Polyethylene molding mass with improved balance between fissuring resistance, hardness, and degree of blowing, method of preparing such mass, and application thereof

FIELD: polymer materials.

SUBSTANCE: invention relates to polyethylene molding mass with multimodule molecular weight distribution intended to manufacture hollow articles such as gas tanks, canisters, barrels, and bottles using extrusion. Molding mass has density at least 0.940 g/cm3, contains low-molecular polyethylene with viscosity index 40-150 cm3/g in amount 30 to 60%, high-molecular copolymer of ethylene with another C4-C10-olefin with viscosity index 150-800 cm3/g in amount 30 to 65%, and ultrahigh-molecular polyethylene with viscosity index in the region 900-3000 cm3/g in amount 1 to 30%. Molding mass is prepared by cascade-based suspension polymerization.

EFFECT: increased degree of blowing and improved balance between hardness and fissuring resistance.

3 cl, 2 tbl, 5 ex

 

The invention relates to a polyethylene molding mass with multimodal molecular mass distribution and the method of production of this molding material in the presence of a catalytic system of the Ziegler catalyst and socializaton through a multi-step sequence of reactions consisting of successive liquid-phase polymerizate, and hollow articles made from the molding material through extrusion molding, blown.

Polyethylene in a large volume is used to obtain extruded products and containers, as it is a material with a low own weight, having, in spite of this, a particularly high mechanical strength, high corrosion resistance against moisture and water in combination with oxygen and absolutely reliable long-term durability, and because the polyethylene is characterized by good chemical resistance and especially can easily be recycled into bottles, cans and tanks for fuel in cars.

In the application EP-A-603935 already described molding composition based on polyethylene having a bimodal molecular weight distribution and suitable, including, for the manufacture of pipes.

Raw materials with a wider molecular weight distribution described in US-PS 5338589 and get it through high is coacting catalyst, known from WO 91/18934, in which the magnesium alcoholate is used in the form of a gel-like suspension. Unexpectedly, it was shown that the use of this material in extruded products, especially in pipes, you can improve the property, usually located in an inverse dependence in partially crystalline thermoplastics: rigidity and tendency to creep, on the one hand, and resistance to cracking and viscosity, on the other hand.

Known bimodal products are particularly good processability while simultaneously increased the ratio of crack - stiffness. This combination of properties is of particular importance in the manufacture of hollow plastic articles, such as bottles, cans and tanks for fuel in cars. But in addition to this combination of properties for the manufacture of hollow plastic articles required the highest possible degree of inflating molten plastic as the degree of inflation during extrusion molding, blow directly responsible for the ability to optimally adjust the thickness of the walls, the formation of the weld and the ability to welding in the manufacture of production.

It is known that plastics with a high degree of inflation can be produced with the so-called Phillips catalysts, which are what utilizatori polymerization based on chromium compounds. But thus obtained plastic insufficient ratio of the crack - stiffness compared with the known plastics having a bimodal molecular weight distribution.

From the application EP-A-0797599 known method according to which receive the polyethylene even with a tri-modal molecular weight distribution by successive gas-phase and liquid-phase polymerizate. Although this polyethylene is already very well suited for the manufacture of hollow products for extrusion blow molding, however, in terms of processing, it should improve due to the low degree of inflation of the melt plastic.

The objective of the present invention consisted in the development of plastic molding material, which is compared to all known materials has a better ratio of rigidity and resistance to cracking and which, moreover, has a high degree of inflation of the melt, allowing for the manufacture of hollow articles by extrusion molding, blow not only to optimally adjust the thickness of the walls, but also provides an exceptional education welds and distribution of wall thickness.

The problem is solved by means of the molding material mentioned at the beginning of a kind, distinctive signs that the are it contains from 30 to 60 wt.% low molecular weight homopolymer ethylene And from 65 to 30 wt.% high molecular weight copolymer of ethylene and another olefin with 4 to 10 C-atoms and from 1 to 30 wt.% ultracytochemical Homo - or copolymer of ethylene, all percentage figures are calculated on the total weight of the molding composition.

Further, the invention also concerns the method of obtaining this molding material by cascading suspension polymerization and hollow products from this molding material with exceptional mechanical strength properties.

