DE102005054877A1 - Process for the preparation of a polyoxymethylene homo- or copolymer end product - Google Patents

Abstract

A process for the production of a polyoxymethylene homo- or copolymer end product of a crude polyoxymethylene homo- or copolymer melt by DOLLAR A a) addition and incorporation of additives, DOLLAR A b) degradation of unstable chain ends and DOLLAR A c) degassing for removal of volatile components, proposed, DOLLAR A, which is characterized in that only a partial flow of a maximum of 10 wt .-% of the raw polyoxymethylene homo- or copolymer melt or a corresponding mass flow of the melt of a specified or poor quality polyoxymethylene homo- or copolymer end product passed through a side extruder for the purpose of carrying out process step a) while obtaining an additive side stream and the process is otherwise carried out without the use of an extruder.

Description

The The invention relates to a process for the preparation of a polyoxymethylene homo- or copolymer (hereinafter abbreviated as POM) final product from a crude POM melt, as well as POM end products, available after the said method.

POM, Also called polyacetals by homo- or copolymerization 1,3,5-trioxane (trioxane for short), formaldehyde or another formaldehyde source receive. The conversion is usually not completely, rather contains the crude POM still up to 40% unreacted monomers. Such Residual monomers are, for example, trioxane and formaldehyde, as well optionally used comonomers such as 1,3-dioxolane, 1,3-butanediol formal or Ethylene oxide.

Around from the raw POM a salable POM end product to receive added various additives, broken down unstable chain ends and volatile components, in particular the ones mentioned above Residual monomers are separated by degassing, extraction or the like. For example, by a downstream deodorization, the is called Storage opposite Ambient temperature increased Temperature of the residual content of monomers are further lowered. As a POM end product In the present case, it will be a specification-compliant, salable product understood that contains additives and their residual monomer content to a low value of less than 500 ppm or less than 50 ppm was depleted. The determination Of the residual content of the monomer formaldehyde is usually about the Sulphite. In the "sulfite method" is POM granules into a jar of water weighed and the water for boiled for several minutes. Subsequently, the solution by means of Caustic soda and sulfuric acid slightly alkaline (pH 9.4). After addition of sodium sulfite solution and short reaction time is back titrated with sulfuric acid. The consumption of sulfuric acid serves as a measure of the residual content of formaldehyde in the granules.

For the above Work-up of crude POM to a POM end product are by known methods Extruders are used, their many functions being: mixing, Shearing, heating, degassing and conveying, be used.

Although individual steps in the refurbishment of raw POM to POM end product, such as in the process of DE 10 2005 012 480.1 or DE 10 2005 002 413.0 , are carried out in static apparatus, however, the cost and maintenance-intensive extruder are always used in overall processes according to the prior art.

It was in contrast Object of the invention, a process for the processing of crude POM too POM end product available to provide that does not have the disadvantages of the prior art.

• a) Zugabe und Einarbeitung von Additiven,
• b) Abbau von instabilen Kettenenden und
• c) Entgasung zum Entfernen von flüchtigen Komponenten,

das dadurch gekennzeichnet ist, dass lediglich ein Teilstrom von maximal 10 Gew.-% der Roh-Polyoxymethylenhomo- oder Copolymer-Schmelze oder ein entsprechender Massenstrom der Schmelze eines spezifikationsgerechten oder qualitativ minderwertigen Polyoxymethylenhomo- oder Copolymer-Endproduktes über einen Seitenextruder zwecks Durchführung des Verfahrensschrittes a) unter Erhalt eines additivierten Seitenstromes geleitet und das Verfahren im Übrigen ohne Einsatz eines Extruders durchgeführt wird.The solution is a process for producing a final polyoxymethylene homo- or copolymer product from a crude polyoxymethylene homo- or copolymer melt

• a) addition and incorporation of additives,
• b) Degradation of unstable chain ends and
• c) degassing to remove volatile components,

which is characterized in that only a partial stream of at most 10 wt .-% of the crude polyoxymethylene homo- or copolymer melt or a corresponding mass flow of the melt of a specification or quality inferior polyoxymethylene homo- or copolymer end product via a page extruder for the purpose of performing the process step a ) is passed to obtain an additive Seitenstromes and the process is otherwise carried out without the use of an extruder.

It was found to be possible is, the individual process steps of known methods for processing of raw POM without using an extruder. It is only necessary, a partial flow of up to 10 wt .-% the crude POM melt or a corresponding mass flow of the melt of a specification-compliant or poor quality POM end product through a side extruder Addition of additives to obtain an additive sidestream to lead.

