U.S. patent number 3,765,974 [Application Number 05/110,576] was granted by the patent office on 1973-10-16 for spot-bonded mats and process for their manufacture.
This patent grant is currently assigned to Firma Carl Freudenberg. Invention is credited to Rudolf Gaertner, Peter Petersik.
United States Patent |
3,765,974 |
Petersik , et al. |
October 16, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
SPOT-BONDED MATS AND PROCESS FOR THEIR MANUFACTURE
Abstract
Improvements in producing a bonded non-woven fabric matting
where the bonding agent is located in discontinuous areas of the
matting or is present in differing and varying proportions in
different areas of the matting. Such a product is made by
substantially uniformly impregnating the matting with a heat
sensitive coagulatable binder latex, non-uniformly heating the
impregnated matting to the coagulation temperature of the latex
only in predetermined areas of the matting whereby coagulating the
binder from the latex only in the preselected areas which have been
subjected to heating to a temperature sufficient to coagulate
binder from the latex, and then removing that portion of the latex
from which the binder was not coagulated by the non-uniform
heating.
Inventors: |
Petersik; Peter
(Luetzelsachsen, DT), Gaertner; Rudolf (Weinheim,
DT) |
Assignee: |
Firma Carl Freudenberg
(Weinheim, DT)
|
Family
ID: |
25757310 |
Appl.
No.: |
05/110,576 |
Filed: |
January 28, 1971 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
848460 |
Aug 8, 1969 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Apr 24, 1969 [DT] |
|
|
P 19 20 836.7 |
Feb 4, 1970 [DT] |
|
|
P 20 04 988.1 |
|
Current U.S.
Class: |
156/84; 156/209;
156/290; 427/354; 427/381; 156/155; 156/278; 156/296; 427/366;
428/198; 428/361 |
Current CPC
Class: |
D04H
1/4258 (20130101); D04H 1/66 (20130101); D04H
1/488 (20130101); D04H 1/435 (20130101); D04H
1/482 (20130101); Y10T 156/1023 (20150115); Y10T
428/2907 (20150115); Y10T 428/24826 (20150115) |
Current International
Class: |
D04H
1/64 (20060101); D04H 1/66 (20060101); B32b
031/20 (); B32b 031/22 (); B32b 003/30 () |
Field of
Search: |
;161/148,170
;117/38,42,62,62.2,63 ;156/155,209,84,290,278,321,322,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ansher; Harold
Parent Case Text
This application is a continuation-in-part of Application Ser. No.
848,460, filed Aug. 8, 1969, now abandoned.
Claims
What is claimed is:
1. Process of producing a spot-bonded non-woven fabric which
comprises:
A. forming a batting of geometrically randomly disposed filaments
or fibers which can be needled and which contain shrinkable
fibers;
B. substantially uniformly impregnating such batting with a liquid
form latex containing a temperature sensitive coagulatable
binder;
C. contacting said impregnated batting with a heated depth
contoured surface means;
D. heating at least portions of said impregnated batting to an
extent sufficient to coagulate at least a portion of said binder
from said latex into spherules in the interstices of said fabric,
wherein the combination of said steps C and D causes said
coagulated binder to concentrate in predetermined areas in said
batting, said binder-containing areas of said fabric having a
greater thickness than the other areas of said fabric, which are
vein-like in appearance;
E. washing out substantially all uncoagulated binder from said
batting; and
F. drying said batting.
2. Process as claimed in claim 1, including passing said
substantially uniformly impregnated batting through the nip of a
pair of heated toothed rollers, each of which has protuberances
which alternate with respect to each other, wherein said
protuberances force said impregnated latex into the area of said
batting between said protuberances, and coagulating said latex in
said areas.
3. Process as claimed in claim 1 wherein said steps C & D are
carried out simultaneously with a contact time of about 1 second at
a temperature of about 120 to 420.degree.C.
4. Process as claimed in claim 1 including the additional step of
applying a polymeric film form coating comprising vinyl chloride or
polyurethane to at least one surface of said spot bonded non-woven
fabric which was contacted by said heated depth contoured surface
means.
5. Process as claimed in claim 1 including needling the batting
produced in step A.
6. Process as claimed in claim 1 including profiling both major
surfaces of said batting.
7. Process as claimed in claim 6 including longitudinally splitting
said profiled, spot-bonded batting between the major surfaces
thereof.
