CA1156001A

CA1156001A - Absorbent structure

Info

Publication number: CA1156001A
Application number: CA000321921A
Authority: CA
Inventors: Yvon G. Levesque
Original assignee: Johnson and Johnson Inc
Current assignee: Johnson and Johnson Inc
Priority date: 1978-02-21
Filing date: 1979-02-20
Publication date: 1983-11-01
Also published as: NL7901380A; BR7901132A; JPS6159733B2; AU4435779A; IN149759B; SE444263B; ATA131579A; GB2015055B; IE790535L; IE47927B1; FR2423171B1; NL191555B; IT7948058A0; IT1114992B; FR2423171A1; LU80953A1; AU528358B2; ZA79789B; SE7901488L; BE874353A

Abstract

Abstract An absorbent structure is provided comprising peat moss in combination with mechanical wood pulp, said wood pulp having a Canadian Standard Freeness of from about 30-600 and present in the ratios, by weight of wood pulp to peat moss, of greater than about 0.35.
The absorbent structure, which may also contain other absorbent materials such as long-fibered chemical wood pulp, rayon or the like, exhibits improved absorbent properties in both liquid-holding capacity and liquid-, retention capacity and maintains its structural integrity.

Description

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The present invention relates to absorbent products and more particularly to an improv~d absorbent structure for use in diapers, sanitary napkins and the like.
Background of the Art Many disposable products such as diapers, sani-tary napkins, some tampons and some absorbent dressings contain a layer or core of highly absorbent material~
which is wrapped or contained by other relatively less absorbent materials. In some instances, such as in a diaper, the absorbent Layer may be contained, at least on one of its surfaces, by an impervious film material.
For example, a diaper may comprise a pervious upper layer, a highly absorptive center layer, and an impervious bottom layer. A sanitary napkin usually comprises a highly absorptive layer wrapped in a pervious layer.
The absorptive layers used in disposable products usually comprise a plurality of layers of creped paper tissue or, in some instances, chemical wood pulp fibers in a fluffed or a looso, lightly compacted configuration.

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For many years peat moss has been known as possessin~ good water-absorbing characteristic~ but~ to date, has not been successfully incorporated as a primary ingredient in a structure suitable for use in diapers, sanitary napkins or dressings. It is believed the reason for this may be the intrinsic, extremely dark color of peat moss, the inability to handle peat moss and place it in a suitable configuration for wrappin~, or perhaps a combination of these undesirable characteristics.
Summary of the Invention What I have discovered is a new and improved absorbent structure or core product. My new product may be handled and utilized as an absorbent core in diapers, napkins absorbent dressings and the like. By incorporating the teachings of this invention, I have found that, unexpectedly, my new product exhibits improved liquid-retentive properties and is capable of maintaining its structural integrity.
The new product comprises peat moss, in combination with finely divided mechanical wood pulp having a Canadian Standard Freeness of from about 30 to 600 and present in ratios, by weight of said wood pulp to peat moss of greater than about 0.35. The term "mechanical wood pulpi' is meant to encompass those wood pulps which have been reduced to a finely divided state from the trunk and branches of trees after removal of bark and dirt but without any prior~ chemical treatment. Included in such materials are the groundwood pulps, refiner pulps and thermo mechanical pulps.
The peat moss may be bleached to improve its white-ness and may be bleached to a whiteness of at least about 70 as measured on the Hunter L~ninus Refleckive Scale. As ~uch, lt will still maintain ik~ raw p~at porous structure~ i.e., kh~re is still a por-kion of humic acids and lignin-like constltuen-t~ remaining in the bleached peat moss to maintain lts open, porous, leaf-like structure~ This open structure is believed -to he the major fac-tor in producing khe hi~hly de~irable, absorbent properkies exhibiked by thi~ peat moss.

