CN1145082A - LLDPE resin blend - Google Patents

Abstract

A resin blend of LLDPE and low-density, high-pressure polyethylene prepared using a metallocene catalyst system can be extruded into films with improved optical properties and impact strength.

Description

LLDPE resin blend

The present invention relates to blends of linear low density ethylene copolymers (LLDPE) and films thereof having excellent optical properties.

Conventional linear low density polyethylene (LLDPE) cannot be used to prepare films requiring excellent optical properties due to the inherently poor optical properties of the resin. The fog value of conventional LLDPE is usually greater than 10 (measured according to ASTM D-1003 method).

An ethylene polymer that can be used in areas requiring excellent optical properties is low density polyethylene (LDPE), which is produced at higher pressures than those used to produce LLDPE. For example, it is reported that the preparation conditions of LDPE are 150-300MPa (1500-3000 atmosphere) and 200-300°C, while LLDPE is 0.3-1.0MPa (or 3-10 atmosphere) and 70-90°C (see KIRK-OTHMER , ENCYCLOPEDIAOF CHEMICAL TECHNOLOGY, Volume 16, Page 433 [Third Edition]). But the impact resistance of LDPE resin is very low.

Recently, new linear low-density products have been prepared using metallocene catalysts. The present invention involves the addition of high pressure PE resin and anti-sticking agent, ie, fine talc powder, to new metallocene LLDPE resins to provide excellent optical properties and acceptable adhesion. The present invention is entirely feasible because metallocene resins have a narrower molecular weight distribution and a more uniform distribution of short chain branching than conventional LLDPE resins.

The present invention is directed to a blend comprising 70-98% by weight of a dry, solvent-free synthetic composition comprising spherical, non-porous particles with an average particle size of 0.05-0.11 cm (0.02 -0.045 inch), the settled bulk density is 400-580kg/m ³ (25-36 lb/ft ³ ), the composition is a copolymer of ethylene and an alpha-olefin, its density is 0.902-0.929, MFR 15-25, M _w /M _n is 2.0-3.0; and 2-30% (weight) in 150-300MPa (1500-3000 atmospheric pressure) and 200-300 ℃ prepared low density polyethylene, wherein the blend The haze value of the product is less than 5 (measured according to ASTM D1003), and the impact resistance of falling dart (measured according to ASTM D-1709) is greater than 400.

LLDPE resins containing the blends of the present invention can be easily processed on commercial LLDPE film extruders without any modification. Films made from this blend have excellent impact properties that far exceed those of LDPE.

Low Density Polyethylene (LDPE) Components

The LDPE component used in the blends of the present invention is conventional LDPE which is prepared at higher pressures than LLDPE. The LDPE is prepared at 150-300 MPa (1500-3000 atmospheric pressure) and 200-300°C, while the usual preparation conditions of LLDPE are 0.3-1.0MPa (or 3-10 atmospheric pressure) and 70-100°C. If LLDPE is not added, the impact resistance of LDPE resin is very low.

Copolymer component

The copolymer component in the blends of the present invention is a linear low density polyethylene (LLDPE) having a density of 0.902-0.929, more preferably 0.915-0.922.

The LLDPE component of the blends of the present invention differs from conventional LLDPE in that it has a haze value (measured according to ASTM D-1003) of less than about 20, preferably 3-10, most preferably 5-7. In comparison, conventional LLDPE has a haze value greater than 10.

The LLDPE component contains 0.1-2ppm Zr (brought from the catalyst used in the synthesis), its average particle size is 0.05-0.11cm (0.02-0.045 inches), and the settled bulk density is 400-580kg/m ³ (25-36 lb/ ^ft3 ). The resulting resin is dry, solvent-free, and contains spherical, non-porous particles.

The melt flow ratio (MFR) of the LLDPE component of the blend of the invention is 15-25, preferably 15-20, most preferably 16-18. MFR is the ratio of _I21 / _I2 (where _I21 is measured at 190°C according to ASTM D-1238, condition F _{and I2} is measured at 190°C according to ASTM D-1238, condition E).

