WO2011009704A1

WO2011009704A1 - Fibres made from copolymers of propylene and 1-pentene

Info

Publication number: WO2011009704A1
Application number: PCT/EP2010/059472
Authority: WO
Inventors: Monica Galvan; Claudio Cavalieri; Antonio Passerini; Gabriella Sartori
Original assignee: Basell Poliolefine Italia S.R.L.
Priority date: 2009-07-21
Filing date: 2010-07-02
Publication date: 2011-01-27

Abstract

A fibre for thermal bonding comprising copolymers of propylene and 1-pentene, the amount of 1- pentene derived units being from 0.1% to 20% wt. Said copolymers possess a value of melt flow rate (MFR) ranging from 0.1 to 100 g /10 min.

Description

Title:

FIBRES MADE FROM COPOLYMERS OF PROPYLENE AND 1-PENTENE

The present invention relates to filaments and fibers made from random copolymers of propylene with 1-pentene. Within the definition of fibres are also included the manufactured products similar to fibres, such as fibrils and cut filaments (staple fibres). The fibres can be advantageously used for the production of soft non-woven fabrics.

It is known in the art that propylene homopolymers have excellent spinnability, but since their melting point is relatively high, i.e. typically up to 165°C, they require high temperatures for producing non-woven fabrics by thermal processes, like thermal spunbonding. Moreover, fibers and non-woven fabrics obtained from propylene homopolymers have rather poor hand. The hand or feel of a fabric plays an important role since there is a growing demand on the market for "soft hand" no n- woven fabrics. Propylene copolymers can be conveniently used to overcome the drawbacks of propylene homopolymers.

WO 99/01485 relates to a process for producing a propylene 1-pentene polymer in the presence of a Ziegler-Natta catalyst system with the monomers reactants being in the vapor phase.

However this document is completely silent about the uses of the material obtained.

WO 96/24623 relates to a copolymer of propylene and pentene, together with a process for producing such copolymer and a polymer composition. The only use taught by this application are films prepared in the examples.

Now it has surprisingly been found that a good balance of mechanical properties can be obtained in fibres made from copolymers of propylene with 1-pentene. In particular, the fibres exhibit a high tenacity value and yet maintain a good elongation at break value, furthermore they have excellent values of softness.

An object of the present invention is a fibre comprising a copolymers of propylene and 1-pentene containing from 0.1% to 20% by weight of 1-pentene derived units; preferably the content of 1- pentene derived units ranges from 0.5 % to 10% by weight more preferably from 1% to 5% by weight, even more preferably from 1.2 to 3% by weight.

The copolymer of the present invention are further endowed of a value of melt flow rate (MFR) ranging from 0.1 to 100 g/10 min, preferably the MFR ranges from 1 to 50 g/10 min, more preferably the MFR ranges from 5 to 30 g/10 min.

The propylene/ 1-pentene copolymer of the fibre of the present invention is further endowed with: - a melting point measured by using DSC ranging from 135 to 160° C; and

- a solubility in xylene at room temperature below 10 wt%, preferably below 5 wt%, more preferably below 3 wt%.

The fibre according to the present invention typically exhibits a value of tenacity higher than 18 cN/tex; preferably higher than 20 cN/tex and a value of elongation at break higher than 190%, preferably higher than 200%.

Futhermore the fibre according to the present invention typically exhibits a value of softness higher than 870 1/gr, preferably higher than 900 1/gr.

Typically, the fibres according to the present invention have a titre ranging from 1 to 8 dtex, preferably 1.5 to 4 dtex, more preferably from 2 to 3 dtex.

The fibers of the present invention can contain formulations of stabilizers suited for obtaining a skin-core structure (skin-core stabilization), or a highly stabilizing formulation. In the latter case, a superior resistance to aging is achieved for durable nonwovens.

According to a first embodiment, the copolymers of propylene and 1-pentene can be directly prepared in at least one polymerization step in presence of highly stereospecific heterogeneous

Ziegler-Natta catalyst systems. Alternatively, and more preferably, the copolymers of propylene and 1-pentene can be prepared by subjecting to chemical degradation a precursor copolymer of propylene and 1-pentene having MFR(Al).

