JP2025529106A - Blow-molding polyethylene compositions with improved swelling behavior - Google Patents

Abstract

A polyethylene composition particularly suitable for the production of blow-molded hollow articles, comprising:
1) The density is 0.948 to 0.960 g/cm ³ ;
2) MIF/MIE ratio greater than 125;
3) MIF is 20 to 40 g/10 min;
4) The ER value is 5 to 10.
[Selected Figure] Figure 1

Description

The present invention relates to a polyethylene composition suitable for producing small items by blow molding.

WO 2005/044866 A1 discloses a method for controlling the flow index and/or molecular weight separation of a polymer composition. In one embodiment, the method for producing a polymer composition includes incorporating a high molecular weight polymer into a low molecular weight polymer in the presence of a polymerizable monomer, a bimetallic catalyst composition, and at least one control agent to form a polymer composition in a single polymerization reactor, wherein the control agent is added in an amount sufficient to control the incorporation level of the high molecular weight polymer, the level of the low molecular weight polymer, or both. Examples of control agents include alcohols, ethers, amines, and oxygen.

US 2012/0220747 A1 provides a bimodal polyethylene composition and a method for making the same. In at least one specific embodiment, the bimodal polyethylene composition can include a high molecular weight component having a weight average molecular weight (Mw) of about 400,000 to about 950,000. The bimodal polyethylene composition can also include a low molecular weight component having a weight average molecular weight (Mw) of about 3,000 to about 100,000. The high molecular weight component can be present in an amount ranging from about 25% to about 40% by weight of the bimodal polyethylene composition. The bimodal polyethylene composition can also have a die swell percentage (%) of less than about 80%.

WO 2008/088464 A1 describes a method for modifying polyethylene. In this method, ethylene or a mixture of ethylene and a C3-C10 alpha-olefin is polymerized in an organic solvent with a Ziegler or single-site catalyst to form an initial polyethylene solution. The initial polyethylene solution is then reacted with a free-radical initiator to produce the modified polyethylene. The modified polymer has improved melt elasticity, an increased long-chain branching index, and is substantially free of gel.

Examples of compositions suitable for such use are disclosed in International Publication Nos. 2018095700, 2018095701, and 2018095702.

By appropriately selecting its molecular structure and rheological behavior, the composition achieves particularly high environmental stress crack resistance (ESCR) across a wide density range, while reducing gel content, in combination with an extremely smooth surface in the final article.

At high density levels, the ESCR is lower but still satisfactory.

However, an important aspect of blow molding that needs to be optimized is the swelling behavior of the polymer composition.

In fact, the overall quality level and consistency of a blow-molded product is highly dependent on swelling.

For example, parison swell is very important in extrusion blow molding.

Parison swell has two components: weight swelling and diameter swelling.

Gravimetric swelling can occur during the short time that the mold is open and the parison is dropping. The parison may actually shrink in length while simultaneously thickening its walls and becoming heavier.

Excessive weight swell must be avoided, especially for producing lightweight blown articles with thin, consistent wall thickness. Die adjustments can be important.

If the weight swelling of the resin used is too great, attempts are often made to reduce the weight by reducing the die gap.

However, reducing the die gap can result in a very thin parison that can easily collapse or break.

Furthermore, narrow die gaps are extremely sensitive to impurities. Narrow die gaps also result in high shear, which can lead to large diameter swells in the parison. The final bottle may be intact but may be surrounded by heavy flash. Crimping can also be a problem.

Grain swell must therefore be kept within practical limits relative to commonly used industry standards.

Diameter swelling causes the parison to bulge outward from the die, in other words, the diameter of the parison becomes significantly larger than the diameter of the die.

Diameter swell is particularly important for blow-molded articles (especially bottles) that include handle portions, and is therefore commonly referred to as "handlewear."

In this case, the diameter swell may be expressed as the distance (length), e.g., in centimeters, that the burr extends from the neck of the handlewear item (including any protruding burrs) to the handle area and, in some cases, beyond the handle area.

In fact, resins with too little diameter swelling can cause smaller handle webbing and, in severe cases, even blowouts.

In this case, the parison is captured in two places by the inner handle pinch-off.

When blown, these areas come together to form heavy areas known as webs.

As mentioned above, resins with too much diameter swell can produce an undesirable amount of flash, which can also result in deburring problems.

In conclusion, it is very important to provide polyethylene compositions that inherently have good and consistent swelling behavior.

It is known that the swelling behavior of polyethylene compositions can be modified by treatment with radical initiators, particularly peroxides, as disclosed, for example, in U.S. Pat. Nos. 4,603,173 and 5,486,575.

Furthermore, high density, high polydispersity polyethylene with improved properties and processes for its manufacture are known in the art, for example, in WO 2018/147968 A1.

It has now been found that by appropriately configuring the molecular structure of the polyethylene composition and selecting rheological properties, for example by post-polymerization treatment with a radical initiator, a particularly favorable balance of parison swell and mechanical properties can be achieved while reducing gel content.

Thus, the present disclosure:
1) the MIF/MIE ratio is greater than 125, preferably 130 or greater, more preferably 132 or greater, and in particular greater than 125 and 180 or less, or greater than 130 and 180 or less, or greater than 132 and 180 or less, where MIF is the melt flow index at 190°C under a load of 21.60 kg, and MIE is the melt flow index at 190°C under a load of 2.16 kg, both determined in accordance with ISO 1133-1 2012-03;
2) MIF is 20 to 40 g/10 min, preferably 25 to 35 g/10 min, more preferably 25 to 34 g/10 min;
3) a density of 0.948 to 0.960 g/cm ³ , in particular 0.950 to 0.958 g/cm ³ , measured at 23°C according to ISO 1183-1:2012;
4) The ER value is 5 to 10, preferably 5.2 to 9;
where ER is calculated as follows:
ER=(1.781* ^10-3 )*G'
where G'' = 5,000 dyn/ ^cm2 ,
where:
G' = storage modulus,
G'' = loss modulus;
A polyethylene composition is provided having the characteristics that G' and G'' are both measured by dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190°C.

The polyethylene composition meets industrial requirements in terms of weight swell and diameter swell and can be easily processed using conventional blow molding equipment.

These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims, as well as the drawings.

FIG. 1 is an exemplary embodiment of a simplified process flow diagram of two series-connected gas phase reactors suitable for use according to various embodiments of the ethylene polymerization process disclosed herein to produce various embodiments of the polyethylene compositions disclosed herein. Figure 2 shows the test bottle used in the weight and diameter swelling test. The test bottle is approximately 28 cm high (excluding the top and bottom flash) and approximately 14 cm wide.

It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.

The expression "polyethylene composition" is intended to alternatively include single ethylene polymers and ethylene polymer compositions, particularly compositions of two or more ethylene polymer components, preferably having different molecular weights; such compositions are also referred to in the art as "bimodal" or "multimodal" polymers.

Typically, the polyethylene composition of the present invention consists of or comprises one or more ethylene copolymers.

All properties defined herein, including characteristics 1) through 4) defined above, refer to the ethylene polymer or ethylene polymer composition. The addition of other components, such as additives commonly used in the art, can modify one or more of the above characteristics.

The MIF/MIE ratio provides a rheological measure of molecular weight distribution.

Another measure of molecular weight distribution is provided by the ratio _Mw / _Mn , where _Mw is the weight average molecular weight and _Mn is the number average molecular weight, as determined by GPC (gel permeation chromatography), as explained in the examples.

The preferred M _w /M _n value of the polyethylene composition is in the range of 15-35, particularly 20-35.

The M _w value is preferably between 150,000 g/mol and 450,000 g/mol, in particular between 150,000 g/mol and 350,000 g/mol.

Furthermore, the polyethylene composition of the present invention preferably comprises
the comonomer content is less than or equal to 1.7% by weight, in particular between 0.1 and 1.7% by weight (FTIR), relative to the total weight of the composition;
- MIP is at least 0.3 g/10 min, more preferably at least 0.5 g/10 min, in particular between 0.3 and 4 g/10 min, or between 0.5 and 4 g/10 min, where MIP is the melt flow index measured according to ISO 1133-1 2012-03 at 190°C under a load of 5 kg;
a (MIF/MIE)ER ratio between MIF/MIE and ER of 26 or less, more preferably 25.5 or less, in particular 26-15, or 25.5-15, or 26-20, or 25.5-20;
a long chain branching index LCBI of not more than 0.55, more preferably not more than 0.60, the upper limit being preferably 0.95 in each case;
where LCBI is the ratio of the measured mean square radius of gyration Rg to the mean square radius of gyration for linear PE of the same molecular weight at a molar weight of 1,000,000 g/mol, as measured by GPC-MALLS;
-η _0.02 is 56,000 Pa s or more, particularly 56,000 to 80,000 Pa s;
where η _0.02 is the complex viscosity of the melt measured at a temperature of 190 ^{° C.} in a parallel plate (or so-called plate-plate) rheometer under dynamic oscillatory shear mode with an applied angular frequency of 0.02 rad/s;
the ratio (η _0.02 /1000)/LCBI, i.e. the value between η _0.02 divided by 1000 and LCBI, is between 85 and 150, preferably between 90 and 130;
an HMWcopo index of 0.5 to 5, in particular 0.5 to 3.5,
wherein the HMWcopo index is determined according to the following formula:
HMWcopo = (η _0.02 x t _maxDSC )/(10^5)

where _tmaxDSC is the time required to reach the maximum heat flow of crystallization (in mW) measured by differential scanning calorimetry (DSC) in isothermal mode at a temperature of 124°C under static conditions (time to reach the maximum crystallization rate, equivalent to the t1/2 crystallization half-life), and has at least one additional characteristic in minutes.
The one or more comonomers present in ethylene copolymers are generally selected from olefins having the molecular formula CH ₂ ═CHR, where R is a straight or branched chain alkyl group having from 1 to 10 carbon atoms.

