Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CARDABLE HYDROPHOBIC POLYOLEFIN FIBRES
COMPRISING CATIONIC SPIN FINISHES
FIELD OF THE INVENTION
The present invention relates to cardable and thermobondable
polyolefin-based synthetic fibres treated with hydrophobic
spin finishes comprising a. cationic antistatic agent and a
hydrophobic lubricant, a method for producing the fibres, and
nonwoven products prepared from the fibres.
The fibres, which have the advantage of being able to be
carded at extremely high speeds, are particularly suitable
for use in the preparation of thermally bonded hydrophobic
nonwoven fabrics in which a dry, water repellant surface
which can function as a liquid barrier is desired, e.g. for
disposable diapers and feminine hygienic products. The fibres
are also suitable for the preparation of thermally bonded
nonwoven fabrics for medical use in which a dry, water repel-
lant surface is desired in order to reduce bacterial penetra-
tion, for example medical gowns and drapes.
BACKGROUND OF THE INVENTIO1V
A number of polyolefin-based hydrophobic synthetic fibres are
known, for example hydrophobic textile fibres with dirt and
stain resistant properties. However, such fibres generally
contain cationic antistatic agents that are undesirable or
unsuitable for personal hygiene and medical products for
toxicological reasons, since they often exhibit skin irritat-
ing properties due to their low pH. Also, some components may
during use release di- or tri-ethanolamine, which is suspect-
ed of causing allergic reactions. It has previously proved
difficult to produce fibres for hygienic or medical use
having good cardability properties together with satisfactory
hydrophobic properties. This is particularly important for
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the many applications in which it is desired that hydrophobic
fibres may be carded using high carding speeds.
Hygienic products such as disposible diapers, sanitary nap-
kins and adult incontinence pads generally have barriers
through which fluids absorbed by the absorbent core are not
able to penetrate, e.g. in the form of side guards, other
structural elements, or as back sheet material opposite to
the skin. Such barriers may comprise a nonwoven material
prepared from hydrophobic staple fibres or a spunbonded
material prepared directly from a hydrophobic polymer. How-
ever, spunbonded materials are very flat and film-like, and
do not have the soft, uniform, textile-like comfort that one
finds in nonwovens. Spunbonded fabrics are therefore not the
optimal choice for liquid barriers designed to be in contact
with the skin of the user. Also, spunbonded nonwovens have a
non-uniform distribution of fibres, which results in Weak
areas (holes? that limit the liquid barrier properties of the
fabrics, so that web uniformity becomes the limiting factor
for the hydrophobic characteristics. As for nonwovens pre-
pared from staple fibres, these tend not to be sufficiently
hydrophobic for such liquid barriers, due to the fact that
during the spinning process, the fibres are treated with a
~~spin finish° which facilitates the spinning pro-cess by
lubricating the fibres and making them antistatic. However,
as a result of the spin finish treatment, in particular the
use of an antistatic agent, which by nature is more or less
hydrophilic, the fibres become somewhat hydrophilic, which in
the present context is undesirable. On the other hand, fibres
with the desired degree of hydrophobicity have generally had
suboptimum antistatic properties.
EP 0 557 024 A1 describes polyolefin fibres treated with an
antistatic agent which is a neutralized phosphate salt, and
optionally with a hydrophobic lubricant selected from mineral
oils, paraffinic waxes, polyglycols and silicones, the fibres
having an hydrostatic head value of at least 102 mm.
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WO 94/20664 describes a method for producing cardable, hydro-
phobic polyolefin-based staple fibres using two spin finish-
es, in which the second spin finish is a dispersion compris-
ing an antistatic agent, preferably an anionic or non-ionic
' S antistatic agent, and, as a hydrophobic agent, a natural or
synthetic hydrocarbon wax or wax mixture, and optionally a
' silicone compound.
The present invention represents a different and highly
effective approach to the problem of providing polyolefin
staple fibres with an optimum combination of hydrophobic and
antistatic properties, thereby making them suitable for the
production, in particular by means of high-speed carding, of
nonwovens with optimum strength and hydrophobic characteris-
tics. Furthermore, the invention is based on the use of
substances which are not irritating to the skin.
An object of-the present invention is therefore to provide -
hydrophobic thermobondable synthetic fibres, in particular
for hygienic applications, with both optimum hydrophobic and
antistatic properties, and thus with improved carding proper
ties suitable for preparation of nonwovens showing superior
strength. A further object of the present invention is to
improve the application and distribution of spin finish on
the fibres, thus improving fibre uniformity, allowing in-
creased carding speed and improved web uniformity in the
carding process, which in turn results in nonwovena with
improved hydrophobic properties.
BRIEF DISCLOSURE OF THE INVENTION
In one aspect, the present invention relates to a method for
producing cardable, hydrophobic polyolefin-based staple
fibres, the method comprising the following steps:
a. applying to spun filaments a first spin finish comprising
at least one cationic antistatic agent,
b. stretching the filaments,
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c. applying to the stretched filaments a second spin finish
in the form of a dispersion comprising at least one
hydrophobic lubricant selected from a fatty acid amide
condensation product and a hydrocarbon wax,
d. crimping the filaments, '
e. drying the filaments, and
f. cutting the filaments to obtain staple fibres. '
Further aspects of the invention relate to texturized, card-
able, polyolefin-based fibres produced by the above method,
as well as hydrophobic nonwoven materials containing such
fibres.
The fibres of the present invention have been found to have
excellent hydrophobic properties as well as excellent anti-
static properties and can therefore be carded at high carding
speeds comparable to carding speeds typically used for hydro-
philic staple fibres. The fibres' suitability for high-speed
carding is also due to their controlled fibre/fibre and
fibre/metal friction properties obtained by varying the
composition of the spin finishes, especially the, second spin
finish. It has furthermore been found that webs prepared from
the fibres have a uniform distribution of the fibres in both
the machine direction and the transverse direction, and that
when these webs are thermobonded by calender bonding non-
wovens with improved strength and excellent hydrophobicity
are obtained.
In anionic systems it is necessary to use a large amount of a
hydrophobic lubricant, often a silicone compound, in order to
obtain a reasonably high degree of hydrophobicity. With the
cationic system of the present invention, however, the inher-
ent hydrophobicity of- the antistatic agent and the hydro-
phobic lubricant is so good that the desired hydrophobic
properties can be obtained without or with only a small
amount of silicone. This is an important advantage, since
reducing the amount of silicone gives a greater and more
WO 95!194G5 2 1 8 0 2 4 7 P~~~y5100024
uniform fibre/fibre friction,-Which in turn facilitates high
speed carding.
Antistatic agents of the quaternary ammonium salt type are
commonly used for polyolefin fibres outside the hygienic
5 sector, in particular for bulk continuous filaments or staple
fibres intended for use in e.g. carpets or technical applica-
tions, rather than for hygienic applications or clothing.
According to the present invention it has been found that
fatty acid amide condensates and natural or synthetic hydro-
carbon waxes can be advantagously used in combination with
cationic antistatic agents, the fatty acid amide condensates
and waxes functioning as hydrophobic lubricants, i.e_- provid-
ing hydrophobic properties as well as the desired frictional
properties.
Certain types of prior art polypropylene fibres are produced
using cationic antistatic .agents, esterified wax components
and a large amount of alkoxylated emulsifiers. However, the
spin finishes of such fibres typically contain a relatively
large amount of acetic acid or another acid that must be
evaporated during bonding to avoid acid-induced skin irrita-
tion. In contrast, the fibres of the present invention are
prepared using non-alkoxylated emulsifiers without esterified
wax components, and also without the use of large amounts of
an acid.
DETAILED DISCLOSURE OF THE INVENTION
The term ~~polyolefin-based" refers to the fact that the
fibres of the present invention are produced from a polyole-
fin or a copolymer thereof, including isotactic polypropylene
homopolymers as well as random copolymers thereof with ethyl-
ene, 1-butene, 4-methyl-i-pentene, etc., and linear poly-
ethylenea of different densities, such as high density poly-
ethylene, low density polyethylene and linear low density
polyethylene. The melts used to produce the polyolefin-based
fibres may also contain various conventional fibre additives,
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such as calcium stearate, antioxidants, process stabilizers,
and pigments, including whiteners and colourants such as
Ti02, etc.
The hydrophobic fibres may be either monocomponent or bicom-
ponent fibres, the latter being for example sheath-and-core _
type bicomponent fibres with the core being located either '
eccentrically (off-center) or concentrically (substantially
in the center). Bicomponent fibres will typically have a core
and sheath which comprise, respectively,
polypropylene/polyethylene, high density polyethylene/linear
low density polyethylene, polypropylene random copolymer/-
polyethylene, or polypropylene/polypropylene random copoly-
mer.
Fibres prepared according to the present invention may be
white (unpigmented) or coloured (pigmented).
The spinning of the fibres is preferably accomplished using
conventional melt spinning (also known as "long spinning~~),
in particular medium-speed conventional spinning. Convention-
al spinning involves a two-step process, the first step being
the extrusion of the melts and the actual spinning of the
fibres, and the second step being the stretching of the spun
fibres, in contrast to so-called "short spinning", which is a
one-step process in which the fibres are both spun and
stretched in a single operation.