The MI of the LLDPE component is 0.01-5, usually 0.1-5, preferably 0.5-4, most preferably 0.8-2.0. The MI of the copolymer for blown film is preferably from 0.5 to 1.5.

The melting point of the LLDPE component is 95-130°C. In addition, the hexane extractive content is very low, typically 0.3-1.0% by weight. M _w /M _n of LLDPE is 2.0-3.0, M _w is a weight average molecular weight, M _n is a number average molecular weight, and each value is calculated from the molecular weight distribution measured by GPC (gel permeation chromatography).

If not according to the present invention, LLDPE without blending LDPE is processed into a film, then the equilibrium tear strength (measured according to ASTM D1922) of the film is 50-600, the axial strength is preferably 220-420, and the transverse strength is 200 -700, preferably 200-600. The film also has a high modulus, 7×10 ⁴ -48×10 ⁴ KPa (1×10 ⁴ -6×10 ⁴ psi), preferably 15-31×10 ⁴ KPa (2.2-4.5 ×10 ⁴ psi) and high tensile yield strength, measured according to ASTM D882, is 4800-21000KPa (700-3000psi), preferably 12000-16000KPa (1800-2300psi).

If not according to the present invention, the LLDPE without blending LDPE is processed into a film, and the optical quality of the film is evaluated as 3-20, preferably 4-10 by haze value (measured according to ASTM D-1003). A film with poor optical properties has a haze value greater than 10. The importance of LLDPE optical properties depends on the intended application of the LLDPE resin. It is generally believed that the poor optical performance of general LLDPE (haze>10, gloss<50) greatly limits their application in occasions requiring high optical performance.

The copolymer component of the resin blends of the present invention is a copolymer of ethylene and one or more _C3 - _C10 alpha-olefins, preferably containing at least 80% by weight of ethylene units. Suitable alpha-olefins include propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, heptene-1 and octene-1. Preferred alpha-olefin comonomers are 1-butene, 1-hexene and 1-octene. The most preferred alpha-olefin is hexene-1. Copolymers are either copolymers containing two monomer units or terpolymers containing three monomer units. Specific examples of such polymers include ethylene/1-butene copolymer, ethylene/1-hexene copolymer, ethylene/4-methyl-1-pentene copolymer, ethylene/1-butene/1-hexene ethylene terpolymer, ethylene/propylene/1-hexene terpolymer and ethylene/propylene/1-butene terpolymer.

The LLDPE copolymers used in the present invention are prepared from a new class of polyolefin catalysts comprising a support, an aluminoxane and at least one metallocene.

The catalyst support is a solid, porous granular inorganic or organic material, preferably an inorganic material, such as oxides of silicon and/or aluminum. The carrier material used is a dry powder having an average particle size of 1-250 microns, preferably 10-150 microns. If desired, the treated support material can be sieved to ensure particles having an average particle size of preferably less than 150 microns. This is necessary to form narrow molecular weight LLDPE to reduce gel content. The support has a surface area of at least about 3 m ² /gm, preferably at least 50 m ² /gm up to 350 m ² /gm. When the support is silica gel, it is preferably heated to a temperature of 100-850°C, most preferably about 250°C. The support material used to prepare the catalyst composition should contain at least some reactive hydroxyl (OH) groups.

In the most preferred embodiment, the carrier is silica gel. Before use, it will be fluidized with nitrogen and heated at about 250° C. for about 4 hours to dehydrate it and make the surface hydroxyl concentration reach about 1.8 mmol/g (mmols /gm). The silica used in the most preferred embodiment is a high surface area amorphous silica gel (surface area = 300 m ² /gm; pore volume of 1.65 cm ³ /gm), commercially available under the trade name Davison 952-1836, Davison 952 or Davison 955, manufactured by WR Grace Corporation's Davison Produced by the Chemistry Department. The silica gel is, for example, spherical particles obtained by spray-drying.