Specific examples include propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, and decene-1. A particularly preferred comonomer is hexene-1.

Preferably, the polyethylene composition is obtained by using a Ziegler-Natta polymerization catalyst in the polymerization stage, details of which are provided hereinafter.

As mentioned above, the polyethylene composition can be advantageously used to produce blow-molded articles, particularly handleware such as bottles with handles that have valuable properties.

Indeed, it is preferably characterized by an environmental stress crack resistance of at least 40 hours, especially 40 to 100 hours, as measured by FNCT 6 MPa/50°C.

The polyethylene composition preferably has a gel content of less than 10 gels/ ^m2 , more preferably less than 5 gels/ ^m2 , and has a diameter of more than 450 μm.

The total gel content is preferably less than 500 gels/ ^m2 , more preferably less than 400 gels/ ^m2 .

The swelling ratio of this polyethylene composition is preferably 160% or more, particularly 160% to 200%.

Details of the test method are provided in the Examples.

The blow molding process is generally carried out by first plasticizing the polyethylene composition in an extruder at a temperature ranging from 180°C to 250°C, then forcing it through a die into a blow mold, where it is cooled.

In a preferred embodiment, the polyethylene composition having the above-defined characteristics is obtainable by contacting a precursor polyethylene composition (I) having a ratio of MIF/MIE 1 ^I ) that is smaller than MIF/MIE 1), preferably 120 or less, more preferably 115 or less, and in particular 90 to 120, or 90 to 115, with a radical initiator, wherein the ratio 1)/1 I ) between MIF/MIE 1) of the final polyethylene composition (after contact with said radical initiator) and MIF/MIE 1 ^I ) of said precursor polyethylene composition ( ^I ) is 1.05 or greater, preferably 1.1 or greater, and in particular 1.05 or 1.1 to 1.8, or 1.05 or 1.1 to 1.6.

Preferably, the ratio 4)/4 ^I ) between ER 4) of the final polyethylene composition (after contact with the radical initiator) and ER 4 ^I ) of the precursor polyethylene composition (I) is from 1.1 to 2.5.

In a particularly preferred embodiment, the precursor polyethylene composition (I) comprises
2 ^I ) MIF is 30 to 50 g/10 min, preferably 35 to 45 g/10 min;
3 ^I ) density is 0.948 to 0.960 g/cm ³ , particularly 0.950 to 0.958 g/cm ³ ;
4 ^I ) The ER value is 2 to 5, preferably 2 to 4.5.

Furthermore, the precursor polyethylene composition (I) preferably comprises:
a comonomer content of not more than 1.7 wt.%, in particular from 0.1 to 1.7 wt.% (FTIR) relative to the total weight of the composition, the comonomer(s) being the same as those reported above for the final polyethylene composition, in particular the type and amount of the comonomer(s) being the same in the final polyethylene composition (after contact with the radical initiator) and in its precursor polyethylene composition (I);
- MIP is 0.3 g/10 min or more, more preferably 0.5 g/10 min or more, in particular 0.3 to 6 g/10 min, or 0.5 to 6 g/10 min,
a (MIF/MIE)/ER ratio between MIF/MIE and ER greater than 26, more preferably greater than or equal to 27, in particular greater than 26 and less than or equal to 40, or greater than 27 and less than or equal to 40, or greater than 26 and less than or equal to 35, or greater than 27 and less than or equal to 35;
a long chain branching index LCBI of at least 0.50, more preferably at least 0.55, most preferably at least 0.60, the upper limit in each case preferably being 0.90;
-η _0.02 is less than 56,000 Pa s, in particular, 55,000 to 30,000 Pa s;
the ratio (η _0.02 /1000)/LCBI, i.e. the value between η _0.02 divided by 1000 and LCBI, is between 55 and 75, preferably between 55 and 70;
- an HMWcopo index of 0.5 to 5, in particular 0.5 to 3.5.

In a particularly preferred embodiment, the precursor polyethylene composition (I) comprises
A) 30 to 70% by weight, preferably 40 to 60% by weight, of an ethylene homopolymer or copolymer (homopolymer is preferred), having a density of at least 0.960 g/cm ³ and a melt flow index MIE according to ISO 1333 at 190°C under a load of 2.16 kg of at least 40 g/10 min, preferably at least 50 g/10 min;
B) 30 to 70 wt. %, preferably 40 to 60 wt. %, of an ethylene copolymer having an MIE value less than that of A), preferably less than 0.5 g/10 min.

The above percentage amounts are given relative to the total weight of A) + B).

Specific MIE ranges for component A) are as follows:
-40 to 150g/10min, or -50 to 150g/10min, or -40 to 100g/10min, or -50 to 100g/10min.

It has been discovered that the precursor polyethylene composition (I) can be prepared by a gas phase polymerization process in the presence of a Ziegler-Natta catalyst.

Ziegler-Natta catalysts consist of the reaction product of an organometallic compound of Group 1, 2 or 13 of the Periodic Table of the Elements with a transition metal compound of Groups 4 to 10 of the Periodic Table of the Elements (new notation). In particular, the transition metal compound can be selected from compounds of Ti, V, Zr, Cr and Hf, and is preferably supported on _MgCl2 .

Preferred organometallic compounds are organoaluminum compounds.

Thus, in a preferred embodiment, the precursor polyethylene composition (I) can be obtained using a Ziegler-Natta polymerization catalyst, preferably a Ziegler-Natta catalyst comprising the following reaction product:

A) a solid catalyst component comprising Ti, Mg, chlorine, and one or more internal electron donor compounds ED;
B) an organoaluminum compound, and optionally
C) External electron donor compound ED _ext .

In particular, the solid catalyst component A) may comprise one internal electron donor ED selected from esters of aliphatic monocarboxylic acids (EAA) and another internal donor ED ^I selected from cyclic ethers (CE) in amounts such that the EAA/CE molar ratio ranges from 0.02 to less than 20.

Preferably, the EAA/CE molar ratio is in the range of 0.2 to 16, more preferably 0.5 to 10.

The internal electron donor compound (EAA) is preferably selected from C ₁ -C ₁₀ , preferably C ₂ -C ₁₀ , C ₂ -C ₅ alkyl esters, preferably C ₂ -C ₆ aliphatic monocarboxylic acids, of which ethyl acetate is particularly preferred.

The (CE) internal donor is preferably selected from cyclic ethers having 3 to 5 carbon atoms, of which tetrahydrofuran, tetrahydropyran, and dioxane are most preferred, with tetrahydrofuran being particularly preferred.

The (EAA + CE)/Ti molar ratio is preferably greater than 1.5, more preferably in the range of 2.0 to 10, particularly 2.5 to 8.

The content of (EAA) is typically in the range of 1 to 30 wt %, more preferably 2 to 20 wt %, based on the total weight of the solid catalyst component. The content of (CE) is typically in the range of 1 to 20 wt %, more preferably 2 to 10 wt %, based on the total weight of the solid catalyst component.

The Mg/Ti molar ratio is preferably in the range of 5 to 50, more preferably 10 to 40.

As discussed above, the catalyst components include Ti, Mg, and chlorine in addition to the electron donor compound. The Ti atoms preferably come from a Ti compound containing at least a Ti-halogen bond, and the Mg atoms preferably come from magnesium dichloride. Preferred titanium compounds are tetrahalides or compounds of the formula TiX _n (OR ¹ ) _4-n , where 0<n<3, X is a halogen, preferably chlorine, and R ¹ is a C ₁ -C ₁₀ hydrocarbon group. Titanium tetrachloride is a preferred titanium compound.

The catalyst components of the present disclosure can be prepared according to a variety of methods.

One preferred method comprises the steps of: (a) contacting an MgX ₂ (R ² OH) _m adduct, wherein the R ² groups are C ₁ -C ₂₀ hydrocarbon groups and X is a halogen, with a liquid medium containing at least a Ti compound having a Ti—Cl bond in an amount such that the Ti/Mg molar ratio is greater than 3, thereby forming a solid intermediate; and (b) contacting the internal donor compounds (EEA) and (CE) as previously defined with the solid intermediate derived from (a), followed by washing the resulting product.

