CN1723241A - Polyethylene compositions for injection molding - Google Patents

Abstract

Polyethylene blend compositions suitable for injection molding, injection molded articles, and processes for injection molding articles are provided. The polyethylene compositions include a first polyethylene having a melt index of 0.1 to 3.0 g/10 min and a density of from 0.905 to 0.938 g/cm<3>; and a second polyethylene having a melt index of 10 to 500 g/10 min and a density of 0.945 to 0.975 g/cm<3>. The composition has a density of from 0.920 to 0.973 g/cm<3> and a melt index of 2 to 200 g/10 min, and the density of the second polyethylene is from 0.037 to 0.062 g/cm<3> greater than the density of the first polyethylene. These compositions exhibit improved physical properties, such as Environmental Stress Crack Resistance, relative to conventional compositions of similar melt index and density.

Description

Polyethylene compositions for injection molding

1. Cross-references to related applications

This application claims the benefit of US Provisional Application Nos. 60/414952, filed October 1, 2002 and 60/424535, filed November 7, 2002.

2. Field of invention

The present invention relates to thermoplastic compositions of polyethylene polymers suitable for making useful products by injection molding.

3. Background technology

Injection molding is the most important process for producing molded bodies from thermoplastic materials. This importance is due to the ability to injection mold complex molding geometries in one step with a high degree of repeatability. Finishing of plastics is mostly unnecessary and can be highly automated. Utilize injection molding of polyethylene thermoplastic materials to manufacture all styles of consumer and commercial articles.

For injection molding parts, thermoplastic pellets, granules or powder of polyethylene are melted and injected under pressure into the cavity of a mold where, by cooling, the molten resin solidifies for subsequent removal. A more detailed discussion of injection molding can be found in Ullman's Encyclopedia of Industrial Chemistry, Vol. A20, Plastics Processing, pp. 688-696 (VCH Publishers, 1992).

Blends of polyethylene resins have been proposed to improve physical properties including impact strength, environmental stress crack resistance (ESCR) and chemical resistance.

US Patent No. 4438238 discloses blends for extrusion processing, injection molding and films, wherein two ethylene-alpha-olefin copolymers differ in density, intrinsic viscosity and number of short chain branches per 1000 carbon atoms The combination provides this physical property.

US Patent No. 4461873 discloses high molecular weight ethylene polymers, preferably copolymers, and low molecular weight ethylene polymers, preferably Ethylene homopolymers, blends of ethylene polymers for improved film properties and ESCR.

EP0423962 discloses an ethylene polymer composition particularly suitable for use in gas pipelines, said composition said to have improved ESCR, comprising two or more ethylene polymers differing in average molecular weight, at least one of which is ethylene polymer at 135°C High molecular weight ethylene polymers having an intrinsic viscosity of 4.5-10.0 dl/g in decalin and a density of 0.910 to 0.930 g/ ^cm3 , and another having an intrinsic viscosity of 0.5- A low molecular weight ethylene polymer of 2.0 dl/g and a density of 0.938-0.970 g/cm ³ .

US Patent No. 5082902 discloses blends of linear polyethylene for injection molding and rotational molding which are said to have reduced crystallization time and improved impact strength and ESCR. The blend comprises: (a) a first polymer having a density of 0.85-0.95 g/ ^cm3 and a melt index (MI) of 1-200 g/10 min; and (b) a density greater than that of the first polymer 0.015-0.15 g/cm ³ and a second polymer that differs by no more than 50 wt% from the MI of the first polymer.

US Patent No. 5306775 discloses polyethylene blends which are said to have a balance of properties for processing by any known thermoplastic process including, inter alia, improved ESCR. These compositions have: (a) low molecular weight vinyl resins produced using a chromia-based catalyst and having a density of at least 0.955 g/ ^cm3 and a MI between 25 and 400 g/10 min; and (b) a density of no greater than 0.955 g/cm ³ and a high molecular weight ethylene copolymer resin with a high load melt index (HLMI) between 0.1 and 50 g/10 min.

