Note: Descriptions are shown in the official language in which they were submitted.
3 1~51~}Z~
Background of the Invention:
Synthetic polymeric fibers that have physical
and morphological characteristics generally similar to
wood pulp ~ibers produced from natural woods have been
known for approximately 10 years. Examples of such
fibers are the synthetic wood pulp fibers formed of
polyethylene that are sold by Crown Zellerbach under the
trademark SWP.
Various methods of making synthetic wood pulp
fibers are known, including (1) solution polymerization
accompanied by stirring, (2) dissolving a preform~d
polymer and subjecting the solution to an anti-solvent,
or (3) forming the polymer at the interface between
,~
'':''
1~5~1
-2- JBP 88
liquid layers, with localized stirring provided to pull
the polymeric material thus produced into fibrillated
forms. Examples of methods of producing synthetic wood
pulp fibers are disclosed in U.S. Patent Nos. 2,999,788;
2,708,617; 2,798,283; 3,560,318; 3,081,519, 3,003,912;
3,068,527; and 3,290,207; South African Patent 697,431;
United Kingdom 1,102,342; and Netherlands Patent Appli-
cation A132/48-7313178.
As used in this specification and the appended
claims, the term "synthetic wood pulp fibers" means
synthetic, water dispersible, thermoplastic, elongated,
supple, randomly bent, polymeric fibers or fibrils
generally similar in size and shape to conventional wood
pulp fibers produced from naturally occurring woods.
Each such "synthetic wood pulp fiber" is of irregular
cross-sectional.shape measured at any given point along
its length, and in addition is non-uniform in cross
section along its length. The predominant shape of the
fibers is usually rather ribbon-like.
The present invention utilizes synthetic wood
pulp fibers in a high loft, low density, nonwoven
fibrous materials such as an air-lai.d web or fabric.
Nonwoven materials are structures which consist of an
assemblage or web of irregularly arranged fibers, joined
randomly or more or less systematically by mechanical,
chemical or other means. These materials are well-
known in the art, having gained considerable prominence
within the last twenty years or so in the consumer
market, the industrial commercial market and the hospital
field. For example, nonwoven materials are becoming
increasingly important in the textile and related fields,
one reason being because of their low cost of manufacture
for a given coverage as compared to the cost of more
conventional textile fabrics made by weaving, knitting
or felting. Typical of their use is the production
of hospital caps, dental bibs, eye pads, dress shields,
3L1~5~2~
-3- JBP 88
shoe liners, shoulder pads, skirts, hand towels, handker-
chiefs, tapes, bags, table napkins, curtains, draperies,
diaper facings, underpads, hospital drapes, and the like.
Generally speaking, nonwoven materials are available
today in a wide range of fabric weights of from as little
as about 100 grains/sq. yd. to as much as about 4,000
grains/sq. yd. or even higher.
A number of processes and types of apparatus
are known for producing nonwoven materials. These in-
clude (1) mechanical techniques (e.g. carding orgarnetting), (2) wet laying techniques (e.g. inclined
wire paper apparatus, cylinder paper apparatus, etc.),
and (3) air-laying techniques. The high loft~ low
density, nonwoven materials such as webs or fabrics to
which this invention relates may suitably be produced,
in the manner to be explained in detail below, from
layers of material manufactured by well-known air-laying
processes.
One product of this invention utilizes
synthetic wood pulp fibers in a novel high loft, low
density, nonwoven, two-ply fibrous material that is use-
ful as one component of an infant's disposable diaper.
The material is also useful in other absorbent products
such as sanitary napkins, surgical bandages, disposable
bed pads, and the like.
The present invention also utilizes synthetic
wood pulp ibers in a high loft, low density nonwoven
fibrous material, such as an air-laid web, which is one
component of a wipe, swab, or other similar cleaning
3 device. Cleaning devices of this t~pe should possess
two characteristics, both of which are important but
which are mutually inconsistent. First, the device must
have a substantial amount of wet strength in order to
hold the desired shape and avoid disintegration of the
fibrous material when in use. This characteristic is
,~ best provided by a compactly assembled aggregation of
1~5~
-4- JBP 88
fibers bonded with an adhesive binder. Second, the
cleaning device must have a high degree of liquid
absorbency, as well as a substantial amount of resiliency
in its structure in order to be most efficient in adapt-
ing to corners to be cleaned. This characteristic isbest provided by a high loft, low density, nonwoven
fibrous material in which the fibers are loosely
assembled.
The two contradictory objectives ~ust described
can be achieved by joining nonwoven webs of different
types to form the desired cleaning device. Thus, a wet-
laid nonwoven web of compactly assembled fibers bonded
with a water insoluble adhesive binder can be used to
provide the necessary wet strength. An air-laid nonwoven
web of loosely assembled fibers can be used to provide
the high loft, low density, liquid absorbent layer.
Use of such different fibrous layers to form
the two-ply cleaning device of this invention presents
difficulties in causing the two layers to adhere to each
other without destroying the liquid absorbent character
of the second layer. These difficulties are surprisingly
avoided by the present invention.
