JPS63125511A - Stabilization of oxymethylene copolymer - Google Patents

Abstract

PURPOSE:To prevent corrosion of an apparatus for producing a stabilized copolymer by removing unstable portions of a crude oxymethylene copolymer by hydrolysis, by making the part of the apparatus which comes into contact with the reaction solution of stainless steel. CONSTITUTION:The part of a stabilization apparatus which comes into contact with the reaction solution is made of stainless steel. A crude oxymethylene copolymer is added to the apparatus and fused together with a hydrolyzing agent selected from water and a water/alcohol mixture to hydrolyze unstable portion of the crude polymer. The hydrolyzing agent and the hydrolyzation products remaining in the copolymer are removed by degassing to obtain a stabilized copolymer. Because that part of the apparatus which comes into contact with the reaction solution is made of stainless steel, a side reaction of forming formic acid from formaldehyde can be controlled, and therefore the apparatus can be protected from corrosion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for stabilizing crude oxymethylene copolymers.

More specifically, the present invention relates to an industrially advantageous method for stabilizing oxymethylene copolymers by appropriately selecting the metal materials constituting the device to reduce the rigid reaction of formaldehyde.

Oxymethylene copolymers are useful engineering plastics that are widely used in various fields due to their excellent physical properties.

Oxymethylene copolymers are produced by copolymerizing trioxane as a main raw material with cyclic ethers or cyclic acetals, but the resulting crude oxymethylene copolymers have nOH groups at their molecular ends; Since the terminal ends undergo so-called zipper decomposition and detach when heated, they cannot be put to practical use as a molding material as they are, and it is necessary to stabilize the unstable terminal ends.

[Conventional technology]

In order to stabilize this crude copolymer, methods such as acetylation, etherification, or urethanization of the terminals or oxyalkylene units derived from the comonomer contained in the molecular chain are necessary. A method is known to obtain a stabilized oxymethylene copolymer by decomposing the copolymer until the unstable part is removed, and one of the latter methods is to melt the crude copolymer and remove the unstable part. A method has been proposed for removing the compound by hydrolysis (Japanese Patent Publication No. 43-1875). As a specific method for carrying out this proposal, the crude copolymer as a hydrolyzing agent is made to coexist with the copolymer in advance, fed to the extruder, a hydrolysis reaction is carried out in the pressurizing section, and then the hydrolyzed products are removed in the low pressure section. In this method, the crude copolymer is first melted using a single screw extruder, etc., then a hydrolyzing agent is added, and the molten copolymer and the hydrolyzing agent are mixed and reacted by the action of a silent mixer, etc. , a method for removing volatile decomposition products at the end (Japanese Patent Application Laid-Open No. 5
8-152012) etc. have been proposed. However, in these methods, damage to the equipment due to corrosion in the area where the hydrolyzing agent and copolymer coexist is extremely large, which seriously impedes long-term stable operation. This is thought to be because formaldehyde produced by the hydrolysis reaction is oxidized or a strong acid such as formic acid is produced by a reaction similar to Canniguaro. Formic acid also causes scission of the main chain of the oxymethylene copolymer. For this reason, it is necessary to add a basic substance such as an amine compound as a substance that captures formic acid. However, although the damage to equipment due to corrosion is somewhat reduced by adding an acid scavenger, it is not enough; conversely, in order to further reduce damage to the equipment, adding a large amount of acid scavenger causes undesirable coloration. , impairing the quality of the copolymer. This is because formaldehyde produced by hydrolysis causes a formose reaction under the action of a base to produce various compounds, and these compounds include colored substances.

Therefore, in order to industrially and stably produce a copolymer of good quality, it is necessary to solve the problem of M-4f during damage to the equipment, reduction in the molecular weight of the copolymer, and coloring.

[Means for solving problems]

As a result of intensive research to solve these problems, the present inventors obtained the knowledge that a side reaction similar to the Cannitzaro reaction, which produces formic acid from formaldehyde, is greatly affected by the type of metal in contact with it. Reached.

That is, the Cannitzaro reaction is a reaction represented by the chemical formula: 2HCHO+H20→HCOOH+CH30H, and the present inventors have determined that 22% of formaldehyde, 280 ppm of formic acid, and 0.00% of hemetaldehyde are used.
Test pieces of various metals were placed in a 95% aqueous solution of polyaldehyde, kept at 97°C, and changes in formic acid concentration over time were investigated, and the results shown in Table 1 were obtained.

Note: It was confirmed by gas chromatography that methanol was produced in the same number of moles as the formic acid produced.

