KR19980024838A - Method for preparing stabilized oxymethylene copolymer - Google Patents

Abstract

In order to provide an economical method for producing oxymethylene copolymer having excellent thermal stability, the crude oxymethylene copolymer discharged from the polymerization reactor is pulverized into a granule having a specific particle size distribution, at the same time the polymerization catalyst is deactivated, and then the pulverized oxymethylene air The coalescence is melt kneaded with a stabilizer to obtain a stabilized oxymethylene copolymer with substantially no stabilization treatment by removing the labile end portions by decomposition.

Description

Method for preparing stabilized oxymethylene copolymer

The present invention relates to an economical process for preparing oxymethylene copolymers having good thermal stability.

Polyoxymethylene copolymers (hereinafter abbreviated as POM copolymers) have excellent mechanical properties, heat resistance, chemical resistance, electrical properties and slidability and at the same time have good moldability or moldability and they are mechanically engineered as engineering plastics. It is used in a wide variety of applications such as parts, automotive parts or electrical / electronic parts.

Stabilized POM copolymers provided for practical use are generally prepared according to the method as described below.

First, the crude POM copolymer uses cyclic acetals such as trioxane as cyclic monomers and cyclic acetals or cyclic ethers having adjacent carbon atoms as comonomers, and optionally adds a chain transfer agent for controlling the degree of polymerization; It is then obtained by copolymerization in the presence of a cationic active catalyst. Such crude POM copolymers generally contain large amounts of labile end portions. When heat is applied to the remaining polymerization catalyst, depolymerization of the copolymer occurs or an increase in unstable terminal portion occurs.

Thus, the polymerization product is then neutralized with a crude POM copolymer which neutralizes the catalyst contained in the copolymer with an organic or inorganic basic compound such as alkylamine, alkoxyamine or hindered amine or a hydroxide of an alkali or alkaline earth metal. After inactivation, it is provided for the decomposition and removal of unstable end portions. The copolymer so treated is then heated in the presence of a basic compound, for example the above-mentioned compound, if necessary in combination with water or an alcohol to be used, whereby unstable end portions are removed by decomposition.

Then, a suitable additive is added to the copolymer to impart thermal stability and long term stability to the POM copolymer in which the unstable end portions are removed by decomposition in this way, and also the desired properties of various additives or reinforcing agents depending on the purpose. Is added to give the copolymer and melt-kneaded, whereby a stabilized POM copolymer suitable for practical use is produced.

Conversely, several studies have been conducted to produce more economically stabilized POM copolymers. Examples of known means for economical manufacture include improvement of the polymerization reactor, polymerization catalyst, etc. in the polymerization process, deactivation of the deactivator, deactivation method, etc. in the catalyst deactivation process, decomposition accelerator, decompression removal apparatus in the decomposition removal process of the unstable end portion. Improvement is included.

However, one of the means is only for a particular process so that the improvement brought about by it naturally has its limitations. There is therefore a need to provide a more economical method for preparing POM copolymers in consideration of the entire process from polymerization to final stabilization of the POM copolymer. In particular, in the above-described processes, the decomposition and removal of the unstable end portion requires complicated operation for treatment and a lot of energy for the treatment. If the POM copolymer can be provided in the final stabilization process with substantially no desorption process, economically advantageous production can be carried out. In order to exclude the decomposition removal step, it is necessary to prepare a high quality (crude) POM copolymer in the polymerization step and / or the catalyst deactivation step. As a method for improving catalyst deactivation, it is known to deactivate the crude POM copolymer, which is a polymerization product, by pulverization from the viewpoint of increasing the efficiency of catalyst deactivation and subsequent desorption efficiency of unstable ends. From that point of view, pulverized copolymers with small particle sizes have been considered desirable. (JP-A-57-80414 and JP-A-58-34819)

Still, as a result of the review, the inventors have found that such inactivation treatment of the crude POM copolymer by milling improves the quality of the resulting POM copolymer but adds a stabilizer to the resulting copolymer without decomposing and removing the unstable end portion. It has been found that if the resultant POM copolymer is provided to a stabilization process and then melt-kneaded, the resulting POM copolymer necessarily has significantly inferior operability.

As mentioned above, no effective and simple method of economically preparing stabilized POM copolymers by providing the POM copolymer to the final stabilization process without decomposing the unstable end portions has not been found so far.

