WO2013006409A1

WO2013006409A1 - Polyethylene with high melt strength for use in extrusion coating

Info

Publication number: WO2013006409A1
Application number: PCT/US2012/044844
Authority: WO
Inventors: Jian Wang; Mehmet Demirors; Nicolas Cardoso MAZZOLA; Jorge Caminero GOMES
Original assignee: Dow Global Technologies Llc; Dow Brasil S.A.
Priority date: 2011-07-06
Filing date: 2012-06-29
Publication date: 2013-01-10
Also published as: TW201313810A; AR087068A1

Abstract

The present invention is a method for producing resin particularly well suited for extrusion coating applications, said method comprising the steps of selecting a target polyethylene resin and then increasing the melt strength of the polyethylene resin by reacting the polyethylene resin with an alkoxy amine derivative, and then forming an extrusion coating from the reacted target polyethylene.

Description

POLYETHYLENE WITH HIGH MELT STRENGTH FOR USE IN EXTRUSION

COATING

Cross-Reference to Related Applications

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61/504,723, filed on July 6, 2011, entitled

"POLYETHYLENE WITH HIGH MELT STRENGTH FOR USE IN EXTRUSION COATING," the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow.

Field of the Invention

This invention pertains to polyethylene extrusion compositions. In particular, the invention pertains to ethylene polymer extrusion compositions having high drawdown and substantially reduced neck-in. The invention also pertains to a method of making the ethylene polymer extrusion composition and a method for making an extrusion coated article, an article in the form of an extrusion profile and an article in the form of an extrusion cast film.

Background and Summary of the Invention

It is known that low density polyethylene (LDPE) made by high-pressure polymerization of ethylene with free -radical initiators as well as homogeneous or heterogeneous linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) made by the copolymerization of ethylene and oc-olefins with metallocene or

Ziegler coordination (transition metal) catalysts at low to medium pressures can be used, for example, to extrusion coat substrates such as paper board, paper, and/or polymeric substrates; to prepare extrusion cast film for applications such as disposable diapers and food packaging; and to prepare extrusion profiles such as wire and cable jacketing.

However, although LDPE generally exhibits excellent extrusion processability and high extrusion drawdown rates, LDPE extrusion compositions lack sufficient abuse resistance and toughness for many applications. For extrusion coating and extrusion casting purposes, efforts to improve abuse properties by providing LDPE compositions having high molecular weights (i.e., having melt index, I₂, less than about 2 g/lOmin) are not effective since such compositions inevitably have too much melt strength to be successfully drawn down at high line speeds. While LLDPE and ULDPE extrusion compositions offer improved abuse resistance and toughness properties and MDPE (medium density polyethylene) extrusion compositions offer improved barrier resistance (against, for example, moisture and grease permeation), these linear ethylene polymers exhibit unacceptably high neck-in and draw instability; they also exhibit relatively poor extrusion processability compared to pure

LDPE. One proposal commonly used in the industry is to blend LDPE with LLDPE. With LDPEs currently used, large amounts (e.g. more than 60%) of LDPE must be used in order to achieve the required neck-in. In some circumstances, the availability of LDPE may be limited, or there may be other reasons for desiring a lower level of LDPE, without unduly increasing neck-in. It has been discovered that if the melt strength of the LLDPE component can be increased without a significant decrease in melt index, the neck-in of its blend with LDPE can be reduced while still maintaining similar extrusion processability. This allows the level of the LDPE portion in the blend to be reduced and the level of the LLDPE portion to be increased, which in turn allows the LLDPE portion to be carefully tailored to meet particular requirements such as sealability or toughness. In the preferred method of the present invention the neck-in is less than approximately two and a half inches (1.25" per side) at a haul-off rate of approximately 440 feet/minute. The neck-in generally decreases with increasing haul-off rates, making neck-in particularly problematic when using older equipment which is limited in the haul off rates obtainable. The practical range of melt index is from about 3 to about 30 g/10 min in most coating applications, and the compositions of the present invention can cover this entire range. It is desirable that the maximum operating speed of the extrusion coating equipment not be limited by the properties of the resin being used. Thus it is desirable to use resin which exhibits neither draw instability nor breaking before the maximum line speed is reached. It is even more desirable that such resin exhibit very low neck-in, less than about 2.5 inches. The resins provided in this invention exhibit low neck-in and excellent draw stability while the drawdown capability required is obtained by selecting the correct melt index. Typically the melt index of the overall blend is in the range of 5-15 g/ 10 min. It is a further feature of this invention that it provides a resin composition at for example 8 MI that will be suitable for extrusion on both older equipment having slow take-off and modern high speed equipment. In both situations the neck-in can be less than 2.5 inches. Melt Strength can be enhanced by using resins with higher molecular weight, but such resins will generally require more robust equipment and more energy use because they tend to generate higher extrusion pressure during the extrusion process. Therefore, properties must be balanced to provide an acceptable combination of physical properties and processability.