This result shows that the surface of aluminum chromium molybdenum steel and chromium molybdenum steel, which are used as metal materials for general extruders, etc., accelerates the reaction significantly compared to general stainless steel. The surface of stainless steel also has a reaction promoting effect, but the effect is small. Furthermore, when comparing 5US316L and SUS 304, it was found that although 5UB316L has higher corrosion resistance to general acids, 5US316L has a greater reaction acceleration effect than SUB 304. Therefore, it is not sufficient to simply use a material with high corrosion resistance.

It can be said that the surface of SUS 304 has almost no reaction promoting effect.

As a result of further research, the present inventors found that side reactions similar to those in the above equation also occur in the process of adding and melting a hydrolyzing agent containing water to an oxymethylene copolymer, and that the effects of the metal surface in this case also occur. The present invention was achieved by confirming the same tendency as above and applying this knowledge to industrial loading.

By melting the crude copolymer with a hydrolyzing agent, the unstable parts of the crude copolymer are hydrolyzed, and then the hydrolyzing agent and decomposition products remaining in the copolymer are removed by degassing and stabilized. A method for stabilizing an oxymethylene copolymer, characterized in that the part of the stabilizing device that comes into contact with the copolymer and the hydrolyzing agent in the range where they coexist is made of stainless steel. It is.

The oxymethylene copolymer to which the method of the present invention is applied is
0.4 to 40 molti in the main chain, preferably 0.4 to 10
It contains a molti oxyalkylene unit, and is mainly made by copolymerizing a cyclic acetal such as trioxane with a cyclic ether or cyclic acetal such as ethylene oxide, 1゜3-dioxolane, 1,3-dioxolane, etc. in the presence of a polymerization catalyst. Manufactured by

Boron trifluoride or a complex compound thereof is mainly used as a polymerization catalyst. Since the copolymer obtained by such a polymerization reaction contains a catalyst, the catalyst can be removed by washing with a cleaning solution containing a neutralizing agent, or by the method previously proposed by the applicant (Japanese Patent Publication No. 55-42085). It is necessary to completely deactivate the catalyst by adding a tertiary phosphine compound.

The proportion of unstable parts in the copolymer in which the catalyst has been neutralized, washed or deactivated is 220
It is measured by the decomposition rate (D)K- when heated at ℃ for 60 minutes. Usually, this value is 15 or less, but preferably it can be made 8 or less by appropriately controlling the operating conditions during polymerization and adjusting the amount of comonomer added.

The melting of the oxymethylene copolymer in the presence of a hydrolyzing agent in the present invention, that is, the hydrolysis reaction, can be carried out at a temperature of 180 to 250°C in a hydrolysis reaction apparatus, and the hydrolysis reaction apparatus includes: For example, a conventional single-screw or twin-screw extruder or a twin-screw self-cleaning kneader can be used.

In the present invention, it is essential that the portion of the hydrolysis reaction apparatus where the copolymer and the hydrolyzing agent coexist be made of stainless steel.

That is, the hydrolyzing agent is usually used in an amount of 1 to 25% by weight based on the copolymer, and may be allowed to coexist with the copolymer before melting, or once melted, or once melted, unstable parts are removed. It may be added to the copolymer after some amount has been removed. In the former case, all the melting equipment must be made of stainless steel, and in the latter case, the equipment downstream from the location where the hydrolyzing agent is added may be made of stainless steel. In order to ensure sufficient reaction between the hydrolyzing agent and the copolymer, volatile components are not removed for 1 to 15 minutes after the addition of the hydrolyzing agent, and the pressure is maintained to the extent that the hydrolyzing agent remains in a liquid state. It is necessary to maintain the temperature and allow the hydrolysis reaction to occur sufficiently.

In the present invention, water is mainly used as the hydrolyzing agent, but mixtures of water and alcohols such as methanol and ethanol can also be used. In order to obtain a copolymer of good quality, it is necessary to completely remove the hydrolyzing agent and decomposition products remaining in the copolymer after the hydrolysis reaction is completed.

These substances can be removed to some extent by using a vented extruder as a hydrolysis reactor, but
It is desirable to use a stabilizing device consisting of a hydrolysis reactor and a degassing device to perform the hydrolysis reaction and degassing separately. Examples of the stabilizing device include, for example, JP-A-54-1).
2748, 54-1) 2749 IC reactor, which constantly renews the surface of the melt, is particularly preferred; in such mixers, unlike ordinary extruders, By increasing the residence time to 5 to 60 minutes, the degassing of volatiles can be fully completed.

Of course, water coexists in the degassing device, which is part of the stabilizing device, until the degassing is complete.
The equipment should be made of stainless steel.

In the present invention, ordinary stainless steel that can be used to manufacture the device can be used as the stainless steel, but SUS
304 is particularly preferred.

