U.S. patent number 3,816,159 [Application Number 05/206,410] was granted by the patent office on 1974-06-11 for process for applying an aqueous dispersion of short, binder coated fibers to a drylaid nonwoven fabric.
This patent grant is currently assigned to The Kendall Company. Invention is credited to Nicholas S. Newman.
United States Patent |
3,816,159 |
Newman |
June 11, 1974 |
PROCESS FOR APPLYING AN AQUEOUS DISPERSION OF SHORT, BINDER COATED
FIBERS TO A DRYLAID NONWOVEN FABRIC
Abstract
Nonwoven fabrics of improved abrasion resistance are produced by
applying to a dry-laid fibrous web an aqueous dispersion of
ultra-short fibers of 50 to 300 microns in length, said ultra-short
fibers being coated with a polymeric binder and being suspended in
an aqueous phase which is substantially free of binder. The
dry-laid fibrous web may be bonded in a separate operation,
optionally with a different polymeric binder and in a discontinuous
pattern.
Inventors: |
Newman; Nicholas S. (West
Newton, MA) |
Assignee: |
The Kendall Company (Boston,
MA)
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Family
ID: |
27386131 |
Appl.
No.: |
05/206,410 |
Filed: |
December 9, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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144607 |
May 18, 1971 |
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831564 |
Jun 9, 1969 |
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Current U.S.
Class: |
427/202;
156/62.2; 162/149 |
Current CPC
Class: |
D04H
1/00 (20130101) |
Current International
Class: |
D04H
1/00 (20060101); B44d 001/02 () |
Field of
Search: |
;162/129,130,149
;161/152,153,156,170 ;156/62.2 ;117/27,28 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Smith; William F.
Attorney, Agent or Firm: Ryan; John F.
Parent Case Text
This application is a continuation-in-part of my copending
application Ser. No. 144,607, filed May 18, 1971, now abandoned,
which in turn is a continuation-in-part of my patent application
Ser. No. 831,564, filed June 9, 1969, now abandoned.
Claims
I claim:
1. The process for providing a nonwoven fabric of improved
abrasion-resistance which comprises assembling an unspun and
unwoven dry-laid fibrous fleece;
forming a dispersion of binder-coated fibers by suspending
substantially unhydrated and unbeaten ultrashort fibers of between
50 and 300 microns in length in water containing a polymeric binder
and precipitating and coating the binder onto said ultrashort
fibers until the water phase is clear and substantially free of
binder;
applying to said fleece on at least one face thereof said aqueous
dispersion of binder-coated fibers; and
drying the fabric thus formed.
2. The process according to claim 1 in which the aqueous dispersion
of binder-coated, substantially unhydrated and unbeaten ultrashort
fibers is formed by concentrating in aqueous phase a
polyelectrolyte onto the fibers, adding a polymeric binder to the
aqueous phase, and agitating the mixture until the clarity of the
water phase indicates that substantially all of the binder is
attached to the solid ultrashort fibers.
3. The process according to claim 1 in which the dry-laid fleece
comprises textile-length fibers of between one-quarter inch and six
inches in length.
4. The process according to claim 1 in which the dry-laid fleece
comprises continuous filaments with an overlay of textile-length
rayon fibers.
5. The process according to claim 4 in which the continuous
filaments are bonded to each other at at least two of their points
of intersection.
6. The process according to claim 1 in which the dry-laid fleece
comprises a mixture of textile-length fibers of between one-quarter
and six inches in length and unbeaten, non-fibrillated fibers of
between 1,000 and 5,000 microns in length.
7. The process according to claim 1 in which the dry-laid fleece
comprises air-laid unbeaten and non-fibrillated fibers of 1,000 to
5,000 microns in length.
8. The process according to claim 1 in which the aqueous dispersion
of ultrashort fibers is of between 1 percent and 4 percent fiber
concentration.
9. The process according to claim 1 in which the binder coating on
the ultrashort fibers is between 5 percent and 100 percent of the
weight of said fibers.