For spinning, the melted fibre components are led from their
respective extruders, through a distribution system, and
passed through the holes of a spinnerette. The extruded melts
are then led through a quenching duct, where they are cooled
and solidified by a stream of air, and at the same time drawn
into filaments, which are gathered into bundles of typically '
several hundred filaments. The spinning speed after the
quenching duct is typically at least about 200 m/min, more
typically about 400-2500 m/min. After having solidified, the
filaments are treated with the first spin finish. This is
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typically performed by means of lick rollers, but alternative
systems, such as spraying the bundles of filaments or dipping
them in the spin finish, are also suitable.
Stretching in a long spin process is performed using so
y called off-line stretching or off-line drawing, which, as
mentioned above, takes place separately from the spinning.
process. The stretching process typically involves a series
of hot rollers and a hot air oven, in which a number of
bundles of filaments are stretched simultaneously. The bun-
dlea of ,filaments pass first through one set of rollers,
followed by passage through a hot air oven, and then passage
through a second set ofrollers. Both the hot rollers and the
hot air oven typically have a temperature of about 50-140°C,
e.g. about 70-130°C, the temperature being chosen according
to the type of fibre, e.g. typically 115-135°C for
polypropylene fibres, 95-105°C for polyethylene fibres, and
110-120°C for polypropylene/polyethylene bicomponent fibres.
The speed of the second set of rollers is faster than the
speed of the first set, and the heated bundles of filaments
are therefore stretched according to the ratio between the
two speeds (called the stretch ratio or draw ratio). A second -
oven and a third set of rollers can also be used (two-stage
stretching), with the third set of rollers having a higher
speed than the second set. In this case the stretch ratio is
the ratio between the speed of the last and the first set of
rollers. Similarly, additional sets of rollers and ovens may
be used. The fibres of the present invention are typically
stretched using a stretch ratio of from about 1.05:1 to about
6:1, e.g. from 1.05:1 to 2:1 for polypropylene fibres, and
from 2:1 to 4.5:1 for polyethylene fibres and polypropylene/-
polyethylene bicomponent fibres, resulting in an appropriate
fineness, i.e. about 1-7 dtex, typically about 1.5-5 dtex,
more typically about 1.6-3..4 dtex.
After stretching, the bundles of filaments are treated with
the second spin finish, for example using lick rollers or by
spraying or dipping. The filaments may optionally be heated
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prior to crimping, e.g. by means of steam, either superheated
or saturated, or infrared heaters, etc. to increase the
temperature and melt the hydrophobic spin finish components.
Ideally, it would be preferable to apply the spin finish
dispersions without melting the hydrophobic lubricant. How-
ever, the spin finish components should be in the form of a
dispersion at the time of application to prevent coalescence
of the particles or droplets of the hydrophobic lubricant,
and afterwards it is therefore generally necessary to melt
these components in order to ensure a uniform distribution on
the fibres. Melting of the hydrophobic lubricant preferably
takes place before the crimper,- but it can also take place in
the crimper itself or during the subsequent drying step. The
energy used to heat and melt the hydrophobic lubricant may
come from the filament tow itself, which becomes heated
during the stretching process, or, alternatively, it can come
from e.g. steam or infrared radiation as explained above.
Friction in the crimper (which in turn influences web cohe-
sion) can be regulated to a certain extent by regulation of
the process parameters, in particular pressure in the etuffer
box chamber. However, this is only possible within certain
boundries, the boundries being defined by the composition of
the spin finishes. Further information on the effect of the
spin finish components on fibre/fibre and fibre/metal fric-
tion is provided below:
The stretched fibres are normally texturized (crimped) in
order to make the fibres suitable for carding by giving them
a "wavy" form. An effective texturization, i.e. a relatively
large number of crimps in the fibres, allows for high pro-
ceasing speeds in the carding machine, e.g. at least 80
m/min, typically at least about 100 m/min, and in many cases
at least 150 m/min or even 200 m/min or more, and thus a high
productivity.
Crimping is typically carried out using a so-called stuffer
box. The bundles of filaments are led by a pair of pressure
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rollers into a chamber in the stuffer box, where they become
crimped due to the pressure that results from the fact that
they are not drawn forwarf, inside the chamber. The degree of
crimping can be controlled by the pressure of the rollers
prior to the stuffer box, the pressure and temperature in the
chamber; and the thickness. of the bundle of filaments. As an
alternative, the filaments can be air-texturized by passing
them through a nozzle by means of a jet air stream. In cer-
tain cases, i.e. for asymmetric bicomponent fibres, crimping
devices may be eliminated, since heat treatment of such
fibres, which releases tension in the fibres, leads to con-
traction and thus three-dimensional self-crimping.
The fibres of the present invention are typically texturized
to a level of about 5-15 crimps/cm, typically about 7-12
crimpa/cm (the number of crimps being the number of bends in
the fibres).
After the fibres have been crimped, e.g. in a stuffer box,
they are typically fixed by heat treatment in order to reduce
tensions which may be present after the stretching and crimp-
ing processes, thereby making the texturization more perma-
nent. Fixation and drying of the fibres are important factors
for the hydrophobicity of the final product. In particular,
it is important that the drying unit, e.g. drum dryer, oven,
drying and heat setting channel, etc., has a uniform distri-
bution of the hot air, since this results in a low and uni-
form distribution of moisture in the fibres, which in turn
effects the hydrophobicity of the final product. The residual
moisture content is preferably less than 2.0%, more prefer-
ably less than 1.5% by weight based on the weight of the
fibre. Fixation and drying of the fibres may take place
simultaneously, typically by leading the bundles of filaments
from the stuffer box, e.g. via a conveyer belt, through a hot
air oven. The temperature of the oven will depend on the
composition of the fibres, but must obviously be below the
melting point of the fibre polymer or (in the case of bicom-
ponent fibres) the low melting component. During the fixation
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the fibres are subjected to a crystallization process Which
°locks" the fibres in their crimped form, thereby making the
texturization more permanent. The heat treatment also removes
a certain amount of the water from the spin finishes. The
5 drying process allows any wax component or other hydrophobic
lubricant to melt and become distributed uniformly on the
surface of the filaments. Forhydrophobic lubricants that. are
already liquid, for example silicone compounds, the heat
treatment provides a reduction in viscosity, which allows a
10 more uniform distribution of such compounds. The filaments
are typically dried at a temperature in the range of
90-130°C, e.g. 95-125°C, depending on factors such as the
type of fibre.
The fixed and dried bundles of filaments are then led to a
cutter, where the fibres are cut to staple fibres of the
desired length. Cutting is typically accomplished by passing
the fibres over a Wheel containing radially placed knives.
The fibres are pressed against the knives by pressure from
rollers, and are thus cut to the desired length, which is
equal to the distance between the knives. The fibres of the
present invention are typically cut to staple fibres of a
length of about 18-150 mm, moretypically about 25-100 mm, in
particular about 30-65 mm, depending on the carding equipment
and the fineness of the fibres. A length of about 38-40 mm
will thus often be suitable for a fibre with a fineness of
about 2.2 dtex, while a length of 45-50 mm is often suitable
for a 3.3 dtex fibre.
Quite generally, the main requirements for a spin finish for
spinning and stretching polymer fibres include the following:
3D 1. It should contain an amount of antistatic agent which
ensures that the fibres do not become electrically
charged during the spinning and stretching process or
during the carding process; anionic, cationic and non-
ionic antistatic agents are all employed in spin finishes
(although, as explained above, cationic antistatic agents
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have generally been unsuitable for use in fibres to be
used in hygienic absorbent products due to the akin
irritating properties of these agents).
2. If necessary, it ahou:Ld contain an amount of cohesion
conferring agent suff:LCient to ensure that the filaments
are held together in bundles, allowing them to be pro-
cessed-without becoming entangled; neutral vegetable
oils, long chained alcohols, ethers and esters, sarco-
aines and non-ionic surface active agents are often
employed for this purpose.
3. It should contain components, typically hydrophobic
lubricants, which regulate both fibre/fibre and fibre/-
metal friction during the production process, eo that the
filaments do not become Worn or frayed during processing.
In particular, fibre/metal friction during the spinning
stage, fibre/metal friction against the stretch rollers,
and fibre/fibre and fj.bre/metal friction in the crimper
need to be regulated.
4. water plus emulsifiers or surface active agents which
keep the more or less lipophilic components in the aque
ous solution are normally necessary. Solvents other than
water should be avoided if at all possible to eliminate
possible environmental. hazards.
Spin finishes also serve t:o regulate the fibre/fibre and
fibre/metal friction during carding, and spin finishes used
for spinning and stretching are generally adapted so that the
fibres do not require any further processing before carding.
Antistatic agents are a necessary component for all spin
finishes used in the production of polyolefin fibres. Such
antistatic agents are by nature polar and therefore also more
or less hydrophilic, whicYa in principle is a necessary evil
one must live with in the case of spin finishes that are
otherwise hydrophobic. In such cases, the amount of anti-
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static agent is reduced to a minimum in order to preserve the
hydrophobic nature of the spin finish. One way of achieving
this is by using a highly effective antistatic agent, of
Which only a small amount is necessary to obtain the desired
antistatic effect. However, commonly employed anionic anti-
static agents such as phosphoric acid eaters are not particu-
larly effective, since they for hydrophobic fibres often
contain long alkyl chains, whereby the concentration of
phosphor groups is relatively low. Since the relative number
of these phosphor groups determines the antistatic proper-
ties, it follows that such agents are relatively ineffective.
