JPH08157517A - Production of polyolefin - Google Patents

Abstract

PURPOSE: To produce a polyolefin having a controlled molecular weight and a wide molecular weight distribution in good productivity without changing the stereoregularity. CONSTITUTION: A polyolefin is produced by using a catalyst component supported by an inorganic oxide and comprising a combination of a reaction product of a transition metal compound having a ligand with an aluminoxane or a reaction product of this compound with an organometallic compound and a compound which reacts with the product to borm an ionic compound. In this process the olefin is polymerized at a polymerization temperature which varies so as to give a difference between the maximum and minimum polymerization temperatures of at least 10 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polyolefin. Specifically, it relates to a method for producing a polyolefin having a desired molecular weight and a wide molecular weight distribution.

[0002]

As an olefin polymerization catalyst, a transition metal compound such as a metallocene compound having a group having a conjugated π electron, particularly cyclopentadiene and its derivative as a ligand, and an alkyl obtained by the reaction of trialkylaluminum and water. A combination with aluminoxane is known. For example, JP-A-58-19309 discloses a method for polymerizing biscyclopentadienyl zirconium dichloride and an olefin using methylaluminoxane as a catalyst, and JP-A-61-130314 and JP-A-61-264010, Kohei
1-301704 and JP-A-2-41303 disclose isotactic poly α-olefins or syndiotactic poly α-
Process for producing olefins and their stereoregular poly α-
Polymerization catalysts for producing olefins are disclosed.

On the other hand, it has been reported that a cationic metallocene compound having cyclopentadiene and its derivative as a ligand polymerizes an olefin without using methylaluminoxane. For example, RFJORDAN et al., J. Am. Chem. Soc., 1986, Vol. 108, page 7410, has tetraphenylborane as an anion, and a zirconium cation complex having a biscyclopentadienyl group and a methyl group as a ligand is ethylene. It has been reported that it has a polymerization activity. Turner et al., J. Am. Chem. Soc., 1989 111
Vol. 2728, it is reported that the ion pair type zirconium complex also has ethylene polymerization activity. Further Za
mbelli et al., Macromolecules, 1989, Vol. 22, pp. 2186-2189, reported that isotactic polypropylene was produced by polymerizing propylene with a combination of a zirconium compound having a cyclopentadiene derivative as a ligand and trimethylaluminum and fluorodimethylaluminum. It reports that it can be obtained.

[0004]

The above method is an excellent method in that the activity per transition metal is good, and the stereoregularity and tacticity of the obtained polymer can be selected depending on the kind of the transition metal compound used. is there.
When a polymer having a desired molecular weight is produced using these catalysts, the molecular weight can be adjusted by using a chain transfer agent such as hydrogen as in the conventional Ziegler-Natta catalyst. However, even if any of the above catalysts is used, the molecular weight distribution of the obtained polymer is very narrow, around 2, and there is a problem in the moldability of the obtained polymer. It is described in JP-A-3-212408 that a polymer having a wide molecular weight distribution can be obtained by polymerizing with at least two kinds of transition metal compounds in order to broaden the molecular weight distribution. In addition, a method of mixing two or more kinds of separately synthesized polymers having different molecular weights to use as a polymer having a wide molecular weight distribution is also under study. However, when the polymer obtained by the method of polymerizing using two kinds of transition metal compounds or the method of mixing two or more kinds of polymers is measured by gel permeation chromatography, the molecular weight distribution is certainly widened. Since the distribution has two or more peaks, the high molecular weight polymer causes a lump when the polymer is formed into a film, and the physical properties of other molded products are deteriorated. I can't get it. In addition, since the homogeneity of the catalyst varies in stereoregularity and molecular weight depending on the polymerization temperature,
Attempts to broaden the molecular weight distribution by changing the polymerization temperature also change the stereoregularity. Since changing the stereoregularity also changes the physical properties of the polymer, industrially, a method is desired in which only the molecular weight distribution can be changed while maintaining the stereoregularity.

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a method for solving the above problems and obtaining a polyolefin having a desired molecular weight with a wide molecular weight distribution. The present invention has been completed by finding that it is effective for controlling the molecular weight distribution while maintaining the stereoregularity by polymerizing the olefin while changing the value.

