ENHANCED FOAM RESIN

TECHNICAL FIELD

The present invention relates to blends of polyethylene that have an enhanced melt strength and are useful in the manufacture of foams and planks having improved properties.

BACKGROUND ART

The use of single site catalyzed polyethylene in blends for foam applications has been taught since at least as early as 1990's. United States Patents

5,288,762; 5,340,840; 5,369,136; 5,387,620; and 5,407,965 all in the name of Park assigned to The Dow Chemical Company, related to a patent filed Oct. 15, 1991 and or filed April of 1993. These patents disclose foams which are blends of substantially linear polyethylene (e.g. have long chain branches and/or improved rheology) with other ethylenic polymers. The foams are typically crosslinked. The blends of the present invention include single site polymer which do not contain long chain branches. In some embodiments the foams of the present invention are not crosslinked.

United States Patents 6,545,094 and 6,723,793, having an earliest filing date of Aug. 9, 2001 in the name of Oswald assigned to Dow Global Technologies Inc., teach polyethylene blends of single site catalyzed linear polyethylene resin (i.e. it has no long chain branches) with low density polyethylene. The blend has a flex modulus of lower than 30,000 psi or greater than 100,000 psi. The blends of the present invention have a flextural modulus between 30,000 and 100,000 psi.

United States Patent 6,096,793 issued Aug. 1 , 2000 from an application filed Dec. 22, 1998 in the name of Lee at al. assigned to Sealed Air Corporation, discloses a foam of a blend of polyethylenes, the blend having a melt flow index (I2 2.16 kg and 190°C) greater than 10 g/10 minutes. The blends of the present invention comprise a LDPE and a LLDPE having a melt flow index (I2 2.16 kg 190°C) of less than 10 g/10 minutes.

United States Patent 7,173,069 (corresponds to GB patent 2,395,948) issued Feb. 6, 2007 from an application filed Dec. 4, 2003 in the name of Swennen assigned to Pregis Innovative Packaging Inc., teaches blending a Ziegler Natta catalyzed polyethylene resin with a high pressure low density polyethylene resin wherein the difference in maximum crystallization peak between the two resins is greater than 8°C. The blends of the present invention have a difference in maximum crystallization peak between the two resins is less than 6°C. Additionally the blends do not contain a Ziegler Natta resin.

The present invention seeks to provide a resin blend of a single site catalyzed polyethylene and a high pressure low density polyethylene resin having an improved melt strength. The resin blend is suitable for use in the production of foams.

DISCLOSURE OF INVENTION

In one embodiment the present invention seeks to provide a polyethylene foam having a density from 10 kg/m ³ (0.6 pounds per cubic foot (pcf)) to 20 kg/m ³ (1 .25 pcf) comprising a blend of polyethylene polymers comprising:

i) from 90 to 60 weight % of polyethylene homopolymer prepared in a high pressure process having a density from 0.915 to 0.920 g/cc, a melt index from 0.70 to 2.5 g/10 min (at 2.16 kg/190°C), a maximum melting temperature from (DSC) 105°C to 1 12°C; a maximum crystallization temperature from 95 to 100°C; a melt strength from 2.5 to 4.5 cN as determined by the Rosand Constant Haul Off method; and

ii) from 10 to 40 weight % of a single site catalyzed polyethylene copolymer having a density from 0.915 to 0.918 g/cc; a melt index from 0.60 to 1 .2 g/10 min (at 2.16 kg/190°C); a maximum melting temperature (DSC) from 108 to

1 12°C; a maximum crystallization temperature (DSC) within 6°C of that of component i); a flexural modulus between 206 MPa (30,000 psi) and 620 MPa (90,000 psi), and a melt strength from 1 to 2 cN as determined by the Rosand Constant Haul Off method;

said blend having a melt strength from 3.50 to 7.40 cN as determined by the Rosand Constant Haul Off method, a melt index of less than 10 g/10 minute and a flexural modulus between 206 MPa (30,000 psi) and 620 MPa (90,000 psi).

In a further embodiment component ii) is a copolymer of from 98 to 85 weight % of ethylene and the balance one or more C4-8 alpha olefins.

In a further embodiment the difference in maximum melting temperature for components i) and ii) is 4°C or less. In a further embodiment the difference between the maximum crystallization temperature of the components is less than 4°C.

In a further embodiment component ii) comprises from 98 to 93 weight % of ethylene.

In a further embodiment component ii) is an ethylene octene copolymer. In a further embodiment the foam has a density from 0.8 pcf (0.0012 g/cc) to 1 .20 pcf (0.0019 g/cc).

A further embodiment provides a blend of polyethylene polymers comprising i) from 90 to 60 weight % of polyethylene homopolymer prepared in a high pressure process having a density from 0.915 to 0.920 g/cc, a melt index from 0.70 to 2.5 g/10 min (at 2.16 kg/190°C), a maximum melting temperature from (DSC) 105°C to 1 12°C; a maximum crystallization temperature from 95 to 100°C; a melt strength from 2.5 to 4.5 cN as determined by the Rosand Constant Haul Off method; and

ii) from 10 to 40 weight % of a single site catalyzed polyethylene copolymer having a density from 0.915 to 0.918 g/cc; a melt index from 0.60 to 1 .2 g/10 min (at 2.16 kg/190°C); a maximum melting temperature (DSC) from 108 to

1 12°C; a maximum crystallization temperature (DSC) within 6°C of that of component i); a flexural modulus between 206MPa (30,000 psi) and 620 MPa (90,000 psi), and a melt strength from 1 to 2 cN as determined by the Rosand Constant Haul Off method;

said blend having a melt strength from 3.50 to 7.40 cN as determined by the Rosand Constant Haul Off method, a melt index of less than 10 g/10 minute and a flexural modulus between 206 MPa (30,000 psi) and 620 MPa (90,000 psi).

