High performance multimodal ultra-high molecular weight polyethylene

Abstract

The present invention relates to a multimodal polyethylene composition, to sheets and hollow articles comprising same, to a process for preparing the sheets or hollow articles, and to the use of the sheets or hollow articles.

Description

[Technical field]

[0001] The demand for polyethylene resins is increasing due to their use in various applications. High performance of polyethylene for new plastic applications is required. To balance the processability and physical properties of ethylene copolymers, multimodal ultra-high molecular weight polyethylene is a promising material.

[0002] Ultra high molecular weight polyethylene (UHMWPE) is a polyethylene with an average molecular weight of several million, usually between 3.5 and 7.5 million. The high molecular weight results in superior mechanical properties in terms of abrasion resistance, impact resistance, fatigue resistance and chemical resistance compared to common engineering plastics. However, due to the high molecular weight, this results in less efficient packing of the chains into the crystalline structure, as observed by a lower density than high density polyethylene (e.g., 0.930-0.935 g / cm3). Furthermore, the main drawback of UHMWPE is processing. UHMWPE does not flow above its melting temperature, and as a result is difficult to process by conventional extrusion, except by ram extrusion.

[0003] Ultra high molecular weight polyethylene (UHMWPE) is well known for its excellent mechanical properties, such as high abrasion resistance and impact strength, for fabrication of plastic sheets for various applications. Typically, UHMWPE is not easily processed by conventional extrusion; specific machinery and fabrication processes, such as compression molding and ram extrusion, are generally required.

[0004] Some reports claim that UHMWPE can improve the toughness and mechanical properties (wear, impact, tensile, low friction, etc.) of the polymer by blending with other polymers, such as polypropylene, polycarbonate, and conventional polyethylene. It is also well known that UHMWPE forms separate islands in the high-density polyethylene (HDPE) matrix, thus resulting in inhomogeneity in the final blend. When severe compounding conditions or re-extrusion are applied to improve homogeneity, degradation of the polymer chains occurs, leading to a decrease in the ultra-high molecular weight fraction.

[0005] A study to improve the processability of UHMWPE was carried out by Jaggi and co-workers. They used a blend system between HDPE and UHMWPE and applied complex viscosity to observe its processability. The study showed that the complex viscosity of UHMWPE decreases as the amount of HDPE increases. Furthermore, the mechanical properties of the blend system improved in terms of tensile strength, Young's modulus, and impact strength (J polym Res 2014,21,482). The complex viscosity can be reduced by blending with another system, for example, by blending UHMWPE with low density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) as shown in the report by Chen and co-workers (polymer science series A vol 56 no 5 2014).

[0006] However, there is another system to improve the balance of UHMWPE processability and mechanical properties. Blend systems of UHMWPE and other low molecular weight polymers, such as polypropylene (PP), to improve processability have been known. They claim that the amount of UHMWPE in HDPE / PP affects the mechanical properties and processability. The optimum blend ratio between UHMWPE and HDPE / PP must be verified to maximize the mechanical properties. However, the mixing behavior between UHMWPE and HDPE / PP is very important for the mechanical properties, and processability is key to control from the blend system, which is very difficult to control.

[0007] EP 1655334 discloses a multimodal production of ethylene polymers produced in a multi-stage process using MgCl2-based Ziegler-Natta catalysts. The polymerization stages are carried out in the following order to obtain first an ultra-high molecular weight polymer, followed by a low molecular weight polymer and finally, in the last step, a high molecular weight polymer. The polymerization catalyst is introduced in a prepolymerization step to prepare the ultra-high molecular weight fraction.

[0008] WO 2013 / 144328 describes a composition of multimodal high density polyethylene for use in molding applications, produced using a Ziegler-Natta catalyst. A small amount of ultra-high density polyethylene, less than 15% by weight, is produced in a third reactor.

[0009] In WO 2014 / 091501, blends of HDPE and UHMWPE can improve the impact strength or tensile strain of HDPE. However, the morphology after blending is one of the important factors.

[0010] Blends of bimodal HDPE and UHMWPE have been successfully made in WO 2015121161 and EP 2907843. It was claimed that the mechanical properties of the bimodal HDPE were increased due to the proportion of UHMWPE. Furthermore, the blends can be prepared by extrusion.