That is, according to the present invention, a reaction product of a transition metal compound having an inorganic oxide as a carrier and having a ligand with an aluminoxane, or a reaction product of a transition metal compound having a ligand with an organometallic compound and reacting with the reaction product In the method for producing a polyolefin by using a catalyst component composed of a compound that forms an ionic compound, the olefin is polymerized by changing the polymerization temperature so that the polymerization temperature difference is at least 10 ° C or more. And a method for producing a polyolefin.

As the inorganic oxide used in the present invention,
_{SiO 2, Al 2 O 3,} CaO, Na 2 O, K 2 O, MgO, MnO, TiO 2,
Various oxides such as inorganic oxides such as ZrO ₂ and complex salts of inorganic oxides such as zeolites, those with cavities inside, those with relatively large pores and large surface areas can be preferably used, and hollow inorganic oxidation You can also use things, oxide gels, etc.
Usually, those having a diameter of about 1 μm to 0.1 mm can be preferably used. Among them, those containing silica or alumina are preferable because the amount of the transition metal compound or aluminoxane supported can be increased.

The inorganic oxide is used to carry a transition metal compound and an aluminoxane, or a reaction product of a transition metal compound having a ligand and an organometallic compound and a compound which reacts with the reaction product to form an ionic compound. It is usually calcined and dried before use, but it may be anhydrous or may have 10% by weight or less of adsorbed water.

As the transition metal compound having a ligand used in the present invention, the compounds described in the above-mentioned documents can be exemplified. In addition, the compounds represented by the following general formulas (Formula 3) or (Formula 4) , A and B are monovalent or divalent unsaturated hydrocarbon residues, or the same or different ligands containing a nitrogen atom, an oxygen atom, a silicon atom, a phosphorus atom or a sulfur atom bonded to M. , A ′ and B ′ are the same or different monovalent or divalent unsaturated hydrocarbon residues bridged by R, or a nitrogen atom, an oxygen atom bonded to M,
A ligand containing a phosphorus atom or a sulfur atom, and R is a linear saturated hydrocarbon which may have a residue or a side chain containing a divalent nitrogen atom, oxygen atom, silicon atom, phosphorus atom or sulfur atom. A residue or a residue in which some or all of the linear carbon atoms thereof are substituted with silicon atoms, germanium atoms or tin atoms, and M is a metal atom selected from Group 4 or 5 of the periodic table. , And X represents a ligand containing a halogen atom, a carbon atom, a nitrogen atom, an oxygen atom, a silicon atom, a boron atom, a phosphorus atom or a sulfur atom bonded to M. The transition metal compound which has the ligand represented by these is illustrated.

[0010]

Embedded image

[0011]

[Chemical 4]

Examples of the unsaturated hydrocarbon residue represented by A and B include monocyclic or polycyclic conjugated π-electron groups having 5 to 50 carbon atoms. Petadienyl or some or all of its hydrogens replaced by a hydrocarbon residue having 1 to 10 carbon atoms (wherein the hydrocarbon residue has a structure in which its terminal is again bound to the cyclopentadiene ring) Or a polycyclic aromatic hydrocarbon residue such as indenyl or fluorenyl, or one in which a part or all of the hydrogen thereof is substituted with a hydrocarbon residue having 1 to 10 carbon atoms.
Further, as a ligand containing a nitrogen atom, an oxygen atom, a silicon atom, a phosphorus atom or a sulfur atom bonded to M, COR ′,
NR ' ₂ , OR', OSiR ' ₃ , SiR' ₃ , GeR ' ₃ , PR' ₂ , POR ' ₂ ,
Examples include ligands represented by SR ', SOR', and SO ₂ R '(R' is hydrogen or a hydrocarbon having 1 to 20 carbon atoms or a residue in which some of them are substituted with heteroatoms). To be done. These may be the same as or different from each other.