Summary of the Invention

It is an object of the present invention to provide an economically extremely advantageous and simple method of preparing a stabilized POM copolymer suitable for practical use thereby overcoming the above-described problems.

In order to achieve the above object, the present inventors have conducted a comprehensive examination of the method from the polymerization process of the POM copolymer to the stabilization process. As a result, the milling of the crude POM copolymer as a polymerization product is an important factor and the above-described objectives can be achieved by appropriately controlling the particle size distribution of the copolymer.

That is, in the present invention, the method for producing a stabilized oxymethylene copolymer comprises pulverizing the crude oxymethylene copolymer discharged from the polymerization reactor into a granule meeting the following requirements (1) to (4) of the particle size distribution and simultaneously burning the polymerization catalyst. It is characterized by melt-kneading the oxymethylene copolymer pulverized with a stabilizer without substantially treating the stabilizing ends of the polymer molecules by activating and then decomposing and removing the unstable end portions.

(1) The average particle diameter is 0.3 to 0.7 mm,

(2) 3 to 20% by weight of the particles have a particle diameter longer than 1.0 mm,

(3) 50 to 97% by weight of the particles have a particle size of 0.18 to 1.0mm,

(4) 0 to 30% by weight of the particles have a particle diameter shorter than 0.18 mm (total amount is 100% by weight).

That is, the present invention is a process for polymerizing an oxymethylene polymer, grinding a crude copolymer product into granules having size distributions (1), (2), (3) and (4), and burning the catalyst remaining in the granules. And a process for activating the powder and melt-kneading the powder with a stabilizer under the condition that the powder is not treated to remove by decomposing the unstable end portions of the molecules. The present invention further provides a method of stabilizing an oxymethylene copolymer by carrying out the process shown above.

Detailed Description of the Preferred Embodiments

The present invention will be explained in more detail below.

First, the (crude) oxymethylene copolymer (POM copolymer) to which the present invention is applied is used by copolymerizing cyclic acetal such as trioxane as main monomer and cyclic ether or cyclic formal as comonomer in the presence of a cationic active catalyst. It becomes possible.

The cyclic ethers or cyclic formals used herein as comonomers are cyclic compounds containing at least one pair of coupling carbon and oxygen atoms. Examples include ethylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane and propylene oxide. Among them, preferred comonomers are ethylene oxide, 1,3-dioxolane, diethylene glycol formal and 1,4-butanediol formal. Co-monomer is used in the amount of 0.1-20 mol%, preferably 0.2-10 mol% with respect to trioxane which is a main monomer.

In the preparation of the (crude) POM copolymer by copolymerization of such monomers and comonomers, a cationic catalyst generally used is used as a polymerization catalyst. Examples of cationic catalysts include Lewis acids, such as halides of boron, tin, titanium, phosphorus, arsenic, and antiions, in particular boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, pentafluoride Compounds such as arsenic and antimony pentafluoride, complexes or salts thereof; Esters of protonic acids such as protonic acids such as trifluoromethanesulfonic acid and perchloric acid, esters of perchloric acid and lower aliphatic alcohols (for example tertiary butyl esters of perchloric acid), anhydrides of protonic acids, in particular perchloric acid and lower aliphatic carboxylic acids Mixed anhydrides (eg acetyl perchlorate), homopolyacids, heteropolyacids (eg phosphomolybdic acid), triethyloxonium hexafluorophosphate, triphenylmethyl hexafluoroarsenate and acetylhexafluoroborate Included.

Among them, coordination compounds between boron trifluoride and boron trifluoride and organic compounds (eg ethers) are most commonly used as catalysts. In addition, since protonic acid, such as heteropolyacids or homopolyacids, has high activity as a catalyst, a small amount of catalyst readily provides a high-quality crude POM copolymer and is easily inactivated. It is therefore desirable to prepare crude POM copolymers by polymerizing in the presence of a catalyst selected from such compounds or mixtures of two or more thereof. When Lewis acids such as boron trifluoride are used as catalysts, it is preferable to add an amount of 15 to 25 ppm relative to the raw material monomers. Preference is given to using monomers having a moisture of 10 ppm or less in order to obtain a high-quality crude POM copolymer.