[0011] In EP 2743305, multimodal HDPE was blended with UHMWPE. UHMWPE was added to a multimodal HDPE pipe resin to improve mechanical properties, including sag properties, but multiple extrusions were required to improve the homogeneity of the blend.

[0012] US 2009 / 0163679 describes a process for producing multimodal ultra-high molecular weight polyethylene, where the polymerization is carried out in a continuous stirred tank reactor (CSTR), the molecular weight of each reactor is controlled by pressure, temperature and hydrogen, and an ultra-high molecular weight ethylene polymer composition can be obtained by this process.

[0013] However, in light of the above prior art, there remains a need to provide a multimodal polyethylene composition for preparing UHMWPE and sheets that overcomes the shortcomings of the prior art, in particular to provide a high density polyethylene composition for producing sheets having improved properties such as abrasion resistance and / or having improved homogeneity and / or processability. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] European Patent No. 1655334 [Patent Document 2] International Publication No. 2013 / 144328 [Patent Document 3] International Publication No. 2014 / 091501 Brochure [Patent Document 4] International Publication No. 2015121161 Brochure [Patent Document 5] European Patent No. 2907843 [Patent Document 6] European Patent No. 2743305 [Patent Document 7] US Patent Application Publication No. 2009 / 0163679 [Non-patent literature]

[0015] [Non-Patent Document 1] J Polym Res 2014,21,482 [Non-Patent Document 2] polymer science series A vol 56 no 5 2014 Summary of the Invention

[0016] The object of the present invention is to overcome the drawbacks of the prior art and in particular to provide a multimodal polyethylene composition having improved mechanical properties.

[0017] The purpose of this is to (A) 7 to 40% by weight, based on the total weight of the multimodal polyethylene composition, of a low molecular weight polyethylene homopolymer having a viscometer molecular weight (Mv) of 31,000 to 260,000 g / mol; (B) 20 to 45% by weight, based on the total weight of the multimodal polyethylene composition, of a first high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight of 1,900,000 to 5,200,000 g / mol; and (C) 28 to 72 wt. % of a second high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight of 3,000,000 to 7,300,000 g / mol, based on the total weight of the multimodal polyethylene composition; This is achieved by a multimodal polyethylene composition comprising: wherein the first high molecular weight polyethylene and the second high molecular weight polyethylene differ from each other in terms of their viscometer molecular weights; The multimodal polyethylene composition has an intrinsic viscosity (IV) of 11 to 22 dl / g, and the intrinsic viscosity is measured in accordance with ISO1872.

[0018] The "viscometer molecular weight" referred to herein with respect to one of the components (A)-(C), i.e., with respect to one of the polyethylene fractions comprised in the multimodal polyethylene composition of the present invention, refers to the viscometer molecular weight of the respective fraction individually. In other words, the individual viscometer molecular weight is not affected by other polyethylene fractions of the multimodal polyethylene composition, such as fractions that may have been previously prepared in the process for preparing the multimodal polyethylene composition.

[0019] The multimodal polyethylene composition of the present invention is produced in a multistage process, in which fractions (A), (B) and (C) are produced in subsequent stages. In such cases, the properties of the fractions produced in the second or third (or further) stages of the multistage process can be inferred from the polymers produced separately in a single stage by applying identical polymerization conditions (e.g., identical temperature, reactant / diluent partial pressures, suspension medium, reaction time) for the stage of the multistage process in which the fractions are produced, and by using a catalyst in which no previously produced polymer is present. Alternatively, the properties of the fractions produced in the higher stages of the multistage process can also be calculated, for example, according to B. Hagstrom, Conference on Polymer Processing (The Polymer Processing Society), Extended Abstracts and Final Programme, Gothenburg, August 19 to 21, 1997, 4:13.

[0020] Thus, the properties of fractions produced in higher stages of such multi-step processes, which cannot be measured directly in the multi-step process product, can be determined by applying one or both of the above methods. Those skilled in the art can select the appropriate method. One particular method of calculating properties such as molecular weight (such as Mv) is to apply a deconvolution process using Excel or other calculation programs. The deconvolution process involves subtraction of the respective signals.