The ligand represented by A'or B'is
Monocyclic or polycyclic conjugated π-electrons with 5 to 50 carbon atoms
Groups with children, COR ', NR'₂, OR ', OSiR'₃, SiR '₃ ,
GeR ' ₃ , PR '₂, POR '₂ , SR ', SOR', SO₂R '(R' is hydrogen
Or a hydrocarbon having 1 to 20 carbon atoms or one of them
Transition represented by a residue in which one or more of the atoms are replaced by a hetero atom
The ligand bonded to the metal atom M is exemplified. these
May be the same or different from each other. Where A'and
And B'have a structure bridged by R.
It

The divalent group represented by R includes -O- and -S-.
, -SS-, -SO-, -SO _2- , -CO-, -NR "-, -PR"-, -PO
R "-, -OSiR" ₂ O-, or a methylene group represented by the following general formula (Formula 5) or a part or all of the carbon atoms of the methylene group is substituted with a silicon atom, a germanium atom, or a tin atom. Examples are silylene groups, germylene groups, and stannylene groups.

[0015]

Embedded image-(R " ₂ C) n- (R" ₂ Si) m- (R " ₂ Ge) p- (R" ₂ Sn) q- (wherein R "is a hydrogen atom or a carbon atom number 1 2 R ″ may represent the same or different and n, m, p and q are integers of 0 to 4 and the following formula 1 ≦
It represents an integer satisfying n + m + p + q ≦ 4. )

X is a halogen atom such as fluorine, chlorine, bromine or iodine, or CR ' ₃ , CH ₂ SiR' ₂ , COR ', NR' ₂ , OR ',
OSiR ' ₃ , SiR' ₃ , GeR ' ₃ , PR' ₂ , POR ' ₂ , SR', SOR ',
SO ₂ R ′ (R ′ is hydrogen or a hydrocarbon having 1 to 20 carbon atoms or a residue in which some of them are substituted with a hetero atom) and the like can be exemplified.

In the present invention, when a catalyst comprising a combination of a transition metal compound having a ligand and an aluminoxane is used, the aluminoxane is represented by the following general formula (Formula 6) obtained by hydrolyzing a trialkylaluminum or Compounds represented by (Chemical Formula 7) (wherein R is a hydrocarbon residue having 1 to 3 carbon atoms, n is an integer of 1 to 50) can be exemplified, and among these, methylaluminoxane in which R is a methyl group is particularly preferable. And those in which n is 5 or more are preferably used.

[0018]

[Chemical 6]

[0019]

[Chemical 7]

The aluminoxane is used in an amount of 1 to 10000 mol times, usually 10 to 5000, relative to the above transition metal compound.
It is mole times.

Ion pair compounds when a catalyst component comprising a combination of a compound (ion pair compound) which reacts with a reaction product of a transition metal compound having a ligand and an organometallic compound to form an ionic compound is used. As the compound, a compound represented by the following general formula (Formula 8) is used.

[0022]

[Chemical Formula 8] [Q] ⁺ [Y] ^-

Here, Q is a cation component of an ionic compound, and examples thereof include carbonium cation, tropylium cation, ammonium cation, oxonium cation, sulfonium cation, and phosphonium cation. Specific examples of these cations include triphenyl carbonium, diphenyl carbonium, cycloheptatrienium, tributyl ammonium, N, N.
Examples include dimethylanilinium, dipropylammonium, dicyclohexylammonium, triphenylphosphonium, trimethylphosphonium, triphenylsulfonium, triphenyloxonium, triethyloxonium, pyrylium, and ferrocenium.

Further, Y is an anion component of an ionic compound, and examples thereof include a boron compound anion, an aluminum compound anion, a gallium compound anion, a phosphorus compound anion, an arsenic compound anion, and an organic antimony compound anion. Phenyl boron,
Examples thereof include tetrakis (pentafluorophenyl) boron, tetraphenylaluminum, tetrakis (pentafluorophenyl) aluminum, tetraphenylgallium, tetrakis (pentafluorophenyl) gallium, hexafluoroline, hexafluoroarsenic and hexafluoroantimony.

The supporting of the transition metal compound is a compound (ion pair compound) which forms an ionic compound by reacting with a reaction product of a transition metal compound having an aluminoxane or a ligand in a solution of the transition metal compound and an organometallic compound. It can be carried by dispersing the carrier carrying the. Further, the transition metal compound and the carrier can be directly contacted and supported. The temperature at which the transition metal compound is supported is not particularly limited, but is usually 0 ° C to 100 ° C.

The solid catalyst component for olefin polymerization thus synthesized can be used as it is as a polymerization catalyst. Further, an organoaluminum compound can be used together during the polymerization.

