JP2764471B2 - Method for producing stabilized oxymethylene copolymer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an oxymethylene copolymer having excellent thermal stability. More specifically, the present invention relates to a method for producing an oxymethylene copolymer having excellent thermal stability by volatilizing and reducing the residual polymerization catalyst of a crude oxymethylene copolymer obtained by copolymerizing trioxane with a cyclic ether and / or cyclic formal.

BACKGROUND ART Crude oxymethylene copolymers obtained by copolymerization of trioxane with cyclic ethers and / or cyclic formals contain an active polymerization catalyst. Usually, after the polymerization catalyst is deactivated, the terminal is stabilized using an extruder. Be transformed into

As a method of deactivating a polymerization catalyst, a method of deactivating a polymerization catalyst in an aqueous solution containing a basic substance is known. But,
This method has the disadvantage that the main chain is decomposed by water at the same time as the deactivation of the polymerization catalyst, resulting in a decrease in molecular weight and an increase in the amount of unstable terminals before terminal stabilization.

As another deactivation method, a method of adding a basic substance to a crude oxymethylene copolymer to deactivate a polymerization catalyst is known. In this method, the main chain is not decomposed at the time of deactivation, and the equipment can be simplified, which is an industrially preferable method. As an example of this method, JP-B-58-51014 discloses a method in which a tertiary phosphine compound is added as a deactivator to a crude oxymethylene copolymer and then supplied to an extruder for terminal stabilization. Also U.S. Patent 4,
751,272 describes a method of deactivating a polymerization catalyst by adding a hindered amine compound to an oxymethylene copolymer after completion of polymerization. However, in these methods, the deactivated polymerization catalyst remains in the oxymethylene copolymer and deteriorates the thermal stability of the product.

In US Pat. No. 5,344,911, copolymerization is carried out by setting the amount of a polymerization catalyst to 1 × 10 ⁻³ to 1 × 10 ⁻² mol% with respect to all monomers, and after copolymerization, the product is heated to 45 ° C. within 30 seconds. A method of cooling to the following temperature to deactivate the polymerization catalyst is described. However, in this method, the main chain is decomposed by water when the polymerization catalyst is deactivated by cooling, and the molecular weight is reduced and the amount of unstable terminals before terminal stabilization is increased.

DISCLOSURE OF THE INVENTION As a result of intensive studies to obtain an oxymethylene copolymer having good heat stability, the present inventors have reduced the residual polymerization catalyst in the oxymethylene copolymer, and obtained an oxymethylene copolymer having good heat stability. I found a method that can be manufactured.

That is, the present invention, boron trifluoride, boron trifluoride hydrate, and at least one selected from the group consisting of a coordination complex compound of boron trifluoride and an organic compound containing an oxygen atom or a sulfur atom After the completion of the polymerization of the oxymethylene copolymer comprising trioxane and cyclic ether and / or cyclic formal in the presence of the polymerization catalyst, without deactivation of the polymerization catalyst, at a temperature below the melting point and in an inert gas atmosphere. By heating and / or reducing the pressure, the polymerization catalyst is volatilized and reduced, and thereafter, the remaining polymerization catalyst is deactivated to stabilize the terminal, or the remaining polymerization catalyst is deactivated. A method for producing an oxymethylene copolymer which is directly terminal-stabilized without using the same.

INDUSTRIAL APPLICABILITY The present invention volatilizes and reduces a polymerization catalyst by a simple method such as heating in an inert gas atmosphere and / or depressurization without deactivation, and has the advantage of simple equipment. In the conventional deactivation operation using an aqueous solution containing a basic substance, a deactivation facility and a recovery facility for the basic substance are required, and a large amount of power is required for removing the deactivated polymerization catalyst because it is difficult to volatilize. It is obvious that the manufacturing method according to the present invention is more effective because of the disadvantage that the equipment is complicated.

 Further, the present invention will be specifically described.

Examples of the method for polymerizing the oxymethylene copolymer in the present invention include a bulk polymerization method and a melt polymerization method. Preferable polymerization methods include a bulk polymerization method using substantially no solvent and a quasi-bulk polymerization method using a solvent of 20% by weight or less based on a monomer, and a method of obtaining a powdery solid polymer as the polymerization proceeds. It is.