A preferred starting MgX ₂ (R ² OH) _m adduct is one in which the R ² group is a C ₁ -C ₁₀ alkyl group, X is chlorine, and m is 0.5 to 4, more preferably 0.5 to 2. This type of adduct can generally be obtained by mixing an alcohol with magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, and operating under stirring at the melting temperature of the adduct (100-130°C). The emulsion is then rapidly quenched, thereby solidifying the adduct in the form of spherical particles. Representative methods for producing these spherical adducts are reported, for example, in U.S. Pat. Nos. 4,469,648, 4,399,054, and WO 98/44009. Another method that can be used for spheronization is the spray cooling method, described, for example, in U.S. Pat. Nos. 5,100,849 and 4,829,034.

Of particular interest are MgCl ₂ (EtOH) _m adducts, where m is in the range of 0.15 to 1.5 and particle sizes are in the range of 10 to 100 μm, which adducts with higher alcohol contents are obtained by thermal dealcoholization treatment in a nitrogen stream at temperatures of 50 to 150° C. until the alcohol content is reduced to the aforementioned values. A process of this type is described in EP 395083.

Dealcoholization can also be accomplished chemically by contacting the adduct with a compound capable of reacting with the alcohol group.

Generally, these dealcoholized adducts are also characterized by a porosity, measured by the mercury method, in the range of 0.15 to 2.5 cm ³ /g, preferably 0.25 to 1.5 cm ³ /g, due to pores with a radius of up to 1 μm.

The reaction with the Ti compound can be carried out by suspending the adduct in TiCl ₄ (which is generally chilled) and subsequently heating the mixture to a temperature in the range of 80-130°C and maintaining this temperature for 0.5-2 hours. The treatment with the titanium compound can be carried out one or more times. Preferably, the treatment is carried out twice. At the end of the process, the intermediate solid is recovered by separating the suspension by conventional methods (settling and removing the liquid, filtration, centrifugation, etc.) and can be washed with a solvent. Washing is usually carried out with an inert hydrocarbon liquid, although more polar solvents (e.g., having a higher dielectric constant), such as halogenated hydrocarbons, can also be used.

As described above, in step (b), the intermediate solid is contacted with an internal donor compound in an amount such that the EAA/CE molar ratio is in the range of 0.02 to less than 20, under conditions such that the internal donor compound is immobilized on the solid.

Although not strictly necessary, the contacting is usually carried out in a liquid medium such as a liquid hydrocarbon. The temperature at which the contacting occurs depends on the nature of the reagents. It generally lies in the range of -10 to 150°C, preferably 0 to 120°C. Obviously, temperatures that cause decomposition or degradation of a particular reagent should generally be avoided, even within appropriate ranges. The treatment time can also vary depending on other conditions such as the nature, temperature, and concentration of the reagents. As a general indication, this contacting step can last from 10 minutes to 10 hours, more often from 0.5 to 5 hours. If desired, this step can be repeated one or more times to further increase the final donor content.

At the end of this step, the solids are recovered by separating the suspension using conventional methods (settling and removal of the liquid, filtration, centrifugation, etc.) and can be washed with a solvent. Washing is typically done with an inert hydrocarbon liquid, although more polar solvents (e.g., with a higher dielectric constant), such as halogenated or oxygenated hydrocarbons, can also be used.

According to a particular embodiment, it is particularly preferred that after step (b), a further step (c) is carried out by subjecting the solid catalyst component derived from (b) to a heat treatment carried out at a temperature of 70 to 150°C.

In step (c) of the process, the solid product recovered from step (b) is subjected to a heat treatment carried out at a temperature ranging from 70 to 150°C, preferably from 80 to 130°C, more preferably from 85 to 100°C.

The heat treatment can be carried out in several ways. According to one of these, the solid from step (b) is suspended in an inert diluent, such as a hydrocarbon, and then subjected to heating while maintaining the system under stirring.

According to an alternative technique, the solids can be heated in the dry state by inserting them into an apparatus with jacketed heated walls. Agitation can be achieved by a mechanical stirrer placed in the apparatus, but it is preferred to use a rotating device to induce agitation.

According to yet another embodiment, the solids derived from (b) can be heated by passing a stream of hot inert gas, such as nitrogen, through them, preferably by maintaining the solids under fluidized conditions.

The heating time is not fixed, but may vary depending on other conditions, such as the maximum temperature reached. Generally, heating times range from 0.1 to 10 hours, more specifically, from 0.5 to 6 hours. Generally, higher temperatures require shorter heating times, while lower temperatures require longer reaction times.

In the described process, each of steps (b)-(c) can be performed immediately after the previous step without requiring isolation of the solid product from the previous step. However, if desired, the solid product from a step can be isolated and washed before being passed to a subsequent step.

According to certain embodiments, a preferred modification of the process comprises subjecting the solids resulting from step (a) to a prepolymerization step (a2) before carrying out step (b).

The prepolymerization can be carried out with any olefin CH ₂ ═CHR, where R is H or a C ₁ -C ₁₀ hydrocarbon radical. It is particularly preferred to prepolymerize ethylene or propylene or a mixture thereof with one or more α-olefins, the mixture containing up to 20 mol % of α-olefin, to form an amount of polymer of from about 0.1 g to up to about 1000 g per gram of solid intermediate, preferably from about 0.5 to about 500 g per gram of solid intermediate, more preferably from 0.5 to 50 g per gram of solid intermediate, and especially from 0.5 to 5 g per gram of solid intermediate. The prepolymerization step can be carried out in the liquid or gas phase at a temperature of from 0 to 80° C., preferably from 5 to 70° C. It is particularly preferred to prepolymerize the intermediate with ethylene or propylene to produce an amount of polymer of from 0.5 to 20 g per gram of intermediate. The prepolymerization is carried out using a suitable cocatalyst, such as an organoaluminum compound. When the solid intermediate is prepolymerized with propylene, it is particularly preferred that the prepolymerization is carried out in the presence of one or more external donors, preferably selected from the group consisting of silicon compounds of the general formula R _a ⁴ R _b ⁵ Si(OR ⁶ ) _c , where a and b are integers from 0 to 2, c is an integer from 1 to 3, the sum (a+b+c) is 4, and R ⁴ , R ⁵ , and R ⁶ are alkyl, cycloalkyl, or aryl radicals having 1 to 18 carbon atoms, optionally containing heteroatoms. Particularly preferred are silicon compounds in which a is 1, b is 1, and c is 2, and at least one of R ⁴ and R ⁵ is selected from branched alkyl, cycloalkyl, or aryl groups having 3 to 10 carbon atoms, optionally containing heteroatoms, and R ⁶ is C ₁ -C ₁₀ alkyl, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane (C donor), diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane (D donor), and diisopropyldimethoxysilane.

All of the above processes are suitable for preparing particles of a solid catalyst component having a substantially spherical morphology and an average diameter of 5 to 150 μm, preferably 10 to 100 μm. By particles having a substantially spherical morphology, we mean particles having a ratio of their major axis to their minor axis of 1.5 or less, preferably 1.3 or less.

Generally, the solid catalyst components obtained according to the above process exhibit a surface area (B.T.E. method) of generally 10 to 200 ^{m 2} /g, preferably 20 to 80 ^{m 2} /g, and a total porosity (B.T.E. method) of more than 0.15 cm ³ /g, preferably 0.2 to 0.6 cm ³ /g. The porosity (Hg method) due to pores with a radius of up to 10,000 Å generally ranges from 0.25 to 1 cm ³ /g, preferably 0.35 to 0.8 cm ³ /g.

As previously explained, the catalyst components of the present disclosure form polymerization catalysts by reaction with Al-alkyl compounds. In particular, Al-trialkyl compounds, such as Al-trimethyl, Al-triethyl, Al-tri-n-butyl, and Al-triisobutyl, are preferred. The Al/Ti ratio is greater than 1, typically between 5 and 800.

Alkyl aluminum halides can also be used, particularly alkyl aluminum chlorides such as diethyl aluminum chloride (DEAC), diisobutyl aluminum chloride, aluminum sesquichloride, and dimethyl aluminum chloride (DMAC). Mixtures of trialkyl aluminum compounds with alkyl aluminum halides can also be used, and are preferred in certain cases. Among these, TEAL/DEAC and TIBA/DEAC are particularly preferred.

Optionally, an external electron donor (DE _ext ) can be used during the polymerization. The external electron donor compound can be the same as or different from the internal donor used in the solid catalyst component. It is preferably selected from the group consisting of ethers, esters, amines, ketones, nitriles, silanes and mixtures thereof. In particular, it can be advantageously selected from C ₂ -C ₂₀ aliphatic ethers, particularly preferably cyclic ethers having 3 to 5 carbon atoms, such as tetrahydrofuran, dioxane, etc.

