Patent Description:
Today, polypropylene fibers or polypropylene nonwoven fabrics have been used in a variety of applications, including filtration medium (filter), diapers, sanitary products, sanitary napkin, panty liner, incontinence product for adults, protective clothing materials, bandages, surgical drape, surgical gown, surgical wear and packing materials. Because of excellent properties such as breathability and softness, polypropylene nonwoven fabrics are widely used as hygiene materials. However, further improvements in softness, bulkiness and mechanical strength have been required.

High loft layers may contribute to the provision of nonwoven fabrics having a high softness as desired in hygiene products such as diapers, sanitary napkins and the like. Nonwoven fabrics comprising high loft layers on the basis of crimped fibers are known in the art. Generally, crimped multicomponent fibers comprise two or more polymers of different physical properties that are asymmetrically distributed over their cross section. The most common is side-by-side. This configuration causes the fibers to crimp when they are physically stressed like, in the case of spunbonded fibers, during fiber drawing and quenching.

For example, <CIT> discloses a fabric comprising at least one high loft nonwoven layer having crimped multicomponent fibers, characterized in that a first component of the multicomponent fibers comprises a first polymer A and a second component of the multicomponent fibers comprises a blend of the first polymer A and a second polymer B, wherein the melt flow rate of polymer A is at least <NUM>% different from the melt flow rate of polymer B and wherein the second component comprises at least <NUM> wt. -% of polymer B. Also the method of manufacturing the SMS type products are claimed.

<CIT> shows a method for making a high loft nonwoven web comprising crimped multicomponent fibers, the process comprising laying down the fibers on a spinbelt and pre-consolidating the fibers after laydown using one or more pre-consolidation rollers to form a pre-consolidated web, characterized in that a first component of the fibers comprises a PP homopolymer and a second component of the fibers comprises a PP/PE copolymer, wherein the pre-consolidation rollers are operated at a certain temperature and contact force.

According to <CIT>, crimped conjugated fibers and nonwoven fabrics comprising the fibers are disclosed. The crimp of the fibers is thereby achieved upon using multicomponent fibers where the two components have similar melt flow rates and melting points, but a certain difference in the ratio of Z-average to weight average molecular weight distributions.

<CIT> describes a spunbonded nonwoven having crimped multicomponent fibers, wherein a first component of the multicomponent fibers consists of a first thermoplastic polymer material comprising a first thermoplastic base polymer and a second component of the multicomponent fibers consists of a second thermoplastic polymer material comprising a second thermoplastic base polymer that is different from the first base polymer. The at least one of the first polymer material or the second polymer material is a polymer blend that comprises, further to the respective base polymer, between <NUM> and <NUM> weight percent of a high melt flow rate polymer that has a melt flow rate of between <NUM> and <NUM>/<NUM>. The fibers have a linear mass density of less than <NUM> denier. The average crimp number of the crimped multicomponent fibers is in the range of at least <NUM> and preferably at least <NUM> crimps per cm in the fiber.

<CIT> describes a spunbond nonvoven laminate that has a stack of at least two and at most four spunbond nonwoven layers each formed by or consisting of crimped continuous filaments. A degree of crimping of the filaments in each of the spunbond nonwoven layers is dilferent from a degree of crimping in each of the other spunbond nonwoven layers and each of the crimped filaments of the spunbond nonwoven layers has a crimp with at least two loops per centimeter of length The crimped filaments of the spunbond nonwoven layers are multicomponent filaments each having at least one first plastic component and at least one second plastic component with each of the plastic components being present in the respective filament in a proportion of at least <NUM> wt%.

<CIT> describes a non-woven fabric of crimped composite fiber and a laminate thereof. The non-woven fabric of crimped composite fiber comprises a first propylene-based polymer and a second propylene-based polymer, wherein in the first propylene-based polymer and the second propylene-based polymer, the melting point of the second propylene-based polymer is higher than the melting point of the first propylene-based polymer by <NUM> or more (DSC), the ratio of melt flow rates (<NUM>, <NUM> load) of the second propylene-based polymer to the first propylene-based polymer is <NUM> or more (ASTM D <NUM>), the ratio of molecular weight distributions (MWD) of the second propylene-based polymer to the first propylene-based polymer is <NUM> or more (GPC), and the component ratio of the first propylene-based polymer and the second propylene-based polymer (weight ratio) is <NUM>/<NUM>-<NUM>/<NUM>.

<CIT> describes a nonwoven fabric comprising a plurality of filaments made of at least two different materials (A, B), said multicomponent filaments having two sub-filaments co-extruded from said materials (A, B) in side-by-side arrangement and adhered to one another, wherein the material (A) of a first sub-filament has melting temperature different from the melting temperature of the material (B) of a second sub-filament by at least <NUM> and wherein, in cross section, the contact surface between said two sub-filaments is substantially wave-shaped.

<CIT> describes a conjugate fiber that demonstrates low-temperature processability and excellent thermal adhesiveness without shrinking significantly, that can be processed with excellent card passability when processed into a nonwoven fabric, and can produce a bulky nonwoven fabric having excellent uniformity. A bulky nonwoven fabric and a formed article having excellent low-temperature processability and excellent feeling are also described. The conjugate fiber has a first component that contains at least <NUM> wt% of an ethylene α-olefin copolymer having a melting point of <NUM> to <NUM>, and a second component that contains a crystalline polypropylene, which form a side-by-side cross section, wherein, in a fiber cross section perpendicular to a fiber axis, the first component accounts for <NUM> to <NUM> % of an outer periphery of the fiber, a borderline between the first component and the second component forms a curve bulging toward the first component, and an area ratio between the first component and the second component is in a range of <NUM>/<NUM> to <NUM>/<NUM>. A nonwoven fabric is obtained by processing the conjugate fiber into a nonwoven fabric.