A further embodiment provides a process for making the above a

polyethylene foam comprising passing the above polyethylene blend through an extruder at a temperature above the melting point of the blend and injecting from 2 to 25 weight % of a blowing agent into the blend, based on the weight of the blend.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is plot of the density of the foams prepared in the experiments in kilograms per cubic meter.

Figure 2 is plot of the tensile strength in the machine direction in kilopascals (kPa) of the foams prepared in the experiments. Figure 3 is plot of the tensile strength in the transverse direction in

kilopascals (kPa) of the foams prepared in the experiments.

Figure 4 is a plot of the elongation in % of the machine direction of the foams prepared in the experiments.

Figure 5 is a plot of the elongation in % in the transverse direction of the foams prepared in the experiments.

Figure 6 is a plot of the tear resistance in kilonewtons per meter (kN/m) in the machine direction of the foams prepared in the experiments.

Figure 7 is a plot of the tear resistance in kilonewtons per meter (kN/m) in the transverse direction of the foams prepared in the experiments.

Figure 8 is a plot of the maximum load in Joules of the puncture properties of the foams prepared in the experiments.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention Rosand Constant Haul off test refers to a test procedure under the following test conditions: Barrel Temperature: 230°C; Die: 2- mm Diameter, L/D=20; Pressure Transducer: 10,000 psi (68.95 MPa); Piston Speed: 5.33 mm/min; Haul-off Angle: 52°; and Haul-off incremental speed: 500 m/(min).

As used in this patent specification Ml means melt index which is I2 as determined by ASTM D-1238 condition (E) (i.e. grams of polymer extruded under a load of 2.16 kg. at 190°C through a standard orifice in 10 minutes.)

As used in this patent specification DSC refers to a process in which the relative flow of heat into a sample of polymer relative to a standard is determined as the sample and standard are heated at a standard rate (e.g. 1 °C per minute) from a temperature at which is it solid to a temperature above its melting point (e.g. from 20°C to 130°C and the heat flow into the polymer is measured and plotted. From the plot one can determine among other things maximum melting point and maximum crystallization temperature.

The blends and foams of the present invention comprise a single site catalyzed polyethylene resin and a high pressure low density polyethylene resin.

High pressure low density polyethylene resins have been known since about the mid 1930's. Polyethylene was originally produced industrially using a high pressure process. Although the process has been modified over time it essentially comprises compressing ethylene to a high enough pressure so that it becomes a supercritical fluid. Typically the pressures range from about 80 to 310 MPa (e.g. about 1 1 ,500 psi to about 45,000 psi) preferably from about 200 to 300 MPa (about 30,000 psi to about 43,500 psi) and the temperature ranges from 130°C to 350°C, typically from 150°C to 340°C. The supercritical ethylene together with one or more of initiators, chain transfer agent and optional comonomers are fed to a high pressure reactor. The reactor may be a tubular reactor. Tubular reactors may have a length from about 200 m to about 1500 m, and a diameter from about 20 mm to about 100 mm.

Thermocouples are along the length of the reactor typically spaced at a distance from 5 to 15, preferably 8 to 12, most preferably from 8 to 1 1 meters. Generally there may be from 100 and 350 thermocouples, typically from 120 to 300 thermocouples spaced along the length of the reactor. The spacing of the thermocouples may not always be uniform along the length of the reactor.

Generally there are a number of injection points spaced along the tubular reactor where additional components such as initiators, chain transfer agents, and monomers (preferably cold monomers), may be added to the reactor. The design and operation of tubular reactors is illustrated by a number of patents including for example United States Patent 3,334,081 issued Aug. 1 , 1967 to Madgwick et al., assigned to Union Carbide Corporation; United States Patent 3,399,185 issued Aug. 27, 1968 to Schappert assigned to Koppers Company, Inc., United States Patent 3,917,577 issued Nov. 4, 1975 to Trieschmann et al. assigned to Badische Anilin & Soda-Fabrik Aktiengesellschaft; and United States Patent 4,135,044 issued Jan. 16, 1979 to Beals assigned to Exxon Research & Engineering Co.

Generally the initiator, or mixture of initiators, is injected into the reactor in amounts from 100 to about 500 ppm, preferably from about 125 to 425 ppm, (based on the weight of the reactants). The initiator(s) may be selected from the group consisting of oxygen, peroxides, persulphates, perborates, percarbonates, nitriles, and sulphides (methyl vinyl sulphide). Some free radical initiators can be selected from the list given in Ehrlich, P. et al., Fundamentals of the Free-Radical Polymerization of Ethylene, Advances in Polymer Science, Vol. 7, pp. 386-448, (1970).

Non-limiting examples of some free radical producing substances include oxygen (air); peroxide compounds such as hydrogen peroxide, decanoyi peroxide, t-butyl peroxy neodecanoate, t-butyl peroxypivalate, 3,5,5-trimethyl hexanoyl peroxide, diethyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t-butyl peroxy isobutyrate, benzoyl peroxide, t-butyl peroxy acetate, t-butyl peroxy benzoate, di-t- butyl peroxide, and 1 ,1 ,3,3-tetramethyl butyl hydroperoxide; alkali metal

persulfates, perborates and percarbonates; and azo compounds such as azo bis isobutyronitrite. Typically initiators are selected from the group consisting oxygen (air) and organic peroxides.

Generally a chain transfer agent (sometimes referred to as a telogen or a modifier) is also present in the reactants. The chain transfer agent may be added at one or more points along the tubular reactor. Some chain transfer agents include the saturated aliphatic aldehydes, such as formaldehyde, acetaldehyde and the like, the saturated aliphatic ketones, such as acetone, diethyl ketone, diamyl ketone, and the like, the saturated aliphatic alcohols, such as methanol, ethanol, propanol, and the like, paraffins or cycloparaffins such as pentane, hexane, cyclohexane, and the like, aromatic compounds such as toluene, diethylbenzene, xylene, and the like, and other compounds which act as chain terminating agents such as carbon tetrachloride, chloroform, etc.