U.S. Patent No. 5,382,631 discloses linear interpolymer polyethylene blends with molecular weight distribution (Mw/Mn) ≤ 3 and composition distribution (CDBI) ≤ 50 wt%, wherein the blends generally do not contain more than other blend components Fractions with high molecular weight and low average comonomer content. Improved properties for films, fibers, coatings and molded articles are attributed to the blends. In one embodiment, the first component is an ethylene-butene copolymer having a density of 0.9042 g/cm ³ , a Mw/Mn of 2.3 and an MI of 4.0 g/10 min, and the second component is a density of 0.9552 g/cm 3 High density polyethylene (HDPE) with cm ³ , Mw/Mn of 2.8 and MI of 5.0 dg/min. The blend has improved tear strength characteristics.

There is a continuing need for polyethylene based compositions having improved environmental stress crack resistance, especially those suitable for injection molding applications.

4. Outline of the invention

According to the present invention there are provided polyolefin based blend compositions suitable for injection molding, injection molded articles and methods of injection molded articles.

In one embodiment, the present invention provides a polyethylene composition comprising a first polyethylene having a melt index (I _2.16 ) of 0.3-3.0 g/10 min and a density of 0.905-0.938 g/cm ³ ; and a melt a second polyethylene having a body index of 10-500 g/10 min and a density of 0.945-0.975 g/cm ³ , wherein the composition has a density of 0.920-0.973 g/cm ³ and a melt index of 2-200 g/10 min, and wherein the density of the second polyethylene is 0.037-0.062 g/ ^cm3 greater than the density of the first polyethylene. In a particular aspect of this embodiment, the first polyethylene is a metallocene-catalyzed polyethylene. In another particular aspect of this embodiment, both the first and second polyethylenes are metallocene-catalyzed polyethylenes.

In another embodiment, the present invention provides an injection molded article formed from or comprising a polyethylene composition comprising a melt index of 0.3-3.0 g/10min and a density of 0.905-0.938 g/cm ³ of a first polyethylene; and a second polyethylene having a melt index of 10-500 g/10 min and a density of 0.945-0.975 g/cm ³ , wherein the composition has a density of 0.920-0.973 g/cm ³ , and a melt index of 2-200 g/10 min, and wherein the density of the second polyethylene is 0.037-0.062 g/cm ³ greater than the density of the first polyethylene. In a particular aspect of this embodiment, the first polyethylene is a metallocene-catalyzed polyethylene. In another particular aspect of this embodiment, both the first and second polyethylenes are metallocene-catalyzed polyethylenes.

In another embodiment, the present invention provides a method of forming an injection molded article, the method being carried out by the steps of: (a) providing a polyethylene composition comprising a melt index of 0.3-3.0 g/10min and A first polyethylene with a density of 0.905-0.938 g/ ^cm3 ; and a second polyethylene with a melt index of 10-500 g/10min and a density of 0.945-0.975 g/ ^cm3 , wherein the composition has a density of 0.920- 0.973 g/cm ³ , and a melt index of 2-200 g/10 min, and wherein the density of the second polyethylene is 0.037-0.062 g/cm ³ greater than the density of the first polyethylene; and (b) injection molding the composition to form Injection molded products. In a particular aspect of this embodiment, the first polyethylene is a metallocene-catalyzed polyethylene. In another particular aspect of this embodiment, both the first and second polyethylenes are metallocene-catalyzed polyethylenes.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the Mw/Mn ratio of the polyethylene of the metallocene catalyst is 1.4- 4.0.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the Mw/Mn ratio of the polyethylene of the metallocene catalyst is 1.8- 3.5.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the first polyethylene has a density of 0.910-0.935 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the melt index of the first polyethylene is 0.1-2.0 g/10min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the melt index of the first polyethylene is 0.1-1.0 g/10min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the melt index of the first polyethylene is 0.3-1.0 g/10min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a density of 0.950-0.972 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a density of 0.955-0.970 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a density of 0.960-0.968 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a melt index of 10-300 g/10 min.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a melt index of 30-200 g/10 min.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the second polyethylene has a melt index of 50-100 g/10 min.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a density of 0.930-0.970 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a density of 0.940-0.965 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a density of 0.950-0.960 g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the density of the second polyethylene is 0.038 greater than the density of the first polyethylene -0.062g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the density of the second polyethylene is 0.040 greater than the density of the first polyethylene -0.060g/cm ³ .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a melt index I _2.16 of 3 to 100 g/10 min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a melt index I _2.16 of 3-50 g/10min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a melt index I _2.16 of 4-30 g/10min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, except that the composition has a melt index I _2.16 of 4-10 g/10 min .