S ~ ion
In the method of this invention, a first layer
of irregularly arranged, intersecting, overlapping,
mechanically interengaged fibers is brought together
with a second layer of similarly disposed loosely
assembled fibers that includes synthetic wood pulp fibers
in portions of the layer that are immediately ad~acent
the first layer when the two layers are brought together.
3 This brings at least some of the synthetic wood pulp
fibers of the second layer into contact with fibers of
the first layer. Both layers may include, and the
second layer does include a multiplicity of interstices
between their respective fibers, at least some of the
interstices of the second layer being of a width at
,,:
. ~
,
2 1
~5~ JBP 88
least two times as wide as the mean diameter o~ the
fibers of the first layer.
In one form of the method of this invention,
wherein the fibers of the first layer are also loosely
assembled, defining a multiplicity of interstices at
least some of which are of a width at least two times
as wide as the mean diameter of the synthetic wood pulp
fibers of the second layer, the second layer is
supported as a base layer, with one of its sur~aces
exposed for positioning of other fibers thereon. The
second layer may or may not be self-supporting, as
desired. In this form of the method, the first layer
is positioned upon the exposed surface of the base layer,
to bring at least some of the synthetic wood pulp fibers
in this second layer into contact with fibers of the
first layer. Or, if desired, the second layer contain-
ing synthetic wood pulp fibers may be positioned upon
the first fibrous layer, either self-supporting or not,
as a base layer.
Because of the supple nature of synthetic wood
pulp fibers, it would be expected that substantially all
such fibers in the second fibrous layer that are position-
ed in contact with fibers of the first layer would be
matted down against the fibrous first layer. For it
would be expected that the contact between fiber segments
in the first layer and fiber segments of synthetic wood
pulp in the second layer would tend to be of the type
in which one fiber segment lies either parallel to or at
an angle to another fiber segment on top of that other
3 fiber, with the areas of contact thus being essentially
only two-dimensional because confined to the precise
interface between the two layers. Consequently, even
though it is well-known that synthetic wood pulp fibers
are thermoplastic and can serve to bond various layers
of material to each other under heat and pressure (as
disclosed, for example, in the section headed
5~Zl
-6- JBP 88
"Applications -- ~onwovens and Laminates" in the September
1974 publication by Crown Zellerbach entitled S~IP), with
the areas of contact between layers of loosely assembled
fibers being only two dimensional it would not be ex-
pected that heating the regions on either side of theprecise interface between the two fibrous layers in the
absence of pressure would produce an adequate bond be-
tween the synthetic wood pulp fibers of the second layer
and the fibrous first layer.
Surprisingly, it has been discovered that
excellent delamination resistance may be provided in
accordance with this invention when the second layer
includes synthetic wood pulp ~ibers in a quantity
sufficient to occupy at least about 10~ of the area
occupied by exposed fiber segments contained in said
second layer at its boundary surface, and the t~o fibrous
layers in contact with each other are heated in the
absence of pressure to produce fusing of the synthetic
wood pulp fibers that are present in at least the second
layer. With a homogenously blended nonwoven fabric,
40~ or more by weight of thermoplastic fibers is usually
required for reliable fusion bonding of one fibrous
layer to another. It has been discovered that with the
method of this invention, which utilizes synthetic wood
pulp fibers, the total quantity of such fibers required
for a reliable bond between layers may be as low as lO~
by weight of a homogenously blended layer. Apparently,
there is in fact sufficient three-dimensional interfiber
contact--which extends beyond or bridges the precise
interface between the two layers of the fibrous material
and into the two layers themselves--to produce a re-
liable bonding, and resulting resistance to delamination,
after heat is applied to the synthetic wood pulp fibers
lying in the region on each side of that interface.
An easily delaminateable two-ply facing
- material is also provided in accordance with this
5~3Zl
-7- JBP 88
invention when the seco~d layer includes no more than 6%
synthetic wood pulp at its boundary surface, and a water
soluble binder is also used at the interface to bond the
layers. The two-ply facing material of this embodiment
comprises a first layer of loosely assembled natural wood
pulp fibers and a second layer of similarly disposed
fibers including intermixed natural wood pulp fibers and
synthetic wood pulp fibers. The synthetic wood pulp
fibers in the second layer, are in contact with and heat
fused with other fibers in the layer to form a fiber
structure of sufficient wet strength and integrity to
` be self-supporting in both dry and wet condition without
any additional binder.
Fibers in each o~ the two layers are also
bonded with one another and with ~ibers in the other
layer by a water soluble adhesive binder to provide the
desired mechanical integrity for normal handling of the
dry material as a whole. In addition, the bonding of
fibers of the first layer to each other by the intro-
duction of adhesive binder avoids disintegration of
the first layer when the bond between the two layers (1)
is first weakened by immersion in the water o~ a flush
toilet for a limited time to dissolve out only a portion
of the water soluble binder, and (2) is then ruptured
by pulling the two layers apart. Following the rupture
of the bond between the layers, the first fibrous layer
can be deposited in the flush toilet, where the re-
mainder of the water soluble adhesive binder will be
dissolved out and the first layer will disintegrate into
separate, individual fibers and small clumps of ~ibers.