The chain transfer agent may be used in amounts from about 0.20 to 2, preferably from 0.24 to 1 mole percent based on the total ethylene feed to the reactor.

In the foams and blends of the present invention the feed for the high pressure low density resin is entirely ethylene. That is the polymer is a

homopolymer.

Typically the homopolymer will have a density from 0.910 to 0.925 g/cc, preferably from 0.915 g/cc to 0.920 g/cc, desirably from 0.917 g/cc to 0.919 g/cc; a melt index (at 2.16 kg/190°C) from 0.60 to 4.35 g/10 min, preferably from 0.70 to 2.5 g/10 min; a maximum melting temperature (DSC) from 105 to 1 12°C in some embodiments from 108 to 1 1 0°C; a maximum crystallization temperature from 95 to 100°C, in some embodiments from 95 to 98.5°C; a melt strength from 2.0 to 7 cN, in some embodiments from 2.5 to 4.5 cN as determined by the Rosland Constant Haul Off method. Typically the homopolymer has a flex modulus (ASTM D790) between about 206 MPa (30,000 psi) and 552KPa (80,000 psi) in some

embodiments between 241 MPa (35,000 psi) and 445 MPa (65, 000 psi).

The other component in the blends of the present invention is a single site catalyzed polyethylene copolymer. The active metal catalyst is typically a group IV or V transition metal, preferably selected from the group consisting of Ti, Zr, and Hf.

The single site catalyst may have a formula selected from the group consisting of:

(L)n— M— (Y)p

wherein M is selected from the group consisting of Ti, Zr , and Hf; L is a

monoanionic ligand independently selected from the group consisting of

cyclopentadienyl-type ligands, and a bulky heteroatom ligand containing not less than five atoms in total of which at least 20%, numerically are carbon atoms and further containing at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon said bulky heteroatom ligand being sigma or pi-bonded to M; Y is independently selected for the group consisting of activatable ligands; n may be from 1 to 3; and p may be from 1 to 3, provided that the sum of n+p equals the valence state of M, and further provided that two L ligands may be bridged.

In one embodiment, the single site catalyst may be a metallocene type catalyst wherein L is a cyclopentadienyl type ligand and n, may be from 1 to 3, preferably 2.

The cyclopentadienyl-type ligand is a C ₅ . ₁₃ ligand containing a 5-membered carbon ring having delocalized bonding within the ring and bound to the metal atom (i.e. the active catalyst metal or site) through η ⁵ bonds and said ligand being unsubstituted or up to fully substituted with one or more substituents selected from the group consisting of C1-10 hydrocarbyl radicals in which hydrocarbyl substituents are unsubstituted or further substituted by one or more substituents selected from the group consisting of a halogen atom, preferably fluorine, a C-i -8 alkyl radical; a Ci-8 alkoxy radical; a Ce-ιο aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two C-i -8 alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two Ci-s alkyl radicals; silyl radicals of the formula -Si-(R)3 wherein each R is independently selected from the group consisting of hydrogen, a Ci -s alkyl or alkoxy radical, and Ce-ιο aryl or aryloxy radicals; and germanyl radicals of the formula Ge-(R)3 wherein R is as defined above. Preferably the cyclopentadienyl ligand (Cp) is independently selected from the group consisting of a cyclopentadienyl radical, an indenyl radical and a fluorenyl radical.

In the single site type catalyst two cyclopentadienyl ligands may be bridged or joined or one cyclopentadienyl ligand may be bridged to a hetero atom ligand. If two cyclopentadienyl ligands are bridged or joined together or a cyclopentadienyl ligand is bridged to a hetero atom ligand, the catalyst may be a constrained geometry catalyst. Non-limiting examples of bridging group include bridging groups containing at least one Group 13 to 16 atom, often referred to a divalent moiety such as but not limited to at least one of a carbon, oxygen, nitrogen, silicon, boron, germanium and tin atom or a combination thereof. Preferably, the bridging group contains a carbon, silicon or germanium atom, most preferably at least one silicon atom or at least one carbon atom. The bridging group may also contain substituent radicals as defined above including halogens.

Some bridging groups include but are not limited to, a di C1-6 alkyl radical (e.g. for example an ethyl bridge), di Ce-ιο aryl radical (e.g. a benzyl radical having two bonding positions available), silicon or germanium radicals substituted by one or more radicals selected from the group consisting of C-i-6 alkyl, Ce-ιο aryl, phosphine or amine radical which are unsubstituted or up to fully substituted by one or more C1 -6 alkyl or Ce-ιο aryl radicals, or a hydrocarbyl radical such as a C1-6 alkyl radical or a Οβ-ιο arylene (e.g. divalent aryl radicals); divalent C1 -6 alkoxide radicals (e.g. -CH2 CHOH CH2-) and the like.

Exemplary of the silyl species of bridging groups are dimethylsilyl,

methylphenylsilyl, diethylsilyl, ethylphenylsilyl, diphenylsilyl bridged compounds. In some embocimentws the bridging species are selected from dimethylsilyl, diethylsilyl and methylphenylsilyl bridged compounds.

Exemplary hydrocarbyl radicals for bridging groups include methylene, ethylene, propylene, butylene, phenylene and the like. In some embodiments the bridging group is methylene. Exemplary bridging amides include dimethylamide, diethylamide, methylethylamide, di-t-butylamide, diisopropylamide and the like.

The activatable Iigands (Y) may be independently selected from the group consisting of a hydrogen atom; a halogen atom, a C1-10 hydrocarbyl radical; a C1-10 alkoxy radical; a C5-10 aryl oxide radical; each of which said hydrocarbyl, alkoxy, and aryl oxide radicals may be unsubstituted by or further substituted by one or more substituents selected from the group consisting of a halogen atom; a C1 -8 alkyl radical; a C1-8 alkoxy radical; a Ce-ιο aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; and a phosphido radical which is unsubstituted or substituted by up to two C1 -8 alkyl radicals. In some embodiments Y is independently selected from the group consisting of a hydrogen atom, a chlorine atom and a C1 -4 alkyl radical.