In the present invention, the production of formic acid is suppressed to a relatively low level, but it is possible to suppress the production of formic acid by using aqueous dispersions of alkali metals or alkaline earth metals, ammonia, amines such as methylamine and ethylamine, and basic substances such as amidine. It is preferable to coexist an acid scavenger in the hydrolysis reaction system, and the amount used is preferably 1% by weight or less of the crude copolymer. In addition, in advance,
When carrying out a hydrolysis reaction after melting and kneading the crude copolymer while degassing and removing about 60 to 90 units of unstable parts, the addition of an acid scavenger is extremely small or unnecessary. be able to. When using a relatively large amount of acid scavenger, it is necessary to use a volatile one to degas and remove it from the copolymer, but when using a small amount, a non-volatile one can be used as needed. It can remain in the copolymer as a stabilizer, expanding the range of acid scavengers that can be used.
Good quality copolymers can be obtained.

A stabilizer can be added in order to prevent the main chain of the oxymethylene copolymer from being broken during melting and to obtain a molding material of good quality. As the stabilizer, known compounds can be used, but compounds selected from the group consisting of hydroxides, inorganic acid salts, carboxylic acid salts, and alkoxides of alkali metals or alkaline earth metals, which the present applicant previously applied for, may be used as stabilizers. A stabilizer consisting of a combination of one or more compounds that have been discovered, (1) a nitrogen-containing high molecular weight compound or an amine-substituted triazine, and a sterically hindered phenol
78256 and Japanese Patent Application No. 54-94075) are particularly suitable.

[Action and effect of the invention]

According to the present invention, since the production of formic acid in the hydrolysis reaction of the oxymethylene crude copolymer is suppressed to an extremely low level,
Damage to equipment due to corrosion is greatly reduced. Furthermore, the amount of basic substance used as an acid scavenger is very small or unnecessary, and problems of coloring of the copolymer and reduction in molecular weight do not occur.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples. The measurement method for each measurement item is as follows unless otherwise specified.

Intrinsic viscosity Measured in p-chlorophenol with 2% by weight of α-pinene added at 60°C (al/9) D 2-5 tm Hfi at 220°C under vacuum
Decomposition rate (wt%) of copolymer when heated for 60 minutes at After heating for 60 minutes, formaldehyde in nitrogen was measured by gas chromatography to determine the weight % relative to the copolymer.

Reference Example 1 (Production of crude polyoxymethylene copolymer) A two-stage polymerization apparatus as shown below was used as a continuous polymerization reaction apparatus. That is, the front polymerization machine is equipped with a pair of shafts inside a long case with a jacket around it, and each shaft is fitted with a number of mutually interlocking elliptical plates, and the long ends of the elliptical plates touch the inner surface of the case and the mating part. A mixer that can clean the surface of an elliptical plate is used, and as a post-polymerizer directly connected to this mixer, it has a pair of shafts inside a long case with a jacket around it. Although these shafts do not have self-cleaning properties, they are suitable for mixing powders. A horizontal stirring device with suitable stirring blades was used.

3.0% by weight of 1.3-dioxolane was added to this first-stage polymerization machine.
supplying trioxane containing 0.0% to trioxane.
0.10 mmol of boron trifluoride diethyl etherate was added per 0.3% by weight of methylal and 1 mole of trioxane. Polymerization was carried out by flowing hot water at 80° C. through the jacket of the first-stage polymerization machine. Unreacted rate in the latter stage polymerizer is 30
The copolymerization reaction mixture of
Copolymerization was carried out by flowing hot water at .degree. C., and the crude copolymer was supplied to the subsequent stopper mixer in a state where the copolymerization reaction was almost completed. 1 ± 0 per mole of trioxane in the stopper mixer
．． A benzene solution containing 2 mmol of triphenylphosphine was added and mixed with the crude copolymer to deactivate the catalyst. The crude copolymer was vacuum dried at 60°C for 10 hours. The properties of this crude copolymer were as follows.

Intrinsic viscosity 1.43 al19”
3,8 ChiD2□.

To the obtained crude copolymer were added 0.1% of calcium hydroxide, 0.2% of melamine, and 0.6% of 2,2'-methylenebis(4-methyl-6-tart-butylphenol) as stabilizers. .

