EP0000765B1 - Process for the preparation of granular oxymethylene polymers having improved mechanical properties - Google Patents

Description

The production of oxymethylene polymers (POM) by copolymerization of formaldehyde or cyclic oligomers of formaldehyde, in particular 1,3,5-trioxane, with suitable comonomers, in particular cyclic ethers or cyclic acetals, is known (cf., for example, US Pat. Nos. 30 27 352 and 38 03 094). It is also known that granular oxymethylene polymers are obtained if a solution of oxymethylene polymers is introduced into a precipitant whose temperature is just below the sintering temperature of the oxymethylene polymer (cf. US Pat. No. 3,371,066).

It is also known to produce granular oxymethylene polymers which, in addition to oxymethylene units, contain 0.1 to 20 percent by weight of oxyalkylene units with 2 to 8 adjacent carbon atoms in the main chain, in that a 3 to 35 percent by weight solution or a fine dispersion of an oxymethylene polymer in a methanol / water Mixture with a methanol content of at least 75 percent by weight, the temperature of which is 5 to 65 ° C above the sintering temperature of the oxymethylene polymer, in a methanol / water mixture serving as a coolant with a methanol content of at least 75 percent by weight, which is in turbulent motion and at a temperature of 1 to 10 ° C below the sintering temperature of the oxymethylene polymer is initiated, the amount of the precipitated oxymethylene polymer in the resulting suspension is at most 25 percent by weight, and the granular oxymethylene polymer obtained is then separated off and dried (cf. German he publication 25 08 886).

The present invention now relates to a further embodiment of the latter method and is characterized in that the granular oxymethylene polymer particles obtained by precipitation with a grain diameter of more than 70 μm are separated off and dried. The invention further relates to granular oxymethylene polymers which are produced by the aforementioned process.

A process for the production of granular oxymethylene polymers was likewise already known from German laid-open documents 2 504 482 and 2 509 924. However, the process is cooled in two stages, namely first from 5 to 65 ° C. above the sintering temperature of the polymer to 0 to 10 ° C. above the sintering temperature and then to 1 to 10 ° C. below the sintering temperature. In addition, there is no separation of the particle _fraction with a particle size above 70 _μm . It was not to be expected that due to the separation according to the invention and the use of only the coarse grain fraction with particle diameters of more than 70 in order to increase the impact strength and that this effect would be so pronounced (cf. the table below with the therein included comparison values).

Oxymethylene polymers in the context of the invention are understood to mean poly (oxymethylenes) which, in addition to oxymethylene units, also have 0.1 to 20, preferably 0.5 to 10 percent by weight oxyalkylene units with 2 to 8, preferably 2, 3 or 4 adjacent carbon atoms in the main valence chain; Oxymethylene polymers whose proportion of oxyalkylene units is 0.7 to 5 percent by weight are particularly suitable.

The oxymethylene polymers are prepared in a known manner by polymerizing the monomers in bulk, suspension or solution in the presence of cationically active catalysts, e.g. at a temperature of 0 to 100 ° C, preferably 50 to 90 ° C (see e.g. U.S. Patent 30 20 352). Here, as cationically active catalysts (1) protonic acids, e.g. Perchloric acid, (2) esters of protonic acids, especially esters of perchloric acid with lower aliphatic alcohols, e.g. Perchloric acid tert. butyl ester, (3) anhydrides of protonic acids, especially mixed anhydrides of perchloric acid and a lower aliphatic carboxylic acid, e.g. Acetyl perchlorate, (4) Lewis acids, especially halides of boron, tin, titanium, phosphorus, arsenic and antimony, e.g. Boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride and antimony pentafluoride and (5) complex compounds or salt-like compounds of Lewis acids, preferably etherates or onium salts, e.g. Boron trifluoride diethyl etherate, boron trifluoride di-n-butyl etherate, triethyloxonium tetrafluoroborate, trimethyloxonium hexafluorophosphate, triphenylhexafluoroarsenate, acetyltetrafluoroborate, acetylhexafluorophosphate and acetylhexafluoro used,.

The amount of the catalysts used in the copolymerization depends primarily on the strength of their effectiveness; in general, the catalysts are used in an amount by weight of 0.1 to 2000, preferably 0.2 to 500 ppm, based on the total amount of the compounds to be polymerized. Highly effective catalysts such as boron trifluoride are advantageously used in an amount by weight of 10 to 150, preferably 20 to 100 ppm, based on the total amount of the compounds to be polymerized. The corresponding molar amounts apply to complex compounds or salt-like compounds of the catalysts mentioned. Very powerful catalysts such as perchloric acid are used in an amount of 0.2 to 10 ppm, preferably 0.3 to 5 ppm.