The water soluble adhesive binder employed should be
substantially less soluble in body fluids such as urine
than in water, and preferably substantially insoluble
in such fluids.
35 The present invention also makes possible the
prod~ction of high loft, low density, nonwoven 4ibrous
J ~5~21
-8- JBP 88
materials having the characteristics o~ high liquid
absorption and high liquid retention. The nonwoven
fibrous material of this embodiment c~mprises loosely
assembled fibers including both natural wood pulp fibers
and synthetic wood pulp fibers; these two types of fibers
being present in different proportions in at least three
different regions or layers positioned parallel to the
median plane of the material.
To produce a high level of liquid absorption
in the product of this embodiment, it is necessary to
have a facing reglon at one external boundary surface of
the nonwoven material that is not too water repellent
to prevent a quantity o~ aqueous liquid from passing
through it into the main body of the material, but has a
lesser affinity for water than the interior region of
the material, in order that liquid that has passed
~through the facing region from the outside will remain
within the material rather than pass back out through
the facing region. While providing this desired balance
of wettability, the facing region must have an external
boundary surface that also exhibits good softness and
abrasion resistance.
Still different characteristics are required
of the central region of the nonwoven material, as well
as the region adjacent the other external boundary
- surface of the material, in order to give the product
of this embodiment of the invention a high level of
liquid retention. Thus, the central portion of the
material must constitute a reservoir region in which
liquid can be sorted once it has passed through the
absorbent facing region. At the same time, the region
of the material that defines the external boundary sur-
face that lies o~posite the facing region should provide
good wet strength, softness and abrasion resistance, as
well as provide an effective barrier to the passage of
- any substantial amount of aqueous liquid such as would
- ' ~
58Zl
~9- JBP 88
defeat the desired property of high liquid retention by
the material.
~ urprisingly, it has been found that this
balance of certain characteristics, and the contrasting
of other characteristics depending upon the location
within the nonwoven material of this embodimen~, can be
achieved by incorporating different, controlled amounts
of natural wood pulp fibers and synthetic wood pulp
fibers in the three regions of the material just de-
scribed. In the manufacture of the product of this
embodiment, the desired proportions of natural and
synthetic wood pulp fibers are first positioned in the
indicated regions of layers, and the fibrous assemblage
is then subjected to heat without pressure to form a
stable fibrous structure in which the three different
regions exhibit different desired characteristics.
The facing region or first layer comprises
synthetic wood pulp in 6~ to 30% by weight of fibers.
The reservoir region or second layer comprises synthetic
wood pulp in a smaller proportion than said first layer,
and the region which defines the external boundary sur-
face tha~ lies opposite the facing region, or third
layer, comprises synthetic wood pulp in a proportion
greater than the proportion of such fibers in the second
layer, but less than that of the first layer.
The method of this embodiment of the invention
co~prises bringing together at least three layers of
fibers in the proportions described above and applying
heat in the absence of pressure to the plurality of
3 fibers making up the various layers, to fuse and bond
at least some of the synthetic wood pulp fibers with
other fibers to form a self-supporting fiber structure
in the absence of any additional binder.
The product of this invention in another
embodiment is a wipe, s~ab, sponge or other cleaning
device which includes a backing la~er and a liquid
$~321 - -
-10- JBP 88
absorbent layer attached thereto. The backing layer or
first layer is formed of irregularly arranged, inter-
secting, overlapping, mechanically interengaged, compactly
assembled natural wood pulp fibers bonded to each other
with an adhesive binder to provide wet strength. The
liquid absorbent layer or second layer is formed of
similarly disposed fibers except that they are loosely
assembled with a multiplicity of interstices between
them and are not necessarily bonded to each other by
means of an adhesive binder. The fibers of the second
layer include both liquid absorbent natural wood pulp
~ibers and wettable synthetic wood pulp fibers.
In another embodimént, the cleaning device
may c~mprise a three-ply material with the first layer
sandwiched between two liquid absorbent layers, each of
which contains wettable thermoplastic synthetic wood
pulp fibers, as described above.
The layers are emboss laminated together, with
segments of some of the synthetic wood pulp fibers of
the second and third layer being heat fused and bonded
to the first layer in a discontinuous pattern of embossed
areas, to provide a reliable bond between the two layers.
The embossed areas alternate with unembossed
areas across the backing layer. The synthetic wood pulp
fibers located in the unembossed areas are heat fused
and bonded to each other and to other fibers in the
second fibrous layer, to provide a three-dimensional
network of stabilized absorbent cellulose fibers which
is not subject to collapsing when wet, and which has
3 good liquid holding capacity, in those unembossed por-
tions of the second layer.
The bonded ~ibrous first layer of the product
of this embodiment is similar to wet strength tissues
sold c~mmercially as disposable cleansing and wiping
tissues. Such bonded fibrous tissues are not ordinarily
- capable o~ being laminated with other fibrous materials
J
. . ,. ~`,.