Polyethylene molding composition according to the invention has a density at a temperature of 23°in the field ≥0,940 g/cm3and wide tri-modal molecular weight distribution. High molecular weight copolymer b contains a minor proportion of up to 5 wt.% other links olefin monomer with 4 to 10 C-atoms. Examples of such comonomers are 1-butene, 1-penten, 1-hexene, 1-octene or 4-methylpentene-1. Ultrasonometry Homo - or copolymer of ethylene may, if necessary, to contain one or more of the aforementioned comonomers in amounts of from 0 to 10 wt.%.

Further, the molding composition according to the invention is characterized by a melt index according to ISO 1133, expressed as IR190/5(MFI190/5in the field of from 0.01 to 10 DG/min coefficients viscosity KV total(VZges), measured according to ISO/R 1191 in decaline at a temperature of 135°in the region from 190 to 700 cm3/g, preferably from 250 to 500 cm3/year

Trimodality can be described as a measure of the position of the centre of gravity of three distinct molecular weight distributions with coefficients of viscosity KB no ISO/R 1191 polymers obtained in successive stages of polymerization. Thus take into account the following bandwidth of the polymers obtained at separate stages of polymerization:

The coefficient of viscosity KB1measured for the polymer after the first stage polymerization, identical to the coefficient of viscosity KVAndlow-molecular-weight polyethylene and is located in the region from 40 to 180 cm3/year

KVInhigh molecular weight polyethylene obtained in the second stage polymerization, can be calculated by the following mathematical formula:

,

and w1denotes the weight fraction of low molecular weight polyethylene obtained in the first stage, measured in wt.%, calculated on the total weight of polyethylene with a bimodal molecular weight distribution obtained on both the first stages, and KV2denotes the coefficient of viscosity of the polymer measured after the second stage polymerization. The value calculated for KVIntypically located in the region from 150 to 800 cm 3/year

KVwithfor ultracytochemical Homo - or copolymer, obtained in the third step of polymerization is calculated by the following mathematical formula:

,

and w2denotes the weight fraction of polyethylene with a bimodal molecular weight distribution obtained on both the first speed, measured in wt.% calculated on the total weight of polyethylene with a tri-modal molecular weight distribution obtained at all three levels, and KV3denotes the coefficient of viscosity measured for the polymer after the third stage of polymerization and which is identical to the above-mentioned KVtotal

The value calculated for KVWithaccording to the invention is in the range from 900 to 3000 cm3/year

Polyethylene is produced through polymerization of monomers in suspension at temperatures in the range from 20 to 120°C, the pressure in the region from 2 to 60 bar in the presence of a highly active Ziegler catalyst composed of a transition metal compounds and alyuminiiorganicheskikh connection. The polymerization carried out a three-stage, that is, in three successive stages, and molecular weight as needed is controlled by adding hydrogen.

Prolonged activity of the polymerization catalyst required is for the above cascade way, delivered through a specially designed catalyst of Ziegler. Measure the suitability of this catalyst is its extremely high reactivity towards hydrogen and high activity, not changing over a long period of time from 1 to 8 hours. Specific examples of suitable catalysts of this kind are the products of interaction of a magnesium alcoholate with compounds of transition metals titanium, zirconium or vanadium and an ORGANOMETALLIC compound of metal I, II or III group of the periodic system of the elements described in the applications EP-A-0532551, EP-A-0068257 and EP-A-0401776.

Polyethylene molding composition according to the invention may contain, together with the polyethylene other additives. Such additives are, for example, stabilizers, antioxidants, UV absorbers, light stabilizers, decontamination officers metals, compounds that destroy peroxides, basic co-stabilizers in amounts from 0 to 10 wt.%, preferably from 0 to 5 wt.%, as well as excipients, enhancers, plasticizers, softeners, emulsifiers, pigments, optical brighteners, flame-retardant means, antistatics, blowing agents, CN, or combinations thereof in total amounts of from 0 to 50 wt.%, calculated on the total weight of the mixture.

Molding composition according to the invention are particularly well suited for manufacturing the means hollow products, such as Jerry cans for fuel, chemical-resistant barrels, cans, kegs and bottles because plastic molding composition, first of all, plastification in the extruder at temperatures in the range from 200 to 250°and then through the nozzle is extruded into the mold for blowing and cools down.