In addition to the aluminum alkyl cocatalyst (B) and the possibility of using an external electron donor (ED _ext ) as component (C), a halogenated compound (D) can be used as an activity enhancer. The compound is preferably a monohalogenated or dihalogenated hydrocarbon. In a preferred embodiment, the compound is selected from monohalogenated hydrocarbons in which the halogen is bonded to a secondary carbon atom. The halogen is preferably selected from chloride and bromide.

Non-limiting exemplary compounds for (D) are propyl chloride, i-propyl chloride, butyl chloride, s-butyl chloride, t-butyl chloride, 2-chlorobutane, cyclopentyl chloride, cyclohexyl chloride, 1,2-dichloroethane, 1,6-dichlorohexane, propyl bromide, i-propyl bromide, butyl bromide, s-butyl bromide, t-butyl bromide, i-butyl bromide, i-pentyl bromide, and t-pentyl bromide. Among these, i-propyl chloride, 2-chlorobutane, cyclopentyl chloride, cyclohexyl chloride, 1,4-dichlorobutane, and 2-bromopropane are particularly preferred.

In another embodiment, the compound can be selected from halogenated alcohols, esters, or ethers, such as 2,2,2-trichloroethanol, ethyl trichloroacetate, butyl perchlorocrotonate, 2-chloropropionate, and 2-chloro-tetrahydrofuran.

The activity enhancer can be used in an amount such that the (B)/(D) molar ratio is greater than 3, preferably in the range of 5 to 50, and more preferably in the range of 10 to 40.

The above-mentioned components (A) to (D) can be fed separately to the reactor under polymerization conditions to utilize their activity. However, in a particularly advantageous embodiment, this constitutes pre-contacting the components, optionally in the presence of a small amount of olefin, for a time ranging from 1 minute to 10 hours, preferably from 2 to 7 hours. Pre-contacting can be carried out in a liquid diluent at a temperature ranging from 0 to 90°C, preferably from 20 to 70°C.

One or more alkylaluminum compounds, or mixtures thereof, can be used in the pre-contacting. When two or more alkylaluminum compounds are used in the pre-contacting, they can be used together or can be added sequentially to the pre-contacting vessel. When pre-contacting is performed, it is not necessary to add the entire amount of aluminum alkyl compound at this stage. A portion can be added in the pre-contacting, while the remaining aliquot can be fed to the polymerization reactor. Furthermore, when two or more aluminum alkyl compounds are used, it is also possible to use one or more in the pre-contacting process and feed the other(s) to the reactor.

In one preferred embodiment, pre-contacting is carried out by first contacting the catalyst components with an aluminum trialkyl, such as tri-n-hexylaluminum (THA), then adding another aluminum alkyl compound, preferably diethylaluminum chloride, to the mixture, and finally adding another trialkylaluminum, preferably triethylaluminum, as a third component to the pre-contacted mixture. According to a variation of this method, the final aluminum trialkyl is added to the polymerization reactor.

The total amount of aluminum alkyl compound used can vary over a wide range, but is preferably in the range of 2 to 10 moles per mole of internal donor in the solid catalyst component.

It has been found that by using the above-described polymerization catalyst, precursor polyethylene composition (I) can be produced by a process comprising the following steps, in any order relative to one another:

a) polymerizing ethylene in a gas phase reactor in the presence of hydrogen, optionally with one or more comonomers;
b) copolymerizing ethylene with one or more comonomers in a separate gas phase reactor in the presence of less hydrogen than in step a).

Here, in at least one of the gas-phase reactors, grown polymer particles flow upward through a first polymerization zone (riser) under fast flow or transport conditions, exit the riser and enter a second polymerization zone (downcomer), flow downward through the second polymerization zone by gravity, exit the downcomer and are reintroduced into the riser, establishing polymer circulation between the two polymerization zones.

In the first polymerization zone (riser), rapid fluidization conditions are established by supplying a gas mixture containing one or more α-olefins (ethylene and comonomers) at a velocity faster than the transport velocity of the polymer particles. The velocity of the mixed gas is preferably between 0.5 and 15 m/sec, more preferably between 0.8 and 5 m/sec. The terms "transport velocity" and "rapid fluidization conditions" are well known in the art. For their definitions, see, for example, D. Geldart, Gas Fluidization Technology, p. 155 et seq., J. Wiley & Sons Ltd., 1986.

In the second polymerization zone (downcomer), the polymer particles flow densely due to gravity, resulting in a high solid density (polymer mass per reactor volume) that approaches the bulk density of the polymer.

In other words, the polymer flows vertically downward through the downcomer in plug flow (pack flow mode), so only small amounts of gas are entrapped between the polymer particles.

Such a process makes it possible to obtain from step a) an ethylene polymer having a lower molecular weight than the ethylene copolymer obtained from step b).

Preferably, ethylene is copolymerized to produce a relatively low molecular weight ethylene copolymer (step a) upstream of ethylene copolymerization to produce a relatively high molecular weight ethylene copolymer (step b). To this end, in step a), a mixed gas containing ethylene, hydrogen, a comonomer, and an inert gas is supplied to a first gas-phase reactor, preferably a gas-phase fluidized bed reactor. The polymerization is carried out in the presence of the aforementioned Ziegler-Natta catalyst.

Hydrogen is supplied in an amount that depends on the specific catalyst used, in particular in an amount suitable for obtaining an ethylene polymer having a melt flow index (MIE) of 40 g/10 min or greater in step a). To achieve this MIE range, step a) specifies a hydrogen/ethylene molar ratio of 1 to 4, and is characterized in that the amount of ethylene monomer is 2 to 20% by volume, preferably 5 to 15% by volume, relative to the total volume of gas present in the polymerization reactor. The remainder of the feed mixture is represented by an inert gas and one or more comonomers (if any). The inert gas, necessary to dissipate the heat generated in the polymerization reaction, can easily be selected from nitrogen or saturated hydrocarbons, most preferably propane.

The operating temperature in the reactor in step a) is 50 to 120°C, preferably 65 to 100°C, and the operating pressure is 0.5 to 10 MPa, preferably 2.0 to 3.5 MPa.

In a preferred embodiment, the ethylene polymer obtained in step a) preferably accounts for 30 to 70% by weight of the total ethylene polymer produced throughout the process, for example in the first and second reactors connected in series.

Next, the ethylene polymer and entrained gas from step a) are passed through a solid/gas separation process to prevent the mixed gas from the first polymerization reactor from entering the reactor of step b) (the second gas-phase polymerization reactor). The gas mixture can be recycled to the first polymerization reactor, and the separated ethylene polymer is fed to the reactor of step b). A suitable point for feeding the polymer to the second reactor is at the junction between the downcomer and the riser, where the solids concentration is particularly low and does not adversely affect the flow conditions.

The operating temperature of step b) is in the range of 65 to 95°C, and the pressure is in the range of 1.5 to 4.0 MPa. The second gas-phase reactor is intended to produce a relatively high molecular weight ethylene copolymer by copolymerizing ethylene with one or more comonomers. Furthermore, to broaden the molecular weight distribution of the final ethylene polymer, the reactor of step b) can be easily operated by varying the monomer and hydrogen concentration conditions in the riser and downcomer.

To this end, in step b), the gas mixture coming from the riser entrained with polymer particles can be partially or completely prevented from entering the downcomer, thereby obtaining two zones with different gas compositions. This can be achieved by supplying a gas and/or liquid mixture to the downcomer through a line located at a suitable point in the downcomer, preferably at its upper portion. The gas and/or liquid mixture must have a suitable composition different from that of the gas mixture present in the riser. The flow of the gas and/or liquid mixture can be adjusted so that the upward gas flow countercurrent to the flow of polymer particles, particularly at its top, acts as a barrier to the gas mixture entrained with polymer particles from the riser. In particular, it is advantageous to supply a mixture with a low hydrogen content to produce a higher molecular weight polymer fraction in the downcomer. One or more comonomers may optionally be supplied to the downcomer in step b), together with ethylene, propane, or other inert gases.

The hydrogen/ethylene molar ratio in the downcomer in step b) ranges from 0.005 to 0.2, the ethylene concentration is 0.5 to 15 volume %, preferably 0.5 to 10 volume %, and the comonomer concentration is 0.05 to 1.5 volume %, based on the total volume of gas present in the downcomer. The remainder is propane or a similar inert gas. Because a very low molar concentration of hydrogen is present in the downcomer, by carrying out the process of the present invention, it is possible to combine a relatively large amount of comonomer into the high molecular weight polyethylene fraction.

The polymer particles coming from the downcomer are reintroduced into the riser in step b).

As the polymer particles continue to react and no more comonomer is fed to the riser, the comonomer concentration drops to a range of 0.05 to 1.2 volume percent, based on the total volume of gas present in the riser. In practice, the comonomer content is controlled to obtain the desired density of the final polyethylene. In the riser of step b), the hydrogen/ethylene molar ratio is in the range of 0.01 to 0.5, and the ethylene concentration is comprised between 5 and 20 volume percent, based on the total volume of gas present in the riser. The remainder is propane or other inert gas.