8. Process as claimed in claim 7 including applying a polymer
coating to the profiled surfaces of said split batting.
Description
This invention relates to non-woven fabrics. It more particularly
refers to non-woven fabrics which are particularly useful for
synthetic leather or leather-like applications.
Non-woven fabrics, as this term is used in the textile arts, are
mats or bats made up of staple fibers or continuous filaments where
the individual fibers or portions of the individual filaments are
geometrically randomly disposed with respect to each other. Such
fabrics are usually made from a card lap (in the case of staple
fibers) which may or may not have been passed through a cross
lapper and/or a needle loom in order to further disorient the
fibers with respect to each other. Non woven fabrics made up of
continuous filaments are often made by laying the filaments down on
a suitable fleece form directly out of the spinnerette in a random
pattern. The term "non-woven" does not include knitted, netted,
crocheted or other fabrics having fibers or filaments in a
geometrically patterned array, regardless of how made.
In any case, regardless of how the randomlay, non-woven fabric is
made, and regardless of whether such fabric is composed of staple
fibers or continuous filaments, it is common in this art to bond in
some way the individual fibers or filament portions together so as
to increase the dimensional stability of the mat or bat product to
an extent sufficient to create a fabric having physical integrity.
Such bonding has been accomplished in the past by many varying
techniques, including:
1. providing at least some thermoplastic fibers or filaments in the
fabric having a lower melting or softening point than the remainder
of the fibers or filaments and then heating the fabric to an extent
sufficient to melt or at least tackify these fibers or filaments
and cause them to bond to other fibers and/or filaments;
2. uniformly impregnating the non-woven fabric with a liquid form
bonding agent, either solution or latex, and removing the carrier
liquid thereby depositing bonding agent throughout the fabric which
effectively bonds the fibers or filaments together;
3. spot impregnating the non-woven fabric and proceeding as in 2);
or
4. providing a plasticizer or other softening agent uniformly or
spotwise through the non-woven fabric in an amount sufficient to
cause the fibers or filaments of the fabric to become tacky to an
extent sufficient to bond them together.
In all of these techniques the bonding generally takes place at the
crossing points of the fibers or filaments, thereby retaining the
textile and sometimes lofty character of the fabric.
In the manufacture of non-woven textile fabrics in the prior art
the uniformly impregnated loose fiber mats were dried, in which
drying process the binding agent collected in the form of lamella
or webs mainly at the intersections between the fibers or
filaments, as can clearly be seen in FIG. 4 of U.S. Pat. No.
2,719,802. The binding agent in this lamella form was vulcanized by
the action of heat simultaneously with the drying of the fabric.
The products thus manufactured, which are commercially available
(under the name "Vlieseline" in Germany, or "Pellon" in the United
States) are especially characterized by their springiness and
elasticity. They are therefore used mainly as lining and stiffening
materials in clothing.
From U.S. Pat. No. 2,545,952, it is furthermore known to imprint
upon an initially loose non-woven mat fabric spots of rubbery latex
or other binding agent having similar properties, such as casein,
glue, natural resins, etc., making use of a roll engraved with spot
depressions for the purpose. The binding agent, which is at first
imprinted as spots on the surface of the mat, then sinks slowly
into the interior of the mat so that a bonding action is produced
also in areas underneath the imprinted surface spot of latex. This
method, which is suitable only in the case of thin matting weighing
up to about 60g/m.sup.2, is also known in Germany by the English
term "spot binding." Also see in this connection West German
Auslegeschriften Nos. 1,098,903, 1,099,983, 1,106,285, and
1,062,204.
The spot-bonded non-woven fabrics known hitherto are softer and
more water-absorbent than otherwise equivalent mats which are
uniformly impregnated with binding agent. However, their tensile
strength is low, as might be expected, and therefore they are
usually used for the manufacture of disposable goods.
Clearly, it would be desirable to provide non-woven textile fabrics
which have the water-absorbency characteristics of spot-bonded
fabrics and the tensile properties of uniformly bonded fabrics. It
would also be more desirable to be able to utilize non-woven
fabrics having a fiber weight of higher than about 60 grams per
meter, which is about the highest weight fabric the prior art has
been able to work with in a spot-bonding technique, such as higher
fiber weights being for example, up to about 1000 grams per meter
or even more.
The objects of this invention are, therefore, to fulfill the
above-recited desirable conditions.