The ethylene/alpha-olefin interpolymer of the present invention provides good neck- in properties. The present invention is a new process for increasing the melt strength of polyethylene involving reacting molten polyethylene with an alkoxyamine derivative through regular extrusion processing. Accordingly, one aspect of the invention is a method for increasing the melt strength of a polyethylene resin comprising first selecting a polyethylene resin having a density, as determined according to ASTM D792, in the range of from 0.90 g/cm³ to 0.955 g/cm³, and a melt index, as determined according to ASTM D1238 (2.16 kg, 190°C), in the range of from 3 g/lOmin to 30 g/10 min and then reacting an alkoxy amine derivative with the polyethylene resin in an amount and under conditions sufficient to increase the melt strength of the polyethylene resin.

The present invention may also increase the Viscosity Ratio of the resin, indicating good processability.

Detailed Description of the Invention

In its broadest sense, the present invention is a method for producing improved extrusion coatings in which the method involves increasing the melt strength of a target polyethylene resin. Polyethylene resin includes all polymers or polymer blends which are derived at least 50% by weight from ethylene monomer units. This includes materials known in the art as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and low density polyethylene made using high pressure reactors (LDPE).

The target polyethylene resin selected should have a density, as determined according to ASTM D792, in the range of from 0.90 g/cm³ to 0.955 g/cm³ and a melt index, as determined according to ASTM D1238 (2.16 kg, 190°C), in the range of from 3 g/lOmin to 30 g/10 min, Suitable polyethylene resins can be produced with conventional Ziegler Natta or Chromium catalysts but also with metallocene or single site catalysts. Such resins may have monomodal or multimodal molecular weight distributions. Preferred target resins are Linear Low Density Resins having a density of from 0.90 to 0.93 g/cm³' more preferably from 0.905 to 0.920 g/cm3, and a melt index of from 4 to 20 g/10 min, more preferably from 6 to 10 g/10 min.

Once the target polyethylene resin is selected, it is reacted with an alkoxy amine derivative. For purposes of the present invention "alkoxy amine derivatives" includes nitroxide derivatives. The alkoxy amine derivative is added in an amount and under conditions sufficient to increase the melt strength of the polyethylene resin. The alkoxy amine derivatives correspond to the formula:

where Ri and R₂ are each independently of one another, hydrogen, C4-C42 alkyl or C4-C42 aryl or substituted hydrocarbon groups comprising O and/or N, and where Ri and R₂ may form a ring structure together; and where R₃ is hydrogen, a hydrocarbon or a substituted hydrocarbon group comprising O and/or N. Preferred groups for R₃ include -Ci-Ci₉alkyl; - C₆-C₁₀aryl; -C₂-C₁₉akenyl; -0-C C₁₉alkyl; -O-C₆-C₁₀aryl; -NH-C C₁₉alkyl; -NH-C₆- Cioaryl; -N-(Ci-Ci₉alkyl)_2.. R₃ most preferably contains an acyl group.