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, wherein the blend comprises 80 wt. %-20 wt% of the first polyethylene and 20 wt%-80 wt% of the second polyethylene.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, wherein the blend comprises 70 wt. %-30wt% of the first polyethylene and 30wt%-70wt% of the second polyethylene.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, wherein the blend comprises 60 wt. %-40wt% of the first polyethylene and 40wt%-60wt% of the second polyethylene.

In another embodiment, the present invention provides a polyethylene composition, injection molded article, or method of forming an injection molded article according to any of the preceding embodiments, wherein at least one of the first and second polyethylenes is two or more Blends of polyethylene resins.

In another embodiment, the present invention provides a polyethylene composition, an injection molded article, or a method of forming an injection molded article according to any of the preceding embodiments except the immediately preceding embodiment, wherein the composition may, in addition to Only the first and second polyethylenes are included in addition to conventional additives in an amount.

5. Detailed description

The compositions of the present invention surprisingly and advantageously provide improved ESCR relative to compositions having the same melt index and density for injection molding applications of polyethylene.

By preparing several samples of the proposed blended polyethylene components and then subjecting the blends prepared from them to analytical tests, it was determined when the difference between the melt index (I _2.16 ) and the density of the blend components was within ESCR peaks were obtained within the specified ranges described here. At smaller differences in the densities of the two components, ESCR is improved relative to single component compositions, but notably less than those within the scope of the compositions of the present invention. Increasing the width of the density range between the components within the scope of the present invention increases the improvement in ESCR until a peak is reached where ESCR no longer improves and begins to decrease. Examination of the melting peaks of the sample blends with differential scanning calorimetry (DSC) helps to illustrate regions where ESCR improvement is no longer achieved by increasing the density difference between the two components. This is indicated by further increasing the width of the density range, the point at which the two components are no longer fully co-crystallized, as evidenced by the presence of a second, lower melting peak within the DSC scan. Evidence of loss of co-crystallization becomes apparent when the density range is wider than the above range, as a second melting peak or shoulder begins to appear in the scan. Blends showing even the smallest incidence of the second shoulder have reduced ESCR improvement.

The first polyethylene in the polymer blend of the present invention is a polyethylene copolymer obtained by coordination polymerization of mainly ethylene with minor amounts of one or more copolymerizable monomers. A particularly improved Final product properties, wherein ranges from any lower limit to any upper limit may be considered. Suitable comonomers include C ₃ -C ₂₀ alpha-olefins, preferably C ₃ -C ₈ , C ₅ -C ₂₀ cycloolefins, preferably C ₇ -C ₁₂ cycloolefins, C ₇ -C ₂₀ vinyl aromatic monomers , preferably styrene, and a C ₄ -C ₂₀ gem-disubstituted olefin, preferably isobutylene. Most preferred comonomers include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. The density of the copolymer is determined primarily by the comonomer content, and typically ranges from 0.905 or 0.910 g/ ^cm3 to 0.938 or 0.935 g/ ^cm3 , with ranges from any lower limit to any upper limit being contemplated. Some amount of long chain branching may be present, but the density is limited mainly by the presence of comonomers. These ethylene copolymers have a higher molecular weight than the second polyethylene in the blend by having a melt index I _2.16 of 0.1 measured according to ASTM D 1238, condition 190°C, 2.16 kg (formerly condition "E") Or 0.3 to 3.0 or 2.0 or 1.0 g/10min to express, wherein the range from any lower limit to any upper limit can be considered.

The second polyethylene in the polymer blend of the present invention has a higher density and lower molecular weight than the first polyethylene. The second polyethylene may be derived from ethylene, and optionally a small amount of any of the comonomers listed above for the first polyethylene. Density may be from a lower limit of 0.945 or 0.950 or 0.955 or 0.960 g/ ^cm to an upper limit of 0.975 or 0.972 or 0.970 or 0.968 g/ ^cm , wherein ranges from any lower limit to any upper limit are contemplated. It should be understood that the particular choice of density must be consistent with the density differentials described herein. The melt index I _2.16 of the second polyethylene is measured according to ASTM D 1238, condition 190°C, 2.16 kg, and may be from a lower limit of 10 or 3 0 or 50 to an upper limit of 500 or 300 or 200 or 100 g/10 min, wherein from Ranges from any lower limit to any upper limit are contemplated. The second polyethylene can be any conventional polyethylene having the properties described herein, and can have a broad or narrow molecular weight distribution. In a particular embodiment, the Mw/Mn value of the second polyethylene has a lower limit of 1.4 or 1.6 or 1.8 or 2.0 to an upper limit of 4.0 or 3.8 or 3.5 or 3.0, wherein the range from any lower limit to any upper limit can be adjusted consider.