In accord with, and fulfilling these objects, one aspect of this
invention resides in a novel technique of bonding a non-woven
fabric. According to this invention, a suitably formed non-woven
fabric of staple fibers or of continuous filaments is substantially
uniformly impregnated with a latex form bonding agent which is
coagulation sensitive as a function of temperature. Such so-called
heat-sensitive, coagulatable latexes are known, and it is per se
known to impregnate a non-woven fabric therewith, according to U.
S. Pat. No. 2,719,802. By heat-sensitized bonding agents are meant
those in which the bonding agent abruptly flocculates (coagulates)
in the form of tiny spheres or beads when a predetermined certain
temperature, e.g., about 20.degree. to 90.degree.C, preferably
40.degree. to 60.degree.C, is applied. This type of heat sensitive
bonding agent is commercially available and is a per se well-known
product. The thus substantially uniformly impregnated non-woven
fabric is then subjected to a procedure whereby binder is caused to
deposit only in predetermined locations.
The impregnated fabric is passed through heating means which may be
an unheated smooth roller or a flat plate on one side and a heated
roller on the other side which heated roller has protuberances on
the surface thereof. The protuberances heat those portions of the
fabric which they contact or which they approach to a greater
degree faster than those portions of the fabric which are disposed
opposite the areas between the protuberances. Therefore, the
residence time or contact time between the impregnated fabric and
the heated roller protuberances and the temperature of the heated
roller protuberance can be so adjusted with respect to each other
and with respect to the coagulation temperature of the latex
impregnant that the area of coagulation of the binder from the
latex can be very carefully controlled. It is not necessary to the
practice of this aspect of this invention that the
protuberance-containing roller be heated in its entirety, although
this is possible and in many cases may be the most practical
solution to effecting the localized heating; the roller therefore
may be constructed in such a manner that only the protuberances are
heated. The roller may be heated by any conventional technique,
e.g., electric resistance, steam, heating liquids, direct fired
heat or the like. Whether the roller acts as a heat exchanger by
having heating means as an integral part of its construction or by
its being heated away from the fabric and then passing the heat on
to the fabric is immaterial to this aspect of this invention. What
is important is only that at least the protuberances of the roller
means are heated to a high enough temperature and are juxtaposed to
the fabric for long enough to cause the binder to coagulate in
certain preselected areas of the fabric but insufficient to cause
the binder to coagulate in other, adjacent areas of the fabric.
It should be appreciated that the latex coagulation temperature,
the roller protuberance temperature and the juxtaposition time are
all interrelated functions and they cannot be individually defined
without reference to the other. That is, for a given latex having a
given coagulation temperature, a certain protuberance temperature,
a particular juxtaposition time and a given spacing between fabric
aNd protuberance (including zero spacing which would define simple
contact or even negative spacing which would define contact
accompanied by pressing of the fabric by the protuberances) are
required to cause coagulation of bonding agent from the latex only
in the required predetermined spots or areas where it is
desired.
The routineer in the art, given the interrelations expressed above,
and knowing the coagulation temperature of the latex as well as the
area of latex to be coagulated by each protuberance, can easily
calculate the required parameters of spacing, juxtaposition time
and protuberance temperature sufficient to cause such coagulation
in such predetermined areas. General operating parameter ranges
are: protuberance temperature 120.degree. to 420.degree. C,
protuberance/fabric juxtaposition time 0.1 to 3 seconds. It will be
appreciated, however, that there will be readily found operating
parameter combinations suitable for the purposes of this invention
which are outside the scope of one or more of the ranges set forth
above. The only critical parameter is that the operation be
sufficient to cause predetermined areas of binder to coagulate
while preventing the remainder of the binder from coagulating.
Another aspect of this invention which will accomplish the
coagulation of binder in predetermined areas of a non-woven fabric
while preventing or minimizing the coagulation of binder in other
areas of the fabric is to pass a substantially uniformly
impregnated non-woven fabric through the nip of a pair of roll
means wherewith the roll means have alternating protuberances
thereon, or where one roll has protuberances and the other is
smooth. As the impregnated non-woven fabric passes between the
rolls, the action of the alternating protuberances exerts a
pressure on the fabric and on the latex impregnated therein to
effectively force some or all of the latex into areas between next
adjacent alternating protuberances. This action effectively
localizes the latex impregnant into predetermined areas from which
the binder is then coagulated by subjecting the thus treated fabric
to uniform localized heating as the case may be. If heating
sufficient to coagulate binder from the heat-sensitive latex is
instituted immediately after treatment by the protuberance roll
means, the liquid form latex will not have time to flow back to a
uniform impregnation condition before the binder is coagulated
therefrom. Thus the binder can be coagulated and disposed
substantially only in those areas where it is desired. It is within
the scope of this invention to use heated roll means or to provide
separate heating means following the protuberance roll means.