In one embodiment of the invention the catalyst may contain a bulky heteroatom ligand. The bulky heteroatom ligand is selected from the group consisting of phosphinimine Iigands, ketimide Iigands, silicon-containing

heteroatom Iigands, amido Iigands, alkoxy Iigands, boron heterocyclic Iigands and phosphole Iigands.

If the catalyst contains one or more bulky heteroatom Iigands the catalyst would have the formula:

(D)m

(L)n— M— (Y)p

wherein M is a transition metal selected from the group consisting of Ti, Hf and Zr; D is independently a bulky heteroatom ligand (as described below); L is a monoanionic ligand of cyclopentadienyl-type Iigands; Y is independently selected from the group consisting of activatable Iigands; m is 1 or 2; n is 0 or 1 ; and p is an integer and the sum of m+n+p equals the valence state of M, provided that when m is 2, D may be the same or different bulky heteroatom Iigands.

Bulky heteroatom Iigands (D) include but are not limited to phosphinimine Iigands and ketimide (ketimine) Iigands.

In a further embodiment, the catalyst may contain one or two phosphinimine Iigands (PI) which are bonded to the metal and the second catalyst has the formula (Pl)m (L)n— M— (Y)p

wherein M is a group 4 metal; PI is a phosphinimine ligand; L is a monoanionic ligand of the cyclopentadienyl-type ligand; Y is independently selected from the group consisting of activatable ligands; m is 1 or 2; n is 0 or 1 ; p is an integer and the sum of m+n+p equals the valence state of M.

The phosphinimine ligand is defined by the formula:

((R ² ) ₃ P=N -); or

R ²¹

/

R ²¹

wherein each R ²¹ is independently selected from a hydrogen atom; a halogen atom; C-1-20, preferably C1-10 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom; a C-i-s alkoxy radical; a Ce-ιο aryl or aryloxy radical; an amido radical; a silyl radical of the formula:

-Si-(R ²² ) ₃

wherein each R ²² is independently selected from the group consisting of hydrogen, a Ci-s alkyl or alkoxy radical, and Ce-ιο aryl or aryloxy radicals; and a germanyl radical of the formula:

-Ge-(R ²² ) ₃

wherein R ²² is as defined above.

The preferred phosphinimines are those in which each R ²¹ is a hydrocarbyl radical, preferably a C1-6 hydrocarbyl radical.

Suitable phosphinimine catalysts are Group 4 organometallic complexes which contain one phosphinimine ligand (as described above) and one ligand L which is either a cyclopentadienyl-type ligand or a heteroatom ligand.

As used herein, the term "ketimide ligand" refers to a ligand which:

(a) is bonded to the transition metal via a metal-nitrogen atom bond;

(b) has a single substituent on the nitrogen atom (where this single substituent is a carbon atom which is doubly bonded to the N atom); and (c) has two substituents Sub 1 and Sub 2 (described below) which are bonded to the carbon atom.

Conditions a, b and c are illustrated below:

Sub 1 Sub 2

\ /

C

N metal

The substituents "Sub 1 " and "Sub 2" may be the same or different.

Exemplary substituents include hydrocarbyl radicals having from 1 to 20, preferably from 3 to 6, carbon atoms, silyl groups (as described below), amido groups (as described below) and phosphido groups (as described below). For reasons of cost and convenience it is preferred that these substituents both be hydrocarbyls, especially simple alkyls and most preferably tertiary butyl. "Sub 1 " and "Sub 2" may be the same or different and can be bonded to each other to form a ring.

Suitable ketimide catalysts are Group 4 organometallic complexes which contain one ketimide ligand (as described above) and one ligand L which is either a cyclopentadienyl-type ligand or a heteroatom ligand.

The term bulky heteroatom ligand (D) is not limited to phosphinimine or ketimide ligands and includes ligands which contain at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon. The heteroatom ligand may be sigma or pi-bonded to the metal.

Exemplary heteroatom ligands include silicon-containing heteroatom ligands, amido ligands, alkoxy ligands, boron heterocyclic ligands and phosphole ligands, as all described below.

Silicon containing heteroatom ligands are defined by the formula:

- (Y)Si RxRyRz

wherein the - denotes a bond to the transition metal and Y is sulfur or oxygen.

The substituents on the Si atom, namely Rx, R _y and R _z are required in order to satisfy the bonding orbital of the Si atom. The use of any particular substituent Rx, R _y or Rz is not especially important to the success of this invention. It is preferred that each of Rx, Ry and Rz is a C1 -2 hydrocarbyl group (i.e. methyl or ethyl) simply because such materials are readily synthesized from commercially available materials. The term "amido" is meant to convey its broad, conventional meaning.

Thus, these ligands are characterized by (a) a metal-nitrogen bond; and (b) the presence of two substituents (which are typically simple alkyl or silyl groups) on the nitrogen atom.

The terms "alkoxy" and "aryloxy" is also intended to convey its conventional meaning. Thus, these ligands are characterized by (a) a metal oxygen bond; and (b) the presence of a hydrocarbyl group bonded to the oxygen atom. The hydrocarbyl group may be a C1-10 straight chained, branched or cyclic alkyl radical or a Ce-13 aromatic radical where the radicals are unsubstituted or further substituted by one or more C1 -4 alkyl radicals (e.g. 2,6 di-tertiary butyl phenoxy).

Boron heterocyclic ligands are characterized by the presence of a boron atom in a closed ring ligand. This definition includes heterocyclic ligands which also contain a nitrogen atom in the ring. These ligands are well known to those skilled in the art of olefin polymerization and are fully described in the literature (see, for example, U.S. Patents 5,637,659; 5,554,775; and the references cited therein).