Industrial methods of producing the polyethylene components of the present invention are well known in the art, as exemplified in the references cited above. Any such process capable of producing the polyethylene polymer component of the invention is suitable. Such processes include gas phase, liquid phase (or solution) and slurry phase polymerization processes, either alone or in combination. By itself, mention may be made of serial or serial production in a single reactor or in more than one reactor. Blends of reactors are also suitable, such as by using mixed catalysts or mixed polymerization conditions in a single reactor. In view of the economic advantages, gas phase polymerization is especially suitable. This process uses a supported catalyst and is carried out in a polymerization reactor under gas phase conditions suitable for the preparation of linear low density ethylene copolymers by coordination polymerization. Examples can be found in US Pat. These processes use either traditional Ziegler-Natta catalysts or later organometallic catalysts characterized as having essentially a single polymerization site due to the arrangement of ancillary ligands on or around the metal center. Metallocene catalysts are representative of "single site catalysts" and are preferred in the narrow molecular weight distribution polyolefin embodiment of the present invention. The process is typically carried out at a temperature of from about -100°C to 150°C, more typically from about 40°C to 120°C, at a pressure of up to about 7000 kPa, typically from about 690 kPa to 2415 kPa. A continuous process using a fluidized bed and a recycle stream as fluidizing medium is preferred.

Slurry polymerization processes are suitable for both components, and especially for the high density components of the present invention. These processes are typically described in which the polymerization medium can be either a liquid monomer, such as propylene, or a hydrocarbon solvent or diluent, advantageously an aliphatic paraffin such as propane, isobutane, hexane, heptane, cyclohexane Alkanes, etc., or those processes for aromatics such as toluene. Slurry solids typically include formed polymer and catalyst supported on an inert support. The catalyst is typically a Ziegler Natta catalyst, and/or one or more single site catalysts, such as metallocenes. Polymerization temperatures may be those considered lower, such as less than 50°C, typically 0°C to 30°C, or may be in the higher range, such as up to about 150°C, typically from 50°C to about 80°C, or Any range between the indicated endpoints. The pressure can vary from about 100 to about 700 psia (0.76-4.8 MPa). Additional descriptions are given in US Pat.

The polyethylene blend composition of the present invention may comprise the first polyethylene in an amount from a lower limit of 20 or 30 or 40 wt% to an upper limit of 80 or 70 or 60 wt% based on the total weight of the first and second polyethylene, wherein Ranges from any lower limit to any upper limit are contemplated. Similarly, the polyethylene blend composition of the present invention may comprise the second polyethylene in an amount from a lower limit of 20 or 30 or 40 wt% to an upper limit of 80 or 70 or 60 wt%, based on the total weight of the first and second polyethylenes. Ethylene, wherein ranges from any lower limit to any upper limit are contemplated.

Additionally, one or both of the first polyethylene and the second polyethylene may be a sub-blend of two or more polyethylenes as long as the sub-blend has the properties described herein. performance.

Although the description herein focuses on the first and second polyethylenes, in some embodiments the polyethylene copolymer composition may further comprise additional polymer components, including additional polyethylenes, provided that the overall The blend composition has the recited properties.

The weight percents of the first and second polyethylene components recited herein are based on the total weight (100%) of the first and second polyethylene components.

The density of the blend is from a lower limit of 0.920 or 0.930 or 0.940 or 0.950 g/ ^cm3 to an upper limit of 0.973 or 0.970 or 0.965 or 0.960 g/ ^cm3 , wherein ranges from any lower limit to any upper limit are contemplated.

The blend may have a density difference of the first and second polyethylenes from a lower limit of 0.037 or 0.038 or 0.040 g/ ^cm to an upper limit of 0.062 or 0.060 g/ ^cm , with the second polyethylene having a greater density, Wherein ranges from any lower limit to any upper limit are contemplated.

The melt index I _2.16 of the blend can be from a lower limit of 2 or 3 or 4 g/10 min to an upper limit of 200 or 100 or 50 or 30 or 10 g/10 min.