In general, it is advisable to use the catalysts in dilute form. Gaseous catalysts are diluted with an inert gas, for example nitrogen or a noble gas such as argon, while liquid or solid catalysts are dissolved in an inert solvent. As a solution In particular, aliphatic or cycloaliphatic hydrocarbons and nitrated aliphatic or aromatic hydrocarbons are suitable. Examples include: cyclohexane, methylene chloride, ethylene chloride, nitromethane and nitrobenzene. The weight ratio of catalyst to diluent is usually 1: 5 to 1: 10000, preferably 1:10 to 1: 100. Very potent catalysts are advantageously diluted in a ratio of 1: 5,000 to 1:20,000.

The polymerization process is preferably carried out under an inert gas atmosphere and in the absence of moisture; inert gases are preferably inert gases, e.g. Argon, and nitrogen suitable.

Suitable compounds which are copolymerizable with trioxane are, in particular, a) cyclic ethers with 3, 4 or 5 ring members, preferably epoxides, b) cyclic acetals, preferably formals, with 5 to 11, preferably 5, 6, 7 or 8 ring members and c) linear polyacetals, preferably polyformals.

geeignet, in der (A) R' und R² gleich oder verschieden sind und jeweils ein Wasserstoffatomen, einen aliphatischen Alkylrest mit 1 bis 6, vorzugsweise 1, 2, 3 oder 4 Kohlenstoffatomen oder einen Phenylrest bedeuten und a) x gleich 1, 2 oder 3 und y gleich Null ist oder b) x gleich Null, y gleich 1,2 oder 3 und z gleich 2 ist oder c) x gleich Null, y gleich 1 und z gleich 3, 4, 5 oder 6 ist, oder (B) R' einen Alkyloxymethylrest mit 2 bis 6, vorzugsweise 2, 3 oder 4 Kohlenstoffatomen oder einen Phenoxymethylrest bedeutet, wobei x gleich 1 und y gleich Null ist und R² die obengenannte Bedeutung hat.Compounds of the formula in particular are suitable as comonomers for trioxane

suitable in which (A) R 'and R ^{2 are} identical or different and each represent a hydrogen atom, an aliphatic alkyl radical having 1 to 6, preferably 1, 2, 3 or 4 carbon atoms or a phenyl radical and a) x is 1, 2 or 3 and y is zero or b) x is zero, y is 1,2 or 3 and z is 2 or c) x is zero, y is 1 and z is 3, 4, 5 or 6, or ( B) R 'is an alkyloxymethyl radical having 2 to 6, preferably 2, 3 or 4, carbon atoms or a phenoxymethyl radical, where x is 1 and y is zero and R ^{2 is} as defined above.

As cyclic ethers e.g. Ethylene oxide, propylene oxide, styrene oxide, cyclohexene oxide, oxacyclobutane and phenylglycidyl ether are used, while 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane and 1,3,6-trioxocane and 4-methyl-1, 3-dioxolane, 4-phenyl-1,3-dioxolane, 1,3-dioxonane and 1,3-dioxacycloheptene (5) can be used. Poly (1,3-dioxolane) and poly (1,3-dioxepane) are particularly suitable as linear polyformals.

For the production of oxymethylene polymers with certain molecular weight ranges, it is expedient to carry out the polymerization in the presence of a regulator. Formaldehyde dialkyl acetals having 3 to 9, preferably 3, 4 or 5 carbon atoms, e.g. Formaldehyde dimethyl acetal, diethyl acetal, dipropylacetal and di-butyl acetal, as well as lower aliphatic alcohols, preferably alkanols with 1 to 4 carbon atoms, e.g. Methanol, ethanol, propanol and butanol. The regulator is usually used in an amount of up to 0.5 percent by weight, preferably from 0.005 to 0.1 percent by weight, based on the total amount of the compounds to be polymerized.

