Patent Description:
Polypropylene has been since long extruded into fibers. International patent application <CIT>, for example, discloses fibers comprising a homo or copolymer of propylene having a melting point in the range from <NUM> to <NUM>°.

Despite polypropylene fibers have been known for decades, there is still a wish to improve their properties. Also, due to recent regulatory restrictions on phthalates, it is desirable to make available polypropylene fibers that are free from phthalate residues coming from typical Ziegler-Natta catalysts used for their preparation. <CIT> relates to a propylene homopolymer having among other features a MFR ranging from <NUM> to <NUM> dg/min, - a content of the xylene soluble fraction in the range from <NUM> wt% to <NUM> wt%, a polydispersity index of at least <NUM> and of at most <NUM>. <CIT> relates to fibers comprising a polypropylene having a melt flow index in the range from <NUM> to <NUM>/<NUM>; a xylene soluble fraction of at most <NUM> wt%, a molecular weight distribution Mw/Mn ranging from <NUM> to <NUM>; and a melting temperature Tm of at most <NUM>. <CIT> relates to Spun and drawn fibres comprising a polypropylene composition of a polypropylene homopolymer, the spun and drawn fibres having an average MFI of <NUM> to <NUM>/<NUM> and a xylene soluble content in the range from <NUM> wt% to <NUM> wt% or <NUM> wt% to <NUM> wt%. relates to a propylene homopolymer comprising at least two propylene homopolymer fractions of different melt flow index, being characterized by a melt flow index in the range from <NUM> to <NUM> dg/min, a xylene solubles content in the range from <NUM> wt% to <NUM> wt%, a tacticity in the range from <NUM> % to <NUM> % of mmmm pentads (determined on the insoluble heptane fraction of the xylene insolubles fraction), and - a recovery compliance in the range from <NUM> • <NUM>-<NUM> Pa-<NUM> to <NUM> • <NUM>-<NUM> P a -<NUM>. None of these documents disclose all the features of the present invention. <CIT> relates to a spunbonded nonwoven fabric comprising a polypropylene homopolymer having: a melt flow rate (MFR, <NUM>, <NUM>, ISO <NUM>) of <NUM> to <NUM>/<NUM> O min, a molecular weight distribution (Mw/Mn) > <NUM>, a melting temperature of <NUM>-<NUM> and being free of phthalic acid esters as well as their respective decomposition products;
the XCS is in the range of <NUM>-<NUM> wt.

However this document is silent about acetone insolubles.

<CIT> relates to a polypropylene composition comprising:
a polypropylene (L-PP) homopolymer having:.

<CIT> relates to a polypropylene homopolymer PP2 having: a melt flow rate of <NUM>/<NUM>, a melting temperature Tm of <NUM>, a xylene cold soluble content (XCS) of <NUM> wt. -% and a polydispersity index (PI) of <NUM>.

The applicant found that fiber with good tenacity can be obtained by using a propylene homopolymer having a particular distribution of molecular weight of xylene soluble fraction.

Thus, the present disclosure is directed to the use of a propylene homopolymer for producing fibers; wherein the propylene homopolymer is characterized in that:.

The polypropylene homopolymer used for the production for the fiber according to the present disclosure has a very low oligomer content this means that it is possible to lower considerably the production of fumes during the production of fibers. The oligomer content is preferably lower than <NUM> ppm; preferably lower than <NUM> ppm; even more preferably lower than <NUM> ppm.

The fibers obtained by using the propylene homopolymer show also an increased tenacity and an improved haptics.

The propylene homopolymers disclosed herein can be prepared by a process comprising polymerizing propylene with ethylene, in the presence of a catalyst comprising the product of the reaction between:.

wherein R<NUM> and R<NUM> are independently selected among alkyl radicals with <NUM>-<NUM> carbon atoms, optionally containing heteroatoms, a is <NUM> or <NUM>, and a+b=<NUM>.

Preferably, in the catalyst component the content of Bi ranges from <NUM> to <NUM>%wt, more preferably from <NUM> to <NUM>%wt, especially from <NUM> to <NUM>%wt and in a very particular embodiment from <NUM> to <NUM>%wt.

The particles of the solid component have substantially spherical morphology and an average diameter ranging between <NUM> and <NUM>, preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>. As particles having substantially spherical morphology, those are meant wherein the ratio between the greater axis and the smaller axis is equal to or lower than <NUM>, and preferably lower than <NUM>.

In general, the amount of Mg preferably ranges from <NUM> to <NUM>%wt, more preferably from <NUM> to <NUM>%wt.