<CIT> describes bicomponent fibers with improved curvature The bicomponent fibers comprise a first region and a second region. The first region comprises a first polyethylene composition and the second region comprises a second polyethylene composition, wherein the first polyethylene composition has a crystallization temperature (Tc) greater than a crystallization temperature (Tc) of the second polyethylene composition The bicomponent fiber can be used to form a nonwoven.

Despite these various improvements, however, there is still a need for optimization and diversification of polymers that can be used for making such materials. The purpose of this invention is to provide an approach on selecting and using polypropylene composition for producing nonwoven fabric sheet comprising fibers having an improved and controllable crimp and a nonwoven fabric having higher loft as compared to these known products while maintaining other desirable properties.

The present inventors have conducted extensive studies, and as a result have found that the aforementioned properties can be achieved by using specific polypropylene composition. It was surprisingly found that with using polypropylene composition according to the present invention different tailor-made curvature of the fibers can be formed, which dominate the formation of crimps. With certain range of the curvature the softness of nonwoven fabric made from the fibers is optimised.

Accordingly, the present invention provides:
Use of polymer composition comprising a first propylene polymer A and a second propylene polymer B for producing crimped multicomponent fibers having a side by side cross-sectional configuration, wherein.

The radial plane is perpendicular to the longitudinal direction of the fibers, and as such at a <NUM>°-angle to the longitudinal axis of the fiber at the given position. The shape of the radial interface line, which defines the present invention, is the shape of the interface line that is contained in this plane. This is to distinguish from the contour of the interface along a longitudinal or oblique line, which in a crimped fiber is naturally curved to some extent by geometrical relation. The curved nature of the radial interface line, which defines the present invention, is not geometrically related to the crimp of the fiber.

In preferred embodiments the curvature (c) of the radial interface line is between <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>. Very favourable crimping behaviour has been observed in many cases when the curvature is within these ranges.

In a preferred embodiment, the crimped multicomponent fibers produced by using polymer composition as defined in the present invention are spunbonded fibers, which form nonwoven fabric sheets, preferably spunbonded fabric sheets. The sheet can comprise the bicomponent fibers following the inventive definition, in addition to other fibers like linear monocomponent fibers, or consist of bicomponent fibers following the inventive definition. As in reality the millions of fibers forming for a nonwoven material are never always identical, the term consisting of must be understood in a sense that the requirement is fulfilled when the fibers are all the same by production and the vast majority of fibers, e.g. more than <NUM>% of the fibers, preferably more than <NUM>% of the fibers show the inventive characteristic.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

Unless clearly indicated otherwise, use of the terms "a," "an," and the like refers to one or more. According to the present invention, the expression "propylene homopolymer" relates to a polypropylene that consists substantially, i.e. of at least <NUM> mol%, more preferably of at least <NUM> mol%, still more preferably of at least <NUM> mol%, like of at least <NUM> mol%, of propylene units. In another embodiment, only propylene units are detectable, i.e. only propylene has been polymerized. Thus the polypropylene homopolymer can contain a maximum of <NUM> wt% of a C<NUM> or C<NUM> to C<NUM> alpha olefin comonomer, preferably a maximum of <NUM> wt%, still more preferably of a maximum of <NUM> wt%, like of a maximum of <NUM> wt% of a C<NUM> or C<NUM> to C<NUM> alpha olefin comonomer.

Such comonomers can be selected for example from ethylene, <NUM>-butene, <NUM>-hexene and <NUM>-octene. Preferably the comonomer if present is ethylene.

In another embodiment only propylene units are detectable, i.e. only propylene has been polymerized. In this case the amount of comonomer is <NUM> wt%.

A propylene/α-olefin random copolymer is a copolymer of propylene monomer units and comonomer units, preferably selected from ethylene and C<NUM>-C<NUM> alpha-olefins, in which the comonomer units are distributed randomly over the polymeric chain. The propylene random copolymer can comprise comonomer units from one or more comonomers different in their amounts of carbon atoms. In the following amounts are given in mol% unless it is stated otherwise.

Typical for propylene homopolymers and propylene/α-olefin random copolymer is the presence of only one glass transition temperature.

The present invention relates to use of specific polymer composition comprising a first propylene polymer A and a second propylene polymer B for producing crimped multicomponent fiber having a side by side cross-sectional configuration. In the following the polymer composition, first propylene polymer A and second propylene polymer B are described in more detail.

It is essential that in the polymer composition according to the present invention, the mass ratio of the first propylene polymer A and the second propylene polymer B [A:B] is in the range of <NUM>: <NUM> to <NUM>:<NUM>, preferably in the range of <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of <NUM>:<NUM> to <NUM>:<NUM>, and the absolute value of the difference of the crystallization temperature [Tc (A)] of the propylene polymer (A) and the crystallization temperature [Tc (B)] of the propylene polymer (B) is in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, like in the range of <NUM> to <NUM>.

The first propylene polymer (A) can be a propylene homopolymer or a propylene/α-olefin random copolymer.

In case the first propylene polymer (A) is a propylene/α-olefin random copolymer, the first propylene polymer (A) may comprise monomers copolymerizable with propylene, for example comonomers such as ethylene and/or C<NUM> to C<NUM> α-olefins, in particular ethylene and/or C<NUM> to C<NUM> α-olefins, e.g. <NUM>-butene and/or <NUM>-hexene. Preferably the first propylene polymer (A) according to this invention comprises, especially consists of, monomers copolymerizable with propylene from the group consisting of ethylene, <NUM>-butene and <NUM>-hexene. More specifically the first propylene polymer (A) of this invention comprises - apart from propylene - units derivable from ethylene and/or <NUM>-butene. In a preferred embodiment, the first propylene polymer (A) comprises units derivable from ethylene and propylene only.

