Note: Descriptions are shown in the official language in which they were submitted.
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Ihe present invention relates to absorbent articles.
A various assortment of absorbent articles of the disposable type,
such as diapers and sanitary pads, have been proposed which are discarded
after a single use. Several factors are of importance in determining ~ ~ -
whether such articles will be acceptable to the consumer. The articles
should rapidly receive and dissipate body fluids without a significant amount
of backwetting to the wearer's skin, and should be available to the consumer
at a relatively low cost, since they are not reused.
Much of the cost and deficiencies in prior articles may be attributed
to the structure of and the materials used in the articles. In the case of
disposable diapers, structures are often provided having an absorbent pad,
a fluid impervious backing sheet covering a back surface of the pad, and a
fluid pervious top sheet covering a front surface of the pad. Particularly
in the case where the absorbent pads are made of a mass of fibers, such as ;
comminuted wood pulp known in the art as fluff, an absorbent wadding sheet
is often placed over the front surface of the pad to prevent balling and
maintain structural integrity of the pad during use. In addition to adding
to the cost of the diapers, such top wadding sheets impair the function of
the diaper in a number of r0spects. The wadding sheets impede the rapidity
2Q of fluid passage from the top sheet into the pad, and retain fluid adjacent
the front surface of the diaper, thus increasing the amount of backwetting ;~
from the diaper to the infant. The wadding sheet also adds stiffness to
the diaper, thus decreasing the amount of comfort the diaper provides for
the infant. In addition to lacking structural integrity, the fibers in the
fluff pads collapse when wetted and placed under loads, thus decreasing the
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absorbent capacity of the pads.
According to one aspect of the invention an absorbent article of
sufficient pliability for placement against a wearer to capture body fluids
comprises an absorbent pad comprising a mass of fluff fibres and particles
of a thermoplastic material attached by fusion and solidification to fibres
in the pad to increase the integrity and resiliency of the fibrous mass, a
fluid-pervious top sheet covering at least a portion of the front surface
of the pad, and a backing sheet of fluid-impervious material covering at -
least a portion of the back surface of the pad.
The increased structural integrity of the fibrous mass minimizes -~
the possibility of breaking up and balling of the pad during use minimizes
collapsing of fibres when the pad is wetted and placed under loads in use,
and eliminates the necessity for top and bottom wadding sheets for the pad,
thereby permitting rapid passage of fluid into the pad from the fluid-pervious
top sheet, reducing back wetting from the pad, and improving the pliability
and hand of the article so that it is more comfortable to the skin of the -~
wearer.
As indicated above, many of the absorbent pads are currently made
from wood fluff which is normally formed by fiberizing or comminuting pulp
board. The pulp board itself is normally formed from trees through a pulping ;
process. The pulping processes may be categorized as chemical, semichemical,
mechanical, and thermomechanical. All of the wood fluff used in absorbent
articles sold in the United States known to the applicant has been exclusive- `~
ly formed from a chemically produced pulp. For a given species of wood, the
chemical pulping process produces a pulp having fibers with a longer length
than the fibers produced by the other pulping processes, particularly the
mechanical pulping process. Accordingly, the industry has sought chemically
produced pulp for use in disposable pads since the long fibers enhance the
structural integrity and loft of the pad.
In spite of the fact that the chemical pulp results in a pad with ' ;
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desirable characteristics, a number of disadvantages are inherent in the use ~-
of such pulp. First, the chemical pulping process is relatively inefficient
in that the yield of pulp to the amount of wood used in pulping is in the
range of 40 to 55%, whereas the yield of the mechanical and thermomechanical
pulping processes is as high as 90-95%. The disparity in yields between the
processes is due to the removal of lignin, cellulose, and hemicellulose from
the wood during digestion in the chemical procedure. Accordingly, chemically
produced pulps are significantly higher in cost than mechanical and thermo-
mechanical pulps, necessarily resulting in a more costly item to the consumer.
Also, the vital raw materials are not used to the desired extent in chemical
pulps, thus detracting from our natural resources.
Second, environmental considerations favor the use of pulps which
are not produced by the chemical process. In the chemical sulfite process, ~ -
it is relatively difficult to reclaim the cooking chemicals used during
pulping. Hence, the manufacturer must dispose of the chemicals, and it is ;~
believed that more than one sulfite processing plant has been closed due to
contamination of water by the chemicals, which the Environmental Protection
Agency considers dangerous. Although it is less difficult to reclaim the
chemicals used in chemical kraft pulping, this process is characterized by
the emission of gases containing malodorous substances, such as mercaptans
and organic sulfides, and is also repugnant to the community at large.
