JPH0220510A - Production of ultrahigh-molecular-weight polyethylene - Google Patents

Abstract

PURPOSE:To prevent the fibril formatioin and improve the solubility, flowability, etc. of polyethylene by polymerizing ethylene in the presence of a catalyst comprising a specific solid catalyst component and an organometallic compd. CONSTITUTION:A solid catalyst component is obtd. by grinding a mixture of a magnesium halide (e.g., MgCl2), an organoaluminum compd. of formula I (wherein R is 1-4C alkyl) (e.g., Al triethoxide) [in a molar ratio of Al to Mg in said magnesium halide of (0.01-1)] and a tetravalent titanium compd. of formula II (wherein R is 1-20C alkyl, aryl or aralkyl; X is halogen; and 0<=n<=4) (e.g., TiCl4) contg. 5-10wt.% Ti based on said solid catalyst component, dissolving the mixture in a liq. electro-donating compd., and precipitating and/or separating using an inert hydrocarbon solvent. the obtd. solid catalyst component is mixed with an organometallic compd. in an amount of 0.1-1000mol per mol of said titanium compd. in said catalyst component to give a catalyst, which is used for the polymerization of ethylene.

Description

[Detailed description of the invention] <Industrial %l field> The present invention relates to a method for producing ultra-high molecular weight polyethylene.

More specifically, the present invention relates to a method for producing ultra-high molecular weight polyethylene that has excellent fluidity, does not generate fibrils, and is easily soluble in solvents by using a specific solid catalyst component and an organometallic compound.

<Prior art and problems to be solved by the invention> Conventionally, in the production of ultra-high molecular weight polyethylene, various inorganic magnesium compounds such as magnesium halides, magnesium oxide, and magnesium hydroxide are used as carriers, and titanium or vanadium, etc. are added to the carriers. It is known that many catalysts are used that are fully supported with transition metal compounds. However, in these known techniques, there are problems such as the bulk density of the ultra-high molecular weight polyethylene obtained is generally low, the particle size distribution is wide, and fibrils are formed in the particles, making them difficult to dissolve in solvents. Furthermore, for the production of ultra-high molecular weight polyethylene n-fibers by the gel spinning method, which has been in increasing demand in recent years, ultra-high molecular weight polyethylene that is easily soluble in solvents and forms a uniform gel is indispensable.

Therefore, it has been desired to develop a new manufacturing method that solves the aforementioned problems.

In view of the above-mentioned situation, the present inventors have conducted intensive studies and have surprisingly found that the following specific solid catalyst components and organometallic compounds have been used. It has been discovered that by producing ultra-high molecular weight polyethylene using this method, the drawbacks of conventional products can be solved.

That is, the present invention provides a method for producing ultra-high molecular weight polyethylene using a solid catalyst component and an organometallic compound as a catalyst, in which the solid catalyst component comprises (1) magnesium halide, (2) general formula AI (OR)3 ( In the formula, R has 1 carbon number
A component consisting of an organoaluminum compound represented by ~4 (representing an alkyl group) and (3) a tetravalent titanium compound is co-pulverized, dissolved in a liquid electron donor compound, and then precipitated with an inert hydrocarbon solvent. The present invention relates to a method for producing ultra-high molecular weight polyethylene, characterized in that and/or the material is a substance obtained by precipitation.

By producing ultra-high molecular weight polyethylene using the specific catalyst of the present invention, ultra-high molecular weight polyethylene having the following excellent features can be obtained.

(1) Ultra-high molecular weight polyethylene with a small average particle diameter, narrow particle size distribution, relatively spherical diameter, and good free-flowing properties can be obtained with high activity. Ultra-high molecular weight polyethylene that is easily soluble in polyethylene chloride is obtained.

(3) Since it has the features (1) and (2) above, it is suitable for producing ultra-high molecular weight polyethylene fibers by the gel spinning method, requiring a small amount of solvent and producing a uniform gel. be.

The present invention will be explained in detail below.

The magnesium halide used in the present invention is substantially anhydrous and includes magnesium heptatide, magnesium chloride, magnesium bromide, and magnesium iodide, with magnesium chloride being particularly preferred.