The term "phosphole" is also meant to convey its conventional meaning. "Phospholes" are cyclic dienyl structures having four carbon atoms and one phosphorus atom in the closed ring. The simplest phosphole is C4PH4 (which is analogous to cyclopentadiene with one carbon in the ring being replaced by phosphorus). The phosphole ligands may be substituted with, for example, C1-20 hydrocarbyl radicals (which may, optionally, contain halogen substituents);

phosphido radicals; amido radicals; or silyl or alkoxy radicals. Phosphole ligands are also well known to those skilled in the art of olefin polymerization and are described as such in U.S. Patent 5,434,1 16 (Sone, to Tosoh).

In one embodiment the catalyst may contain no phosphinimine ligands as the bulky heteroatom ligand. The bulky heteroatom containing ligand may be selected from the group consisting of ketimide ligands, silicon-containing

heteroatom ligands, amido ligands, alkoxy ligands, boron heterocyclic ligands and phosphole ligands. In such catalysts the Cp ligand may be present or absent.

Useful metals (M) are from Group 4 including titanium, hafnium or

zirconium).

For gas phase or slurry phase polymerization the catalyst may be supported. The catalyst system of the present invention may be supported on an inorganic or refractory support, including for example alumina, silica and clays or modified clays or an organic support (including polymeric support such as polystyrene or cross-linked polystyrene). The catalyst support may be a

combination of the above components. However, preferably the catalyst is supported on an inorganic support or an organic support (e.g. polymeric) or mixed support. Some refractories include silica, which may be treated to reduce surface hydroxyl groups and alumina. The support or carrier may be a spray-dried silica. Generally the support will have an average particle size from about 0.1 to about 1 ,000, in some embodiments from about 10 to 1 50 microns. The support typically will have a surface area of at least about 10 m ² /g, in some embodiments from about 150 to 1 ,500 m ² /g. The pore volume of the support should be at least 0.2, in some embodiments from about 0.3 to 5.0 ml/g.

Generally the refractory or inorganic support may be heated at a

temperature of at least 200°C for up to 24 hours, typically at a temperature from 500°C to 800°C for about 2 to 20, in some embodiments from 4 to 10 hours. The resulting support will be essentially free of adsorbed water (e.g. less than about 1 weight %) and may have a surface hydroxyl content from about 0.1 to 5 mmol/g of support, in some embodiments from 0.5 to 3 mmol/g.

A silica suitable for use in the present invention has a high surface area and is amorphous. For example, commercially available silicas are marketed under the trademark of Sylopol ^® 958 and 955 by Davison Catalysts, a Division of W.R. Grace, and Company and ES-70W sold by Ineos Silica.

The amount of the hydroxyl groups in silica may be determined according to the method disclosed by J. B. Peri and A. L. Hensley, Jr., in J. Phys. Chem., 72 (8), 2926, 1968, the entire contents of which are incorporated herein by reference.

While heating is the most preferred means of removing OH groups

inherently present in many carriers, such as silica, the OH groups may also be removed by other removal means, such as chemical means. For example, a desired proportion of OH groups may be reacted with a suitable chemical agent, such as a hydroxyl reactive aluminum compound (e.g. triethyl aluminum) or a silane compound. This method of treatment has been disclosed in the literature and two relevant examples are: U.S. Patent 4,719,193 to Levine in 1988 and by Noshay A. and Karol F.J. in Transition Metal Catalyzed Polymerizations, Ed. R. Quirk, 396, 1989. For example the support may be treated with an aluminum compound of the formula AI((O) _a R ¹ )bX3-b wherein a is either 0 or 1 , b is an integer from 0 to 3, R ¹ is a C-1 -8 alkyl radical, and X is a chlorine atom. The amount of aluminum compound is such that the amount of aluminum on the support prior to adding the remaining catalyst components will be from about 0 to 2.5 weight %, in some embodiments from 0 to 2.0 weight % based on the weight of the support.

The clay type supports are also preferably treated to reduce adsorbed water and surface hydroxyl groups. However, the clays may be further subject to an ion exchange process, which may tend to increase the separation or distance between the adjacent layers of the clay structure.

The polymeric support may be cross linked polystyrene containing up to about 50 weight %, in some embodiments not more than 25 weight %, in further embodiments less than 10 weight % of a cross linking agent such as divinyl benzene.

The single site catalysts in accordance with the present invention may be activated with an activator selected from the group consisting of:

(i) a complex aluminum compound of the formula

R ¹² 2AIO(R ¹² AIO)mAIR ¹² 2 wherein each R ¹² is independently selected from the group consisting of C1-20 hydrocarbyl radicals and m is from 3 to 50, and optionally a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present;

(ii) ionic activators selected from the group consisting of:

(A) compounds of the formula [R ¹³ ] ⁺ [B(R ¹⁴ ) ₄ ] ^" wherein B is a boron atom, R ¹³ is a cyclic C5-7 aromatic cation or a triphenyl methyl cation and each R ¹⁴ is independently selected from the group consisting of phenyl radicals which are unsubstituted or substituted with a hydroxyl group or with 3 to 5 substituents selected from the group consisting of a fluorine atom, a C1-4 alkyl or alkoxy radical which is unsubstituted or substituted by a fluorine atom and a silyl radical of the formula -Si-(R ¹⁵ )3 wherein each R ¹⁵ is independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical; and (B) compounds of the formula [(R ¹⁸ )t ZH] ⁺ [B(R ¹⁴ ) ₄ ]- wherein B is a boron atom, H is a hydrogen atom, Z is a nitrogen atom or phosphorus atom, t is 2 or 3 and R ¹⁸ is independently selected from the group consisting of C-i -18 alkyl radicals, a phenyl radical which is unsubstituted or substituted by up to three Ci-4 alkyl radicals, or one R ¹⁸ taken together with the nitrogen atom may form an anilinium radical and R ¹⁴ is as defined above; and

(C) compounds of the formula B(R ¹⁴ )3 wherein R ¹⁴ is as defined above; and

(iii) mixtures of (i) and (ii).

