellulose acetate to achieve a different type of material, the following experimentwasperformed.Absorbentcoreswere made using cellulose acetate (CA) and triacetin in combination with Pulp 1. The CAfibers 

### (1'h", 1.8 Denier) were obtained from Eastman Chemical Company. All cores were made at 520 gsmwith55% SAP. The control sample did not contain any CAand triacetin. In Core 1, the fiber make-up be characterized having dimension of 1"x12" wasprepared. The sample was marked every inch along the length of the sample. The sample wasthen placed on the ramp ofthe test cellensuringthat one ofthe edgesofthe sampledipsinto the trough. The test was conducted for thirty minutes, after which time the sample was removed and cut along the 15 marked distances. The cut pieces were placed into preweighed aluminum weighing dishes. The weighing dish, containing wet samples, was weighed again and then ovendried to a constant weight. By conducting a proper mass balance on the data, absorbency of the sample was deter- 20 mined at every inch. For each sample, the amount of fluid absorbed per gram of sample was plotted against distance from the origin (source of fluid). The area under the curve was calculated using the following formula: 25 comprised of 92% Pulp 1 and 8% CAfibers. In Core 2, the fiber make-up comprised of89% Pulp 1, 8% CAfibers and 3% Triacetin. Core 3 was an absorbent core was also made with Pulp 2 (treated with 3% triacetin). The absorbent cores tested were comprised of a tissue layer at the bottom, [(y,)(X2-X,)+0.5(Y2-y,)(X2-X,)+(Y2) (X3-X2 )+ 0.5(Y3-Y2)(X3-X2 )+

... +(Yn) xn-xn _,)+ O.5(Yn-Yn_') (xn-xn _,)], where Xi is distance at the 

### ith inch and Yi is absorbency at the 

### ith inch.

This area was then multiplied by the gravitational constant (981 cm/s2) and the sine of 45° to result in the work value of ergs/g. A higher value for 45° wicking energy indicates greater absorbency. The total amount of liquid absorbedby the strip dividedby the weightofthe strip gives the efficiency in gig.

Each sample had abasisweightof320gsm and contained 30 followed by two layersofpulp and SAPandthen a top layer offluffpulp. In the treated samples, CA and triacetin were added to the bottom two layers. The CAfibers were added through the hammer mill along with the woodpulp. In Core 2, the triacetin was sprayed on to the absorbent core after
35 addition of the CA fibers. The samples so formed were evaluated using the GATS 45° Wicking test procedure described in Example 9.

no SAP. Table 11 shows that the cores made with the debonded pulp had significantly lower wicking properties when compared to the untreated and plasticized samples. 40 Thus the cores made with plasticized pulps have a significantly lower stiffness without any negative impact on 45° wicking, unlike the cores made with the debonded pulps. Table 13 shows that, using CA in combination with triacetin in the formation of an absorbent core results in a negative impact on absorbentproperties. On the other hand, Core 3 madewithjustthe triacetintreatedpulpofthepresent invention, did not show any negative impact on absorbent properties when compared to control sample.

TABLE 11
Pulp 1 Pulp 5 Pulp 5 Pulp 2 Pulp 3

% Treatment None 0.25% 0.5% 3% 3% Debonder Debonder Triacetin Triethyl citrate Density 0.37 0.36 0.36 0.33 0.33 (glee) Efficiency 3.7 1.6 1.56 4.0 3.1 (gig) Energy 67752 35359 31463 65926 42226 (ergs/g)

EXAMPLE 10

GATS Radical Wicking was carried out on the above samples in accordance with the procedure described in Example 1 to determine the rate of absorbency for each sample and to determine whetherthere were any differences between the cores made using the plasticizer treated pulps and debondedpulps. Each sample had abasisweight of320 gsm and contained no SAP. The results are presented in Table 12,which showsthatthe absorbentcoresformedusing plasticizer-treated pulps have a better rate of absorbency 45

50

55 TABLE 13

Core 2 Core 3 Corel (With CA+ (With 3% Control (WithCA) triacetin) triacetin) Density (glee) 0.4 0.4 0.4 0.39 Efficiency (gig) 8.1 7.8 7.5 8.2 Energy (ergs/g) 119095 107365 110000 122000