According to a preferred embodiment, the copolymers of propylene and 1-pentene are obtainable by a process comprising the following steps:

(1) polymerizing suitable monomers in at least one polymerization step in presence of a heterogeneous Ziegler-Natta catalyst system to obtain a precursor copolymer of propylene and 1- pentene propylene having a MFR(Al) ranging from 0.4 to 10 g/10min, preferably from 0.9 to 5 g/10min; and

(2) subjecting said precursor copolymer of propylene and 1-pentene to chemical degradation to obtain a copolymer of propylene and 1-pentene having MFR(A) ranging from 10 to 60 g/10min, wherein the ratio MFR(A)/MFR(A1) ranges from 6 to 30.

The copolymer of the present invention can be prepared by polymerisation in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron- donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound.

An external donor is optionally added.

The catalysts generally used in the process of the invention are capable of producing polypropylene with a value of xylene insolubility at room temperature greater than 90%, preferably greater than 95%.

Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in US patent 4,399,054 and European patent

45977. Other examples can be found in US patent 4,472,524. The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and/or S atoms and and esters of mono- and dicarboxylic acids. Particularly suitable electron-donor compounds are 1,3- diethers of formula:

Wherein

R and R are the same or different and are C₁-C₁₈ alkyl, C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R and R are the same or different and are C₁-C₄ alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5,6, or 7 carbon atoms, or of 5-n or 6-n' carbon atoms, and respectively n nitrogen atoms and n' heteroatoms selected from the group consisting of N, 0 , S and Si, where n is 1 or 2 and n' is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both.

Ethers of this type are described in published European patent applications 361493 and 728769.

Representative examples of said dieters are 2-methyl-2-isopropyl-l,3-dimethoxypropane, 2,2- diisobutyl- 1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl- 1 ,3-dimethoxypropane, 2- isopropyl-2-isoamyl- 1,3-dimethoxypropane, 9,9-bis (methoxyrnethyl)fluorene.

Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate. The preparation of the above mentioned catalyst components is carried out according to various methods. For example, a MgC12.nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiCU containing the electron-donor compound. The reaction temperature is generally from 80 to 120' C. The solid is then isolated and reacted once more with TiCU, in the presence or absence of the electron-donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.

In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The quantity of electron-donor compound which remains fixed on the solid catalyst component generally is 5 to 20% by moles with respect to the magnesium dihalide.

The titanium compounds, which can be used for the preparation of the solid catalyst component, are the halides and the halogen alcoholates of titanium. Titanium tetrachloride is the preferred compound.

The reactions described above result in the formation of a magnesium halide in active form.

Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Altriethyl, Al- triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or SO₄ or SO₃ groups.

The Al-alkyl compound is generally used in such a quantity that the Al/Ti ratio be from 1 to

1000. The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, where R is a hydrocarbon radical.

Examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclohexyl)(methyl)Si(OCH3)2, (cyclopentyl)₂Si(OCH₃)₂, (phenyl)₂Si(OCH₃)₂ and (l,l,2-trimethylpropyl)Si(OCH₃)3, which is preferred.

1,3-diethers having the formulae described above can also be used advantageously. If the internal donor is one of these dieters, the external donors can be omitted. In particular, even if many other combinations of the previously said catalyst components may allow to obtain propylene polymer compositions according to the present invention, the copolymers are preferably prepared by using catalysts containing a phthalate a inside donor and (cyclopentyl)2Si(OCH₃)2 as outside donor, or the said 1 ,3-di ethers as inside donors.

The copolymers according to the present invention are produced in accordance with known polymerisation processes.

For example, a polymerisation process is carried out in one or more stage(s). In case the two or more stages of polymerisation are carried out, the copolymers are prepared in sequential stages. In each stage the operation takes place in the presence of the copolymer obtained and the catalyst in the preceding stage.

According to another polymerisation process the copolymers are produced by a polymerisation process carried out in at least two interconnected polymerisation zones. The process according to the preferred process is illustrated in EP application 782 587. In detail, the said process comprises feeding the monomers to said polymerisation zones in the presence of catalyst under reaction conditions and collecting the polymer product from the said polymerisation zones. In the said process the growing polymer particles flow upward through one (first) of the said polymerisation zones (riser) under fast fiuidisation conditions, leave the said riser and enter another (second) polymerisation zone (downcomer) through which they flow downward in a densified form under the action of gravity, leave the said downcomer and are reintroduced into the riser, thus establishing a circulation of polymer between the riser and the downcomer.