The oxymethylene polymers are expediently subjected to a thermal, controlled, partial degradation down to primary alcohol end groups in order to remove unstable fractions (cf. US Pat. Nos. 31,74948, 32,19623 and 36,66,714). The thermal treatment is carried out at a temperature of 130 to 200 ° C, preferably 140 to 190 ° C, especially under non-acidic conditions in aqueous / methanolic solution, advantageously in the manner of a basic reacting compound, e.g. a lower tertiary aliphatic amine such as triethyl or triethanolamine or a secondary alkali phosphate such as disodium hydrogen phosphate. A temperature of 150 to 180 ° C is particularly favorable. The duration of the thermal treatment is 10 seconds to 2 hours, preferably 1 minute to 60 minutes, depending on the temperature. The higher the temperature, the shorter the residence time can be measured. At 180 ° C approximately 1 to 2 minutes are sufficient, at 160 ° C approximately 5 to 10 minutes, at 150 ° C approximately 10 to 30 minutes and at 140 ° C approximately 20 to 60 minutes. The treatment is preferably carried out with the substantial exclusion of oxygen.

A solution or a dispersion of an oxymethylene polymer, the polymer content of which is 3 to 35, preferably 5 to 30, percent by weight is used as the starting material for the process according to the invention. Very good results are obtained with a polymer solution or dispersion which contains 10 to 20 percent by weight of oxymethylene polymers.

A methanol / water mixture with a methanol content of at least 75 percent by weight is used as the solvent or dispersant; preferably a mixture is used which consists of 99.9 to 80 percent by weight of methanol and 0.1 to 20 percent by weight of water. A mixture of 99.5 to 85 percent by weight of methanol and 0.5 to 15 percent by weight of water is particularly advantageous, the best results being obtained with a mixture of 99 to 90 percent by weight of methanol and 1 to 10 percent by weight of water.

The temperature of the solution or dispersion is 5 to 65 ° C., preferably 10 to 60 ° C. above the sintering temperature of the oxymethylene polymer, the temperature range from 25 to 55 ° C. above the sintering temperature being particularly advantageous.

A mixture of methanol and water, the composition of which is in the same range as that of the aforementioned solution or dispersion, also serves as the coolant and precipitant by means of. The coolant has a temperature of 1 to 10 ° C, preferably 1 to 5 ° C, in particular 2 to 4 ° C below the sintering temperature of the oxymethylene polymer. The amount of the precipitated oxymethylene polymer in the suspension resulting from the introduction of the polymer solution or dispersion is at most 25, preferably 5 to 15 percent by weight.

The methanol used in the context of this invention may contain up to 30, preferably up to 10 percent by weight of methanol-soluble organic impurities which are usually formed as by-products in the synthesis of oxymethylene polymers, e.g. Formaldehyde, cyclic oligomers of formaldehyde, methylal, glycol, glycol formal, glycol monomethyl ether, glycol dimethyl ether and lower aliphatic alcohols, lower aliphatic esters and acetone.

The sintering temperature (T _s ) is the temperature at which the solid polymer particles suspended in the methanol / water mixtures soften and adhere to the surface without completely melting. The sintering temperature depends on the composition and molecular weight of the polymer and also on the type of solvent or dispersant. The sintering temperature of the oxymethylene polymers used according to the invention is in the range from 100 to 140 ° C., in particular from 125 to 135 ° C.

The process according to the invention is carried out, for example, in an autoclave provided with a stirrer. The coolant and precipitant are placed in this autoclave, and the solution or dispersion of the oxymethylene polymer is expediently introduced into the precipitant through a heated immersion tube or a nozzle, the latter being kept in turbulent motion by stirring. The process can be carried out batchwise or continuously; in the case of continuous operation, the polymer suspension obtained is removed at the bottom of the autoclave to the extent that the solution or dispersion and, if appropriate, additional precipitant are added. The average residence time of the oxymethylene polymer in the precipitation vessel is 1 minute to 12 hours, preferably 2 to 120 minutes. Depending on the temperature used in the individual case, the pressure is 5 to 40, preferably 8 to 30 bar.

When the POM solution or dispersion is cooled, solid polymer particles with different grain sizes are formed by precipitation or agglomeration. The majority of the POM particles obtained consist of granular particles with a grain diameter of more than 70 μm, while a small amount consists of fine-grain particles with a grain diameter of preferably less than 50 μm (sieve analysis). The granular particles preferably have grain diameters of 100 to 1000 μm and in particular of 150 to 400 μm. The amount of fine-grained product to be separated off is generally less than 20 percent by weight, based on the total amount of solid polymer particles; the fine grain fraction is preferably less than 15 and in particular 3 to 10 percent by weight.

