JPH10101756A - Method for producing stabilized oxymethylene copolymer - Google Patents

Abstract

(57) [Problem] To economically produce an oxymethylene copolymer excellent in thermal stability. SOLUTION: A crude oxymethylene copolymer discharged from a polymerization machine is pulverized into powders satisfying a specific particle size distribution, and after a polymerization catalyst is deactivated, decomposition of an unstable terminal portion is performed. The pulverized oxymethylene copolymer is melt-kneaded with a stabilizer without substantially undergoing a terminal stabilization treatment by removal to obtain a stabilized oxymethylene copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an economical method for producing an oxymethylene copolymer having excellent heat stability.

[0002]

2. Description of the Related Art Polyoxymethylene copolymers (hereinafter referred to as P
OM copolymer) may have mechanical properties,
Excellent properties such as heat resistance, chemical resistance, electrical properties, slidability, etc.
And because of its excellent moldability, it can be used as engineering plastics for mechanical parts, automobile parts,
It is used for a wide range of applications such as electronic equipment parts. It is known that a practically used stabilized POM copolymer is generally produced by the following process. First, a cyclic acetal such as trioxane is used as a main monomer, a cyclic acetal or a cyclic ether having adjacent carbon atoms is used as a comonomer, and a chain transfer agent for adjusting the degree of polymerization is added according to the purpose. The resulting copolymer is used to obtain a crude POM copolymer. Generally, such crude POM copolymers have a significant amount of unstable terminal moieties. In addition, the polymerization catalyst remains in an active state and causes depolymerization of the copolymer when heat is applied,
This causes an increase in the unstable terminal portion. Therefore, the crude POM copolymer which is a polymerization product is then catalyzed by an organic or inorganic basic compound such as an alkylamine, an alkoxyamine, a hindered amine or a hydroxide of an alkali metal or an alkaline earth metal. And then subjected to a step of decomposing and removing the unstable terminal portion, and heating in the presence of a basic compound, for example, a compound as described above, and optionally water, alcohol, etc. As a result, the unstable terminal portion is decomposed and removed. The POM copolymer from which the unstable terminal portion has been decomposed and removed in this manner is then blended with various stabilizers for imparting heat resistance, long-term stability, etc., and further, if desired, depending on the purpose. By blending various additives, reinforcing agents and the like for imparting properties and melt-kneading, a stabilized POM copolymer which can be practically used is obtained. On the other hand, various studies have been made to produce a stabilized POM copolymer more economically, for example, improvement of a polymerization machine and a polymerization catalyst in a polymerization step, and a deactivator in a catalyst deactivation step. It is known to improve the deactivation method and the like, and to improve the decomposition accelerator and the decomposition removing device in the step of decomposing and removing unstable terminals. However, each of these methods focuses on a specific process, and its improvement is naturally limited.
There has been a demand for a more economical method for producing a stabilized POM copolymer that comprehensively considers the steps of stabilizing the copolymer.
In particular, the step of decomposing and removing the unstable terminal portion among the above steps requires a complicated processing operation and requires a large amount of energy for the processing, and the POM copolymer is substantially not subjected to this step. If can be subjected to the final stabilization step, very economical production is possible,
For this purpose, it is necessary to obtain a high-quality (crude) POM copolymer in the polymerization step and / or the catalyst deactivation step. Among these, as a method for improving catalyst deactivation, from the viewpoint of catalyst deactivation efficiency and subsequent efficiency of decomposition and removal of unstable terminals, the crude POM copolymer as a polymerization product is finely pulverized. It is known that inactivation treatment is performed, and from these viewpoints, it is considered that the smaller the particle size of the pulverized product is, the more preferable it is (Japanese Patent Application Laid-Open Nos. 57-80414 and 58-34819). However, the present inventor studied that, when the crude POM copolymer was finely pulverized and deactivated as described above, although the quality of the obtained POM copolymer was improved,
It has been found that when the stabilizer is blended with the stabilizer and subjected to a melt kneading step without undergoing the step of decomposing and removing the unstable terminal portion, the operability becomes extremely poor. Thus, the PO process can be performed without a simplified process, in particular, a step of decomposing and removing an unstable terminal portion.
An effective method for producing a stabilized POM copolymer economically by subjecting the M copolymer to a final stabilization step has not been found so far.

