KR20060010750A - Metallocene produced polyethylene for fibres applications - Google Patents

Abstract

The present invention provides monofilaments or stretched tapes, unwoven or woven into raffia, prepared with metallocene-produced polyethylene having long chain branches.

Description

METALLOCENE PRODUCED POLYETHYLENE FOR FIBRES APPLICATIONS

The present invention relates to the field of short fibers and stretch tapes made from polyethylene produced from metallocenes.

Short fibers are strands of uniaxially oriented wire polymer having a circular cross section. They are produced by the melt spinning method, the size of which ranges from 0.1 to 2.5 mm in diameter depending on the end use application. Polyethylene, polypropylene, nylon and polyester are commonly used as raw materials for the production of short fibers.

Stretched tapes are made from primary films made by blown or cast film methods. The film can be cut into tape and then oriented, or vice versa and then cut into tape. The orientation is carried out by stretching the film or tape while passing over an air oven or hot plate whose temperature is below the melting point. Stretching is effected by passing a film or tape over two sets of rollers, each arranged before and after the air oven / hot plate, wherein the two sets of rollers operate at different speeds and the speed of the second set of rollers is set to the first set. Is greater than the speed of the roller.

Preferred polymers on the market for this application are high density polyethylene (HDPE) made from Ziegler-Natta catalysts, which are, for example, Solvay Eltex A4009MFN1325 resins or Basell Hostalen GF 7740 F1, GF7740 F2, GF7740 F3, GF7750 M2 grades. Or MI2 less than 1 g / 10 min, such as the polyethylene resin disclosed in GB-0023662. The molecular weight distribution (MWD) of these resins is very wide, which means that the resin can contain high long chains and high short chains.

Semi-crystalline polyethylene (PE) and polypropylene (PP) have also been used as materials for short fiber stretch tapes and raffia as disclosed, for example, in FR-A-2814761, JP-2001342209 or JP-2001220405. . Throughout this specification, raffia is defined as woven short fibers or woven stretched tape. Stretched tapes and short fibers made of polyethylene have higher elongation at break, greater flexibility, and a lower tendency to form small fibers than those made of polypropylene. These properties are advantageous, for example, in the manufacture of woven tape fabrics. However, products made from polyethylene have the disadvantage that they are much lower in viscosity than products made from polypropylene. Viscosity increases as a function of molecular weight, density, chain / crystal orientation, and as molecular weight distribution narrows. Impact strength increases with decreasing density, increasing molecular weight and decreasing molecular weight distribution.

Accordingly, there is a need for short fibers or stretched tapes woven or woven from raffia that have improved property balance.

It is an object of the present invention to produce high viscosity short fibers or stretch tape products.

It is another object of the present invention to produce short fibers or stretched tape articles having high impact strength.

It is also an object of the present invention to produce short fibers or stretched tape products having high elongation at break.

It is another object of the present invention to produce short fibers or stretched tape products having a soft feel.

It is yet another object of the present invention to produce highly flexible short fibers or stretched tape products.

Accordingly, the present invention provides raffia woven or nonwoven short fibers or stretched tapes having long chain branches and made from polyethylene resin (mPE) produced from metallocenes.

Preferred metallocene catalyst components are based on the tetrahydroindenyl component or on components of limited geometry, more preferably the tetrahydroindenyl component.

The invention also

a) providing a medium density polyethylene resin produced with metallocene, having long chain branches;

b) preparing a film from the polyethylene resin of step a);

c) stretching and orienting the film obtained from step b);

d) cutting the stretched film of step c) into strips

It provides a method for producing a raffia or stretched tape from a polyethylene produced with a metallocene.

Alternatively, the primary film may be first cut into strips and then stretched to orient.

The film may be a blown film or a cast film. The use of high melt strength processing materials such as polyethylene with long chain branches and / or very long linear chains makes film manufacture easier. Metallocene catalyst systems based on tetrahydroindenyl components or components of geometrically constrained structures are particularly useful for the production of polyethylene resins having long branches.

In the preparation of blown films, resins made with the tetrahydroindenyl catalyst component provide very stable bubbles, resulting in films with uniform thickness and little or no crease. Wrinkles and non-uniform thicknesses are disadvantages when the film is cut or stretched with tape.

In the production of cast films, resins made with tetrahydroindenyl catalyst components have stable elongational viscosities so that a stable and regular thickness is obtained.

It is also observed that resins with long branches maintain good mechanical properties such as traction resistance and viscosity at densities lower than those of linear resins having the same mechanical properties. Working at low densities has the advantage of providing materials with improved flexibility, low melting point and good processability.

The orientation of the primary film or cut tape is carried out by stretching the primary film or cut tape while passing air through an air oven or hot plate maintained at a temperature below the melting point. Stretching of the primary film or cut tape is carried out by passing the film or tape onto two sets of rollers (Godette rollers) respectively placed in front of and behind the air oven / hot plate. The draw ratio S2 / S1 is defined as the ratio of the speed S2 of the second roller to the speed S1 of the first roller, where S2 is greater than S1.