For the control of the molecular weight of the crude POM copolymers useful by copolymerization, it is also possible to carry out the polymerization, if necessary, by addition of a suitable chain transfer agent, for example an appropriate amount of acetal compound such as methylal or dioxymethylene dimethylether.

Alternatively, it is possible to prepare such crude POM copolymers in the presence of a hindered phenol compound which is an antioxidant. This method controls the oxidative degradation of the resulting POM copolymer during polymerization or inhibits the oxidative degradation of the POM copolymer caused by heat treatment in subsequent processes to provide the final stabilization process with a high-quality maintained POM copolymer. Effective to make that possible. Thus the crude POM copolymer so obtained is preferably used in the present invention.

The crude POM copolymer can be copolymerized by using conventionally known equipment and methods, for example batch or continuous or melt polymerization or melt block polymerization. From an industrial point of view, a continuous bulk process in which a liquid monomer is used and the polymer is obtained in the form of solid granules with the progress of polymerization is generally used and preferred. In this case, the polymerization can be carried out in the presence of an inert liquid medium as required. Examples of the polymerization apparatus include Ko-Kneader, twin screw continuous extrusion mixer, and twin screw puddle continuous mixer.

The process of the present invention breaks the crude POM copolymer obtained as above into a granule having a specific particle size distribution and simultaneously inactivates the polymerization catalyst contained in the granule and then removes the ends by decomposing the unstable end portions by decomposition. It is characterized by melt-kneading the POM copolymer ground with a stabilizer substantially free of treatment to stabilize.

Here, the POM copolymer so pulverized needs to satisfy the particle size distribution described in (1) to (4) below.

(1) the average particle diameter is 0.3 to 0.7 mm,

(2) 3 to 20% by weight of the particles have a particle diameter longer than 0.1 mm,

(3) 50 to 97% by weight of the particles have a particle size of 0.18 to 1.0mm,

(4) 0 to 30% by weight of the particles have a particle diameter shorter than 0.18 mm (total amount is 100% by weight).

The particle size distribution satisfies both the quality of the useful POM copolymer by grinding and inactivation of the catalyst, in particular the amount of unstable ends and the operability of the stabilization process for melt-kneading the ground POM copolymer with a stabilizer. It has been found as a result of extensive investigation by the inventors for stabilizing the copolymer.

Among the above requirements, the upper limit of the average particle diameter of (1) (0.7 mm) and the upper limit of the ratio of particles having a particle diameter of more than 1.0 mm of (2) are mainly important requirements for determining the quality of the POM copolymer. On the other hand, the lower limit of the average particle diameter of (1) (0.3 mm), the lower limit of the proportion of particles having a particle diameter exceeding 1.0 mm of (2), and the upper limit of particles having a particle size smaller than 0.18 mm of (4) are mainly stable. These are important requirements for determining the operability of the stabilization process by topic.

When the particle size exceeds the particle size distribution, for example when the proportion of particles having an average particle size above its upper limit or having a particle size longer than 1.0 mm exceeds its upper limit, POM copolymers deteriorate their quality, in particular increase the amount of unstable ends and stable POM copolymers that can be provided on the market are only stabilizers without treatment to stabilize the ends by removal by decomposing unstable end parts. It cannot be obtained by stabilization of. On the other hand, when the particle size is less than the particle size distribution, for example, the average particle size is less than its lower limit, or the proportion of particles having a particle size longer than 1.0 mm is less than its lower limit, or shorter than 0.18 mm When the ratio exceeds the upper limit, the operability of the stabilization process by kneading with a stabilizer instead of satisfactory quality of the POM copolymer becomes remarkably inferior, making it difficult to economically prepare a stabilized POM copolymer.

In this respect, the preferred particle size distributions that can satisfy both the better quality of the POM copolymer and the better operability of the stabilization process are as follows:

(1) the average particle diameter is 0.4 to 0.7 mm,

(2) 5 to 15% by weight of the particles have a particle diameter longer than 1.0 mm,

(3) 60 to 95% by weight of the particles have a particle diameter of 0.18 to 1.0 mm,

(4) 0 to 25% by weight of the particles have a particle diameter shorter than 0.18 (total amount is 100% by weight).