In the present invention, trioxane which is a cyclic oligomer of formaldehyde is used as the main monomer. The comonomer is a cyclic ether and / or cyclic formal. The cyclic ether and / or cyclic formal refers to a compound represented by the following general formula (1).

[Wherein, R ₁ to R ₄ are the same or different and represent a hydrogen atom, an alkyl group or a methylene group or an oxymethylene group substituted with a halogen, and R ₅ represents a methylene group or an oxymethylene group or A methylene group or an oxymethylene group each substituted with an alkyl group or a halogenated alkyl group (where p is 0 to 3)
Represents an integer. ) Means, or the formula _{- (CH 2) q -O-} CH 2 - or _{- (OCH 2 CH 2) q} -O-CH 2 - ( in this case, p is represents 1, q is 1 to 4 Represents an integer.) Means a divalent group represented by

The alkyl group has 1 to 5 carbon atoms, and 1 to 3 hydrogen atoms may be replaced by a halogen atom. As typical examples, for example, ethylene oxide,
Propylene oxide, 1,3-dioxolan, 1,
3,5-trioxepane, 1,4-butanediol formal, diethylene glycol formal, epichlorohydrin diglycol formal, and the like. Preferred comonomers in the present invention are cyclic formals, particularly preferred comonomers are 1,3-dioxolane,
Or 1,4-butanediol formal. These comonomers are added in an amount of 0.0002 to 0.15 mol per 1 mol of trioxane. Preferably it is 0.001 to 0.1 mol. In the present invention, an antioxidant may be added to the comonomer.

The polymerization catalyst in the present invention is at least one selected from the group consisting of boron trifluoride, boron trifluoride hydrate, and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride. And used as a gas or as a solution in a suitable organic solvent. A particularly preferred polymerization catalyst is boron trifluoride diethyl ether (boiling point = 126
° C), boron trifluoride dibutyl ether (boiling point = 142
C) as a coordination complex compound of boron trifluoride. These polymerization catalysts are used in an amount of 0.2 × 10 ⁻⁵ to 1 mol of all monomers.
From 100.0 × 10 ^-5 mol are added. Preferably it is from 0.3 × 10 ^-5 to 10.0 × 10 ^{-5 based} on 1 mol of all monomers. More preferably, the amount is 0.5 × 10 ⁻⁵ to 5 × 10 ⁻⁵ mol per 1 mol of all monomers.

The polymerization machine used in the present invention may be either a batch type or a continuous type. As the batch type polymerization machine, a reaction vessel with a stirrer generally used can be used. As the continuous polymerization machine, a self-cleaning mixer such as a co-kneader, a twin-screw continuous extruder, or a twin-screw paddle-type continuous mixer can be used.

The polymerization temperature is from 60 ° C to 200 ° C, preferably from 60 ° C to 120 ° C
Temperature range. The polymerization time is not particularly limited,
Generally in the range of 10 seconds to 100 minutes.

The unstable terminal portion of the oxymethylene copolymer discharged from the polymerization machine is preferably 3000 ppm or less.
Most of the molecular chain ends of polyoxymethylene copolymer is stable, but some end - (OCH ₂₎ having a structure of _n -OH, is unstable terminal to decompose by heat. When the unstable terminal portion exceeds 3000 ppm, it is necessary to perform terminal stabilization a plurality of times in order to completely perform terminal stabilization, and the equipment becomes large.

In the present invention, the granular oxymethylene copolymer discharged from the polymerization machine is heated and / or reduced under an inert gas atmosphere at a temperature equal to or lower than the melting point, and the polymerization catalyst is volatilized and reduced.

The oxymethyl copolymer discharged from the polymerization machine is preferably ground before heating and / or reducing the pressure. The pulverizer may be of a batch type or a continuous type, and a pulverizer of an impact type, a ball mill type, a jet mill type or the like can be used.

