JPH07233230A - Production of polyoxymethylene excellent in color tone and thermal stability - Google Patents

Abstract

PURPOSE:To improve color tone and thermal stability by hydrolyzing a melt of a specific oxymethylene copolymer with a specific hydrolyzing agent. CONSTITUTION:One mole of trioxane is polymerized with 0.001-0.75mol of 1,3- dioxolane and/or 1,3,5-trioxepane each containing 10-500ppm sterically hindered phenol in the presence of 0.1X10<-5> to 5X10<-5>mol of an acid catalyst in a batch or continuous polymerizer at 0-200 deg.C for 2min to 3hr at a reduced pressure to 100atm to obtain a crude oxymethylene copolymer having a content of unstabilized terminals of 300-3,000ppm. This copolymer is supplied to a continuous extruder, as a terminal stabilizer, together with 5-500ppm at least one alkali (alkaline earth) metal hydroxide, 0.01-5wt.% aliphatic amine, and 0.1-5wt.% water or alcohol having a boiling point of 50-150 deg.C. The copolymer is hydrolyzed at a temp. between the melting point of the copolymer and 265 deg.C for 0.1-3min, excluding 3min. The hydrolyzate is deaerated at a reduced pressure in a deaeration zone, and then pelletized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for industrially producing an oxymethylene copolymer excellent in color tone and thermal stability.

[0002]

2. Description of the Related Art Oxymethylene copolymers are well known as extremely useful engineering resins with well-balanced physical properties. However, in order to obtain oxymethylene copolymers having practical thermal stability, the polymerization reaction must be completed. After that, the polymerization catalyst is neutralized and deactivated, and the catalyst is removed by washing,
Stabilization of polymer terminals and addition of stabilizers have been carried out. As a method for stabilizing the polymer terminal, Japanese Patent Publication No. 56-33
As disclosed in Japanese Patent No. 416, a hydroxide of an alkali metal or an alkaline earth metal, ammonia, an amine,
A method of hydrolyzing with water or alcohol in the presence of an alkaline substance such as amidine is known.

[0003]

SUMMARY OF THE INVENTION In these conventional methods,
It is difficult to obtain a stabilized oxymethylene copolymer having excellent thermal stability and having almost no unstable portion,
It was necessary to increase the reaction time, the reaction temperature, the amount of the alkaline substance, etc., but when such reaction conditions were increased, the polymer was colored yellow. Therefore, it has been difficult to obtain a stabilized oxymethylene copolymer excellent in color tone and excellent in thermal stability having almost no unstable portion.

[0004]

[Means for Solving the Problems] In order to solve the above problems,
As a result of various studies, it was found that an oxymethylene copolymer excellent in color tone and thermal stability can be obtained by using a limited oxymethylene copolymer and a hydrolyzing agent. That is, according to the present invention, in stabilizing an oxymethylene copolymer having an unstable terminal, an oxymethylene copolymer having an unstable terminal portion of 300 to 3000 ppm of the oxymethylene copolymer is used as a raw material, and an alkali metal hydroxide is added to the oxymethylene copolymer. 5 or 5 of at least one of the compounds or alkaline earth metal hydroxides
00 ppm, 0.01 to 5 wt% of an aliphatic amine, 0.1 to 5 wt% of water or an alcohol having a boiling point in the range of 50 to 150 ° C. are coexisted with the oxymethylene copolymer to melt and hydrolyze, and then in a molten state. The present invention relates to a method for producing an oxymethylene copolymer excellent in color tone and thermal stability, which is characterized by degassing under reduced pressure.

The polymerization method of the oxymethylene copolymer in the present invention includes a bulk polymerization method and a melt polymerization method. As a preferable polymerization method, there is a bulk polymerization method using substantially no solvent or a quasi-bulk polymerization method using 20% or less of a solvent with respect to a monomer. is there.

The polymerization apparatus used in the present invention may be either a batch type or a continuous type, and as the batch type polymerization apparatus, a reaction vessel with a stirrer which is generally used can be used. As the continuous polymerization apparatus, a self-cleaning type mixer such as a cokneader, a twin-screw type continuous extrusion kneader, or a twin-screw paddle type continuous mixer can be used. The polymerization temperature is 0 to 200 ° C, preferably 60 to 170 ° C, more preferably 80 to 120 ° C. Reaction time is about 2 minutes
3 hours. The reaction pressure is from reduced pressure to 100 atm, preferably 1 atm to 10 atm.