It is preferred that the melt flow rate (MFR<NUM>, <NUM>, <NUM>, ISO <NUM>) of the first propylene polymer (A) is in the range of <NUM> to <NUM>/<NUM>, more preferably in the range of <NUM> to <NUM>/<NUM> and even more preferably in the range of <NUM> to <NUM>/<NUM>.

It is further preferred that the molecular weight distribution (Mw/Mn) of the first propylene polymer (A) is in the range of <NUM> to <NUM> (measured by size exclusion chromatography according to ISO <NUM>), preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>. In a specific embodiment of this invention, the first propylene polymer (A) is preferably a crystalline propylene homopolymer. The term "crystalline" indicates that the propylene homopolymer has a rather high melting temperature. Accordingly throughout the invention the propylene homopolymer is regarded as crystalline unless otherwise indicated. In this embodiment, first propylene polymer (A) being a propylene homopolymer has preferably a melting temperature Tm measured by differential scanning calorimetry (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, and a crystallization temperature Tc (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, and a comonomer content < <NUM> wt%, preferably in the range of <NUM>-<NUM> wt%.

In another specific embodiment of this invention, the first propylene polymer (A) is preferably propylene/α-olefin random copolymer with a comonomer content in the range of <NUM>-<NUM> wt%, preferably in the range of <NUM>-<NUM> wt%, more preferably in the range of <NUM>-<NUM> wt%. In this embodiment, the first propylene polymer (A) being a propylene/α-olefin random copolymer has preferably a melting temperature Tm measured by differential scanning calorimetry (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, and a crystallization temperature Tc (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

In a further preferred embodiment, the first propylene polymer (A) being a propylene/α-olefin random copolymer has preferably a molecular weight distribution (Mw/Mn) in the range of <NUM> to <NUM> (measured by size exclusion chromatography according to ISO <NUM>), preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

It is further preferred that the first propylene polymer (A) has preferably a xylene cold soluble content (XCS) in the range of <NUM> to <NUM> wt%, more preferably in the range of <NUM> to <NUM> wt%.

The amount of xylene cold solubles (XCS) additionally indicates that first propylene polymer (A) is preferably free of any elastomeric polymer component, like an ethylene propylene rubber. In other words, the first propylene polymer (A) shall be not a heterophasic polypropylene, i.e. a system consisting of a polypropylene matrix in which an elastomeric phase is dispersed. Such systems are featured by a rather high xylene cold soluble content.

The second propylene polymer (B) can be a propylene homopolymer or a propylene/α-olefin random copolymer.

In case the second propylene polymer (B) is a propylene/α-olefin random copolymer, the second propylene polymer (B) may comprise monomers copolymerizable with propylene, for example comonomers such as ethylene and/or C<NUM> to C<NUM> α-olefins, in particular ethylene and/or C<NUM> to C<NUM> α-olefins, e.g. <NUM>-butene and/or <NUM>-hexene. Preferably the second propylene polymer (B) according to this invention comprises, especially consists of, monomers copolymerizable with propylene from the group consisting of ethylene, <NUM>-butene and <NUM>-hexene. More specifically the second propylene polymer (B) of this invention comprises - apart from propylene - units derivable from ethylene and/or <NUM>-butene. In a preferred embodiment, the second propylene polymer (B) comprises units derivable from ethylene and propylene only.

It is preferred that the melt flow rate (MFR<NUM>, <NUM>, <NUM>, ISO <NUM>) of the second propylene polymer (B) is in the range of <NUM> to <NUM>/<NUM>, more preferably in the range of <NUM> to <NUM>/<NUM> and even more preferably in the range of <NUM> to <NUM>/<NUM>.

It is further preferred that the molecular weight distribution (Mw/Mn) of the second propylene polymer (B) is in the range of <NUM> to <NUM> (measured by size exclusion chromatography according to ISO <NUM>), preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

In a specific embodiment of this invention, the second propylene polymer (B) is preferably a crystalline propylene homopolymer. The term "crystalline" indicates that the propylene homopolymer has a rather high melting temperature. Accordingly throughout the invention the propylene homopolymer is regarded as crystalline unless otherwise indicated. In this embodiment, second propylene polymer (B) being a propylene homopolymer has preferably a melting temperature Tm measured by differential scanning calorimetry (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, and a crystallization temperature Tc (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, and a comonomer content < <NUM> wt%, preferably in the range of <NUM>-<NUM> wt%.

In another specific embodiment of this invention, second propylene polymer (B) is preferably propylene/α-olefin random copolymer with a comonomer content in the range of <NUM>-<NUM> wt%, preferably in the range of <NUM>-<NUM> wt%, more preferably in the range of <NUM>-<NUM> wt%. In this embodiment, the second propylene polymer (B) being a propylene/α-olefin random copolymer has preferably a melting temperature Tm measured by differential scanning calorimetry (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, and a crystallization temperature Tc (DSC, ISO <NUM>-<NUM> & -<NUM>) in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

In a further preferred embodiment, the second propylene polymer (B) being a propylene/α-olefin random copolymer has preferably a molecular weight distribution (Mw/Mn) in the range of <NUM> to <NUM> (measured by size exclusion chromatography according to ISO <NUM>), preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

It is further preferred that the second propylene polymer (B) has preferably a xylene cold soluble content (XCS) in the range of <NUM> to <NUM> wt%, more preferably in the range of <NUM> to <NUM> wt%.

The amount of xylene cold solubles (XCS) additionally indicates that second propylene polymer (B) is preferably free of any elastomeric polymer component, like an ethylene propylene rubber. In other words, the first propylene polymer (A) shall be not a heterophasic polypropylene, i.e. a system consisting of a polypropylene matrix in which an elastomeric phase is dispersed. Such systems are featured by a rather high xylene cold soluble content.

The propylene polymers including the first propylene polymer (A) and the second propylene polymer (B) of the present invention fulfilling the above mentioned requirements may be produced by polymerization process known in the state of the art. Commercially available propylene polymers may be used, with examples including HG475FB manufactured and sold by Borealis Polyolefin.