[0003]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for producing a practically usable stabilized POM copolymer by a very economically advantageous and simple process. Aim.

[0004]

Means for Solving the Problems In order to achieve the object, the present inventors have comprehensively studied processes from a polymerization step of a POM copolymer to a stabilization step, and as a result, the crude product which is a polymerization product has been obtained. It has been found that pulverization of the POM copolymer is the key factor, and that the above object can be achieved by appropriately controlling the particle size distribution, thereby completing the present invention. That is, the present invention pulverizes the crude oxymethylene copolymer discharged from the polymerization machine into particles satisfying the particle size distribution defined by the following (1) to (4) and performs a deactivation treatment of the polymerization catalyst. After that, the pulverized oxymethylene copolymer is melt-kneaded with a stabilizer without substantially undergoing a terminal stabilization treatment by decomposing and removing an unstable terminal portion. This is a method for producing a polymer. (1) Average particle size 0.3 to 0.7mm (2) 3 to 20% by weight exceeding 1.0mm (3) 50 to 97% by weight from 0.18mm to 1.0mm (4) Particle size 0-30% by weight less than 0.18mm (However, the total amount is 100% by weight)

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the (crude) oxymethylene copolymer (POM copolymer) to which the present invention is applied is a copolymer containing a cyclic acetal such as trioxane as a main monomer and a cyclic ether or cyclic formal as a comonomer in the presence of a cationically active catalyst. It is obtained by polymerization. Here, the cyclic ether or cyclic formal used as a comonomer is a cyclic compound having at least one pair of a connecting carbon atom and an oxygen atom, for example, ethylene oxide, 1,3-dioxolan, 1,3,5-trioxepane, diethylene glycol formal, Examples thereof include 1,4-butanediol formal, 1,3-dioxane, propylene oxide and the like. Among these, preferred comonomers are ethylene oxide, 1,3-dioxolan, diethylene glycol formal, and 1,4-butanediol formal.
The amount used is based on trioxane, the main monomer.
It is 0.1 to 20 mol%, preferably 0.2 to 10 mol%. The (coarse) PO
In producing the M copolymer, a general cationic catalyst is used as a polymerization catalyst. Such cationic catalysts include Lewis acids, especially halides such as boron, tin, titanium, phosphorus, arsenic and antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, pentafluoride. Compounds such as phosphorus, arsenic pentafluoride and antimony pentafluoride, and their complex compounds or salts, protic acids such as trifluoromethanesulfonic acid, perchloric acid, esters of protic acids, in particular perchloric acid and lower aliphatic alcohols Esters (for example, perchloric acid tertiary butyl ester), anhydrides of protic acids, especially mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids (for example, acetyl perchlorate), or isopoly acids, heteropoly acids (for example, , Phosphomolybdic acid), or triethyloxonium hexafluorophosphate, Le hexafluoro ARUZE diisocyanate, acetyl hexafluoro borate and the like. Among them, boron trifluoride or a coordination compound of boron trifluoride and an organic compound (for example, ethers) is the most common. Further, protonic acids such as heteropolyacids and isopolyacids have a high activity as a catalyst, and it is easy to obtain a high-quality crude POM copolymer with a small amount of a catalyst, and it is easy to deactivate the catalyst. The crude POM copolymer to which is applied is preferably one obtained by polymerizing one or a mixture of two or more selected from such compounds as a catalyst. When a Lewis acid such as boron trifluoride is used as a catalyst, the amount of addition is 15
~ 25 ppm is preferred. In order to obtain a high quality crude POM copolymer, it is preferable to use a monomer containing 10 ppm or less of water. In addition, crude P obtained by copolymerization
In order to control the molecular weight of the OM copolymer, if necessary, a suitable chain transfer agent, for example, an appropriate amount of an acetal compound such as methylal or dioxymethylene dimethyl ether may be added for polymerization. Further, the production of the crude POM copolymer obtained by such a copolymerization can be carried out in the presence of a hindered phenol compound as an antioxidant. The crude POM to which the present invention is applied is effective in suppressing the oxidative decomposition and the like of the POM copolymer at a high temperature in the subsequent step and providing the POM copolymer with high quality to the final stabilization step. It is suitable as a copolymer.