Example 1 The crude copolymer wetted part obtained in Reference Example 1 was made of SUS'50
The mixture was continuously supplied to a jacketed kneader having self-cleaning properties prepared in step 4. 20 on the jacket
A heat medium at 0°C was flowed. Total length h from the supply port of the kneader
Then, water as a hydrolyzing agent and triethylamine as a trapping agent were heated to 1'60°C in the form of an aqueous solution of 1 tidyethylamine and added to the copolymer in an amount of 1 oxts. The residence time of the crude copolymer in this kneader was 5
It was a minute. The melted crude copolymer taken out from the kneader was directly introduced into a surface renewal type mixer whose wetted parts were made of 5US304. The conduit connecting the kneader and the surface renewal type mixer was also made of SUS 304. In the surface renewal type mixer, the residence time is 20 minutes and the temperature of the copolymer is 20 minutes.
The mixture was slowly stirred while maintaining the temperature at 10°C, and a pressure of 150 flHg was applied to remove the hydrolyzing agent and decomposition products by degassing. When the inside of the equipment was inspected after continuous mixing operation, no corrosion was found. The properties of the obtained pellets were as follows.

Intrinsic viscosity 1.43 dl/I Pellet color pure white Formaldehyde generation amount 0.1)% Comparative example 1 The copolymer obtained in Reference example 1 was used in two parts in which the wetted parts were made of chrome-molybdenum steel and aluminum-chrome-molybdenum steel. Continuously fed into a axial screw extruder. A heating medium of 200'(':) was flowed through the jacket.A hydrolyzing agent and a basic substance were added at a point A along the entire length from the feed port of the extruder, at a rate of 10% by weight based on the crude copolymer, which was an aqueous solution of triethylamine. The copolymer was heated to 160°C and added.The residence time in the extrusion mode was set to 5 minutes for melt kneading.The molten copolymer was directly fed to a vented twin-screw extruder made of the same metal material as above. , 400fl ventro
The copolymer was mixed and degassed while being evacuated.The residence time was 5 minutes, and the temperature was controlled at 210°C.The copolymer discharged from the extruder was cooled and cut into pellets.

When the equipment was inspected after continuous operation for M, it was found that the first extruder had significant corrosion downstream from the location where the hydrolyzing agent was added. Clear traces of corrosion were also observed throughout the second vented extruder.

The properties of the obtained pellet were as follows.

Intrinsic viscosity: 1.57 dl19 Pellet color: White, but slightly yellowish when compared to the pellet of Example 1.

Formaldehyde generation amount: 0.25% Comparative Example 2 Using the same equipment as in Comparative Example 1, using a hydrolyzing agent and basic substance at 10%) IJ ethylamine aqueous solution Clearly traces of corrosion were observed in the areas where the solution was used. The properties of the obtained pellet were as follows.

Intrinsic viscosity: 1,41 dl19 Pellet color: Slightly brownish Formaldehyde generation: 0.23% Example 2 The crude copolymer obtained in Reference Example 1 was heated using the same vented twin screw as that used in Comparative Example 1. Continuously fed to the extruder. By flowing a 200°C heat medium through the jacket, melting and kneading, and degassing from the vent, D60 was 0.60.
A melt copolymer of c4 was obtained. This molten copolymer was immediately introduced through a static mixer made of SUS304 into a surface renewal type mixer also made of SUBSO4. The residence time in the static mixer and mixer was 2 minutes and 15 minutes, respectively, and the temperature was 2 minutes.
The temperature was controlled at 20°C. To the static mixer, a 0.3% aqueous melamine solution was added as a hydrolyzing agent and a basic substance in an amount of 10% by weight based on the copolymer and heated to 160°C. For the surface renewal type mixer, the pressure is 40oflH.
，! Water and decomposition products were removed by degassing as i'. A pellet was obtained in the same manner as in Example 1.

When the apparatus was inspected after continuous operation for 30 days, no corrosion was expected throughout the apparatus.

The properties of the obtained pellet were as follows.

Intrinsic viscosity 1.44 dl19 Color tone Pure white

Claims (4)

[Claims] (1) By melting the crude oxymethylene copolymer with a hydrolyzing agent selected from water or a mixture of water and alcohol in a stabilizing device, the unstable parts of the crude copolymer are hydrolyzed; In a method for obtaining a stabilized copolymer by subsequently removing the hydrolyzing agent and decomposition products remaining in the copolymer by degassing, the range in which the copolymer and the hydrolyzing agent in the stabilizing device coexist. A method for stabilizing an oxymethylene copolymer, characterized in that the contact portion with the oxymethylene copolymer is made of stainless steel. (2) As a stabilizing device, a device consisting of a hydrolysis reaction device and a deaerator which is a surface renewal type mixer is used, and the residence time in the mixer is 5 to 60 minutes. The method described in (1) (3) The method according to claim (1) or (2), wherein the stainless steel is SUS304. (4) The method according to claim (1) or (2), in which hydrolysis is carried out in the coexistence of an acid scavenger made of a basic substance.