[0021] The polymer HDPE produced in the multi-stage process is also called an "in-situ" blend. The final product obtained consists of a homogeneous mixture of polymers from three or more reactors, the different molecular weight distribution curves of which together form a molecular weight distribution curve with a broad maximum or two or three or more maxima. The low molecular weight polyethylene homopolymer having a viscometer molecular weight (Mv) of 31,000 to 260,000 g / mol may be referred to herein as component (A). The first high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight (Mv) of 1,900,000 to 5,200,000 g / mol may be referred to herein as component (B). The second high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight (Mv) of 3,000,000 to 7,300,000 g / mol may be referred to herein as component (C). The three components (A), (B) and (C) may also be referred to as fractions of a multimodal polyethylene composition. The multimodal polyethylene composition may comprise the three polyethylene fractions (A), (B) and (C) in a total amount selected from the group consisting of at least 50% by weight, at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, at least 99% by weight, based on the total weight of the multimodal polyethylene composition. The multimodal polyethylene composition may essentially consist of the three polyethylene fractions (A), (B) and (C). The multimodal polyethylene composition may consist of the three polyethylene fractions (A), (B) and (C).

[0022] The multimodal polyethylene composition may comprise component (A) in an amount of 7 to 40 wt%, based on the total weight of the multimodal polyethylene composition.

[0023] The multimodal polyethylene composition may comprise component (B) in an amount of 20 to 45 wt%, based on the total weight of the multimodal polyethylene composition.

[0024] The multimodal polyethylene composition may comprise component (B) in an amount of 28 to 72 wt%, based on the total weight of the multimodal polyethylene composition.

[0025] Component (A) may have a viscometer molecular weight (Mv) of 31,000 to 260,000, preferably 31,500 to 236,000 g / mol.

[0026] Component (B) may have a viscometer molecular weight (Mv) of 1,900,000 to 2,600,000, preferably 2,100,000 to 4,700,000 g / mol.

[0027] Component (C) may have a viscometer molecular weight (Mv) of 3,000,000 to 7,300,000, preferably 3,400,000 to 6,700,000 g / mol.

[0028] When the first high molecular weight polyethylene, component (B), is a copolymer, the comonomer copolymerized with the polyethylene may be a C4 monomer (butene) and / or a C6 monomer (hexene). The amount of the comonomer in the copolymer may be 0.01 to 1.0 mol%.

[0029] When the second high molecular weight polyethylene, component (C), is a copolymer, the comonomer copolymerized with the polyethylene may be a C4 monomer (butene) and / or a C6 monomer (hexene). The amount of the comonomer in the copolymer may be 0.01 to 1.0 mol%.

[0030] The total amount of comonomers in the multimodal polyethylene composition may be from 0.01 to 2.0% mol, preferably from 0.01 to 1.5% mol, more preferably from 0.01 to 1.0% mol, even more preferably from 0.01 to 0.5% mol, and most preferably from 0.01 to 0.2% mol, based on the total weight of the multimodal polyethylene composition.

[0031] The multimodal polyethylene composition has a weight average molecular weight (M) determined by gel permeation chromatography (GPC). w ) may be from 1,200,000 g / mol to 2,500,000 g / mol, in particular from 1,300,000 g / mol to 2,300,000 g / mol.

[0032] The multimodal polyethylene composition has a number average molecular weight (M n ) may be from 20,000 g / mol to 130,000 g / mol.

[0033] The multimodal polyethylene composition has a molecular weight distribution (M w / M n ), and polydispersity index (PDI).

[0034] The multimodal polyethylene composition may have an intrinsic viscosity (IV) of 11 to 20 dl / g, in particular 11 to 19.5, for example 11.1 to 19.3, where the intrinsic viscosity is measured according to ISO1872.

[0035] The multimodal polyethylene composition has a thermal conductivity of 170 to 300 kJ / m, as measured by ISO 11542-2. 2 The multimodal polyethylene composition may have a double notched Charpy impact strength of 185 to 278 kJ / m as measured by ISO 11542-2. 2 , especially 188.0~278.0kJ / m 2 The steel may have a double notched Charpy impact strength of 0.01 to 0.05.

[0036] The viscometer molecular weight (Mv) of the multimodal polyethylene composition, i.e. the composition comprising all components (A), (B) and (C), may be from 1,800,000 g / mol to 4,600,000 g / mol, in particular from 1,900,000 g / mol to 4,500,000 g / mol, for example from 1,930,000 g / mol to 4,420,000 g / mol.