The production of a crude POM copolymer by copolymerization is as follows:
Conventionally known equipment and methods can be used. That is, any of a batch system and a continuous system can be used, and any of a melt polymerization, a melt bulk polymerization, and the like may be used. However, a continuous bulk method using a liquid monomer to obtain a solid powder bulk polymer with the progress of polymerization. Is industrially common and preferred. In this case, an inert liquid medium can coexist as necessary.
As a polymerization apparatus, a co-kneader, a twin-screw type continuous extrusion mixer, a twin-screw paddle type continuous mixer and the like can be used.

[0007] The present invention relates to a crude P
The OM copolymer is pulverized into powder having a specific particle size distribution, and after deactivating the polymerization catalyst contained therein, end stabilization by decomposing and removing unstable terminal portions. It is characterized in that the pulverized POM copolymer is melt-kneaded with a stabilizer and stabilized without substantially undergoing treatment. Here, the pulverized POM copolymer has the following (1)
It is necessary to satisfy the particle size distribution defined by (4). (1) Average particle size 0.3 to 0.7mm (2) 3 to 20% by weight exceeding 1.0mm (3) 50 to 97% by weight from 0.18mm to 1.0mm (4) Particle size The particle size distribution is 0 to 30% by weight (however, the total amount is 100% by weight). This particle size distribution indicates the quality of the POM copolymer obtained by grinding and deactivating the catalyst, especially From the viewpoint of satisfying both the stable terminal amount and the operability of a stabilization step of stabilizing a pulverized POM copolymer by melt-kneading with a stabilizer, the present inventors have made intensive studies and found out. Of these, the upper limit (0.7 mm) of the average particle size in (1) and the upper limit of the ratio of those exceeding 1.0 mm in (2) are mainly determined by PO
It is an important requirement that holds the key to the quality of M copolymer.
The lower limit of the average particle size (0.3 mm) of (2), the lower limit of the ratio of those exceeding 1.0 mm in (2), and the upper limit of the ratio of less than 0.18 mm in (4) are determined mainly in the stabilization process using a stabilizer. This is an important requirement that holds the key to operability. If the particle size is biased to a larger one than the particle size distribution shown here, for example, if the average particle size exceeds the upper limit or the ratio of those exceeding 1.0 mm exceeds the upper limit, the obtained ground POM The quality of the coalescence, especially the amount of unstable terminals, becomes large, and when subjected to a stabilization step with a stabilizer without going through a terminal stabilization treatment by decomposing and removing the unstable terminal portion, a stable POM copolymer which can be supplied to the market You will not be able to get coalesced. on the other hand,
When the particle size is biased toward the smaller one from the particle size distribution, for example, the ratio of those having an average particle size less than the lower limit and exceeding 1.0 mm is less than the lower limit or the ratio of those having a particle size of less than 0.18 mm satisfies the upper limit. In this case, although the quality of the POM copolymer is satisfactory, the operability of the stabilization step by kneading with the stabilizer becomes extremely poor, and it becomes difficult to economically produce the stabilized POM copolymer. From such a viewpoint, a preferable particle size distribution for satisfying both the better quality of the POM copolymer and the operability of the stabilization step is as follows. (1) 'Average particle size 0.4 to 0.7mm (2)' 5 to 15% by weight with a particle size exceeding 1.0mm (3) '60 to 95% by weight with a particle size of 0.18mm to 1.0mm ) '0 to 25% by weight having a particle size of less than 0.18 mm (however, the total amount is 100% by weight) In performing the above-mentioned pulverization, a pulverizer to be used is not particularly limited. For example, a rotary mill, a hammer mill, a jaw crusher, a feather mill, a rotary cutter mill, a turbo mill, a classifying impact crusher, or the like is used. The particle size distribution can be controlled by the rotation speed and clearance of the crusher, a screen mesh provided in the crusher, and / or a sieve provided separately as required.