The organometallic compound to be reacted with the transition metal compound in the present invention is a metal atom of Groups 1, 2, 12 and 13 of the Periodic Table, preferably aluminum, zinc or magnesium, halogen atom, oxygen atom or When a hydrogen atom or a residue such as alkyl, alkoxy or aryl is coordinated and a plurality of ligands are present, they may be the same or different, but at least one of them is an alkyl group. Some are exemplified. For example, an alkyl metal compound in which one or more alkyl residues having 1 to 12 carbon atoms are coordinated, an alkyl metal halide in which the above alkyl residue and another atom or residue are coordinated, an alkyl metal alkoxide, etc. It is illustrated. Among them, an alkylaluminum compound in which at least one alkyl residue having 2 or more carbon atoms is coordinated is preferably used.

Examples of preferred organometallic compounds for those in which the metal atom is aluminum include trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropylaluminum, tributylaluminum, triisobutylaluminum, tripentylaluminum, trihexylaluminum. ,
Triheptyl aluminum, trioctyl aluminum, tridecyl aluminum, isoprenyl aluminum, diethyl aluminum hydride, diisopropyl aluminum hydride, diisobutyl aluminum hydride, diethyl aluminum chloride, di-n-propyl aluminum chloride, diisopropyl aluminum chloride, diisobutyl aluminum chloride, diethyl aluminum Ethoxide, diisopropyl aluminum isopropoxide, ethyl aluminum sesquichloride, isopropyl aluminum sesquichloride, isobutyl aluminum sesquichloride, ethyl aluminum dichloride, isopropyl aluminum dichloride, isobutyl aluminum dichloride, ethyl acetate Mini Umm diisopropoxide, and the like.

The method for treating the transition metal compound with the organometallic compound is not particularly limited, and both may be simply mixed. Usually, the transition metal compound is solid, and the organometallic compound is liquid or solid in many cases, and therefore it is preferable to treat it in a hydrocarbon solvent. The ratio of the organic metal compound used to the transition metal compound is 1 to 100,000 mol times, usually 1
~ 5000 times mole. The treatment temperature is not particularly limited,
Usually, it is preferably carried out at a temperature of -20 to 100 ° C. The temperature at which these mixtures are stored is also not particularly limited, but it is preferable to store at a temperature of −20 to 100 ° C. as well. The treatment time is not particularly limited, and when both are solutions, it may be at the point of time when they are uniformly mixed, and when insolubles are present, they can be used any time after they have been dissolved in the solvent. Of course, as described above, it is also possible to store it as it is until use and use it as needed. Further, the concentration of the reaction product in the hydrocarbon solvent is stable even at a considerably high concentration as described above, and therefore it is not particularly limited, but is usually 10 ^-7 to 1 mol / liter, preferably the molar concentration based on the metallocene compound. Is 10 ^-5
~ 0.1 mol / l.

The amount of the above-mentioned ionic compound-forming compound used is based on the transition metal compound used in the catalyst.
It is 0.1 to 100,000 mole times, usually 0.5 to 10,000 mole times.

Further, hydrogen, a hydrosilane compound represented by R _n SiH _4-n , or a cyclic diene can be used as a chain transfer agent for controlling the molecular weight of the polymer obtained by polymerizing an olefin.

Examples of the hydrosilane compound include methylsilane, ethylsilane, propylsilane, butylsilane, pentylsilane, hexylsilane, heptylsilane, octylsilane, dimethylsilane, diethylsilane, dipropylsilane, dibutylsilane, dipentylsilane, dihexylsilane, Examples thereof include diheptylsilane, dioctylsilane, trimethylsilane, triethylsilane, tripropylsilane, tributylsilane, tripentylsilane, trihexylsilane, triheptylsilane, trioctylsilane and branched alkyl groups thereof.

The amount of the chain transfer agent added to the above transition metal compound varies depending on the molecular weight of the target polymer, but is usually 1/100000 to 1/10 of propylene, and if it is less than this, it is not effective in controlling the molecular weight. If it is used more than this, not only the effect is not improved, but also the activity is greatly reduced and it is not practical.