The following typical values for normal antistatic components
serve as a guideline for the relative efficiency of their
antistatic properties: inorganic salts 100, cationic 80-100,
anionic 75-90, nonionic 50-70, fixing agents 30, mineral oils
and silicones 0-10, lubricants 30-50.
Cationic antistatic agents are known to be more effective
than anionic agents and can therefore be used in much smaller
concentrations, thereby preventing or minimizing hydrophilic
properties in the hydrophobic spin finish, but se mentioned
above, such cationic antistatic agents have not been suitable
for personal hygiene and medical products for toxicological
reasons.
The present invention is based on spin finishes used in
connection with both the spinning and stretching steps which
fulfil the requirements listed above with regard to the
content of antistatic agent, hydrophobic lubricant(s), water
and optional cohesion conferring agent, as well as regulation
of fibre/fibre and fibre/metal friction. These spin finishes
have the further advantage that they function as a processing
aid during carding and thus provide the fibre/fibre and
fibre/metal friction necessary to obtain sufficient carding
of the fibres. As a result, a carding web with a uniform
distribution of the fibres is obtained, even when using
relatively high carding speeds.
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In the method of the present invention, the majority or even
all of the antistatic agent is applied in the spinning stage. -
The use of the cationic antistatic agent will normally be
unneccessary in the stretching stage, and ie preferably
avoided. The reason for this is that cationic antistatic
agents typically form a stable foam upon stirring or agita-
tion, and they also have a relatively high viscosity. The
amount of cationic antistatic agent is therefore preferably
kept to a minimum in the second spin finish to reduce the
viscosity and eliminate or reduce air bubbles, both of which
lead to a non-uniform application of the spin finish. When
the second spin finish comprises a cationic antistatic agent,
this is therefore preferably present in an amount of at the
most 20%, more preferably at the most 10%, based on the total
active content of the second spin finish.
The total concentration of the active components (i.e. anti-
static agent, hydrophobic lubricant(s), emulsifier, cohesion
conferring agent) is typically lower in-the first spin finish
(generally about 0.7-2.5% active content) than in the second
spin finish (generally about 4-12% active content), and the
viscosity of the first spin finish is thus also normally
lower. It is therefore advantageous to employ any high vis-
cosity components in the dispersion with the lowest viscosi-
ty, i.e. in the first spin finish.
When the hydrophobic lubricant is a wax or a silicone com-
pound, this is only applied in the stretching stage. However,
when the hydrophobic lubricant is a fatty acid amide conden-
sation product, it may be also be applied in the spinning
stage. There are several reasons for choosing this approach.
First of all, the use of wax as a hydrophobic lubricant
during spinning results in problems for-both spinning and
stretching:
1. During spinning, the fibre/metal friction will be in-
creased and part of the wax components will be deposited
on various machine surfaces which are in contact with the
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filament bundles. Deposition of wax during spinning will
also cause the bundle of filaments to be so sticky that
it will partially stick to -itself. If this happens, the
fibre bundles will be difficult to take up out of the
cans (boxes in which the bundles arestored until a
number of bundles areready to be stretched simultaneous-
ly) when they are to be stretched in the two-step pro-
cess.
2. During stretching, wax deposits will also be formed on
the heated rollers and other machine parts that are in
contact with the bundles. This is due to the fact that
the bundle of filaments is heated during the stretching
process. At elevated temperatures some of the water will
evaporate from the applied spin finish, and a film of
melted wax will easily be deposited on the rollers, etc.
If this happens, friction between the bundles of fila-
ments and the surface of -the rollers will be reduced to a
level below that which is necessary for maintenance of
the drawing forces necessary to stretch the fibres. If,
as a result, the fibres slide along the surface of the
rollers, they will obviously not become stretched.
The use of silicone compounds as hydrophobic lubricants
during the spinning process would also give problems for both
spinning and stretching:
1. During spinning, silicone would reduce fibre/metal fric-
tion, so that the bundles of filaments would slide along
the various drive rollers rather than being moved forward
by the rollers. As a result, it would not be possible to
pull the fibres out of the spinnerette at a predetermined
and constant speed. This applies especially at the high
speeds used in conventional spinning.
2. During stretching, silicone applied in the spinning stage
would have the same negative effect as wax. Friction
between the bundle of filaments and the stretch rollers
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would be reduced, resulting in the well-known slip prob-
lems caused by silicone.
By only applying a small s~mount of relatively hydrophobic
cationic antistatic agent and a very small amount, if any, of
5 a cohesion conferring agent during the spinning stage (i.e.
without a hydrophobic lubricant in any significant amount),
the above-mentioned processing problems are avoided. The
cationic antistatic agent should have sufficient antistatic
properties, should contribute to the cohesion of the fila-
10 meats, and should not have such a high molecular weight that
it leads to problems with deposits on the machinery.
The cationic antistatic agents used according to the inven-
tion have a particular advantage that is related to the fact
that polyolefins, and particularly polypropylene during
15 processing by long spin techniques, become partially oxidized
on the surface. Thus, while polyolefina are known to be
hydrophobic, they can in certain cases have surface proper-
ties that are not strictly hydrophobic. As a result of this
partial oxidation, some hydroxy and carboxy groups as well as
aldehyde and ketone groups are introduced on the surface. In
addition to being polar and thus hydrophilic, such polymer
bound groups are also anionic. This means that they will in
principle repel any aqueous solution of anionic antistatic
agent that one attempts to apply to the fibres. This leads to
a non-uniform, less efficient coating of the antistatic agent
onthe fibre surface, and thus poorer antistatic properties,
as well as the risk that agglomerations of antistatic agent
will be deposited on the equipment during carding. Also,
there is a risk of having regions on the surface that are
relatively hydrophilic and other regions that are hydro-
phobic. The presence of such hydrophilic regions would tend
to conduct liquids through a nonwoven, thus diminishing the
hydrophobic properties. In the case of cationic (positively
charged) antistatic agents, however, the oppositely (i.e.
negative) charged groups on the polymer surface will ensure a
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uniform distribution of the antistatic agent on the fibre
surface.
This in turn contributes to the efficiency of the cationic
agents, allowing the obtainment of improved antistatic-prop
erties necessary to be able to card the produced fibres- at
high carding speeds of e.g. 200 m/min.
Since a relatively small amount of the cationic antistatic
agent is sufficient to obtain the desired antistatic effect,
the fibres will be more hydrophobic compared to fibres pre-
pared using a prior art anionic antistatic agent. As a re-
sult, it is possible to reduce the amount of the hydrophobic . -
lubricant (e. g. silicone) which is otherwise added to render
the fibres more hydrophobic. As mentioned above, the use of
silicone compounds, which tends to make the fibre surface
slippery, has a number of disadvantages in terms of reduction
of fibre/fibre and fibre/metal friction. As a result, aili-
cone-treated fibres tend to be difficult to texturize and
therefore also difficult to card at high carding speeds.
Cationic antistatic agents have the further advantage that
they are less sensitive to humidity than the commonly em-
ployed anionic alkyl phosphate salts during the subsequent
processing of the fibres. As a result of this sensitivity of
antistatic agents based on alkyl phosphate salts, the carding
of fibres treated with these agents must normally be carried
out under controlled relative humidity (e.g. 65%).
The cationic antistatic agents used according to the present
invention are typically quaternary ammonium salts. Such
cationic antistatic agents may be included in the polyolefin
as e.g. alkyl alkanol amines, alkoxylated allylene diamines,
or the hydroxyethyl-dodecyl-oxypropylamine salt of hydroxy-
propionic acid, or as quaternary ammonium salts such as
stearyl polyether acetal ammonium salt. (Ahmed, Polypropylene
Fibres - Science and Technology, Elsevier Scientific Publish-
ing Co., 1982, p. 375). Fatty acid amine condensates provide
W O 95119465 218 0 2 4 7 PCT/DK95/00024
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good antistatic behaviour and also high friction under wet
conditions, which aids in the obtainment of good texturiza-
tion in a stuffer box crimper.
The pH of prior art spin finishes comprising a cationic
antistatic agent or a fatty acid amide condensate is general-
ly somewhat acidic, typically below pH 4. Under these condi-
tions, the amide nitrogen is often.protonized and can thus
act as a cationic antistatic. It is likely that this protoni-
zation also contributes to making the di~peraions more ata-
ble. However, at higher pH values, e.g. 5-6, the amide group
is not protonized, and the amide is thus not cationic in
nature. For applications i.n which an absence of akin irrita-
tion is-not important, e.g. for technical applications such
as carpet fibres, these amides are therefore often used at a
low pH.-This is also related to the fact that a low pH tends
to prevent microbial growth and reduces the possibility of
gasfading diacolouration in textiles.
In the present invention, in which it is important to avoid
akin irritation, such amides are preferably used at higher pH
values to avoid acid-induced skin irritation. In cases in
which some acid is necessary to stabilize an emulsion or
dispersion, it is preferred to use acetic acid or another
volatile acid which will at least partly evaporate during the
drying step of the stretching process so that the pH of the
coating on the finished fibres is sufficiently high to avoid
acid induced skin irritation.