Further details regarding the above polymerization process are described in WO2005019280.

The precursor polyethylene composition (I) thus obtained is then contacted with a radical reaction initiator.

"Contacted" means that the precursor polyethylene composition (I) and the radical initiator are mixed together and react with each other.

The radical reaction initiator is preferably selected from organic peroxides.

Particularly useful organic peroxides are organic monoperoxides and/or organic diperoxides. These organic monoperoxides and diperoxides can have a half-life of 1 hour at temperatures ranging from about 125°C to about 145°C, alternatively from about 130°C to about 140°C, or alternatively from about 132°C to about 136°C. Further alternatives include organic peroxides having a half-life of 0.1 hours at temperatures ranging from about 145°C to about 165°C, or from about 150°C to about 160°C, or alternatively from about 154°C to about 158°C. The organic peroxides can have a molecular weight ranging from about 175 g/mol to about 375 g/mol, or alternatively from about 200 g/mol to about 350 g/mol. Mixtures of two or more peroxides can be used if desired.

Suitable organic peroxides include, but are not limited to, dicumyl peroxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexoxonane, representative examples of 3,6,9-trimethyl-3,6,9-tris(alkyl)-1,2,4,5,7,8-hexoxonane in which the alkyl group is propyl or ethyl, tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate, 1,3-bis(tert-butylperoxyisopropyl)benzene, etc.

Preferably, the organic peroxide is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexane, or, typically, 3,6,9-trimethyl-3,6,9-tris(alkyl)-1,2,4,5,7,8-hexane (where alkyl is propyl or ethyl).

In a preferred embodiment of the present disclosure, the organic peroxide is used in the form of a polyolefin mixture, which is preferably prepared by adding the organic peroxide to a polyolefin powder either in pure form or as a solution in a diluent such as a hydrocarbon. Preferred polyolefin mixtures have an organic peroxide content in the polyolefin mixture ranging from 0.5 to 25% by weight, preferably from 1 to 20% by weight, and more preferably from 2 to 10% by weight.

Preferably, the amount of organic peroxide added corresponds to a content of the initiator in the precursor polyethylene composition (I) of 10 to 100 ppmw, more preferably 25 to 90 ppmw, and particularly 25 to 80 ppmw.

Contact with the radical initiator can be carried out by any means and under conditions known in the art to be effective for radical-initiated reactions in olefin polymers.

It is known that such conditions can be achieved in conventional equipment commonly used to process polymers in the molten state.

In particular, the polyethylene composition of the present disclosure can be prepared by contacting the precursor polyethylene composition (I) with a radical initiator in an extrusion apparatus. Suitable extrusion apparatuses are extruders or continuous mixers. These extruders or mixers are single- or two-stage machines that melt and homogenize the polyethylene composition. Examples of extruders include pin-type extruders, planetary extruders, and co-rotating disk processors. Other possibilities include the combination of a mixer with a discharge screw and/or a gear pump. Preferred extruders are screw extruders, especially those configured as twin-screw machines. Particularly preferred are twin-screw extruders and continuous mixers equipped with a discharge element, especially continuous mixers equipped with two counter-rotating rotors, or extrusion apparatuses comprising at least one co-rotating twin-screw extruder. Machines of this type are common in the plastics industry and are manufactured, for example, by Coperion GmbH, Stuttgart, Germany; KraussMaffei Berstorff GmbH, Hanover, Germany; The Japan Steel Works, Tokyo, Japan; Farrel, Ansonia, USA; or Kobe Steel, Ltd., Japan. Suitable extruder equipment is usually further equipped with a unit for pelletizing the melt, such as an underwater pelletizer.

The contact and reaction temperature is preferably in the range of 180 to 350°C, particularly 180 to 300°C, and is usually above the decomposition temperature of the radical reaction initiator.

In most operations, particularly large-scale operations, contact and reaction times of several initiator half-lives are preferred. This results in a substantially complete reaction and minimizes the possibility of undesirable initiator residue in the polyethylene composition. While small amounts of undecomposed initiator are not harmful, the presence of significant amounts of unreacted initiator can lead to gel formation and other undesirable effects during subsequent processing of the polyethylene composition.

In addition, one or more additives may be provided in the polyethylene composition.

These additives can be added before, during, or after contacting the precursor polyethylene composition (I) with the radical reaction initiator.

Such additives are common in the art. Suitable types of additives for preparing polyethylene compositions are, for example, antioxidants, melt stabilizers, light stabilizers, acid scavengers, lubricants, processing aids, antiblocking agents, slip agents, antistatic agents, antifogging agents, pigments or dyes, nucleating agents, flame retardants or fillers. It is common for several additives to be added. The additives may be of different types. However, it is also possible to add several representatives of one type of additive to the polyethylene composition. Additives of all these types are generally commercially available and are described, for example, in "Handbook of Plastic Additives," by Hans Zweifel, 5th edition, Munich, 2001.
Example

Examples and advantages of the various embodiments, compositions, and methods provided herein are disclosed in the following examples. These examples are merely illustrative and are not intended to limit the scope of the appended claims in any way.

The following analytical methods were used to characterize the polymer compositions.
Melt Flow Index

Measurement was carried out at 190°C and a specified load in accordance with ISO 1133-1 2012-03.
density

Measured at 23°C according to ISO 1183-1:2012.
Molecular weight distribution measurement

Measurement of the average Mw and Mn values, and the resulting Mw/Mn ratio, was performed by high-temperature gel permeation chromatography using the method described in ISO 16014-1, -2, -4, published in 2003. Specific conditions based on the ISO standard were as follows: Solvent: 1,2,4-trichlorobenzene (TCB); Apparatus and solution temperature: 135°C; Concentration detector: PolymerChar (Valencia, Paterna 46980, Spain) IR-4 infrared detector compatible with TCB. A WATERS Alliance 2000 was used, equipped with the following serially connected precolumn: SHODEX UT-G, and separation columns: SHODEX UT 806M (3x) and SHODEX UT 807 (Showa Denko Europe GmbH, Konrad-Zuse-Platz 4, 81829 Munich, Germany).

The solvent was vacuum distilled under nitrogen and stabilized with 0.025 wt% 2,6-di-tert-butyl-4-methylphenol. The flow rate used was 1 ml/min, the injection volume was 500 L, and the polymer concentration ranged from 0.01% to less than 0.05% w/w. Molecular weight calibration was established using monodisperse polystyrene (PS) standards from Polymer Laboratories (now Agilent Technologies, Herrenberger Str. 130, 71034 Böblingen, Germany) ranging from 580 g/mol up to 11,600,000 g/mol, as well as hexadecane.

A calibration curve was then applied to polyethylene (PE) using the universal calibration method (Benoit H., Rempp P. and Grubisic Z., & in J. Polymer Sci., Phys. Ed., 5, 753 (1967)). The Mark-Houwing parameters used here are: PS: k _PS =0.000121 dl/g, α _PS =0.706; PE: k _PE =0.000406 dl/g, α _PE =0.725, valid at a TCB of 135°C. Data recording, calibration, and calculations were performed using NTGPC_Control_V6.02.03 and NTGPC_V6.4.24 (hsGmbH, Hauptstra 36, D-55437 Ober-Hilbersheim, Germany), respectively.
Long Chain Branching Index (LCBI)

The LCB index corresponds to the branching factor g' measured at a molecular weight of 10 ⁶ g/mol. The branching factor g', which allows for the determination of long-chain branching at high molecular weights, was measured by gel permeation chromatography (GPC) combined with multi-angle laser scattering (MALLS). The radius of gyration of each fraction eluted from GPC was measured by analyzing light scattering at various angles using MALLS (detector: Wyatt Dawn EOS, Wyatt Technology, Santa Barbara, CA) (flow rate: 0.6 ml/min, column packed with 30M particles, as described above). A 120 mW laser source with a wavelength of 658 nm was used. The relative refractive index was 0.104 ml/g. Data evaluation was performed using Wyatt ASTRA 4.7.3 and CORONA 1.4 software. The LCB index was determined as follows:

The parameter g' is the ratio of the measured mean square radius of gyration to that of a linear polymer with the same molecular weight. Linear molecules exhibit a g' of 1, while values less than 1 indicate the presence of LCB. The value of g' is a function of moles. The weight M is calculated according to the following formula:
g'(M) = <Rg ² > _{sample, M} / <Rg ² > _{linear reference, M}

In <Rg ² >, M is the root mean square of the radius of gyration due to the molar weight M.

The radius of gyration of each fraction eluted from the GPC was measured by analyzing light scattering at different angles (as previously described, the flow rate was 0.6 ml/min and the column was packed with 30 m particles). Therefore, the molecular weight M and ^<Rg2> _{sample, M} were measured from this MALLS setup, allowing g' to be defined with the measured M = ¹⁰⁶ g/mol. ^<Rg2> _{linear reference, M} was calculated by establishing the relationship between the radius of gyration and molecular weight of linear polymers in solution (Zimm and Stokemeyer WH 1949) and confirmed by measuring a linear PE standard using the same equipment and method as previously described.