In some embodiments the activator is a complex aluminum compound of the formula R ¹² 2AIO(R ¹² AIO) _m AIR ¹² 2 wherein each R ¹² is independently selected from the group consisting of C1-20 hydrocarbyl radicals and m is from 3 to 50, and optionally a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present. In some embodiments in the aluminum compound R ¹² is methyl radical and m is from 10 to 40. In some embodiments the molar ratio of Al:hindered phenol, if it is present, is from 3.25:1 to 4.50:1 . In some embodiments the phenol is substituted in the 2, 4 and 6 position by a C2-6 alkyl radical. Desirably the hindered phenol is 2,6-di-tert-butyl-4-ethyl-phenol.

The aluminum compounds (alumoxanes and optionally hindered phenol) are typically used as activators in substantial molar excess compared to the amount of metal in the catalyst. Aluminum:transition metal molar ratios may be from 10:1 to 10,000:1 , in some instances from 10:1 to 500:1 in other embodiments from 40:1 to 120:1 .

Ionic activators are well known to those skilled in the art. The "ionic activator" may abstract one activatable ligand so as to ionize the catalyst center into a cation, but not to covalently bond with the catalyst and to provide sufficient distance between the catalyst and the ionizing activator to permit a polymerizable olefin to enter the resulting active site.

Examples of ionic activators include:

triethylammonium tetra(phenyl)boron,

tripropylammonium tetra(phenyl)boron,

tri(n-butyl)ammonium tetra(phenyl)boron,

trimethylammonium tetra(p-tolyl)boron,

trimethylammonium tetra(o-tolyl)boron, tributylammonium tetra(pentafluorophenyl)boron,

tripropylammonium tetra(o,p-dimethylphenyl)boron,

tributylammonium tetra(m,m-dimethylphenyl)boron,

tributylammonium tetra(p-trifluoromethylphenyl)boron,

tributylammonium tetra(pentafluorophenyl)boron,

tri(n-butyl)ammonium tetra(o-tolyl)boron,

Ν,Ν-dimethylanilinium tetra(phenyl)boron,

Ν,Ν-diethylanilinium tetra(phenyl)boron,

Ν,Ν-diethylanilinium tetra(phenyl)n-butylboron,

di-(isopropyl)ammonium tetra(pentafluorophenyl)boron,

dicyclohexylammonium tetra(phenyl)boron,

triphenylphosphonium tetra(phenyl)boron,

tri(methylphenyl)phosphonium tetra(phenyl)boron,

tri(dimethylphenyl)phosphonium tetra(phenyl)boron,

tropillium tetrakispentafluorophenyl borate,

triphenylmethylium tetrakispentafluorophenyl borate,

tropillium phenyltrispentafluorophenyl borate,

triphenylmethylium phenyltrispentafluorophenyl borate,

benzene (diazonium) phenyltrispentafluorophenyl borate,

tropillium tetrakis (2,3,5,6-tetrafluorophenyl) borate,

triphenylmethylium tetrakis (2,3,5,6-tetrafluorophenyl) borate,

tropillium tetrakis (3,4,5-trifluorophenyl) borate,

benzene (diazonium) tetrakis (3,4,5-trifluorophenyl) borate,

tropillium tetrakis (1 ,2,2-trifluoroethenyl) borate,

triphenylmethylium tetrakis (1 ,2,2-trifluoroethenyl) borate,

tropillium tetrakis (2,3,4,5-tetrafluorophenyl) borate, and

triphenylmethylium tetrakis (2,3,4,5-tetrafluorophenyl) borate.

Readily commercially available ionic activators include:

Ν,Ν-dimethylaniliniumtetrakispentafluorophenyl borate;

triphenylmethylium tetrakispentafluorophenyl borate (tritylborate); and

trispentafluorophenyl borane.

Ionic activators may also have an anion containing at least one group comprising an active hydrogen or at least one of any substituent able to react with the support. As a result of these reactive substituents, the ionic portion of these ionic activators may become bonded to the support under suitable conditions. One non-limiting example includes ionic activators with tris (pentafluorophenyl) (4- hydroxyphenyl) borate as the anion. These tethered ionic activators are more fully described in U.S. Patents 5,834,393, 5,783,512 and 6,087,293.

In accordance with the present invention, the polyethylene may be prepared by solution, slurry or gas phase processes.

Solution and slurry polymerization processes are fairly well known in the art. These processes are conducted tubular (e.g. loop reactors), and tank reactors (continuously stirred tank reactors) in the presence of an inert hydrocarbon solvent typically a C4-12 hydrocarbon which may be unsubstituted or substituted by a C1 -4 alkyl group such as butane, pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane or hydrogenated naphtha. An additional solvent is Isopar E (C8-12 aliphatic solvent, Exxon Chemical Co.).

The polymerization may be conducted at temperatures from about 20°C to about 250°C. Depending on the product being made, this temperature may be relatively low such as from 20°C to about 180°C, typically from about 80°C to 150°C and the polymer is insoluble in the liquid hydrocarbon phase (diluent) (e.g. a slurry polymerization). The reaction temperature may be relatively higher from about 180°C to 250°C, preferably from about 180°C to 230°C and the polymer is soluble in the liquid hydrocarbon phase (solvent). The pressure of the reaction may be as high as about 15,000 psig for the older high pressure processes or may range from about 15 to 4,500 psig.