The cationic antistatic agent of the present invention should
therefore have a pH (in a 10% aqueous solution) of not less
than 4Ø More preferably, the pH is not less than 4.5, e.g.
between 4.5 and 6.5, such as 5.0-6Ø
A further factor that can lead to skin or eye irritation in
cationic antistatic agents of the quaternary ammonium salt
type is the presence of free secondary and tertiary amine end
groups. Preferred cationic antistatic agents for use accord-
2180247
WO 95119465 PC'TIDK95100024
18
ing to the present invention are thus end group modified With
long alkyl chains.
The cationic antistatic agents of the invention are therefore-
preferably selected from compounds with fatty acid amide end
groups, tertiary long chain amine end groups or ester groups,
in particular compounds of the general formula I
R1 X-
Z1-(CH?)n-~N+-(CH2) am-Z2 I
R2
wherein Z1 and Z2 are Alk-CONH-, (Alk)2-N-, Alk-COO-, or H,
wherein Alk is a linear aliphatic alkyl or alkenyl group
containing 10-24 carbon atoms or a mixture of more than one
such group, with the proviso that both Zl and Z2 cannot be H;
R1 is H, CH3, alkyl with up to 24 carbon atoms, or a dimethy-
lene fatty acid ester; R2 ie H or CH3; n is an integer great-
er than 0; m is an integer greater than 0; and X- is a
counterion. With the exception of the above proviso, i.e.
that Z1 and Z2 cannot both be H, Z1 and Z2 may be the same or
different, and are preferably the same.
Otherpossibilities for modifying the end groups are by use
of ether br ethoxy groups, e.g. compounds of the general
formula II
R1 X-
i I
R3-~O-CH2-CHZ~y-O-(CHs)n-~N+-(CHZ)~m-O-[CH2-CH2-O~y-R3
i
~2
R
wherein R1 is H, CH3, alkyl with up to 24 carbon atoms, or a
dimethylene fatty acid ester; R2 is H or -CH3; each R3 is
independently H, methyl, ethyl or Alk-carbonyl, where Alk is
a linear aliphatic alkyl or alkenyl group containing 10-24
carbon atoms or a mixture of more than one such group; n is
2180247
W0 95119465 -- PCTIDK95/00024
19
an integer greater than 0; m is an integer greater than 0; y
is an integer greater than 0; and X- is a counterion.
In the above compounds of formulas I and II, Alk is in par
ticular an alkyl group containing 12-22 carbon atoms, prefer
s ably 14-2D carbon atoms, e.g. 16-18 carbon atoms; n is typi-
cally 1-4; when R3 is alkyl, it is preferably alkyl with 10-
24 carbon atoms; m is typically 1-10; y is typically 1-20;
and X- is typically an acetate, citrate,:lactate, metasulfate
or chloride ion.
1D The cationic antistatic agents will often be in the form of
oligo-cationic compounds, i.e. compounds with several quater-
nary ammonium groups, typically less than 10 such groups,
since a higher number would result in polycationic components
having a high viscosity, thereby leading to problems obtain-
15 ing a uniform distribution of the spin finish on the fibres.
Antistatic compounds for use in the present invention will
therefore typically have a molecular weight of at least 50D
but less than 10,000, preferably less than 5000, more prefer-
ably leas than 2000.
20 A common characteristic of the cationic antistatic agent used
according to the present invention is that they are non-
irritant compounds. The term "non-irritant" refers to the
fact they would be classified as "non-irritant" in a skin
irritation teat or an eye irritation test. Among the test
25 methods available are those of the DECD Guideline No. 404:
"Acute Dermal Irritation/Corrosion", May 1981, and the DECD
Guideline No. 405: "Acute Eye Irritation/Corrosion", Feb.
1987, performed on rabbits. Classification can be according
to that described in the Official Journal of-the European
30 Communities, L 257, 1983.
The second spin finish may contain a certain minimum amount
of the antistatic agent to provide the fibres with sufficient
antistatic properties to be able to be carded without prob-
lems of tatic electric build-up, but it may also, depending
2180247
WO 95119465 PCTIDK95I00024
on the nature of the hydrophobic lubricant used in the second
spin finish as well as the antistatic agent used in the first
spin finish, be free of an antistatic agent.
The viscosity of the spin finish dispersions is influenced by
5 the size of the dispersed particles or droplets. A small
particle size thus generally provides a low viscosity, which
enables the obtainment of a thin and uniform coating of the
spin finish components on the fibre surface. This in turn
provides the fibres With uniform fibre/fibre and fibre/metal
10 friction characteristics, which allows a uniform texturiza-
tion in the crimper and subsequently the production of a
uniform carding web during carding. The end result is a
consistent nonwoven material with good hydrophobicity. It is
important to note, however, that ultrafine particles, e.g.
15 with a diameter of less than about 0.1 hem, can lead to an
increased viscosity. The particle size in the spin finish
dispersions is therefore preferably in the range of 0.1-5 pm,
more preferably 0.1-2 Eun.
In general, the average size of the dispersed particles
20 should be significantly less than the fibre diameter. For
typical fine fibres with a diameter of e.g. 15-20 fun, this
means that the particle size in the spin finish dispersions
is preferably at the most about 5 um, more preferably at the
moat about 2 ~cm, more preferably at the most about 1 Ecm. As a
rule of thumb, the average particle size should normally be
at least about one order of magnitude smaller than the diame-
ter of the fibres, although this depends to a certain degree
on the nature of both materials.
The desired small particle size of the dispersed particles
can be accomplished in two ways. The first of these is by use
of a relatively large amount of emulsifier. However, this is
undesirable since it leads to problems of increased
hydrophilicity, which for obvious reasons is undesired in -
hydrophobic fibres. The second way that a small particle size
may be obtained, and that which is preferred, is by means of
W O 95119465 218 0 2 4 7 PC,I,~~~00024
21
mechanical methods during preparation of the dispersions,
such as use of special homogenizing devices, high shear
dispersion devices or high. speed mixers.
While-it is desired that the amount ofemulsifier is kept to
a minimum, emulsifiers aid in the creation and maintainance
of a stable dispersion of very small dispersed particles
(typically with an average size of leas than 2 pm) or of a
stable emulsion with droplets, and are..therefore generally
necessary as such in limited amounts. The emulsifier is
therefore typically present in an amount of less than 10% by
weight, more typically less than 8% by weight, such as 4-7%
by weight. Ideally, the amount of emulsifier is as small as
possible or even completely eliminated. In the latter case,
with no emulsifier or only a very small amount (e. g. less
than 5% by weight) of an emulsifier, an anti-coalescent agent
such as ligninosulfate may be added. Another reason for
maintaining the amount of emulsifier se low as possible is
that this helps to ensure that phase inversion takes place as
intended (see below regarding phase inversion).
The emulsifier should for obvious reasons not be particularly
hydrophilic, and it is clear that it must be compatable in
terms of electric charge with the chosen antistatic agents)
and hydrophobic lubricanta(s). Suitable emulsifiers are for
example fatty acid alkyl esters, fatty acid alkyl amides,
alkyl ethers and ethoxylated long chain alcohols (fatty
alcohols). More generally, preferred emulsifier compounds
contain a cationic group with one or two (preferably two)
fatty acid chains, e.g. with 8-22 carbon atoms, typically
12-20 carbon atoms, more typically 16-18 carbon atoms. These
may be saturated or unsaturated, although saturated fatty
acid chains are preferred. Commercially available products
are often mixtures containing emulsifier compounds with fatty
acid chains of different lengths, as in coconut oil, palm
oil, etc.
- 2180247
WO 95119465 PCT1DK95100024
22
As explained above, the viscosity of the spin finishes is
preferably as low as possible. In particular, the viscosity
of the second spin finish is preferably at the most 7 mPa~s,
more preferably at the moat 5 mPa~s, more preferably at the -
moat 3 mPa-s, moat preferably at the most 2 mPa~s, as deter
mined e.g. by viscosimetry at 23°C and a shear rate of 2.0
sec-1 using a viscosimeter of the couvette type. '
It is important that after application of the spin finishes,
which are in the fog of dispersions or emulsions in water,
with water as the continuous phase, the active compounds in
the spin finishes are able to dissipate into a uniform layer
on the fibre surface. In order for this to take place, the
temperature must be above the melting point of the main
active compound in the dispersion, and enough water must
evaporate to provoke a phase inversion. The phase inversion
' can take place before the crimper using steam or infrared
radiation as a heat source, and should at the latest take
place in the drying oven after_crimping. However, it is
preferred that phase inversion takes place before crimping,
since this results in a uniform distribution of the spin
finish components at an early stage, which means that the
fibre/metal friction will be constant for the filaments,
resulting in a uniform texturization. Also, this improves the
web uniformity in the subsequent carding process, Which
ultimately leads to improved hydrophobic properties, in
particular improved strike-through-time, in the finished
nonwovens. A further advantage of ensuring a uniform and high
degree of texturization ie that this is a prerequisite for
high speed carding.
An antifoaming agent may be added to the antistatic agent.