Stretching at such high temperatures results in a chain / crystal orientation with increased crystallinity. This structural change increases the tensile strength and at the same time reduces the elongation. Tensile strength increases with increasing draw ratio and draw temperature. The stretching temperature is as close as possible to the melting point but preferably lower than the melting point. In the high density polyethylene, the general draw ratio is 5.0 to 7.0. Typical stretching temperatures depend on the melting point of the polyethylene resin, which should be as close as possible to the melting point. In general, the stretching temperature is 5 to 70 ° C lower than the melting point of the resin, and preferably 10 to 50 ° C lower than the melting point of the resin.

Preferably, the drawn tape is annealed immediately after the stretching operation to minimize shrinkage that may occur as a result of residual stress. Annealing is performed by heating the stretched tape while the stretched tape moves from the second goth roller over a third roller having a speed S3 lower than the speed S2 of the second roller. The speed S3 of the third roller is preferably 95% of the speed S2 of the second roller. Annealing ratio (AR) is defined as (S2-S3) / S2 at temperatures slightly below the stretching temperature. In general, the annealing temperature is 5 to 10 ° C. lower than the stretching temperature.

Polymers that do not contain very long linear or long chain branched molecules have better stretchability. For example, low density polyethylene (LDPE) with long chain branching cannot be stretched to some extent, while pure linear polyethylene chains typically obtained with Ziegler-Natta catalysts have a high degree of stretchability.

The metallocene used in the preparation of the high density polyethylene is bis-indenyl represented by the following formula (I) or bis-cyclopentadienyl represented by the formula (II) or a component of the geometrically constrained structure represented by the following formula (III). Can be:

R "(Ind) ₂ MQ ₂

R "(Cp) ₂ 2MQ ₂

R "(Cp) (NR ') MQ ₂

In the above formulas,

(Ind) is substituted or unsubstituted indenyl or hydrogenated indenyl,

Cp is a substituted or unsubstituted cyclopentadienyl ring,

R 'is hydrogen or C _1-20 hydrocarbyl,

R ″ is a substituted or unsubstituted structural crosslinking between two indenyls that confers stereorigidity and represents a C ₁ -C ₄ alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical Including,

Q is a C _1-20 hydrocarbyl radical or halogen,

M is a Group IVb transition metal or vanadium.

In formula (I), each indenyl or hydrogenated indenyl compound may be substituted in the same way or differently from each other at one or more positions in the cyclopentadienyl ring, the cyclohexene ring and the crosslink.

In formula (I), each substituent on indenyl is independently selected from substituents of formula (XR _v) , wherein X is selected from group IVA, oxygen and nitrogen, each R is the same or different, hydrogen or 1-20 Is selected from hydrocarbyl having 2 carbons, and v + 1 is the valence of X. X is preferably C. When the cyclopentadienyl ring is substituted, the substituents should be bulky enough to affect the coordination of the olefin monomers to the metal (M). The substituent on the cyclopentadienyl ring preferably has R, such as hydrogen or CH ₃ . Preferably at least one, most preferably both cyclopentadienyl rings are unsubstituted.

In a preferred embodiment, both indenyl is unsubstituted and the most preferred catalyst component is tetrahydroindenyl.

In formula (II), each cyclopentadienyl ring may be substituted in the same way or differently from each other at one or more positions in the cyclopentadienyl ring.

In formula (II), each substituent on the cyclopentadienyl may be independently selected from substituents of formula (XR ^* _v) , wherein X is selected from group IVA, oxygen and nitrogen, and each R ^* is the same or different And selected from hydrogen or hydrocarbyl having 1 to 20 carbons, v + 1 is the valence of X. X is preferably C and the most preferred substituent is n-butyl.

R "preferably denotes a C1-C4 alkylene radical (referred to herein as bifunctional radical and also referred to as alkylidene), most preferably a substituted or unsubstituted ethylene crosslinked (referred to herein as bifunctional radical) Also called alkylidene).

The metal (M) is preferably zirconium, hafnium or titanium, most preferably zirconium.

Each Q is the same or different and can be a hydrocarbyl or hydrocarbyl radical having 1 to 20 carbon atoms or halogen. Suitable hydrocarbyls are aryl, alkyl, alkenyl, alkylaryl or arylalkyl. Each Q is preferably halogen.

Among the preferred metallocenes used in the present invention, bis tetrahydro-indenyl compounds and bis indenyl compounds or bis (cyclopentadienyl) compounds disclosed, for example, in WO 96/35729 can be mentioned. Most preferred metallocene catalyst is isopropylidene-bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride.

The metallocene may be supported according to any method known in the art. When supported, the carrier used in the present invention may be any organic or inorganic solid, in particular dendritic carrier materials such as porous carriers such as talc, inorganic oxides and polyolefins. The carrier material is preferably an inorganic oxide in finely divided form.

Agents that work with the carrier and undergo an ionization reaction are added to the carrier to form the active site.