In the pulverization as described above, there is no particular limitation on the pulverizer used. Examples include rotary mills, hammer mills, jaw crushers, feather mills, rotary mills, turbo mills and classifiers. The particle size distribution can be controlled by the number of revolutions, clearance or screen mesh attached to the mill and / or the shift attached separately as needed.

In deactivation of the catalyst contained in the crude POM copolymer, conventionally known methods can be used. Inactivation in the present invention is carried out by using an aqueous solution of an organic or inorganic basic compound represented by triethylamine, triethanolamine, sodium carbonate or calcium hydroxide as the inactivating agent and simultaneously the crude POM copolymer is used to wet the particle size distribution by wet grinding. It is preferable that the eggplant is pulverized into powder. First of all, it is preferable to add an inactivating agent from a position just before the outlet of the polymerizer to the inlet of the polymerizer, whereby a high quality POM copolymer can be obtained.

After deactivation and pulverization of the catalyst, the POM copolymer is washed, dried and the like as necessary.

In the present invention, a high quality POM copolymer having few unstable ends can be obtained by inactivating the catalyst of the above-mentioned polymerization product, the crude POM copolymer, and simultaneously crushing it into a granule having a specific particle size distribution. In particular, it is preferable that the resultant copolymer having an unstable terminal amount of 0.3 to 0.8 goes through a subsequent stabilization process.

Incidentally, as used herein, the term unstable terminal amount of a POM copolymer refers to the amount of formaldehyde in wt% of the copolymer, which amounts to 1 g of POM copolymer containing 50% methanol containing 0.5% ammonium hydroxide. The solution was placed in a pressure-tight container with 100 ml of aqueous solution, heated at 180 ° C. for 45 minutes, cooled, and taken out of the container, and then determined by quantitative analysis of the formaldehyde dissolved in the liquid.

The pulverized POM copolymer, which is ground to have such a specific particle size distribution and then subjected to inactivation of the catalyst contained therein, is then substantially free from the conventional treatment of removing unstable end portions by decomposition. Melt kneading with the agent can thereby obtain a stabilized POM copolymer. Stabilizers useful here are not particularly limited. Any known stabilizer may be used, but in general, antioxidants and heat stabilizers are used in combination.

Examples of the antioxidant include 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], penta-erythryltetrakis [3- (3 , 5-di-tert-butyl-4-hydroxyphenyl) -propionate], triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] And N, N'-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-cyanamide).

Examples of heat stabilizers include triazine compounds such as melamine and melamine-formaldehyde condensates, polyamides such as nylon 12 and nylon 6 · 10, hydroxides of alkali or alkaline earth metals, carbonates, phosphates, acetates And metal salts of higher fatty acids such as oxalates and stearic acid or metal salts of higher fatty acids with substituents such as hydroxy groups.

Various additives may be added to the POM copolymer of the present invention depending on the purpose. Examples include weather stabilizers, lubricants, nucleating agents, mold release agents, antistatic agents, dyes, pigments, other organic polymeric materials, inorganic or organic fibrous, plate or granular fillers.

Melt-kneading with stabilizers and the like is generally carried out in an extruder.

Examples and comparative examples will be described below. It is clear that the present invention is not limited to them.

Examples 1-5, Comparative Examples 1-4

In each example, trioxane (containing 15 ppm or 8 ppm of water) and 2.5 wt% (in total monomers) of 1,3-dioxolane are successively fed into a twin-screw puddle type continuous polymerizer and the polymerization is 3-fluorine as a catalyst. It was carried out in the presence of boron fluoride or phosphomolybdic acid (supplied in a mixture with comonomer). The crude POM copolymer discharged from the outlet of the polymerizer end is subjected to wet or dry pulverization by the method described below and simultaneously with deactivation of the catalyst followed by dehydration and drying. Thereby, a granular POM copolymer having a particle size distribution shown in Table 1 was obtained. The particle size distribution was controlled by changing the number of revolutions of the mill or the size or shape of the screen mesh.

Wet Grinding:

An aqueous solution containing 500 ppm of triethylamine was fed to the outlet of the polymerizer as a catalyst deactivator. It was contacted with the crude POM copolymer discharged directly from the outlet to cause inactivation of the catalyst, while the resulting mixture was introduced into a ball mill with a screen mesh attached and milled therein. The slurry containing the granular POM copolymer and the catalyst deactivator was discharged from the grinder and then introduced into a storage tank where further deactivation was performed followed by dehydration and drying.