For processing into hollow articles can be used as a conventional single-screw extruders with a smooth loading area, and high-performance extruders with finely-fold cylinder and effective loading area. Traditionally screws are decompression screws with a length of from 25 to 30 D (D=diameter). Decompression screws have a discharge area in which the equalized temperature differences in the melt and must be reduced relaxation of stresses in the result.

EXAMPLE 1 (according to the invention)

Polymerization of ethylene was conducted in the usual way in a series of three adjacent reactors. In the first reactor was loaded a Ziegler catalyst, a sufficient amount of a suspending agent, ethylene and hydrogen. The amount of ethylene and hydrogen was regulated in such a way that nine parts by volume of ethylene had one volume part of the hydrogen.

The catalyst was the catalyst of the Ziegler described in example 2 application WO 91/18934, which included components the NT and the catalyst to operating room 2.2 and which was added together with acetalization of the ORGANOMETALLIC compound of metal I, II or III group of the Periodic system of elements.

In the first reactor was continuously dosed out the catalyst with socialization and triethylamine in the ratio of 1:10 (mol/mol).

The polymerization in the first reactor was carried out at a temperature of 76°and the pressure to 0.78 MPa for 3.3 hours when the hydrogen content in the gas volume from about 67 to 68. %.

Then the suspension from the first reactor was transferred into the second reactor, in which the amount of hydrogen in the gas volume was reduced to 5 parts by volume, and was introduced With4-monomer in an amount of 5 parts by volume. Reducing the amount of hydrogen was carried out through an intermediate pressure drop H2.

The polymerization in the second reactor was carried out at a temperature of 84°and the pressure of 0.5 MPa for 54 minutes

The slurry from the second reactor was transferred to the third reactor after further intermediate pressure reduction N2, which established the amount of hydrogen in the gas volume of the third reactor ≤about 5. %.

The polymerization in the second reactor was carried out at a temperature of 47°and the pressure ≤to 0.23 MPa for 30 minutes

The polymer suspension, after the third reactor, after separation of the suspending agent and drying was granulated.

The coefficients of viscosity and mass fraction wAnd, wInand wWithpolymer a, b and C, characterizes the polyethylene molding composition, obtained in example 1, together with corresponding data of the moulding mass obtained in the following examples 2 to 4, are presented in the following table 1.

EXAMPLE 2 (according to the invention)

Worked example 1 with the following changes.

The polymerization in the first reactor was carried out at a temperature of 82°and the pressure of 0.89 MPa for 2.6 hours when the content of hydrogen gas in the reactor volume 68 about. %.

Then the suspension from the first reactor was transferred into the second reactor, in which the amount of hydrogen in the gas volume is reduced by 10 parts by volume, in the gas space of the reactor was introduced With4-comonomer in the amount of 0.7 parts by volume. Lowering the amount of hydrogen was again carried through the intermediate pressure drop H2.

The polymerization in the second reactor was carried out at a temperature of 80°and the pressure of 0.37 MPa for 66 minutes

The slurry from the second reactor was transferred to the third reactor and set the amount of hydrogen in the gas volume of the third reactor 0,6 about. % and4-co monomer about 0.8. %.

The polymerization in the second reactor was carried out at a temperature of 80°and a pressure of 0.15 MPa for 36 minutes

The coefficients of viscosity and mass fraction wAnd, wInand wWithpolymer a, b and C, which characterizes a polyethylene molding composition obtained in example 2,together with corresponding data of the moulding masses from other examples presented in the following table 1.

EXAMPLE 3 (according to the invention)

Worked example 2 with the following changes.

The polymerization in the first reactor was carried out at a temperature of 80°and the pressure of 0.74 MPa for 2.1 hours when the hydrogen content in the gas volume of the reactor 65. %.

Then the suspension from the first reactor was transferred into the second reactor, in which the amount of hydrogen gas in the reactor volume was down by 4.1 parts by volume, in the gas space of the reactor was introduced With4-comonomer in the amount of 1.1 parts by volume. Lowering the amount of hydrogen was again carried through the intermediate pressure drop H2.