The important point in the present invention is that the unstable terminal portion of the crude oxymethylene copolymer is 300 to 30.
It is to be 00 ppm. 300 unstable ends
When the content is 0 ppm or more, it is difficult to stabilize the end of the polymer without coloring the polymer, and it becomes difficult to produce an oxymethylene copolymer having excellent color tone and thermal stability. Most molecular chain terminals of the crude oxymethylene copolymer is stable, but some end - is unstable with respect to (0CH ₂₎ heat has the structure of -OH. This unstable terminal is produced during the polymerization and during the subsequent post-treatment by water contained in the raw materials such as trioxane and cyclic ether, and trace impurities having active hydrogen such as methanol and formic acid.

Therefore, in order to reduce the unstable terminal portion, it is necessary to carry out the polymerization while paying attention to the following comonomer, polymerization catalyst concentration, and impurity concentration in the raw material. The main monomer used in the present invention is formaldehyde or trioxane which is a cyclic oligomer of formaldehyde. As the comonomer, cyclic ether and / or cyclic formal represented by the following formula (1) can be used.

[0009]

[Chemical 1] However, in the formula, R ₁ to R ₄ are the same or different and mean a hydrogen atom, an alkyl group, or a halogen-substituted methylene group or an oxymethylene group,
R ₅ represents a methylene group or an oxymethylene group, or a methylene group or an oxymethylene group substituted by an alkyl group or a halogenated alkyl group (in this case, p represents an integer of 1 to 3), or- (C
H ₂₎ q-OCH ₂ - or - (OCH ₂ CH ₂₎ q
It means a divalent group represented by —O—CH ₂ — (in this case, p represents 1 and q represents an integer of 1 to 4).
The alkyl group has 1 to 5 carbon atoms, and 1 to 3 hydrogens may be replaced by halogen atoms.

Typical examples thereof include 1,3-dioxolane, 1,4-butanediol formal, epichlorohydrin diglycol formal and the like. Particularly preferred comonomers in the present invention are cyclic formal such as 1,3 dioxolane, 1,3,5 trioxepane, and 1,4 butanediol formal, and further, a sterically hindered phenol compound is added to the cyclic formal.
Those containing 0 to 500 ppm are preferable. Here, the sterically hindered phenols are antioxidants or free radical scavengers generally used in the field of plastics.

Specifically, 2-2'-methylenebis (4
Methyl-6-t-butylphenol), hexamethyleneglycol-bis (3,5-di-t-butyl-4hydroxyhydrocinnamate), tetrakis [methylene (3,5-di-t-butyl-4hydroxyhydrocinnamate) Mate)] methane, triethylene glycol-bis-3
-(3-t-Butyl-4-hydroxy-5-methylphenyl) propionate, 1,3,5-trimethyl-2,
4,6-Tris (3,5-di-butyl-4-hydroxy-benzyl) benzene, 4,4'methylenebis (2,6
-Di-t-butylphenol, octadecyl-3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-
Butyl-6- (3-t-butyl-5-methyl-2-hydroxybenzyl) -4-methylphenyl acrylate and the like can be mentioned.

The amount of comonomer of the present invention is trioxane 1
0.001 to 0.75 mol, and more preferably 0.
005 to 0.1 mol is preferable.

Preferred polymerization catalysts in the present invention are boron trifluoride, boron trifluoride hydrate, and coordination complex compounds of boron trifluoride with an organic compound containing an oxygen atom or a sulfur atom, which are gaseous. Alternatively, it is used as a solution of a suitable organic solvent. A particularly preferable polymerization catalyst is a coordination complex compound of boron trifluoride, and specific examples thereof include boron trifluoride diethyl ether and boron trifluoride dibutyl ether. These polymerization catalysts are added in an amount of 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mol based on 1 mol of all monomers. Particularly preferably, it is 0.5 × 10 ⁻⁵ to 2 × 10 ⁻⁵ mol.

It is necessary to reduce the concentration of trace impurities having active hydrogen such as water, methanol and formic acid in raw materials such as trioxane and cyclic ether as much as possible. 3 unstable ends
In order to reduce the concentration to 0.00 to 3000 ppm or less, it is necessary to convert the concentration of trace impurities having active hydrogen into the concentration of water, and to make the total concentration 20 ppm or less with respect to trioxane. Specifically, the conversion value to the water concentration is obtained by multiplying the methanol concentration by 0.28 times in the case of methanol and by the formic acid concentration by 0.20 times in the case of formic acid.