Preferably the propylene polymers (A and B) according to this invention are produced in the presence of.

It is preferred that the internal donor is selected from optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-<NUM>,<NUM>-dicarboxylates, benzoates and derivatives and/or mixtures thereof, preferably the internal donor is a citraconate.

Additionally or alternatively, the molar-ratio of co-catalyst to external donor (ED) [Co/ED] is <NUM> to <NUM>.

In view of the above, it is preferred that the polypropylene polymer is free of phthalic compounds as well as their respective decomposition products, i.e. phthalic acid esters, typically used as internal donor of Ziegler-Natta catalysts (e.g. <NUM>th generation Ziegler-Natta catalysts).

The term "free of" phthalic compounds in the meaning of the present invention refers to a polypropylene homopolymer in which no phthalic compounds as well as no respective decomposition products at all originating from the used catalyst, are detectable.

According to the present invention the term "phthalic compounds" refers to phthalic acid (<NPL>), its mono- and diesters with aliphatic, alicyclic and aromatic alcohols as well as phthalic anhydride.

As already indicated above, the polypropylene polymers of the present invention are optionally produced in a sequential polymerization process.

The term "sequential polymerization system" indicates that the polypropylene polymer is produced in at least two reactors connected in series. Accordingly, the polymerization system for sequential polymerization comprises at least a first polymerization reactor and a second polymerization reactor, and optionally a third polymerization reactor. The term "polymerization reactor" shall indicate that the main polymerization takes place. Thus, in case the process consists of two polymerization reactors, this definition does not exclude the option that the overall system comprises for instance a pre-polymerization step in a prepolymerization reactor. The term "consist of" is only a closing formulation in view of the main polymerization reactors.

Preferably the first polymerization reactor is, in any case, a slurry reactor and can be any continuous or simple stirred batch tank reactor or loop reactor operating in bulk or slurry. Bulk means a polymerization in a reaction medium that comprises of at least <NUM> % (w/w) monomer. According to the present invention the slurry reactor is preferably a (bulk) loop reactor.

The optional second polymerization reactor can be either a slurry reactor, as defined above, preferably a loop reactor or a gas phase reactor.

The optional third polymerization reactor is preferably a gas phase reactor.

Suitable sequential polymerization processes are known in the state of the art.

A preferred multistage process is a "loop-gas phase"-process, such as developed by Borealis (known as BORSTAR® technology) described e.g. in patent literature, such as in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, or in <CIT>.

A further suitable slurry-gas phase process is the Spheripole process of Basell.

It is within the skill of art skilled persons to choose the polymerization conditions in a way to yield the desired properties of the polypropylene polymer.

In an especially preferred embodiment of the present invention, the first propylene polymer A and second propylene polymer B are different, and at least one of the propylene polymers (A and B) is visbroken.

Thus in this embodiment preferably the melt flow rate (<NUM>/<NUM>, ISO <NUM>) of either propylene polymers (A or B) before visbreaking is much lower, like from <NUM> to <NUM>/<NUM>. For example, the melt flow rate (<NUM>/<NUM>) of either propylene polymer (A or B) before visbreaking is from <NUM> to <NUM>/<NUM>, like from <NUM> to <NUM>/<NUM>.

Preferably, the ratio of the MFR after visbreaking [MFR final] to the MFR before visbreaking [MFR start]
[MFR final]/ [MFR start] is > <NUM>.

Preferably the polypropylene polymer (A or B) has been visbroken with a visbreaking ratio [final MFR<NUM> (<NUM>/<NUM>) / start MFR<NUM> (<NUM>/<NUM>)] of greater than <NUM> to <NUM>.

The "final MFR<NUM> (<NUM>/<NUM>)" is the MFR<NUM> (<NUM>/<NUM>) of the polypropylene polymer (A or B) after visbreaking and the "start MFR<NUM> (<NUM>/<NUM>)" is the MFR<NUM> (<NUM>/<NUM>) of the polypropylene polymer (A or B) before visbreaking.

More preferably, the polypropylene polymer (A or B) has been visbroken with a visbreaking ratio [final MFR<NUM> (<NUM>/<NUM>) / start MFR<NUM> (<NUM>/<NUM>)] of <NUM> to <NUM>.

Even more preferably, polypropylene polymer (A or B) has been visbroken with a visbreaking ratio [final MFR<NUM> (<NUM>/<NUM>) / start MFR<NUM> (<NUM>/<NUM>)] of <NUM> to <NUM>.

Preferred mixing devices suited for visbreaking are known to an art skilled person and can be selected i. from discontinuous and continuous kneaders, twin screw extruders and single screw extruders with special mixing sections and co-kneaders and the like.

The visbreaking step according to the present invention is performed either with a peroxide or mixture of peroxides or with a hydroxylamine ester or a mercaptane compound as source of free radicals (visbreaking agent) or by purely thermal degradation.

Typical peroxides being suitable as visbreaking agents are <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-bis(tert. butylperoxy)hexane (DHBP) (for instance sold under the tradenames Luperox <NUM> and Trigonox <NUM>), <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-bis(tert. butyl-peroxy)hexyne-<NUM> (DYBP) (for instance sold under the tradenames Luperox <NUM> and Trigonox <NUM>), dicumyl-peroxide (DCUP) (for instance sold under the tradenames Luperox DC and Perkadox BC), di-tert. butyl-peroxide (DTBP) (for instance sold under the tradenames Trigonox B and Luperox Di), tert. butyl-cumyl-peroxide (BCUP) (for instance sold under the tradenames Trigonox T and Luperox <NUM>) and bis(tert. butylperoxy-isopropyl)benzene (DIPP) (for instance sold under the tradenames Perkadox <NUM> and Luperox DC).