By adjusting the nip pressure of the protuberance roll means it is
possible to control the proportion of binder which will be forced
out of those areas impressed by the protuberances into the areas
between protuberances. By controlling this pressure, all or only
part of the impregnated binder can be moved as desired.
Although it is considered to be less desirable, the protuberances
on the pressure-exerting roll can be in mating configuration as
well as alternating configuration.
In all aspects of this invention, regardless of how the latex is
moved within the non-woven fabric or how spotwise coagulation is
accomplished, after coagulation of the binder, the fabric is then
treated to remove any remaining uncoagulated binder from the
fabric. This can be accomplished by simply washing the coagulated
binder containing latex with water.
It has been found that the product produced by the above-described
process is quite unique. This uniqueness manifests itself in the
fact that the final spot-bonded product does not have a uniform
thickness and the fact that at least one of the major surfaces of
the fabric product is profiled, that is, it has hills and valleys
corresponding to the binder-containing areas and the areas of low
or no binder concentration. One of the surprising things about the
product is that the surface valleys do not correspond to those
portions of the fabric which were juxtaposed to the coagulating
protuberances during binder-impregnation and coagulation but rather
correspond to those portions of the fabric which were between these
protuberances.
While not wishing to be bound by any particular theory, it is
thought that the valley portions of the spot-bonded product are the
result of a partial collapse of the unbonded non-woven fabric
structure on washing out the uncoagulated binder while the hill
portions correspond to the binder-containing portions of the fabric
because these portions have greater resilience and dimensional
stability.
Understanding of this invention will be facilitated by reference to
the drawing in which:
FIG. 1 is a schematic side elevation of a uniformly impregnated
batting being juxtaposed to a protuberance containing heated
roller;
FIG. 2 is an enlargement of the contacting portion of the roller
and batting of FIG. 1, schematically showing collimated coagulation
within the batting;
FIG. 3 is a schematic side elevation of a batting having
spot-coagulated binder therein as it leaves the coagulation
process;
FIG. 4 is a schematic side elevation of the spot-impregnated
product after washing;
FIG. 5 is a schematic side elevation of a uniformly impregnated
batting being treated with two opposing protuberance-containing
rollers; and
FIG. 6 is an enlarged side elevation of the rollers of FIG. 5;
FIGS. 7 and 8 show examples of the surface of mats that have been
spot-bonded according to the invention.
Referring now to the drawing, a roller 1, having protuberances 2 of
given predetermined size, configuration and spacing, is rolled over
a batting 3 just touching the batting, which was previously
uniformly impregnated with the heat-sensitized binding agent, using
a flat plate or table 1a as a base. In this depicted aspect of this
invention, only the protuberances 2 of the roll 1 press against the
batting 3, as it can be seen in FIG. 1. As shown in FIG. 2, the
heat of the protuberance 2 is transferred to the batting by
radiation and conduction such that the binding agent which is
uniformly distributed in the batting, coagulates only in those
areas of the batting where it has been heated by the protuberance
to a coagulating temperature, e.g., in the darker area shown in
FIG. 2.
The heat radiated into the batting -- symbolized by arrows in FIG.
2 -- is so intense in the juxtaposed area of the batting that after
about 1 second of contact the binding agent coagulates
(flocculates) in the areas directly below the protuberance 2. Heat
also radiates into the batting from the adjacent areas 4 (recesses)
of the roll, but the spacing of the recesses from the batting and
the short contact time are so chosen that the combination is
insufficient to heat that portion of the impregnant to a
temperature which is sufficiently high to cause coagulation
(flocculation) of the binder. The pressure exerted by the roll 1 on
the batting 3 and the roll temperature are so chosen to produce the
above heating and coagulation effect and the effective contact time
between the roll and the mat is preferably maintained at only about
1 second at both the leading and trailing edges of the
protuberances. Consequently, when the protuberance 2 touches the
fabric 3 only the binding agent in the area 3a will coagulate,
while the binding agent in the adjacent areas 4' and 4" will not
coagulate at all or will coagulate only to a significantly lesser
extent. This selective coagulation process is repeated constantly
as the hot roll 1 passes over the uniformly impregnated batting.