In the downcomer high values of density of the solid are reached, which approach the bulk density of the polymer. A positive gain in pressure can thus be obtained along the direction of flow, so that it become to possible to reintroduce the polymer into the riser without the help of special mechanical means. In this way, a "loop" circulation is set up, which is defined by the balance of pressures between the two polymerisation zones and by the head loss introduced into the system. Generally, the condition of fast fluidization in the riser is established by feeding a gas mixture comprising the relevant monomers to the said riser. It is preferable that the feeding of the gas mixture is effected below the point of reintroduction of the polymer into the said riser by the use, where appropriate, of gas distributor means. The velocity of transport gas into the riser is higher than the transport velocity under the operating conditions, preferably from 2 to 1 5 m/s. Generally, the copolymers and the gaseous mixture leaving the riser are conveyed to a solid/gas separation zone. The solid/gas separation can be effected by using conventional separation means. From the separation zone, the copolymers enter the downcomer. The gaseous mixture leaving the separation zone is compressed, cooled and transferred, if appropriate with the addition of make-up monomers and/or molecular weight regulators, to the riser. The transfer can be effected by means of a recycle line for the gaseous mixture. The control of the copolymer circulating between the two polymerisation zones can be effected by metering the amount of polymer leaving the downcomer using means suitable for controlling the flow of solids, such as mechanical valves.

The operating parameters, such as the temperature, are those that are usual in gas-phase olefin polymerisation process, for example between 5O⁰C to 120⁰C.

This first stage process can be carried out under operating pressures of between 0.5 and 10 MPa, preferably between 1.5 to 6 MPa. Advantageously, one or more inert gases are maintained in the polymerisation zones, in such quantities that the sum of the partial pressure of the inert gases is preferably between 5% and 80% of the total pressure of the gases. The inert gas can be nitrogen or propane, for example.

The various catalysts are fed up to the riser at any point of the said riser. However, they can also be fed at any point of the downcomer. The catalyst can be in any physical state, therefore catalysts in either solid or liquid state can be used. The copolymers and polymer compositions may be blended with additives commonly employed in the art, such as nucleating agents, colorants and fillers in addition to the abovementioned stabilisers.

The fibres of the present invention can be prepared by way of any known melt spin process. In the preferred process for preparing the copolymer of propylene and 1-pentene, the chemical degradation step (2) can be carried out by treating the precursor copolymer of propylene and 1 - pentene or copolymer of propylene and 1-pentene precursor with appropriate amounts, preferably from 0.001 to 0.20 wt%, more preferably from 0.04 to 0.10 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 that the decomposition temperature of the free radical initiator. Preferred free radical initiators are peroxides having a decomposition temperature ranging from 150° to 250⁰C, such as di-tert-butyl peroxide, dicumyl peroxide, the 2,5-dimethyl- 2,5-di (tert-butylperoxy)hexyne, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (traded by Akzo under the name Luperox 101 or Trigonox 101).

Fibers or filaments comprising copolymer of propylene and 1-pentene of the invention may be prepared using processes and apparatuses well known in the art, i.e. by melt-spinning the propylene copolymer in conventional devices suitable for producing single or composite fibers or filaments. According to a further embodiment, the composite fibers or filaments may have a "sheath-core structure". By "fibers or filaments having a sheath-core structure" is meant herein fibers or filaments having an axially extending interface and comprising at least two components, i.e. at least an inner core and at least an outer sheath, said at least two components comprising different polymeric materials and being joined along the axially extending interface. In sheath- core fibers or filaments the sheath thickness may be uniform or the sheath thickness may not be uniform around the circumference of a fiber or filament cross-section. Said fibers or filaments having sheath-core structure can be produced using conventional melt-spin equipments having concentric annular dies. The copolymer of propylene and 1-pentene of the invention may be conveniently used to for the outer sheath of fibers or filaments having a sheath-core structure. The inner core may comprise any polymeric material commonly used for spunbonding applications, depending on the desired end properties of the composite fibers or filaments. Preferably, the sheath-core fibers or filaments comprise 50-90 wt%, more preferably 65-80 wt%, of polymeric material forming the core-layer and 10-50 wt%, more preferably 20-35 wt%, of the copolymer of propylene and 1-pentene of the invention forming the outer sheath-layer. Particularly advantageous are sheath-core fibers or filaments comprising 70 wt% of polymeric- material forming the core layer and 30 wt% of the copolymer of propylene and 1-pentene of the invention forming the outer sheath. Fibers or filaments having improved tenacity/softness balance in combination with excellent spinnability can be conveniently prepared using the copolymer of propylene and 1-pentene of the invention, said fibers or filaments having sheath-core structure, wherein the skin layer comprises the propylene polymer composition of the invention and core layer comprises a propylene homopolymer having low xylene-soluble fraction at 25°C, preferably lower than 5.0 wt%, more preferably lower than 3 wt%, and high flexural modulus, preferably higher than 1100 MPa, more preferably higher than 1300 MPa. Said propylene homopolymers are commercially available. Preferably, the skin layer of fibers or filaments of the invention having sheath-core structure represent a proportion ranging from 20 to 40 wt% with respect to the whole weight of the filament.