From the suspension obtained by the cooling, which is optionally further cooled to a temperature below 100 ° C, preferably to 20 to 60 ° C, the POM particles with a particle diameter of above 70 are separated by conventional separation processes, e.g. by filtration, centrifugation or decanting. From the remaining mixture, the POM particles with a particle diameter of less than 70 µm can be removed by means of a separator, and the solvent can be reused as a liquid coolant. The separated oxymethylene polymer is finally dried at a temperature of 20 to 135 ° C, preferably 50 to 120 ° C. Drying under an inert gas atmosphere, e.g. in an inert gas or nitrogen atmosphere is recommended.

It is also possible to separate the total amount of solid polymer particles from the liquid and to carry out the separation according to particle size during or after drying, e.g. through wind sightings or sieving.

The granular oxymethylene polymers obtained according to the invention are macromolecular; the values of their reduced specific viscosity (RSV) are 0.3 to 2.0, preferably 0.5 to 1.5 dl / g (measured on a 0.5 percent by weight solution of the polymer in y-butyrolactone which contains 2 percent by weight diphenylamine Stabilizer contains, at a temperature of 140 ° C). The crystallite melting points of the oxymethylene polymers are in the range from 140 to 180 ° C, their melt index values (MFI 190/2) are 0.1 to 50, preferably 1 to 30 g / 10 min (measured according to DIN 53 735 at a temperature of 190 ° C and a load of 2.16 kg). The bulk density of the granular oxymethylene polymers obtained according to the invention is generally more than 300, preferably 350 to 550 g / l (determined on the polymer dried under nitrogen at a temperature of 70 ° C. after two minutes of homogeneous mixing in a laboratory fluid mixer at a speed of 3000 rpm). The RSV values of the separated fine-grained products are below 0.3 dl / g and are preferably 0.05 to 0.25 and in particular 0.1 to 0.2 dl / g.

The oxymethylene copolymers obtained according to the invention can additionally be stabilized by homogeneously mixing them with stabilizers against the influence of heat, oxygen and / or light. The homogenization is usually carried out in a commercially available mixing device, e.g. an extruder, at a temperature above the melting point of the polymer up to 250 ° C, preferably at 180 to 210 ° C. The total amount of stabilizers added is 0.1 to 10, preferably 0.5 to 5 percent by weight, based on the total mixture.

Bisphenol compounds, alkaline earth metal salts of carboxylic acids, are particularly suitable as stabilizers as well as guanidine compounds. The bisphenol compounds used are mainly esters of mono- or di-core-substituted monobasic 4-hydroxyphenylalkanoic acids which contain 7 to 13, preferably 7.8 or 9, carbon atoms with aliphatic di-, tri- or tetravalent alcohols which have a 1- or 4-carbon atom-containing alkyl radical Containing 2 to 6, preferably 2, 3 or 4 carbon atoms, for example esters of w- (3-tert-butyl-4-hydroxy-phenyl) -pentanoic acid, β- (3 = methyl-5-tert-butyl -4-hydroxy-phenyl) propionic acid, (3,5-di-tert-butyl-4-hydroxyphenyl) acetic acid, β- (3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid or (3rd , 5-di-isopropyl-4-hydroxyphenyl) acetic acid with ethylene glycol, propanediol- (1,2), propanediol- (1,3), butanediol- (1,4), hexanediol- (1,6), 1, 1,1-trimethylolethane or pentaerythritol.

The alkaline earth metal salts of carboxylic acids used are, in particular, alkaline earth metal salts of aliphatic, preferably hydroxyl-containing, mono-, di- or tri-base carboxylic acids having 2 to 20, preferably 3 to 9 carbon atoms, e.g. the calcium or magnesium salts of stearic acid, ricinoleic acid, lactic acid, mandelic acid, malic acid or citric acid.

verwendet, in der R ein Wasserstoffatom, eine Cyanogruppe oder einen Alkylrest mit 1 bis 6 Kohlenstoffatomen bedeutet, z.B. Cyanoguanidin, N-Cyano-N'-methyl-guanidin, N-Cyano-N'-äthyl-guanidin, N-Cyano-N'-iso-propylguanidin, N-Cyano-N'-tert.-butyl-guanidin oder N,N'-Dicyanoguanidin. Die Guanidinverbindung wird gegebenenfalls in einer Menge von 0,01 bis 1, vorzugsweise 0,02 bis 0,5 Gewichtsprozent, bezogen auf das Gesamtgemisch, eingesetzt.Compounds of the formula are used as guanidine compounds

used, in which R represents a hydrogen atom, a cyano group or an alkyl radical having 1 to 6 carbon atoms, for example cyanoguanidine, N-cyano-N'-methyl-guanidine, N-cyano-N'-ethyl-guanidine, N-cyano-N '-iso-propylguanidine, N-cyano-N'-tert-butyl-guanidine or N, N'-dicyanoguanidine. The guanidine compound is optionally used in an amount of 0.01 to 1, preferably 0.02 to 0.5 percent by weight, based on the total mixture.