Examples of the compound represented by the general formula At (OR)3 (where R is an alkyl group having 1 to 4 carbon atoms) used in the present invention include aluminum trimethoxide, aluminum triethoxide, aluminum triethoxide, and aluminum triethoxide. Examples include propoxide, aluminum triisopropoxide, aluminum tri-n-butoxide, aluminum tri-5ee-butoxide, and aluminum tri-t-butoxide, with aluminum trimethoxide and aluminum triethoxide being particularly preferred.

1-Jl as a tetravalent titanium compound used in the present invention
, physically has the general formula Tt (OR)1X4-n (where R
represents an alkyl group, an aryl group, or an aralkyl group of several 1 to 2 degrees on the carbon, and X represents a halogen atom. n is 0≦
n≦4. ) are preferred, specifically titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monomethoxytrichlorotitanium, dimethoxydichlorotitanium, trimethoxymonochlorotitanium, tetramethoxytitanium, monoethoxytrichlorotitanium, Toxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoinpropoxytrichlorotitanium, diisopropoxydichlorotitanium, triisopropoxymonochlorotitanium, tetrainpropoxytitanium, monobutoxytrichlorotitanium, dibutoxydichlorotitanium,
It can exclude monopentoxytrichlorotitanium, monophenoxytrichlorotitanium, diphenoxydichlorotitanium, triphenoxymonochlorotitanium, tetraphenoxytitanium, etc.

In the present invention, a substance obtained by co-pulverizing these components, dissolving them in an electron donor compound, and then precipitating and/or precipitating them with an inert organic solvent is used as the solid catalyst component.

Co-pulverization may be carried out by simultaneously grinding the magnesium halide, the aluminum compound and the tetravalent titanium compound, or by co-pulverizing the magnesium halide and the aluminum compound, and then adding and grinding the tetravalent titanium compound. Good too. Of course, it is preferable to carry out these operations in an inert gas atmosphere, and it is preferable to avoid moisture as much as possible.

Regarding the mixing ratio of magnesium halide and aluminum compound, polymerization activity tends to decrease if the amount of aluminum compound is too small or too large, and the Mg/A1 molar ratio is usually 110. 01~1/
1, preferably 110.05 to 1/
A range of 0.5 is desirable.

The amount of the Ti compound is most preferably adjusted so that Ti1- contained in the produced solid is in the range of 0.5 to 10% by weight, and particularly preferably in the range of 1 to 8% by weight.

The equipment used for co-pulverization is not particularly limited, but ball mills, vibration mills, rod mills, impact mills, etc. are usually used, and conditions such as mixing order, grinding time, and grinding temperature are appropriate depending on the grinding method. This is something that can be easily determined by businesses.

Further, as the electron donor compound in the present invention, a halogenated magnesium compound, an organoaluminum compound,
A liquid organic compound in which all the tetravalent titanium compounds are soluble is used.

These electron donor compounds include alcohols, ethers, ketones, aldehydes, organic acids, organic acid esters,
Examples include acid halides, acid amides, amines, nitriles, and the like. Specific examples of these include the following.

Alcohol Toshitesha, methyl alcohol, ethyl alcohol, n-7'' lobil alcohol, isobutyl alcohol, 7'J alcohol, n-butyl alcohol, isobutyl alcohol, 5ec-butyl alcohol, t
-butyl alcohol, n-amyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, tepyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol, benzyl alcohol, naphthyl alcohol, phenol, cresol, etc. with 1 or more carbon atoms 18 alcohol can be opened.

Examples of the ether include ethers having 2 to 20 carbon atoms, such as dimethyl ether, diethyl ether, dibutyl ether, isoamyl ether, anisole, phenethole, diphenyl ether, phenyl allyl ether, benzofuran, and tetrahydrofuran.

The ketone can be a ketone having 3 to 18 carbon atoms, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl phenyl ketone, ethylphenyl ketone, diphenyl ketone.

Examples of the aldehyde include aldehydes having 2 to 15 carbon atoms, such as acetaldehyde, propionaldehyde, octylaldehyde, benzaldehyde, and nandaldehyde.

Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, pivalic acid, caproic acid, caprylic acid, stearic acid, oxalic acid, malonic acid, succinic acid, adipic acid, methacrylic acid, benzoic acid, toluic acid, Examples include organic acids having 1 to 24 carbon atoms, such as anisic acid, oleic acid, linoleic acid, and lylunic acid.