In gas phase polymerization a gaseous mixture comprising from 0 to 15 mole % of hydrogen, monomers as noted above, and from 0 to 75 mole % of an inert gas at a temperature from 50°C to 120°C, preferably from 75°C to about 1 10°C, and at pressures typically not exceeding 3,447 kPa (about 500 psi), preferably not greater than 2,414 kPa (about 350 psi) is contacted with a supported catalyst in a fluidized bed in a reactor typically comprising a vertical tubular reactor having a gas inlet at the bottom, a disperser or bed plate above the inlet upon which the bed is supported, a catalyst injector above the bed plate, a letdown system to withdraw polymer granules from the bed, a disengagement zone above the tubular reactor and a recycle system comprising piping and an inlet for make-up monomer(s), a compressor and a heat exchanger to recycle gas from the top of the disengagement zone to the inlet for the reactor. The velocity of the gas passing through the bed is sufficient to fluidized the bed.

In addition to monomers, and ballast gas (e.g. nitrogen) the gas phase typically comprises a condensable lower (C4-6) alkane which condenses as it passes through the heat exchanger. The condensed phase evaporates in the bed to remove heat from the reaction. The gas phase may contain from 10 to 50 weight % of condensable phase, typically from about 18 to 35 weight %, preferably from 20 to 30 weight % of condensable gas.

Typically the single sited catalyzed polymer will comprises from 80 to 95, in some embodiments from 85 to 95 weight % of ethylene and from 20 to 5, 15 to 5 weight % of one or more C4-8 alpha olefins such as hexene and octene, in some embodiments octene.

The polymer resulting from the polymerization in the presence of the single site catalyst (singles site polymer) should have the following properties: a density from 0.915 to 0.918 g/cc; a melt index from 0.60 to 1 .2 g/10 min (at 2.16 kg/190°C); a maximum melting temperature (DSC) from 108 to 1 12°C; a maximum

crystallization temperature (DSC) within 6°C of that of component i) (e.g. 98 to 102°C in some embodiments 99 to 100°C); a flextural modulus between 206 MPa (30,000 psi) and 620 MPa (90,000 psi) in some embodiments a flex modulus between 241 MPa (35,000 psi) and 448 MPa (65,000 psi,) in other embodiments the flex modulus may be between 241 MPa (35,000 psi ) and 379 MPa (55,000 psi) and a melt strength from 1 to 2 cN as determined by the Rosand Constant Haul Off method.

The components for the blends of the present invention are selected so that the difference in maximum melting temperature for components i) and ii) is 4°C or less in some embodiments less than 2°C; and the difference between the maximum crystallization temperature of the component is less than 4°C, in some

embodiments less than 2°C.

The blends of the present invention may be prepared in any convenient manner. Typically the components are dry blended in an amount to provide from 60 to 90 weight %, in some embodiments from 80 to 60 weight % of the

homopolymer (i.e. component (i)) and correspondingly from 40 to 10 weight %, in some embodiments from 40 to 20 weight % of the single site polymer (i.e. component (ii)). The blends are typically dry blended, tumble blended before being extruded or blended in the extruder. The components could be solution blended but that is an expensive process as the removal of solvent is required. The blend may have a flexural modulus between 206 MPa (30,000 psi) and 620 MPa (90,000 psi) in some embodiments a flexural modulus between 241 MPa (35,000 psi) and 448 MPa (65,000 psi,) in other embodiments the flexural modulus may be between 241 MPa (35,000 psi) and 379 MPa (55,000 psi).

The blend is passed through an extruder and blown to form a foam.

Typically, a small amount from about 5 to 25, in some embodiments from 8 to 20, in other embodiments from 10 to 18 weight % of a blowing agent based on the weight of the polymer blend. Some blowing agents include the following types of compounds. Lower (C4-6) aliphatic hydrocarbons which are unsubstituted or substituted by one or more atoms selected from the group consisting of a chlorine atom and a fluorine atom is injected into the polymer melt in the extruder. Aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, and the like. Aliphatic alcohols include methanol, ethanol, n-propanol, and isopropanol. Fully and partially halogenated aliphatic

hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons.

Examples of fluorocarbons include methyl fluoride, perfluoromethane, ethyl fluoride, 1 ,1 -difluoroethane (HFC-152a), 1 ,1 ,1 -trifluoroethane (HFC-143a), 1 ,1 ,1 ,2- tetrafluoro-ethane (HFC-134a), pentafluoroethane, difluoromethane,

perfluoroethane, 2,2-difluoropropane, 1 ,1 ,1 -trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride, 1 ,1 ,1 -trichloroethane, 1 ,1 -dichloro-1 -fluoroethane (HCFC-141 b), 1 -chloro-1 ,1 -difluoroethane (HCFC- 142b), chlorodifluoromethane (HCFC-22), 1 ,1 -dichloro-2,2,2-trifluoroethane (HCFC- 123) and 1 -chloro-1 ,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-1 1 ),

dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-1 13), 1 ,1 ,1 - trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-1 14),

chloroheptafluoropropane, and dichlorohexafluoropropane.

A less used approach it to incorporate an inorganic compound into the blend prior to extrusion which decomposes in the extruder to produce a gas typically carbon dioxide such as a metal carboxylate typically a group 1 or 2 metal carbonate such as calcium carbonate. A solid organic compound may also be added to the blend to produce nitrogen when the compound decomposes under the extrusion conditions such as azodicarbonamide (1 , 1 '-azobisformamide). Some inorganic blowing agents include azodicarbonamide, azodiisobutyro-nitrile,

benzenesulfonhydrazide, 4,4-oxybenzene sulfonylsemicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,N'-dimethyl-N,N'- dinitrosoterephthalamide, Ν,Ν'-dinitrosopentamethylenetetramine, 4-4-oxybis (benzenesulfonylhydrazide), and trihydrazino triazine. Azodicarbonamide is preferred.

The polyethylene components or the blend will typically contain the usual additives including heat and light stabilizers and UV stabilizers and any pigments required.