Substantially immediately -- or as soon as it is sufficiently
heated -- after the juxtaposing of protuberance 2 against the
batting 3, the binding agent directly under the contact surface in
the batting coagulates, but it does not coagulate in the areas
immediately adjacent thereto. The cross-section of coagulated
binder in FIG. 2 has been shown to be rectangular. Actually it will
probably be more conical, or possibly eliptical; however, since the
fabric thickness is so small the actual cross-section is most
difficult to determine.
If the pressure between the roll 1 and the fabric 3 is such that
the protuberances 2 press into the fabric 3, the binding agent
latex will be forced out from immediately below the protuberances
into the interstices of the fabric disposed between protuberances
(see areas marked 4' and 4" in FIG. 2). The heated roll will cause
such displaced latex to coagulate in these areas 4' and 4" provided
the contact time, the temperature and pressure of the roll are
appropriately adjusted. Thus, since the heat passage from the roll
to the latex takes longer than the time to displace the latex,
short contact times and relatively high roll pressure will cause
displacement and coagulation to occur sequentially.
After the passing of the hot roll 1, some of the binding agent in
the batting 3 is in the coagulated state and some remains
uncoagulated. FIG. 3 is a diagrammatic representation of such a
batting. It can be seen how areas 3a containing coagulated binding
agent alternate with areas 41a in which the binding agent is
present in the uncoagulated form. When the binding agent coagulates
from a latex, it separates in the form of many small spherules,
which is the reason why the structure is often referred to as a
caviar or birdshot structure. It is for this reason that the
structure of the coagulated binding agent is represented by dots in
FIG. 3. The uncoagulated binding agent is represented by lines.
After the hot roller treatment the coagulated binding agent has
become fixed, but the uncoagulated binding agent can be removed
from a batting simply by washing it out with water.
Therefore, if the batting shown in FIG. 3 is immersed in running
water, only the uncoagulated binding agent is washed away from
areas 4a, but the coagulated binding agent will not be washed away
from areas 3a.
The spot-bonded fabric resulting from the washing process is
represented diagrammatically by FIG. 4. The areas 3a containing
coagulated binding agent alternate with areas 4a, which are
substantially free of binding agent. Such a fabric is very soft,
elastic and air-permeable. Its water absorbency is remarkably high.
It is distinguished from the spot-bonded fabrics that have
previously been known, by its substantially better mechanical
properties, particularly its tensile strength. It is outstandingly
suitable for further working into artificial leathers, household
products, clothing, luggage, lining materials, surface fabrics,
show materials, automobile roof liners, upholstery, floor
coverings, etc.
It should be noted from considering FIG. 4 that one of the major
surfaces of the spot-bonded fabric, that is, the surface which was
juxtaposed to the roller having protuberances thereon, does not
have a flat profile as do uniformly bonded or unbonded fabrics.
Rather, it has hills 10 and valleys 11 which correspond to the
bonded and unbonded portions thereof, respectively.
According to one particular embodiment of the invention shown in
FIG. 5, a similar product can be produced except that the washing
step can be dispensed with, or at least reduced. In this embodiment
the batting 3, which is first uniformly impregnated with binding
agent, is run between a pair of rolls 5, 6 (see FIG. 5), both rolls
being provided with protuberances 8 and 9, and 7, respectively. The
rolls are rotated synchronously so that in the gap between them a
protuberance 7 of the lower roll 6 will mesh with and be disposed
in an area between the protuberances 8 and 9 of the upper roll 5,
as shown in FIG. 6. As the impregnated batting 3 passes through the
gap between such studded rolls, the pressure distribution is, of
course, irregular, and the binding agent tends to be displaced from
the high-pressure areas toward the low-pressure areas, that is,
from the area of smallest gap to the area of largest gap. Thus the
binder tends to be concentrated in the areas between the
protuberances 8 and 7 or 7 and 9, respectively, while the portion
of the fabric directly adjacent each protuberance tends to have
little or no binder latex left therein. If the roll protuberances
are heated as set forth above, substantially all of the impregnated
binder will be coagulated but since the binder latex has also been
displaced, the profile of concentration of coagulated binder in the
product will also generally correspond to that shown in FIG. 4. In
this embodiment of this invention the final product also has a
profiled surface. However, in this case the hills, while
corresponding to the portions of high binder concentration, also
correspond to those areas of the impregnated batting which were
between the roller protuberances rather than juxtaposed to the
roller protuberances as in the embodiment depicted in FIGS. 1 and
2.