Third, the energy required to fiberize pulp board solely of the
chemical type is greater than that necessary for a pulp board containing
mechanical or thermomechanical produced pulp. This follows since lignin
of the fibers is removed during chemical pulping, thus increasing hydrogen
bonding between dry fibers of the chemical pulp.
The invention enables short fibres, such as fluffs formed from
mechanical, thermomechanical, or semichemically produced pulps, to be used
in the pad because the plastics material maintains sufficient structural
integrity of the pad.
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The invention also includes methods of making such absorbent
articles. One method includes making the absorbent pad of the article by
a procedure including the steps of forming a mass of wood fluff fibres,
positioning particles of the thermoplastic material in the mass, and heating
and cooling the mass whereby the thermoplastic particles become attached to
fibres in the mass by fusion and solidification. Another method includes
making the absorbent pad by a procedure inciuding the steps of forming a mass
of wood fluff fibres, spraying a thermoplastic material in molten form on
the mass, and permitting the thermoplastic material to solidify as particles
attached to fibres in the mass.
Thus, according to one aspect of the present invention there is ~ :
provided an absorbent article of sufficient pliability for placement against
a wearer to capture body fluids, comprising an absorbent pad comprising a
mass of wood fluff fibres and particles of a thermoplastic material attached
by fusion and solidification to fibres in the pad to increase the integrity
and resiliency of the fibrous mass, a fluid-pervious top sheet covering at `least a portion of the front surface of the pad, and a backing sheet of -~-~
fluid-impervious material covering at least a portion of the back surface
of the pad. `
In the accompanying drawings, which illustrate exemplary embodiments
of the present invention:
Figure 1 is a diagrammatic view illustrating an apparatus for
making an absorbent article according to a method of the present invention;
Figure 2 is a fragmentary front plan view illustrating an article
in the form of a disposable diaper of the present invention;
Figure 3 is a fragmentary sectional view taken along line 3-3 of ~ ~
the diaper of Figure 2; ~ -
Figure 4 is a fragmentary sectional view of another embodiment of
an article of the present invention;
Figure 5 is a fragmentary sectional view of another embodiment of
the article of the present invention; and
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Fig. 6 is a fragmentary sectional view of another embodi-
ment of the article of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although, for convenience, the absorbent article of the
present invention will be described as a disposable diaper, it
will be understood that the description is applicable to other
suitable absorbent articles. For example, other illustrative
articles which may be constructed according to the present inven-
; tion are sanitary pads, maternity napkins, and wound dressings.
10~ Referring now to Fig. 1, there is shown an apparatus,
generally designated 10, for making an absorbent article, such
as a~disposable~diaper, according to a method of the present inven-
tion. The apparatus 10 has a first section 12 which receives pulp
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~ board from a plurality of fee~ rolls 14, and fiberizes the pulp
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board into a mass of fibers termed by the art as comminuted wood
pulp or wood fluff. The types of wood pulp utilized in the feed
rolls~14, or fed lnto the first sectlon 12 by other suitable
means, will be described in greater detail below. The first sec-
~; ~ tion 12 also recelves a supply 16 of heat-sensitive plastic par-
ticles 18, and mixes the particles with fibers in the wood fluff.
The particles of pLastic material may be in any suitable form, such
as powder, fibers, flakes, spheres, or shredded material, and may
be of a thermoplastic material such as polyethylene, polypropylene,
and Vinyon, a trademark of Union Carbide Corp., Charleston, West
Virginia, or particles of a thermosetting plastic which may have a
~ melting temperature less than the temperature which would other-
`,~ wise damage the fluff.
As shown, the first section 12 forms the mlxture of fluff
and plastic particles into a web 20, and passes the web 20 onto an
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endless belt 22 which is supported and driven by a pair of rollers
24 in a direction such that the web 20 is carried from the first
section 12. The web 20 may be cut into lengths by suitable means,
such as a reciprocating knife 26, in order to define pad sections
28.
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The pad sections 28 pass from the belt 22 into a second
section 30 where the pads are heated in order to fuse the plastic
particles to fibers in the pad. The second section may comprise
an oven, a hot air applicator, or other suitable heating device.