10. The process according to claim 3 in which the dry-laid fibrous
fleece of textile-length fibers is bonded in a secondary
operation.
11. The process according to claim 10 in which the dry-laid
textile-length fibers are bonded at at least two of their points of
intersection in a discontinuous bonding operation leaving
substantial portions of the lengths of said fibers free of bonding
material.
12. The process according to claim 4 in which the dry-laid fleece
of continuous filaments with an overlay of textile-length rayon
fibers is bonded in a secondary bonding operation wherein a binding
agent is applied to said fleece in a pattern of discrete and
spaced-apart areas, the binder in said areas extending through the
continuous filaments and into the overlying layer of rayon
fibers.
13. The process for providing a nonwoven fabric of improved
abrasion resistance which comprises:
assembling an unspun and unwoven dry-laid fibrous fleece;
forming a dispersion of binder-coated fibers by suspending
substantially unhydrated and unbeaten ultrashort fibers of between
50 and 300 microns in length in water containing a polymeric
binder, and precipitating and coating the binder onto said
ultrashort fibers until the water phase is clear and substantially
free of binder;
applying to said fleece on one face thereof said aqueous dispersion
of binder-coated fibers;
applying to said fleece a secondary bonding agent;
applying a second deposit of said binder-coated fibers to the other
face of said fleece; and
drying the fabric thus formed.
Description
This invention relates to a process for the preparation of bonded
nonwoven fabrics, and the products thereof. More particularly, it
relates to the preparation of medium or lightweight nonwoven
fabrics of high opacity and high abrasion resistance, suitable for
fashioning into items such as disposable or limited-use
garments.
Bonded nonwoven fabrics, comprising dry-assembled, textile-length
unspun and unwoven fibrous webs bonded by polmeric binding
materials, are produced by a variety of processes and are staple
articles of commerce. In addition to numerous industrial
applications, they are finding increasing use in the field of
disposable items such as garments, sheets, pillowcases, surgical
drapes, and the like. Conventional nonwoven fabrics, however, are
planar and uniform, not closely resembling the woven fabrics which
they are intended to replace. Additionally, and of paramount
importance in disposable clothing, sheets, and drapes, conventional
nonwoven fabrics of a weight range which may economically be used
are undesirably translucent, and lack covering or concealing
power.
Attempts have been made to remedy this translucency by embossing
the surface of the nonwoven fabric, or printing design thereon, to
increase the light-scattering effect. Such attempts are expensive
and of limited utility. Recourse has also been had to the use of
highly delustered fibers, such as viscose rayon fibers with
abnormally high titanium dioxide contents. The opacity and dullness
of such fibers reaches a limit, however, at a rather low level of
pigment content, and the increase in opacity of nonwoven fabrics
produced therefrom is marginal. The same is true of attempts to
opacify nonwoven fabrics by adding clay or other fillers to the
binder used to unify the fibrous structure.
It has also been proposed to deposit a layer of papermaking fibers,
1,000 microns or more in length, upon a web or fleece of
textile-length fibers. Due to the length of papermaking fibers,
however, and perhaps also in part to their swollen and hydrated
condition, papermaking fibers tend to filter out onto a web of
textile-length fibers without penetrating into the web sufficiently
to form a satisfactory interlocking bond with the textile-length
fibers. Furthermore, hydrated and fibrillated papermaking fibers
tend to dry down to a rather stiff sheet, with an undesirable hand,
due to the formation of papermakers' bonds.
It is also known to combine papermaking fibers with textile-length
fibers in a conventional papermaking machine, using a headbox and
inclined Fourdrinier screen. The equipment needed, however, is very
expensive compared with the equipment used in processing nonwoven
fabrics, and the processing is also expensive and slower than
normal papermaking since very low concentrations of fiber, down to
0.01 percent fiber content in water, must be used.
In my copending application Ser. No. 779,318 filed Nov. 25, 1968
now U.S. Pat. No. 3,616,180, there is described a process for
producing nonwoven fabrics of increased opacity.