The average particle size of the milled oxymethylene copolymer is
2 mm or less. Preferably, it has an average particle size of 1 mm or less and is pulverized if necessary. If the average particle size exceeds 2 mm, the efficiency of volatilization and removal of the polymerization catalyst in the oxymethylene copolymer decreases.

The temperature at the time of heating and / or reducing the pressure of the oxymethylene copolymer is preferably from 50 ° C. to the melting point or lower. The temperature is more preferably from 100 ° C to 150 ° C. If the temperature is low, the polymerization catalyst and impurities other than the polymerization catalyst (eg, unreacted trioxane, formic acid, and alcohols) will be insufficiently removed, and if the temperature exceeds the melting point, the copolymer will melt.

Further, the heating and / or decompression time of the oxymethylene copolymer is preferably from 5 minutes to 200 minutes. More preferably, the time is from 10 minutes to 90 minutes. heating,
Alternatively, if the decompression time is short, the removal of the polymerization catalyst and other impurities will be insufficient, and if it exceeds 200 minutes, the removal of the polymerization catalyst and other impurities will be sufficient, but the apparatus will be large.

It is preferable to reduce the volatilization of the polymerization catalyst by heating and / or reducing the pressure so that the concentration of the remaining polymerization catalyst after volatilization is reduced to 10 ppm or less, because an oxymethylene copolymer having better heat stability can be obtained.

Conventionally, an oxymethylene copolymer is generally heated and dried after being brought into contact with a basic substance to deactivate the polymerization catalyst in order to suppress the main chain decomposition by the polymerization catalyst.

In the present invention, the oxymethylene copolymer and the basic substance can be heated or depressurized without being brought into contact with each other to volatilize and reduce the polymerization catalyst.

In the oxymethylene copolymer obtained in this manner, a trace amount of an active polymerization catalyst or an unstable terminal still remains. Therefore, the polymerization catalyst is deactivated and the terminal is stabilized. It is directly used for terminal stabilization without being activated.

As a method for deactivating the polymerization catalyst, a method of deactivating with a water and / or an organic solvent containing a basic substance, or a method of mixing and deactivating a basic substance in a molten state using an extruder can be used. .

Examples of the basic substance used for deactivating the polymerization catalyst include alkali metal or alkaline earth metal hydroxides, inorganic weak acid salts, and organic acid salts. As a specific example,
Lithium, sodium, calcium, magnesium, potassium, strontium, or barium hydroxide, carbonate, phosphate, silicate, borate, formate,
Acetate, stearate, palmitate, propionate, oxalate and the like. Amine compounds such as ammonia, triethylamine, and tributylamine can also be used as the deactivator.

Terminal stabilization of the copolymer can be performed by a conventionally known method, for example,
It can be carried out by melt hydrolysis in the presence of a basic substance by using a vented single screw type extruder or a vented twin screw type extruder.

As basic substances, ammonia, triethylamine,
Examples thereof include aliphatic amine compounds such as tributylamine. Other basic substances include hydroxides, inorganic weak acid salts and organic acid salts of alkali metals or alkaline earth metals. Specific examples include sodium, potassium, magnesium, calcium, or barium hydroxide, carbonate, phosphate, silicate, borate, formate, acetate, stearate, palmitate. , Propionate, oxalate and the like. Particularly, amine compounds such as ammonia, triethylamine and tributylamine are preferred.

The amount of the basic substance to be added for stabilizing the terminal is, in the case of an amine compound, relative to the oxymethylene copolymer.
0.01 to 5% by weight, alkali metal or alkaline earth metal hydroxide, inorganic weak acid salt, organic acid salt etc.
2 ppm to 5000 ppm are added.

In the present invention, water and / or an organic solvent can be added to the terminal stabilizing zone together with a basic substance.

The oxymethylene copolymer whose terminal stabilization is completed is
Unreacted monomers contained in the oxymethylene copolymer before terminal stabilization, formaldehyde generated by terminal stabilization, and the like are removed under reduced pressure in a devolatilization zone, and then pelletized.

In the present invention, the stabilizer against decomposition caused by heat, light, oxidation and the like and other additives can be added either before or after the terminal stabilization zone.