Examples of organic acid esters include methyl formate, methyl acetate, ethyl acetate, propyl acetate, octyl acetate, ethyl propionate, methyl butyrate, ethyl valerate, methyl methacrylate, methyl benzoate, ethyl benzoate, and propyl benzoate. , octyl benzoate, phenyl benzoate, benzyl benzoate, ethyl 0-methoxybenzoate, ethyl p-methoxybenzoate, butyl p-ethoxybenzoate, methyl p-toluate, p-)ethyl leifivate, p- Examples include organic acid esters having 2 to 30 carbon atoms, such as ethyl ethylbenzoate, methyl salicylate, phenyl salicylate, methyl naphthoate, ethyl naphthoate, and ethyl anisate.

Examples of the acid halide include acid halides having 2 to 15 carbon atoms, such as acetyl chloride, benzyl chloride, toluic acid chloride, and anise acetic acid chloride.

Examples of acid amides include acetic acid amide, benzoic acid amide, and toluic acid amide.

Examples of the amine include amines such as methylamine, ethylamine, diethylamine, tributylamine, piperidine, tribenzylamine, aniline, pyridine, picoline, and tetramethylenediamine.

Nitriles include acetonitrile, benzonitrile,
Examples include nitriles such as tolnitrile.

These electron donors can be used in 18+ or 2 or more glazes.

Among these electron donors, organic acid esters or ethers are particularly preferred.

The dissolution method is not particularly limited, and the co-pulverized material may be added to the electron donor, or the electron donor may be added to the co-pulverized material.

During dissolution, the h1 ratio of the co-pulverized material to the female force is usually 0.1 to 300 - 1 part of the co-pulverized material to the electron donor.
Preferably it is 1 to 150-. Further, the temperature f& during dissolution is usually -10 to 300°C, preferably 0 to 150°C.
℃, and the dissolution time is not limited as long as the co-pulverized material is completely dissolved, but it is usually 1 minute to 5 minutes.
0 hours, preferably Vis minutes to 10 hours.

The inert hydrocarbon solvent used to precipitate and/or precipitate the solid catalyst component from the solution of the electron donor in which the co-pulverized product is dissolved is usually a saturated aliphatic hydrocarbon having 4 to 12 carbon atoms. Examples of these are:
Examples include n-pentane, n-hexane, n-hebutane, n-octane, n-decane, and the like. Among these, n-hexane and n-octane are particularly preferred.

The solid catalyst component is precipitated and /'=! The method of precipitation is not particularly limited, and a bath solution of an electron donor in which the co-pulverized material is dissolved may be added to an inert hydrocarbon solvent, or an inert hydrocarbon solvent may be added to the solution. May be added to.

In this case, the amount of inert hydrocarbon solvent used is usually 0.1 to 10,100 O, preferably 1 to 500 O, based on the co-pulverized mixture 17.

The temperature at which the solid catalyst component is precipitated and/or precipitated is usually -20 to 300°C, preferably -10 to 150°C.
1, the time at that time is 1 minute to 50 hours, preferably 5 minutes to 10 hours.

Next, the solid catalyst component obtained by precipitation and/or precipitation with an inert hydrocarbon solvent is repeatedly washed with the inert hydrocarbon solvent, and then heated in a temperature range of 60 to 130°C for 10 minutes to It is desirable to vacuum dry for 2 hours. Alternatively, a method in which diethylaluminum chloride or the like is added and treated by a conventional method is also preferably used.

The solid catalyst component thus obtained is used in combination with an organometallic compound to produce ultra-high molecular weight polyethylene.