821
-11- JBP 88
without the use of adhesive binder, or the full-area
lamination ~ith synthetic wood pulp fibers disclosed
in the section headed 'tApplications -- Nonwo~ens and
Laminates" in the September 1974 publication by Crown
Zellerbach entitled SWP. Surprisingly, the presence of
the synthetic wood pulp fibers in the second, liquid
absorbent, layer of the product of this invention pro-
duces a reliable bond between the two layers without
any such adhesive binder, and with only discontinuous
emboss bonding as described. Another surprising result
is the fact that the double bonding actions of the emboss
lamination and the generalized heating of the synthetic
wood pulp fibers of the unembossed areas appear to oper~
ate independently of each other, to render the unembossed
areas a three-dimensional fibrous network of stabilized `
absorbent cellulose ~ibers having good liquid holding
capacity.
Brief D_scription of the Drawing
The invention will now be described with
reference to the accompanying drawing, in which:
Figure 1 is a diagrammatic representation of
a portion of a first layer of irregularly arranged,
loosely assembled fibers that contains no synthetic wood
pulp fibers and may be one component of the fibrous
material of this in~ention,
Figure 2 is an enlarged diagrammatic represen-
tation of the fibrous material of Figure l;
Figure 3 is a diagrammatic representation of
a portion of another layer of irregularly arranged,
loosely assembled fibers, including textile length
3 fibers but no synthetic wood pulp fibers, that may
constitute the first layer of the fibrous material of
this invention,
Figure 4 is an enlarged diagrammatic represen-
tation of a portion of a second layer of irregularly
: 35 arranged, loosely assembled flbers that is one component
~ S8%~
-12- JBP 88
of the product of this invention, in which synthetic wood
pulp fibers are intermingled with natural wood pulp
fibers;
Figure 5 is an enlarged diagra~atic represen-
tation in cross-section of the first fibrous layer of
Figure 3 being brought together in the first step of the
method of this invention with a second layer of synthetic
wood pulp fibers that is positioned below it;
Figure 6 is a diagrammatic representation in
cross-section of the fibrous material formed by bringing
together the two fibrous layers of Figure 5;
Figure 7 is an enlarged cross-sectional view of
a cleaning device constructed in accordance with this
invention;
Figure 8 is an enlarged cross-sectional view of
another cleaning device constructed in accordance with
this invention;
Figure 9 is an enlarged, fragmentary diagrammat-
ic representation in cross-section of a fibrous material
having good liquid absorbency and retention, which is
constructed in accordance with this invention,
Figure 10 is a diagrammatic side elevation view
of one form of apparatus for producing a fibrous material
of this invention; and
Figure 11 is a diagrammatic side elevation view
of another form of apparatus for producing another
fibrous material of the invention.
Detailed Descri~tion of the_Invention-
Figure 1 is a diagrammatic representation of
a first layer 20 of irregularly arranged, intersecting~
overlapping, mechanically interengaged, loosely assembled
fibers defining interstices therebetween which may com-
prise one component of the product of this invention.
The term "mechanically interengaged" is used in this
specification and claims to refer to fibers (usually
- 35 randomly bent) that are interlocked or interentangled
~SB2~
-13- JBP 88
with other fibers to provide a degree of structural
integrity whether or not binder is present in the layer
of fibers.
The fibers of fibrous layer 20 may comprise
natural fibers such as cotton, flax, silk, wool, wood
pulp, ~ute, etc., mineral fibers such as glass; artifi-
cial fibers such as viscose rayon, ethyl cellulose or
cellulose acetate; synthetic fibers ~uch as polyamides,
polyesters, acrylics, vinylidene chloride, poly~inyl-
chloride, polyurethane, etc., alone or in combinationwith one another. The melting point or degradation
temperature of these fibers must be higher, preferably
by as much as 10 to 20C., than the melting point of
the synthetic wood pulp fibers contained in the second
fibrous layer of the product of this invention. The
fibers represented by the drawing of Figure 1 are
approximately 1/4 inch to 1/2 inch viscose rayon fibers.
Relatively long textile type fibers above
normal papermaking lengths and close to normal textile
length~ say of about 3/8 inch to 2 inches or longer, are
preferred for some applications. Shorter fibers below
1/4 inch in length and within the papermaking range may
be used in other applications. It is preferred, however,
that any shorter papermaking fibers employed be unbeaten
or substantially unhydrated if a textile-like fibrous
material is desired as the end product. Shorter wood
fibers may be used to decrease the cost of the product
of this invention, with longer fibers intermixed there-
with to provide the strength desired-in the resulting
product.
F~gure 2 is a diagrammatic representation
giving an enlarged view of first fibrous layer 20 of
Figure 1, and the fibers shown in the figure are thus
again 1/4 inch to 1/2 inch viscose rayon fibers. In
Figure 2 the fibers are disposed in the same manner as
in the fibrous layer of Figure 1, with the fibers
- ~
, .
5 ~ 2 ~
-14- JBP 88
de~ining interstices 32 between adjacent fibers of the
layer. Some interstices in fibrous layer 20 are quite
s~all, but at least some of the interstices between
flbers in the layer, as shown in Figure 2, have a width
at least twice as large as the mean diameter of the
fibers that ~ake up second fibrous layer 32 to be de-
scribed below.