The polymerization in the second reactor was carried out at a temperature of 80°and the pressure of 0.24 MPa for 54 minutes

The slurry from the second reactor was transferred to the third reactor and set the amount of hydrogen in the gas volume of the third reactor 1,1 about. % and4-co monomer - 0,8 about. %.

The polymerization in the second reactor was carried out at a temperature of 60°and a pressure of 0.12 MPa for 30 minutes

The coefficients of viscosity and mass fraction wAnd, wInand wWithpolymer a, b and C, which characterizes a polyethylene molding composition obtained in example 3, together with the corresponding molding masses from other is the reamers, presented in the following table 1.

EXAMPLE 4 (according to the invention)

Worked example 3 with the following changes.

The polymerization in the first reactor was carried out at a temperature of 80°and the pressure of 0.82 MPa for 2.2 hours when the content of hydrogen gas in the reactor volume 74 about. %.

Then the suspension from the first reactor was transferred into the second reactor, in which the amount of hydrogen in the gas volume of the reactor was decreased by 4.0 volume parts, and in the gas space of the reactor was introduced With4-comonomer in the amount of 1.3 parts by volume. Lowering the amount of hydrogen was again carried through the intermediate pressure drop H2.

The polymerization in the second reactor was carried out at a temperature of 80°and the pressure of 0.20 MPa for 54 minutes

The slurry from the second reactor was transferred to the third reactor and set the amount of hydrogen in the gas volume of the third reactor of 1.0 vol.% and C4monomer 1.0 about. %.

The polymerization in the second reactor was carried out at a temperature of 60°and the pressure of 0.08 MPa for 30 minutes

The coefficients of viscosity and mass fraction wAnd, wInand wWithpolymer a, b and C, which characterizes a polyethylene molding composition obtained in example 4, together with the corresponding molding masses obtained for the other examples in the cm is authorized the following table 1.

COMPARATIVE EXAMPLE

Worked example 1, but with the difference that the polymerization was stopped after the second stage of the reaction.

The polymerization in the first reactor was carried out at a temperature of 84°and the pressure of 0.90 MPa for 4.2 hours when the hydrogen content in the gas volume of the reactor 76%vol.

Then the suspension from the first reactor was transferred into the second reactor, in which the amount of hydrogen gas in the reactor volume was reduced by 3.0 volume parts, and in the gas space of the reactor was introduced With4-comonomer in the amount of 1.9 parts by volume. Lowering the amount of hydrogen was again carried through the intermediate pressure drop H2.

The polymerization in the second reactor was carried out at a temperature of 83°and the pressure of 0.21 MPa for 80 minutes

When this got polyethylene with a bimodal molecular weight distribution, which corresponded to the state of the art in the application EP-A-603935.

TABLE 1
Example1234Compare. example
wAnd0,350,450,550,550,52
wIn0,550,450,350,35 0,48
wWith0,100,100,100,100
KB1[cm3/g]80801006055
IL (2)3,52,32,32,00,7
IL(3)1/20,70,550,56-
IL/5 [g/10’]1,070,550,300,360,4
IL/21,6 [g/10’]17,9119,513,8the 13.4
The degree of fluidity (FRR) of 21.6/5172031,636,333,6
KVobsh[cm3/g]306325392373329
Density

[g/cm3]
0,9540,9520,9530,9540/954
BP 0°

[kJ/m2]
9,610,712,67,86
 DIF [N/mm2]12701200124012801275
CF-riomet historical, %20015115314391
NRC [h]3,71654,254,139

Reduction of the physical properties in table 1 have the following meanings:

- DIF (VKM) = modulus of creep in bending, measured according to ISO 54852-Z4 in N/mm2as the value in one minute.