Suitable amounts of peroxide to be employed in accordance with the present invention are in principle known to the skilled person and can easily be calculated on the basis of the amount of propylene homopolymer to be subjected to visbreaking, the MFR<NUM> (<NUM>) value of the propylene homopolymer to be subjected to visbreaking and the desired target MFR<NUM> (<NUM>) of the product to be obtained.

Accordingly, typical amounts of peroxide visbreaking agent are from <NUM> to <NUM> wt%, more preferably from <NUM> to <NUM> wt%, based on the total amount of polypropylene polymer (A or B) employed. Typically, visbreaking in accordance with the present invention is carried out in an extruder, so that under the suitable conditions, an increase of melt flow rate is obtained. During visbreaking, higher molar mass chains of the starting product are broken statistically more frequently than lower molar mass molecules, resulting as indicated above in an overall decrease of the average molecular weight and an increase in melt flow rate.

After visbreaking the polypropylene polymer (A or B) according to this invention is preferably in the form of pellets or granules. The instant polypropylene polymer (A or B) is preferably used in pellet or granule form for the spunbonded fiber process.

In one specific embodiment of the present invention, only one of the propylene polymers (A and B) is visbroken, and the absolute value of the difference of Mz/Mw between propylene polymer A and B is from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, even more preferably from <NUM> to <NUM>.

In another embodiment of the present invention, both of the Propylene polymers (A and B) are visbroken, and the absolute value of the difference of Mz/Mw between propylene polymer A and B is between <NUM> to <NUM>, preferably between <NUM> to <NUM>, more preferably between <NUM> to <NUM>, even more preferably between <NUM> to <NUM>.

In a further preferred embodiment of the present invention, at least one of the propylene polymers A and B is nucleated, and the amount of nucleating agent is in the range of <NUM>-<NUM> ppm, preferably in the range of <NUM>-<NUM> ppm, more preferably <NUM>-<NUM> ppm, like <NUM>-<NUM> ppm based on the total amount of the nucleated propylene polymer.

In case the propylene polymer A or B is nucleated, it may comprise a nucleating agent, preferably an α-nucleating agent. The α-nucleating agent is preferably selected from the group consisting of.

Such additives are generally commercially available and are described, for example, in "<NPL>.

Preferably the propylene polymer A or B, contains up to <NUM> wt. -% of the α-nucleating agent. In a preferred embodiment, the propylene homopolymer contains <NUM> to <NUM> ppm, preferably <NUM>-<NUM> ppm, more preferably <NUM>-<NUM> ppm, most preferably <NUM>-<NUM> ppm of an α-nucleating agent, in particular selected from the group consisting of dibenzylidenesorbitol (e.g. <NUM>,<NUM> : <NUM>,<NUM> dibenzylidene sorbitol), dibenzylidenesorbitol derivative, preferably dimethyldibenzylidenesorbitol (e.g. <NUM>,<NUM> : <NUM>,<NUM> di(methylbenzylidene) sorbitol), or substituted nonitol-derivatives, such as <NUM>,<NUM>,<NUM>,-trideoxy-<NUM>,<NUM>:<NUM>,<NUM>-bis-O-[(<NUM>-propylphenyl)methylene]-nonitol, sodium <NUM>,<NUM>'-methylenebis (<NUM>, <NUM>,-di-tert-butylphenyl) phosphate, vinylcycloalkane polymer, vinylalkane polymer, and mixtures thereof.

In an especial preferred embodiment of the present invention, the first propylene polymer A is a propylene homopolymer, and the second propylene polymer B is a propylene random copolymer. In this case, the amount of first propylene polymer A is preferably less than the amount of second propylene polymer B. More preferably the mass ratio of the first propylene polymer A, like the propylene homopolymer, and the second propylene polymer B, like the propylene/α-olefin random copolymer [A:B] is in the range of <NUM>:<NUM> to <NUM>:<NUM>, preferably in the range of <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of <NUM>:<NUM> to <NUM>:<NUM>.

The use of polymer compostion of the present invention as defined above is for producing crimped multicomponent fiber having a side by side cross-sectional configuration. Preferably the multicomponent fibers are bicomponent fibers consisting of the first and second components. In the use of present invention, the first and second components are arranged in a side-by-side arrangement. The term "side-by-side" arrangements includes variants such as, for example, hollow side-by-side arrangements, eccentric hollow side-by-side arrangements and side-by-side multilobal arrangements.

The crimped bicomponent fibers are typically helically crimped. In one embodiment the average crimp number of the crimped multicomponent fibers is in the range of at least <NUM> and preferably at least <NUM> crimps per cm in the fiber, as measured as per Japanese standard JIS L-<NUM>-<NUM> under a pretension load of <NUM>/denier. The crimp amplitude is preferably in the range of below <NUM> and preferably between <NUM> and <NUM> when measured according to JIS L-<NUM>-<NUM> under a pre-tension load of <NUM>/denier.

The fibers preferably have a linear mass density in the range of between <NUM> to <NUM> denier, preferably <NUM> to <NUM> denier.

The basis weight of each of the spunbonded layers within the multilayer sheet may be between <NUM>-<NUM>/m<NUM>, preferably between <NUM>-<NUM>/m<NUM>.

The density of the nonwoven fabric sheet is preferably less than <NUM>/cm<NUM> and preferably less than <NUM>/cm<NUM>, which are values that are typical for high loft nonwovens with crimped fibers. Standard loft nonwovens with uncrimped fibers, as a comparison, typically have densities higher than <NUM>-<NUM>/cm<NUM>.

The thickness of the nonwoven fabric sheet is preferably greater than <NUM>, more preferably greater than <NUM>, for basis weights of <NUM>/m<NUM> or more, when measured according to WSP. <NUM>, option A, pressure of <NUM> kPa on a <NUM><NUM> plate.