[0037] In preparing a multimodal polyethylene composition in a cascade reactor process, a composition comprising only components (A) and (B), i.e., the composition received after the second reactor, may have a viscometer molecular weight (Mv) of from 1,000,000 g / mol to 2,700,000 g / mol, in particular from 1,050,000 g / mol to 2,690,000 g / mol.

[0038] The multimodal polyethylene composition may have a complex viscosity Eta(0.1) at high shear rate (0.1 1 / s at 190° C.) of 2,550 to 5,800 kPa.s, in particular 2,600 to 5,780 kPa.s.

[0039] The multimodal polyethylene composition has a modulus of 0.930 to 0.960 g / cm according to ASTM D 1505. 3 , in particular, may have a density of 0.9320 to 0.9520.

[0040] This object is further achieved by a sheet comprising the multimodal polyethylene composition according to the invention.

[0041] This object is further achieved by a hollow article comprising the multimodal polyethylene composition according to the invention.

[0042] This object is further achieved by a method for the preparation of a sheet according to the invention or a hollow article according to the invention, comprising a step of compression moulding the multimodal polyethylene composition according to the invention. The compression moulding process is a method in which the material is pre-heated by a heated plate or mould. Pressure and heat are applied to the material for an appropriate time until it is completely melted in the mould. The final product can be a sheet or a specific shape depending on the mould design.

[0043] This object is further achieved by a process for the preparation of a sheet according to the invention or a hollow article according to the invention, comprising the step of extruding a multimodal polyethylene composition according to the invention.

[0044] This object is further achieved by a sheet or hollow article comprising the multimodal polyethylene composition according to the invention.

[0045] Finally, this objective is achieved by the use of the sheets or hollow articles as compressed sheets, liners, profiles, profile extrusions, machines, fibers, tapes, industrial parts, high impact parts, high abrasive parts, sliding materials, RAM extrusion profiles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The multimodal polyethylene of the present invention can be prepared by the process for producing the multimodal polyethylene compositions of Table 1. The comparative and inventive examples were produced by using either a small scale reactor or a large scale reactor, as described in detail below.

[0047] Small-scale reactor The polymerization was carried out in a 10 liter autoclave reactor using 6 liters of purified n-hexane as diluent. The Ziegler-Natta catalyst is described in Hungarian Patent Application No. 0800771R, e.g. in Example 1 thereof. The amount of catalyst used, as indicated in Table 1, was added. Triethylaluminum was introduced. The temperature was then heated to the desired value and the feeding of ethylene was started. Hydrogen was charged into the reactor to adjust the intrinsic viscosity of the polymer produced in the first reactor. Ethylene was fed continuously, while maintaining the total pressure of the reaction. Once the desired amount of powder was prepared, the polymerization was stopped by releasing the pressure and cooling the slurry contents. The second stage of the reaction was started by increasing the temperature to the desired value. Ethylene was fed continuously, while maintaining the total pressure of the reaction. Once the blend ratio of the second stage was reached, the polymerization was stopped. The polymerization was stopped by releasing the pressure and cooling the slurry contents. The third stage of the reaction was started by increasing the temperature to the desired value. Optionally, C4-C12 α-olefin comonomers were added in this process to produce copolymers in the third stage. Ethylene was fed continuously while maintaining the total pressure of the reaction. Once the blend ratio of the second stage was reached, the polymerization was stopped by releasing the pressure and cooling the slurry contents. The blend ratio can be calculated directly by comparing the ethylene uptake during the different polymerization stages.

[0048] Large-Scale Reactors The polymerization was carried out in a sequential process using three reactors connected in series. The Ziegler-Natta catalyst was described in Hungarian Patent Application No. 0800771R, e.g. in Example 1 thereof. The catalyst in the dosage shown in Table 1 was introduced into the first reactor together with a sufficient amount of hexane and triethylaluminum as cocatalyst. The amounts of ethylene and hydrogen were set so that the polymer composition and intrinsic viscosity in the first reactor achieved the desired values.

[0049] The polymer slurry from the first reactor was depressurized before being transferred to the second reactor where unreacted gas was removed. Polymerization in the second reactor was continued by feeding ethylene set to achieve the desired polymer composition. Optionally, a C4-C12 α-olefin comonomer was also fed to the second reactor to produce the copolymer.

[0050] The polymer slurry from the second reactor was then transferred to the third reactor. Polymerization in the third reactor was continued by feeding ethylene set to achieve the desired polymer composition. Optionally, C4-C12 α-olefin comonomer was also fed to the third reactor to produce the copolymer. Optionally, hydrogen was fed to control the intrinsic viscosity of the third reactor to the desired value.

