DE1570379C3 - Process for the thermal stabilization of oxymethylene copolymers - Google Patents

Description

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Salts of a strong base and a weak acid are added and the suspension is replaced by an ammonia or amine or amidines. Exchangers conducted in the form of a double pipe, in which cial examples of suitable alkaline agents are a temperature between 110 and 180 ° C, ammonium hydroxide, sodium hydroxide, potassium range and a pressure of up to 7 atmospheres. Unhydroxide, sodium carbonate, sodium acetate, hexa- 5 ter these conditions dissolve the polymer. The min and tributylamine. The amount of residence time present in the heat exchanger is 30 to 160 alkaline agent can be 0.001 to 10.0 weight seconds. In a mixing zone, water will be added, but is preferably between sets, whereby the temperature is between 30 and 95 ° C -0.001 and 1.0 percent by weight. If no basic subsides and the copolymer is precipitated.
With the process of the invention, oxymelion can be found in a buffered system to let ethylene copolymers be obtained, the average of which, since some of the hydrolysis products are acidic, has a very decisive bulk density System were pissed off. is improved over oxymethylene copolymers, the

In general, the reagent liquid cannot be subjected to this special procedure.

Quantities between 1 and 50 kg / kg of copolymer are used. So has a treated according to the invention

but it is preferably used in an oxymethylene copolymer, e.g. B. a bulk density

Amount of 3 to 20 kg per kg of copolymer of 400 g / liter, while one according to the method

needs. the Belgian patent specification 602 869 stabilized po-

The duration of the stabilization treatment can only have a bulk density of 176 g / liter per lymeres, ie

according to the temperature and the desired stability, it is not even half that. Because of the high

degree of efficiency, for example 15 seconds to 1 hour, weight per unit volume have the invention

wear, with a treatment time of 1 to 2 mi according to stabilized oxymethylene copolymers under

grooves is preferred. among other things, the great advantage that they have over the

The treatment is generally carried out as long as previously known products not only the storage

taken until the speed of weighting but also drying eases at the same time.

loss to a value between 0.1 and 5% of the learners.

Weight Loss Rate Before Stabilization In the following examples, all parts are gelation has fallen, taking as the speed of the most important parts.

Weight loss is the weight loss per minute. . .
applies if the copolymer is in an open vessel, 30 ^a ) Preparation of the starting polymer.sats
which is placed in an oven with air circulation, a mixture of 99.5 parts trioxane, 2.0 parts is kept at 230 ° C. The ethylene oxide is in this phase and 2.5 parts of cyclohexane are usually at 0.0053 ppm (based on the mixture) at a rate of weight loss below 0.1 percent by weight per minute, from which boron trifluoride is recognizable as a di-n-butyl etherate complex that at least 95% of the molecules of the 35 elongated continuous mixer copolymer are supplied with relatively stable units at one end. The temperature contained in Mi-CC bonds as end groups. scher rose to a maximum of 75 bis on the exit side

After the stabilization treatment, the 85 ° C. The formed copolymer was in a

common chemical stabilizers against heat dissipation - methanol-water solution (weight ratio 60:40)

construction, e.g. B. a bisphenol as an antioxidant and a 4 ° quenched, washed with acetone and dried.

Nitrogen compound that helps prevent Ket- _R. .

contributes to cleavage, added to the copolymer e 1 s ρ 1 e

to improve its suitability as a molding compound. A reagent liquid was made by mixing

sern. 70 parts of trioxane, 30 parts of water and 0.05 part

The temperature of the treatment must be above 45 len ammonia. A mixture of 70 parts

the dissolution temperature of the copolymer in the len of this liquid and 30 parts of the under a)

Reagent liquid lie and is generally produced polymer was in a closed-

100 to 250 ° C. At higher temperatures, heated quickly to 160 ° C in a shaking autoclave. the

Within this range the treatment under autoclave was then from the shaker

made a pressure at which the solution is taken in ⁵ ° and its contents by immersion in a

the liquid phase remains. A temperature water bath is preferably cooled quickly to room temperature,

temperature range between 150 and 185 ° C. The precipitated copolymer was removed from the car

In an advantageous way of working, the raw klav can be removed, twice with water and once

Copolymerization product with a liquid washed off with acetone and dried. The dried

quenching, which was found for the stabilizing copolymers, was then carried out in the usual manner

treatment is suitable. For example, a copoly- 7 minutes at 210 ° C with 0.5 percent by weight

merization product, which at a temperature between 2,2'-methylene-bis (4-methyI-6-t-butylphenol) and 0.1

see 60 and 116 ° C from the polymerization zone weight percent cyanguanidine (based on the

is withdrawn, mixed with 5 to 50 times its weight of the copolymer),

weight of a water-trioxane mixture, which is 50 to ^6o The average speed of thermal dissipation

70 percent by weight consists of trioxane, the degradation of the stabilized copolymer was 0.008

be frightened. The mixture of Copolymerisa- weight percent / min. If the polymer in one

The product and the liquid are ground wet in order to

to crush the larger particles of the polymer. was held at 230 ° C.

The suspension, which is 2 to 20 percent by weight of solid ⁶ 5 """i" _m ";" _tr

contains substances, is suitable for the hydrolytic sta- ^b ) production of the starting polymer.sats

bilization. Ammonia in the amount of 10 to A mixture of 97 parts of trioxane, 2 parts

1000 parts per million parts by weight of the polymer ethylene oxide, 1 part cyclohexane, 0.006 parts Me-

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thylal and 0.0085 parts of boron trifluoride as dibutyl- the pressure rose to 14 atmospheres. After the temperature

etherate was an elongated, continuously reached 185 'C, the mixture was through

working mixer fed at one end. The one heated line in a separation vessel

Residence time in the mixer was about 3 minutes. That led to an equal volume of water from

copolymers formed were quenched to contain room temperature. The precipitated polymer

wash and dry. was filtered off, washed four times with water and

. -It b ^c '145' C under nitrogen in a heat-

Example 2 cupboard dried to constant weight.