The preferred compound may form nitroxyl radical (Rl)(R2)N-0* or amynil radical (R1)(R2)N* after decomposition or thermolysis.

A particularly preferred species of alkoxy amine derivative is 9-(acetyloxy)-3,8,10- triethyl-7,8,10-trimethyl-l,5-dioxa-9-azaspiro[5.5]undec-3-yl]methyl octadecanoate which has the followi

Examples of some preferred species for use in the present invention include the following:

In general hydroxyl amine esters are more preferred with one particularly favored hydroxyl amine ester being 9-(acetyloxy)-3,8,10-triethyl-7,8,10-trimethyl-l,5-dioxa-9- azaspiro[5.5]undec-3-yl]methyl octadecanoate.

The alkoxy amine derivatives are added in an amount sufficient to increase the melt strength and/or increase the elongational viscosity to the desired level. In general the alkoxy amine derivatives are added in an amount of from 1 to 900 ppm of the total amount of polyethylene polymer by weight (that is from 1 to 900 parts alkoxy amine derivative per million parts (by weight) of target resin plus carrier resin, if any), more preferably from 50 to 500 ppm, more preferably from 75 to 400 ppm and still more preferably from 100 to 300 ppm.

The addition to the polyethylene polymer can be carried out in all customary mixing machines in which the polymer is melted and mixed with the additives. Suitable machines are known to those skilled in the art. They are predominantly mixers, kneaders and extruders.

The process is preferably carried out in an extruder by introducing the additive during processing. Particularly preferred processing machines are single-screw extruders, contra rotating and co rotating twin-screw extruders, planetary-gear extruders, ring extruders or co-kneaders. It is also possible to use processing machines provided with at least one gas removal compartment to which a vacuum can be applied. Suitable extruders and kneaders are described, for example, in Handbuch der Kunststoftextrusion, Vol 1 Grundlagen, Editors F. Hensen, W. Knappe, H. Potente, 1989, pp. 3-7, ISBN.3-446-14339- 4 (Vol 2 Extrusionsanlagen 1986, ISBN 3-446-14329-7). For example, the screw length can be 1-60 times the screw diameter, preferably 35-48 times the screw diameters. The rotational speed of the screw is preferably 10-600 rotations per minute (rpm), more preferably 25-300 rpm. It is also possible to first prepare a concentrated mixture of the additive in a carrier polyethylene resin, preferably at 1,000 to 10,000 ppm, and then introduce this concentrate or "masterbatch" via an extruder into a melted polyethylene using a static mixer to blend the two materials, preferably at 1 to 20 wt of the concentrate in the melted resin. The concentrate could be processed in an extruder, preferably at temperatures from 180 to 220°C. The temperatures in the static mixer could range from 200 to 250°C, with a residence time in the mixer ranging from 1 to 10 minutes.

The maximum throughput is dependent on the screw diameter, the rotational speed and the driving force. The process of the present invention can also be carried out at a level lower than maximum throughput by varying the parameters mentioned or employing weighing machines delivering dosage amounts.

If a plurality of components is added, these can be premixed or added individually. The polymers need to be subjected to an elevated temperature for a sufficient period of time, so that the desired changes occur. The temperature is generally above the softening point of the polymers. In a preferred embodiment of the process of the present invention, a temperature range lower than 280°C, particularly from about 160°C to 280°C is employed. In a particularly preferred process variant, the temperature range from about 200°C to 270°C is employed.

The period of time necessary for reaction can vary as a function of the temperature, the amount of material to be reacted and the type of, for example, extruder used. It is usually from about 10 seconds to 30 minutes, in particular from 20 seconds to 20 minutes.

The alkoxy amine derivative can advantageously be added to the mixing device by use of a masterbatch. As will be appreciated by those of ordinary skill in the art, the carrier resin for the masterbatch should be chosen to be compatible with the resin to be modified. LDPE high pressure low density polyethylene polymers (referred to in the industry as "LDPE") were unexpectedly found to be the preferred carrier due to the lower reactivity as evidenced by little variation of the extrusion pressure during masterbatch production.