EXAMPLE 12 Absorbentcoreswere generatedusingthe air-laid process at a pilot facility, and various pulps, treated as indicated in Table 14. The air-laid system consisted of two forming heads. In the first forming head a mixture ofpulp and SAP 60 was added whereas in the second forming head only pulp
was added. After air-laying the pulp and SAPon the carrier layer (comprising of a tissue) the resultant web was heat calendered to achieve the target density. Resultant cores had
a total amount ofSAP of40%, and the target basis weight 65 of the absorbent core and tissue was 400 gsm. Gurley stiffness measurements were carried out on the absorbent cores generatedusingthesepulp samples, follow-

## US 6,310,268 Bl 

## 19 20 dividing the 45° wicking energyvaluesby the percentage of superabsorbent polymer present in the absorbent core. The results in Table 17 illustrate that cores formed from plasticizer-treated pulps have comparable wicking perforing the procedure described in Example 1. The results of Table 14 indicate that use ofplasticizer in treated pulps can result in a substantial decrease in the stiffness ofthe absorbent cores. Similar decreases in stiffness can also be obtained by using pulps treated with debonders. 5 mance to cores formed from untreated pulps.

The 45° wicking energy values were obtained according TABLE 16 to the procedure described in Example 9. The normalized wicking energy values in Table 15 were calculated by dividing the 45° wicking energyvaluesby the percentage of superabsorbent polymer present in the absorbent core. The resultsofTable 15 illustratethatcorescontainingplasticizertreated pulps exhibit a significantly better wicking performance than cores containing debonder-treated pulps. Also, the wicking performance of some of the absorbent cores containing plasticized pulps is comparable to the cores 15 containing untreated pulps. Pulp 10 Sample ID Treatment Basis Weight (gsm) Density (g/ee) Stiffness (mg) Suppleness (l/g)

TABLE 14

Density Stiffness Suppleness Sample ID Pulp Pulp Treatment (glee) (mg) (l/g) Sample A none 0.29 803 1.24 Sample B 4 caustic-treated 0.28 511 1.90 Sample C 2 1 % triacetin 0.32 583 1.72 Sample D 2 3% triacetin 0.30 448 2.23 Sample E 3 1% triethyl citrate 0.30 442 2.26 Sample F 7 1% acetyl triethyl 0.31 390 2.56 citrate Sample G 5 0.25% debonder 0.32 513 1.95

TABLE 15

Normalized 45° Wieking Wicking Pulp Density energy energy Sample ID Pulp Treatment (g/ee) (ergs/g) (ergs/g)
Sample A none 0.29 142614 3565 Sample B 4 Caustic 0.28 112559 2814 treated Sample C 2 1% 0.32 134064 3352 triacetin Sample D 2 3% 0.30 112260 2807 triacetin Sample E 3 1% triethyl 0.30 97518 2438 citrate Sample F 7 1% acetyl 0.31 98728 2469 triethyl citrate Sample G 5 0.25% 0.32 81510 2038 debonder

EXAMPLE 13 Absorbentcoreswere generatedusing the air-laidprocess at a commercial scale machine facility under the following conditions. The air-laid system consisted of three forming heads. In the first two forming heads a mixture ofpulp and SAPwas added whereas in the third forming head onlypulp
was added. After air-laying the pulp and SAP on the carrier layer (comprising of a tissue) the resultant web was heat calendered to achieve the target density. Resultantcoreshad Sample H

Sample I 83% pulp 1 and 17% pulp 4 100% pulp 2 containing 1% triacetin 515

504 0.36 1053 0.95

0.35 625 1.6

20 Sample J 83% pulp 2 538 0.37 660 1.51

25

30

35

40

45 Sample ID Sample H
Sample I

Sample J containing 1% triacetin and 17% pulp 1

Pulp Treatment

83% pulp 1 and 17% pulp 4 100% pulp 2 containing 1 % triacetin 83% pulp 2 containing 1 % triacetin and 17% pulp 1 TABLE 17

Basis Weight (gsm)

515

504

538 Density (glee)

0.36

0.34

0.33

EXAMPLE 14 45° Normalized Wicking Wicking energy energy (ergs/g) (ergs/g)