After the usual stabilization with 2,2'-methylene

A mixture of 10 parts of the bis (4-methyl-6-t-butylphynol) and cyanguanidine produced under b)

ten copolymers, 90 parts of a trioxane-water in the manner described in Example 1 had the

Solution (weight ratio 50:50) and 0, I ⁰ Ai Am polymers an average speed of the thermal

given moniak. The mixture was within mix degradation of 0.012 weight percent per

Heated to 180 to 185 ° C for 40 to 50 minutes, with minute.

Claims (1)

1 2 Product obtained during deformation under one patent claim: effect of heat and pressure a higher thermal Stability than the original copoly- Method of thermal stabilization of kidney. In the description of this process it is stated that oxymethylene 5 is solid under normal conditions that it is preferable to treat the copolymers in solution with copolymers which are essentially in their chain. The specifically described job search for oxymethylene units in addition to oxyalkylene consists in heating the copolymer with units with adjacent carbon atoms in a liquid in which it dissolves only at elevated temperatures, by heating the copolymers at low temperatures, so that the solid copolymer is not acidic aqueous medium in which, after stabilization, up to 50% of the water can be separated off simply by cooling. The stabilization process of niche compounds with one or more can also very satisfactorily be replaced on the solid, fine-hydroxyl groups, ethers, ketones or ester-part copolymers with saving of heat, the heating to Tem- ""<-! takes place without the need to comminute the temperature, at which the copolymers 15 stabilized copolymers are dissolved in the fine form, characterized, for example, according to the German method that with an aqueous medium, which 50 to Auslegeschrift 1 495 382 are carried out, where- Contains 99 percent by weight of trioxane, worked with a reagent liquid that contains trioxane, e.g. B. _w j _{r (} j a liquid that contains 5 to 60%, preferably less 20 less than 40 percent by weight, contains trioxane, use will be. The invention relates to a method for the thermal stabilization of under normal conditions Oxymethylene homopolymers, d. H. Polymers containing solid oxymethylene copolymers used in consist of chains of -CH2 · O units, the 25 of their chain being essentially oxymethylene units free or etherified or esterified terminal next to oxyalkylene units with adjacent carbon Contain hydroxyl groups, can contain polymer atoms by heating the copoly- ization of anhydrous formaldehyde or trimers in a non-acidic aqueous medium, in oxane. These polymers can optionally be added to water up to 50% by organic in the form of solids that have sufficient compounds with one or more hy- Have adequate thermal stability in order to be replaced as press hydroxyl groups, ethers, ketones or esters sen to be used, however, they have been subject to heating to temperatures inherently a certain thermal instability occurs, in which the copolymers are dissolved, which usually leads to damage to the molded parts which is characterized in that with a water- and a very careful control of the pressed medium, which contains 50 to 99 percent by weight of tri- conditions required. contains oxane, is being worked on. Oxymethylene copolymers in which the length of the The advantage of this process is that in the Polymer chain of oxymethylene groups other carrying out stabilization with the dissolved Copolymers of aqueous trioxane are very effective for groups with adjacent carbon atoms are divided and which is hereinafter referred to as copolymers 4 ° reagent liquid. The one in the overall procedure must be subscribed to have a much higher ther- apy of recovery measures Mix stability than the homopolymers, whose Ket- simplifies, since unused trioxane from the crude th polymer must be recovered exclusively from oxymethylene units and its hen. However, these copolymers show during use as a component of the reagent liquid A slight thermal instability, so 45 therefore the recovery of an additional sub- that there is a risk that the pressed parts damage, punch makes superfluous. Furthermore, this can be omitted in particular surface defects as a result of the co- such a reagent liquid deposited show formation of gaseous decomposition products. polymers extremely easy to handle. It has now been found that this slight thermal stabilization takes place by hydrolysis. Instability from the tendency of these copolymers to 5 ° The water can, however, up to 50% through an or- stirs, terminal oxyme- ganic compound are replaced by the polymer chains, the one or to lose ethylene units, this ver containing several hydroxyl groups that remove the lust continues until a unit with adjacent cohesion of terminal oxymethylene groups from is reached. In this phase, polymers obtained through alcoholysis effect. Likewise can the copolymers have a remarkably high thermal 55 the dissolving effect of the liquid on the copolymers Stability. This fact has been exploited, copolymers by the presence of one or more copolymers to produce mers which, under heat and pressure, change into ethers, ketones or esters in the liquid. improved molded parts can be processed that are changed. These connections can be up to by replacing the copolymer of a previous degradation- 50% of the water that is otherwise used action to remove terminal oxymethylene ^6o would. groups is subjected. One possibility for the hydrolytic implementation of this previous degradation is the stabilization under non-acidic, in particular under Belgian patent specification 602 869. They are subjected to alkaline conditions. An alkaline is that the copolymer with water's material, which is soluble in the reagent liquid and / or an organic hydroxyl compound ⁶ 5, can be used to ensure that, preferably in the presence of a basic substance, the pH of the liquid does not drop below 7 falls. Implemented. Under these conditions, for example, strongly basic hydige oxymethylene groups are removed, and a droxyde, z. B. alkali or alkaline earth metal hydroxides, or