Basically, the steps involved in that process comprise:
1. Assembling textile-length fibers into a dry, unspun and unwoven
web as by means of cards, garnetts, air-lay devices, or the
like.
2. Saturating the fibrous web with an appropriate binder solution
containing ultra-short fibers suspended therein in dilute
concentration, said ultra-short fibers being substantially
unbeaten, unhydrated, and uniformly distributed in a
nonagglomerated condition.
3. Mechanically removing a major portion of the binder solution
from the web while leaving the ultra-short fibers upon and within
the web.
4. Completing and drying of the bonded nonwoven fabrics.
The procedure set forth immediately above results in nonwoven
fabrics wherein the opacity is increased from a value of 0.40 -
0.45 to value of 0.60 - 0.70, as measured by a Bausch and Lomb
Opacimeter 33-88-12, according to Textile Research Journal, Volume
38, No. 1, January, 1968, page 8. For certain apparel uses,
however, and for other uses where the nonwoven fabric is subjected
to repeated frictional contact with itself or with another rubbing
surface, products formed in the above manner are found deficient in
abrasion resistance.
Moreover, since the binder dispersion in which the ultrashort
fibers are suspended serves to bond both the ultrashort fibers and
the underlying fibrous web, the versatility of the above process is
limited. In many cases it may be deemed desirable to bond the
ultrashort fibers into a cohesive surface layer with a binder that
is firm and tough, while bonding the other underlying fibers with a
binder of quite different characteristics.
Also, the process of application Ser. No. 779,318 results in an
overall saturation of both the ultrashort fiber fraction and the
underlying fiber fraction. It is recognized that for maximum
flexibility and softness, it is often desirable to bond a web of
fibers discontinuously -- that is, in a pattern of separate or
interconnected spots, lines, or geometric figures, so that while
every fiber is bonded one or more times along its length, there
remain substantial lengths of unbonded fibers which are free to
flex or move laterally.
Finally, the process of Ser. No. 779,318, in common with most
binder saturation techniques, necessitates a complicated recovery
system for reclamation of excess binder applied to the web, in
order to be economically feasible.
The process described below is intended to overcome the above
disadvantages, and to yield nonwoven fabrics of improved
characteristics.
It is therefore an object of the present invention to provide
opacified nonwoven fabrics of enhanced flexibility and resistance
to abrasion.
It is an additional object of the invention to provide a process
for nonwoven fabrics comprising at least one substrate of dry-laid
fibers and a superposed layer of ultrashort fibers where the two
species of fibers are bonded in separate operations.
Another object of the invention is to provide a novel process for
bonding nonwoven fabrics which involves no binder recovery
system.
Other objects of the invention will be better understood from the
following description and drawings, in which:
FIG. 1 is a schematic representation of an apparatus suitable for
conducting the process of the invention.
FIG. 2 is a cross-sectional representation of a preferred product
of the invention,
FIG. 3 is a still more highly magnified view of one of the
ultra-short fibers of FIG. 2, and FIG. 4 is a cross-sectional
representation of another product of the invention.
The process of the present invention comprises the following
steps:
1. Forming an aqueous suspension of substantially unbeaten and
unhydrated ultrashort fibers in a dispersion of a polymeric
binder.
2. Exhausting the binder in the suspension to substantial
completeness onto and in the ultrashort fibers until the water
phase is substantially free of binder.
3. Forming an open, porous, substantially unbonded fibrous web of
dry-laid fibers or filaments.
4. Applying to the fibrous web the binder-containing ultrashort
fibers.
5. Mechanically removing a major portion of the substantially
binder-free water phase while leaving the binder-enriched
ultrashort fibers at and near the upper surface of the web.
6. Bonding the dry-laid fibers or filaments in a separate bonding
operation.
7. Completing the drying of the fabric.
As an optional additional step, if a product is desired which has a
deposit of ultra-short fibers on both faces, the product after step
6 above may be mechanically reversed and steps 4, 5, and 7
repeated.