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Unortunatel~, peat moss in this open, porous condition is quite brittle and does not, by itse.l, withstan~ the kind of handling absorbent products such as dLapers, napkins, tampons and the like are subject ko. Still further, the particles of peat moss are not self-entangliny~ such as are lon~-Eibered absorbent material, or sel~-adherent.
In short, the peat moss, per se, has been ~ound to be difficult to handle and incapable of being formed 1nto a self-sustaining form having any structural integrity.
It has now been discovered that those short-comings of the peat moss described herein can be overcome and that an absorbent structure having both surprisingly good absorbent properties as well as structural integrity can be provided by including, in admixture ~ith the peat moss, relatively fine mechanical wood pulp having a Canadian Standard Freeness (hereinafter, CSF) of ~rom about 30-600. Such wood pulp, which may be selected Erom pulps such as ~roundwood pulp, refiner wood pulp and/or thermomechanical wood pulp, generally have shorter fiber leng~hs than the chemical pulps, e.g., the sul~it:e or su~fate pulps usually associated with diapers~.napkins and tampon products. The fine mechanical wood pulps are generally characterized by their drainage and compacting characteristics which are measured by "freeness"; i.e., Canadian Standard Freeness as measured by TAPPI Test Method T-227. It has been discovered that the structural integrity of pulp ~luff that has bee~ made by grinding.
board formed ~rom an aqueou~ ~lurry of a mix~ure ~f peat moss and the herein prescribed ~inely divided mechanical wood pulp i5 extremely sensitive to the rati.o by weight,of the wood pulp to the peat moss. Spaci~iJ
cally, the mix~ure 105eS essentiall~ all i~5 cohesive-ne~s at such ratios below 0.35~ Pre~erably such ratio should ba maintained above 0.38.
3S 1'he mix~ura o~ pea~ moss and meahaniaal wood ~uLp ~ay be suppl~mented wi~h o~he~ ahsorbent In~erial~ suc~
~8 the more commonly u~ed long-~ibered wovd pulps su~h a~
~ul~ite or ~ul~a~e pulp QX rayon ~ibers or mix~ur~ o~
~e~e~ In ~oxming products ~ro~ the absorbent ~txuature o~ this inven~ion, a core v~ the prescribed material may ~e , 1 ~ S6~0 ~

wrapped about its entire periphery with a pervious layer such as a non-woven fabric, as for example in a sanita.ry napkin. Alternatively, the core may be interspersed between a pervious layer such as a non-woven fabric and an impervious layer such as thermoplastic film as in a disposable diaper.
According to a further broad aspect of the present invention -there is provided an absorbent product comprising peat moss and mechanical wood pulp~ The wood pulp has a Canadian Standard Freeness of from about 30-600, and present in a ratio, by weight of the mechanical wood pulp to the peat moss, of more than about 0.35.
Brief Description of the Drawinas The present invention will be more fully described when taken in conjunction with the accompanying drawings wherein:
Figure 1 is a perspective view of a new, improved absorbent product of the present invention.
Figure 2 is a photomicrograph at an original en~argement of 160 times of a new and improved absorbe.nt product of the present invention, Figure 3 is a photomicrograph at an original enlargement of 160 times of the bleached peat moss used .in the absorbent products of the present invention, Figure 4 is a perspective view, with a portion cuk away, of a disposable diaper incorporating the absorbent product of the present invention;
Figure 5 is a perspective view, with a portion cut away, of a sani-tary napkin incorporating the absorbent product of the present invention' F'igure 6 is a perspective view of a tampon, with a pQrtiorl cut away, which incorpora-ted the absorberlt product o~ the preSQnt invention, and Figure 7 i9 a graphical presentation of data showin~ -the rela-tion~hip of the ratiol by weigh~ of mechanical wood puLp to p~at mos~, to the structuraL
integrity of the resultin~ struct-lre.

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Detailed De~cription of the Drawlnqs Figures 1 and 2 show the new and improved absor-bent product or core 10 of the present invention. This core 10 comprises bleached peat moss 12 having a whiteness of at least about 70, as measured on the Hunter Luminus Reflective Scale, combinecl with finely-ground mechanical wood pulp 14 having a Canadian Standard Freeness of from about 30-600 and present in the ratios, by weight of wood pulp to peat moss, of at least about 0.35. Preferably, this ratio is at least about 0.4 and still more preferably at least about 0.5. Also included in the core 10 are other absorbent materials such as long-fibered chemical wood pulp 16 and long-fibered rayon.
The peat moss 12, as can be seen more clo~ely in the photomicrograph of Figure 3, has a leaf-like structure with open pores 18 and maintains this structure in the absorbent core 10. The bleached peat moss 12 has a degree of whiteness of at least about 70, when measured on the Hunter Color and Color Difference Scale, as set forth by ASTM D-2244 Color Scale System "C" method.
I prefer to start with peat moss (sphagnum~ which will hold at least 15 and preferabLy 20 times its weight of water. I screen the peat moss between 10 and 100 rnesh screens. The material that stays on a 10 mesh screen, primarily roots and branches, is discarded~ The matqrial that passes through a 100 mesh screen, namely, fines, which add little to absorbency and are difficult to bleach, is also discarded. Hence, my startiny peat mo~ is from about .15 mm (100 mesh) to 1~8 mm (10 rnesh).
The peat moss is bleached by treatment with both chlorine and calcium in the form of lime stone. The bleaching may be carried out as a batch operation; that is, where the peat moss i.~ dilute:d with water to a con~qntra-tion of about 2% by wei~ht, treatecl with chlorine, Eollowed by a calcium carbonatq treatmqn-t, eollowed by acid washe~
and wa ter washes to provicle the de~lred decJree Oe whitqne99~