Figure 3 is another diagramm~tic representation
of a first fibrous layer 23 for use in the method of
this invention. In this fibrous layer, shorter fibers
24, approximately 1/4 inch to 1/2 inch in length, are
intermixed with longer fibers 25 (shown as dark fibers
in Figure 3) which are about 1 inch to 2 inches in length.
Figure 4 is a diagrammatic representation of
a second layer 26 of irregularly arranged, loosely
assembled fibers comprising one c~mponent of the product
of this invention. In this embodiment, synthetic wood
pulp fibers 27 (stippled in the drawing) a~e inter-
mingled with natural wood pulp fibers 28.
If desired, fibrous layers 20, 23 and 26 may
be formed by means of an air deposition process.
Figure 5 is a diagrar~natic representation of
an enlarged cross-sectional view of first fibrous layer
23 of Figure 3, shown being brought together in the
first step of the method of this invention with second
fibrous layer 32 that is- positioned below it. First
fibrous layer 23 contains shorter fibers 24 and longer
fibers 25 (stippled in Figure 5) interrningled therewith.
Loosely assembled fibers 24 and 25 of first
fibrous layer 23 are irregularly arranged, intersecting,
overlapping and mechanically interengaged with each
other.
In the embodirnent shown, second fibrous layer
32 is constituted of synthetic wood pulp fibers 34,
which are disposed in a similar l-nanner to fibers 24 and
25 of first fibrous layer 23. This includes the fact
~S~Z:l
-15- JBP 88
that synthetic ~ood pulp fibers 34 ~orm interstices
between individual fiber se~ments some of which inter-
stices have a width at least twice as large as the mean
diameter of the fibers that make up fibrous layer 23.
Fibers 34 have an average length of about 1/4 inch.
As is seen from Figure 5, the greater part of
, the fibrous mass that comprises first fibrous layer 23
lies within the interior of the fibrous structure as a
whole. In fact, in the case of a number of the fibers
the individual fiber lies within the interior of the
fiber structure for the entire fiber length. However,
a number of fibers of layer 23 have free fiber ends 36
extending outwardly from at least one boundary surface
of the layer.
In Figure 5, a substantial number of free fiber
ends -36 extend downwardly f,rom plane 38, which is the
effective lower boundary surface of fibrous layer 23 as
the layer is being moved into position on second fibrous
layer 32 below it. Second fibrous layer 32 likewise
20 has free fiber ends 40 extending outwardly from the
layer. In Figure 5, a substantial number of free fiber
ends 40 extend upwardly from the plane of upper boundary
surface 42 of layer 32.
In the embodiment under discussion, all the fibers
25 34 present at upper boundary surface 42 of second fibrous
layer 32 are synthetic wood pulp fibers, and all these
,fibers are mechanically interengaged with other fibers 34
in layer 32. - Excellent reslstance to delamination is
obtained when synthetic wood pulp fibers 34 mechanically
30 interengaged with other fibers in second layer 32 are
present at boundary surface 42 in a quantity sufficient
to occupy at least about 10% of the area occupied by
exposed fiber segments of all kinds contained'in layer
32 at the boundary surface in question.
I~ another embodiment of the inventiong
synthetic wood pulp fibers are present at the boundary
. ' '
:
,
-16- JBP 88
surface in a quantity sufficient to occupy no more than
6~ of the area occupied by exposed fiber segments at the
boundary surface and a water soluble adhesive binder is
present in the first and second layers at least at the
inter~ace thereof, creatin~ a bond between the layers of
sufficient strength to-avoid damage to the bond between
the layers during no-rmal handling in the dry state, but
allowing the first layer to be removed from the second
layer in the manner referred to above.
In another embodiment of the invention shown
in Figure 7, the first layer 12 is comprised of irregular-
ly arranged, intersecting, overlapping, mechanically
interengaged, compactly assembled natural wood pulp
fibers such as a wet-laid nonwoven web. The fibers of
first layer 12 are bonded to each other with adhesive
binder to provide wet strength, the binder preferably
being a hydrophilic binder with no surfactant. First
layer 12 is similar in construction to fibrous webs
sold com~ercially for use as disposable cleansing and
wiping tissues.
A liquid absorbent fibrous layer, the second
layer 16. The fibers in second layer 16, the liquid
absorbent fibrous layer, includes both liquid absorbent
natural wood pulp fibers and wettable synthetic wood
pulp fibers, all of which have generally the same
morphology and appearance. The fibers are disposed in
the same manner as are the fibers of first layer 12,
except that they are loosely assembled rather than
compacted, resulting in a high loft, low density structure
such as an air-laid nonwoven web. Layer 16 does not
have an adhesive binder distributed throughout the fibers
as does first layer 12.
As indicated in Figure 7, the remaining
synthetic wood pulp fibers that are not heat fused and
bonded to backing layer 12 are heat fused and bonded to
each other and to other fibers in second layer 16 in
- . , .
.
.
-
~5821
-17- JBP 88
regions 20 of that layer lying between embossed areas 14.
A three-dimensional network of stabilized absorbent
cellulose fibers which is not subject to collapsing when
wet and has good liquid holding capacity is thus provided
in unembossed areas 20 of second fibrous layer 16.