- NRC (SRB) = resistance to cracking under stress molding material according to the invention, is determined by the internal measurement method. This laboratory technique described in the publication .Fleissner, Kunststoffe 77 (1987), S. 45ff', where it is shown that between the definition of the slow growth of cracks in the test of long-term strength incised circle designs in the shape of a bar and the broken trajectories of cracks in the test on the long-term compressive strength according to ISO 1167 relationship exists. Reducing the time until failure is achieved by reducing the time of initiation of cracks using cuts (1.6 mm/razor blade) in ethylene glycol as the environment required for the formation of fatigue cracks at a temperature of 80°and the stress at break of 3.5 MPa. Manufacturing of samples carried out so that the molded sheet with a thickness of 10 mm saw off three test pieces measuring 10 on; 10×90 mm Samples for testing in the middle of nidresource in a circle with a razor blade in made specifically for this device cuts (presented on figure 5 in publication Fleissner). The depth of the incision is 1.6 mm

- BP (BZ) = viscosity at break of the molding material according to the invention, also is determined by the internal method on samples in the form of a block with dimensions of 10×10×80 mm, cut from a molded sheet with a thickness of 10 mm In the aforementioned device to cut six of these subjects rods make an incision with a razor blade in the middle. The depth of the incision is 1.6 mm, the Measurement was conducted in accordance with the well-known way of measuring by Sharlee on ISO 179 for volatile samples and variable geometry strike (int support). All the samples was maintained at a temperature of dimension 0°C for 2 to 3 hours. Then the test sample was placed on a support pendulum copra according to ISO 179. The support interval was 60 mm Causes a drop hammer strength 2 j, and set the angle 160°, the length of the pendulum 225 mm and strike speed of 2.93 m/s. To determine the quantitative evaluation of measurement calculate the quotient of the energy consumed shock and the initial square cross-section incision andFMin MJ/mm2. However, only the values obtained with the nome and joint destruction, can serve as the basis of total average values (see ISO 179).

SR (SR) = the degree of inflation, measured in a capillary rheometer high pressure when shift module 1440 1/sec in one nozzle with round holes 2/2 with a tapered entrance (angle=15°) at a temperature of 190°C.

The measurement results clearly show that the molding composition according to the invention always has the best strength properties and also easier processing during production (see table 2).

TABLE 2

For testing hollow articles produced by Bekum BAE 3 500 ml round bottle under the following conditions and with the following characteristics
Example1234Compare. Example 1
The main lumen150150150150200
The number of revolutions [rpm]17,717,717,717,7-
Time blowing

[sec]
1514,0to 12.011,212
Weight [g]41,437,436,035,638
The thickness of Enki [mm] 1/21,000,900,85-
The thickness of the weld [mm]2,02,01,01,0(0,5)

(V-notch)
The gap melt [score]22222
Clots [score]22231
NoteMattMattMattMattMatt

It is seen that the molding composition in comparative example forms a thin weld bead, which also has a V-shaped incision, which is the weak point, which can break under compressive load.

1. Polyethylene molding composition with multimodal molecular weight distribution, characterized by the total density of greater than or equal to 0,940 g/cm3and melt index, determined at 190°and a load of 5 kg, in the range from 0.01 to 10 DG/min, characterized in that it contains a low molecular weight homopolymer of ethylene And having a coefficient of viscosity KVDin the region from 40 to 150 cm3/g in an amount of from 30 to 60 wt.%, high molecular weight copolymer of ethylene and another olefin with 4 to 10 C-atoms is mi, having a coefficient of viscosity KVInin the area of from 150 to 800 cm3/g in an amount of from 30 to 65 wt.% and ultrasonometry Homo - or copolymer of ethylene having a coefficient of viscosity KVWithin the region from 900 to 3000 cm3/g in an amount of from 1 to 30 wt.%, when this molding composition has an exceptional processability to hollow products, a strong degree of inflation in the region from 100%to 300%.

2. A method of obtaining a polyethylene molding composition according to claim 1, wherein conducting the polymerization of the monomers in suspension at temperatures in the range from 20 to 120°C, the pressure in the region from 2 to 60 bar in the presence of a highly active Ziegler catalyst composed of a transition metal compounds and alyuminiiorganicheskikh connection, characterized in that the polymerization is conducted a three-stage, with molecular weight polyethylene obtained at each step, as needed can be adjusted with hydrogen.

3. Method of making hollow articles, such as tanks for fuel cans, barrels or bottles, by plastifitsirovanie plastic molding material into the extruder, followed by extrusion of the molding material through the nozzle in the form of blow molding and cooling, characterized in that the polyethylene molding composition according to claim 1, first the plastification extruder at temperatures in the range from 200 to 250° And then use the nozzle is forced into a form for molding blow and cools down.



 

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