The following examples are given to illustrate the present invention without limiting purpose.

EXAMPLES

The data relating to the polymeric materials and the fibres of the examples are determined by way of the methods reported below.

- Melting temperature: Determined by differential scanning calorimetry (DSC). weighting 6 + 1 mg, is heated to 220 + 1° C at a rate of 20 °C/min and kept at 220 + 1° C for 2 minutes in nitrogen stream and it is thereafter cooled at a rate of 20° C/min to 40 + 2° C, thereby kept at this temperature for 2 min to crystallise the sample. Then, the sample is again fused at a temperature rise rate of 20° C/min up to 220° C + 1. The melting scan is recorded, a thermogram is obtained, and, from this, temperatures corresponding to peaks are read.

- Melt Flow Rate: Determined according to ISO method 1133 (230° C, 2.16 kg).

- Solubility in xylene: Determined as follows. 2.5 g of polymer and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetical stirrer. The temperature is raised in 30 minutes up t the boiling pint of the solvent. The so obtained clear solution is then kept under reflux and stirring for further 30 minutes. The closed flask is then kept for 30 minutes in a bath of ice and water and in thermostatic water bath at 25° C for 30 minutes as well. The so formed solid is filtered on quick filtering paper. 100 ml of the filtered liquid is poured in a previously weighed aluminium container, which is heated on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80° C under vacuum until constant weight is obtained. The weight percentage of polymer soluble in xylene at room temperature is then calculated.

- Intrinsic viscosity (IV): Determined in tetrahydronaphthalene at 135° C.

- Comonomer content: Determined by IR spectroscopy.

- Titre of fibres: from a 10 cm long roving, 50 fibres are randomly chosen and weighed. The total weight of the said 50 fibres, expressed in mg, is multiplied by 2, thereby obtaining the titre in dtex.

- Tenacity and elongation at break: from a 500 m roving a 100 mm long segment is cut. From this segment the single fibres to be tested are randomly chosen. Each single fibre to be tested is fixed to the clamps of an Instron dinamometer (model 1122) and tensioned to break with a traction speed of 20 mm/min for elongations lower than 100% and 50 mm/min for elongations greater than 100%, the initial distance between the clamps being of 20 mm. The ultimate strength (load at break) and the elongation at break are determined. The tenacity is derived using the following equation:

Tenacity = Ultimate strength (cN) x 10/titre (dtex)

Softness on fibers

Through this method the Softness Index of fibers is determined. The Softness Index is calculated as weight (1/g) of a bundle of fibers, whose length is determined in standard conditions. A fiber bundle of about 4000 dtex in linear density and 0.6 m in length is prepared. The end of the bundle is fixed on the clamps of the twist measuring device (Torcimetro Negri e Bossi SpA) and a 120 leftward twist runs applied. The twisted bundle is taken off from the device carefully avoiding any un-twisting. The two ends of the twisted bundle are joint and the halves are wound around each other until the bundle looks like a rope. 3 specimens are prepared for each test. The bundle is bent in two and the ends are fixed between the rolls of a Clark softness tester keeping a distance of 1 cm between the two halves. The device is rotated rightwards and stopped when the bundle reverses its bending direction, taking note of the rotation angle (a). Then, the bundle is rotated leftward and till it reverses its bending side, taking note of the rotation angle (b). The height of the bundle above the two rolls is subsequently adjusted to have the sum (a)+(b)=90° and said height (h) is measured with a proper device having sensitivity of lmm. Each of the two angles, a and b, should not exceed the limits of 45°+- 15°. The bundle is removed from the device and cut to a height (h) corresponding to that previously measured. The cut bundle is weighted by an analytical balance with a precision of 0.1 mg. The Softness index is calculated from the formula:

S.I.= (l/w)*100

- where w is the weight, in grams, of the cut bundle. The given result is the average over 3 specimens.

- Tensile Strain Recovery: The test is based on ASTM method D- 1774-64. The method concerns procedures for the measurements of the elastic behaviour of fibres by assessing their ability to recover strain or their original dimension following a known extension. The multifilament sample subjected to the test is 40 cm length and has a titre of 500 dtex. The operative conditions are reported in the following table A.