Dry grinding:

The crude POM copolymer discharged from the outlet of the polymerizer was introduced into the grinder through a closed line and pulverized to avoid contact with moisture and air. The granular POM copolymer discharged from the mill was then introduced into a storage tank of an aqueous solution containing 500 ppm of triethylamine, inactivated, and dehydrated and dried.

The granular POM copolymer obtained by the above method is 0.5 wt% of pentaerythritol tetrakis [3- (3,5-di-tertiary) as a stabilizer without conventional treatment for decomposing and removing unstable terminal portions. -Butyl-4-hydroxyphenyl) propionate] and 0.1 wt% calcium stearate, followed by melt-kneading in an extruder, whereby a stabilized POM copolymer was obtained in pellet form. The evaluation results are shown in Table 1.

Incidentally, the evaluation methods and criteria are as follows.

[Thermal Stability of Stabilized POM]

The weight loss when the stabilized POM copolymer (5 g) was heated at 220 ° C. for 45 minutes in air was measured and expressed as a percentage weight loss per minute.

[Extrudeability]

· Feeding properties of raw materials

When the stabilizer was mixed with the granular POM copolymer and the resultant mixture was melt-kneaded in the extruder, the feeding state of the raw material into the extruder and the discharge state of the stabilized POM from the extruder were observed. It evaluated according to the following four A-D grades.

A: Both feeding and drained strands are stable

B: Occasional feeding failure sometimes occurs and strand thickness fluctuates

C: Variation in feeding condition is slightly large, strand thickness is large, and sometimes strand breakage occurs.

D: Variation in feeding condition is severe, the feeding amount is low overall, and no strand can be formed.

Motor load amplitude

The difference between the maximum value and the minimum value of the motor current value during extrusion (unit: amps)

Fluctuation of resin pressure

The difference between the maximum and minimum values shown on the resin pressure gauge installed just behind the screw tip of the extruder (unit: kg / cm ² )

The present invention describes an effective and simple method of economically preparing a stabilized POM copolymer by providing the POM copolymer to the final stabilization process without decomposition and removal of the labile end portions.

Claims (8)

Termination of the crude oxymethylene copolymer discharged from the polymerizer into granules satisfying the following requirements (1) to (4) of the particle size distribution, simultaneously inactivating the polymerization catalyst, and then decomposing and removing the unstable terminal portion A method of producing a stabilized oxymethylene copolymer, characterized in that the oxymethylene copolymer pulverized with a stabilizer is melt-kneaded without substantially treating the particles. (1) The average particle diameter is 0.3 to 0.7 mm, (2) 3 to 20% by weight of the particles have a particle diameter longer than 1.0 mm, (3) 50 to 97% by weight of the particles have a particle size of 0.18 to 1.0mm, (4) 0 to 30% by weight of the particles have a particle diameter shorter than 0.18 mm (total amount is 100% by weight). The method of claim 1, wherein the pulverized oxymethylene copolymer has unstable ends of 0.3 to 0.8% by weight (in the copolymer). 3. Process according to claim 1 or 2, characterized in that the crude oxymethylene copolymer is obtained by polymerization carried out in the presence of protonic acid as a catalyst. The method for producing a stabilized oxymethylene copolymer according to claim 1 or 2, wherein the crude oxymethylene copolymer is obtained in the presence of 15-25 ppm Lewis acid based on the raw material monomer as a catalyst. The method for producing a stabilized oxymethylene copolymer according to any one of claims 1 to 4, wherein the crude oxymethylene copolymer is obtained by polymerization carried out in the presence of a hindered phenolic compound. The method for producing a stabilized oxymethylene copolymer according to any one of claims 1 to 5, wherein the crude oxymethylene copolymer is obtained by polymerization of a monomer having water of 10 ppm or less. 7. The stabilization oxymethylene copolymer preparation according to any one of claims 1 to 6, wherein grinding is performed by a wet grinding method and an inactivation treatment is performed using an aqueous solution of a basic compound as an inactivating agent of the polymerization catalyst. Way. 8. A method according to claim 7, wherein the deactivation process is carried out by adding an inactivating agent of the polymerization catalyst just before the polymer outlet of the polymerizer and the inlet of the mill.