The method and process of production of crimped multicomponent fiber having a side by side cross sectional configuration in the form of spunbonded nonwoven fabric sheet using polymer composition of the present invention is defined below:
The spunbonded nonwoven fabric sheet is made in an apparatus comprising at least two extruders with a spinnerette, a drawing channel and a moving belt, wherein the fibers are spun in a spinnerette, drawn in a drawing channel and laid down on a moving belt, wherein the apparatus comprises a pressurized process air cabin from which process air is directed through the drawing channel to draw fibers.

The drawing channel may comprise more than one section. The drawing channel or a section of the drawing channel may get narrower with increasing distance from the spinnerette. In one embodiment the converging angle can be adjusted. The apparatus may form a closed aggregate extending between at least the point of process air entry until the end of the drawing channel, so no air can enter from the outside and no process air supplied can escape to the outside. In one embodiment the apparatus comprises at least one diffuser, which is arranged between the end of the drawing channel and the moving belt.

The pressure difference between the ambient pressure and the pressure in the process air cabin is usually higher than <NUM> Pascal. It has been observed that, within reasonable overall ranges, higher cabin pressures tend to lead to curvatures in the desired ranges and have a positive influence on crimp. In preferred embodiments, the cabin pressure is hence higher than <NUM> Pascal, more preferably higher than <NUM> Pascal or even higher than <NUM> Pascal. For process stability, on the upper end, the cabin pressures preferably are less than <NUM> Pascal and preferably less than <NUM> Pascal.

Suitable process air temperatures are usually greater than <NUM>. It has been observed, however, that, within reasonable overall ranges, higher process air temperatures tend to lead to curvatures in the desired ranges and have a positive influence on crimp. In preferred embodiments, the process air temperature is hence higher than <NUM>, more preferably higher than <NUM>. On the upper end, the process air temperatures are preferably below <NUM>. If process air of two different temperatures is applied to the fibers during drawing, the above description relates to the process temperature of the air contacting the filaments first.

The maximum air speed in the drawing channel is usually higher than <NUM>/s.

Further details and advantages of the invention will become apparent from the figures and examples described in the following. The figures show:.

<FIG> shows schematic illustration of a cross-section of a side-by-side bicomponent fiber. The fiber F comprise first and second propylene polymer A and B arranged side-by-side. The arrangement extends over the entire length of the fiber.

<FIG> is a schematic illustration of a section of a crimped fiber F as comprised in a nonwoven fabric sheet of the invention. The fiber is curved and comprises a certain crimp radius and a certain crimp count.

<FIG> shows a spinning machine <NUM> that is suitable for producing spunbonded nonwovens according to the invention. Spunbonded nonwovens NW are produced from continuous fibers F of thermoplastic material, which are spun in a spinnerette <NUM> and subsequently passed through a cooling device <NUM>. A monomer suctioning device <NUM> to remove gases in the form of decomposition products, monomers, oligomers and the like generated during the spinning of the fibers F is arranged between the spinnerette <NUM> and the cooling device <NUM>. The monomer extraction device <NUM> comprises suction openings or suction gaps.

In the cooling device <NUM>, process air is applied to the fiber curtain from the spinnerette <NUM> from opposite sides. The cooling device <NUM> is divided into two sections 102a and 102b, which are arranged in series along the flow direction of the fibers. Thus, process air of a relatively higher temperature (for example <NUM>) can be applied to the fibers at an earlier stage in chamber section 102a and process air of a relatively lower temperature (for example <NUM>) can be applied to the fibers at a later stage in chamber section 102b. The supply of process air takes place via air supply chambers 105a and 105b, respectively. The cabin pressure within chambers 105a and 105b can be the same and can, for example, be about <NUM> Pascal above ambient pressure, for example.

A drawing device <NUM> to draw and stretch the fibers <NUM> is arranged below the cooling device <NUM>. The drawing device includes an intermediate channel <NUM>, which preferably converges and gets narrower with increasing distance from the spinnerette <NUM>. In one embodiment the converging angle of the intermediate channel <NUM> can be adjusted. After the intermediate channel <NUM> the fiber curtain enters the lower channel <NUM>.

The cooling device <NUM> and the drawing device <NUM>, including intermediate channel <NUM> and lower channel <NUM>, are together formed as a closed aggregate, meaning that over the entire length of the aggregate, no major air flow can enter from the outside and no major process air supplied in the cooling device <NUM> can escape to the out-side. Some fume extraction devices directly under the spinneret extracting a minor air volume can be incorporated.

The fibers <NUM> leaving the drawing device <NUM> are then passed through a laying unit <NUM>, which comprises two successively arranged diffusers <NUM> and <NUM> are provided, with diffuser <NUM> having a divergent section and diffuser <NUM> having a convergent section and an adjoining divergent section. The diffuser angles, in particular the diffuser angles in the divergent regions of the diffusers <NUM> and <NUM>, are adjustable. Between the diffusers <NUM> and <NUM> is a gap <NUM> through which ambient air is sucked into the fiber flow space.

After passing through the laying unit <NUM>, the fibers F are deposited as nonwoven web NW on a spinbelt <NUM>, formed from an air-permeable web. A suctioning device <NUM> is arranged below the laydown area of the spinbelt <NUM> so suck off process air, which is illustrated in <FIG> by the arrow <NUM>.

Once deposited the nonwoven web NW is first guided through the gap between a pair of pre-consolidation rollers <NUM> for pre-consolidating the nonwoven web NW.

<FIG> illustrates a production line <NUM> for producing SMS-type nonwoven laminate fabric sheets NWLS of the present invention.