0'~ 1 The bleached peat moss is dried to a degree where it can ~e handled and ~ay actually be fonmed into a board or sheet-type layer if desired. When formed into a board, it is preferred tha~ it be foxmed along with the finely-ground mechanical wood pulp 14 and optimally the long-fibered wood pulp 16, and then this admixture further dried together into the finished board. In producing the absorbent core, the peat moss and mechanical wood pulp are ground by standard wood pul~p grinding operations, such as a ham~er mill, and laid down on a carrier sheet, which may be the wrapping sheet or a piece of tissue, in the desired amounts as is well known in the art.
The finely-ground mechanica} wood pulp may be selected from the group consisting of groundwoodpulpr th~r~
mechanical pulp and xefiner wood pulp. Groundwood pulp is essentially trees and branches which have been debarked, cleaned and then ground into particle mat~er. Refiner wood pulp differs from groundwood pulp only in that the grinding step utilizes a refiner, i.e9, a disk-like device well known in the art and generally hav~ng metalic ribs at the peripheral-sections thereof which last contact the wood particles and help to separate the wood Eibers without excessively damaging them. Thermomechanical wood pulp is similar to re~iner pulp with the exception that the wood particles are heated when in the refiners, usually with steam, and this heating further aids in separating the wood ~ibers~ ~he common characteristic o~ these mechanical pulps ~s ~hat no attempt has be~ made to ~epa~ate the ~ibers by chemic~l me~n~ al~hou~
they m~y l~ r, a~ter being reduced to ~ine partlculate ma~t~r, ~e subjec~ed ~o c~emical -~reatment, e.~, bleaching.

1 ~560'0 1 These mechanical pulps are commonly characterized by the term "freeness," which is measured by the Canadian Standard Freeness Test (TAPPI Test Method T-227). This test essentially measures the rate of drainage of pulp andr in e~fect, the degree of compac~ness. The preferred Canadian Standard Freeness value for the mechanical wood pulp materials incorporated in the absorbent cores of this in~ention should vary between about 30-600 and preferably from about 60-300.
The long-fibered wood pulp may comprise approximately 5-20% by weight of the total weight o the core and may be chosen from such chemically treated or formed wood pulp as sulphite and sulphate wood pulp.
It is preferxed that the wood pulp selected be chosen from soft wood materials, although hard wood fibers may also be used. The term "long-fibered wood pulp" is meant to describe pulps having at least 40% by weight, made up of fibers of a length of 1/16" or more, and preferably, about 50% by weight of the wood pulp consisting of fibers of at least 1/16" in length.

