WO2008040675A1 - Verfahren zum entfernen von restmonomeren aus polyoxymehtylenhomo- oder -copolymeren - Google Patents
Verfahren zum entfernen von restmonomeren aus polyoxymehtylenhomo- oder -copolymeren Download PDFInfo
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- WO2008040675A1 WO2008040675A1 PCT/EP2007/060259 EP2007060259W WO2008040675A1 WO 2008040675 A1 WO2008040675 A1 WO 2008040675A1 EP 2007060259 W EP2007060259 W EP 2007060259W WO 2008040675 A1 WO2008040675 A1 WO 2008040675A1
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- frequency field
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L59/00—Compositions of polyacetals; Compositions of derivatives of polyacetals
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
- C08G2/28—Post-polymerisation treatments
Definitions
- the invention relates to a process for removing residual monomers from polyoxymethylene homopolymers or copolymers using a high-frequency electromagnetic field and to polyoxymethylene homopolymers or copolymers prepared by the process.
- Polyoxymethylene polymers are obtained by homo- or copolymerization of 1, 3,5-trioxane (trioxane in short), formaldehyde or other formaldehyde source. The conversion is usually not complete, but the POM crude polymer contains between 1 and 40% or between see between 10 and 40% unreacted monomers. Such residual monomers are, for example, trioxane and formaldehyde, and optionally comonomers used, such as 1,3-dioxolane, 1,3-butanediol formal or ethylene oxide. In summary, POM stands for homo- and copolymers.
- the residual monomers are removed during the preparation of the POM molding compositions by workup by degassing from the crude polymer.
- the degassing can be carried out at atmospheric pressure or underpressure, as described in EP-A 638 599, EP-A 999 224 or DE-A 31 47 309, or under elevated pressure, according to the method of DE 102 005 002 413.0.
- the degassing is caused by relaxation, that is, a pressure drop. That a medium cools when pressure drops, is known for gases as Joule-Thomson effect.
- Heating that a medium cools when pressure drops, is known for gases as Joule-Thomson effect.
- Joule-Thomson effect In the case of polymer melts, an analogous effect occurs, there is an increased evaporation of volatile constituents, which draw energy from the polymer melt, whereby it cools.
- the degassing of polymer melts is therefore usually associated with the cooling of the same.
- the melt temperature may drop below its fixed point, where it crystallizes and clogged leads.
- the cooling of the polymer melt impedes its degassing.
- the first degassing step of the polyoxymethylene melt is usually carried out prior to extrusion, that is, a Rohpolyoxymethylen is degassed, which is not fully additiviert and thus is particularly sensitive to heat, since the complete additization usually takes place in the extruder.
- a Rohpolyoxymethylen is degassed, which is not fully additiviert and thus is particularly sensitive to heat, since the complete additization usually takes place in the extruder.
- this can lead to damage to the polymer melt.
- DE 10 2005 032 700.1 describes the aftertreatment of an extrudate from a thermoplastic by means of an electromagnetic high-frequency field for the reduction of thermal stresses in the extrudate.
- DE-A 44 37 042 describes the treatment of solid polymer molding compositions or moldings of polyacetates in a high-frequency electromagnetic field, but to reduce the residual content of monomer residues.
- the solution consists in a process for removing residual monomers from polyoxymethylene homo- or copolymers using a high-frequency electromagnetic field, comprising the following process steps:
- Process steps b) and c) is exposed to the electromagnetic high frequency field, wherein it is heated or wherein its cooling is prevented.
- the polyoxymethylene homopolymers or copolymers (POM) from which the unreacted residual monomers are removed by the process according to the invention are known as such and are commercially available.
- the homopolymers are polymerized formaldehyde or, preferably, trioxane; Comonomers are also used in the preparation of the copolymers.
- POM polymers have at least 50 mole% of recurring units - CH 2 O - in the polymer backbone.
- Polyoxymethylene copolymers are preferred, in particular those which in addition to the recurring units - CH 2 O- even up to 50, preferably 0.01 to 20, especially 0.1 to 10 mol% and most preferably 0.5 to 6 mol% at recurring units
- R 1 to R 4 independently of one another are a hydrogen atom, a C 1 to C 4 alkyl group or a halogen-substituted alkyl group having 1 to 4 C atoms and R 5 is a -CH 2 -, -CH 2 O-, a d- to C 4 alkyl or C 1 to C 4 haloalkyl substituted methylene group or a corresponding oxymethylene group and n has a value in the range of 0 to 3.