According to the method for producing a stabilized oxymethylene copolymer of the present invention, an oxymethylene copolymer having excellent heat stability and a very small amount of formaldehyde generated during melt molding can be obtained by reducing the residual polymerization catalyst of the oxymethylene copolymer. .

BEST MODE FOR CARRYING OUT THE INVENTION (Examples) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The values shown in the examples and comparative examples were measured as follows.

(Average particle size of oxymethylene copolymer) The oxymethylene copolymer was sieved, and the particle size at which the weight integrated value of the oxymethylene copolymer that had passed through the screen was 50% of the total weight of the oxymethylene copolymer was defined as the average particle size.

(Amount of residual polymerization catalyst) Oxymethylene copolymer (5 g) was added to 1N hydrochloric acid (15 g)
Decompose by heating in a fluorine ion meter (HORIBA N-8
F) The fluorine concentration (ppm) was measured.

(Amount of unstable terminal before terminal stabilization) A part of oxymethyle copolymer before terminal stabilization is taken out after polymerization is completed, inactivated with an aqueous solution containing 1% by weight of triethylamine, and heated in nitrogen at 200 ° C. for 50 minutes. The formaldehyde (ppm) generated at the time of absorption was absorbed into water and titrated and measured.

(Amount of Formaldehyde Generated) Formaldehyde (ppm) generated when the terminal-stabilized oxymethylene copolymer was heated at 230 ° C. for 100 minutes in nitrogen was absorbed into water and titrated and measured.

(Thermal stability) Resin is retained in an injection molding machine (Arburg Allrounder 100, manufactured by Western Trading) with a cylinder temperature of 230 ° C to form a molded piece of 12 × 120 × 3mm, and silver streaks are formed on the surface of the molded piece. The time (minutes) that occurred was determined.

Example 1 A twin-screw paddle type continuous mixer equipped with a jacket through which a heat medium can pass was adjusted to 80 ° C., and 12 kg / Hr of trioxane and 1,3-dioxolane as a comonomer per 1 mol of trioxane were used. 0.045 mol of methylal as a molecular weight regulator was continuously added at 0.7 × 10 ⁻³ mol. Further, 2.0 × 10 ⁻⁵ mol of boron trifluoride diethyl etherate as a polymerization catalyst was continuously added to 1 mol of trioxane to carry out polymerization. The unstable terminal amount of the obtained oxymethylene copolymer is 1950 ppm.

The oxymethylene copolymer discharged from the mixer is
Average particle size 1mm by impact type crusher under nitrogen atmosphere
In a jacketed hopper, the mixture was heated at 140 ° C. for 60 minutes under a nitrogen stream, and further heated at 50 ° C. under a nitrogen stream.
Cooled to ° C. 2,2'-methylenebis (4-methyl-6-
After adding 0.3 parts by weight of (t-butylphenol), the mixture was supplied to a twin-screw extruder with a 30 mm vent manufactured by Ikegai Iron Works. The end stabilization zone of the extruder has a blade thickness of 0.15 x (screw diameter)
It consists of a Knee Dein disk and has a length of
6.0 times.

The rotation speed of the extruder was 100 rpm, and the temperature was 200 ° C. An aqueous triethylamine solution was used as a basic substance used for terminal stabilization. The triethylamine aqueous solution was adjusted to have a ratio of water 2 to triethylamine 1 by weight. The addition amount of the triethylamine aqueous solution depends on the oxymethylene copolymer.
3 parts by weight per 100 parts by weight was added continuously to the molten oxymethylene copolymer just before the end stabilization zone of the extruder. The end-stabilized oxymethylene copolymer has a vent vacuum of 30 torr after the end-stabilization zone.
Devolatilized under the following conditions. The oxymethylene copolymer obtained from the extruder die was extruded as a strand and pelletized.

After the polymerization of the oxymethylene copolymer, the residual polymerization catalyst (fluorine concentration) after heating and after terminal stabilization, the amount of formaldehyde generated after terminal stabilization, and the thermal stability were measured. Table 1 shows the results.

(Example 2) Example 1 was repeated except that the oxyretylene copolymer discharged from the mixer was not pulverized (average particle size: 3.5 mm).
The same operation as described above was performed. Table 1 shows the results.