[0051] The powder remaining in the third reactor was separated from the solvent and dried.

[0052] Definitions and Measurement Methods MI The melt flow index (MI) of a polymer, which determines the flowability of the polymer under test conditions at 190° C. under a load of 2.16 kg (MI2), was measured according to ASTM D 1238 and is reported in g / 10 min.

[0053] density The density of polyethylene was measured by observing the level to which the pellets sank in a liquid column gradient tube compared to standards of known density. This method is a measurement of the solid plastic after annealing at 120°C according to ASTM D 1505 and is expressed in g / cm 3 It is expressed in units of.

[0054] Molecular weight and polydispersity index (PDI) : Weight average molecular weight (Mw), number average molecular weight (Mn) and Z average molecular weight (M Z) (g / mol) were analyzed by gel permeation chromatography (GPC). The polydispersity index was calculated by Mw / Mn. Approximately 8 mg of sample was dissolved in 8 ml of 1,2,4-trichlorobenzene at 160°C for 90 min. Then, 200 μl of the sample solution was injected into a high-temperature GPC equipped with an IR5, infrared detector (Polymer Char, Spain) at a flow rate of 0.5 ml / min, at 145°C in the column zone and 160°C in the detector zone. The data were processed by GPC One® software (Polymer Char, Spain).

[0055] Intrinsic viscosity (IV) : This test method covers the measurement of dilute solution viscosity of polyethylene at 135°C or ultra high molecular weight polyethylene (UHMWPE) at 150°C. Polymer solutions were prepared by dissolving the polymer in decalin containing 0.2% wt / vol stabilizer (Irganox 1010 or equivalent). Details are described for the measurement of IV according to ISO 1628.

[0056] viscometer molecular weight The viscometer molecular weight (MV) can be calculated based on the IV determined above, as shown in the following formula: Mv = 5.37 × 10 4 ×(IV) 1.49 where Mv is the viscometer molecular weight, Mv has units of (g / mol), and η is the intrinsic viscosity (dl / g).

[0057] Individual molecular weight calculations and individual intrinsic viscosities The multimodal polyethylene composition of the present invention is produced in a multistage process, in which fractions (A), (B) and (C) are produced in subsequent stages. In such cases, the properties of the fractions produced in the second or third (or further) stages of the multistage process can be inferred from the polymers produced separately in a single stage by applying identical polymerization conditions (e.g., identical temperature, reactant / diluent partial pressures, suspension medium, reaction time) for the stage of the multistage process in which the fractions are produced, and by using a catalyst in which no previously produced polymer is present. Alternatively, the properties of the fractions produced in the higher stages of the multistage process can also be calculated, for example, according to B. Hagstrom, Conference on Polymer Processing (The Polymer Processing Society), Extended Abstracts and Final Programme, Gothenburg, August 19 to 21, 1997, 4:13.

[0058] Thus, the properties of fractions produced in higher stages of such multi-step processes, which cannot be measured directly in the multi-step process product, can be determined by applying one or both of the above methods. Those skilled in the art can select the appropriate method. One particular method of calculating properties such as molecular weight (such as Mv) is to apply a deconvolution process using Excel or other calculation programs. The deconvolution process involves subtraction of the respective signals.

[0059] The polymer HDPE produced in a multi-stage process is also called an "in-situ" blend. The final product obtained consists of a homogeneous mixture of polymers from three or more reactors, whose different molecular weight distribution curves together form a molecular weight distribution curve with a broad maximum or two or three or more maxima.

[0060] The individual IV and individual Mv calculations for each example in Reactors 1, 2 and 3 are shown in Table 1.

[0061] Comonomer Content : Comonomer content is high resolution 13 The NMR spectra were determined by C-NMR. 13C-NMR spectra were recorded on a 500 MHz ASCEND™ (Bruker) using a cryogenic 10 mm probe. TCB was used as the main solvent and TCE-d2 as the locking agent in a volume ratio of 4:1. NMR experiments were performed at 120°C using the pulse program inverse gated 13C (zgig) with a pulse angle of 90°. The delay time (D1) for full spin recovery was set to 10 s. Finally, the comonomer content is calculated in % molar.