As the organometallic compound used in the present invention, organometallic compounds of groups 1 to 1 of the periodic table, which are known as components of Ziegler type catalysts, can be used, but organoaluminum compounds and organozinc compounds are particularly preferred. Specific examples include the general formula Rs At , R2AI X%RAI
Xs, R2A10R1RA, 1(OR)X and R
5A1. X, an organoaluminum compound (where R
Vi alkyl group or aryl group having 1 to 20 carbon atoms, X
represents a halogen atom, and RFi may be the same or different. ) or general 2 RIZn (however, R is an alkyl group having 1 to 20 carbon atoms and may be the same or different), including triethylaluminum, triimbutylaluminum, tri-butylaluminum, tri-5ee-butylaluminum, tri-tert-butylaluminum,
trihexylaluminum, trioctylaluminum, diethylaluminium chloride, diisopropylaluminum chloride, diethylaluminum ethoxide,
Ethyl aluminum sesquichloride, diethyl zinc and mixtures thereof etc. can be drilled. Preferably, triethylaluminum and diethylaluminum chloride are used in combination.

There is no particular restriction on the use of the organometallic compound, but it can usually be used in an amount of 0.1 to 1000 mo1 times that of the titanium compound.

In the present invention, the organozinc compound component can be used as a mixture or addition compound of the organometallic compound and organic acid ester.

When using an organometallic compound and an organic acid ester as a mixture, the organic acid ester is usually 0.1 to 1 mol and 0.2 to 0.5 mol of the organic acid ester per 1 mol of the organometallic compound.
Use moles. In addition, when used as an addition compound of an organometallic compound and a specific acid ester, an organometallic compound;
It is preferable that the molar ratio of the organic acid ester is 2:1 to 1:2.

The organic acid ester used at this time has 1 to 1 carbon atoms.
It is an ester of 24 saturated or unsaturated monobasic or dibasic organic carboxylic acids and an alcohol having 1 to 3 carbon atoms. Specifically, methyl formate, ethyl acetate, amyl acetate, phenyl acetate, octyl acetate, methyl methacrylate, ethyl stearate, methyl benzoate, ethyl benzoate, benzo[n-propyl, isopropyl benzoate, benzoic acid] Butyl, hexyl benzoate, cyclopentyl benzoate, cyclohexyl benzoate, phenyl benzoate, 4-tolyl benzoate, methyl salicylate, ethyl salicylate, methyl p-oxybenzoate, ethyl p-oxybenzoate, phenyl salicylate, p -cyclohexyl oxybenzoate, benzyl salicylate, ethyl α-resorucinate, ethyl anisate, ethyl anisate, phenyl anisate, pencil anisate, methyl p-ethoxybenzoate, methyl p-toluate, methyl p-toluate, p-phenyl toluate, ethyl toluate,
m-) ethyl ruylate, methyl p-aminobenzoate, p
Examples include ethyl aminobenzoate, vinyl benzoate, allyl benzoate, benzyl benzoate, methyl naphthoate, and ethyl naphthoate.

Among these, particularly clever are alkyl esters of benzoic acid, 0- or p-)ruyl or anisic acid, and methyl and ethyl esters thereof are particularly preferred.

The present invention uses the above catalyst to produce ultra-high molecular weight polyethylene as follows. The ultra-high molecular weight polyethylene produced in the present invention has a molecular weight of 600,000 to 12 million, preferably 900,000 to 6 million, and more preferably 1.2 million to 500,000.
6 to 50 ttt/y, preferably 8 to 30 dt/9,
More preferably, it corresponds to 9 to 28 dl/f.

In the present invention, polymerization to obtain ultra-high molecular weight polyethylene can be carried out by slurry polymerization, solution polymerization or gas phase polymerization. In particular, the catalyst of the present invention can be suitably used for slurry polymerization, and the polymerization reaction is carried out in the same manner as the polymerization reaction of olefins using ordinary Ziegler type catalysts. That is, in all reactions, ethylene with a hydrogen concentration of 0 to 20 molar, preferably 0 to 10 molar, is polymerized in the presence of an inert hydrocarbon in a state where oxygen, water, etc. are substantially excluded, and ultra-high molecular weight polyethylene is produced. . The polymerization conditions at this time include a temperature of 0 to 120°C, preferably 20 to 100°C.
℃, and the pressure is 0 to 70 kl/crt?・G Preferably O to 60 k4/cnt" Further, organic solvents with high boiling points such as decalin, tetralin, decane, and kerosene can also be used depending on the needs of the molding process of the obtained ultra-high molecular weight polyethylene.