158356 2879

134773 2450

130044 2364

Absorbentcoreswere generatedusingthe air-laid process at a commercial scale machine facility under the following conditions: The air-laid system consisted of three forming heads. In the first two forming heads a mixture ofpulp and 50 SAPwas added whereas in the third forming head onlypulp
was added. After air-laying the pulp and SAPon the carrier layer (comprising of a tissue) the resultant web was heat calendered to achieve the target density. Resultant cores had
a total amount ofSAP of 30%, and the target basis weight of the absorbent core and tissue was 200 gsm. 55 The results ofTable 18 illustrate that cores formed from plasticizer-treated pulps have comparable wicking performance to cores formed from untreated pulps.

a total amount of SAP of55%, and the target basis weight 60 of the absorbent core and tissue was 500 gsm. TABLE 18

45° Normalized

Gurley stiffness measurements were carried out on the absorbent cores generatedusingthesepulp samples, following the procedure described in Example 1.

The 45° wicking energy values were obtained according to the procedure described in Example 9. The normalized wicking energy values in Table 17 were calculated by Sample ID
65 Sample K Basis Pulp Weight Treatment (gsm)

83% pulp 1 203 and 17% pulp 4 Wicking Wicking Density energy energy (glee) (ergs/g) (ergs/g)

0.30 110046 3668

## US 6,310,268 Bl 

## 21

TABLE 1S-continued

45° Basis Wicking Pulp Weight Density energy Sample ID Treatment (gsm) (glee) (ergs/g) Sample L 100% pulp 2 215 0.31 101229 containing 1% triacetin Sample M 83% pulp 2 211 0.29 106015 containing 1% triacetin and 17% pulp 1 Normalized Wicking energy (ergs/g)

3374

3534 5

10 

## 22 9. The core of claim 8 wherein said citrate IS of the formula

wherein Rl, R2 and R3 are each independently alkyl groups, and

R4 is selected from the group consisting of hydrogen, alkyl groups and _C(O)R5,

wherein R5 is an alkyl group. Allreferencescited arc hereby incorporatedbyreference. 15 10. The core ofclaim 8 wherein said core has a wicking energy greater than about 40,000 ergs/g. The present invention is illustrated by way of the foregoing description and examples. The foregoing description is intended as a non-limiting illustration, since many variations willbecome apparentto those skilled in the art in view thereof. It is intended that all such variations within the 20 11. The core ofclaim 8 wherein said core has a wicking energy greater than about 60,000 ergs/g.

12. 

### An absorbent core comprising: from about 30weight percent to about 90 weight percent

of cellulosic fibers; from about 9.99 weight percent to about 60 weight percent of superabsorbent polymer; from about 0.1 weight percent to about 10 weight percent of at least one non-ionic plasticizer; wherein saidcore has asupplenessofgreaterthan about0.7g-l;
a density offrom about 0.25 g/cc to about 0.5 g/cc and scope and spirit of the appended claims be embraced thereby.

Changes can be made in the composition, operation and arrangement of the method of the present invention described herein without departing from the concept and 25 scope of the invention as defined in the following claims. a basis weight of from about 200 g/m2 to about 550 glm2

. We claim: 

### 1. A wood pulp sheet comprising: from about 90 weight percent to about 99.9 weight 30

percent of cellulosic fibers; and, 13. The core of claim 12 wherein said plasticizer is selected from the group consisting of esters and ethers.

14. The core of claim 13 wherein said ethers are glycol derivatives. from about 0.1 weight percent to about 10 weight

percent of at least one citrate wherein said sheet has a defiberization energy of from

about 35 to about 60 Whlkg. 2. The sheet of claim 1 wherein said citrate is of the formula 15. The core ofclaim 14wherein said glycol derivatives
are selected from the group consisting ofalkyl ethers oflow
35 molecular weight glycols and aryl ethers of low molecular weight glycols.

16. The core ofclaim 13 wherein said esters are selected from the group consisting offormic esters oflow molecular weight glycols, ethanoic esters of low molecular weight 40 glycols, propanoic esters of low molecular weight glycols and citrates.