Preferably alumoxane is used to ionize the catalyst during the polymerization procedure, any alumoxane known in the art is suitable.

Preferred alumoxanes include oligomer straight chain alumoxanes and / or oligomer cyclic alkyl alumoxanes represented by Formulas IV and V, respectively:

In the above formulas, n is 1 to 40, preferably 10 to 20, m is 3 to 40, preferably 3 to 20, and R is a C ₁ to C ₈ alkyl group, preferably methyl.

Preference is given to using methylalumoxane.

One or more aluminum alkyl (s) can be used as cocatalyst in the reactor. Aluminumalkyl is represented by the formula AlR _x , where each R is the same or different and is selected from halides or alkoxy or alkyl groups having 1 to 12 carbon atoms, x being 1 to 3. Particularly suitable aluminum alkyls are trialkylaluminums, most preferably triisobutylaluminum (TIBAL).

In addition, the catalyst may be prepolymerized before injecting the catalyst into the reaction zone and / or before stabilizing the reaction conditions in the reactor.

The density of the polyethylene resin of the present invention is 0.925 to 0.950 g / cm 3, preferably 0.930 to 0.940 g / cm 3, most preferably about 0.935 g / cm 3. Melt index MI2 is in the range of 0.1 to 5 g / 10 minutes, preferably 0.2 to 1.5 g / 10 minutes.

Density is measured according to the standard test ASTM D 1505 method at 23 ° C., and melt index (MI2) is measured according to the standard test ASTM D 1238 method at 190 ° C. and a load of 2.16 kg.

Polyethylenes made of metallocenes usually produce very strong stretched tapes and raffia products because of their narrow molecular weight distribution and long chain branches. The final product has improved tensile and elongation properties while at the same time improved flexibility and processing properties.

Several resins were tested for the production of raffia products.

Resin R1 is a medium density polyethylene resin made of isopropylene (tetrahydroindenyl) zirconium dichloride. The resin had a density of 0.934 g / cm 3 and a melt index (MI 2) of 0.9 g / 10 min. The following is added to this resin.

94.5 weight% R1 resin;

Cariant's 4% Red Masterbatch PE 44930;

1% polymer processing aid AMF 702 from Schuman;

Cariant's 0.5% antiblock masterbatch B1981.

Resin (R2) was a commercially available resin made with a Ziegler-Natta catalyst system (GF7740 F1 from Hostalen). The resin had a density of 0.946 g / cm 3 and a melt index (MI 2) of 0.5 g / 10 min.

These two resins were treated under the same conditions to prepare and stretch the blown film.

Melting die temperature: 220 ℃

Primary film thickness: 60 microns

-Orientation temperature: gradually change from 80 to 120 ℃

Elongation ratio: 7: 1

The final product obtained from the resin (R1) made of metallocene was high in viscosity, excellent in elongation at break and very high in impact resistance, whether or not (net) was woven. Moreover, this resin was soft in touch and high in flexibility.

The properties of the stretched tape obtained from the resins (R1) and (R2) are summarized in Table I.

R1 R2 Breaking Viscosity (cN / Tex) 24.9 22.1 Elongation at Break (%) 33.2 29.3 Breaking strength (cN) 593 525 Fiber Thickness (Tex) 23.8 20.8

Elongation at break, strength and viscosity of the stretched tape were measured according to the method of standard test ISO-2062 (1993).

Fiber thickness is measured in tex or g / km, which is a measure of the linear mass of short fibers or fibers.

The properties of the woven stretched tape or raffia are shown in Table II below.

R1 R2 Elongation at Break (%) 30.6 29.4 Breaking strength (cN) 997 811

Thus, the raffia product produced according to the invention has improved properties compared to the raffia product of the prior art.

Elongation at break and strength at break of raffia were measured according to standard test ISO-5081 (1977) method.

Claims (8)

A short fiber or stretch tape woven or woven from raffia, made from polyethylene resin produced from metallocene with long chain branches. The short fiber or oriented tape according to claim 1, wherein the metallocene component is tetrahydroindenyl. a) providing a medium density polyethylene resin produced with metallocene, having long chain branches; b) preparing a film from the polyethylene resin of step a); c) stretching and orienting the film obtained from step b); d) cutting the stretched film of step c) into a strip; e) optionally annealing the stretched tape Method for producing a stretched tape comprising a. The method of claim 4, wherein step d) is performed before step c). The manufacturing method of the extending | stretching tape of Claim 4 or 5 whose extending | stretching temperature is 10-70 degreeC lower than the melting temperature of resin. The method for producing a stretched tape according to claim 6, wherein the stretching temperature is 15 to 50 ° C lower than the melting temperature of the resin. The manufacturing method of the stretched tape in any one of Claims 4-7 whose speed ratio of a roller exists in the range of 5-7. The method for producing a stretched tape according to any one of claims 4 to 8, wherein the annealing temperature is 5 to 10 ° C lower than the stretching temperature when the annealing is performed.