The aluminoxanes used in the LLDPE catalyst composition include oligomeric, linear and/or cyclic alkyl aluminoxanes represented by the general formula:

R-(Al(R)-O) _n -AlR ₂ : oligomeric linear aluminoxane and

(-Al(R)-O-) _m : oligomeric cyclic aluminoxane, wherein n is 1-40, preferably 10-20; m is 3-40, preferably 3-20 and R is C ₁ -C ₈ , preferably methyl. Methylaluminoxane (MAO) is a mixture of oligomers with a broad molecular weight distribution, usually with an average molecular weight of about 1000. MAO is usually stored in toluene solution.

The general formula of the metallocene compound is Cp _m MA _n B _p , wherein Cp is unsubstituted or substituted cyclopentadienyl, M is a transition metal selected from zirconium or hafnium, and A and B are halogen atoms, hydrogen or Alkyl groups. In the above general formula of the metallocene compound, the preferred transition metal atom is zirconium. In the above general formula of the metallocene compound, the Cp group is an unsubstituted, monosubstituted or polysubstituted cyclopentadienyl group. The substituent on the cyclopentadienyl group is preferably a linear or branched C ₁ -C ₆ alkyl group. Cyclopentadienyl can also be a part of a bicyclic or tricyclic group such as indenyl, tetrahydroindenyl, fluorenyl or partially hydrogenated fluorenyl and a part of a substituted bicyclic or tricyclic group, when in the general formula of the above metallocene compound When m is equal to 2, the cyclopentadienyl group can also be replaced by polymethylene or dialkylsilyl groups such as -CH ₂ -, -CH ₂ -CH ₂ -, -CR'R"-, and -CR'R"-CR'R"-(whereR' and R" are short-chain alkyl or hydrogen), -Si(CH ₃ ) ₂ -, -Si(CH ₃ ) ₂ -CH ₂ -CH ₂ -Si(CH ₃ ) ₂ - and so on similar abutments are bridged. If the substituents A and B in the above general formula of the metallocene compound are halogen atoms, they are fluorine, chlorine, bromine or iodine. If the substituents A and B in the general formula of the above metallocene compound are alkyl or aryl, they are preferably linear or branched C ₁ -C ₈ alkyl such as methyl, ethyl, n-propyl, iso Propyl, n-butyl, isobutyl, n-pentyl, n-hexyl or n-octyl.

Suitable metallocene compounds include bis(cyclopentadienyl)metal dihalides, bis(cyclopentadienyl)metal hydrohalides, bis(cyclopentadienyl)metal-alkyl-halides, dialkylbis(cyclopentadienyl)metal Cyclopentadienyl) metals and bis(indenyl) metal dihalides, wherein the metal is titanium, zirconium or hafnium, the halide is preferably chlorine, and the alkyl is C ₁ -C ₆ alkyl. Illustrative, non-limiting examples of metallocenes include bis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)hafnium dichloride, dimethylbis(cyclopentadienyl)zirconium, dichlorobis(cyclopentadienyl)zirconium, Methylbis(cyclopentadienyl)hafnium, bis(cyclopentadienyl)zirconium hydrochloride, bis(cyclopentadienyl)hafnium hydrochloride, bis(pentamethylcyclopentadiene dichloride) base) zirconium, bis(pentamethylcyclopentadienyl) hafnium dichloride, bis(n-butylcyclopentadienyl) zirconium dichloride, bis(isobutylcyclopentadienyl) zirconium dichloride, dichloro Cyclopentadienyl zirconium, bis(indenyl) zirconium dichloride, bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride and ethylene-[bis (4,5,6,7-tetrahydro-1-indenyl)] zirconium.

The molar ratio of aluminum-providing aluminoxane (expressed as Al) to metallocene metal M (eg zirconium) is 50-500, preferably 75-300, most preferably 100-200. An additional advantage of the present invention is that the Al:Zr ratio can be directly controlled. In a preferred embodiment, the aluminoxane and metallocene compound are mixed together in a suitable co-solvent at 20-80°C for 0.1-6.0 hours before reacting with the support. Co-solvents for metallocenes and aluminoxanes can be aromatic hydrocarbons, halogenated hydrocarbons or halogenated aromatic hydrocarbons, preferably toluene.