- these groups can be introduced into the copolymers by ring opening of cyclic ethers.
- Preferred cyclic ethers are those of the formula
- R 1 to R 5 and n have the abovementioned meaning.
- Oxymethylenterpolymerisate for example, by reacting trioxane, one of the cyclic ethers described above with a third monomer, preferably bifunctional compounds of the formula
- Preferred monomers of this type are ethylene diglycide, diglycidyl ether and diether from glycidylene and formaldehyde, dioxane or trioxane in the molar ratio 2: 1 and diether from 2 mol glycidyl compound and 1 mol of an aliphatic diol having 2 to 8 carbon atoms such as the diglycidyl ethers of ethylene glycol, 1 , 4-butanediol, 1, 3-butanediol, cyclobutane-1, 3-diol, 1, 2-propanediol and cyclohexane-1, 4-diol, to name just a few examples.
- End-group-stabilized polyoxymethylene polymers which have predominantly C-C or -O-CH 3 bonds at the chain ends are particularly preferred.
- the preferred polyoxymethylene copolymers have melting points of at least 150 ° C. and weight average molecular weights M.sub.w in the range from 5,000 to 300,000, preferably from 7,000 to 250,000, g / mol. Particular preference is given to POM copolymers having a non-uniformity (MJM n ) of from 2 to 15, preferably from 2.5 to 12, particularly preferably 3 to 9.
- the measurements are generally carried out by gel permeation chromatography (GPC) SEC (size exclusion chromatography).
- the M n value number average molecular weight
- GPC-SEC number average molecular weight
- the molecular weights of the polymer can be adjusted to the desired values by the regulators customary in the trioxane polymerization and by the reaction temperature and residence time.
- Suitable regulators are acetals or formals of monohydric alcohols, the alcohols themselves and the small amounts of water which function as chain transfer agents and whose presence can generally never be completely avoided.
- the regulators are used in amounts of from 10 to 10,000 ppm, preferably from 20 to 5,000 ppm.
- Initiators are the cationic initiators customary in the trioxane polymerization.
- Proton acids are suitable, such as fluorinated or chlorinated alkyl- and arylsulfonic acids, for example perchloric acid, trifluoromethanesulfonic acid or Lewis acids, for example tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride, and their complex compounds and salt-like compounds, for example boron trifluoride etherates and triphenylmethylene hexafluorophosphate.
- fluorinated or chlorinated alkyl- and arylsulfonic acids for example perchloric acid, trifluoromethanesulfonic acid or Lewis acids, for example tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride, and their complex compounds and salt
- the initiators are used in amounts of about 0.01 to 1000 ppm, preferably 0.01 to 500 ppm and in particular from 0.01 to 200 ppm. puts. In general, it is advisable to add the initiator in dilute form, preferably in concentrations of 0.005 to 5 wt .-%.
- Suitable solvents for this purpose may be inert compounds such as aliphatic, cycloaliphatic hydrocarbons, for example cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. Particularly preferred is triglyme (triethylene glycol dimethyl ether) as a solvent, 1, 4-dioxane, ⁇ -butyrolactone or propylene carbonate.
- Monomers, initiators, cocatalyst and, if appropriate, regulators can be premixed in any desired manner or else added separately to the polymerization reactor.
- the stabilizing components may contain sterically hindered phenols as described in EP-A 129369 or EP-A 128739.
- the polymerization mixture is deactivated directly after the polymerization, in particular without a phase change taking place.
- the deactivation of the initiator residues is generally carried out by adding deactivators (terminating agents) to the polymerization melt.
- deactivators are e.g. Ammonia and primary, secondary or tertiary, aliphatic and aromatic amines, e.g. Trialkylamines such as triethylamine, or triacetonediamine.
- basic-reacting salts such as soda and borax, furthermore the carbonates and hydroxides of the alkali metals and alkaline earth metals, and also alkoxides, such as sodium ethanolate.
- the deactivators are usually added to the polymers in amounts of preferably 0.01 ppmw (parts per million by weight) up to 2 wt .-%.
- alkali metal or alkaline earth metal alkyls are preferred as deactivators which have 2 to 30 C atoms in the alkyl radical.
- Particularly preferred metals are Li, Mg and Na, with n-butyllithium being particularly preferred.
- Formaldehyde POM can be prepared in a customary manner by polymerization in the gas phase, in solution, by precipitation polymerization or in bulk (substance).
- Trioxane POMs are typically obtained by bulk polymerization using any reactors with high mixing efficiency.