[0062] Viscosity at shear rate of 0.1 (1 / s) (Eta(0.1)) The rheological parameters are determined by using a controlled strain rheometer model ARES-G2 TA instrument. The geometry is plate-plate 8 mm diameter. The measurement gap was prescribed at 1 mm. Dynamic oscillatory shear was carried out at angular frequencies between 0.1 and 200 rad / s at a temperature of 190 °C under nitrogen atmosphere. The sample preparations were prepared by compression molding at 190 °C. The viscosity at 0.1 1 / s [η0.1] was obtained by Cox-Mertz transformation of the complex viscosity at a specific angular frequency equal to 0.1 rad / s. The viscosity at a shear rate of 0.1 (1 / s) was given in units of kPa.s.

[0063] Double notched Charpy impact strength Compression specimens were prepared according to ISO 11542-2. The Charpy impact strength (respectively, double-notched Charpy impact strength) was determined according to ISO 11542-2 at 23°C and is expressed in kJ / m 2 As shown in. EXAMPLES

[0064] Experiments and Examples To prepare the inventive sheets from the above compositions, it has been found that the subrange of multimodal polyethylene compositions obtainable using the inventive reactor system by polymerization in a small-scale reactor and in a large-scale reactor is particularly preferred. In detail, compositions suitable for forming the inventive sheets are as follows and have the following characteristics: The following comparative examples refer to sheet-related compositions:

[0065] The inventive and comparative examples were prepared according to the process conditions set forth in Table 1. Most of the UHMWPE samples were prepared to provide improved melt processing and impact properties comparable to common polyethylene. The compositions were then prepared into sheets whose properties are defined in Table 1.

[0066] Example 1 (E1) of the present invention Inventive Example 1 (E1) was produced to prepare a multimodal polyethylene composition using a small scale reactor using the protocol disclosed above and the amounts of reactants shown in Table 1. A homopolymer was produced in the first reactor to obtain a medium molecular weight portion before transferring such polymer. The low to medium molecular weight polymer was then transferred to the second reactor to produce the first ultra-high molecular weight polymer. Finally, the produced polymer from the second reactor was transferred to the third reactor to produce the second ultra-high molecular weight polymer. The second and third reactors are operated under hydrogen starved polyethylene polymerization. A UHMWPE powder with an IV of 11.1 dl / g was obtained.

[0067] Example 2 (E2) of the present invention Inventive Example 2 (E2) was carried out similarly to E1 with various types of IV by adjusting the multimodal composition and polymerization conditions using 1-hexene comonomer. Inventive Example 2 (E2) with an IV of 13.7 dl / g and 0.03% molar comonomer content shows higher impact strength compared to the comparative blend sample.

[0068] Example 3 (E3) of the present invention Example 3 (E3) of the present invention was prepared similarly to E1 and E2, using different blend compositions as shown in Table 1. The percentage of 1-butene comonomer incorporation in the final product is 0.17% molar. A UHMWPE powder with an IV of 15.8 dl / g was obtained.

[0069] Example 4 (E4) of the present invention Inventive Example 4 (E4) was carried out in a similar manner to E1, E2 and E3, but synthesis was carried out using a different large-scale reactor by adjusting the multimodal composition and polymerization conditions. The IV is higher than E1, E2 and E3 without comonomer. A UHMWPE powder with an IV of 16.4 dl / g was obtained.

[0070] Example 5 (E5) of the present invention Inventive Example 5 (E5) was synthesized in a small scale reactor in a manner similar to E1, E2, E3, and E4, but with different blend compositions and IVs in the second and third reactors due to polymerization conditions using 1-butene comonomer. A UHMWPE powder with an IV of 18.2 dl / g and a comonomer content of 0.03% molar was obtained.

[0071] Example 6 (E6) of the present invention Inventive Example 6 (E6) was synthesized in a large scale reactor in a manner similar to E1, E2, E3, E4 and E5, but with different blend compositions and IVs in the second and third reactors without comonomer. A UHMWPE powder with an IV of 19.3 dl / g was obtained. The inventive example has the highest IV with a high Eta(0.1), 5,772 kPa.s, limiting processability.

[0072] Example 7 (E7) of the present invention Example 7 (E7) of the present invention was carried out in the same manner as E1, E2, E3, E4, E5 and E6, except that the synthesis was carried out in a small-scale reactor with different blend compositions and IVs in the second and third reactors without comonomers. A UHMWPE powder with an IV of 11.6 dl / g was obtained.