The first and second polyethylenes respectively have weight average molecular weights _Mw1 and _Mw2 satisfying the following relationship:

M _w1 /M _w2 >1

The densities of the first and second polyethylenes, ρ ₁ and ρ ₂ , satisfy the following relationship, respectively:

ρ ₁ /ρ ₂ <1

It is well known in the art that, all other factors being equal, ESCR is inversely proportional to density, and inversely proportional to melt index. It has surprisingly been found that polyethylene blend compositions of the present invention exhibit ESCR values greater than those having the same density and melt index, but do not have the inventive combination of properties described herein, such as melt index, melt index, Those ESCR values for conventional compositions of density and density difference.

Additives can be used as desired. Typical additives include one or more of antioxidants, antistatic agents, UV stabilizers, blowing agents, processing aids, nucleating agents, nanocomposites, fiber reinforcements and pigments. Exemplary pigments or colorants include titanium dioxide, carbon black, cobalt alumina such as cobalt blue, and chromium oxides such as chromium oxide green. Pigments such as Ultramarine Blue (which is a silicate). Phthalocyanine blue and iron oxide red are also suitable. These are typically used in amounts of 0 wt% to not greater than about 15 wt%, based on the combined weight of the first and second polyethylene components.

6. Example

Mz, Mw and Mn can be measured using gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC). This technique utilizes an instrument comprising a column packed with porous beads, an elution solvent, and a detector in order to separate polymer molecules of different sizes. In typical measurements, the GPC instrument used was a Waters chromatograph equipped with an ultrastyro gel column operated at 145°C. The elution solvent used was trichlorobenzene. The column was calibrated using 16 polystyrene standards of precisely known molecular weight. Corresponding the polystyrene retention volume obtained from this standard to the retention volume of the polymer tested yields the molecular weight of the polymer.

The average molecular weight M can be calculated by the following expression:

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; no</span>}}}$

where N _i is the number of molecules with molecular weight _Mi. When n=0, M is the number average molecular weight Mn. When n=1, M is the weight average molecular weight Mw. When n=2, M is the Z-average molecular weight Mz. The desired MWD function (eg Mw/Mn or Mz/Mn) is the ratio of the corresponding M values. The measurement of M and MWD is well known in the art and discussed in more detail in, for example, Slade, PEEd., Polymer Molecular Weights Part II, Marcel Dekker, Inc., NY, (1975) 287-368; Rodriguez, F., Principles of Polymer Systems 3rd ed., Hemisphere Pub. Corp., NY, (1989) 155-160; US Patent No. 4540753; Verstrate et al., Macromolecules, vol. 21, (1988); and in various references cited herein.

Environmental Stress Crack Resistance (ESCR) was determined according to ASTM D 1693, Condition B, 10 wt% IGEPAL ^™ (bent bar). IGEPAL ^™ is a nonylphenoxy poly(ethyleneoxy)ethanol surfactant available from Rhone Polenc, Cranbury, NJ. All ESCR values recited here are ASTM D1693 Condition B, 10 wt% IGEPAL ^™ F50 values and are given in hours.

Polymer density (g/ ^cm3 ) was determined using compression molded samples according to ASTM D 1505-68 and ASTM D1928, procedure C, cooling at 15°C/hour and conditioning at room temperature for 40 hours.

The melt flow rate of a polymer can be measured at 190°C according to ASTM D-1238. I _21.6 is the "flow index" or melt flow rate of the polymer measured according to ASTM D-1238, condition 190°C, 21.6 kg, and I _2.16 is the polymer measured according to ASTM D-1238, condition 190°C, 2.16 kg The "melt index" or melt flow rate. The ratio of I _21.6 to I _2.16 is the "melt flow ratio" or "MFR". Melt flow rate I _21.6 is also sometimes referred to as "high load melt index" or HLMI. Melt flow rate is reported in units of grams per 10 minutes (g/10min) or equivalently in decigrams per minute (dg/min).

Embodiment 1-8, comparative example 1-2

Table 1 shows the invention in Examples 1a-b to 8a-3b, and Comparative Examples Comp1 and Comp2a-c. Each "a" row shows the first polyethylene component, and each "b" row shows the second polyethylene component. In Comp2, row "c" indicates the third polyethylene component. The "Delta Density" column provides the difference in density of the two components for each listed blend. In Comp2, the density difference is the difference between components 2a and 2c. Comp 1 shows comparative single polyethylene components in the range of density and melt index typical for injection molding compositions. Comp 2 shows a blend for comparison where the difference in density is less than 0.037 g/cm ³ , but the blend has the same melt index and density as Example 1 .