Specifically, the machine is configured for producing an SMS-type nonwoven laminate fabric sheet NWLS in the form of, specifically, an SMMSH sheet, where "S" stands for a regular spunbonded layer, i.e. a layer formed from uncrimped fibers, "M" stands for a meltblown layer, and "SH" stands for a high loft spunbonded layer formed from crimped bicomponent fibers. The layer "SH" within this fabric is the layer that is according to the invention. An SMS-type sheet where the spunbonded structure on one side of the internal meltblown structure is high loft and the spunbonded structure on one side of the internal meltblown structure is a regular spunbonded sheet are known as semi-high-loft structures. The regular S layer provides mechanical stability, the M layer improves liquid barrier properties, and the loft S layer enhances softness and flexibility of the fabric.

The production line <NUM> comprises a spinning machine <NUM> for producing the SH-layer, which is configured as illustrated in <FIG>. The two reservoirs 118a and 118b contain the two different polymer components A and B used for spinning the bicomponent fibers. An annex reservoir <NUM> may contain a masterbatch with an additive such as a nucleating agent or a visbreaking additive.

Further, the production line <NUM> comprises a spinbelt <NUM>, a first spinning machine <NUM>, comprising only one polymer reservoir <NUM> and configured for spinning monocomponent fibers, for forming the regular S layer, two meltblowing machines <NUM> for forming the MM double layer meltblown structure. The machines <NUM>, <NUM> and <NUM> are serially arranged along the spinbelt <NUM>.

Downstream each spinning machine <NUM> and <NUM> a pair of pre-consolidation rollers <NUM> and <NUM> is arranged. A calender / embossing roll <NUM> for firmly bonding the layers of the laminate sheet NWLS is arranged downstream the last spinning machine.

<FIG> shows an SEM picture (Scanning Electron Microscope) of a cross-section of a bicomponent fiber having a curved interface line between the polymer components.

The picture of <FIG> was taken by the method explained in the following, which is generally a good method to measure the curvature that defines the present invention. The curvature, in principle, is an absolute geometrical property of the fibers and not dependent on how it is measured. There are naturally some variations of curvature within a single fiber over its length, and not every fiber in the fabric sheet is the same. For practical purposes, it is most preferred that at least ten fibers are picked from a nonwoven sheet, the curvature of each of the picked fiber measured at a randomly selected length position, and the average number used.

When measured from a nonwoven sheet, firstly the machine direction is identified and the sheet encapsulated and demobilized in a polyester or epoxy resin. The resulting polymer block is then cut in a cross-machine directional plane that is perpendicular to the plane of the encapsulated nonwoven sheet. The cut surface is polished to have a visible interface after etching. The cross-sectional surface of the fibers exposed at the polished cut surface are etched to etch away the more amorphous of the polymer components. Fiber ends having the most circular cross sections and hence being oriented in machine direction as strictly as possible at the cut surface are selected for measurement. Small direction deviations can be corrected for distortion. In practical terms, a useful fiber-cross-section is an ellipse with a ratio between the major and minor axis below <NUM>. Preferred is that the fibers show up as circle. After the SEM pictures are taken in a manner generally known to practitioners, picture based measurement systems like DatInf measure from Datlnf GmbH can be used to determine curvature.

It can be seen that the interface between the two polymers is curved. In this example of <FIG>, the polymer on the left hand side was a propylene-α-olefin copolymer with a relatively lower crystallization temperature and the polymer on the right hand side was a propylene homopolymer with a relatively higher crystallization temperature. The curved interface is arched toward the left side, i.e. arched toward the propylene-α-olefin copolymer with a relatively lower crystallization temperature. The polymer component with the higher crystallization temperature has the more compact cross-section.

The curvature "c" is measured and calculated according to the following description. First the distance "b" between the polymer surface intersections is measured with a line drawn between the polymer intersections of the fiber surfaces. This line is the imaginary baseline. It is <NUM> pixels in the given example. Next the bow height "h" is measured by drawing a line orthogonally from the baseline (usually the middle of the baseline) to the crest of the curved interface line. The length of the line corresponds to the bow height "h" and, in the given example, is <NUM> pixels.

The curvature is then given by <NUM>/<NUM> = <NUM>. <FIG> hence shows a fiber having a curvature within the range required by the invention.

MFR<NUM> (<NUM>) was measured according to ISO <NUM> (<NUM>, <NUM> load). The MFR<NUM> of the polypropylene composition is determined on the granules of the material, while the MFR<NUM> of the melt-blown web is determined on cut pieces of a compression-molded plaque prepared from the web in a heated press at a temperature of not more than <NUM>, said pieces having a dimension which is comparable to the granule dimension.

The xylene soluble fraction at room temperature (xylene cold soluble XCS, wt%): The amount of the polymer soluble in xylene is determined at <NUM> according to ISO <NUM>; <NUM>th edition; <NUM>-<NUM>-<NUM>.

DSC analysis, melting temperature (Tm), melting enthalpy (Hm), crystallization temperature (Tc) and crystallization enthalpy (Hc): measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on <NUM> to <NUM> samples. DSC is run according to ISO <NUM>-<NUM>, -<NUM> and -<NUM> / method C2 in a heat / cool / heat cycle with a scan rate of <NUM>/min in the temperature range of -<NUM> to +<NUM>. Crystallization temperature (Tc) and crystallization enthalpy (Hc) are determined from the cooling step, while melting temperature (Tm) and melting enthalpy (Hm) are determined from the second heating step respectively from the first heating step in case of the webs.