In this embodiment, the roll temperature should be kept as low as
possible, for it can be seen that the displacement of the binding
agent must take place before the coagulation begins. If the studded
rolls had high temperatures, the coagulation might occur before or
during the displacement of the binder latex. It is essential to
avoid this because, as already stated above once the binding agent
has coagulated, it is fixed in place, and then cannot be removed
either by pressure or by washing.
In the embodiment represented in FIGS. 1 and 2, the roll 1 can be
at a higher temperature than in the embodiment of FIGS. 5 and 6
because the pressure in this first embodiment may be substantially
less, or even non-existent, and hence the heat transfer is not as
intense as in the embodiment of FIGS. 5 and 6. The contact pressure
and the speed of the revolving roll (the contact time) depends upon
the pattern of the roll protuberances and the dimensions of the
roll, and on the sensitization temperature of the binding agent in
the mat. The optimum values in each case can, however, be
determined quite simply by experiment or calculation. The minimum
temperature of the roll, when considered in combination with the
roll speed, must, of course, be high enough to produce coagulation
of the binding agent in the areas 3a directly beneath the
protuberance 2 (see FIG. 2). On the other hand, the temperature
should not be so high as to induce coagulation, at the same running
speed, in the adjacent areas 4a.
Whereas in the spot-bonding technique that has been practiced
hitherto, the binding agent is deposited only locally on the
surface of the batting in the areas where the bonding spots were
desired, the new method differs from the prior art in that the
batting is first impregnated quite uniformly as in
non-spot-bonding, prior-art fabric production methods. This makes
it possible to manufacture denser mats. It is readily understood
that when binding agent is printed only on the batting surface, and
will then be caused to penetrate through the batting thickness,
only thin mats can be used, since the imprinted dot of binding
agent only slightly penetrates into the batting interstices
underneath it. Deep penetration -- all the way to the back of the
mat, if possible -- is most desired in producing spot-bonded
fabrics because otherwise the fabric structure, which is not too
strong to begin with, may delaminate. It is for this reason that
only thin batts having a weight up to 60 g/m.sup.2 have been
imprinted by the prior-art spot-bonding methods, whereas the
process of this invention is capable of spot-bonding batts having
fiber weights of up to about 1000 g/m.sup.2 or more.
Uniform binder latex impregnations, such as practiced in the method
of the invention, may be accomplished according to any of the known
procedures (see, e.g., NONWOVEN FABRICS, published by Non-Woven
Associates, P.O. Box 328, Cambridge 39, 1959, pp 25-28). These
impregnations are substantially independent of the thickness of the
batting. It is easily possible to uniformly impregnate batts having
a fiber weight of 1000 g/m.sup.2. In these batts, then, the binder
can be made to coagulate according to the invention at certain
points through the entire structure, while other areas in the final
product will then be rendered substantially free of binding
agent.
The spot-bonding method according to the invention, therefore, is
not limited, as is the prior-art spot-bonding method, to thin
batting.
The starting batt according to the invention can be produced with a
card or cross lapper or in any other conventional manner. It may be
in needled or unneedled form. The filaments may be staple or
continuous and may be of substantially any conventional fiber
material. There are no limitations with respect to the composition
of the fibers or the use of a multiplicity of different fibers
and/or filaments in the same mat. It can be said, therefore, that
any desired batting can be spot-bonded according to the process of
the invention.
The binding agents to be used according to the invention must, of
course, all be coagulatable and in addition, heat coagulation
sensitive, i.e., the binding agent present initially in the latex
impregnant must be capable of coagulating as a function of
temperature in the form of "bird-shot" when a certain temperature
is reached -- usually between 20.degree. and 90.degree. C.