The antifoaming agent is e.g. a silicone compound, for exam-
ple a dimethylailoxane or a polydimethylsiloxane, and is -
typically added in an amount of less than 1% by weight, more
typically less than 0.5% by weight, such as about 0.25% by
Weight. Other non-silicone based antifoaming agents may also
be used.
2180247
WO 95/19465 PCTIDK95100024
23
The nature of the process dictates certain limits on the
relative amounts of any wax, fatty acid amide condensation
product or polydiorganosiloxane present as a hydrophobic
lubricant. An excessive amount of wax or fatty acid amide
S condensation product will increase fibre/fibre friction and
in particular fibre/metal friction in the crimper, leading to
' increased development of heat and a risk of the filaments
becoming melted together and ruined. The friction conditions
will also be detrimental for high speed carding. It is impor
tant that the friction-induced development of heat during
carding is kept to a minimum, in particular when carding at
high speeds. An excessive amount of polydiorganosiloxane will
reduce friction in the crimper and during carding. Fibres
with an excessive amount of polydiorganoailoxane will be
slippery and difficult to stretch and card. Such fibres are
also difficult to texturize in the crimper, since this re-
quires a certain minimum fibre/metal friction.
Similarly, it is clear that considerations of hydrophobicity
dictate certain limits on the relationship between the amount
of antistatic agent on the one hand and the hydrophobic
lubricants on the other hand.
The spin finish in the spinning section (first spin finish)
should thus be an antistatic and lubricating finish that is
as hydrophobic as possible. For lubrication purposes it may
optionally contain a hydrophobic lubricant of the fatty acid
amide condensate type. When a fatty acid amide condensate is
used in the second spin finish, it is preferred to also
include a fatty acid amide condensate in the first spin
finish.
The "hydrophobic lubricant's is selected from i) a fatty acid
amide condensation product, ii) a hydrocarbon wax, and iii) a
polydiorganosiloxane. The definitions of these terms are
explained in detail in the following. Note, however, that the .
term "hydrophobic lubricant" refers to compounds that exert
an influence on the friction (fibre/fibre and fibre/metal
2180247
WO 95/19465 PCT/DK95/00024
24
friction) of the fibres, and that the "lubricant" can also
refer to compounds, in particular waxes, that increase fric-
tion.
The term "fatty acid amide condensation product" refers to
compounds based on mono- and diamines, in particular com-
pounds of the general formula III
O
Alk-C-N-(Alk)2 III
and compounds of the general formula IV
O O
Alk-C-~NH-(CHa)~m-NH-C-Alk IV
wherein each Alk is independently a linear aliphatic alkyl or
alkenyl group containing 10-24 carbon atoms or a mixture of
more than one such group, n is an integer greater than 0, and
m is an integer greater than 0. In the compounds of formulas
III and IV, Alk is in particular an alkyl group containing
12-22 carbon atoms, preferably 14-20 carbon atoms, e.g. 16-18
carbon atoms; n is typically 1-4; and m is typically 1-10.
The fatty acid amide condensation products are often mixtures:
with different molecular weights, and the alkyl chains, which
are typically from natural fatty acid mixtures, are often of
varying chain length. Also, such compounds may contain small
amounts of non-reacted fatty acids or amines. The melting
range of these components differs depending on structure and
molecular weight. For the purposes of the present invention,
melting points in the range of 40-100°C are preferred, in
particular 60-90°C.
3D The hydrocarbon wax used in the second spin finish of the
present invention is in particular a paraffin wax or micro-
2180247 .
WO 95119465 PCTIDK95100024
crystalline wax. However, it is also contemplated that natu-
ral waxes, i.e. an insect or plant wax, may also be suitable.
Paraffin wax is a crystalline hydrocarbon mixture which is
solid at room temperature and which is obtained from the
5 light petroleum fractionknown as "pressable wax distillate".
Paraffin wax normally consists mainly of straight-chained
hydrocarbons and some branched-chain hydrocarbons (isoparaf-
fins). Microcrystalline wax, which is also a hydrocarbon
mixture that is solid at room temperature, is obtained from
10 heavy petroleum distillates and residues. Microcrystalline
wax normally consists mainly of branched-chain hydrocarbons
(isoparaffins) and naphthenea (large side chains) along with
small amounts of straight-chain hydrocarbons and aromatic
hydrocarbons.
15 The melting point of paraffin waxes is typically in the range
of about 45-65°C, while that of microcrystalline waxes is
typically in the range of about 50-95°C. (The solidifying
point of a hydrocarbon wax. is normally about 2-3°C below the
meltingpoint).
20 In the context of the present invention the term "hydrocarbon
wax" refers to a paraffin or microcryatalline wax of natural
or synthetic origin, in particular to a wax with a melting
point in the range of 40-120°C, e.g. 40-90°C, corresponding
to an average molecular weight of about 250-900 (as deter-
25 mined by high temperature gel permeation chromatography,
using e.g. trichlorobenzene as an eluent, or by mass spec-
troscopy), or to a mixture of waxes containing a major pro-
portion of a paraffin or microcrystalline wax and having a
melting point in the above-mentioned range. While a wax or
wax mixture with a relatively low melting point (i.e. about
40-80°C) is preferred according to the present invention to
ensure that the wax may be easily and uniformly distributed
on the surface of the fibres without use of excessively high
temperatures, it is, however, also contemplated that wax or
wax mixtures having a higher melting point, e.g. up to about
2180247
WO 95119465 " PCf/DK95l00024
26
120°C, will-also be suitable for certain applications. Pre-
ferred hydrocarbon waxes have in particular a melting point
in the range of 50-SO°C, corresponding to an average molecu-
lar weight in the range of about 400-800, e.g. a melting
point in the range of 55-75°C. For waxes lying within these
preferred temperature ranges, the second spin finish is
typically applied at a temperature in the range of 25-60°C, '
e.g. 40-55°C (the fibres generally having a somewhat higher
temperature during application of the second spin finish).
Since waxes normally consist of a mixture of different hydro-
carbons, this will also be the case for the waxes used for -
the purpose of the present invention. The "wax" will there-
fore typically be a mixture of different wax types, some of -
which may be Waxes having higher or lower molecular weights
and melting points than those given above, as long as the
melting point of the total mixture lies within the range
stated above.
The wax may also contain a certain amount of a °hydrocarbon
resin's, i.e. a partially cross-linked hydrocarbon wax with a
relatively high melting point, e.g. up to about 120°C. Hydro-
carbon resins are prepared synthetically by radical polymeri-
sation of hydrocarbon waxes containing aromatic hydrocarbons.
For wax mixtures containing other components than~a hydrocar-
bon wax with a melting point in the range of 40-80°C, e.g. a
hydrocarbon wax with a higher melting point or a hydrocarbon
resin, the amount of these other components will typically
comprise no more than 40% by weight of the wax mixture;
preferably no more than 30% by weight of the wax mixture,
more preferably no more than 20% by weight of the wax mix-
ture.
As mentioned above, it is also contemplated that natural
insect or plant waxes may also be used as the wax component
in the second spin finish of the present invention. While
natural waxes may contain a variety of different components,
~ WO 951fi9465 218 0 2 4 7 p~~Kg5~0002J
27
hydrocarbons are a major component in many of these. One
natural wax of interest i:a beeswax, which contains a mixture
of hydrocarbons, monoesters, diesters, triesters, hydroxy-
monoesters, hydroxypolyesters, free acids, acid monoesters
and acid polyesters, as well as a small amount of unidenti-
fied material. Other insect waxes of interest are for example
those from crickets, grasshoppers and cockroaches.
The waxes of many plant species contain a major proportion of
hydrocarbons, mainly in the form of unbranched alkanea with
an odd number of carbon atoms. However, branched alkanes as
well as alkenes have also been reported and are probably
present in many plant waxes. Also, some vegetable waxes, such
as carnauba wax, contain a relatively small percentage of
unbranched alkanes. Like the animal waxes, plant waxes also
contain various amounts oi' other components, including mono-
esters, diesters, hydroxyesters, polyesters, primary and
secondary alcohols, acids" aldehydes, ketones, etc.
Natural waxes used for the purpose of the present invention
should have a melting point which lies within the ranges
given above for hydrocarbon waxes.
It has been found according to the invention that fibre/fibre
and fibre/metal friction properties can be regulated, and the
hydrophobic properties can be improved, when the second spin
finish contains a polydiorganosiloxane (silicone) compound.
Thus, the second spin finish may optionally contain a small
amount, e.g. up to 15% by weight, preferably less than 10% by
weight, e.g. 1-8% by weight, typically 2-5% by weight, based
on the total active content of the second spin finish, of a
silicone compound. For fibres designed for use in nonwovens
in which a very high degree of hydrophobicity is desired, and
where a-high carding speed is not crucial or necessary, the
content of the silicone component may be higher, e.g. up to
10% by weight or 15% by weight. Higher levels, e.g. up to
20-25% by weight, will, however, tend to result in slippery
2180247
W0 95/19465 PCT/DK95100024
28
fibres with a very low fibre/metal friction which can only be
processed using a carefully selected combination of the other
spin finish components.