[0008] In deactivating the catalyst contained in the crude POM copolymer, known methods can be used as the deactivation method. In the present invention, in performing such catalyst deactivation treatment, an aqueous solution of an organic or inorganic basic compound represented by triethylamine, triethanolamine, sodium carbonate, calcium hydroxide, or the like is used as a deactivation treatment agent. While performing the deactivation treatment, it is preferable to obtain the particle size distribution as described above by pulverization by wet pulverization, among which such deactivation treatment agent, from just before the polymer outlet of the polymerization machine to the pulverizer inlet. It is preferable to add the POM copolymer during this time, whereby a high quality POM copolymer can be obtained. The POM copolymer which has been subjected to the catalyst deactivation treatment and pulverized is subjected to washing, drying and the like as necessary.

In the present invention, the polymerization product crude P
By performing the catalyst deactivation treatment as described above and pulverizing the OM copolymer into powder having a specific particle size distribution, a high quality POM copolymer having few unstable terminals can be obtained. Preferably, those having an unstable terminal amount of 0.3 to 0.8 are subjected to the next stabilization step. Incidentally, the amount of unstable terminal of the POM copolymer specified here is the value of the POM copolymer 1
g in a pressure-tight container together with 100 ml of a 50% aqueous methanol solution containing 0.5% ammonium hydroxide, heat-treated at 180 ° C. for 45 minutes, cooled, taken out, and quantitatively analyzed the amount of formaldehyde decomposed and eluted in the liquid. , In terms of% by weight based on the copolymer.

As described above, the pulverized POM copolymer that has been pulverized so as to have a specific particle size distribution and has been subjected to a catalyst deactivation treatment is:
Without substantially undergoing the step of decomposing and removing the unstable terminal portion, which is usually performed, the mixture is melt-kneaded with a stabilizer to obtain a stabilized POM copolymer. The stabilizer used here is not particularly limited, and any known stabilizer can be used. Generally, an antioxidant and a heat stabilizer are used in combination. As the antioxidant, for example, 1,6-
Hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityltetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate ], Triethylene glycol-bis [3- (3-t-butyl-5-
Methyl-4-hydroxyphenyl) propionate],
N, N'-hexamethylenebis (3,5-di-t-butyl-4
-Hydroxy-cinnamamide) and the like.

Examples of the heat stabilizer include triazine compounds such as melamine, melamine-formaldehyde condensate, polyamides such as nylon 12, nylon 6, and 10; hydroxides and carbonates of alkali metals or alkaline earth metals;
Examples thereof include metal salts of higher fatty acids such as stearic acid and higher fatty acids having a substituent such as a hydroxyl group, such as phosphates, acetates, and oxalates.

[0012] In addition, the POM copolymer of the present invention can contain various additives depending on the purpose.
Weather (light) stabilizers, lubricants, lubricants, nucleating agents, mold release agents, antistatic agents, dyes, pigments, other organic polymer materials, inorganic and organic fibrous, plate-like, powder-like fillers, etc. Can be blended. Melt kneading with a stabilizer or the like is generally performed using an extruder.

[0013]

EXAMPLES Examples and comparative examples will be shown below, but it goes without saying that the present invention is not limited to these examples. Examples 1 to 5 and Comparative Examples 1 to 4 Trioxane (containing 15 ppm or 8 ppm of water) and 2.5% by weight of 1,3-dioxolane (in all monomers) were continuously fed using a biaxial paddle type continuous polymerization machine. The mixture was supplied and polymerized using boron trifluoride or phosphomolybdic acid (supplied as a mixture with a comonomer) as a catalyst. The crude POM copolymer discharged from the discharge port at the end of the polymerization machine was subjected to a wet pulverization or a dry pulverization and a catalyst deactivation treatment by the following method, followed by dehydration and drying. A powdery POM copolymer having a particle size distribution shown in Table 1 was obtained. The particle size distribution was controlled by changing the rotation speed of the pulverizer and the size and shape of the screen mesh. Wet pulverization: An aqueous solution containing 500 ppm of triethylamine as a catalyst deactivator is supplied to the outlet of the polymerization machine, and is immediately brought into contact with the crude POM copolymer discharged from the outlet to screen deactivate the catalyst. And pulverize it with a ball mill. POM discharged from the pulverizer
A slurry containing the copolymer and the catalyst deactivator was introduced into a storage tank, and after deactivation treatment, dehydrated and dried. Dry pulverization: The crude POM copolymer discharged from the outlet of the polymerization machine is introduced into the above-mentioned pulverizer through a closed line so as to avoid contact with moisture and air, pulverized, and then discharged from the pulverizer. The powdery POM copolymer was introduced into a storage tank of an aqueous solution containing 500 ppm of triethylamine, deactivated, dried, and dried.