Although the molecular weight γj can be adjusted to some extent by changing polymerization conditions such as polymerization temperature and catalyst molar ratio, it is effectively controlled by adding hydrogen to the polymerization system. Of course, using the catalyst of the present invention, two-stage or more multi-stage polymerization reactions with different polymerization conditions such as hydrogen concentration and polymerization temperature can be carried out without any problems.

Further, for the purpose of modifying the ultra-high molecular weight polyethylene of the present invention, copolymerization with α-olefins or 6-dienes can also be carried out. The α-olefin used at this time is U, such as clopyrene, butene-1, hexene-1
, 4-methylpentene-1, and the like. In addition, examples of the diene include phytadiene, 1.4-
Examples include hexadiene, ethylnorbornene, dicyclopentadiene, etc. <Effects of the Invention> As mentioned above, by the method of the present invention, the average particle size is small,
It is possible to obtain ultra-high molecular weight polyethylene that has a narrow particle size distribution, good free-flowing properties, no formation of fibrils in the particles, and is easily soluble in solvents.

<Examples> The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

Example 1 (a) Production of catalyst Commercially available anhydrous magnesium chloride (MCIC)
7'd 9.5t (0.1mol
), Aluminum Ethoquid 4.1? (0,02
5 mol ) and titanium tetrachloride 0,832 contents 84007 containing 25 stainless steel balls with A inch diameter! The sample was placed in a stainless steel pot and ball milled for 16 hours at room temperature under a nitrogen atmosphere. The white solid powder 11 obtained after ball milling contained 42.1 μ of titanium.

The above-mentioned white powder 29 was placed in a 3-Low flask under a nitrogen atmosphere, and tetrahydrofuran (THF) 2 (1 m/'i) was added and held at 30°C for 1 hour to dissolve the white powder. 100ml of hexane was added to the mixture, and the entire amount of the white powder dissolved in THF was dropped into the hexane by pressing with a finger. Stirring was performed at 30°C for 30 minutes to precipitate the solid catalyst component, and then washing was repeated 4 times with 50ml of hexane. After washing with hexane, remove the supernatant hexane and incubate at 120℃ for 1 hour.
A solid catalyst component was obtained by vacuum drying for hours.

(b) Polymerization of ethylene Hexane 1 in a 2t autoclave at room temperature under a nitrogen atmosphere
000m, triethylaluminum 1.0 mrnol
, and the above-mentioned solid catalyst component 10119 were added in this order, the temperature was raised to 65°C, and ethylene was fully pressurized to bring the total pressure to 10.
Polymerization was carried out for 1 hour at kV/crPP·G. Ultra high molecular weight polyethylene was obtained. Catalytic activity is 25009
It was polyethylene/f solid catalyst/hr-C2H4 pressure.

(c) Physical property evaluation As a result of physical property evaluation of the produced ultra-high molecular weight polyethylene using conventional methods, the bulk density was 0.32 f/err? ,
Intrinsic viscosity (135°C, in decalin) 16.1 dl/f,
It had an average particle size of 260 pm and had good free-flowing properties, and no fibrils were observed when observed under an electron microscope at 3000 times.

Note that the solubility in organic solvents is 135°C in decalin.
Evaluation was made based on the variation in the intrinsic viscosity of the polymer.

That is, 0.029 of the obtained 7'c polymer was mixed with 20 of decalin.
- In addition, 0.25 wt% of ditertiary-butylhydroxytoluene is added to the polymer as an antioxidant.
The mixture was added at a ratio of
Viscosity F was measured at 35°C. To measure the viscosity, 20 mm of the polymer solution was transferred to a viscometer and the number of seconds it fell was measured three times, then 10 mm of decalin was added and the same operation was repeated, and then 10 mm of decalin was added and the same operation was repeated. Thereafter, the polymer solution was replaced with a new one, and the number of seconds of falling was measured again in the same manner. This operation was repeated five times, and [η] was calculated each time from the average value of the number of seconds of falling, and the standard deviation/average value (CV value %) was calculated as the degree of variation. The Cv value calculated from this was 2.5%, and the solubility was extremely good.

The results of these physical property evaluations are listed in Table 1.

Example 2 The amount of aluminum ethoxide in Example 1 was changed from 4.19 to 1.02, and the solvent THFf;tI O+++/'k
An experiment was conducted in the same manner except that roomt was used instead. Table 1 shows the results of physical property evaluation of the obtained polyethylene.