The polydiorganoailoxane is in particular a polydialkyl-
ailoxane of the general formula V,
R R R
i
X-Si-O-[Si-O~n-Si-X V
I
R R R -
in which each R is independently an alkyl group containing
1-4 carbon atoms, phenyl or H, n is a number in the range of
500-3000, and X is OH, methyl, ethyl, H, O-methyl or
0-acetyl. A preferred polydialkylsiloxane is polydimethyl-
siloxane.
The hydrophobic properties of the fibres can also be ex-
pressed in terms of the contact angle between water and the
surface of the fibres. Fibres with non-wettable characteris-
tics should have a contact angle of more than 90° (as mea-
sured e.g. using the i~ilhelmy technique-force measurement for
single fibre wettability). It is believed that relatively
less hydrophobic fibres of the present invention will have a
contact angle of slightly above 90°, while the highly hydro-
phobic fibres will have a contact angle that approaches 180°
(a contact angle of 180° being a theoretical maximum for
total non-wetting).
Control of the fibres' processing characteristics, i.e.
fibre/fibre and fibre/metal friction, may be obtained by
varying the amount of polydiorganoailoxane in the second spin
finish. Fibres without any polydiorganosiloxane will have a
high fibre/fibre and fibre/metal friction.
As mentioned above, one of the major advantages of the fibres
of the present invention is that they are suitable for-high-
W O 95119465 218 0 2 4 7 pCT~~y51000?A
29
speed carding, this being ofparticular interest for
polypropylene fibres. Thus, the fibres of the present inven-
tion may be processed to a uniform carding web at high speeds
in the carding machine, e.g. at least about 80 m/min, typi-
cally at least 100 m/min, such as at least 150 m/min, and (in
particular for polypropylene fibres) in many cases at least
175 m/min or even 225 m/min or more. The carding speed chosen
in each case will depend on factors such as the type of fibre
(e.g. polypropylene, polyethylene, bicomponent, etc.) and the
nature of the nonwoven being produced. Carding will typically
be by means of a dry-laid carding process.
Polypropylene fibres according to the invention are prefera-
bly able to be carded, at a carding speed of at least 100
m/min, preferably at least 150 m/min, more preferably at
least 200 m/min, into a web which can be thermally bonded to
a nonwoven in which the ratio between the tensile strength in
the machine direction and the tensile strength in the cross
direction is at the most 7, preferably at the most 5 (the
strengths being determined as explained below).
Polypropylene/polyethylene bicomponent fibres of the present
invention are preferably able to be carded, at a carding
speed of at least 80 m/min, preferably at least 100 m/min,
into a web which can be thermally bonded to a nonwoven in
which the ratio between the tensile strength in the machine
direction and thetensile strength in the cross direction is
at the most 6. Polyethylene fibres of the present invention
are preferably able to be carded, at a carding speed of at
least SO m/min, into a web which can be thermally bonded to a
nonwoven in which the ratio between the tensile strength in
the machine direction and the tensile strength in the cross
direction is at the moat 5. In all cases, the randomization
of fibres in the web expressed as the ratio between the two
tensile strengths should be as close to 1 as possible.
The strengths of different nonwoven materials may be compared
by using a so-called "bondability index", which compensates
for differences in fibre randomization and which is calculat-
2180247
WO 95/19465 PCTIDK95l00024
ed as explained below on the basis of nonwoven tensile -
strength measured in the machine direction and the cross
direction. A standardized carding test for determining the
tensile strength of nonwovena is performed as follows:
5 From about 95-105 kg offibres, webs ofa least 15 kg with a
base weight of 20-25 g/m2 fibre web are produced by carding
at the chosen speed at optimum roller settings with respect
to evenness of the web. The webs are subsequently thermobond-
ed, the individual webs being thermobonded at different
10 temperatures at intervals of typically 2°C within a range
chosen according to the type of fibres. For polypropylene
fibres, a web with a base weight of about 20 g/m2 is prepared -
by thermobonding at temperatures in the range of 145-157°C,
using a calender pressure of 64 N/mm and a typical carding
15 speed of 100 m/min. For polyethylene fibres, a web with a
base Weight of about 25 g/m2 is prepared by thermobonding at
temperatures in the range of 126-132°C, with a calender
pressure of 40 N/mm and a typical carding speed of 80 m/min.
For bicomponent fibres with a polypropylene core and a poly-
20 ethylene sheath, a web with-a base weight of about 20 g/mz is
prepared by thermobonding at temperatures in the range of
137-147°C, with a calender pressure of 40 N/mm and a typical
carding speed of 90 m/min. The tensile strengths of the webs
are then determined in the machine direction and the cross
25 direction, the measurements being performed according to the
EDANA recommended test: Nonwovena Tensile Strength, 20 Febru-
ary, 1989, which is based on ISO 9073-3:1989 ("Determination
of tensile strength and elongation"); however, for the pur-
poses of the present invention the relative humidity was
30 between 50% and 65%. Finally, a bondability index is calcu-
lated for each of the bonding temperatures, the bondability
index being defined as the square root of the product of the
machine direction strength and the cross direction strength.
In order to arrive at a standard bondability index for a
standard nonwoven base weight of 20 g/m2 (BIZO), the calcu-
lated bondability index for a given sample is multiplied by
20 and divided by the actual base weight in g/m2, thereby
2180247
WO 95/19465 PCT1DK95100024
31
compensating for the fact that the strength of a nonwoven
varies with the base weight.
For polypropylene-based fibres, the bondability index (BI2o)
should be at least 15 N/5 cm when carded at a speed of 100
m/min and at least 10 N/5 cm when carded at a speed of 150
m/min, and is preferably at least 17 N/5 cm when carded at a
speed of 100 m/min and at least 10 N/5 cm when carded at a
speed of 150 m/min.
For polyethylene-based fibres, the bondability index (BI2o)
should be at least 7 N/5 cm when carded at a speed of 80
m/min, and is preferably at least 10 N/5 cm when carded at a
speed of 80 m/min.
For sheath-and-core type bicomponent fibres having a
polypropylene-based core and a polyethylene-based sheath, the
bondability index (BI2o) should be at least 8 N/5 cm when
carded at a speed of 80 m/'min, and is preferably at least 10
N/5 cm at 80 m/min.
The viscosities of the spin finishes can be determined using
a Brookfield Viscosimeter model LVT DVII equipped with a UL-
adaptor: This is a viscosimeter of the couvette type (concen-
tric cylinder, or cup & bob geometry), and even low viscosity
spin finishes can be measured at different shear rates. The
viacosities are determined at 23°C and a shear rate of 2.0
sec-1.
The hydrophobic properties of nonwovens prepared from the
fibres of the invention may be tested according to various
methods. These include a repellency test, a test for liquid
absorbency time, a test for liquid strike-through time and a
runoff test. The test for liquid absorbency time may also be
used for testing the hydrophobic properties of fibres, as
described below.
2180247
WO 95119465 PCTIDK95/00024
32
The repellency test is performed according to the EDANA
recommended test for nonwovens repellency (NO. 120.1-80),
with conditioning of the samples for at least 2 hours at a
temperature of23°C and a relative humidity of 50%. This test
involves measuring the pressure (expressed as cm water col-
umn) required to effect water penetration through a nonwoven
subjected to an increasing water pressure. Briefly, a circu-
lar section ofa nonwoven sample of the desired base weight
(typically about 22 g/m2) with a diameter of 60 mm is sub-
jected to a water column whose height increases at a rate of
3 cm/min., and the repellency of the nonwoven is determined
as the height of the water column at the moment when the
third drop of water penetrates the sample.
In the above repellency teat, nonwovena containing the fibres
of present invention should show a repellency of at least
1.5 cm. For nonwovens prepared from fibres with a medium
degree of hydrophobicity, the repellency should be at least
2.5 cm, typically at least 3.0 cm. For nonwovens containing
highly hydrophobic fibres the repellency should be at least
3.5 cm, more preferably at least 4.0 cm, e.g. at least about
5.0 cm.
Another suitable teat method for determining the hydrophobic
properties of nonwovens is a test for liquid absorbency time
according to the EDANA recommended test for nonwovens abaorp-
tion (No. 10.1-72). This test involves determining the time
required for the complete wetting of a specimen strip (5 g)
loosely rolled into a cylindrical wire basket (3 g) and
dropped onto the surface oftheliquid (typically water) from
a height of 25 mm. Nonwoven samples for use in this test are
for the purpose of the present invention conditioned for at
least 2 hours at a temperature of 23°C and a relative humidi-
ty of 50%.
The above liquid absorbency test may also be used, with
certain minor amendments, for determining the hydrophobic
properties of fibres. For determining the absorbency of
2180241
WO 95119465 PCT/DK95100024
33
fibres, a carding web with a base weight of approximately 10
g/m2 is prepared from the fi.brea to be tested by carding at
15 m/min., and samples having a weight of 5 g are then taken
from the web. The remainder of the test is carried out ac-
s cording to the FDANA test procedure (10.1-72). When testing
either nonwovens or fibres, the absorbency time is defined as
the time interval from the moment the wire basket containing
the nonwoven or fibre sample hits the liquid to the moment
the sample is completely immersed under the surface of the
liquid.
Inthe above test for liquid absorbency in water, the wetting
time (i.e. the sinking time) for a sample of hydrophobic
fibres should be at least about 1 hour, preferably at least
about 2 hours, more preferably at least about 4 hours: For
highly hydrophobic fibres the wetting time should be at least
about 24 hours.