With respect to the powdery POM copolymer obtained by the above method, pentaerythrityltetrakis [3- (3,5-di- [t-butyl-4-hydroxyphenyl) propionate] 0.5% by weight and calcium stearate 0.1% by weight were mixed and melt-kneaded with an extruder to obtain a pelletized stabilized POM copolymer.
Table 1 shows the evaluation results.

The evaluation methods and criteria are as follows. [Thermal stability of stabilized POM] 5 g of stabilized POM copolymer
Was heated at 220 ° C. for 45 minutes in the air, and the weight loss was measured and expressed as a weight loss rate (%) per minute. [Extrusion property]-Raw material biting property Observation of raw material biting into the extruder and discharge of stabilized POM from the extruder when a stabilizer is mixed with the powdery POM copolymer and melt-kneaded with the extruder. A to D below
Was evaluated in four steps. A: Both biting and discharging strands are stable. B: Occasional biting occurs and the thickness of the strand fluctuates. C: Biting fluctuates slightly, and the thickness of the strand fluctuates greatly. Fluctuations are large, the bite amount is low overall, and the strand cannot be drawn.-Motor load amplitude Difference between the maximum and minimum motor current values during extrusion (unit: ampere)-Resin pressure fluctuation width Extruder screw tip Difference between the maximum and minimum readings of the resin pressure gauge installed immediately after (unit: kg / cm ² )

[0016]

[Table 1]

Claims (8)

[Claims] A crude oxymethylene copolymer discharged from a polymerization machine is pulverized into powders satisfying a particle size distribution defined by the following (1) to (4), and a polymerization catalyst is deactivated. After that, the pulverized oxymethylene copolymer is melt-kneaded with a stabilizer without substantially undergoing a terminal stabilization treatment by decomposing and removing an unstable terminal portion. A method for producing a polymer. (1) Average particle size 0.3 to 0.7mm (2) 3 to 20% by weight exceeding 1.0mm (3) 50 to 97% by weight from 0.18mm to 1.0mm (4) Particle size 0-30% by weight less than 0.18mm (However, the total amount is 100% by weight) 2. A pulverized oxymethylene copolymer having a particle size of 0.3
2. The method for producing a stabilized oxymethylene copolymer according to claim 1, wherein the copolymer has unstable terminals of from 0.8 to 0.8% by weight (in the copolymer). 3. The process for producing a stabilized oxymethylene copolymer according to claim 1, wherein the crude oxymethylene copolymer is obtained by polymerization using a protonic acid as a catalyst. 4. The crude oxymethylene copolymer is obtained by polymerization by adding 15 to 25 ppm to a raw material monomer using a Lewis acid as a catalyst.
A method for producing the stabilized oxymethylene copolymer described above. 5. The stabilized oxymethylene copolymer according to claim 1, wherein the crude oxymethylene copolymer is obtained by polymerizing in the presence of a hindered phenol compound. Manufacturing method of coalescence. 6. The stabilized oxymethylene copolymer according to claim 1, wherein the crude oxymethylene copolymer is obtained by polymerization using a monomer containing 10 ppm or less of water. A method for producing a polymer. 7. The method according to claim 1, wherein the pulverization is wet pulverization, and the deactivation treatment is performed using an aqueous solution of a basic compound as a deactivation treatment agent for the polymerization catalyst. A method for producing a stabilized oxymethylene copolymer. 8. The method according to claim 7, wherein the deactivating treatment is carried out by adding a deactivating agent for the polymerization catalyst from immediately before the polymer discharge port of the polymerization machine to the entrance of the pulverizer. For producing an oxymethylene bromide copolymer.