By dry-laid fibers is meant here fibers of textile length, capable
of being carded or garnetted; shorter fibers, unfibrillated and
unbeaten, adapted for dry deposition in an air-lay device; and
mixtures thereof. Textile length fibers, usually one-quarter to six
inches in length (6,250 to 150,000 microns) may be cotton, staple
rayon synthetics, mixtures thereof, and the like. Shorter fibers,
down to papermaking length (1,000 - 3,000 microns), may be used
alone or in admixture with textile-length fibers, provided that the
shorter fibers have not been beaten or fibrillated, and are
incapable of forming a papermaker's bond. Methods for forming
dry-laid webs from such fibers, by an air-lay process, are set
forth, for example, in Canadian patent 813,290.
By ultrashort fibers is meant herein fibers which are below the
length of papermaking fibers and which for the purposes of this
invention are not beaten, hydrated, or fibrillated to any
substantial degree, and therefore are also incapable of forming
what is known as a papermakers' bond. Suitable fibers average from
50 to 300 microns in length, and may be typified by bleached ground
or knife-cut wood pulp which has fibers of varying lengths
distributed over that range, or by specially processed ultrashort
cellulosic fibers known as Solka-Floc, a trademarked name for
fibers supplied by the Brown Company. In the latter case, the
length of the ultrashort fibers is closely grouped around a mean,
and mixtures of fibers of different lengths may be used.
By a substantially unbonded fibrous web is meant a web which is
either completely unbonded, such as a web of fibers as delivered
from a card, garnett, or air-lay machine, or a similar web which is
so lightly bonded that its porosity and fiber freedom are
substantially unaltered. This latter alternative is desirable in
cases where it is not convenient to mount a web-forming apparatus
ahead of the wet section of the process, and where transporting and
unwinding the web requires a certain low degree of coherence
between fibers. In general, such light bonding may be effected by
the use of 5 percent or so of a bonding agent, or by mingling with
the textile-length fibers a small percentage of thermoplastic
fibers and subjecting the web to heat to develop autogenous
fiber-to-fiber bonds, or by other conventional methods.
Also included in the definition of substantially unbonded fibrous
webs are webs of continuous filaments, such as are produced by
extruding filament-forming polymers directly from a bank of
spinnerets and intermingling them on a conveyor belt. Such webs may
be unbonded, or more preferably the filaments may be bonded to each
other at least two of their points of intersection.
Whatever the nature of the substrate, it is desirable that it be
basically an open and porous network, free of resist spots which
impede the free passage of water therethrough, and characterized by
an air porosity of at least 150 cubic feet of air per minute per
square foot of product at one-half inch hydrostatic head.
The process may be illustrated by reference to FIG. 1, which is
schematic and not to scale. A web of unspun and unwoven fibers 10
is delivered from a supply roll 12 to a porous conveyor screen 14
driven by guide rolls 15. Alternatively, the web 10 may be
delivered directly to the screen 14 from an assembly of cards,
garnetts, or air-lay machines.
The fibrous web is advanced by the conveyor screen 14 to pass
underneath a flooder box 16, so arranged that a constant
fluid-suspended sheet of ultrashort fibers, coated with a film of
polymeric binder, is deposited on the web. The flooder box is fed
from a supply tank 21, in which the binder-coated ultrashort fibers
are kept in even suspension 19 by means of constant agitation. The
rate of feed of the suspension to the flooder box is controlled by
the valve 23.
For heavy deposits, or for the deposition of ultrashort fibers of
different lengths or ultrashort fibers associated with different
binders, a plurality of such flooder boxes may be used.
The supply tank 21 in turn is supplied with a dilute suspension of
binder-coated fibers from a reaction tank 20 by means of the pump
22. For batch processing, the tank 20 is of sufficient capacity to
supply all of the ultrashort fiber needed for the desired run of
fabric. Alternatively, in continuous processing a multiplicity of
tanks 20 may be used, so that the binder-exhaustion process may be
completed in a stand-by tank while another tank is feeding
binder-coated fibers to the tank 21. The binder-exhaust process
will be described separately below.