The crude oxymethylene copolymer thus obtained contains an active polymerization catalyst. Therefore, the polymerization catalyst is usually deactivated. As a method of deactivating the polymerization catalyst, a method of deactivating the polymerization catalyst in an aqueous solution containing a basic substance or in an organic solvent can be used. As another deactivating method, a method of adding a basic substance to the crude oxymethylene copolymer and deactivating it in a molten state by using an extruder can also be used.

Examples of the basic substance used for deactivation include alkali metal or alkaline earth metal hydroxides, weak inorganic acid salts, organic acid salts and the like. As a concrete example,
Lithium, sodium, potassium, magnesium, calcium, strontium, or barium hydroxide, carbonate, phosphate, silicate, borate, formate,
Examples thereof include acetate, stearate, palmitate, propionate and oxalate. Further, amine compounds such as ammonia, triethylamine and tributylamine can also be used as the quenching agent. Since the deactivated crude oxymethylene copolymer has a thermally unstable terminal portion as it is, it is necessary to perform terminal stabilization.

As the terminal stabilizer in the present invention, a continuous extruder such as a twin screw type extruder with a vent and a single screw type extruder with a vent can be used. The terminal stabilizer removes the melting zone that melts the crude oxymethylene copolymer, the terminal stabilization zone that hydrolyzes the unstable terminal portion, the formaldehyde generated by the decomposition of the unstable terminal portion, and the water added to the terminal stabilization zone. It consists of a devolatilization zone, and can be performed using one extruder or a plurality of extruders.

Unstable end portion is 300 to 3000 ppm
The crude oxymethylene copolymer of (1) is fed to an extruder and first melted. Extrusion temperature is from the melting point of the polymer to 265 ° C.
Temperature range. Particularly preferred temperature is 200 ° C to 2
It is 30 ° C. When the temperature is 265 ° C. or higher, the molecular weight is reduced due to the main chain breaking of the polymer, which is not preferable. The molten crude oxymethylene copolymer is stabilized in the end stabilization zone in the presence of the end stabilizer in the unstable end.

One of the more important points of the present invention is the selection of the end stabilizer. The terminal stabilizer of the present invention is one or more alkali metal hydroxides or alkaline earth metal hydroxides such as sodium, potassium, magnesium, calcium, or barium, and triethylamine,
One type of aliphatic amine such as tributylamine and one or more types of alcohol having a boiling point in the range of 50 to 150 ° C. such as water or methanol, ethanol, isopropyl alcohol and the like are used.

Surprisingly, in the terminal stabilization of the crude oxymethylene copolymer having an unstable terminal portion of 300 to 3000 ppm, which is a feature of the present invention, triethylamine, tributylamine and the like which are often used for terminal stabilization are usually used. It is difficult to achieve sufficient terminal stabilization only by using an aliphatic amine and water or an alcohol.

The amount of the terminal stabilizer used in the present invention is
5 ~ 500p for alkali metal hydroxide or alkaline earth metal hydroxide for oxymethylene copolymer
Water or alcohol having a boiling point in the range of 50 to 150 ° C. is 0.1 to 5 wt%. Further, the amount of aliphatic amine is 0.01-5 wt%. If the amount of the alkali metal hydroxide or alkaline earth metal hydroxide exceeds 500 ppm, the oxymethylene copolymer is colored, which is not preferable.

Addition of an alkali metal hydroxide or alkaline earth metal hydroxide to the oxymethylene copolymer may be fed to the extruder end stabilization zone with water or alcohol, or the oxymethylene copolymer may be fed to the extruder. Before addition, the polymer is added and mixed, and water or alcohol is separated and fed to the extruder end stabilization zone.

The reaction time for terminal stabilization in the present invention is 0.1 minute or more and 3 minutes or less, preferably 0.3 to 1.5 minutes. When the reaction time is 0.1 minutes or less, the terminal hydrolysis reaction is not completely carried out, so that an oxymethylene copolymer having unstable terminal portions remains is obtained, and the thermal stability is poor. Further, when the reaction time is 3 minutes or more, coloring of the oxymethylene copolymer occurs, which is not preferable.

The polymer whose terminal stabilization has been completed is pelletized after water, formaldehyde generated by terminal stabilization and the like are removed under reduced pressure in a devolatilizing zone. In addition, in the present invention, the addition of the stabilizer against the decomposition caused by heat, light, oxidation and the like and the addition of other additives can be added before or after the terminal stabilization.