1 ~6~0 1 In Figure 4, there is shown a disposable diaper 20 which incorporates the new and improved absorbent core of the present invention. The diaper comprises a backing 21 which may be a thermoplastic, fluid impervious, film material. The diaper also comprises a facing ~2 Layer which is a material pervious to fluids and may be a non-woven fabric of any of the standard types such as the spunbond products, the spunlaced products, standard carded non-woven fabrics, or in some instances, aven pervious film materials may be used. Disposed between the ~acing layer and backing layer, and slightly smaller than the layers, is the new and improved absorbent core 23 of the present invention.
In Figure 5, there is shown a sanitary napkin 24 which incorporates the absorbent core of the present invention. In this construction the napkin may comprise a center barrier sheet 25 which may be a thermoplastic ~ilm. On each side of this center sheet is an absorbent core product which in this instance is ~he absorbent core 26 of the present invention. The three-piece laminate is wrapped about its entire periphery with a suitable pervious material 27 such as the standard non-woven fabrics. The wrapping extends beyond the ends o~
the absorbent core product to form tabs 28 for attaching ~he napkin.
In Figure 6 there is shown a tampon 29 which incorporates in its centex ~he ab orbent core product 30 o~ the presen~ inven~ion~ The absorbent core i~ wrappqd about i~ entire periphexy with ~ui~able pervious wrapping materlal 31 such a~ the s~andard non-woven ~abxics.
The invention will be ~ur~her described i.n conjunc~ion with the PolLowing examples. In each 0 1 ~800 1 these examples the absorbent has been;tr~ated so as to include a wetting agent in quantities of less than 0.5 by weigh~ of dry absorbent. The wetting agent used i8 a sodium dioctyl sulfo succinate containing age~t manu-factured by the Rohm & Haas Company and sold by themunder the tradename Triton GR-5.
EXAMPLE I
Approximately 28 pounds of raw peat moss is classified using a Sweco classifier. The wet classifica-tion re~oves the fines; that is, materials less than 100 mesh or smaller than lS0 microns in diameter. The classi-Eication also removes the large pieces o material; that is, materials larger ~han 10 mesh, which are the roots, etc. The 10 to 100 mesh fraction is bleached by reac~tion with 21 pound~ of calcium carbonate and 18.9 pounds oP
chlorine. The bleached peat is dewatered to remov~ liquid from a 1% solids dispersion tQ-a 5% solids dispersion.
The peat is washed with tap water back to a consistency of 1% solids and dewatered again to 5% solids. The peat is placed in a tank and brought to 1~ co~sistency with water and 10 pounds of 22 Baume' hydrochloric acid. The resultant bleached peat moss has a whiteness of about 72 on the Hunter scale as pre~iously described.
The 1% bleached peat moss is held in a tank~
About 26 1/4 pounds of groundwood pulp and 5 1/4 pound~
o~ hleached ~raft woodpulp are di~persed in water to a

2~ solids consistency. Thi~ wood pulp mixture and the acidi~ied bleached peat are mixed together to form a misture of 0.~% solids consis~ency and containing 21 pounds bleached peat, ~6 1/4 pounds groundwood pulp and 5 1/4 pounds of long-fibered wood pulp. The mixture is beaten With a minox amount of agita~ion or shear so as no~ to ab~ade ~ha peat moss leaP, and the mixture Plowed onto a Fc~urdrlnier wire wi~h vacU~ ~o dewa~er the mixture and ~orm a board. rr~e board i~ Eorcqd air dri~d at about ' 350F and rollqd up. rrhe board is grc~und by convqn~iunal equipm~n-k in a Hamm~r mill to produce a ~lu~ed,ab~orban-t co~e produc~.

lo 1 ~ 5~0~ 1 As previously men-tioned, the resultant improved absorbent product has improved capillarity compared to chemical wood pulps or groundwood pulps per se. Furthermore, our new product has improved liquid retention properties, that is, holding of absorbed liquids under increased pressure, than either the groundwood pu}ps or the chemically formed wood pulps when used alone.

A plura~ity of absorbent core products are }O made by mixing and grinding togethe~ various combinations of chemical, long fibered, wood pulps; groundwood pulp;
unbleached peat moss; and bleached peat moss. The absorbent core products are ormed and measured or Liquîd Uptake, Liquid Retention After Saturationr and Liquid Retention Under Pressure as described in the ~ollowing test methods.
Li~uid Uptake Test Method A 7.7 cm. di~neter piece of the absorbent core`
to be tested is placed on top o~ a fritted glass filtar plate and pressed with a con~ining pressure of 2.5 grams/
per cm. . The underside of the fritted glass plate is in contact with liquid in the form of a column o~ liquid extending 40 centimeters below the porous plate.
The column of liquid is in a calibrated burette and the volume amount absorbed is me~sured a~ter a five-minute pexiod, and a one-da~ ~eriod (reachinq essentiall~ equilib-rium). The column is moved ~pwards to within 7 1/2 centimeters below the porous plate and allowed to come to equilibrium and the volume amount ahsorbed measured.
The column is moved to within 1 centimeter o~ the porous plate and again allowe~ to come to equilibrium and the volume amount absorbed measured.
Liquid Retention After Saturation Test Method The same piace o~ absorbent core used in the Llquid Uptake ~est is ~ully s~turated ~nd the column m~ved back to 1 centimetQr below t~e core leval and a volum~
me~u~emen-~ taken, and then movqd back to 4~ centirnetexs below t~e ooXe level and a volume measureme~k ~aken~
~hi~ ~esk determin~s ~he amoun~ o~ Uld ~etained a~te~
sakuration.