- the reaction can be carried out homogeneously, e.g. in a melt, or heterogeneous, e.g. as polymerization to a solid or solid granules.
- Suitable examples are tray reactors, plowshare mixers, tubular reactors, list reactors, kneaders (e.g., Buss kneaders), extruders with, for example, one or two screws, and stirred reactors, which reactors may comprise static or dynamic mixers.
- kneaders e.g., Buss kneaders
- extruders with, for example, one or two screws
- stirred reactors which reactors may comprise static or dynamic mixers.
- the melted-on polymer forms a so-called melt seal, as a result of which volatile constituents remain in the extruder.
- the above monomers are metered into the im Extruder polymer melt, either together or separately from the initiators (catalysts), at a preferred temperature of the reaction mixture from 62 to 114 0 C.
- the monomers (trioxane) are metered in a molten state, for example at 60 to 120 0 C. Due to Exothermicity of the process usually requires melting the polymer in the extruder only at the start of the process; Subsequently, the amount of heat released is sufficient to melt the molten POM polymer or to keep it molten.
- the melt polymerization is generally carried out at 1, 5 to 500 bar and 130 to 300 0 C, and the residence time of the polymerization mixture in the reactor is usually 0.1 to 20, preferably 0.4 to 5 min.
- the polymerization is preferably carried out to a conversion of more than 30%, for example 60 to 90%.
- a crude POM which, as mentioned, contains considerable proportions, for example up to 40%, of unreacted residual monomers, in particular trioxane and formaldehyde.
- Formaldehyde can also be present in the crude POM if only trioxane was used as the monomer since it can be formed as a degradation product of the trioxane.
- other oligomers of formaldehyde may also be present, e.g. the tetrameric tetroxane.
- Trioxane is preferably used as the monomer for the preparation of the POM, which is why the withdrawn residual monomers also contain trioxane, moreover usually 0.5 to 10% by weight of tetroxane and 0.1 to 75% by weight of formaldehyde.
- the process according to the invention can be operated batchwise or, preferably, continuously.
- step a) of the process according to the invention the polymer (POM) is brought at a pressure of 1 to 100 bar to a temperature of 140 to 270 0 C, wherein a melt is formed.
- step a) If the POM is present at the end of the polymerization reactor or the deactivation under these pressure and temperature conditions, the features of step a) are already fulfilled. Otherwise, the POM is brought by conventional measures for pressure and temperature adjustment to a pressure of 1 to 100 bar and to a temperature of 140 to 270 0 C. Usually, the temperature of the POM before step a) is below the temperature to be set in step a), ie the polymer is heated in step a). This heating is also called overheating. However, the POM temperature - in particular in the case of POM production by melt polymerization - before step a) can also be above the temperature to be set in step a); In this case, the polymer is cooled in step a).
- the pressure is preferably from 5 to 60 bar, more preferably from 15 to 50 bar.
- the temperature is 150 to 240 ° C., more preferably 160 to 220 ° C.
- the pressure is 5 to 60 bar and the temperature is 150 to 240 ° C .; and more preferably the pressure is 15 to 50 bar and the temperature 160 to 220 0 C.
- the residence time of the polymer in step a) is generally 1 second to 30 minutes, preferably 5 seconds to 15 minutes.
- the temperature of the polymer in step a) is carried out in the usual manner by heat exchangers, double jacket heating (or cooling), tempered static mixer, internal heat exchanger or other suitable devices.
- the adjustment of the pressure is also carried out in a manner known per se, e.g. by means of pressure control valves or pumps.
- the crude POM obtained in the POM preparation can be allowed to cool first and then heated in step a).
- step a) follows immediately after the polymerization or deactivation. Hence, this can be accomplished in a simple manner by immediately following the polymerization zone or deactivation zone of the reactor with a tempering zone (e.g., overheating zone) which adjusts the temperature of step a).
- This tempering zone can be designed, for example, as a heat exchanger.
- the pressure of step a) is preferably adjusted by the reactor geometry and the reaction conditions of the POM preparation.
- step a) the pressure and the temperature of step a) are to be adjusted such that the polymer is in the form of a melt.
- melt should not exclude that the polymer contains small amounts of solids, for example at most 5% by weight.
- the feed line b) is exposed to an electromagnetic high-frequency field.
- Polyoxymethylene homopolymers or copolymers can be heated by a high-frequency electromagnetic field since they contain the polar CH 2 O units.
- additional indirect heating can be achieved by adding to the crude polyoxymethylene homo- or copolymer melt an additive which has, for example, polar structures or is metal or graphitic and can therefore be heated in the electromagnetic high frequency field.