For the same protocol, see the following document:

Zimm BH, Stockmayer WH (1949) Dimensions of chain molecules including branches and rings. J Chem Phys 17
Rubinstein M., Colby RH. (2003), Polymer Physics, Oxford University Press. Complex shear viscosity η _0.02 (eta(0.02)) and ER
When measured at an angular frequency of 0.02 rad/sec and 190°, the results are as follows:

The samples were melt-pressed at 200 °C and 200 bar for 4 min to produce plates with a thickness of 1 mm. Disks with a diameter of 25 mm were punched and inserted into the rheometer, which was preheated to 190 °C. Measurements can be performed using any commercially available rotational rheometer. In this case, an Anton Paar MCR300 in plate-plate configuration was used. A so-called frequency scan (after annealing the sample at the measurement temperature for 4 min) was performed at T = 190 °C under a constant strain amplitude of 5% to measure and analyze the stress response of the material over the excitation frequency range ω from 628 to 0.02 rad/s. The rheological properties, i.e., storage modulus G', loss modulus G'', phase lag δ (= arctan(G''/G')), and complex viscosity η*, were calculated as a function of applied frequency using standardized basic software, as follows: η*(ω) = [G'(ω) ² + G''(ω) ² ] ^1/2 /ω. The latter results in η _0.02 at an applied frequency ω of 0.02 rad/s.

ER is determined by the method of R. Shroff and H. Mavridis, "A New Measurement of Polydispersity from Rheological Data of Polymer Melts," J. Applied Polymer Science 57 (1995) 1605 (see also U.S. Pat. No. 5,534,472, column 10, lines 20-30). The calculation method is as follows:

ER=(1.781* ^10-3 )*G'
Here, G''=5,000 dyn/ ^cm2 , where G' is defined as the storage modulus and G'' is defined as the loss modulus.

While defining the ER value as the polydispersity at the high end, we reviewed approaches presented in the literature for extracting polydispersity indices from rheological data. We identified the requirements for an effective polydispersity measurement. Because the ER value does not include contributions from the low MW end, the ER measurement is specifically designed to quantify high MW (or long-term) polydispersity.

As one skilled in the art will recognize, when the minimum G" value is greater than 5,000 dyne/ ^cm2 , determining ER involves extrapolation. The ER value calculated then depends on the degree of nonlinearity in the log G' log G' plot. The temperature, plate diameter, and frequency range are selected to result in a minimum G" value close to or less than 5000 dyne/ ^cm2 , within the resolution of the rheometer.
HMWcopo index

To quantify the crystallization and processability potential of a polymer, the HMWcopo (High Molecular Weight Copolymer) index is used, which is defined as:
HMWcopo=(η _0.02 x t _maxDSC )/(10^5)

This value decreases with increasing ease of processing (low melt viscosity) and the likelihood of rapid crystallization of the polymer. It is also possible to describe and quantify the amount of high molecular weight fraction associated with the melt complex shear viscosity η _0.02 at a frequency of 0.02 rad/s measured as described above, and the amount of mixed comonomer that retards crystallization as quantified by DSC, the heat flow maximum time of steady-state crystallization, t _max .

_tmaxDSC was measured under isothermal conditions at 124°C using a TA Instruments Q2000 differential scanning calorimeter. 5-6 mg of sample was weighed and placed on an aluminum DSC disc. The sample was heated to 200°C at 20 K/min and cooled to the test temperature at 20 K/min to remove thermal history. The isothermal test was then immediately initiated, and the time until crystallization occurred was recorded. The vendor software (TA Instruments) was used to determine the time interval to the maximum heat flow (peak value) of crystallization, _tmaxDSC . Measurements were repeated three times, and the average value was calculated in minutes. If no crystallization was observed beyond 120 minutes under these conditions, the HMWcopo index was further calculated using _tmaxDSC = 120 minutes.

The melt viscosity η _0.02 value was multiplied by the t _{max DSC} value and the product was normalized to a factor of 100000 (10^5).
Swell Ratio

The swell ratio of the polymers of interest was measured at T = 190 °C using a commercially available 30/2/2/20 die (total length 30 mm, effective length = 2 mm, diameter = 2 mm, L/D = 2/2, and 20° approach angle) and a capillary rheometer GOTTFERT Rheotester 2000 and Rheograph 25 equipped with an optical device (GOTTFERT laser diode) to measure the thickness of the extruded strand. The samples were melted in the capillary barrel at 190 °C for 6 min and extruded at a piston speed corresponding to a die shear rate of 1440 ^s .

When the piston reaches a position 96 mm from the die entrance, the extrudate is cut at a distance of 150 mm from the die exit (using an automatic cutting device from GOTTFERT). The extrudate diameter is measured as a function of time using a laser diode at a distance of 78 mm from the die exit. The maximum value corresponds to the D _extrudate . The swell ratio is determined according to the following formula:
SR = (D _extrusion - D _die ) 100% / D _die

where D _die is the corresponding diameter of the die exit as measured by the laser diode.
Environmental stress crack resistance by full notch creep test (FNCT)

The environmental stress crack resistance of polymer samples was measured in aqueous surfactant solutions according to international standard ISO 16770 (FNCT). Polymer samples were compression-molded into 10 mm thick sheets. Square-section bars (10 x 10 x 100 mm) were notched on all four sides perpendicular to the stress direction using a razor blade. Sharp notches 1.6 mm deep were produced using the notching device described by M. Fleissner, Kunststoffe 77 (1987), pp. 45.

The applied load was calculated by dividing the tension by the initial ligament area. The ligament area is the remaining area = total cross-sectional area of the specimen minus the notch area. For FNCT specimens: 10x10 ^mm² - 4 times the trapezoidal notch area = 46.24 ^mm² (remaining cross-section for the fracture process/crack propagation). The specimens were loaded with a constant load of 6 MPa at 50°C in a 2% (by weight) aqueous solution of the non-ionic surfactant ARKOPAL N100, under the standard conditions suggested by ISO 16770. The time to fracture of the specimen was determined.
Weight Swell and Diameter Swell (Uniloy Test)

Weight swell and diameter swell measurements were performed using a Uniloy regression blow molding machine model 5630, simulating industrial process conditions, using a 1-gallon center-weighted bottle mold with an approximate parison drop time of 1.1 seconds.

Gravimetric swelling was measured by adjusting the bottle weight to the desired amount of 90 g with the reference resin Petrothene LR732002 and then comparing the weight of a bottle of the resin under investigation produced under the same machine parameters.

The test bottle is shown in Figure 2.

Thus, weight swelling is given by:
_WB -90
where W _B is the weight of the bottle tested in grams.

Diameter swelling was measured using a bottle with the same weight as the reference resin, i.e., 90 g, by measuring the length of the bottle's burr from the top (including the protruding top burr) to the bottom and along the bottle handle using the graduated lines. The mold relative to the parison was adjusted so that the top burr edge of the reference resin was within the 9 cm mark on the handle.

The machine parameters were as follows:
Prime Mover Load/AMP. - Approximately 40 amps;
Screw speed - approximately 370 rpm (adjusted to adjust parison tail length);
Hydraulic oil temperature -27~32°C (80~90°F);
Mold cooling temperature - inlet 4°C (39°F), outlet 8°C (47°F);
Shot pressure - 7 MPa (1050 psi);
Head pressure - 14 MPa (2000 psi);
Parison fall time - about 1.1 seconds;
Total cycle time - approximately 15.30 seconds;
Heating Zone:
Feed - 330°F;
Transition - 177°C (350°F);
Measurement 1 - 190°C (375°F);
Measurement 2 - 190°C (375°F);
Adapter - 190°C (375°F);
Die - 190°C (375°F);
timer:
Delay before blowing -0.0 seconds;
Clamp pause - 0.0 seconds;
Charge delay -0.0 seconds;
Blow delay -0.45 seconds;
Blow time - 10.0 seconds;
Exhaust time - 2.0 seconds;
Shot delay -0.0 seconds.

The reference resin, Petrothene LR732002, is a Cr-catalyzed ethylene polymer with a FNCT of approximately 0.4 seconds at 6 MPa/50°C, measured as described above.

Other features of Petrothene LR732002 are as follows:
Density: 0.953g/cm ³ ;
MIF: 36g/10min;
MIF/MIE: 100;
ER: 5.4.

In these examples, diameter swelling was considered satisfactory when it fell within the range of 8-10 cm.
Cast Film Measurement

Gel film measurements were performed on an OCS extruder, type ME 202008-V3, with a screw diameter of 20 mm, screw length of 25D, and slit die width of 150 mm. The casting line was equipped with a chill roll and winder (model OCS CR-9). The optical equipment included an OSC film surface analyzer camera, model FTA-100 (flash camera system), with a resolution of 26 m x 26 m. The resin was first purged for 1 hour to stabilize the extrusion conditions, followed by inspection and recording for 30 minutes. The resin was extruded at 220°C with a take-up speed of approximately 2.7 m/min, producing a 50 μm thick film. The cold rolling temperature was 70°C.