Generally, the amount of Ti ranges from <NUM> to <NUM>%wt, and more preferably from <NUM> to <NUM>%wt.

The Mg/Ti molar ratio is preferably equal to, or higher than, <NUM>, preferably in the range of <NUM> to <NUM>, and more preferably from <NUM> to <NUM>. Correspondingly, the Mg/donor molar ratio is preferably higher than <NUM>, more preferably higher than <NUM> and usually ranging from <NUM> to <NUM>.

The Bi atoms are preferably derived from one or more Bi compounds not having Bi-carbon bonds. In particular, the Bi compounds can be selected from Bi halides, Bi carbonate, Bi acetate, Bi nitrate, Bi oxide, Bi sulphate, and Bi sulfide. Compounds in which Bi has the valence state of <NUM>+ are preferred. Among Bi halides, preferred compounds are Bi trichloride and Bi tribromide. The most preferred Bi compound is BiCl<NUM>.

The preparation of the solid catalyst component can be carried out according to several methods.

According to one method, the solid catalyst component can be prepared by reacting a titanium compound of the formula Ti(OR)q-yXy, where q is the valence of titanium and y is a number between <NUM> and q, preferably TiCl<NUM>, with a magnesium chloride deriving from an adduct of formula MgCl<NUM>•pROH, where p is a number between <NUM> and <NUM>, preferably from <NUM> to <NUM>, and R is a hydrocarbon radical having <NUM>-<NUM> carbon atoms. The adduct can be prepared in spherical form by mixing alcohol and magnesium chloride, operating under stirring conditions at the melting temperature of the adduct (<NUM>-<NUM>). Then, the adduct is mixed with an inert hydrocarbon immiscible with the adduct, thereby creating an emulsion which is quickly quenched, causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in <CIT> and <CIT>. The resulting adduct can be directly reacted with a Ti compound, or it can be previously subjected to thermally controlled dealcoholation (<NUM>-<NUM>) so as to obtain an adduct in which the number of moles of alcohol is generally lower than <NUM>, preferably between <NUM> and <NUM>. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or not) in cold TiCl<NUM> (generally <NUM>); the mixture is heated up to <NUM>-<NUM> and kept at this temperature for <NUM>-<NUM> hours. The treatment with TiCl<NUM> can be carried out one or more times. The electron donor compound can be added in the desired ratios during the treatment with TiCl<NUM>.

Several ways are available to add one or more Bi compounds in the catalyst preparation. According to the preferred option, the Bi compound(s) is/are incorporated directly into the MgCl<NUM>•pROH adduct during its preparation. In particular, the Bi compound can be added at the initial stage of adduct preparation by mixing it together with MgCl<NUM> and the alcohol. Alternatively, it can be added to the molten adduct before the emulsification step. The amount of Bi introduced ranges from <NUM> to <NUM> mole per mole of Mg in the adduct. Preferred Bi compound(s) to be incorporated directly into the MgCl<NUM>•pROH adduct are Bi halides, and in particular BiCl<NUM>. The alkyl-Al compound (ii) is preferably chosen from among the trialkyl aluminum compounds such as, for example, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides, such as AlEt<NUM>Cl and Al<NUM>Et<NUM>Cl<NUM>, possibly in a mixture with the above cited trialkylaluminums. The Al/Ti ratio is higher than <NUM> and is generally between <NUM> and <NUM>.

The external electron donor compound (iii) is a silicon compound having the general formula.

wherein R<NUM> and R<NUM> are independently selected among alkyl radicals with <NUM>-<NUM> carbon atoms, optionally containing heteroatoms, wherein a is <NUM> or <NUM> and a+b=<NUM>. A first group of preferred silicon compounds of formula (II) are those for which a is <NUM>, b is <NUM> and R<NUM> and R<NUM> are independently selected from among alkyl radicals having <NUM>-<NUM>, preferably <NUM>-<NUM>, carbon atoms, with isobutyl triethoxysilane (iBTES) being particularly preferred. A further group of preferred silicon compounds of the formula (II) are those for which a is <NUM>, b is <NUM>, and R<NUM> is independently selected from among alkyl radicals with <NUM>-<NUM>, preferably <NUM>-<NUM>, carbon atoms, tetraethoxysilane being particularly preferred.

The external electron donor compound (c) is used in such an amount to give a molar ratio between the organoaluminum compound and said external electron donor compound (iii) of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>.

The polymerization process can be carried out according to known techniques, for example, slurry polymerization using as a diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example, propylene) as a reaction medium. Moreover, it is possible to carry out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.