Examples of the solvent used in the preparation, polymerization or treatment of the catalyst using the catalyst component of the present invention include propane, butane, isobutane, pentane, hexane, heptane, octane, nonane, decane, cyclopentane, cyclohexane, Saturated hydrocarbon compounds such as cycloheptane and methylcyclohexane, aromatic hydrocarbon compounds such as benzene, toluene and xylene, and halogenated hydrocarbon compounds such as methylene chloride and chlorobenzene can also be used.

In the present invention, as the olefin, ethylene, propylene, butene-1, pentene-1, hexene-
1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene
-1, pentadecene-1, hexadecene-1, octadecene-1
In addition to linear α-olefins such as 3-methylbutene-1,4-
Branched α such as methylpentene-1,4,4-dimethylpentene-1
-Olefins and cycloolefins such as cyclopentene, cyclooctene and norbornene are exemplified, and α-
Not only olefins but also mixtures with one another or with small amounts of ethylene and dienes are indicated. Further, styrene, α-methylstyrene and the like can be used.

Regarding the polymerization conditions, an important point in the present invention is to polymerize the olefin by changing the polymerization temperature so that the difference in the polymerization temperature is at least 10 ° C. or more. There is no particular limitation on the method of changing the polymerization temperature to at least two levels or more so that the difference in the polymerization temperature is at least 10 ° C. or more, and the polymerization temperature may be changed continuously or gradually. There is a method. In addition, the order of changing the polymerization temperature can be arbitrarily changed in consideration of the physical properties of the obtained polymer such as temperature increase, temperature decrease or random change.

How much the polymerization temperature is changed depends on how much the molecular weight distribution of the desired polymer is set.
The polymerization temperature must be changed so that the difference in polymerization temperature is at least 10 ° C or more. When the difference in polymerization temperature is smaller than 10 ° C., the spread of the molecular weight distribution is small and the effect of improving the moldability of the obtained polymer is small, which is not preferable. Usually, the polymerization temperature is selected in the range of -100 to 200 ° C.

The other polymerization conditions are not particularly limited, and a solvent polymerization method using an inert medium, a bulk polymerization method or a gas phase polymerization method substantially free of an inert medium can be used. As the polymerization pressure, general conditions used in a known method are used, and it is general to carry out the polymerization under normal pressure to 100 kg / cm ² -G.

[0039]

EXAMPLES The present invention will be further described with reference to the following examples.

Example 1 Methylaluminoxane (manufactured by Tosoh Akzo, degree of polymerization 1
6.2) 254 g was dissolved in 1500 ml of toluene and placed in a 4-liter flask, and silica gel (manufactured by Fuji Divison Co., HT
G30908 was dried under reduced pressure at room temperature for 4 hours and contained 8% by weight of adsorbed water. 300 g) was dispersed and the temperature was raised with stirring to reflux for 8 hours. Then filter under a stream of nitrogen, then
Excess methylaluminoxane was removed by washing 3 times with 1000 ml of toluene, and further washed with 1000 ml of n-hexane twice, and dried under reduced pressure to obtain aluminoxane-supporting silica gel.

Next, 17.8 g of diphenylmethylene (cyclopentadienyl-2,6-di-tert-butylfluorenyl) zirconium dichloride synthesized according to a conventional method was added to 400
It was dissolved in 1 ml of toluene, 432 g of silica gel supporting aluminoxane was suspended in 1 liter of toluene, and the mixture was stirred at room temperature for 2 hours. Next, the operation of filtering under a nitrogen stream and further washing with 1000 ml of toluene was repeated 5 times, and then dried under reduced pressure to obtain 425.4 g of a solid catalyst component.

0.5 g of the solid catalyst component thus obtained and 0.9 g of triisobutylaluminum were placed in a 5 liter autoclave, 1.5 kg of propylene was added, and polymerization was continued while continuously raising the temperature from 30 ° C. to 60 ° C. for 2 hours. Unreacted propylene was purged, the polymer was taken out, dried and weighed to obtain 657 g of the polymer. The bulk specific gravity of this polymer is
It was 0.41 g / ml, the syndiotactic pentad fraction was 0.82 according to ¹³ C-NMR, and the intrinsic viscosity (hereinafter referred to as η) measured with a 135 ° C. tetralin solution was 1.32, 1, 2,
Ratio of weight average molecular weight and number average molecular weight measured by GPC using 4-trichlorobenzene as a solvent (hereinafter, MW / MN
) Was 4.8.