Fig~re 8 shows a three-ply cleaning device with
two liquid absorbent layers, the second and third layers,
reinforced by a single first layer 112. The second and
third layers, 116A and 116B respectively, are similar to
absorbent layer 16 described above with unembossed area
120A in layer 116A and unembossed areas 120B in layer
116B similar to unembossed areas 20 in layer 16 described
above. Embossed areas-114 provide the bonding o~ the
layers to each other.
The product of another embodiment of this in-
vention illustrated in Figure 9, is a high lo~t, low
density, nonwoven fibrous material having good wet
strength, softness, abrasion resistance, and liquid
absorbency and retention. The material-comprises a
plurality of irregularly arranged, intersecting, over-
lapping, mechanically interengaged, loosely assembled
fibers including both natural wood pulp fibers and
synthetic wood pulp fibers. The two types of fibers are
present in different proportions in various regions or
layers positioned parallel to the median plane of the
material.
As indicated in Figure 9, nonwoven ~ibrous
material 10 is comprised of fibers arranged as described
above in first layer or facing region 12, second layer
3 or absorbent reservoir region 14, and third layer or
capillary distribution network region 16. Regions 12
and 16 are contiguous with region 14 and lie on opposite
sides thereof.
With synthetic wood pulp fibers distributed
throughout all three layers of the absorbent fibrous
~aterial of this invention, a plurality of contacts of
'
1~!5~21
-18- JBP 8~
synthetic wood pulp fibers with each other and with the
other fibers of the material are present from one exter-
nal surface of the material to the other. At at least
some of these contact points, segments of synthetic wood
pulp fibers are heat fused with other segments of syn-
thetic wood pulp fibers or with segments of other fibers,
to form a self-supporting fibrous structure in the
absence of any additional binder.
The desired characteristics of first layer 12
are obtained when synthztic wood pulp fibers are present
in an amount from about 6~ to about 30~ by weight of all
the fibers present in the layer.
The wet strength and abrasion resistance of
absorbent fibrous material 10 are improved if exposed
boundary surface portions 18 of first layer 12 contain
about 20% to about 30~ by weight of synthetic wood pulp
fibers. In such case, the remainder of layer 12 may
contain about 6~ to about 30~ by weight of synthetic
wood pulp fibers.
Second layer, or absorbent reservoir region
14, like first facing region 12, includes both natural
wood pulp fibers and synthetic wood pulp fibers. Or-
dinarily, no other types of fibers are included in this
region. Segments of synthetic wood pulp fibers are heat
fused with other segments of synthetic wood pulp fibers
and with segments of natural wood pulp fibers, to form
a self-supporting fibrous structure in the absence of
any additional binder.
Synthetic wood pulp fibers are present in
3 second layer 14 ln a smaller proportion than the pro-
portion of synthetic wood pulp fibers in first layer 12.
Third layer 16 of fibrous ~aterial 10, which
provides a capillary distribution network, contains both
natural wood pulp fibers and synthetic wood pulp fibers,
and usually no other types of fibers. Synthetic wood
. pulp fibers are present in this layer in a proportion
... . .
"
., . ~ . ~ : :.
,
1~S~32~
-19- JBP 88
greater than the proportion of synthetic wood pulp fibers
in second layer 14, but less than the proportion in
first layer 12.
~ith respect to Figure 9, it should be pointed
out that while ~or purposes of clarity this figure shows
fibrous layers 12 through 20 adjoining each other at
sharply defined interfaces, this is only a diagrammatic
showing. In the actual product of this invention there is
a more or less gradual transition from o~e fibrous layer
or region to another, with fibers intermingled with each
other while each layer or region merges into the ad-
~oining one.
In the first step of one method of this inven-
tion, first layer 23 and second layer 32 are brought
together as illustrated, for example, in Figure 5. In
the embodiment shown, second layer 32 consisting of
synthetic wood pulp fibers 34 is supported as a base
layer for positioning the fibers of first layer 23 there-
upon. First layer Z3 is positioned upon base layer 32,
as illustrated in Figures 5 and 6, in the form of a self-
supporting web of fibers, which may be already bonded,
or unbonded, as desired.
If desired, first layer 23 shown in Figure 3
may be deposited upon second layer 32 by forming layer
23, by means of an air deposition process and simul-
taneously positioning it upon layer 32 as a base layer.
The left-hand portion of Figure 10 provides a diagrammat-
ic showing in side elevation of apparatus for this form
of the method of this invention, similar to the web
forming apparatus disclosed in ~ommonly assigned~Patent
Nos. 3,740,797 to Farrington, 3,768,118 to Ruffo et al,
and 3,772,739 to Lovgren.
In Figure 10, second layer 32 is fed from
supply roll 50 onto the upper reach of endless belt 52,
which is moving fr~m left to right as shown. At the
same time, first layer 23, such as shown in Figure 3, is
iL1~5~21
-20- JBP 88
simultaneously formed and deposited upon second layer 32,
to move from left to rig~t with layer 32 while interfiber
contact such as described below in some detail in connec-
tion with Figure 6 is produced.