HDPE may be a better carrier as it will react even less because it does not have tertiary carbons and very low vinyls. Another advantage of this invention is the discovery that polypropylene is not a good carrier for this additive, as it tends to degrade at typical processing temperatures. Another discovery is that the carrier resin should be substantially free of any antioxidant additives, meaning that the carrier resin should preferably have less than 1,000 ppm of antioxidant additives, preferably less than 500 ppm and more preferably less than 100 ppm by weight, as antioxidants tend to suppress the activity of the additive.

The preferred carrier resin should be compatible with the application at hand; it should have similar viscosity with the target polyethylene resin with which it is going to be blended. It should be preferably an LDPE or HDPE resin with minimal trisubstituted unsaturation units, preferably fewer than 70 per 1,000,000 carbon atoms. The preferred carrier resin should have a molecular weight (Mn) that is less than 50,000 so that it is easy to process, as demonstrated by the pressure drop through the extruder. The carrier resin could incorporate other additives for processing aids but it should be substantially free of antioxidant compounds, preferably containing less than 1,000 ppm, more preferably less than 500 ppm and still more preferably less than 100 ppm by weight, of any antioxidant compound.

The target polyethylene resin could be a copolymer of ethylene with any alkene monomer containing 3 to 12 carbons. Preferably, the target polyethylene resin should have a level of trisubstituted unsaturation units per 1,000,000 carbon atoms in the range of from 200 to 450. It should have a molecular weight slightly lower than the carrier resin, as measured by the melt index (g/10 min). Preferably, the melt index of the polyethylene resin should be higher by 0.2-0.5 units (g/10 min) than the final desired resin. Preferably, the polyethylene resin should contain minimal or no antioxidant additives, and any additives should be well- dispersed in the resin prior to being blended with the carrier resin.

The amount of the alkoxy amine derivative material in the carrier resin should be in the range of 0.1 to 30% by weight, preferably from 0.1 to 5%, and more preferably in the range of 0.2 to 1%. The amount of the masterbatch is added so that the alkoxy amine derivative is added to the target product is in the range of 1 to 900 ppm, more preferably from 50 to 500 ppm, more preferably from 75 to 400 ppm and still more preferably from 100 to 300 ppm. It will be readily understood by one of ordinary skill in the art that the amount of alkoxy amine derivative in the final product will be reduced from the added amounts, as the compound reacts with the target and carrier polyethylene. It should be understood that after the alkoxy amine derivative has been allowed to react with the target resin, it may be desirable to add one or more antioxidant additives, to protect the properties of the modified target resin. One way to accomplish this is to blend the resin after reaction with the alkoxy amine derivative with another resin that is rich in antioxidants.

As previously indicated, it may be advantageous to use the reacted target polyethylene resin together with a low density polyethylene resin. In such compositions, the reacted target polyethylene resin may comprise from 1 to 99 percent by weight of the reacted target polyethylene resin, more preferably from 1 to 90 percent, with the low density polyethylene composition comprising from 1 to 90 percent, preferably 10 to 90 percent. In many applications it may be desirable for the composition to comprise less than 60% of the low density polyethylene composition.

Testing Methods

Melt Index

Melt index, or I₂, is measured in accordance with ASTM D 1238, Condition

190°C/2.16 kg, and is reported in grams eluted per 10 minutes. The I₁₀ was measured in accordance with ASTM D 1238, Condition 190°C/10 kg, and was reported in grams per 10 minutes.

Density

Compression molded samples for density measurement are prepared according to

ASTM D 4703. Density measurements are performed following ASTM D792, Method B within one hour of molding.

Dynamic Mechanical Spectroscopy

Resins were compression-molded into "3 mm thick x 1 inch" circular plaques at 350°F for five minutes, under 1500 psi pressure in air. The sample was then taken out of the press, and placed on the counter to cool.