From the flooder box 16 the web is advanced to a section where
excess water is removed, said water being substantially free of
binder due to the particular nature of this process. For most
purposes, this extraction of water may be effected by one or more
suction boxes 29. For high speed operation, the action of the
suction box 29 may be supplemented by a set of table rolls 24, as
shown. Such rolls, as used in the paper industry, revolve against
the lower surface of the screen 14 which supports the web, and thus
exert a wiping action or even a gentle suction which removes a
substantial part of the water, thus expediting subsequent
drying.
The water thus removed is drained to a sewer; with the
interposition of a settling tank if desired. In cases where it is
desired to recover any ultrashort fiber content in the white water
a conventional recovery and make-up system, not shown, may be
employed.
The screen 14, driven by guide rolls 15, may be washed free of any
fiber or debris, if desired, by means of a water spray 27. It is an
advantage of this process that there is little or no contamination
and clogging of the screen by the polymeric binder.
As this system is processed, it is for most purposes necessary to
carry out a secondary bonding operation to bond the fibers of the
dry-laid base web, which otherwise would be quite fuzzy and
abrasion-susceptible on its lower surface. This may be accomplished
in a variety of ways, as by including thermoplastic fibers in the
base web, with subsequent exposure to heat. An equally convenient
process is shown in FIG. 1, where the unbonded lower surface of the
web is passed over a print roll 34, revolving in a trough 36 of
polymeric binder 38, whereby a pattern of polymeric binder is
applied to the web, as explained more fully below.
Subsequent drying, and the completion of the setting of the binder
or binders, may be accomplished by transferring the web to an
auxiliary screen 26, driven by drive rolls 28, upon which it passes
under infrared heaters 30. The final drying may be accomplished by
a steam-heated dry can 32, or a multiplicity thereof. The drying
process is not critical, and various other drying expedients may be
employed.
Preparation of Binder-coated Ultrashort Fibers
Basically the steps involved in exhausting non-ionic polymeric
binders onto ultrashort fibers resemble the process in use for
exhausting such polymeric binders onto papermaking fibers by beater
addition, or as set forth in U.S. Pat. Nos. 2,601,598 to Daniel et
al. and 2,765,229 to McLaughlin. An aqueous suspension of fibers is
formed, with the aid of a dispering agent if desired; an aqueous
solution of a polyelectrolyte is added, and agitation is continued
until the polyelectrolyte has been absorbed or adsorbed by fibers;
an aqueous dispersion of a polymeric binder is then added and
agitation is continued until the clarity of the water phase
indicates that substantially all of the polymeric binder is
attached to the solid fiber phase.
As a specific example of the preparation of 100 gallons of 1
percent ultrashort fiber stock coated with an acrylic binder, the
following steps are taken:
1. To 35 gallons of water in an agitated tank of 100 gallon
capacity or more there are added 8 grams of a nonionic wetting
agent, and agitation is continued until the wetting agent is
dispersed: The use of the wetting agent assists in the dispersion
of the ultra-short fibers added subsequently.
2. 3,785 grams of Solka-Floc BW40 are added to the solution and are
agitated for 10 minutes to insure thorough dispersion.
3. The pH of the suspension is adjusted to 8.0 using a solution of
sodium hydroxide.
4. 3,750 grams of a 1 percent solution of a polyelectrolyte such as
Lufax 295 (Rohm and Haas trademark for a salt of a complex
polyamine) are added to the fibrous suspension, agitation is
continued for 5 minutes, the p.sup.H is lowered to 4.5 using
hydrochloric acid, and agitation is continued for 10 more
minutes.
5. 1,270 cc. of Rhoplex HA-8 and 665 cc. Rhoplex K-3 (both Rohm and
Haas trademarks for non-ionic polyacrylic emulsions) are diluted
with water from their 46 percent solids content to 10 percent
solids, after which they are slowly added to the fiber
suspension.