Example 3 In Example 1, instead of aluminum ethoxide 4.19f aluminum methoxide 2.02, the solvent THF
The experiment was carried out in the same manner except that the inert hydrocarbon solvent, hexane, was changed from 100 to 200.

Table 1 shows the results of physical property evaluation of the obtained polyethylene.

Real milk example 4゜(a) Production of catalyst Commercially available anhydrous magnesium chloride 9.52, aluminum ethoxide 2. , Of, and tetraethoxytitanium29
25 stainless steel balls having a diameter of 72 inches were placed in a stainless steel pot with an internal volume of 400 balls, and ball milling was performed at room temperature under a nitrogen atmosphere for 16 hours.

The white solid powder 1y obtained after ball milling contains 4 Ti
He was carrying Z1 Misaki.

The above white powder 22 was placed in a three-loaf flask under a nitrogen atmosphere, 50 mZi of THF was added, and the mixture was stirred at 30° C. for 1 hour to dissolve the white powder. Under a nitrogen atmosphere, add 100 ml of heptane to another three-ring flask, and drop the white powder dissolved in THF' into the hexane by pressing with your fingers. Stir at 30°C for 3 minutes.
After precipitating the solid catalyst component for 0 minutes, hexane 50
Washing was repeated 4 times with m1. After washing with hexane, the supernatant hexane was removed and vacuum drying was performed at 120° C. for 1 hour to obtain a solid catalyst component.

(b) Polymerization of ethylene Hexane 1 in a 21 autoclave at room temperature under a nitrogen atmosphere
000m, to! 7 ethyl aluminum 1.0 耶o1
, diethylaluminum monochloride 1. Ommo
! , and the solid Pr! - After adding 10 Wqe of medium components in this order, the temperature was raised to 85° C., ethylene was introduced under pressure, and polymerization was carried out for 1 hour while maintaining the total pressure at 10 → /d·G. Ultra high molecular weight polyethylene was obtained. The catalyst activity was 2000f polyethylene/f solid catalyst/hr"02H4 pressure.

(→ Evaluation of Physical Properties The produced ultra-high molecular weight polyethylene was evaluated in the same manner as in Example 1, and the results are listed in Table 1.

Practical X+i Example 5゜Example 1i/(Then, aluminum ethoxide was replaced with aluminum secondary butoxide, the amount of titanium chloride was changed to 1.62, and the amount of hexane as an inert hydrocarbon solvent was changed to 50- The experiment was carried out in the same manner except for the above.The results of evaluating the physical properties of the obtained large polyethylene are shown in Table IK.

Example 6 In Example 1, the amount of aluminum ethoxide was changed to 0.5
2, and the amount of hexane in the inert carbide oxide solvent was changed to 20m/
The same procedure as in Example 1 was carried out except that the temperature of the polymerization vortex was changed to 55°C.

Table 1 shows the results of physical property evaluation of the obtained polyethylene.

Comparative Example 1 An experiment was carried out in the same manner as in Example 1, except that the -7 catalyst component was not precipitated in the bath W4ζ.The results of evaluating the physical properties of the obtained polyethylene are shown in Table 1 and IF was carried out.

Comparative Example 2 An experiment was conducted in the same manner as in Example 1 except that aluminum ethoxide was not added. The property evaluation results of the tested polyethylene are shown in Cloth 1.

[Brief explanation of the drawing]

FIG. 1 is a flow chart 1 showing a process for preparing a catalyst component of the present invention. Figure 1 (A) Transition metal components

Claims (1)

[Scope of Claims] 1. A method for producing ultra-high molecular weight polyethylene using a solid catalyst component and an organometallic compound as a catalyst, wherein the solid catalyst component comprises (1) magnesium halide, (2) general formula Al(OR )_3 (wherein, R has 1 or more carbon atoms
A component consisting of an organoaluminum compound represented by (4) representing an alkyl group and (3) a tetravalent titanium compound is co-pulverized and dissolved in a liquid electron donor compound, and then precipitated and treated with an inert hydrocarbon solvent. 1. A method for producing ultra-high molecular weight polyethylene, characterized in that the material is obtained by/or precipitation.