A constant temperature frequency sweep was performed using a TA Instruments

"Advanced Rheometric Expansion System (ARES)," equipped with 25 mm (diameter) parallel plates, under a nitrogen purge. The sample was placed on the plate, and allowed to melt for five minutes at 190°C. The plates were then closed to a gap of 2 mm, the sample trimmed (extra sample that extends beyond the circumference of the "25 mm diameter" plate is removed), and then the test was started. The method had an additional five minute delay built in, to allow for temperature equilibrium. The experiments were performed at

190°C over a frequency range of 0.1 to 100 rad/s. The strain amplitude was constant at

10%. The stress response was analyzed in terms of amplitude and phase, from which the storage modulus (G'), loss modulus (G"), complex modulus (G*), complex viscosity η*, tan

(δ) or tan delta, viscosity at 0.1 rad/s (V0.1), the viscosity at 100 rad/s (V100), and the

Viscosity Ratio (V0.1/V100) were calculated.

Determination of melt elastic modulus G' at G"=500 Pa at 190°C:

In order to calculate the corresponding G' value at G" equals to 500 Pa, the G' vs. G" data from dynamic mechanical spectroscopy measurement at 190°C was interpolated using the Akima spline interpolation algorithm with the 3rd order piecewise polynomial fits.

This is described in detail in

Hiroshi Akima. "A new method of interpolation and smooth curve fitting based on local procedures", J. ACM, 17(4), 589-602 (1970).

Melt Strength

Melt strength measurements were conducted on a Gottfert Rheotens 71.97 (Goettfert Inc.; Rock Hill, SC), attached to a Gottfert Rheotester 2000 capillary rheometer. The melted sample (about 25 to 30 grams) was fed with a Goettfert Rheotester 2000 capillary rheometer, equipped with a flat entrance angle (180 degrees) of length of 30 mm, diameter of 2.0 mm, and an aspect ratio (length/diameter) of 15. After equilibrating the samples at 190°C for 10 minutes, the piston was run at a constant piston speed of 0.265 mm/second. The standard test temperature was 190°C. The sample was drawn uni-axially to a set of accelerating nips located 100 mm below the die, with an acceleration of 2.4 mm/s². The tensile force was recorded as a function of the take-up speed of the nip rolls. Melt strength was reported as the plateau force (cN) before the strand broke. The following conditions were used in the melt strength measurements: plunger speed = 0.265 mm/second; wheel acceleration = 2.4 mm/s²; capillary diameter = 2.0 mm; capillary length = 30 mm; and barrel diameter = 12 mm.

Triple Detector Gel Permeation Chromatography (TDGPC) - Conventional GPC

For the GPC techniques used herein (Conventional GPC, Light Scattering GPC, and gpcBR), a Triple Detector Gel Permeation Chromatography (3D-GPC or TDGPC) system was used. This system consists of a Waters (Milford, Mass) model 150C High Temperature Chromatograph (other suitable high temperatures GPC instruments include Polymer Laboratories (Shropshire, UK) Model 210 and Model 220), equipped with a Precision Detectors (Amherst, Mass.) 2-angle laser light scattering (LS) detector Model 2040, an IR4 infra-red detector from Polymer ChAR (Valencia, Spain), and a Viscotek (Houston, Texas) 150R 4-capillary solution viscometer (DP).

A GPC with these latter two independent detectors and at least one of the former detectors is sometimes referred to as "3D-GPC" or "TDGPC," while the term "GPC" alone generally refers to conventional GPC. Data collection is performed using Viscotek TriSEC software, Version 3, and a 4-channel Viscotek Data Manager DM400. The system is also equipped with an on-line solvent degassing device from Polymer Laboratories (Shropshire, United Kingdom).

The eluent from the GPC column set flows through each detector arranged in series, in the following order: LS detector, IR4 detector, then DP detector. The systematic approach for the determination of multi-detector offsets is performed in a manner consistent with that published by Balke, Mourey, et al. (Mourey and Balke, Chromatography Polym., Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym., Chapter 13, (1992)), optimizing triple detector log (MW and intrinsic viscosity) results from using a broad polyethylene standard, as outlined in the section on Light Scattering (LS) GPC below in the paragraph following Equation (5).