The Process variant in which a poor quality POM end product is used for the addition or mixing of additives is particularly advantageous because this non-salable product is recycled.

in this connection is referred to as a poor quality POM end product, although from raw POM by the above steps of the addition of additives, Degradation of unstable chain ends and degassing to remove volatile But subject to the specification requirements given above for a salable POM end product does not match.

The polyoxymethylene homopolymers or copolymers (POM) are known as such. The homopolymers are prepared by polymerization of formaldehyde or, preferably, trioxane; in the preparation of the copolymers are also Como co-used nomere.

enthalten, wobei R¹ bis R⁴ unabhängig voneinander ein Wasserstoffatom, eine C₁- bis C₄-Alkylgruppe oder eine halogensubstituierte Alkylgruppe mit 1 bis 4 Atomen und R⁵ eine -CH₂-, -CH₂O-, eine C₁- bis C₄-Alkyl- oder C₁- bis C₄-Haloalkyl substituierte Methylengruppe oder eine entsprechende Oxymethylengruppe darstellen und n einen Wert im Bereich von 0 bis 3 hat. Vorteilhafterweise können diese Gruppen durch Ringöffnung von cyclischen Ethern in die Copolymere eingeführt werden. Bevorzugte cyclische Ether sind solche der Formel

wobei R¹ bis R⁵ und n die oben genannte Bedeutung haben. Nur beispielsweise seien Ethylenoxid, 1,2-Propylenoxid, 1,2-Butylenoxid, 1,3-Butylenoxid, 1,3-Dioxan, 1,3-Dioxolan und 1,3-Dioxepan (= Butandiolformal, BUFO) als cyclische Ether sowie lineare Oligo- oder Polyformale wie Polydioxolan oder Polydioxepan als Comonomere genannt.In general, such POM polymers have at least 50 mole percent of recurring units -CH ₂ O- in the polymer backbone. Polyoxymethylene copolymers are preferred, in particular those which, in addition to the repeating units -CH ₂ O-, have up to 50, preferably 0.01 to 20, in particular 0.1 to 10 mol% and very particularly preferably 0.5 to 6 mol%. at recurring units

in which 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 atoms and R ^{5 is} a -CH ₂ -, -CH ₂ O-, a C ₁ - 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. Advantageously, these groups can be introduced into the copolymers by ring opening of cyclic ethers. Preferred cyclic ethers are those of the formula

wherein R ¹ to R ⁵ and n have the abovementioned meaning. For example, only ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepane (= butanediol, BUFO) as cyclic ethers and linear oligo- or polyformals such as polydioxolane or polydioxepane called comonomers.

und/oder

wobei Z eine chemische Bindung, -O-, -ORO- (R C₁- bis C₈-Alkylen oder C₃- bis C₈-Cycloalkylen) ist, hergestellt werden.Also suitable are Oxymethylenterpolymerisate, for example, by reacting trioxane, one of the cyclic ethers described above with a third monomer, preferably bifunctional compounds of the formula

and or

wherein Z is a chemical bond, -O-, -ORO- (RC ₁ - to C ₈ -alkylene or C ₃ - to C ₈ -cycloalkylene) are prepared.

preferred Monomers of this type are ethylene diglycidyl, 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 Diols with 2 to 8 atoms such as the diglycidyl ethers of ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-dio, 1,2-propanediol and cyclohexane-1,4-diol, to name just a few examples to call.

End-group-stabilized polyoxymethylene polymers which have predominantly CC 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 _w in the range of 5,000 to 300,000, preferably 7,000 to 250,000 g / mol. Particular preference is given to POM copolymers having a nonuniformity (M _{w / 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) is generally determined by GPC / SEC.

The If appropriate, molecular weights of the polymer can be determined by customary in trioxane polymerization Regulator as well as by the reaction temperature and residence time the desired values are set. As regulators come acetals or Formal monohydric alcohols, the alcohols themselves as well as the Chain transfers acting small Quantities of water whose presence is usually never completely avoided leaves, in question. The regulators are used in quantities of 10 to 10,000 ppm, preferably from 20 to 5,000 ppm.

Initiators (also referred to as catalysts) are the cationic initiators customary in trioxane polymerization. Suitable are protic acids, such as fluorinated or chlorinated alkyl and arylsulfonic acids, for example perchloric acid, trifluoromethanesulfonic acid or Lewis acids, such as 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. The initiato (Catalysts) 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. In general, it is advisable to add the initiator in dilute form, preferably in concentrations of 0.005 to 5 wt .-%. As the solvent for this, inert compounds such as aliphatic, cycloaliphatic hydrocarbons, for example, cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. may be used. Particularly preferred is triglyme (triethylene glycol dimethyl ether) as the solvent and 1,4-dioxane or cyclic carbonates such as propylene carbonate or lactones such as γ-butyrolactone.