The polymerization is generally carried out at temperatures of from <NUM> to <NUM>, preferably of from <NUM> to <NUM>. When the polymerization is carried out in gas-phase, the operating pressure is generally between <NUM> and <NUM> MPa, preferably between <NUM> and <NUM> MPa. In bulk polymerization, the operating pressure is generally between <NUM> and <NUM> MPa, preferably between <NUM> and <NUM> MPa. Hydrogen is typically used as a molecular weight regulator.

The fibers according to the present invention can be stable fibers or spunbond fibers.

When spunboud fibers are needed the propylene homopolymer can be subjected to visbreaking in order to achieve the desired melt flow rate (MFR). The visbreaking, or controlled chemical degradation can be carried out by treating the precursor polypropylene with appropriate amounts, preferably from <NUM> to <NUM> wt%, more preferably from <NUM> to <NUM> wt%, of free radical initiators according to processes well-known in the art. Preferably, the chemical degradation is carried out by contacting under high shear conditions the polymeric material with at least one free radical initiator at a temperature equal to or higher than the decomposition temperature of the free radical initiator. Preferred free radical initiators are peroxides having a decomposition temperature higher than <NUM> preferably ranging from <NUM>° to <NUM>, such as di-tert-butyl peroxide, dicumyl peroxide, the <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di (tert-butylperoxy)hexyne, and <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(tert-butylperoxy)hexane (traded by Akzo or Arkema under the name Trigonox <NUM> or Luperox <NUM> respectively).

The fibers of the present invention can also contain additives commonly employed in the art, such as antioxidants, light stabilizers, heat stabilizers, nucleating agents, colorants and fillers.

The fibers of the invention typically exhibit a value of tenacity at least equal to or higher than <NUM> cN/tex, preferably higher than <NUM>. cN/tex, more preferably higher than <NUM> cN/tex.

Typically, the fibers according to the present invention have a titre ranging from <NUM> to <NUM> dtex, preferably from <NUM> to <NUM> dtex.

The fibers of the present invention can be efficiently spun at speeds that are typically higher than <NUM>/min, preferably higher than <NUM>/min, more preferably higher than <NUM>/min.

The fibers of the invention can be spun at temperatures generally varying from <NUM>° to <NUM>° C. Preferably, the spinning temperature is lower than <NUM>, even more preferably, the spinning temperature is comprised between <NUM>° and <NUM>.

The fibers of the present invention can be used for the manufacture of non-woven fabrics showing excellent properties.

Such non-woven fabrics may be produced with various methods, preferably through the well-known spunbonding technique. The spunbonding process is a non-woven manufacturing technique, whereby polymers are directly converted into endless filaments and stochastically deposited to form a non-woven material.

The following examples are given in order to illustrate, but not limit the present disclosure.

Xylene Solubles fraction has been measured according to ISO <NUM><NUM> - <NUM>; with solution volume of <NUM>, precipitation at <NUM> for <NUM> minutes, <NUM> of which with the solution in agitation (magnetic stirrer), and drying at <NUM>°.

A second aliquot of the filtered solution obtained according to the method for the determination of xylene soluble fraction at <NUM> is added with acetone (<NUM>) so that the precipitation of the amorphous part takes place. Then the suspension is filtered on a Teflon membrane coupled with a steel frit on a flask, dried in an oven at <NUM> overnight and weighed so that the soluble and insoluble fraction can be determined.

Measured according to ISO <NUM> at <NUM> with a load of <NUM>, unless otherwise specified.

From a <NUM> long roving, <NUM> fibers are randomly chosen and weighed. The total weight of the <NUM> fibers, expressed in mg, is multiplied by <NUM>, thereby obtaining the titre in dtex.

From a <NUM> roving a <NUM>-long segment is cut and single fibers randomly chosen. Each single fiber is fixed to the clamps of a Dynamometer and tensioned to break with a traction speed of <NUM>/min for elongations lower than <NUM>% and <NUM>/min for elongations greater than <NUM>%, the initial distance between the clamps being of <NUM>. The ultimate strength (load at break) and the elongation at break are determined in machine (MD) direction.

The tenacity is calculated by way of the following equation:
<MAT>.

The maximum spinning speed gives indication of the spinnability of the propylene polymer composition of the invention. The value corresponds to the highest spinning rate that can be maintained for <NUM> minutes with no filament break.

Softness index is a conventional measure of flexibility of fibers, calculated as weight [<NUM>/g] of a bundle, whose length is determined in standard conditions. Softness values, so obtained, are in excellent agreement with the results of the empirical tests on non-woven. The apparatuses used for such analysis are the following:.