6. Agitation is continued for 10-15 minutes, preferably until
filtration of a sample of the suspension through No. 1 Whatman
filter paper yields a water-clear filtrate, indicating complete
exhaustion of the acrylic binder onto the ultrashort fibers.
7. The volume of the suspension is then brought to 100 gallons by
the addition of water; preferably a dispersing agent in the amount
of 0.1 percent - 0.2 percent of the fiber weight, is added to
insure stability of the suspension and rapid wetting of the
underlying web of dry-laid fibers.
8. For convenience in operation, a colloidal defoaming agent is
added and mixed with the stock solution, in the amount of 0.1
percent - 0.2 percent of the fiber weight.
A process of this sort has been found to produce a binder-coated
suspension of ultrashort fibers free from agglomeration and free
from polymer particles not associated with fibers.
Alternatively, anionic binders may be substantially quantitatively
exhausted onto ultrashort fibers, as by the following
procedure.
To a dispersion of 180 pounds of Solka Floc BW40 in 300 gallons of
water, containing a trace of wetting agent, there were added 230
grams of Fixing Agent FP (BASF tradename for a formaldehyde-amide
condensation product) in 2.5 gallons of water. After 15 minutes, 20
gallons of ACRONAL 35D (BASF tradename for an anionic acrylic
latex), of 25 percent concentration, and containing 1,900 c.cm. of
10 percent Hercosett 57 (Hercules tradename for a
polyamide-epichlorohydrin polyectrolyte) diluted with 2 liters of
water, were added.
After 15 minutes standing, a filtered sample of the suspension gave
a clear water phase, indicating exhaustion of the binder polymer
onto the ultrashort fibers. A trace (0.01 percent) of defoaming
agent and an equal amount of a surfactant were added, and the
volume of the suspension was adjusted to 400 gallons.
Although on a theoretical basis cationic binders should exhaust
onto ultrashort cellulosic fibers, in the absence of a
polyelectrolyte the anionic charge borne by the fibers is of such a
low potential that commercially available cationic latices are only
slowly exhausted. In the use of cationic latices, therefore, it is
desirable to choose a latex with a relatively high percentage of
cationic groups, and to select a highly stable latex to guard
against coagulation.
Other methods of binder exhaustion onto ultrashort fibers will
readily occur to those skilled in the art.
The ultrashort fibers thus prepared are represented in schematic
cross-section in FIG. 3, where a fiber 44 is shown as having a
central cellulosic core 46 and a coating or absorbed layer 48 of
polymeric binder.
It is an advantage of the process of this invention that
concentrations of 1 percent to 4 percent of ultrashort fibers in
water may be employed to flood onto the fibrous substrate, thus
offering economies in the handling and disposal of the aqueous
phase. By contrast, the concentration of beaten and hydrated
papermaking fibers may range from 0.1 percent down to 0.01 percent
in conventional techniques for combining papermaking fibers with
textile-length fibers. In general, fabrics made by the process of
this invention require less than 5 percent of the water
consumption, and associated handling apparatus, which are required
for fabrics of similar weight using conventional papermaking
techniques. In the present invention, it has been generally found
that when the concentration of ultrashort fibers reaches 5 percent
in the aqueous suspension, the viscosity of the suspension is so
high that a smooth and even flooding process becomes difficult.
A wide variety of polar polymeric bonding agents may thus be
exhausted onto the ultrashort fibers, the acrylic and vinyl
dispersions being exemplary. Depending on the nature of the binder
and on the particular effect desired, from 5 percent to 100 percent
of binder (dry basis) may be exhausted onto a given weight of
ultrashort fibers.
EXAMPLE 1.