In addition to the initiators can Cocatalysts are used. These are alcohols of any kind Type, for example, aliphatic alcohols having 2 to 20 carbon atoms, such as t-Amyl alcohol, methanol, Ethanol, propanol, butanol, pentanol, hexanol; aromatic alcohols having 2 to 30 C atoms, such as hydroquinone; halogenated alcohols with 2 to 20 C atoms, such as hexafluoroisopropanol; very particularly preferred are glycols of any kind, especially diethylene glycol and triethylene glycol; and aliphatic dihydroxy compounds, in particular diols with 2 to 6 carbon atoms, such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol.

monomers Initiators, cocatalyst and optionally regulators can any way premixed or separated from each other the polymerization reactor be added.

Further can the components for stabilization contain hindered phenols as described in EP-A 1 293 69 or EP-A 1 287 39.

Preferably will be followed directly the polymerization mixture deactivates the polymerization mixture, preferably without a phase change takes place. The deactivation the initiator residues (catalyst residues) are usually carried out by Addition of deactivators (demulsifiers) to the polymerization melt. Suitable deactivators are, for example, ammonia and primary, secondary or tertiary, aliphatic and aromatic amines, for example trialkylamines such as Triethylamine, or triacetonediamine. Also suitable are basic-reacting Salts, such as soda and borax, continue to contain the carbonates and hydroxides the alkali and alkaline earth metals, as well as alcoholates such as Ethoxide. The deactivators are usually the polymers in amounts of preferably 0.01 ppmw (parts per million by weight) added up to 2 wt .-%. Furthermore, alkali or Erdalkalialkyle as Deactivators are preferred which have 2 to 30 C atoms in the alkyl radical. As particularly preferred metals Li, Mg and Na may be mentioned, where n-Buyllithium is particularly preferred.

The Interruption agents are usually in organic solvents dosed. At RT solid stopping agents, the dosage is carried out for example via side extruder in a POM melt.

POM from formaldehyde is in common Manner by polymerization in the gas phase, in solution, by precipitation polymerization or in mass (substance) to produce. POM from trioxane is used in the Usually obtained by bulk polymerization, to which any Reactors with high mixing effect can use. The reaction can be homogeneous, for example in a melt, or heterogeneous, for example, as polymerization to a solid or solid granules. Suitable are, for example, shell reactors, plowshare mixers, tubular reactors, List reactors, kneaders (for example Busskneter), extruder with example one or two screws, and stirred reactors, the reactors having static or dynamic mixers can.

at bulk polymerization, for example in an extruder, introduces Partial flow of molten polymer usually to such a mentioned melt seal to the gearbox, creating volatile components remain in the extruder. The above monomers are metered downstream into the Polymer melt present in the extruder, together or separately from the initiators (catalysts), at a preferred temperature the reaction mixture from 62 to 114 ° C. Also preferred are the Monomers (trioxane) dosed in the molten state, for example at 60 to 120 ° C.

The Melt polymerization usually takes place at 1.5 to 500 bar and 130 to 300 ° C, and the residence time of the polymerization mixture in the reactor is usually 0.1 to 20 minutes, preferably 0.4 to 5 minutes. Preferably, one leads the polymerization up to a conversion over 30%, for example 60 to 90%.

you receives in each case, a raw POM, as mentioned, considerable shares, for example contains up to 40% of unreacted residual monomers, in particular Trioxane and formaldehyde. It can also formaldehyde in the crude POM be present when only trioxane was used as the monomer, since it as a degradation product of trioxane and POM can arise. Besides, too other oligomers of formaldehyde are present, for example the tetramer Tetroxane.

Trioxane is preferably used as monomer for the preparation of the POM, which is why the withdrawn residual monomers also contain trioxane, except usually 0.5 to 10 wt.% Tetroxane and 0.1 to 75 wt.% Formaldehyde.

The raw POM obtained becomes common first Degassed, that is a first method step c) is carried out, subsequently Additives added and incorporated (process step a)), unstable Chain ends dismantled (step b)) and in another Process step c) degassing residual monomers.

Here, the first degassing c) one or more preferably be carried out in several stages, for example in the DE 10 2005 012 480 .1 described manner, according to which the crude POM melt is degassed at a pressure of 1 mbar to 9 bar and a temperature of 160 to 240 ° C in at least one degassing.