The sample is prepared by providing a fiber bundle of about <NUM>,<NUM> dtex in linear density and <NUM> in length. The ends of the bundle are fixed on the clamps of the twist measuring device and a <NUM> leftward twist runs is applied. The twisted bundle is taken off from the device (carefully avoiding any untwisting). The two ends of the twisted bundle are taken in the same side and the halves winded around each other until the bundle assumes the stable form of a cord. Three specimens of each test at least are prepared. The bundle is bended in two and the ends fixed between the rolls of the Clark softness tester, leaving a distance of <NUM> between the two halves. The plane of the device is rotated rightward and stopped, when the bundle reverses its bending direction, taking note of the rotation angle (a). Subsequently the plane rotated leftward and again stopped, when the bundle reverses its bending side. Take note of the rotation angle (b). The height of the bundle above the two rolls is adjusted so to have the sum a ± b equal to <NUM>° +/- <NUM>° and this height is measured with a proper device (sensitivity <NUM>). Each of the two angles, a and b, should not exceed the limits of <NUM>° +/- <NUM>°. The bundle is taken off from the device and cut to an height corresponding to that previously measured. The cut bundle is weighed by an analytical balance with a precision of <NUM>. The Softness index can be calculated from: S. = (<NUM>/W) * <NUM>, in which W is the weight, in grams, of the cut bundle. The final result is the average of the <NUM> samples. The sensitivity in measuring the bundle weight is <NUM>.

The melting points of the polymers (Tm) were measured by differential scanning calorimetry (DSC) on a Perkin Elmer DSC-<NUM> calorimeter, previously calibrated against indium melting points, and according to ISO <NUM>-<NUM>, <NUM> and <NUM>-<NUM>, <NUM>, at <NUM>/min. The weight of the samples in every DSC crucible was kept at <NUM> ± <NUM>. In order to obtain the melting point, the weighted sample was sealed into aluminium pans and heated to <NUM> at <NUM>/minute. The sample was kept at <NUM> for <NUM> minutes to allow a complete melting of all the crystallites, then cooled to <NUM> at <NUM>/minute. After standing <NUM> minutes at <NUM>, the sample was heated for the second run time to <NUM> at <NUM>/min. In this second heating run, the peak temperature (Tp,m) was taken as the melting temperature.

The determination of Mg and Ti content in the solid catalyst component has been carried out via inductively coupled plasma emission spectroscopy on "I. P Spectrometer ARL Accuris".

The sample was prepared by analytically weighting, in a "Fluxy" platinum crucible", <NUM>÷<NUM> grams of catalyst and <NUM> grams of lithium metaborate/tetraborate <NUM>/<NUM> mixture. After addition of some drops of KI solution, the crucible is inserted in a special apparatus "Claisse Fluxy" for the complete burning. The residue is collected with a <NUM>% v/v HNO<NUM> solution and then analyzed via ICP at the following wavelengths: Magnesium, <NUM>; Titanium, <NUM>.

The determination of Bi content in the solid catalyst component has been carried out via inductively coupled plasma emission spectroscopy on an "I. P Spectrometer ARL Accuris". The sample was prepared by analytically weighting in a <NUM><NUM> volumetric flask <NUM>-<NUM> grams of catalyst. After the slow addition of both ca. <NUM> milliliters of <NUM>% v/v HNOs solution and ca. <NUM><NUM> of distilled water, the sample undergoes a digestion for <NUM>-<NUM> hours. Then the volumetric flask is diluted to the mark with deionized water. The resulting solution is directly analyzed via ICP at the following wavelength: bismuth, <NUM>.

The determination of the content of internal donor in the solid catalytic compound was done through gas chromatography. The solid component was dissolved in acetone, an internal standard was added, and a sample of the organic phase was analyzed in a gas chromatograph, to determine the amount of donor present in the starting catalyst compound.

The determination of oligomer content by solvent extraction consists of treating <NUM> of polypropylene sample with <NUM> of methylenedichloride (CH<NUM>Cl<NUM>) in an ultrasonic bath at <NUM> for <NUM> hours. <NUM>µl of the extracted solution is injected into a capillary column and analysed by using FID, without any filtration. For quantitative estimation of oligomer content a calibration based on external standard method has been applied. In particular, a series of hydrocarbons (C12-C22-C28-C40) is used.

Microspheroidal MgCl<NUM>·pC<NUM>H<NUM>OH adduct was prepared according to the method described in Comparative Example <NUM> of <CIT>, with the difference that BiCl<NUM> in a powder form and in an amount of <NUM> mol% with respect to the magnesium is added before the feeding of the oil.