As shown in Table 1, the above inspection using a surface analysis camera resulted in the total gel content and the content of gels with a diameter of more than 450 μm.
Comonomer Content

The comonomer content was measured by IR according to ASTM D624898 using a Bruker FT-IR spectrometer Tensor 27 calibrated with a stoichiometric model to measure butyl side chains of hexene in PE. The results were compared with the estimated comonomer content obtained from the mass balance of the polymerization process and were found to be in agreement.
- Process Settings

The polymerization process was carried out under continuous conditions in a plant consisting of two gas-phase reactors connected in series, as shown in the drawing.

The polymerization catalyst was prepared as follows.
Preparation of spherical catalyst supports

A magnesium chloride and alcohol adduct containing approximately 3 moles of alcohol was prepared according to the method described in Example 2 of U.S. Pat. No. 4,399,054, but operated at a speed of 2,000 RPM instead of 10,000 RPM.

The adduct thus obtained was dealcoholized by heat treatment under a nitrogen flow over a temperature range of 50-150° C. up to an alcohol content of 25 wt. %.
Preparation of solid catalyst component

1 _L of TiCl4 was introduced into a 2 L four-necked round-bottom flask purged with nitrogen at 0 °C. Then, 70 g of the spherical _MgCl2 /EtOH adduct thus prepared, containing 25 wt. % ethanol, was added with stirring at the same temperature. The temperature was increased to 130 °C within 3 hours and maintained at that temperature for 60 minutes. The stirring was then stopped, the solid was allowed to settle, and the supernatant was siphoned off. Fresh _TiCl4 was added up to a total volume of 1 L, and the treatment at 130 °C was repeated for 60 minutes. After settling and suction, the solid residue was washed five times with hexane at 50 °C and twice with hexane at 25 °C, and then dried under vacuum at 30 °C.

812 cc of hexane at 10°C was added to a 2 L four-neck glass reactor equipped with a stirrer. While stirring, 50 g of the catalyst component prepared above was introduced at 10°C. While maintaining a constant internal temperature, 15 g of tri-n-octylaluminum (TNOA) in hexane (approximately 80 g/L) and a certain amount of cyclohexylmethyl-dimethoxysilane (CMMS) (so that the TNOA/CMMS molar ratio was 50) were slowly introduced into the reactor, maintaining the temperature at 10°C. After stirring for 10 minutes, a total of 65 g of propylene was introduced into the reactor at a constant rate for 6.5 hours at the same temperature. The entire contents were then filtered and washed three times with hexane (100 g/L) at 30°C. After drying, the resulting prepolymerized catalyst (A) was analyzed and found to contain 55 wt% polypropylene, 2.0 wt% Ti, 9.85 wt% Mg, and 0.31 wt% Al.

Approximately 100 g of the solid prepolymerized catalyst thus prepared was placed in a nitrogen gas purged glass reactor and slurried with 1.0 L of heptane at 50°C.

Next, ethyl acetate (EAA) and tetrahydrofuran (CE) were carefully added dropwise (over 60 minutes) in amounts such that the molar ratio of Mg/EAA was 4 and the molar ratio of Mg to CE was 4.

The slurry was stirred for 1.5 hours while maintaining the internal temperature at 50°C. Then, stirring was stopped, the solids were allowed to settle, and the supernatant liquid was siphoned off. The solids were washed in one portion with anhydrous heptane at 50°C, with stirring, to a volume of up to 1 L. Then, stirring was stopped, the solids were allowed to settle, and the supernatant liquid was siphoned off. The volume was then adjusted back to 1 L with anhydrous heptane, and the temperature was raised to 85°C and maintained with stirring for 2 hours. Then, stirring was stopped, the solids were allowed to settle, and the supernatant liquid was siphoned off.

The solid was washed three times with anhydrous hexane (3 x 1000 mL) at 25°C, collected, dried under vacuum, and analyzed, revealing that the resulting EAA/CE molar ratio was 0.93.
Example 1 - Reference

As shown in the drawing, polyethylene was produced in a series of fluidized bed reactors and a multi-zone circulating reactor with two interconnected reaction zones.

To carry out the polymerization, 9.8 g/h of the above-described solid catalyst was added to the first stirred pre-contact vessel using 0.75 kg/h of liquid propane, and a mixture of triisobutylaluminum (TIBA) and diethylaluminum chloride (DEAC) was also added. The weight ratio of tributylaluminum to diethylaluminum chloride was 7:1. The alkyl to solid catalyst ratio was 5:1. The first pre-contact vessel was maintained at 50°C with an average residence time of 35 minutes. The catalyst suspension in the first pre-contact vessel was continuously transferred to the second stirred pre-contact vessel, which was operated with an average residence time of 35 minutes and maintained at 50°C. The catalyst suspension was then continuously transferred to the fluidized bed reactor (FBR) (1) via line (2).

In the fluidized-bed reactor (1), ethylene was polymerized in the presence of propane as an inert diluent using hydrogen as a molecular weight regulator. 47.5 kg/h of ethylene, 175 g/h of hydrogen, and 11 kg/h of propane were fed to the fluidized-bed reactor (1) via line 3. No comonomer was added. The polymerization was carried out at a temperature of 80°C and a pressure of 3.0 MPa. The selected feed rates resulted in an ethylene concentration of 10.9% by volume in the reactor and a hydrogen/ethylene molar ratio of 2.6 in the reactor.

The polyethylene obtained in the fluidized bed reactor (1) had an MIE of 76 g/10 min and a density of 0.967 g/cm ³ .

The polyethylene obtained in the fluidized-bed reactor (1) was continuously transferred to a multi-zone circulation reactor (MZCR) operated at a pressure of 2.6 MPa measured at the reactor gas outlet and a temperature of 85°C. The riser (4) had an inner diameter of 200 mm and a length of 19 m. The downcomer (5) had a total length of 18 m, with the upper half divided into 5 m sections with an inner diameter of 300 mm and the lower half divided into 13 m sections with an inner diameter of 150 mm. To broaden the molecular weight distribution of the final ethylene polymer, the second reactor was operated under different monomer and hydrogen concentration conditions in the riser (4) and the riser (5). This was achieved by feeding a liquid flow (liquid barrier) of 330 kg/h to the top of the downcomer (5) via line (7). The liquid stream in line 19 is sourced from a condensation step in condenser 6, which operates at 56°C and 2.6 MPa, where a portion of the recycle stream is cooled and partially condensed. A pump is positioned downstream of condenser 6 as shown.

Monomers were fed to the downcomer at three points. At input point 1 (8), 25 kg/h of liquid condensate (10), 9 kg/h of ethylene (9), and 1025 g/h of 1-hexene (9) were introduced. At input point 2 (11), 15 kg/h of liquid condensate (13) and 4.5 kg/h of ethylene (12) were introduced. At input point 3 (14), 15 kg/h of liquid condensate (16) and 4.5 kg/h of ethylene (15) were introduced. 5 kg/h of propane, 27.8 kg/h of ethylene, and 34 g/h of hydrogen were fed to the recycle system via line 19.

The final polymer was discharged discontinuously via line 18.

The first reactor produced approximately 50% by weight (split weight %) of the total amount of final polyethylene resin produced by the first and second reactors.

The final MIF of the resulting precursor polyethylene composition (I) was 39.6/10 min. The resulting density was 0.954 g/cm3.

The amount of comonomer (hexene-1) was approximately 1.05% by weight.

A portion of the resulting polymer powder (polymerized, i.e. without additives) was finally extruded in a Kobe mixer LCM80, adding the following additives:
- 1000 ppm calcium stearate;
-800 ppm Irganox 1010; and -1600 ppm Irgafos 168 (all ppmw).

Irganox 1010® is 2,2-bis[3-[,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropoxy]methyl]-1,3-propanediyl-3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropionate, supplied by BASF SE, Ludwigshafen, Germany.

Irgafos 168® is tris(2,4-di-tert-butylphenyl) phosphite sold by Ciba Geigy.

The polymer powder and the additives were introduced into the mixer inlet at a rate of 170 kg/h and a screw speed of 800 rpm. A throttle gate was located between the two mixing zones and adjusted to a temperature of 220°C in front of the gate. A gear pump was located beyond the second mixing zone and set to a suction pressure of 0.1 MPa (1.0 bar).

The polymerization conditions and polymer data (after extrusion) are reported in Table 1.
Example 2 - Comparative

A portion of the polymer powder from Example 1 (polymerized) was extruded with 1000 ppm calcium stearate, 800 ppm Irganox 1010, 1600 ppm Irgafos 168, and 133 ppm Pergaprop 7.5PP (all ppmw).

Pergaprop 7.5 PP® is a 7.5% by weight mixture of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and polypropylene, supplied by PERGAN GmbH, Bocholt, Germany.

The same extrusion equipment and conditions were used as in Example 1.