Suitable high temperature GPC columns can be used, such as four 30 cm long Shodex HT803 13 micron columns, or four 30 cm Polymer Labs columns of 20-micron mixed-pore-size packing (MixA LS, Polymer Labs). Here, the MixA LS columns were used. The sample carousel compartment is operated at 140°C, and the column compartment is operated at 150°C. The samples are prepared at a concentration of "0.1 grams of polymer in 50 milliliters of solvent." The chromatographic solvent and the sample preparation solvent is 1 ,2,4-trichlorobenzene (TCB) containing 200 ppm of 2,6-di-tert-butyl- 4methylphenol (BHT). The solvent is sparged with nitrogen. The polymer samples are gently stirred at 160°C for four hours. The injection volume is 200 microliters. The flow rate through the GPC is set at 1 ml/minute. Conventional GPC

For Conventional GPC, the IR4 detector is used, and the GPC column set is calibrated by running 21 narrow molecular weight distribution polystyrene standards. The molecular weight (MW) of the standards ranges from 580 g/mol to 8,400,000 g/mol, and the standards are contained in 6 "cocktail" mixtures. Each standard mixture has at least a decade of separation between individual molecular weights. The standard mixtures are purchased from Polymer Laboratories. The polystyrene standards are prepared at "0.025 g in 50 mL of solvent" for molecular weights equal to or greater than 1,000,000 g/mol, and at "0.05 g in 50 mL of solvent" for molecular weights less than 1,000,000 g/mol. The polystyrene standards are dissolved at 80°C, with gentle agitation, for 30 minutes. The narrow standards mixtures are run first, and in order of decreasing highest molecular weight component to minimize degradation. The polystyrene standard peak molecular weights are converted to polyethylene molecular weight using Equation (1) (as described in Williams and Ward, J. Polym. Sci., Polym. Letters, 6, 621 (1968)):

Mpolyethylene = A x (Mpolystyrene)^B (Eq. 1), where M is the molecular weight of polyethylene or polystyrene (as marked), and B is equal to 1.0. It is known to those of ordinary skill in the art that A may be in a range of about 0.38 to about 0.44, and is determined at the time of calibration using a broad polyethylene standard. Use of this polyethylene calibration method to obtain molecular weight values, such as the molecular weight distribution (MWD or Mw/Mn), and related statistics, is defined here as the modified method of Williams and Ward. The number average molecular weight, the weight average molecular weight, and the z- average molecular weight are calculated from the following equations.

EXPERIMENTAL

The linear low density polyethylene, LLDPE1, used is produced in a dual reactor configuration using constrained geometry catalysts and has an 8.6 melt index (I₂ or MI), 0.913 g/cm³ density, without any antioxidant package.

Examples were produced from this LLDPE1 and extruded with different concentrations of an alkoxy amine derivative additive. The specific additive used is 9- (acetyloxy)-3,8,10-triethyl-7,8,10-trimethyl-l,5-dioxa-9-azaspiro[5.5]undec-3-yl]methyl octadecanoate, which was added as an LDPE masterbatch having less than 1% of the additive (note that the ppm levels reported below refer to the active ingredient only and not the entire masterbatch).

LLDPE1 and the alkoxy amine derivative additive are compounded in a 30mm co- rotating, intermeshing Coperion Werner-Pfleiderer ZSK-30 (ZSK-30) twin screw extruder. The ZSK-30 has ten barrel sections with an overall length of 960 mm and a 32 length to diameter ratio (L/D). A two hole strand die is used without a breaker plate or screen pack. The extruder consists of a DC motor, connected to a gear box by V-belts. The 15HP motor is powered by a GE adjustable speed drive located in a control cabinet. The control range of the screw shaft speed is 1: 10. The maximum screw shaft speed is 500 RPM. A pressure transducer was positioned in front of the die to measure die pressure.