Natural wood pulp fibers 24 and textile length
fibers 25 (Figure 3) are deposited by air deposition
apparatus 54 on second fibrous layer 32 to form first
layer 23. Wood pulp board 56 is fed into apparatus 54
between guide plate 57 and feed roll 58, into edgewise
contact with lickerin 60, which breaks the board up into
individual natural wood pulp fibers. At the same time,
a supply of textile length fibers in the form of carded
web 61 is fed between guide plate 62 and feed roll 63
into lickerin 6~, and from there-the ~ibers are directed
onto fibrous layer 32 where they are intermingled with
the natural wood pulp fibers deposited thereon as ~ust
described. The vertical location of baffle 65 determines
the degree of crossover, or the relative proportions of
short fibers 24 and longer fibers 25 that are deposited
at each thickness level to form fibrous layer 23.
The resulting fibrous material made up of two
components, first layer 23 and second layer 32, is carried
to the right by endless belt 52 in Figure 7 for further
treatment.
When fiber end portions 36 an~ 40 that extend
outwardly beyond their respective boundary surfaces 38
and 42 penetrate the opposing fibrous layer as layers
23 and 32 are brought together in the first step of this
invention, considerable contact is effected between
fiber segments of synthetic wood pulp fibers in second
layer 32 and ~ibers of first layer 23. The resulting
interfiber contact--with fiber segments of synthetic
wood pulp fibers 34 of second layer 32 resting in con-
tact with first layer 23 after either free fiber ends
36 or 40~ or some of both, have inserted themselves
F~ into interstices between the fibers of the other layer--
,i
Zl
-21- JBP 88
is illustra~ed in Figure 6 in diagrammatic ~ashion.
Figure 6 is not inte~ded to suggest that the precise
types of contact zones shown there are necessarily
identifiable in the product of this invention, but the
contact zones shown are intended to suggest some
considerable degree of contact between the fibers in
question
It may happen that some exposed fiber end
portions 36a and 40a as shown in Figure 5 will move into
contact with each other as seen in Figure 6 when ~ibrous
layers 23 and 32 are brought together in the first step
of the method of this invention. Contact zones of this
type are indicated by the letter "a" in Figure 6 at
several locations in the left-hand portion of the figure,
and also in the right-hand portion.
In some cases, outwardly extending fiber end
portions 36b and 40b may collide with each other as
fibrous layers 23 and 32 are brought together, and be
bent into positions where they maintain fiber contact.
Such fiber contact is indicated by the letter "b" in
the left-hand portion, the middle, and the right-hand
portion of Figure 6.
The interfiber contact thus far described is
believed to provide the major portion of the structural
integrity of the fibrous material. The contact described
may in some instances be further supplemented by an
actual "intermeshing" of exposed fiber end portions with
one fiber end sliding behind another fiber end to pro-
vide not only fiber contact but a more positive engage-
3 ment somewhat similar to the mechanical interengagement
or interentanglement of the bent fibers that is present
throughout the body of fibrous layers 23 and 32. How-
ever, it is believed that the incidence of such inter-
meshing of fiber ends is typically not very high.
Another type of interfiber contact of less
importance, but still adding to the structural integrity
~s~z;~
-22- JBP 88
of the fibrous material, is the essentially two-
dimensional contact of parallel fiber segments lying at
the respective boundary surfaces 38 and 42 of fibrous
layers 23 and 32 when they arebrought together. Examples
5 of this supplementary interfiber contact are shown at
"c" at the left-hand side~ the middle, and the right-
hand side of Figure 6.
Some exposed and protruding fiber end portions
36d and 40d fail to make contact with any fibers in the
opposing fibrous layers. Examples of such situations
are shown at the left-hand end, and at several places
near the middle, of Figure 6.
In the second step of this method of this
invention, heat is applied in the absence of pressure
15 at least to the portions of fibrous layers 23 and 32 in
which synthetic wood pulp fibers 34 of layer 32 are in
contact with fibers 24 and 25 of layer 23, to raise
the temperature of fibers 34 to or a little above the
melting point of the synthetic wood pulp fibers. In
20 other words, heat as described is applied at least to
the fibrous regions in which contact zones, a, b, and
c in Figure 6 are located. As a result, some or all of
synthetic wood pulp fibers 34 that are in contact with
fibers of first layer 23 are fused and bonded to the
25 'latter fibers.
As indicated, heat is applied during this
second step at least to the portions of layers 23 and 32
that lie immediately adjacent interface 38/42 located
between them. The remaining portions of the'fibrous
material produced by-the method of this invention may,
if'desired, also be subjected to heat in the absence of
pressure, and this will be particularly useful if
synthetic wood pulp fibers are distributed in other
portions of the fibrous material in addition to those
35 immediately adjacent interface 38/42.
The right-hand portion of Figure 10 shows
2~
-23- JBP 88
diagrammatically means for applying heat to fibrous layers
23 and 32. Heating means 66, which may be a dielectric
heater, infra-red heater, radiant heater, or other
heating means, applied heat to the two fibrous layers
supported on endless belt 52, as they move to the right
in Figure 10.
- Synthetic wood pulp fibers 3~ in second layer
32 should have a melting point lower than the melting
point or degradation temperature of every other type of
fibers contained in layers 23 and 32. Preferably, the
melting point of the synthetic wood pulp fiber should
be at least 10~ to 20C. lower than the melting point of
the other fibers.