[0073] Example 8 (E8) of the present invention Inventive Example 8 (E8) was carried out in the same manner as E1, E2, E3, E4, E5, E6, and E7, except that the synthesis was carried out in a small-scale reactor with different blend compositions and IVs in the second and third reactors without comonomers. A UHMWPE powder with an IV of 12.3 dl / g was obtained.

[0074] Example 9 (E9) of the present invention Inventive Example 9 (E9) was carried out in the same manner as E1, E2, E3, E4, E5, E6, E7 and E8, except that the synthesis was carried out in a large-scale reactor with different blend compositions and IVs in the second and third reactors without comonomer. A UHMWPE powder with an IV of 13.5 dl / g was obtained. The inventive example shows the highest impact properties compared to all comparative examples and inventive examples.

[0075] Comparative example 1 (CE1) The unimodal homopolymer was a commercial grade (U521) with an IV of 25.0 dl / g.

[0076] Comparative Example 2 (CE2) Comparative Example 2 (C2) was carried out in a similar manner to E1 by using a large scale reactor with a multimodal composition with a blend ratio of 12 / 30 / 58 and varying IV by adjusting the polymerization conditions. Comparative Example 2 (CE2) had an IV of 24.8 dl / g.

[0077] Comparative Example 3 (CE3) Comparative Example 3 (CE3) is a multimodal polyethylene polymerized with a blend ratio of 49 / 25 / 26. The polymerization process was carried out in small scale reactors. The MFR of the first reactor is 20 g / 10 min. The intrinsic viscosities of the second and third reactors are 4.4 dl / g and 6.7 dl / g, respectively, for polymerization with 0.2% molar 1-butene comonomer.

[0078] Comparative Example 4 (CE4) Comparative Example 4 (CE4) is a blend of homopolyethylene and unimodal UHMWPE synthesized by the inventors with an IV of 23 dl / g. Homopolyethylene powder with an MI2 of 0.04 g / 10 min and an IV range of 2-3 dl / g was blended with UHMWPE powder and an IV of 23 in a single screw extruder at a composition of 10 parts homopolyethylene and 90 parts UHMWPE by weight. The temperature profile of the single screw extruder was set at 130°C-180°C from the barrel to the die. The blend was extruded and granulated into pellets with a resulting IV of 20.9 dl / g.

[0079] Comparative Example 5 (CE5) Comparative Example 5 (CE5) is a multimodal polyethylene polymerized with a blend ratio of 45 / 35 / 20. The polymerization process was carried out in a small-scale reactor. A UHMWPE powder with an IV of 13.0 dl / g was obtained.

[0080] Comparative example 6 (CE6) Comparative Example 6 (CE6) is a multimodal polyethylene polymerized with a blend ratio of 15 / 30 / 55. The polymerization process was carried out in a large-scale reactor. A UHMWPE powder with an IV of 8.2 dl / g was obtained.

[0081] Comparative example 7 (CE7) Comparative Example 7 (CE7) is a multimodal polyethylene polymerized with a blend ratio of 5 / 20 / 75. The polymerization process was carried out in a small-scale reactor. A UHMWPE powder with an IV of 23.9 dl / g was obtained.

[0082] [Table 1A]

[0083] [Table 1B]

[0084] [Table 1C]

[0085] [Table 2]

[0086] Consideration The samples E1 to E9 of the present invention have a 185 kJ / m 2 were produced by a multimodal polymerization process in small- to large-scale reactors with various IV ranges from 11.1 to 19.3 dl / g, providing significant improvements in double-notched Charpy impact strength over the previous study.

[0087] Both properties were improved by the balance of low-medium molecular weight and ultra-high molecular weight fractions in the multimodal polyethylene composition. The main reason why the multimodal sample shows better impact resistance is the low molecular weight fraction, which can promote chain diffusion across the boundaries between adjacent UHMWPE particles and reduce the void formation between adjacent particles. This means that the low molecular weight plays an important role in eliminating grain boundaries and improves the degree of sintering. Example 9 of the present invention has the highest impact strength, 278 kJ / m 2 When incorporating comonomers into multimodal UHMWPE, 1-butene and 1-hexene comonomers were added to the polymerization process. The results show that even with comonomer contents ranging from 0.03 to 0.17% mol, the UHMWPE examples still maintain good impact resistance. Even CE2, CE5, CE6 and CE7 produced by the multimodal process containing low molecular weight fractions cannot achieve high impact resistance exceeding 190 kJ / m2.