17. The core of claim 13 wherein said plasticizer is triacetin.

18. The core ofclaim 16 wherein said citrates are ofthe wherein R\ R2 and R3 are each independently alkyl groups, and 45 formula

R4 is selected from the group consisting of hydrogen, alkyl groups and _C(O)R5,

wherein R5 is an alkyl group. 3. 

### An absorbent core comprising from 0.1% to 10% of at 50 least one non-ionic plasticizer.

4. The core ofclaim 3 wherein said plasticizer is a citrate
or triacetin.

5. The core ofclaim 3 having a supplenessofgreater than about 0.7 g-l.

6. The core ofclaim3 having adensity offrom about 0.25 g/cc to about 0.5 g/cc.

7. The coreofclaim3 having abasisweightoffrom about 200 glm2 to about 550 glm2

.

8. 

### An absorbent core comprising: from about 90 weight percent to about 99.9 weight

percent of cellulosic fibers; and, from about 0.1 weightpercent to about 10weightpercent

of at least one citrate wherein said core has a suppleness ofgreater than about 0.7 g-\ a density offrom about 0.25 g/cc to about 0.5 glcc and
a basis weight of from about 200 glm2 to about 550 glm2

. wherein Rl, R2 and R3 are each independently alkyl groups, and
55 R4 is selected from the group consisting of hydrogen, alkyl groups and _C(O)R5,

wherein R5 is an alkyl group. 19.The core ofclaim 12wherein saidcellulosic fibers are derived from at least one type ofpulp sheet.
60 20. The core ofclaim 12wherein saidcellulosic fibers are derived from a mixture of at least two types ofpulp sheets.

21. The core ofclaim 12 wherein said core has a normalized wicking energy greater than about 2,300 ergs/g.

22. A method for manufacturing a softened absorbent
65 material from cellulosic fibers comprising the steps of: a) defiberizing cellulosic fibers to form defiberized cellulosic fibers;

## US 6,310,268 Bl 

## 23 b) blending said defiberized cellulosic fibers with superabsorbent material to form a blended material; c) depositing said blended material onto a carrier layer

under vacuum to form a layered absorbent web; and d) compressing said web to form an absorbent material, 5 wherein an effective softening amount of at least one nonionic plasticizer is added to at least one of said cellulosic fibers, said defiberized cellulosic fibers, said blended material, said web and said absorbent material.

23. The method of claim 22 wherein said absorbent 10 material is an absorbent core. 

## 24 31. The method of claim 29 wherein said citrates are of the formula

wherein 

### R\ R2 and 

### R3 are each independently alkyl groups, and



### R4 is selected from the grow consisting of hydrogen,

alkyl groups and 

### -C(O)R , wherein R5 is an alkyl group. 24. The method of claim 22 wherein said plasticizer is anti-microbial and said softened absorbent wood pulp product is an anti-microbial, softened, absorbent wood pulp product. 32. The method ofclaim 22 wherein said cellulosic fibers 15 are derived from at least one type ofpulp sheet. 33. The method ofclaim 32 wherein said cellulosic fibers
are derived from a mixture of at least two types of pulp sheets. 25. The method of claim 22 wherein said plasticizer is odor-preventing and said softened absorbent wood pulp product is an odor-preventing, softened absorbent wood pulp product.

26. The method of claim 22 wherein said plasticizer is selected from the group consisting of esters and ethers. 34.A method for softening woodpulp sheets comprising 20 the step ofaddingto saidsheets an effective woodpulp sheet softening amount of at least one citrate of the formula
27. The methodofclaim26wherein saidethers are glycol derivatives.

28. The method of claim 27 wherein said glycol derivatives are selected from the group consisting of alkyl ethers 25 of low molecular weight glycols and aryl ethers of low molecular weight glycols.

29. The method of claim 26 wherein said esters are selected from the group consisting of formic esters of low molecular weight glycols, ethanoic esters oflow molecular 30 weight glycols, propanoic esters of low molecular weight glycols and citrates.

30. The method of claim 22 wherein said plasticizer is triacetin. wherein 

### Rl, R2 and 

### R3 are each independently alkyl groups, and



### R4 is selected from the grow consisting of hydrogen,

alkyl groups and 

### -C(O)R , wherein R5 is an alkyl group. 

## * * * * *