A further test for determining the hydrophobic properties of
nonwovens is a test for liquid strike-through time (EDANA
recommended test: Nonwoven coveratock liquid strike-through
time (simulated urine); No. 150.2-93). In this teat, the time
required for a known vohur~e of liquid to pass through a
nonwoven is measured. The liquid is applied to the surface of
a test piece of nonwoven coverstock with the embossed side
upwards which is in contact with an underlying standard
absorbent pad. The test is designed to compare the atrike-
through.time of different nonwoven coverstocks.
The nonwoven samples are for the purpose of the present
invention conditioned for at least 2 hours at a temperature
of 23°C and a relative humidity of 50%. 5 ml of the test
liquid (a 0.9% aqueous NaCl solution, "simulated urine") is
discharged onto the sample (typical base weight 22 g/m2), and
the time required for the liquid to penetrate the nonwoven is
measured electronically.
2180247
W095119465 PCTIDK95100024 r
34
In the liquid strike-through test, nonwovens according to the
present invention should have a strike-through time of at
least about 2D sec, preferably at least about 60 sec, more
preferably at least 120 sec. For nonwovens containing highly
hydrophobic fibres the strike-through time is preferably at
least about 5 min.
The hydrophobicity of nonwovens may further be determined by
evaluating the runoff percentage according to the following
procedure:
Runoff is measured using "synthetic urine" (68-72 dyne/cm;
19.4 g urea, 8 g NaCl, 0.54 g MgS04 (anhydrous), 1.18 g
CaC12~6HZ0, 970.9 g demineralised water). The test involves
pouring 25 ml of test liquid in 3.75 sec. onto a test materi-
al (31 cm in the machine direction and 14 cm in the cross
direction) containing a top layer of a nonwoven coverstock
and a bottom layer of filter paper, the test material being
placed at angle of 10 degrees from horizontal and a collect-
ing tray being placed under the lower end of the test materi-
al. The coverstock should be placed in the machine direction
with the embossed side upwards. The runoff percentage is
defined as the amount of test liquid which is collected in
the tray, expressed as a percentage of the original 25-ml of
liquid. A good hydrophobic nonwoven should using this method
give a runoff of at least 95%. For materials with superior
hydrophobic-properties, the runoff percentage is preferably
at least 98%, and can be as high as 99% or more (which essen-
tially corresponds to 0% penetration). In addition to the
hydrophobicity of the fibres used to prepare the aonwoven,
the runoff percentage is also to a certain extent dependent
upon the weight of the material, a heavier material giving a
slightly higher runoff percentage, the above-mentioned runoff
percentages being based on nonwovena with a base weight of 20
g/m2.
WO95/19465 2180247
EXAMPLES
Fibres and nonwovens were prepared as follows:
The polyolefin raw material (polypropylene) was spun into
fibres by conventional spinning (long spinning) technology,
5 using spinning speeds of 7L500-2000 m/min, resulting in a .
bundle of several hundred filaments. After quenching of the
filaments by air cooling, the filaments were treated by means
of a lick roller with a first spin finish containing the
antistatic agents mentioned below.
10 The dispersions of the first spin finish were prepared pri-
marily by mixing the proprietary mixtures Novostat 1105 or
Beistat LXO (from CHT R. Beitlich, GmbH, Germany) or the
proprietary mixtures Silaatol VP33G213/1 or VP33G213/2 (from
Schill & Seilacher GmbH, Germany) in various ratios. The
15 amount (active content based on the weight of the fibres)
applied at this stage varied somewhat, but generally about
0.06-0.11% of the Novostat or Beistat products was applied,
and about 0.12-0.16% of the VP33G213 products. Also, about
0.07-0.12% of a hydrophobic lubricant (NOVOlub 2440 or Beilub
20 6993, CHT R. Beitlich GmbH, Germany) was applied in the first
spin finish in a number of cases, and in Example 10 about
0.20% of the hyrophobic lubricant Beilub 6995 (CHT R. Beit-
lich GmbH, Germany) was applied in the first spin finish.
The Novostat/Beistat products contain mainly a quaternary
25 ammonium salt with end groups functionalized with fatty acid
amides. They correspond to compounds covered by the general
formula I above in Which Z1 and Zz are Alk-CONH-. The
counterion in these products is acetate. The major difference
between the two types of products is their pH, Beistat having
30 a pH of 5-6 and Novostat having a pH of 4 at an active con-
tent of 10%.
The VP33G213 products each contain two cationic antistatic
agents, both of which are quaternary ammonium salts with end
2180247
W0 95/19465 PCT/DK95100024
36
groups functionalized with fatty acid amides, corresponding
to compounds encompassed by the general formula I above in
which Z1 and Z2 are either Alk-CONH- or (Alk)2-N-. Different
counterions have been used, including acetate, chloride and
metasulfate.
Note that all of the antistatic products are in fact product
mixtures, a part of which may not be totally reacted in the
condensation process.
The Novolub/Beilub products contain mainly a fatty acid amide
condensate corresponding to compounds covered by the general
formula IV above, the melting point of the condensate being
about 80°C. The main difference between the two products is
their particle size, Novolub having an average particle size
of about 3-8 dun, whereas Beilub has a submicron (<1 Eun)
average particle size. The Beilub product has a pH of 5-6 and
Novolub a pH og about 4-5 at 10% active content.
In comparative Examples 1 and 3 the antistatic agent was
anionic and consisted of a neutralized C16-C18 alcohol phos-
phoric acid ester, the major part of which was a neutralized
stearyl alcohol phosphoric acid ester (Silastol F203, Schill-
& Seilacher GmbH, Germany).
The filaments were off-line stretched in a two-stage drawing
operation using a combination of hot rollers and a hot air '
oven, with temperatures in the range of 115-135°C. The
stretch ratios were generally in the range of from 1.05:1 to
1.5:1. The stretched filaments were then treated (by means of
a lick roller) with different second spin finishes. The
second spin finishes were aqueous dispersions containing
varying amounts of hydrophobic lubricants, and in certain
cases cationic antistatic agents. In two examples (3 and 8),
the second spin finish also contained polydimethylsiloxane
(silicone).
2180247
WO 95119465 PCT/DK9510007A
37
For the hydrophobic lubricants of the fatty acid amide con-
densation type (Examples 2, 4, 5, 8, 9 and 10), the disper-
sions were, except as otherwise noted, prepared using the
proprietary mixtures Novo:Lub 2440, Beilub 6993 or Beilub
6995. Example 2 also contained Novostat 1105. In Example 8,
Beilub 6993 was mixed with a cationic emulsified polydi-
methylsiloxane in the form of the proprietary mixture ZWP73
(CHT R. Beitlich GmbH, Germany), and in Example 3 the polydi-
methylailoxane was present in the form of the proprietary
mixtureSilastol 5072 (Schill & Seilacher GmbH, Germanyj. The
typical-amount of hydrophobic lubricant (and any antistatic
agent) applied in the second spin finish was 0.15-0.35% by
weight of the fibres.
For the hydrophobic lubricants of the wax type (Examples 6
and 7), the dispersions were prepared by using the propri-
' etary mixtures VP33G216 as the wax component, which in cer-
tain cases Was mixed with vP33G213/2 as an antistatic agent
(all from Schill & Seilacher GmbH, Germany). The typical
amount of the wax component (and any antistatic agent) ap-
plied was about 0.5% by weight of the fibres. The wax compo-
nent itself was a hydrocarbon wax mixture containing mostly a
linear saturated hydrocarbon wax with a melting point of 55°C
and an average molecular weight of about 500.
The filaments were then crimped in a stuffer-box crimper and
subsequently annealed in an oven at a temperature of about
125°C to reduce contraction of the fibres during the thermal
bonding process and to allow the hydrophobic components of
the second spin finish to become uniformly distributed on the
surface of the filaments. Staple fibres were then produced by
cutting the filaments to the desired length.
All fibres were of polypropylene, with a fineness of 2.2-2.4
dtex for Examples 1-9 and 1.7 dtex for Example 10, a fibre
tenacity of I.8-2.1 cN/dtex, an elongation at break of
350-420%, and a cut length of 41or 45 mm. The fineness of
the finished fibres was measured according to DIN 53812/2,
2180247
WO 95/19465 PCTIDK95100024
38
the elongation at break and tenacity of the fibres was mea-
sured according to DIN 53816, and the crimp frequency was
measured according to ASTM D 3937-82.
Nonwovens were prepared from the various fibres by carding at
various speeds and thermally bonding the webs at various
temperatures (see Table 2). For each nonwoven, the tensile
strength and elongation was measured in both the machine
direction and the cross direction as described above (i.e.
using the EDANA recommended teat), and a bondability index
was calculated as described above on the basis of the mea-
sured tensile strengths. For comparison purposes, the bondab-
ility indices were converted as explained above to an index
for a standard nonwoven With a base weight of 20 g/m2 ($I2o)~
In addition, the runoff percentage, strike-through and repel-
lency were also determined, the methods used also being those
described above.