The invention is of particular value, however, in the production of
imitation leathers comprising a composite of a continuous coating
of suitable polymeric material joined to one major surface of a
non-woven fabric. There is now often a desire to produce an
imitation leather the surface of which appears to have folds or
creases in it, which thus resembles worn leather which has been
crumpled. The effect is generally called "wet leather." Attempts
have been made to achieve this effect by applying a suitable
coating of a polymer onto a non-woven fabric, thereby producing a
product having a smooth surface; and then crumpling the composite
product so as to give the desired creases in the surface. This
product has proven to be somewhat less than satisfactory because
after a short time the creases generally disappear and the product
regains its smooth surface.
The spot-bonded or line-bonded non-woven fabrics made according to
this invention, however, are exceptionally well-suited to use in
producing such creased surfaced "wet leather." This is achieved by
producing a spot-bonded non-woven fabric according to the practice
set forth hereinabove so that the first and second areas, that is,
the binder-containing and binder-free areas, respectively, are
arranged in an irregular pattern with at least some of the second
areas (i.e., the areas having less or no coagulated bonding agent)
being in the form of elongated irregular streaks. Generally the
bonded and the bond-free areas are arranged in a pattern resembling
that obtained in the surface of leather or crumpling the leather. A
coating of a suitable polymeric material such as polyvinyl
chloride, is applied to a major surface of this non-woven fabric
and adhered thereto in the usual way whereby producing a resultant
imitation leather which has a permanent pattern of elongated
irregular streaks in it. This product has the desired creased
effect permanently in its surface.
Although any non-woven fabric can be used in the practice of this
invention, the preferred non-woven fabric is a needled fabric. The
fabric preferably is one that contains shrinkable fibers and which
has been shrunk by conventional techniques in order to consolidate
it, generally after needling. The area of fabric shrinkage should
be at least 20 percent, and preferably 50 percent or more. The
shrunken fabric is then impregnated with coagulatable binder in the
manner described above and the desired distribution of binding
agent achieved. The desired polymeric coating can then be applied
on the spot-bonded nonwoven fabric by any convenient process. For
example, a "counter coat" process can be used. In this process a
polyurethane or other suitable coating material is spread on a
carrier and the non-woven fabric is then pressed onto the coating
material and the composite so produced subsequently stripped from
the carrier. This type of coating is usually glossy.
It may be desirable to additionally crumple the laminated product
in a conventional mechanical manner so as to accentuate the veined
effect that is obtained by practing this invention. The veined
effect is permanent.
The following is an Example of the invention.
A fleece consisting of 70 percent of viscose rayon fibers and 30
percent of polyester shrinkable fibers with a total fiber weight of
200 g per square meter is prepared, needled and then shrunk by
heating in the conventional manner. The shrinkage in area is 45 -
50 percent. Accordingly, the weight of the fabric after shrinking
is 440 - 500 g/sq.m. This shrunk fleece is then uniformly
impregnated with a conventional commercial heat-sensitive colored
polyacrylate latex (Perbunan N 4 M produced by Farbenfabriken
Bayer) to a wet pickup of latex of about 150 percent. Impregnation
is by conventional techniques. The impregnated fleece is then
passed through the nip of two heated contoured rolls having
protuberances in the form of irregular longitudinal lines which
resemble veins. The rolls are heated externally to about
250.degree.C.
The impregnated latex is thereby first displaced away from the
protuberances into the areas between next adjacent protuberances
(see FIGS. 5 and 6) in accordance with the pattern thereof and the
binder is then coagulated in such location by the heating effect of
the rolls. The temperature of the rolls and the speed of travel of
the fabric through their nip are selected appropriately to achieve
the desired effect. The fabric is thereafter passed through a cold
water bath and uncoagulated binder and/or auxiliary agents are
washed out. After subsequently drying the product, a sheet-like
structure having the roll pattern on both sides is obtained.
This product may be split longitudinally if desired, for example,
on a conventional leather splitting machine, in order to produce a
partially bonded non-woven fabric having one profiled surface and
one smooth surface. The upper and lower splits can both
satisfactorily be used for the next stage in the process, just as
the unsplit product can so be used.
The next stage in the process is to apply a coating of 50 grams per
square meter of a conventional polyurethane onto the profiled
surface by the counter coat process. After curing, the product is
subjected to an additional mechanical creasing and crumpling
operation and thus attains an irreversible creased effect. This
product is excellently adapted to use in the manufacture of, for
example, purses, handbags, shoes, clothing, upholstery and the
like.
* * * * *