[0088] The impact properties as well as the extrudability of the multimodal samples are dramatically improved. The low molecular weight in the polymer composition acts as a lubricant, promoting the compliance of the UHMWPE molecules in the molten state.

[0089] Eta(0.1) values, an important rheological parameter, were also observed in all examples. Eta(0.1) is directly related to the processability of UHMWPE in single screw extruders and flowability at the die. Examples with Eta(0.1) less than 5,772 kPa.s show good trackability in the sheet extrusion process. However, the unimodal example CE1 with Eta(0.1) of 8,781 kPa.s cannot be extruded under the same processing conditions due to the lack of low molecular weight fraction in the composition to improve flowability in the molten state. CE2, produced from a multimodal reactor, cannot be extruded under the same conditions due to too high Eta(0.1), 7,000 kPa.s. CE3 is the lowest molecular weight sample with IV=6.7 dl / g and shows the lowest Eta(0.1), 265 kPa.s, which is the best flowability compared to the others. CE4 is a blend system with IV=20.9 dl / g having Eta(0.1), 4,216 kPa.s that can be extruded under the same conditions, but the mechanical properties, especially the double notched Charpy impact, are not achieved to a high level due to poor homogeneity or fusion effects in the polymer blend.

[0090] It can be clearly seen that the inventive examples containing low to ultra-high molecular weight polyethylene can promote processability and impact strength. All the results show the distinctive features and advantages of the novel inventive examples over the prior art.

[0091] The features disclosed in the foregoing description and in the dependent claims may, both separately and in any combination thereof, be material for realising the aspects of the disclosure made in the independent claims in diverse forms thereof.

Claims

1. (A) 7 to 40 wt. % of a low molecular weight polyethylene homopolymer having a viscometer molecular weight (Mv) of 31,000 to 260,000 g / mol, based on the total weight of the multimodal polyethylene composition; (B) 20 to 45 wt. % of a first high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight of 1,900,000 to 5,200,000 g / mol, based on the total weight of the multimodal polyethylene composition; and (C) 28 to 72 wt. % of a second high molecular weight polyethylene homopolymer or copolymer having a viscometer molecular weight of 3,000,000 to 7,300,000 g / mol, based on the total weight of the multimodal polyethylene composition. Including, the first high molecular weight polyethylene and the second high molecular weight polyethylene differ from one another in terms of their viscometer molecular weights; A multimodal polyethylene composition, wherein the intrinsic viscosity of the multimodal polyethylene composition is 11 to 22 dl / g, said intrinsic viscosity being measured in accordance with ISO 1872.

2. The multimodal polyethylene composition has a thermal conductivity of 170 to 300 kJ / m as measured by ISO 11542-2. ２ 2. The multimodal polyethylene composition of claim 1, having a double-notched Charpy impact strength of

3. The multimodal polyethylene composition has a thermal conductivity of 185 to 278 kJ / m as measured by ISO 11542-2. ２ 2. The multimodal polyethylene composition of claim 1, having a double-notched Charpy impact strength of

4. 2. The multimodal polyethylene composition of claim 1, wherein the multimodal polyethylene composition has a complex viscosity at high shear rate (0.1 1 / s at 190°C) of 2,550 to 5,800 kPa s.

5. The multimodal polyethylene composition has a modulus of elasticity of 0.930 g to 0.960 g / cm according to ASTM D 1505. ３ 2. The multimodal polyethylene composition of claim 1, having a density of

6. A sheet comprising the multimodal polyethylene composition described in claim 1.

7. A hollow article comprising the multimodal polyethylene composition described in claim 1.

8. 8. A method for preparing the sheet of claim 6 or the hollow article of claim 7, comprising the step of compression molding the multimodal polyethylene composition of any one of claims 1 to 4.

9. 8. A method for preparing a sheet according to claim 6 or a hollow article according to claim 7, comprising the step of extruding a multimodal polyethylene composition according to any one of claims 1 to 5.

10. 8. Use of the sheet according to claim 6 or the hollow article according to claim 7 as a liner, profile, pipe, tape, fiber, industrial part, high impact part, high abrasive part, sliding material or RAM extrusion profile.