A particularly preferred method of making linear low density polyethylene is to make the polymer in a single fluidized bed reactor such as that described in US Patent No. 4,481,301. Process conditions include a temperature below the sintering temperature of the polymer particles, preferably 60-115° C., more preferably 75-95° C.; a pressure of 150-350 psig (1100-2500 KPa).

During LLDPE copolymerization, a "diluent" gas such as nitrogen, argon, helium, methane or ethane which is inert under the reaction conditions is preferably present in the polymerization reactor. Hydrogen may also be added as a chain transfer agent.

Blends of the invention

The blend of the present invention comprises 70-98%, preferably 90-98%, most preferably 95-98% by weight of the above-mentioned LLDPE copolymer and 95-98% by weight of the above-mentioned LLDPE copolymer and 2-30% , preferably 2-10%, most preferably 2-5% (by weight) of conventional LDPE resins.

The blend product may also contain various additives usually added to polymer compositions, such as lubricants, fine talc, stabilizers, antioxidants, compatibilizers, pigments, and the like. These additives can be used to stabilize the product against oxidation. For example, an additive composition comprising 400-1200 ppm hindered phenol, 700-2000 ppm phosphite, 250-1000 ppm antistatic agent and 250-1000 ppm stearate can be added to the resin powder for granulation.

The polymer blend can be fed directly into a blown film extruder, such as a Sterling extruder, to produce a film having a thickness of, for example, 0.5-5 mil (0.013-0.13 mm).

Films made from the blends of the invention had improved optical properties (haze < 5, gloss > 70). Films made from the blends of the present invention have a dart impact resistance (measured according to ASTM D-1709) greater than 400, typically 500-1500.

The following examples will further illustrate the main features of the present invention.

The performance of the polymkeric substance that makes in the embodiment is measured with following test method:

Density: ASTM D-1505-Preparation-flat-plate specimen, make it stand at 100℃

Let stand for 1 hour to reach equilibrium crystallinity. then measured in a density gradient column

Constant density, denoted as gms/cc.

Melt Index: ASTM D-1238, Condition E

(MI), I ₂ : Measured at 190°C, expressed as g/10 minutes.

High load melting

Body Index: ASTM D-1238, condition F

(HLMI), I ₂₁ : Measured at 10.5 times the weight of the above melt index test

melt flow

Ratio (MFR): I ₂₁ /I ₂

Example 1

The LLDPE metallocene resin produced by the pilot plant of ₁ and density of 0.918 prepared by the following embodiment A is mixed with 1000ppm Irganox 1010, 2000ppm Irgafos168, 1000ppm Erucamide, 5000ppm ABT2500, 500ppm AS990 in a Banbury mixer Combined with 500ppm Znst. Then the granulated metallocene resin was blended with industrial high-pressure low-density polyethylene resin (Mobil LBA-133) with an I2 of 2 and a density of 0.924 at three different contents: 0%, 5% and 10%. Each blend was then made using a 2.5 inch (6.4 cm) Brampton blown film extruder at 440°C, a die gap of 100 mils (2.5 mm) and a resin feed rate of 150 lbs/hour (68 kg/hr). 1 mil (0.03mm) thick film. For comparison, a commercial LLDPE resin with a broad molecular weight distribution, Mobil NTX-095, was also blended with LBA-133 at two different levels. These results were then compared to a 1 mil film made of Rexene 1065 (I2 1.9, density 0.924), a highly transparent commercial LDPE resin.