Known light stabilizers such as benzophenone, acetophenone or triazine derivatives can also be added to the oxymethylene polymers prepared according to the invention. Other conventional additives such as dyes, pigments, reinforcing and filling agents or nucleating agents can also be added.

The oxymethylene polymers obtained according to the invention are characterized in that they have improved mechanical properties, in particular toughness properties, compared to known oxymethylene polymers. They can be processed by all the usual methods for thermoplastics, e.g. by injection molding, extrusion, extrusion blow molding, melt spinning and deep drawing. They are suitable as a material for the production of semi-finished and finished parts such as moldings, e.g. Ingots, rods, plates, tapes, bristles, threads, fibers, films, foils, pipes and hoses, as well as household items, e.g. Bowls and cups, and machine parts, e.g. Housings and gears. They can be used primarily as a technical material for the manufacture of dimensionally stable and dimensionally stable molded parts.

The following examples illustrate the invention. Here, "%" means "weight percent" and "parts" each means "parts by weight".

Examples 1 to 9

Different parts of a copolymer of 98% trioxane and 2% ethylene oxide with an RSV of 0.76 or 0.81 dl / g and an MFI (190/2) of 9 or 7 g / 10 min are mixed with 100 parts under nitrogen a methanol / water mixture containing 500 ppm triethylamine. The resulting mixture is heated to a temperature of 170 ° C. for 5 minutes, during which the polymer goes into solution.

This solution is introduced within 30 min through an immersion tube into 30 parts of a methanol / water mixture of the same composition, which is in a turbulent movement in an autoclave and has a temperature of 125 ° C. (Example 2: 129 ° C.). At a sintering temperature of the polymer of 127 ° C (Example 2: 131 ° C), the temperature of the precipitant is 2 ° C below the sintering temperature. After a further 10 min, the suspension obtained is cooled to room temperature.

Half of the suspension is passed through a fine-pored filter, which allows quantitative separation of the solids content (polymer A). The remaining second half of the suspension is separated by centrifugation with the aid of a sieve centrifuge (sieve width 70 μm) into solids with a particle diameter above 70 μm (polymer B) and smaller (polymer C, in filtrate). The finely divided polymer C is then removed from the centrifugate using a separator.

Products A and B are dried at 70 ° C under nitrogen. The bulk weights and RSV values are then determined on the dried products. Part of the products are then mixed with stabilizers (0.1% dicyandiamide; 0.5% bis (2-hydroxy-3-tert.butyl-5-methylphenyl) methane) and processed into test specimens by injection molding.

The impact behavior is tested in accordance with DIN 53 443 in a dart bolt test. For this, square plates with an edge length of 60 mm and a thickness of 2 mm as well as a drop bolt with a weight of 100 g are used; the ring opening of the contact surface is - in deviation from the norm - 25 mm. The determined head is a measure of the toughness of the material.

Further details and results are shown in the following table.

Claims (2)

1. Process for the preparation of a granular oxymethylene polymer containing besides oxymethylene units from 0.1 to 20% by weight of oxyalkylene units having from 2 to 8 adjacent carbon atoms in the main chain, by introducing a 3 to 35% by weight solution or dispersion of the oxymethylene polymer in a methanol/water mixture having a methanol content of at least 75% by weight, the temperature of which solution or dispersion being from 5 to 65°C above the sintering temperature of the oxymethylene polymer, into a methanol/water mixture having a methanol content of at least 75% by weight which is kept in turbulent motion and at a temperature of from 1 to 10°C below the sintering temperature of the oxymethylene polymer, and precipitating the oxymethylene polymer, in which process the amount of the precipitated oxymethylene polymer in the suspension formed is at most 25% by weight, and by subsequently separating and drying the granular oxymethylene polymer obtained, which comprises separating and drying those oxymethylene polymer particles which show a grain diameter of more than 70 µm.

2. Process as claimed in claim 1, wherein the separated and dried particles show a grain diameter of from 100 to 1,000 µm.