The extruder has 8 heated/cooled barrel sections along with a 30 mm spacer, which makes up five temperature controlled zones. It has a cooled only feed section and a heated only die section, which is held together by tie-rods and supported on the machine frame. Each section can be heated electrically with angular half-shell heaters and cooled by a special system of cooling channels.

The screws consist of continuous shafts on which screw-flighted components and special kneading elements are installed in any required order. The elements are held together radially by keys and keyways and axially by a screwed-in screw tip. The screw shafts are connected to the gear-shafts by couplings and can easily be pulled out of the screw barrel for dismantling.

A Conair pelletizer is used to pelletize the blends. It is a 220 volt variable speed, solid cutter unit. The variable speed motor drives a solid machined cutting wheel, which in turn drives a fixed metal roller. A movable rubber roller presses against the fixed roller and helps pull the strands by friction into the cutting wheel. The tension on the movable roller may be adjusted as necessary.

The temperatures are set in the feed zone, 4 zones in the extruder, and the die as:

Feed: 80°C

Zone 1: 160°C

Zone 2: 180°C

Zone 3: 185°C

Zone 4: 190°C

Die: 230°C

The screw shaft speed is set at 325 revolutions per minute (RPM), resulting in an output rate of approximately 40 lb/hr.

LLDPE1 is extruded with 200 ppm and 300 ppm of the alkoxy amine derivate additive. LLDPE1 is also extruded alone as a comparative. These three samples along with LLDPE1 before extrusion are characterized, with the results shown in Table 1. With the addition of the alkoxy amine derivate additive, the melt index decreases, the melt index ratio (110/12) remains about the same, the Viscosity Ratio increases, the tan delta decreases, the G' at G"=500 Pa increases and the melt strength increases as compared to the initial LLDPE1. Further it can be seen that there are no significant differences between the virgin LLDPE1 and the extruded LLDPE1 without the addition of the alkoxy amine derivative additive. This indicates that the change in the properties of the inventive examples were due to the addition of the alkoxy amine derivate additive. The processing parameters are listed in Table 2. With the addition of the alkoxy amine derivate additive, neck-in at both 440 feet per minute (fpm) and 880 fpm are significantly reduced compared to CE-1, drawdown remains greater than 1500 fpm, while extrusion processability is also improved as reflected by the lower horse power, amperage and head pressure,

Extrusion coating

All coating experiments are performed on a Black-Clawson extrusion

coating/lamination line. The amount of neck-in (the difference in actual coating width versus deckle width with a 6" (15 cm) air gap) is measured at 440fpm and 880 fpm resulting in 1 mil and ½ mil coatings respectively. Drawdown is the speed at which edge

imperfections were noticed or that speed at which the molten curtain completely tears from the die. Although the equipment is capable of haul-off speeds of 3000 fpm, in these experiments the maximum speed used was 1500 fpm. This is normal operation and is done to conserve paper and maximize the number of experiments that can be done on the machine for each roll of paper board purchased. Motor current is also recorded on the 150 horsepower 3 ½ inch diameter extruder during screw speeds of approximately 90 rpm resulting in 250 lb/h throughput. The amount of backpressure is recorded for each polymer without changing the valve position. The blends for use in the extrusion coating experiments consisted of 70% by weight of the LLDPE of Comparative Example 1 and Examples 3 and 4 together with a LDPE produced in an autoclave reactor having a melt index of 8.0 g/10 min and a density of 0.918 g/cm³. Blends of the various components are produced by weighing out the pellets and then tumble blending samples until a homogenous blend was obtained (approximately 30 minutes for each sample).

Table 1: Melt Indexes, Densities, DMS Viscosity, DMS G' at G"=500 Pa, Melt strength, and TDGPC data from conventional calibration (cc) of LLDPE1, LLDPE1 Extruded, and

LLDPE1 with 200 ppm and 300 ppm alkoxy amine derivate additive.

Table 2: Neck-in, drawdown and other processing conditions at the extrusion coating trial.