1 ~L5~0 1 ~gLui.d Retention Under Pressure Tes-t Method Using another apparatus, a piece of absorbent core i5 placed on top of perforated steel plate and fully saturated with liquid. The volume amount of saturation S is measured with no pressure on top of the absorbent core, with a pressure of 20 grams per square centimeter on top o~ the core, and with a pressure o~ 105 grams per square centimeter on top of the absorbent core.
As previously mentioned, a number of cores having the composition as shown across the top o~ the ~ollowing table I were measured for varlous absorptive properties as shown along the lefthand side o~ the table.

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1 15~001 -A series of fluff material is prepared by grinding, into fluf, board formed from slurries of mixtures of peat moss, mechanical pulp (ground wood) and chemical pulp. The composition of each of the samples is shown in Table II
below. The samples are tested for their structural inte-grity by placing a 5 gram sample in the pan of a RoTap*
Testing Sieve Shaker equipped with a 10 mesh Tyler screen.
This apparatus is manufactured by W. F. Tyler Inc., a L0 subsidiary of Combustion Engineering Inc. of Ohio, U.S.A.
The pan of the Roq'ap* Shaker, which measures 8 inches in diameter, is filled to a depth of 2 inches. The RoTap*
Sieve Shaker is operated for 25 cycles, and the quantity of material passing through the Tyler screen during opera-tion is collected, weighed and reported, on a weight percent based on the original 5 gram sample, as Losses in Table II
below. Figure 7 is a graphical representation of the data in Table II, showing the relationship between the ratio, by weight of the finely-ground wood pulp to the peat moss, and the structural integrity of the resulting structure as manifested by percent Loss through the scr2en.

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As Table II and Figure 7 illustrate, the losses and, hence, the structural integrity of the flu~f is greatly dependant upon the ratio o~ mechanical wood pulp tu peat moss. At ratios of essentially zero, extremely large losses result var~ing from about 40-100~. Such losses would be intolerable in absorbent products such as diapers, napkins and ta~pons. If material exhibiting such lossas were incorporated in such products~ a great quantity of the peat moss would separate from the remainder of the absorbent material and dust out o~ the product, Additionally~ the o~f-color of the peat moss would become evident to the user, The separated peat moss would be ~urther broken down owing to it~ brittleness and would lose its e~fectiveness a~
an absorbent material. Tolerable losses are encountered only when the ratios of mechanical wood pulp approach the value of about 0.35 and pre~erably around 0.4.
At the very high ratios, it can be seen that the losses, are reduced to negligible levels.

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An absorbent product comprising peat moss and mechanical wood pulp, said wood pulp having a Canadian Standard Freeness of from about 30-600, and present in a ratio, by weight of said mechanical pulp to said peat moss, of more than about 0.35.

2. The absorbent product of Claim 1 wherein said peat moss has a color intensity of at least 70 on the Hunter Color Scale System "C".

3. The absorbent product of Claim 1 wherein said mechanical wood pulp is present in a ratio, by weight of said mechanical wood pulp to peat moss, of more than about 0.38.

4. The absorbent product of Claim 1 wherein said mechanical wood pulp is refiner wood pulp.

5. The absorbent product of Claim 1 wherein said mechanical wood pulp is thermomechahical wood pulp.

6. The absorbent product of Claim 1 further comprising long-fibered absorbent material.

7. The absorbent product of Claim 6 wherein said long-fibered material is chemical wood pulp.

8. The absorbent product of Claim 6 wherein said long-fibered absorbent material is rayon.

9. The absorbent product of Claim 1 wherein said peat moss has a particle size distribution range of from 10-100 mesh.

10. The absorbent product of Claim 1 wherein said finely-ground wood pulp has a Canadian Standard Freeness of from about 60-300.

11. A disposable diaper comprising an impervious backing sheet, a pervious facing sheet and an absorbent core smaller than said sheets and disposed therebetween.
said absorbent core comprising peat moss and mechanical wood pulp, said wood pulp having a Canadian Standard Freeness of from about 30-600 and present in a ratio, by weight of said mechanical wood pulp to said peat moss, of more than about 0.35.

12. A sanitary napkin comprising an absorbent core having a fluid-pervious cover overlying at least one surface of said core, said absorbent core comprising peat moss and mechanical wood pulp, said mechanical wood pulp having a Canadian Standard Freeness of from about 30-600 and present in a ratio, by weight of said wood pulp to said peat moss, of more. than about 0.35

13. A catamenial tampon comprising an absorbent core and a fluid-pervious cover enveloping said core, said absorbent core comprising peat moss and mechanical wood pulp, said wood pulp having a Canadian Standard Freeness of from about 30-600 and present in a ratio, by weight of said wood pulp to said peat moss, of more than about 0.35.