~ 10~ After the plastia materials have been melted in the heating sec-
3' tion 30, the pad sections pass between upper and lower endless
belts 32 and 34, respectively, which are respectively supported
and driven by associated pairs of ro~lers 36 and 38. The belts
~ 32 and 34 are driven in a direction such that the pad sections 28
f~ 5 are carried between the belts and are compressed by the belts while
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~ the plastic particles are still hot and are being fused to the
c fibers in the pad sections. In this manner, the plastic particles
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j~ are pressed into the fibers and are fused to the fibers by compres-
'~ ~ sion of the pad sections. However, it is noted at this point, that
~ 20 the pad sections may be heated and compressed simultaneously by
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~ suitable means, such as by heated rolls. Alternatively, the pad
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~ sections need not be comprecsed if the sections are heated to a
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sufficient temperature or the relative percentage of the plastic
materials to the fibrous mass is sufficiently large.
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After compression, the pad sections 28 pass from the
belts 32 and 34 into a third section 40 where final steps in the
formation of the absorbent article take place. For example, in
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the case of a disposable diaper, a backing sheet of fluid impervi-
s ous material may be placed against a back surface of the pad sec-
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tion, a fluid pervious top sheet may be placed against the front
surface of the pad section, the top and backing sheets may be
secured together, and tll~ article or diaper is folded into the
desired configuration, after which the diaper 42 passes from the
third section 40 onto a belt 44 which carries the diapers to suit-
able apparatus for packaging the diapers.
In an alternative form, the thermoplastic particles may
be placed against a surface of the web 20 or pad sections 28 by a
supply 46 of plastic material. The thermoplastic or thermosetting
plastic material may be spread in solid form on the pad sections,
or the plastic material may be placed or sprayed in liquid form
on the pad sections to form the particles, in which case further
heating by the section 30 is not required. It will also be under-
stood that the plastic materials may be placed against either of
the outer surfaces of the pad section, or may be placed against
both outer surfaces by inverting the pad or in another suitable
manner. If desired, a carrier web 48 of tissue, such as a wadding
sheet, may be unwound from a roll 50, and may be placed against
the lower surface of the web 20, as shown, in order to facilitate
movement of the web 20 prior to heating, particularly in the case
where the plastic material i5 placed against the opposed surface
by the supply 46.
According to a method of the present invention, the pad
is made by forming a fibrous mass, po itioning particles of heat-
sensitive plastic material in the mass, and heating the mass tofuse the plastic particles to fibers in the mass. The fibrous mass
may be compressed either during or after the heating step, and the
plastic particles may be mixed with the fibers in the mass, or may
be placed against an outer surface of the mass. Alternatively, the
plastic material may be placed or sprayed on the pad sections in
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liquid form, after which the plastic material is permitted to
harden and fuse particles of plastic material to fibers in the
fibrous mass.
An absorbent article in the form of a disposable diaper
is illuætrated in Figs. 2 and 3 in which different reference
numerals will be utilized for purpose of clarity. The article or
diaper generally designated 60 has an absorbent pad assembly 62
having a backing sheet 64 of fluid impervious material, such as
polyethylene, defining a back surface 66 of the pad assembly 62,
a fluid pervious top or cover sheet 68, such as a nonwoven material,
defining a front surface 70 of the pad assembly 62, and an absorb-
ent pad 72 located intermediate the backing sheet 64 and cover
sheet 68. The pad assembly 62 has a pair of side edges 74, and
, end edges 76 connecting the side edges 74. The absorbent pad 72
; 15 has a front ~urface 78, a back ~urface 80, a pair of side edges
82, and end edges 84 connecting the side edges 82. In a preferred
form, as shown, the side edges 82 of the pad 72 are located adja-
cent the side edges 74 of the pad assembly 62, and the backing
sheet 64 ha~ lateral side margins 86 folded over and secured to
20 ~ the front of the pad assembly and covering lateral side margins
of the absorbent pad 72. The diaper 60 may have suitable tape
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fasteners 88 for use in securing the diaper about an infant.
As previou~ly discussed, the absorbent pad 72 is made
~from a mass of fibers 90, and has particles 9-2 of heat-sensitive
plastic material fused to the fibers 90 in the fibrous mass of the
absorbent pad 72. In the embodiment shown, the plastic particles
92 extend substantially throughout the pad, and are dispersed
between the side and end edges 82 and 84, respectively, of the pad
72, and between the opposed front and back surfaces 78 and 80,
respectively, of the pad 72. As ~hown, the particles 92 are spaced
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throughout the pad in order to permit passage of fluid into the pàd.