The results in Table 1 show that at a 5% LLDPE blend concentration, the metallocene resin/LDPE blend has comparable haze to Rexene 1065 (4.4 vs. 750gms compared to Rexene 1065's 64gms). In addition, under the same LDPE blending content, the impact performance of the metallocene resin/LDPE blend is also better than that of NTX-095/LDPE blend. The metallocene resin blend had lower haze (4.4% vs. 10.3% for the NTX-095 blend) and higher dart impact (750 gms vs. 166 gms for the NTX-095 blend).

Table 1

High transparency metallocene blend research base resin LDPE% haze% DDI, gms metallocene production 5 NT 4.4 750 resin (a) metallocene production 0 7.0 >800 resin (a) NTX-095 X 1 0 0 6 095 0 0 17.0 264Rexene1065(b) 0 4.6 64(a) was prepared according to Example A. (b) When Rexene 1065 is formed into a film in a Brampton blown film extruder, other conditions remain unchanged except for a temperature of 360°C and a die gap of 400 mils (1mm).

Example A

The starting materials used to prepare the catalyst included 504 g of Davison 952-1836 silica, 677 g of methylaluminoxane in toluene (30% by weight MAO), 7.136 g of bis(n-butylcyclopentadienyl)zirconium dichloride.

The steps of catalyst preparation are as follows:

1. Dehydrate 952-1836 silica gel at 250°C for 4 hours and blow with air. It was then purged with nitrogen while cooling.

2. Transfer the silica gel to the mixer.

3. Add 7.136 g of bis(n-butylcyclopentadienyl)zirconium dichloride and 677 g of methylalumoxane to a bottle.

4. Stir the catalyst solution in the bottle until the metallocene dissolves in the MAO solution.

5. Slowly transfer the MAO and metallocene solution into a mixer containing dehydrated 955 silica gel while vigorously agitating the silica gel layer to ensure that the catalyst solution is evenly dispersed in the silica gel layer.

6. After the addition is complete, continue to agitate the catalyst for 0.5 hours.

7. Dry the catalyst by purging with nitrogen at 45°C.

8. Sieve the catalyst to remove particles larger than 150 microns.

9. The analysis results of the catalyst are as follows:

Yield = 767g catalyst (made from 500g silica gel)

Al = 9.95% (weight)

Zr＝0.19% (weight)

LLDPE resin is prepared by the above-mentioned catalyst in a fluidized bed gas phase reactor, and the process conditions are as follows:

Process conditions:

Fluidization Velocity 1.7 ft/s (0.5m/sec)

Duration of stay 2.5 hours

Temperature 84℃

Vinyl 220psi

Hexene 3.6psi

Isopentane 50psi

Carbon dioxide 3ppm

Ash content 200-300ppm

The obtained resin has the following properties:

I2 1

Density 0.918

M _w /M _n 2.6

MFR 18

Melting point 115℃

Claims (6)

1. A blend comprising 70-98% by weight of a dry, solvent-free synthetic composition comprising spherical, non-porous particles with an average particle size of 0.05-0.11 cm (0.02-0.045 inch), the settled bulk density is 400-580kg/m ³ (25-36 lb/ft ³ ), the composition is a copolymer of ethylene and an α-olefin, the density is 0.902-0.929, and the MFR is 15 -25, _Mw / _Mn is 2.0-3.0; and 2-30% (by weight) of low-density polyethylene prepared at 150-300MPa (1500-3000 atmospheres) and 200-300°C, wherein the blend The fog value is less than 5 (measured according to ASTM D1003), and the impact resistance of falling dart (measured according to ASTM D-1709) is greater than 400. 2. The blend of claim 1, wherein the alpha-olefin of the copolymer has 3-10 carbon atoms. 3. The blend of claim 1, wherein the alpha-olefin is selected from the group consisting of butene, hexene, octene, and mixtures thereof. 4. A blend as claimed in any one of the preceding claims comprising 90-98% by weight of said copolymer and 2-10% by weight of said low density polyethylene. 5. A blend as claimed in any one of the preceding claims comprising 95-98% by weight of said copolymer and 2-5% by weight of said low density polyethylene. 6. A film made from a blend as claimed in any one of the preceding claims.