Using the procedure set forth above, a 100 gallon stock suspension
of binder-coated ultrashort fibers was applied to a card web of 50
percent 1.5 denier - 50 percent 3 denier rayon fibers weighing 25
grams per square yard. After drying, the coated web weighed 56
grams per square yard, consisting of 25 grams of textile-length
fibers, 22 grams of ultrashort fibers, and 9 grams of acrylic
binder, with the binder substantially confined to the ultrashort
fiber layer covering the textile-length fibrous web. The
textile-length fibrous web was adherent to the unified coating of
ultrashort fibers, but was not bonded internally, being soft and
fuzzy. It was given substance and integrity by a secondary
line-bonding operation with a different and firmer acrylic
binder.
The bonded assembly 40 is represented in FIG. 2, wherein the rayon
fibers 42 are shown as intermingled at and near the top surface by
the binder-coated ultrashort fibers 44, and wherein the secondary
set of bonding lines 45 gives strength and integrity to the rayon
web.
This material, Example 1, was then compared in properties with a
similar material containing ultrashort fibers, Example 2 of the
process set forth in U.S. Pat. application Ser. No. 779,318, in
which the ultrashort fibers were merely suspended in the acrylic
binder dispersion which was then flooded onto the web of
textile-length rayon fibers. Example 2 of Ser. No. 779,318 weighed
62 grams per square yard.
In tensile strength, tear strength, and elongation both samples
were on the average substantially comparable and were satisfactory
for use as disposable nonwoven garments in drape and hand. The
opacity of Example 1, however, was 0.75 to 0.80, a definite
improvement over Example 2 which rated 0.65 - 0.72, both measured
on the Bausch and Lomb Opacimeter mentioned above.
Even more pronounced was the superiority of Example 1 over Example
2 in abrasion resistance.
Various methods have been suggested and tried for measuring the
abrasion resistance of nonwoven fabrics, such as the Chemstrand
Aerodynamic Blanket Tester, wherein a fabric sample is caused to
whirl in a circularly-revolving air stream in a closed container,
the walls of which are lined with an abrading fabric.
Alternatively, it has been proposed to affix the nonwoven fabric to
the walls of this apparatus and to bombard it with small plastic or
cork balls in the whirling air stream.
I have found, however, that a more realistic test, more readily
correlated with the behavior of these nonwoven fabrics in actual
use, is provided by a modification of the standard Crockmeter
Tester, AATCC 8-1961 (AATCC Technical Manual, 1967, Howes
Publishing Company, New York, Volume 43, page B-71).
In this test, a fabric-covered weight-loaded plastic foot is rubbed
back and forth across a horizontally-mounted test specimen.
In order to speed up the abrasive action, the 5/8 inch diameter
plastic foot was replaced by a foot 11/2 inches in diameter. Also,
since the woven fabrics suggested for a crocking test proved too
gentle in abrasive action, the 11/2 inch plastic foot was covered
with a polyvinyl acetate-coated nylon scrim, J. P. Stevens style
S/28018/1-100/101.
In such an abrasion test, Example 2 of Ser. No. 779,318 showed
surface damage and separation of short-fibered covering from the
substrate in 20 cycles. Example 1 survived 100 cycles with no sign
of breakage or delamination. In a similar test, a commercially
available disposable nonwoven, comprising a scrim adhesively
laminated to a creped paper tissue, also failed after 25
cycles.
In a second set of experiments illustrating the process of this
invention, a three-component assembly was prepared. The lowermost
fleece was a light spunbonded web of substantially continuous
synthetic filaments such as polypropylene, polyester, or polyamide.
For handling purposes, it is preferred that the filaments of such
spunbonded webs be bonded to each other at between 5 percent and 10
percent of their crossover points, which may for example be
accomplished by an autogenous spot-bonding by heat and pressure
during the formation of the spunbonded web.
Such spunbonded webs, being formed of continuous filaments in a
randomly entangled and interlaced pattern, add a desirable element
of crosswise strength to the products of this invention. However,
they are generally so open and hydrophobic that they do not
satisfactorily retain a layer of ultrashort fibers. It is
preferred, therefore, that there be superimposed upon the
spunbonded web a layer of fibers such as viscose rayon, weighing
for example 10 to 15 grams per square yard.