The fused plastic particles hold the pad fibers together
and maintain the structural integrity of the pad without the neces-
sity of top and back wadding sheets, and may be used with the same
results to maintain structural integrity of fluffs formed from
pulps other than chemical pulp. Accordingly, the cost of the pad
72 and diaper is reduced, since the top and back wadding sheets
have been eliminated, and the non-chemical fluffs may be obtained
.
; at a significantly reduced cost In addition, elimination of the
top wadding sheet permits a more rapid passage of fluid from the~
;~ i top~sheet into the pad, and reduces back wetting from the pad which
is normally caused by the presence of the top wadding sheet. Fur-
ther, the article is pliab}e and has a better hand due to elimina-
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tion of the top wadding sheet, thus ~roviding additional comfort to
~lS ~ the~skin of the wear-x. In addltion to adding structural integrity
to~the pad 72, the~fused plastic particles 92 also increase the
resiliency of the pad when wetted and placed under loads during use.
In the past~ the fibers in the usual chemical fluff collapse when
; wetted and placed under loads, thus reducing the interfiber spac-
2~0 ~`ings of the fluff~and the absorbent capacity of the pad. In con-
t~rast,~the fused particles 92 provide the pads 72 with resiliency,
and increase the bulk and absorbent capacity during use.
:~ ~ As indicated above, the fused plastic particles 92 may
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~ be used to maintain the structural integrity of the pad even when
`~ 25~ formed from a non-chemical fluff having relatively short fiber
is will be discussed below, the pad 72 may be formed from a single
~ type of such lower cost pulps, or the fibers from various pulps
!~ may be mixed into the pad.
-~ ~ As a baGkground, the various pulping processes are
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discussed as follows. Pulping itself may be defined for the pres-
ent purposes as a procedure for rupturing the fibers of wood. The
resulting pulp may be ~sed ~or making paper or in this case absorb-
ent pads. The separated fibers of the pulp are normally formed
S into pulp board which may be wound into the feed rolls for conveni-
ence of handling during shipment and by the user. As discussed
above, the rolls are fiberized or comminuted by the user to form
the loosely formed fibrous mass which is cut into lengths as
absorbent pads for the disposable articles.
10 Wood itself i8 primarily composed of cellulose, hemi-
cellulose, and lignin. Lignin is an amorphous polymer of rela-
tively high molecular weight that serves to hold the fibers of
wood together. Cellulose i8 highly hydrophilic, while lignin has
a significantly reduced affinity for liquid than cellulose and is 15 re~Iatively hydrophobic. Since pulping is concerned with ruptur-
ing the bonds between the wood fibers, the middle lamella between
the~fibers, which is composed mostly of lignin, must be ruptured
~; ~ during the procedure.
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Wood logs are transported to the processor, after which
bark from the logs may~be removed. Generally, the logs are ground
; into chips, and the chips are used in the pulping procedure to
~`separate fibers in the chips. The fibers are then washed to pro-
duce the unbleached pulp, after which the pulp may be bleached to
a lighter color pulp. The process differs primarily in the manner
the wood is pulped.
The pulping procedures may be categorized as mechanical,
chemical, semichemical and thermomechanical. In mechanical pulp-
ing, the logs themselves may be ground by a roughened stone to
grind fibers out of the wood. Altern~tively, wood chips may be
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shredded or ground between metaI shearing discs in a machine
called a refiner. The mechanical pulps produced in this manner
are characterized by relatively short fibers due to damage of the
fibers during the procedure. Such groundwood processes are rela-
tively efficient in that approximately 95% of the dry weight ofthe wood is converted into pulp, since materials, such as lignin,
are not specially removed from the pulp.
In chemical pulping, the wood chips are cooked in a
vessel or digester with chemical reagents to separate the fibers,
termed a digesting procedure. During digesting, the pulping
reagents degrade and dissolve the lignin to break the bond
between the fibers in order that they may be separated. However,
the reagent~ also degrade some of the cellulose and hemicellu-
lose, and the loss of these materials, including lignin, accounts
~ for the relative inefficiency of chemical pulping. Thus, the yield
from chemical pulping may range from 40 to 50% of the weight of
the wood, with a maximum yield of 55~. Accordingly, ahemically
produced pulp8 are significantly higher in cost than mechanical
~ and thermomechanical pulps, the yield of the latter also believed
; 20 to approach 95~, not to mention the 1088 of valuable materials
during chemical pulping.
The chemically produced pulp is characterized by rela-
tively long fiber~ which are mostly completely separated. As
noted above, the lignin is removed, and the hydrophilic fibers
thus produced are susceptible to increased wetting.