The cardability, i.e. the suitability of the fibres for
carding Was determined using a simple web cohesion teat. This
test is carried out by measuring the length a thin carding
web of approximately 10 g/m2 can support in a substantially
horizontal position before it breaks due to its own weight,
the length of the carding web being increased at a rate of
about 15 m/min. This it performed by taking the carding web
off the card in a horizontal direction at a speed of 15
m/min, which is the carding speed used for this test.
A higher cardability as a result of a higher fibre/fibre
friction gives a higher web cohesion length. The fibre/fibre
friction is dependent upon factors such as the composition of
the second spin finish and the degree of texturization, as
well as how permanent the texturization is. Fibre/metal
friction is also important for the cardability; if it is
either too high or too low, the fibres are difficult to
transport through the card.
O WO 95119465 2 1 8 0 2 4 7
PCT/DK95100024
39
Polyolefin fibres which are well suited for carding will
typically be able to support about 1.5 m or more, e.g.
1.5-2.5 m, in the above-described web cohesion length test.
Fibres designed for high speed carding should preferably be
able to support somewhat more, 1.e. at least about 2.0 m.
In the -tables below, the fibre properties of a number of
different fibres prepared as described above are given, along
with the properties of-nonwovens prepared from these fibres.
Table 1 shows, in addition to the type of fibre, the follow-
ing characteristics of the fibres: amount of first and second
spin finish applied (active content, in percent by weight of
the fibres), total amount of spin finish applied (total
active content in percent by weight of the fibres), the
viscosity of the second spin finish, the composition (active
content) of the total spin finish applied (percent by weight
antistatic agent, hydrophobic lubricant and silicone; the
remainder of the active content up to 100% being an emulsifi-
er), number of crimps per 10 cm, the web cohesion length and
the liquid absorbency time of the fibres.
Table 2 shows the following characteristics of nonwovens
prepared from the fibres of Table 1: carding speed (m/min),
bonding temperature (°C), maximum tensile strength in the
machine direction (Nm-max; N/5 cm), maximum tensile strength
in the cross direction (CD-max; N/5 cm), maximum bondability
index (BI-max), standard bondability index (BI2p), base
weight (g/m2), runoff percentage, repellency (cm), strike-
through and a rough classification of the cardability.
2180247
WO 95119465 PC'TIDK95I00024
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2180247
WO 95!19465 PCTIDK95/00024
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2180247
WO 95119465 PCTIDK95100024
42
In the following, some additional comments regarding the
various teats are provided:
Example 1 (comparative example)
A silicone-free fibre prepared ueing spin finishes with
anionic antistatic agents (a neutralized C16-Clg alcohol
phosphoric acid ester, the major part of which was a neutral
ized stearyl alcohol phosphoric acid ester). Web cohesion
length 1.75 m.
A comparison of Example 1 with Examples 4, 5 and 7 shows the
effect of going from an anionic to a cationic antistatic
agent when the fibres are not treated with a silicone compo-
nent to improve their hydrophobic properties. The liquid
absorption time of the fibres is increased from about 10
minutes (Example 1) to from I hour to over 24 hours for the
other examples. For nonwovens, the water repellency is in-
creased from 1.5 cm to 3-5 cm, and strike-through from less
than 10 seconds to over 300 seconds (note that all the
strike-through tests are discontinued after 300 seconds, if
the liquid has not penetrated the nonwoven). Thus, replacing
the anionic antistatic agent with a cationic antistatic agent
resulted in a dramatic improvement in the hydrophilic proper-
ties.
Example 2 (comparative example)
Fibre prepared using an antistatic agent in the second spin
finish, which had a very high viscosity (34 mPa~s), and which
formed a significant amount of stable foam that gave problems
in applying the correct amount. This also resulted in a poor
distribution of spin finish on the fibre surface, which may
be seen in the results for hydrophobicity of the fibre-(liq-
uid absorption time) and the nonwoven (strike-through 11
seconds, water repellency 0.5 cm). These values are much
poorer than e.g. Examples 4 and 8, in which the viscosity is
much lower.
2180247
WO 95119465 PCTIDK95100024
43
Example 3 (comparative example)
A silicone-containing fibre prepared using the same anionic
antistatic agent as in Example 1 and a large amount of sili-
cone. The fibre has a good hydrophobicity, but a limited web
cohesion, and therefore only a moderate cardability. A "nor-
mal" carding speed of 100 m/min-gave good hydrophobicity
(strike-through > 300 sec), while a somewhat higher carding
speed of 151 m/min resulted in a significantly lower strike-
through of only about 41 sec, due to the poor distribution of
the fibres in the carding web. The web cohesion length was
1.75 m.
A comparison of Example 3 with Examples 4, 5b and 5c shows
the effect of using a cationic antistatic agent without
silicone or with only a small amount of silicone. In all of
these examples, the hydrophobic properties are very good,
with a water repellency of over 3 cm and a strike-through of
over 300 seconds (although the strike-through was only 41
seconds for the nonwoven prepared from the fibres of Example
3b carded at 151 m/min), but the use of a cationic antistatic
agent and no silicone or only a small amount of silicone in
the latter examples gave a greater fibre friction. This may
be seen by the fact that the greater web cohesion of Examples
5b and 5c (2.25 and 2.0 m,. respectively, compared to a maxi-
mum of 1.75 m in Example 3). As for Example 4, it should be
noted that while the web cohesion values given in Table 1 are
not higher than the value given for Example 3, this is due to
the fact that the nonwovens of Example 3 were prepared using
the maximum possible crimper box pressure, while those of
Example 4 Were prepared using close to the minimum crimper
box pressure. Thus, use of a higher crimper box pressure in
Example 4 would have resulted in web cohesion values compar-
able to those of Examples 5b and 5c.
Improved fibre friction allows a higher carding speed: for
example maximum 151 m/min for the fibres of Example 3, while
the fibres of-Example 9 could be carded at 200 m/min to high
2180247
WO 95/19465 PCTIDK95100024
44
quality, unifozxn nonwovens, and could also be carded at 230
m/min. Although the hydrophobic properties of the fibres of
the invention (e. g. those of Example 9a) at very high carding
speeds are not quite as good as at slightly lower speeds,
they are still acceptable for many applications.
Example 4
The spin finish mixtures were used in different-amounts. Good
hydrophobicity, although hydrophobicity was poorer with
increased viscosity of the spin finishes. The fibres are
produced under conditions that give a good liquification of
the hydrophobic lubricant in the drying oven (after crimp-
ing), i.e. a temperature sufficiently above the melting
temperature of the lubricant to ensure thorough melting of
the lubricant component.
Example 5
Differences in texturization due to differences in particle
size, viscosity and crimper box pressure give differences in
hydrophobicity in nonwovena, even though the properties of
the fibres themselves are otherwise nearly the same.
Example 5 shows fibres prepared using steam heating after
application of the second spin-finish, but before the crimp-
er. This gave an increased fibre/fibre friction, as expressed
by web cohesion, which in turn allows a higher carding speed.
Furthermore, a low viscosity of the second spin finish (Exam-
plea 5b and 5c) resulted in excellent hydrophobic properties
(strike through and repellency).
Example 6
Example 6 shows fibres treated with a cationic emulsified wax
component as the hydrophobic lubricant. The hydrophobic
properties are moderately good. Compared to the similar fibre
of Example 7b, the addition of-a relatively small amount of-
WO 95/19465 218 0 2 4 7
PCT/DK95/00024
antistatic agent to the second spin finish of Example 6 gave
poorer results.
Example 7
Two cationic antistatic mixtures were used in the first spin
5 finish, with the same wax component being used in the second
spin finish. In Example 7a the second spin finish contained
an antistatic agent (VP33G213/2), while the second spin
finish of Example 7b did not. Both fibres and nonwovens
showed good to excellent hydrophobic and strength properties,
10 with 7b-being slightly better in terms of hydrophobicity than
7a.
Example 8
Similar to Examples 4 and 5, although with a small addition
of a cationic emulsified polydimethylailoxane. Addition of
15 the silicone gave slightly improved hydrophobicity.
Example 9
High speed carding test. Good web uniformity and hydrophobic-
ity at 180-200 m/min. Web cohesion length 2.25 m. Compare
with Example 3, in which the fibres could not be carded at
20 more than 151 m/min, and Which even then showed poor web
formation. The fibres of this example were prepared under
conditions similar to those of Example 5c, but were textur-
ized under conditions that gave higher fibre/fibre friction
(higher crimper box pressure) The fibres could be carded at
25 230 m/min. to a somewhat less uniform web than that obtained
at 200 m/min.
Example 10
In this example, a relatively large amount (0.20%) of hydro-
phobic lubricant of the fatty acid amide type was applied to
30 fine (1.7 dtex) fibres in the first spin finish, which gave a
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uniform coating of the hydrophobic lubricant onthe fibres.
During application of the first spin finish the width of the
fibre tow is greater than during application of the second
spin finish, and a better distribution of the lubricant can
therefore be obtained by applying it in the first spin fin-
ish.
Applying to fine dtex fibres an amount of spin finish similar
to that applied to fibres with a higher dtex gave a better
spin finish coverage of the fibres and improved uniformity in
nonwoven materials produced from these fibres. The relatively
high content of hydrophobic lubricant in the first spin
finish gave an improved cohesion and better processability of
the fibres during carding.
Fine dtex fibres can also be combined with other fibres
having a higher dtex to provide good product processability.