Example 3 The polymerization catalyst was added in an amount of 1.2 to 1 mol of trioxane.
The same operation as in Example 1 was performed except that the amount was changed to × 10 ^-5 mol. Table 1 shows the results.

(Example 4) Except that the comonomer was changed to 1,4-butanediol formal, the same operation as in Example 1 was performed. Table 1 shows the results.

(Example 5) Example 4 was repeated except that the oxyretylene copolymer discharged from the mixer was not pulverized (average particle size: 3.5 mm).
The same operation as described above was performed. Table 1 shows the results.

(Example 6) The polymerization catalyst was added in an amount of 1.2 to 1 mol of trioxane.
The same operation as in Example 4 was performed except that the amount was changed to × 10 ^-5 mol. Table 1 shows the results.

Example 7 Example 1 was repeated except that the heated oxymethylene copolymer was stirred and mixed with an aqueous solution containing 4% by weight of 5% by weight of triethylamine to deactivate the catalyst, followed by dehydration and conversion at 140 ° C. for 60 minutes. The same operation as described above was performed. Table 1 shows the results.

Example 8 The same operation as in Example 1 was performed except that the catalyst was deactivated by adding 0.03% by weight of calcium hydroxide to the heated oxymethylene copolymer. Table 1 shows the results.

(Comparative Example 1) The same operation as in Example 1 was performed except that pulverization and heating were not performed. Table 1 shows the results.

(Comparative Example 2) Without heating the ground oxymethylene copolymer,
Exactly the same operation as in Example 1 was performed, except that after deactivation with an aqueous solution containing 5% by weight of triethylamine, dehydration and drying at 140 ° C. for 6 minutes. Table 1 shows the results.

INDUSTRIAL APPLICABILITY As is clear from the examples, according to the present invention, by reducing the residual polymerization catalyst in the oxymethylene copolymer, excellent heat stability and very low formaldehyde odor during melt molding are obtained. A methylene copolymer is obtained.

Claims (6)

(57) [Claims] 1. Trioxane and a cyclic ether and / or cyclic formal are formed from boron trifluoride, boron trifluoride hydrate, and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride. After copolymerization in the presence of at least one polymerization catalyst selected from the group consisting of, and after completion of the polymerization of the resulting oxymethylene copolymer, without passing through the polymerization catalyst deactivation operation, at a temperature below the melting point, an inert gas By heating and / or reducing the pressure in an atmosphere, the polymerization catalyst is volatilized and reduced, and thereafter, the remaining polymerization catalyst is deactivated to stabilize the terminal, or the remaining polymerization catalyst is stabilized. A method for producing an oxymethylene copolymer which directly stabilizes the terminal without deactivating oxymethylene. 2. The method for producing an oxymethylene copolymer according to claim 1, wherein the oxymethylene copolymer is pulverized to an average particle size of 2 mm or less before volatilization of the polymerization catalyst is reduced. (3) Trioxane and cyclic formal are copolymerized at a polymerization catalyst concentration of 5.0 × 10 ^-6 to 5.0 × 10 ^-5 mol per 1 mol of all monomers, and the amount of oxymethylene copolymer discharged from the polymerization machine is reduced. 3. The method for producing an oxymethylene copolymer according to claim 1, wherein the stable terminal portion is 3000 ppm or less. 4. The method according to claim 1, wherein the cyclic ether and the cyclic formal are each 1,1.
2. The method for producing an oxymethylene copolymer according to claim 1, wherein said copolymer is 3-dioxolane and 1,4-butanediol formal. 5. The polymerization by heating and / or reducing the pressure in an inert gas atmosphere at a temperature from 50 ° C. to the melting point for 5 minutes to 200 minutes without deactivating the polymerization catalyst. The method for producing an oxymethylene copolymer according to claim 1, wherein the catalyst is volatilized and reduced. 6. The concentration of the remaining polymerization catalyst in the oxymethylene copolymer after the volatilization of the polymerization catalyst has been reduced to a fluorine concentration of 10%.
2. The method for producing an oxymethylene copolymer according to claim 1, wherein the amount is not more than ppm.