The polyethylene resins in Table 1 were generally prepared according to the examples in US Patent No. 5,382,631, unless otherwise noted. Zirconocene activated with aluminoxane on a silica support, 12 wt% methylalumoxane and 3.5 wt% zirconium were used as polymerization catalysts in a gas phase reactor operated at about 185°F (85°C) , wherein the gas phase is composed of 70 volume wt% ethylene, 0.5-2.0 volume wt% hexene, 200-800 ppm hydrogen, and the rest being nitrogen. Approximately 50-75 lbs (22.6-33.9 kg)/hour were produced in each polymerization run.

The ESCR values given as ranges in Table 1 represent failure of the samples that occurred at unspecified times during the time period indicated. The ESCR value for blend 6a/6b indicated that the sample was intact when the test was terminated at 605 hours.

Comparative Examples 1 and 2 have the same density as Example 1, and the same or comparable melt index, but exhibit poor ESCR performance (4.5 hours vs. 78.5-143 hours).

Table 1 Example wt% Melt index I _2.16 (g/10min) Density (g/cm ³ ) Mw/Mn Δdensity (g/cm ³ ) ESCR, F ₅₀ (hr) 1a1b1a/1b blend 30.669.4100 0.4656.66.8 0.9110.9700.952 2.503.8 0.059 78.8-143 2a2b2a/2b blend 27.272.8100 0.4656.67.5 0.9110.9700.954 2.503.8 0.059 69.5 3a3b3a/3b blend 25.574.5100 0.4656.68.6 0.9110.9700.955 2.503.8 0.059 6.5-23.5 4a4b4a/4b blend 23.876.2100 0.4656.69.3 0.9110.9700.956 2.503.8 0.059 6.5-23.5 5a5b5a/5b blend 22.277.8100 0.4656.610.0 0.9110.9700.957 2.503.8 0.059 5-6.5 6a6b6a/6b blend 3070100 0.4556.64.8 0.9190.9700.955 2.593.8 0.051 >605 7a7b7a/7b blend 2476100 0.4556.65.4 0.9190.9700.958 2.593.8 0.051 60-78 8a8b8a/8b blend 35.564.5100 0.8656.67.0 0.9190.9700.952 2.433.8 0.051 21-39 Comp1* 100 6.5 0.952 3.6 4.5 Comp2aComp2bComp2cComp2a/2b/2c blend 293437100 3.03.056.66.8 0.9350.9470.9700.952 2.822.873.8 0.035 4.5

*Commercial HDPE for injection molding (HD6706, ExxonMobil Chemical)

Various trade names used herein are indicated by the symbol ^TM , which indicates that these names may be protected by certain trademark rights. Some of these names may also be registered trade names, in various jurisdictions.

All patents, test procedures, and other documents cited herein, including priority documents, are incorporated by reference in their entirety to the extent their disclosure was not inconsistent with the present invention and for all jurisdictions in which such incorporation was permitted.

Claims (37)

1. polyethylene composition, it comprises:

(a) melt index is that 0.1-3.0g/10min and density are 0.905-0.938g/cm ³First polyethylene; With

(b) melt index is that 10-500g/10min and density are 0.945-0.975g/cm ³Second polyethylene,

Wherein the density of said composition is 0.920-0.973g/cm ³And melt index be 2-200g/10min and wherein the second poly density than the big 0.037-0.062g/cm of the first poly density ³

2. the composition of claim 1, wherein at least a in first and second polyethylene is the polyethylene of metallocene catalysis.

3. the composition of claim 1, wherein first and second polyethylene are polyethylene of metallocene catalysis.

4. the composition of claim 2, wherein the ratio of the poly Mw/Mn of metallocene catalysis is 1.4-4.0.

5. the composition of claim 1, wherein first polyethylene is that the ratio of Mw/Mn is the polyethylene of the metallocene catalysis of 1.4-4.0.