The two most common chemical procedures are the sulfite
and kraft processes. In the sulfite procedure, an acidic mixture
is used as the reagent which is relatively difficult to reclaim,
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thus posing a risk to the environment when disposed by the pro-
cessor. In the kraft or ~ulfate process, the chips are cooked
in a solution of sodium hydroxide, sodium carbonate and sodium
sulfide. This process results in the emission of gases contain-
ing malodorous substances, and is also repugnant to the environ-
ment.
In the semichemical process, such as the neutral-sulfite
process, the wood chips or logs are softened with a chemical,
after which the wood is fiberized mechanically, frequently in disc
refiners. The yield of the semichemical process i8 also higher
than that of the chemical process.
Finally, in the thermomechanical procedure, wood chips
are steamed at an elevated temperature and pressure to soften the
lignin. Thus, the binding force between the fibers is greatly
lessened through~ application of heat to permit separation of the
fibers. The fibers may be separated by a refiner under pressure
or pressure changes.
For convenience, the fibrous mass formed from a mechanic-
; ally produced pulp will be termed a mechanical fluff, the fibrous
mass formed from a thermomechanically produced pulp will be termeda thermomechanical fluff, the fibrous mass formed from a semichem-
ically produced pulp will be termed a semichemical fluff, while
the fibrous mass formed from a chemicallv produced pulp will be
termed a chemical fluff. The average fiber length of the mechani-
f
cal fluff i~ less than that of the thermomechanical fluff, theaverage fiber length of the thermomechanical fluff is less than
that of the semichemical fluff, while the average fiber length of
the semichemical fluff is less than that of the chemical fluff.
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Thus, under normal conditions the structural integrity and loft
of the chemical fluff is ~reater than that of the other fluffs and
accounts for the widespread use of chemical fluff. However, rela-
tive chemical fluffs, the fibers in the mechanical, thermomechani-
cal, and semichemical fluffs contain a greater portion of theirnatural }ignin, and the wet resilience of the fibers in the non-
chemical fluffs is greater than that of the chemical fluff, thus
providing the non-chemical fluffs with greater resiliency and
fluid holding capacity when wetted and placed under loads.
In accordance with the present invention, the mechanical,
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thermomechanical, and semichemical fluffs may be used in the pad
72 with the~fused plastic particles 92 providing the desired struc-
tural integrity of the pad, in spite that the fibers of the non-
i~ chemical fluffs have an average fiber length less than that of the
usual chemical fluff. The pad may be made solely of mechanicalfluff, thermomechanical fluff, or semichemical fluff, or may com-
prise a mixture of the non-chemical fluffs, a mixture of the non-
chemical fluffs and a chemical fluff, or, if desired, solely from
the more costly chemical fluff. Accordingly, due to higher pulp
yields, the mechanical, thermomechanical, and semichemical fluffs
are lessicost}y than the usual chemical fluff, and to the extent
that the mechanical, thermomechanical, or semichemical fluffs are
used in the pad, the cost of the pad and diaper is reduced.
Another embodiment of the article or diaper 60 of the
present invention is illustrated in Fig. 4, in which like refer-
ence numerals designate like parts. In this embodiment, the
plastic particles 92 are placed on the front surface 78 of the pad
72, and are fused to the pad at this location. Accordingly, the
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particles 92 maintain the structural integrity of the pad adja-
cent the front surface in a manner as previously described. If
desired, a back wadding sheet 94 may be placed against the back
surface 80 of the pad 72.
Another embodiment of the invention is illustrated in
Fig. 5, in which like-reference numerals designate like parts.
In this embodiment, the particles 92 of plastic material are placed
on the back surface 80 of the pad 72 and are fused into place adja-
cent the lower part of the pad. Thus, the fused particles 92 main-
~ 10 ~ tain the structural integrity of the lower portion of the pad. If
;~ ~ desired, the pad 72 may have a top wadding sheet 96 covering the
~ front surface 78 of the pad 72.
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~ Another embodiment of the present invention is illus-
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' trated in Fig. 6, in which like reference numerals designate like" ~
~ 15 parts. In this embodiment, the par*icles 92 of plastic material
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are placed on both the front and back surfaces 78 and 80, respec-
tiveIy, of the ab~orbent pad 72. $he particles 92 are fused to
the pad fibers in a manner as previously described, and maintain
the structural integrity of the ~ront and back portions of the
absorbent pad 72.
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The foregoing detailed description is given for clear-
ness of understanding only, and no unnecessary limitations should
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be understood therefrom, as modifications will be obvious to those
skilled in the art.
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