- the present invention may be additives commonly used in plastics technology, in particular colorants, additives, fillers, reinforcing agents or the like.
- suitable additives are graphite, carbon fibers, metal powders, in particular iron powder, ZnO, TiO 2 , Al 2 O 3 , CaTiO 3 , BaTiO 3 , ⁇ -Fe 2 O 3 , BaO-18Fe 2 O 3 , Fe 3 O 4 , polyphenylene sulfides, ferrites, Ti or Zr hydroxyethyl phosphonates, bentonites, alkali metal or alkaline earth metal-containing aluminum silicates or dyes such as spinnel black, aluminum pigment paste, gold bronze powder or carbon black.
- the inventive method has a number of advantages.
- the high frequency field used allows contactless heating without temperature peaks. Since the energy is not entered via the interface heat exchanger / melt, but in the entire high-frequency field, a faster and more uniform heating, without overheating of the surface layer is achieved.
- Devices for generating electromagnetic high frequency fields (for example microwave ovens) remain cold themselves, so that increased safety at work is ensured.
- the energy input can also be selectively controlled, for example by varying the number and power of microwave sources.
- the sources can be positioned so that the energy is introduced as evenly as possible in the melt. However, the sources can also be specifically positioned so that an uneven input of energy occurs. The shorter heating time allows a compact and therefore space-saving design.
- a high-frequency field in this context is any suitable for the electrical heating of the melt or optionally of additives to the melt electromagnetic field.
- the electromagnetic high-frequency field used in the method according to the invention preferably has a frequency in the range of 100 kHz to 900 GHz.
- the high-frequency field has a frequency in the range of 0.3 to 300 GHz.
- this is microwave radiation.
- the power input of the electromagnetic high-frequency field is controlled such that the temperature of the crude Polyoxymethylenhomo- or copolomerschmelze by 5 to 50 Kelvin, more preferably increased by 5 to 40 Kelvin and more preferably by 5 to 30 Kelvin, or that a cooling during the Degassing is prevented.
- the high-frequency field is designed so that the most homogeneous possible heating of the melt takes place in the high-frequency field.
- rectangular waveguides are used as feed line in step b), in which the distance of the opposite sides is in each case an integer multiple of half the wavelength of the electromagnetic radiation.
- cylindrical waveguides are used as the feed line in step b).
- waveguides are used as feed line in step b) in which standing waves of the electromagnetic high-frequency field form.
- a standing wave is formed when it is reflected in the direction of propagation at boundaries whose spacing is an integer multiple of half the wavelength.
- an additional heat source may be provided for heating the crude polyoxymethylene homo- or copolymer melt, for example heat exchangers, heating strips or the like.
- the invention also provides polyoxymethylene homo- or copolymers obtainable by the process described above.
- the process according to the invention provides rapid and uniform heating of the crude polyoxymethyl homo- or copolymer melt before degassing. ranges, in particular, an overheating of the melt is avoided at the edge zone to the usual heat exchangers.
- crude polyoxymethylene homo- or copolymer melts can be degassed faster, more uniformly and more gently than the prior art, whereby a particularly low residual monomer content can be achieved and the consequences of temperature damage minimized, whereby improved product qualities, in particular color numbers, are achieved ,
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- Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)
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BRPI0713655-2A BRPI0713655A2 (pt) | 2006-10-02 | 2007-09-27 | processo para remover monÈmeros residuais de homopolìmero ou copolìmero de polioximetileno |
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EP06121620.6 | 2006-10-02 | ||
EP06121620 | 2006-10-02 |
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WO2008040675A1 true WO2008040675A1 (de) | 2008-04-10 |
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PCT/EP2007/060259 WO2008040675A1 (de) | 2006-10-02 | 2007-09-27 | Verfahren zum entfernen von restmonomeren aus polyoxymehtylenhomo- oder -copolymeren |
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WO (1) | WO2008040675A1 (de) |
Citations (1)
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DE4437042A1 (de) * | 1994-10-17 | 1996-04-18 | Hoechst Ag | Verfahren zur Desodorierung von Polyacetalformmassen |
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- 2007-09-27 BR BRPI0713655-2A patent/BRPI0713655A2/pt not_active Application Discontinuation
- 2007-09-27 WO PCT/EP2007/060259 patent/WO2008040675A1/de active Application Filing
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DE4437042A1 (de) * | 1994-10-17 | 1996-04-18 | Hoechst Ag | Verfahren zur Desodorierung von Polyacetalformmassen |
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