The method of exhausting the binder onto the ultrashort fibers, and
the application of the binder-coated ultrashort fibers onto the
rayon fibers, were the same as in Example 1.
In the resulting structure, substantially all of the binder-coated
ultrashort fibers remain on or near the uppermost layer of rayon
fibers. Therefore in order to impart unity and coherence to the
three-component composite, a secondary bonding operation was
applied to the spunbonded web in the form of a set of printed
transverse lines of a polymeric binder, applied by passing the
assembly over an engraved print roll with the spunbonded web
contacting the roll. The printing was carried out in such a manner
that at least a part of the secondary bonding agent penetrated
through the spunbonded web and up into the overlying layer of rayon
fibers. The other part of the binder provides strength, integrity
and abrasion resistance to the bottom component, the spunbonded
web.
The composite product 41, shown more or less schematically in FIG.
4, comprises a spunbonded web of continuous filaments 47, a
superimposed layer of rayon fibers 42, and a layer of binder-coated
ultrashort fibers 44 intermingled with the rayon fibers 42 at an
near the upper surface thereof. The spunbonded web is bonded into
the structure by a set of transverse lines 50 of polymeric binder,
applied to the lower (spunbonded) surface by an engraved print roll
in a conventional manner.
It should be realized that for the sake of clarity of detail, only
a few of the multiplicity of the fibers in these products are shown
in FIGS. 2 and 4, and that the secondary bonding lines 45 and 50
are actually more diffuse than shown, due to inter-fiber
capillarity. The structures shown in FIGS. 2 and 4 are therefore to
be regarded as schematic and idealized rather than as
restrictive.
In a third and similar experiment, the substrate was an air-laid
web of unbeaten and unhydrated long paper-length fibers, ranging
from 1,000 to 5,000 microns in length, dry deposited by the process
of Canadian Patent 813,290. The binder applied to the ultrashort
fibers, and the method of application, were the same as in Example
1. The air-laid dry web weighed 40 grams per square yard before the
deposition of the ultrashort fibers, which raised the weight of the
fabric by 30 grams per square yard. The substrate web was then
bonded by a line bonding operation applying 5 grams of binder per
square yard.
The final dried product had very good abrasion resistance and an
opacity reading of between 80 and 85.
Essentially similar results were obtained when the above
experiments were repeated using as a base substrate a mixture of
one-third rayon fibers averaging 6 inches in length, two-thirds
rayon fibers averaging one-quarter inch in length, the two fibers
being intimately blended in an air-lay process. Mixtures of
textile-length fibers and unbeaten and non-fibrillated fibers of
1,000 to 5,000 microns in length may also be used.
As mentioned above, the present invention has the advantage of
allowing different binders to be used in the different species of
fibers. Also, since the dry-laid substrate fibrous web is bonded in
a separate operation, its softness and esthetic appeal may be
further enhanced by distributing the selected binder not uniformly
throughout the web, but in a set of discrete and spaced-apart lines
extending transversely across the web, in the manner known in the
art as "line bonding." Alternatively, it may be bonded by so-called
"spot bonding," or by a set of broken transverse or oblique lines,
by an overall diamond or lozenge print pattern, or by any of the
other well-known and widely practiced patterns of discontinuous
bonding. Either the binder associated with the ultrashort fiber
fraction, or the binder associated with the substrate fiber
fraction, may carry an associated dye or pigment, leading to
patterns which differ on the two faces of the product. Also, it
will be apparent that special auxiliary finishing agents, such as
flame-retardants and the like, may be incorporated into one binder
and one species of fiber but not into the other. Flame-retardants
frequently have a stiffening effect on fabrics of all sorts: in
this manner, it is possible to produce an opaque,
abrasion-resistant and flame-retardant outer layer of ultrashort
fibers on a soft and flexible inner layer of dry-laid fibers.
Also, by avoidance of the use of fibrillated or hydrated fibers,
the products of this invention are characterized by a softness and
drape factor which renders them exceptionally suitable for
disposable garments, sheets, drapes, and the like.
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