Additional bonding may be provided by deposit-
ing adhesive binder on fibrous layers 23 and 32 from
applicator means 67 shown diagrammatically in Figure 10.
Applicator means 67 is typically a source of binder
coupled with a suction box. Alternatively, applicator
means 67 may comprise spray apparatus for the application
of binder in the form of droplets. The binder is prefer-
ably distributed throughout both layers. After its
introduction into the two layers, the adhesive binder is
activated by drying and/or heating, which can be supplied
by diagrammatically shown means 68.
In another method of this invention a first
layer of compactly assembled, adhesive bonded, natural
wood pulp fibers, such as a wet-laid web, is brought
together with a second, and optionally, a third layer
of loosely assembled fibers having a multiplicity of
3 interstices between them, such as an air-laid web,
comprised of liquid absorbent natural wood pulp fibers
and ~ettable synthetic wood pulp fibers of a lower melt-
ing point than the other fibers of the two layers as
indicated above.
In the second step of this method, conventional
emboss laminating equipment is employed to apply heat
~5~32~
-24- JBP 88
and pressure to the layers in a discontinuous embossing
pattern across the layers. The combination of pressure
and temperature applied to the synthetic wood pulp
fibers softens them, and may in fact, melt them. The
synthetic wood pulp fibers of the second, and optionally
the third layer are thus heat fused and reliably bonded
to the fibers of the backing layer of the device.
In the final step of this method, heat is
applied in the absence of pressure to the rest of the
second and third layers in the unembossed areas re-
maining after the embossing pattern has bee~ imposed
on the material. In this step, synthetic wood pulp
fibers contained in the second and third layers are
heat fused and bonded to each other and to other fibers
in that layer. A three-dimensional network of stabilized
absorbent cellulose fibers having good liquid holding
capacity is thus provided in the portions of the second
and third layers lying in the unembossed areas of the
discontinuous pattern.
In yet another method of this invention, a
plurality of irregularly arranged, intersecting, over-
lapping, mechanically interengaged, loosely assembled
fibers, including both natural wood pul-p fibers and
synthetic wood pulp fibers, is brought together to posi-
tion the two types of fibers in different proportions inthree different layers positioned parallel to the median
plane of the material. Heat is then applied in the
absence of pressure to the plurality of fibers thus
arranged, to fuse and bond at least some of the synthetic
3 wood pulp fibers with other segments of fibers at a
plurality of junctures throughout the ~ibrous material.
A fiber structure that is self-supporting in the absence
of any additional binder is thus produced.
As indicated above, fibrous material 10 shown
in Figure 9 may if desired be formed by ~eans of an air
deposition process. Figure 11 provides a diagrammatic
S~l
-25- JBP 88
drawing in side elevation of apparatus that may be used
in this manner.
The left-hand portion of the apparatus in
Figure 11 is similar to the~ web forming apparatus dis-
closed in co~monly assigned~Patent Nos. 3,740,797 to
Farrington, 3,768,118 to Ruffo et al, and 3,772,739 to
~ovgren. A board 50 of synthetic wood pulp fibers is
fed into air deposition apparatus 52 between guide plate
54 and feed roll 56, into edgewise contact with lickerin
58, which separates the web into individual fibers of
synthetic wood pulp. At the same time, a board 60 of
natural wood pulp fibers is fed into air deposition
apparatus 52 between guide plate 62 and feed roll 64,
into edgewise contact with lickerin 66, which separates
the web into individual fibers of natural wood pulp.
As synthetic wood pulp fibers and natural wood
pulp fibers are directed downward from lickerins 58 and
66, respectively, they are intermingled to form fibrous
material 10, which moves from left to right with the
endless belt in Figure 11. Air deposition apparatus 52
can be adjusted, as explained in the patents referred
to above which disclose such apparatus, to produce
different proportions of synthetic ~ood pulp fibers and
other fibers in the various regions of the resulting
nonwoven fibrous material at or parallel to the median
plane of the material.
For additional fabric strength, if desired,
adhesive binder in latex form may be sprayed on the
exposed boundary surface portions 18 of region 12 of the
resulting fibrous material 10. If added, the binder
should be applied in an amount equivalent to about 1~
by dry weight of the resulting fibrous material. Any
suitable binder employed with nonwoven fibrous materials
may be used. Binder applying means 70 is shown
diagrammatically in Figure 11, and drying means 72, such
as a dielectric heater, infra-red heater, radiant heater,
~s~z~
-26- JBP 88
or other heating means, is shown diagrammatically at 72.
As a subsequent step in the method of this
invention, exposed boundary surface 18 of region 12 of
fibrous material lO can be lightly calendered to
partially smooth the boundary surface. Calendering means
74 is shown diagrammatically in ~igure ll.
The product resulting from use of the method
described is a high loft, low density, nonwoven fibrous
material having good wet strength, softness, abrasion
resistance, and good liquid absorbency and liquid reten-
tion.
The above detailed description is given for
clearness of understanding only. No unnecessary limita-
tions should be understood therefrom,`as modifications
will be obvious to those skilled in the art.