The polymer data is reported in Table 1.
Example 3 - Comparison

A portion of the polymer powder from Example 1 (polymerized) was extruded with 1000 ppm calcium stearate, 800 ppm Irganox 1010, 1600 ppm Irgafos 168, and 267 ppm Pergaprop 7.5PP (all ppmw).

The same extrusion equipment and conditions as in Example 1 were used.
Example 4

A portion of the polymer powder from Example 1 (polymerized) was extruded with 1000 ppm calcium stearate, 800 ppm Irganox 1010, 1600 ppm Irgafos 168, and 400 ppm Pergaprop 7.5PP (all ppmw).

The same extrusion equipment and conditions were used as in Example 1.

The polymer data is reported in Table 1.
Example 5

A portion of the polymer powder from Example 1 (polymerized) was extruded with 1000 ppm calcium stearate, 800 ppm Irganox 1010, 1600 ppm Irgafos 168, and 533 ppm Pergaprop 7.5PP (all ppmw).

The same extrusion equipment and conditions were used as in Example 1.

The polymer data is reported in Table 1.
Example 6

A portion of the polymer powder from Example 1 (polymerized) was extruded with 1000 ppm calcium stearate, 800 ppm Irganox 1010, 1600 ppm Irgafos 168, and 800 ppm Pergaprop 7.5PP (all ppmw).

The same extrusion equipment and conditions were used as in Example 1.

The polymer data is reported in Table 1.
Table 1

Note: _C2H4 = _ethylene ; _C6H12 = _hexene ; *2% Arkopal N100 aqueous solution

Claims (16)

1. A polyethylene composition comprising:
1) the MIF/MIE ratio is greater than 125, preferably 130 or greater, more preferably 132 or greater, and in particular greater than 125 and 180 or less, or greater than 130 and 180 or less, or greater than 132 and 180 or less, where MIF is the melt flow index at 190°C under a load of 21.60 kg, and MIE is the melt flow index at 190°C under a load of 2.16 kg, both determined in accordance with ISO 1133-1 2012-03;
2) MIF is 20 to 40 g/10 min, preferably 25 to 35 g/10 min, more preferably 25 to 34 g/10 min;
3) a density of 0.948 to 0.960 g/cm ³ , in particular 0.950 to 0.958 g/cm ³ , measured at 23°C according to ISO 1183-1:2012;
4) The ER value is 5 to 10, preferably 5.2 to 9;
where ER is calculated as follows:
ER=(1.781* ^10-3 )*G'
where G'' = 5,000 dyn/ ^cm2 ,
where:
G' = storage modulus,
G'' = loss modulus;
The polyethylene composition, wherein G' and G'' are both measured by dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190°C. The polyethylene composition according to claim 1, wherein the polyethylene composition is obtainable by contacting a precursor polyethylene composition (I) having a ratio of MIF/MIE 1 ^I ) smaller than MIF/MIE 1), preferably 120 or less, more preferably 115 or less, in particular 90 to 120, or 90 to 115, with a radical initiator, wherein the ratio 1)/1 I ) between MIF/MIE 1) of the final polyethylene composition (after contact with the radical initiator) and MIF/MIE ^{1 I )} of the precursor polyethylene composition (I) is 1.05 or greater, preferably 1.1 or greater, in particular 1.05 or 1.1 to 1.8, or 1.05 or 1.1 to 1.6. The precursor polyethylene composition (I) is
2 ^I ) MIF is 30 to 50 g/10 min, preferably 35 to 45 g/10 min;
3 ^I ) density is 0.948 to 0.960 g/cm ³ , particularly 0.950 to 0.958 g/cm ³ ;
4 ^I ) ER value of 2 to 5, preferably 2 to 4.5. The precursor polyethylene composition (I) is
A) 30 to 70% by weight, preferably 40 to 60% by weight, of an ethylene homopolymer or copolymer (homopolymer is preferred), having a density of at least 0.960 g/cm ³ and a melt flow index MIE according to ISO 1333 at 190°C under a load of 2.16 kg of at least 40 g/10 min, preferably at least 50 g/10 min;
3. The polyethylene composition according to claim 2, comprising: B) 30 to 70 wt. %, preferably 40 to 60 wt. % of an ethylene copolymer having an MIE value less than that of A), preferably less than 0.5 g/10 min. The polyethylene composition according to claim 1, obtained by using a Ziegler-Natta polymerization catalyst in the polymerization stage. The Ziegler-Natta polymerization catalyst
A) a solid catalyst component comprising Ti, Mg, chlorine, and one internal electron donor ED selected from esters of aliphatic monocarboxylic acids (EAA) and another internal donor ED ^I selected from cyclic ethers (CE), in amounts such that the EAA/CE molar ratio is from 0.02 to less than 20;
B) an organoaluminum compound, and optionally
C) an external electron donor compound. The polyethylene composition of claim 1, which is composed of or contains one or more ethylene copolymers. The polyethylene composition is
a swell ratio of 160% or more, in particular 160% to 200%;
- FNCT 6 MPa/50°C for 40 hours or more, in particular 40 to 100 hours;
the comonomer content is less than or equal to 1.7% by weight, in particular between 0.1 and 1.7% by weight, relative to the total weight of the composition;
- MIP is at least 0.3 g/10 min, more preferably at least 0.5 g/10 min, in particular between 0.3 and 4 g/10 min, or between 0.5 and 4 g/10 min, where MIP is the melt flow index measured according to ISO 1133-1 2012-03 at 190°C under a load of 5 kg;
a (MIF/MIE)ER ratio between MIF/MIE and ER of 26 or less, more preferably 25.5 or less, in particular 26-15, or 25.5-15, or 26-20, or 25.5-20;
a long chain branching index LCBI of not more than 0.55, more preferably not more than 0.60, the upper limit being preferably 0.95 in each case;
where LCBI is the ratio of the measured mean square radius of gyration Rg to the mean square radius of gyration for linear PE of the same molecular weight at a molar weight of 1,000,000 g/mol, as measured by GPC-MALLS;
-η _0.02 is 56,000 Pa s or more, particularly 56,000 to 80,000 Pa s;
where η _0.02 is the complex viscosity of the melt measured at a temperature of 190 ^{° C.} in a parallel plate (or so-called plate-plate) rheometer under dynamic oscillatory shear mode with an applied angular frequency of 0.02 rad/s;
the ratio (η _0.02 /1000)/LCBI, i.e. the value between η _0.02 divided by 1000 and LCBI, is between 85 and 150, preferably between 90 and 130;
an HMWcopo index of 0.5 to 5, in particular 0.5 to 3.5,
wherein the HMWcopo index is determined according to the following formula:
HMWcopo = (η _0.02 x t _maxDSC )/(10^5)
2. The polyethylene composition according to claim 1, having at least one of the following additional characteristics: _tmaxDSC is the time required to reach the maximum heat flow of crystallization (in mW) measured by differential scanning calorimetry (DSC) in isothermal mode at a temperature of 124°C under quiescent conditions (time to reach the maximum crystallization rate, equivalent to t½ crystalline half-life), expressed in minutes. 2. A process for preparing a polyethylene composition according to claim 1, wherein the process comprises contacting a precursor polyethylene composition (I) having a ratio of MIF/MIE 1 ^I ) which is smaller than MIF/MIE 1), preferably 120 or less, more preferably 115 or less, in particular 90 to 120, or 90 to 115, with a radical initiator, wherein the ratio 1)/1 ^I ) between MIF/MIE 1) of the final polyethylene composition (after contact with the radical initiator) and MIF/MIE 1 ^I ) of said precursor polyethylene composition (I) is 1.05 or greater, preferably 1.1 or greater, in particular 1.05 or 1.1 to 1.8, or 1.05 or 1.1 to 1.6. The precursor polyethylene composition (I) is
2 ^I ) MIF is 30 to 50 g/10 min, preferably 35 to 45 g/10 min;
3 ^I ) density is 0.948 to 0.960 g/cm ³ , particularly 0.950 to 0.958 g/cm ³ ;
4 ^I ) A process according to claim 9, with the additional feature that the ER value is between 2 and 5, preferably between 2 and 4.5. The process of claim 9, carried out by contacting the radical initiator with the precursor polyethylene composition (I) in an extrusion apparatus at a temperature of 180 to 350°C. The process of claim 9, wherein the radical reaction initiator is selected from organic peroxides. The process of claim 12, wherein the amount of organic peroxide or peroxide added corresponds to a content of initiator in the precursor polyethylene composition (I) of 10 to 100 ppmw, more preferably 25 to 90 ppmw, and especially 25 to 80 ppmw. The process of claim 12, wherein the organic peroxide or peroxide is selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,2,4,5,7,8-hexane, or, typically, 3,6,9-trimethyl-3,6,9-tris(alkyl)-1,2,4,5,7,8-hexane (wherein alkyl is propyl or ethyl). An article of manufacture comprising the polyethylene composition of claim 1. 16. An article of manufacture according to claim 15 in the form of a blow-molded article, in particular handleware.