6. the composition of claim 1, wherein the first poly density is 0.910-0.935g/cm ³

7. the composition of claim 1, wherein the second poly density is 0.950-0.972g/cm ³

8. the composition of claim 1, wherein the second poly density is 0.955-0.970g/cm ³

9. the composition of claim 1, wherein the density of said composition is 0.930-0.970g/cm ³

10. the composition of claim 1, wherein the density of said composition is 0.940-0.965g/cm ³

11. the composition of claim 1, wherein the density of said composition is 0.950-0.960g/cm ³

12. the composition of claim 1, wherein the second poly density is than the big 0.038-0.060g/cm of the first poly density ³

13. the composition of claim 1, wherein the melt index I of composition _2.16Be 4-30g/10min.

14. the composition of claim 1, wherein based on the first and second poly gross weights, this blend comprises 80wt%-20wt% first polyethylene and 20wt%-80wt% second polyethylene.

15. the composition of claim 1, wherein based on the first and second poly gross weights, this blend comprises 70wt%-30wt% first polyethylene and 30wt%-70wt% second polyethylene.

16. the composition of claim 1, wherein based on the first and second poly gross weights, this blend comprises 60wt%-40wt% first polyethylene and 40wt%-60wt% second polyethylene.

17. the composition of claim 1, wherein this blend is made up of first and second polyethylene basically.

18. the composition of claim 1, the wherein at least a blend that comprises two or more polyvinyl resins in first and second polyethylene.

19. an injection-molded item, it comprises polyethylene composition, and described polyethylene composition comprises:

(a) melt index is that 0.1-3.0g/10min and density are 0.905-0.938g/cm ³First polyethylene; With

(b) melt index is that 10-500g/10min and density are 0.945-0.975g/cm ³Second polyethylene,

Wherein the density of said composition is 0.920-0.973g/cm ³And melt index be 2-200g/10min and wherein the second poly density than the big 0.037-0.062g/cm of the first poly density ³

20. the injection-molded item of claim 19, wherein at least a in first and second polyethylene is the polyethylene of metallocene catalysis.

21. the injection-molded item of claim 19, wherein first and second polyethylene are polyethylene of metallocene catalysis.

22. the injection-molded item of claim 20, wherein the ratio of the poly Mw/Mn of metallocene catalysis is 1.4-4.0.

23. the injection-molded item of claim 1, wherein first polyethylene is that the ratio of Mw/Mn is the polyethylene of the metallocene catalysis of 1.4-4.0.

24. the injection-molded item of claim 19, wherein the first poly density is 0.910-0.935g/cm ³

25. the injection-molded item of claim 19, wherein the second poly density is 0.950-0.972g/cm ³

26. the injection-molded item of claim 19, wherein the second poly density is 0.955-0.970g/cm ³

27. the injection-molded item of claim 19, wherein the density of said composition is 0.930-0.970g/cm ³

28. the injection-molded item of claim 19, wherein the density of said composition is 0.940-0.965g/cm ³

29. the injection-molded item of claim 19, wherein the density of said composition is 0.950-0.960g/cm ³

30. the injection-molded item of claim 19, wherein the second poly density is than the big 0.038-0.060g/cm of the first poly density ³

31. the injection-molded item of claim 19, wherein the melt index I of composition _2.16Be 4-30g/10min.

32. the injection-molded item of claim 19, wherein based on the first and second poly gross weights, this blend comprises 80wt%-20wt% first polyethylene and 20wt%-80wt% second polyethylene.

33. the injection-molded item of claim 19, wherein based on the first and second poly gross weights, this blend comprises 70wt%-30wt% first polyethylene and 30wt%-70wt% second polyethylene.

34. the injection-molded item of claim 19, wherein based on the first and second poly gross weights, this blend comprises 60wt%-40wt% first polyethylene and 40wt%-60wt% second polyethylene.

35. the injection-molded item of claim 19, wherein this blend is made up of first and second polyethylene basically.

36. the injection-molded item of claim 19, the wherein at least a blend that comprises two or more polyvinyl resins in first and second polyethylene.

37. a method that forms injection-molded item, this method comprises the steps:

(a) provide polyethylene composition, described polyethylene composition comprises:

(i) melt index is that 0.1-3.0g/10min and density are 0.905-0.938g/cm ³First polyethylene; With

(ii) melt index is that 10-500g/10min and density are 0.945-0.975g/cm ³Second polyethylene,

Wherein the density of said composition is 0.920-0.973g/cm ³And melt index be 2-200g/10min and wherein the second poly density than the big 0.037-0.062g/cm of the first poly density ³With

(b) this polyethylene composition of injection moulding forms injection-molded item.