Comparative Example 1 Propylene was polymerized in the same manner as in Example 1 except that the polymerization temperature was kept constant at 60 ° C. As a result, 875 g was obtained.
A polymer of The syndiotactic pentad fraction of this polymer is 0.81, η is 1.21 and MW / MN is
It was 2.3.

Example 2 Isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride prepared by a conventional method 2.
To 2 g, 15 ml of a cyclohexane solution containing 6.64 g of triethylaluminum was added. After stirring at room temperature for 24 hours, -78
The mixture was cooled to ℃ and left still for 24 hours. A small amount of insoluble matter was removed by filtration with a glass filter to obtain a mixed solution of the reaction product.

5 g of γ-alumina heat-treated at 600 ° C. for 6 hours under reduced pressure was put into a 200 ml four-necked flask which had been purged with nitrogen.
25 ml of toluene was added and 5 ml of the above reaction mixture solution was added dropwise with stirring. After stirring at room temperature for 24 hours, the mixture was filtered through a glass filter, washed with 50 ml of pentane three times, and dried under reduced pressure to obtain a solid catalyst component.

To 100 mg of the above solid catalyst component (corresponding to 3 mg of isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride), 12.8 mg of triphenylmethanetetrakis (pentafluorophenyl) boron was added to 10 parts of toluene.
Further loaded in ml.

Next, 0.08 g of triethylaluminum was placed in an autoclave having an internal volume of 5 liters, and propylene 1.5 was added.
30kg by adding toluene slurry of above catalyst
Polymerization was performed while continuously raising the temperature from 1 to 60 ° C. in 2 hours.
Unreacted propylene was purged to take out the polymer,
Drying gave 120 g of polymer (corresponding to 189 kg polypropylene / g zirconium). According to ¹³ C-NMR, the syndiotactic pentad fraction was 0.81, η was 0.85, and MW / MN was 4.1.

Comparative Example 2 Propylene was polymerized in the same manner as in Example 2 except that the polymerization temperature was kept constant at 60 ° C. As a result, 155 g was obtained.
A polymer of The syndiotactic pentad fraction of this polymer is 0.80, η is 0.72 and MW / MN is
It was 2.2.

[0049]

By carrying out the method of the present invention, it is possible to produce a polyolefin having a controlled molecular weight and a wide molecular weight distribution without changing the stereoregularity with high productivity, which is of great industrial value. is there.

Claims (2)

[Claims] 1. A reaction product of a transition metal compound having an inorganic oxide as a carrier and having a ligand and an aluminoxane, or a reaction product of a transition metal compound having a ligand and an organometallic compound and reacting with the reaction product to obtain ionicity. A method for producing a polyolefin using a catalyst component comprising a compound forming a compound, wherein the olefin is polymerized by changing the polymerization temperature so that the difference in polymerization temperature is at least 10 ° C or more. Manufacturing method. 2. A transition metal compound having a ligand is represented by the following general formula (Chemical formula 1) or (Chemical formula 2) (wherein A and B are 1
A divalent or divalent unsaturated hydrocarbon residue, or mutually identical or different ligands containing a nitrogen atom, an oxygen atom, a silicon atom, a phosphorus atom or a sulfur atom bonded to M, A ′ and B ′ Is a monovalent or divalent unsaturated hydrocarbon residue bridged with R, or a ligand containing a nitrogen atom, an oxygen atom, a phosphorus atom or a sulfur atom bound to M, and R is A linear saturated hydrocarbon residue which may have a residue or a side chain containing a divalent nitrogen atom, oxygen atom, silicon atom, phosphorus atom or sulfur atom, or a part or all of the linear carbon atom thereof Is a residue substituted with a silicon atom, a germanium atom or a tin atom, M is a metal atom selected from Group 4 or Group 5 of the periodic table, and X is a halogen atom, a carbon atom bonded to M, Nitrogen atom, oxygen atom, silicon atom, boron atom, Shows a ligand containing an atom or a sulfur atom. ) The method according to claim 1, represented by Embedded image Embedded image