Into a <NUM> round bottom flask, equipped with mechanical stirrer, cooler and thermometer, <NUM> of TiCl<NUM> were introduced at room temperature under a nitrogen atmosphere. After cooling to <NUM>, <NUM> of the spherical adduct (prepared as described above) were added while stirring, then diethyl <NUM>,<NUM>-dipropylglutarate was sequentially added into the flask. The amount of charged internal donor was such to meet a Mg/donor molar ratio of <NUM>. The temperature was raised to <NUM> and maintained for <NUM> hours. Thereafter, stirring was stopped, the solid product was allowed to settle and the supernatant liquid was siphoned off at <NUM>.

After siphoning, fresh TiCl<NUM> and an amount of <NUM>,<NUM>-bis(methoxymethyl)fluorene for producing a Mg/diether molar ratio of <NUM> was added. The mixture was then heated at <NUM> and kept at this temperature for <NUM> hour under stirring. Stirring was stopped again, the solid was allowed to settle and the supernatant liquid was siphoned off. The solid was washed with anhydrous hexane six times in a temperature gradient down to <NUM> and one time at room temperature. The obtained solid was then dried under vacuum and analyzed.

Before introducing it into the polymerization reactors, the solid catalyst component described above is contacted with triethyl aluminum (TEAL) and isobutyl-trietoxysilane (iBTES) as described in Table <NUM>.

The polymerization run was carried out in continuous mode in a liquid phase loop reactor. Hydrogen was used as a molecular weight regulator. Polymerization conditions are indicated in table <NUM>.

Comparative example <NUM> has been carried out as in example <NUM> with the exception that <NUM>,<NUM>-bis(methoxymethyl)fluorene has been used instead of diethyl <NUM>,<NUM>-dipropylglutarate in an equivalent molar amount so that the catalyst contains the same total molar amount <NUM> of internal donors of the catalyst of example <NUM>.

Thereafter the polymer particles are mixed with a usual stabilizing additive composition in a twin screw extruder Berstorff ZE <NUM> (length/diameter ratio of screws: <NUM>) and extruded under nitrogen atmosphere in the following conditions:.

The stabilizing additive composition is made of the following components:.

all percent amounts being referred to the total weight of the polymer and stabilizing additive composition.

The said Irganox® <NUM> is <NUM>,<NUM>-bis[<NUM>-[,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxyphenyl)-<NUM>-oxopropoxy]methyl]-<NUM>,<NUM>-propanediyl-<NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxybenzene-propanoate, while Irgafos® <NUM> is tris(<NUM>,<NUM>-di-tert. -butylphenyl)phosphite. The characteristics relating to the polymer composition, reported in Table <NUM>.

The features of the polymer of examples <NUM> and comparative example <NUM> are reported on table <NUM>.

The polymers are extruded in a Leonard <NUM> spinning pilot line with screw LID ratio of <NUM>. The line is marketed by Costruzioni Meccaniche Leonard-Sumirago (VA). The operative spinning conditions are here reported.

The properties of the filaments are reported on Table <NUM>.

During the spinning process fuming generated from the homopolymer of example <NUM> were negligible with respect to fumes generated from the homopolymer of comparative examples <NUM> and <NUM>.

Claim 1:
The use of a propylene homopolymer for producing fibers; wherein the propylene homopolymer is characterized in that:
- the melting point ranges from <NUM> to <NUM>;
- the fraction soluble in xylene at <NUM> is comprised between <NUM> wt% and <NUM> wt%;
- the fraction soluble in acetone <NUM> is comprised between <NUM> wt% and <NUM> wt%
- the ratio fraction soluble in acetone at <NUM>/ fraction insoluble in acetone <NUM> is comprised between <NUM> and <NUM>.
- the polydispersity index ranges from <NUM> to <NUM>
- the melt flow rate (ISO <NUM>, <NUM>/<NUM>) is comprised between <NUM> to <NUM>/<NUM>;
wherein the melting point is measured by using the DSC with heating and cooling rate of <NUM>/min;
the fraction soluble in xylene at <NUM> is measured according to ISO <NUM><NUM> - <NUM>; with solution volume of <NUM>, precipitation at <NUM> for <NUM> minutes, <NUM> of which with the solution in agitation (magnetic stirrer), and drying at <NUM>°;
the fraction soluble and insoluble in acetone at <NUM> is measured on a second aliquot of the filtered solution obtained according to the method for the determination of xylene soluble fraction at <NUM>; this second aliquot is added with acetone (<NUM>) so that the precipitation of the amorphous part takes place; then the suspension is filtered on a Teflon membrane coupled with a steel frit on a flask, dried in an oven at <NUM> overnight and weighed so that the soluble and insoluble fraction can be determined.