The fibres of the example and comparative examples are obtained by using the operative conditions reported on table A

Table A

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 30 minutes with no filament break.

Example 1

Preparation of the solid catalyst component

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL of TiCU are introduced at 0 ⁰C. While stirring, 10.0 g of microspheroidal MgCl₂^-SC₂HsOH (prepared according to the method described in example 2 of USP 4,399,054 but operating at 3000 rpm instead of 10000 rpm), 9.1 mmol diisobutylphthalte as internal electron-donor compound is added. The temperature is raised to 100° C and maintained for 120 min. Then, the stirring is discontinued, the solid product is allowed to settle and the supernatant liquid is siphoned off. Then 250 ml of fresh TiCU are added. The mixture is reacted at 120° C for 60 min and, then, the supernatant liquid is siphoned off. The solid is washed six times with anhydrous hexane (6 x 100 ml) at 60 ⁰C.

The solid catalyst component is used with dicyclopentyldimethoxysilane (DCPMS) as external-donor component and triethylaluminium.

Polymerization

Copolymers are prepared by polymerising propylene and 1 -pentene in the presence of the above catalyst under continuous conditions in a plant comprising a gas-phase polymerisation apparatus. The apparatus comprises two interconnected cylindrical reactors (riser and downcomer). Fast fluidisation conditions are established in the riser by recycling gas from the gas-solid separator. The polymer composition shows a narrow distribution of the molecular weights obtained without using a liquid barrier, the hydrogen concentration is kept at the same concentration in both riser and downcomer and the hexene- 1 is fed only into the downcomer.

The polymer particles exiting the reactor are subjected to a steam treatment to remove the reactive monomers and volatile substances and then dried.

Other operative conditions and the properties of the produced copolymers are indicated in Table 1.

Table 1

C ^" 1 -pentene C ^"propylene

Comparative Examples 1

Propylene and 1 -hexene have been polymerized by using the same procedure indicated in example 1 of WO 2005/059210 to obtain a polymer having an MFR of 2. The polymer obtained has the characteristics indicated in table 2. The obtained copolymer has been spun to produce fibres. The spinning conditions and the proprieties of the fibres thus obtained are reported in

Table 2.

Comparative example 2

Propylene and 1-butene have been polymerized by using the same procedure described in example 1 but using 1-butene instead of 1 -pentene. The polymer obtained has the characteristics indicated in table 2. The obtained copolymer has been spun to produce fibres. The spinning conditions and the proprieties of the fibres thus obtained are reported in Table 3.

Table 2

The copolymer of example 1 and comparative examples 1 and 2 are stabilised by adding a stabiliser package suitable for fibres and a visbroking agent luperox 101®. The visbreaked pellets obtained are spun to produce fibres. The spinnability tests are carried out at 280⁰C and spinning speed in thermal bonding standard conditions. The draw ratio is 1.5. The spinning conditions and the proprieties of the fibres thus obtained are reported in Table 3.

Table 3

1C, 2C = comparative examples 1 and 2

From table 2 it is possible to note that when 1-penten is used as comonomer the tenacity of the fiber increases when the titre is the same. Furthermore there is an increasing of the softness.

Claims

1. A fibre comprising a copolymers of propylene and 1-pentene containing from 0.1% to 20% by weight of 1-pentene derived units; said copolymer having a value of melt flow rate (MFR) ranging from 0.1 to 100 g/10 min.

2. The fibre according to claim 1 wherein the content of 1-pentene derived units ranges from 0.5 % to 10% by weight.

3. The fibre according to anyone of claims 1-2 wherein the content of 1-pentene derived units ranges from 1 % to 5% by weight.

4. The fibre according to anyone of claims 1-3 wherein the copolymer has a solubility in xylene at room temperature below 10 wt%.

5. The fibre according to anyone of claims 1-4 having a value of tenacity higher than 18 cN/tex.

6. The fibre according to anyone of claims 1-5 having a value of elongation at break higher than 190%.

7. The fibre according to anyone of claims 1-4 having a value of softness higher than 870 1/gr,

8. Spun-bonded nonwoven fabric comprising the copolymers of propylene and 1-pentene of claim 1.

9. Process for the preparation of fibers or filaments characterized in that it comprises the step of melt-spinning the copolymers of propylene and 1-pentene of claim 1.

10. Process for the preparation of a spun-bonded nonwoven fabric characterized in that it comprises the step of spun-bonding fibers or filaments comprising the copolymers of propylene and 1-pentene of claim 1.