Number average molecular weight (Mn), weight average molecular weight (Mw), Z-average molecular weight (Mz), and MWD (Mw/Mn) of polypropylene were determined by Gel Permeation Chromatography (GPC) according to ISO <NUM>-<NUM>:<NUM> and ASTM D <NUM>-<NUM>. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with <NUM> x Olexis and <NUM> x Olexis Guard columns from Polymer Laboratories and <NUM>,<NUM>,<NUM>-trichlorobenzene (TCB, stabilized with <NUM>/L <NUM>,<NUM>-Di tert butyl-<NUM>-methyl-phenol) as solvent at <NUM> and at a constant flow rate of <NUM>/min. <NUM>µL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO <NUM>-<NUM>:<NUM>) with at least <NUM> narrow MWD polystyrene (PS) standards in the range of <NUM>/mol to <NUM><NUM>/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D <NUM>-<NUM>. All samples were prepared by dissolving the polymer sample to achieve concentration of ~<NUM>/ml (at <NUM>) in stabilized TCB (same as mobile phase) for <NUM> hours for PP at max. <NUM> under continuous gently shaking in the autosampler of the GPC instrument. The MWD of the polypropylene composition is determined on the granules of the material, while the MWD of the melt-blown web is determined on a fiber sample from the web, both being dissolved in an analogous way.

The unit weight (grammage) of the webs in g/m<NUM> was determined in accordance with ISO <NUM>:<NUM>. The Thickness of the webs was measured in webs with a grammage of <NUM>/m<NUM>.

Curvature (c) of the fibers was determined by the method as specified above in connection with <FIG>.

The filament fineness in denier has been calculated from the average fibre diameter by using the following correlation: <MAT>.

The preparation of propylene polymers (PP1-PP4) used in inventive examples (IE1-<NUM>) and the comparative Examples (CE1-<NUM>) were described in details below.

Base polymers: the base polymers were produced as follows:.

Mg alkoxide solution was prepared by adding, with stirring (<NUM> rpm), into <NUM> of a <NUM> wt-% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et)), a mixture of <NUM> of <NUM>-ethylhexanol and <NUM> of butoxypropanol in a <NUM> stainless steel reactor. During the addition the reactor contents were maintained below <NUM>. After addition was completed, mixing (<NUM> rpm) of the reaction mixture was continued at <NUM> for <NUM> minutes. After cooling to room temperature <NUM> of the donor bis(<NUM>-ethylhexyl)citraconate was added to the Mg-alkoxide solution keeping temperature below <NUM>. Mixing was continued for <NUM> minutes under stirring (<NUM> rpm).

<NUM> of TiCl<NUM> and <NUM> of toluene were added into a <NUM> stainless steel reactor. Under <NUM> rpm mixing and keeping the temperature at <NUM>, <NUM> of the Mg alkoxy compound prepared in example <NUM> was added during <NUM> hours. <NUM> of Viscoplex® <NUM>-<NUM> and <NUM> of heptane were added and after <NUM> hour mixing at <NUM> the temperature of the formed emulsion was raised to <NUM> within <NUM> hour. After <NUM> minutes mixing was stopped catalyst droplets were solidified and the formed catalyst particles were allowed to settle. After settling (<NUM> hour), the supernatant liquid was siphoned away. Then the catalyst particles were washed with <NUM> of toluene at <NUM> for <NUM> minutes followed by two heptane washes (<NUM>, <NUM>). During the first heptane wash the temperature was decreased to <NUM> and during the second wash to room temperature.

The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane donor (D-donor) as external donor.

Polymerizations were performed in a Borstar PP-type polypropylene (PP) pilot plant, comprising one loop reactor and one gas phase reactor.

Polymerization conditions for PP3 base polymer are described in Table <NUM>.

The base polymer of PP3 has been visbroken together with <NUM> wt% of PP-MB, <NUM> ppm of Irganox <NUM> (BASF), <NUM> ppm of Irgafos <NUM> (BASF), <NUM> ppm of Ceasit FI (Baerlocher) by a co-rotating twin-screw extruder at <NUM>-<NUM> using an appropriate amount of (tert. butylperoxy)-<NUM>,<NUM>-dimethylhexane (Trigonox <NUM>, distributed by Akzo Nobel, Netherlands).

PP4: The production of base polymer of PP4 is described in <CIT> as inventive example IE3.

A series of options with two polymers in a side-by-side configuration was processed on a machine as illustrated in <FIG>.

For all options, a basis weight of <NUM>/m<NUM> for the spunbonded nonwoven material sheet was used. Specific polymer throughput in the spinnerette <NUM> was approximately <NUM> polymer per hole per minute. The cabin pressure was kept mostly constant at <NUM> Pascal. Other process settings were kept in a normal range for the production of crimped fibers. For instance, the ceramic pre-consolidation rollers <NUM> on the spinbelt at the outlet side of the beam were run with a temperature of <NUM>-<NUM>. The calender (not shown in <FIG>, but positioned downstream the pre-consolidation rollers <NUM>) was a standard open dot calender with <NUM>% bonding area and <NUM> circular bonding points per cm<NUM>. The temperature of the calender was in the range of <NUM>-<NUM>.

Table <NUM> summarizes data regarding polymer composition used in the fiber preparation process, bow hight of the cross-section of the fiber and thickness of the fabric made from the fibers with respect to inventive examples IE1, IE2, IE3, IE4, IE5 and IE6 and CE1 to CE2.

Claim 1:
Use of polymer composition comprising a first propylene polymer A and a second propylene polymer B for producing crimped multicomponent fibers having a side by side cross-sectional configuration, wherein
(i) the first propylene polymer A and second propylene polymer B are distributed over the cross section of the fiber in a side by side arrangement, wherein the interface line, contained in the radial plane of the fibers, between the two propylene polymers A and B is curved and its curvature (c) is <MAT> wherein the baseline length (b) is the length of the imaginary straight baseline connecting the two endpoints of the curved interface line, and the bow height (h) is the distance of the crest of the curved interface line from the baseline,
(ii)the mass ratio of the first propylene polymer A and the second propylene polymer B [A:B] is in the range of <NUM>: <NUM> to <NUM>:<NUM>, and
(iii) the absolute value of the difference of the crystallization temperature [Tc (A)] of the first propylene polymer A and the crystallization temperature [Tc (B)] of the second propylene polymer B determined according to ISO11357 with a scan rate of <NUM>/min is in the range of <NUM> to <NUM>.