The process of foaming the blends of the present invention is well known. The blend is fed to an extruder, either single or twin screw. The extruder will have a number of different temperature zones, typically from three to five or more. The screws may have kneading elements in some sections. The blend is melted by a combination of temperature control in the barrel and friction and kneading in the barrel. The blend is heated to above its melting point (e.g. about 80 to 130°C, in some instances from about 95 to 1 15°C) and the blowing agent may be injected into the blend or if a solid blowing agent is used mixed with the blend and the blend is heated to the decomposition temperature of the blowing agent. The extruder has a number of zones in it from 1 to about 6 and a heated die. The temperatures through the extruder and die may fall within the range from about 90°C to 140°C). In the extruder the molten polymer blend is under pressure and does not foam. The blend exits the extruder through a die and is exposed to atmospheric pressure and the melt foams. The foam is stabilized and fairly quickly cooled to a solid foamed mass. Depending on the processing conditions the foam may be closed cell, open cell or a mixture of closed and open cell foam. In some embodiments the foam may comprise from about 20 to 30% of closed cells. The foam may then be further processed by cutting into required size and shape.

The resulting foam blend has melt strength from 3.50 to 12 cN, in some embodiments from about 4 to 8 cN, as determined by the Rosand Constant Haul Off method; a difference of less than 6°C in some embodiments less than 4°C, in other embodiments less than 2°C, between the maximum melting temperatures of the components, a difference of less than 4°C, in some embodiments less than 2°C maximum crystallization temperature of the components, and a melt index of less than 10 g/10 minutes. The foam may have a density froml 0 kg/m ³ (0.6 pounds per cubic foot (pcf)) to 20 kg/m ³ (1 .25 pcf), in some embodiments from about 13 kg/ M ³ (0.8 pcf) to 19 kg/m ³ (1 .20 pcf).

The profile of the foam is partially determined by the shape of the die. The foam may be oval or circular in cross section but generally is square or rectangular in cross section. In some embodiments the slab or plank of foam may be split (e.g. formed as a half inch thick foam and split into two slabs ¼ inch thick) or may be cut into smaller widths.

The present invention will now be illustrated by the following experiments.

In the experiments, the melt strength was determine by the Rosand

Constant Haul Off Method (cN) as described in U.S. Patent 6,185,349 from Col. 4 line 53 through Col. 5 line 5 wherein using 10 incremental haul-off speed starting at 1 mm/min each stage increasing by 1 mm/min the haul off speed is increased by 1 m/ minute at each stage a piston speed is 5 mm per minute under a force of 0.54 kN.

Ml (I2) was determined by ASTM D-1238 condition (E) (i.e. grams of polymer extruded under a load of 2.16 kg at 190°C through a standard orifice in g/10 minutes).

DSC refers to a process in which the relative flow of heat into a sample of polymer relative to a standard is determined as the sample and standard are heated at a standard rate (e.g. 1 °C per minute) from a temperature at which is it solid to a temperature above its melting point (e.g. from 20°C to 130°C and the heat flow into the polymer is measured and plotted. From the plot one can determine among other things maximum melting point and maximum crystallization

temperature.

Stress exponent is determine by measuring the throughput of a melt indexer at two stresses (2160 g and 6480g loading) using the procedures of the ASTM melt index test method, and applying the following formula: Stress exponent = 1 /0.447X (Log(weight of polymer extruded with 6480 g load)/ weight of polymer extrude with a 2160 g load).

In the experiments the following resins were used.

The low density resins (homopolymers) were NOVAPOL ^® LA0219-A (219), NOVAPOL LA-0522-A (522) and NOVAPOL LF-Y819. The single site resins were

SURPASS ^® FPs 016.

The resins had the following properties:

Blends were made of the LDPE (homopolymer) with 10 weight % of the resin produced with a single site catalyst.

The properties of blends of the invention are summarized in the table below.

2701 2702 2703

LA-0522-A + 10% LA-0219-A + 10% LF-Y819-A + 1 0%

Formulation

FPS01 6-C FPS016-C FPS016-C

Density G/CM3 0.92 0.9182 0.9192

Melt index, 12 G/10 MIN 2.66 1 .54 0.66

Melt index, 121 G/10 MIN 137 85.2 39.2

MFR G/10 MIN 51 .7 55.2 59.1

SEX G/10 MIN 1 .63 1 .64 1 .68

Melt Strength, AHO CN 5.81 10.62 18.87

Melt Strength, CHO CN 2.63 4.58 7.65

Mn BY GPC-VISC - 18154 17545 19488

Mw BY GPC-VISC - 131723 1 70566 178439

Mz BY GPC-VISC - 3661 13 522489 5131 19

Polydispersity - 7.26 9.72 9.16 The blends were foamed using a Gemini GP twin screw extruder with an L/D ratio of 32. The extruder had a number of zones heated at from 195°F (90°C) to 280°F (193°C). The die was designed to produce a 48 inch (122 cm) wide slab having a thickness of 1 /32 (0.08cm) of an inch or ¼ of an inch (0.6 cm).

The amount of blowing agent fed to the extruder was varied from 44 to 84 pounds per hour. The initial goal was to reduce the density of the foam.

Figure 1 shows the densities of the resulting foams. The amount of blowing agent was increased to reduce density of the foam. The practical upper limit of the amount of blowing agent was the solubility of the blowing agent in the polymer blend melt. The figure shows that it was possible to reduce the density of the foam below 1 pcf relative to the control.

In practice moving to lower density permits the manufacturer to reduce the amount of polymer used I the foam.

Figures 2 and 3 show that the tensile properties of the foams of the present invention are comparable to those of the prior art.

Figures 4 and 5 show that the elongation properties of the foams of the present invention are comparable or better than the foam of the prior art.

Figures 6 and 7 show that the elongation properties of the foams of the present invention are comparable or better than the foam of the prior art.

Figure 8 shows that the puncture resistance of the foams of the present invention are comparable or superior to the foams of the prior art.

In view of the above the present invention provides an expanded formulation window for making polyethylene foams of comparable or superior properties.

INDUSTRIAL APPLICABILITY

A blend of a single site catalyzed polyethylene and a high pressure low density polyethylene resin is suitable for the production of polyethylene foam having an improved melt strength.