Although the invention has been described in considerable detail through the preceding description and examples, this detail is for the purpose of illustration and is not to be construed as a limitation on the scope of the invention as it is described in the appended claims. All United States patents, published patent applications and allowed patent applications identified above are incorporated herein by reference.

Claims

WHAT IS CLAIMED IS:

1) A method for producing resin suitable for extrusion coating, said method comprising the steps of:

a) selecting a target polyethylene resin having a density, as determined according to ASTM D792, in the range of from 0.90 g/cm³ to 0.955 g/cm³, and a melt index, as determined according to ASTM D1238 (2.16 kg, 190°C), in the range of from 3 g/lOmin to 30 g/10 min;

b) reacting an alkoxy amine derivative in an amount less than 500 parts derivative per million parts by weight of total polyethylene resin with the target polyethylene resin in an amount and under conditions sufficient to increase the melt strength of the polyethylene resin; and

c) using the reacted target polyethylene resin in an extrusion coating process.

2) The method of Claim 1 wherein the alkoxy amine derivative corresponds to the formula:

where Ri and R₂ are each independently of one another, hydrogen, C4-C42 alkyl or C4-C42 aryl or substituted hydrocarbon groups comprising O and/or N, and where Ri and R₂ may form a ring structure together; and R3IS hydrogen, a hydrocarbon or a substituted hydrocarbon group comprising O and/or N.

3) The method of claim 1 wherein the alkoxy amine derivative is a hydroxylamine ester.

4) The method of claim 3 wherein the hydroxyl amine ester is hydroxyl amine ester being 9-(acetyloxy)-3,8,10-triethyl-7,8,10-trimethyl-l,5-dioxa-9-azaspiro[5.5]undec-3- yljmethyl octadecanoate.

5) The method of claim 1 wherein from 50 to 500 ppm alkoxy amine derivative is reacted.

6) The method of claim 1 wherein from 75 to 400 ppm alkoxy amine derivative is reacted.

7) The method of claim 1 wherein from 100 to 300 ppm alkoxy amine derivative is

reacted.

8) The method of claim 1 wherein the target polyethylene resin has a density of from .

0.905 to 0.920 g/cm3.

9) The method of claim 1 wherein the target polyethylene resin has a melt index of from 6 to 10 g/10 min. 10) The method of Claim 1 wherein the target resin is a linear low density polyethylene resin.

11) An extrusion coating comprising:

a) from 10 to 99 percent by weight of a polyethylene polymer made by the process of: i) selecting a target polyethylene resin having a density, as determined according to

ASTM D792, in the range of from 0.90 g/cm³ to 0.955 g/cm³, and a melt index, as determined according to ASTM D1238 (2.16 kg, 190°C), in the range of from 3 g/lOmin to 30 g/10 min;

ii) reacting said target polyethylene with an alkoxy amine derivative in an amount less than 500 parts derivative per million parts by weight of total polyethylene resin under conditions sufficient to increase the melt strength of the target polyethylene resin; and

b) from 1 to 90 percent by weight of a low density polyethylene composition.

12) The extrusion coating of claim 11 wherein the extrusion coating comprises less than about 60% by weight of the low density polyethylene composition.

13) The extrusion coating of claim 11 wherein said target polyethylene has a density in the range of from 0.905 to 0.92 g/cm³.

14) The extrusion coating of claim 11, wherein said target polyethylene has a melt index in the range of 6 to 10 g/10 minutes.

15) The coating of claim 11 wherein from 50 to 500 ppm alkoxy amine derivative is reacted.

16) The coating of claim 11 wherein from 75 to 400 ppm alkoxy amine derivative is reacted.

17) The coating of claim 11 wherein from 100 to 300 ppm alkoxy amine derivative is

reacted.

18) The coating of claim 11 wherein the target polyethylene resin has a density of from .

0.905 to 0.920 g/cm3.

19) The coating of claim 11 wherein the target resin comprises a linear low density

polyethylene resin.

20) The coating of claim 19 wherein the target resin further comprises a low density

polyethylene ("LDPE") resin.