In a process step a) are conventional additives, that is additives and processing aids. Such additives are for Example lubricants or thickeners, colorants such as Pigments or dyes, flame retardants, antioxidants, stabilizers against exposure to light, formaldehyde scavengers, thermal stabilizers such as polyamides, nucleating agents, fibrous and powdery fillers or reinforcing agents or Antistatic agents, as well as other additives, or mixtures thereof.

The Addition of additives takes place according to the invention in a side extruder, by a partial flow of at most 10 wt .-% of the crude POM melt, preferably a maximum of 5 wt .-% of the same or a corresponding mass flow the melt of a specification-compliant or low-quality POM end product is initiated. For this must be the specification-appropriate or low-quality POM end product are first melted.

Of the obtained in Seitenextruder additivierten side stream is with the Stream of crude POM melt preferably mixed in a static mixer.

The Process steps b) (degradation of unstable chain ends) and c) (Degassing to remove volatile Components) are preferably used in separate static apparatuses carried out.

Prefers The degradation of unstable chain ends in at least one static Apparatus for the Entry of shearing tips and / or at least one heat exchanger for the Entry of heat energy carried out.

When Apparatus for the introduction of shearing tips can in particular one or several nozzle flaps and / or one or more static mixers are used.

The Process stage c), the degassing to remove volatile In particular, components can be used in flash pots, thin film evaporators, falling film evaporators or Strandentgasern carried out become.

At Process step c) may be followed by a deodorization step, which is called storage for several hours at a temperature above the ambient temperature, thereby further decreasing the monomer content allow.

The advancement the crude POM melt between the individual process steps can be carried out in particular by means of gear pumps.

The inventive method has the advantage of being a cost and maintenance intensive extruder for the Main flow of the raw POM melt is not required. It's just a much smaller side extruder, for a maximum mass flow 10 wt .-%, or even a maximum of 5 wt .-% of the main stream for the admixture of additives required.

The remaining process steps are carried out in static apparatuses, which are much lower Investment costs require and less prone to failure.

By doing the individual process steps in separate apparatuses carried out can, can these far better individually on the specific tasks be optimized over one Extruder, adding a variety of features-mixing, shearing, heating, degassing and Promote - at the same time Fulfills Need to become.

For example lie in the extruder with respect to Speed competing requirements: High speed for surface renewal and high degassing performance-low Speed to avoid excessive shear stress and unwanted product damage. In contrast, have the individual devices according to the invention much more degrees of freedom.

Furthermore is for the individual apparatuses the scale-up compared to the complex extruder much easier.

By doing the individual process steps each optimized separately can, can the quality the POM end product compared to conventional Procedure to be improved.

Claims (9)

A process for the preparation of a polyoxymethylene homo- or copolymer end product from a crude polyoxymethylene homo- or copolymer melt by a) addition and incorporation of additives, b) degradation of unstable chain ends and c) degassing to remove volatile components, characterized in that only a partial stream of not more than 10% by weight of the crude polyoxymethylene homo- or copolymer melt or a corresponding mass flow of the melt of a specification-compliant or low-quality polyoxymethylene homo- or copolymer end product via a side extruder for carrying out process step a) to obtain an additized side stream Otherwise, the process is carried out without the use of an extruder. Method according to claim 1, characterized in that that is the partial stream of the crude polyoxymethylene homo- or copolymer melt or the corresponding mass flow of the melt of a specification-compliant or low quality polyoxymethylene homo- or copolymer end product at most 5% by weight of the crude polyoxymethylene homo- or copolymer melt is. Method according to claim 1 or 2, characterized that the polyoxymethylene homo- or copolymer-end product to a Residual monomer content determined by the sulphite method, less than 500 ppm, preferably less than 50 ppm was depleted. Method according to one of claims 1 to 3, characterized that the additized side stream with the main stream of the crude polyoxymethylene homo- or copolymer melt is mixed in a static mixer. Method according to one of claims 1 to 4, characterized that the process steps b) and c) in each case separate static Apparatus performed become. Method according to one of claims 1 to 5, characterized that the method step b) in at least one static apparatus for the entry shearing tips and / or at least one heat exchanger for the entry of heat energy carried out becomes. Method according to one of claims 1 to 6, characterized that for the entry of shearing tips one or more nozzle flaps and / or one or multiple orifices and / or one or more static mixers used become. Method according to one of claims 1 to 7, characterized that the method step c) in one or more flash pots and / or one or more thin film evaporators and / or one or more polymeric falling film evaporators and / or a or more Strandentgasern is performed. Method according to one of claims 1 to 8, characterized that the raw polyoxymethylene homo- or copolymer melt by means of gear pumps promoted becomes.