[0025]

According to the present invention, an oxymethylene copolymer having excellent color tone and thermal stability can be easily obtained.

[0026]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. The values shown in Examples and Comparative Examples are
The polymer was dried in a vacuum dryer at 80 ° C. for 2 hours and then measured as follows. Unstable terminal portion: Heat-melted at 200 ° C. under a nitrogen stream, formaldehyde generated in 50 minutes was absorbed in a sulfite aqueous solution, and then titrated with a sulfuric acid aqueous solution for measurement. MI; using the Toyo Seiki MELTINDER,
The fluidity was measured under the conditions of 190 ° C. and 2160 gr. Color tone: The color tone was measured using MODEL 1000DP manufactured by Nippon Denshoku.

Example 1 A 5 L kneader having two stirring blades with a jacket through which a heat medium can be passed was adjusted to 80 ° C., and trioxane (3 Kg) and triethylene glycol as a sterically hindered phenol were used. Bis- (3- (3-t-butyl-
1,3-Dioxolane (4.5 mol% based on trioxane) containing 100 ppm of 5-methyl-4-hydroxyphenyl) propionate) and methylal (0.3 mol% based on trioxane) were mixed. The concentration of trace impurities (water, methanol, formic acid) contained in this mixture was 6 ppm in terms of water.

Boron trifluoride dibutyl etherate was added to this mixture as a polymerization catalyst in an amount of 0.1 to trioxane.
Polymerization was carried out by adding 2 × 10 ⁻² mol%. 30 minutes later 30
2 L of an aqueous solution containing 1% of triethylamine was added through a heating medium at a temperature of 0 ° C. to carry out deactivation treatment for 1 hour. The obtained content was filtered and dried to obtain 2.7 kg of polymer. The unstable terminal portion of the obtained oxymethylene copolymer is
It was 1200 ppm and MI = 10.4.

2,2'-as an antioxidant to this polymer
After adding 0.3 parts by weight of methylenebis (4-methyl-6-t-butylphenol), 30 mm manufactured by Ikegai Iron Works
It was fed to a twin-screw extruder with a vent. The extruder had a screw configuration having a melting zone divided by a seal ring, an end stabilization reaction zone and a degassing zone.
The temperature was 200 ° C., calcium hydroxide / triethylamine / water was used as the terminal stabilizer, and 100 ppm / 0.15 / 3 wt% of the polymer was supplied to the extruder terminal stabilization zone. The degassing zone was devolatilized under the condition that the vent vacuum degree was 30 torr. The polymer obtained from the extruder die part was extruded as a strand and pelletized. Table 3 shows the measurement results of the unstable terminal portion after the terminal stabilization and the measurement results of MI and color tone.

Examples 2 to 12 L / D has a cross section in which circles having an inner diameter of 50 mm partially overlap each other.
= 14. A continuous mixing reactor (KRC) consisting of a barrel with a jacket that allows a heat medium to pass through it, and two rotating shafts with multiple paddles that mesh with each other inside.
-Kneader manufactured by Kurimoto Steel Co., Ltd., with a jacket temperature of 80 ° C, trioxane (3 kg / h), and triethylene glycol-bis- as sterically hindered phenol.
1,3 containing 100 ppm of (3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate)
-Dioxolane, methylal (0.
3 mol%) and boron trifluoride dibutyl etherate as a polymerization catalyst were continuously supplied to carry out polymerization. The concentrations of trace impurities (water, methanol, formic acid), the amount of comonomer, and the amount of polymerization catalyst in the raw material monomer were the concentrations shown in Table 1.

1 part of the polymer discharged from the polymerization machine was taken out into an aqueous solution containing 1% of triethylamine under a nitrogen atmosphere, deactivated for 1 hour, filtered and dried to evaluate the polymer. I went. The results are shown in Table 1. The other polymer discharged from the polymerizer was taken out under a nitrogen atmosphere, and then the polymer was added to 2,2-
After adding 0.3 part by weight of methylene bis- (4 methyl-6-t-butylphenol), it was subjected to end stabilization by the twin-screw extruder used in Example 1. The end stabilization conditions were exactly the same as in Example 1 except that the end stabilizers shown in Table 3 were used to obtain pellets. Table 3 shows the measurement results of the unstable terminal portion after the terminal stabilization and the measurement results of MI and color tone.

Comparative Examples 1 to 5 Using the same continuous mixing reactor as in Example 2, trioxane (3 Kg / h), ethylene oxide (4.5 mol% based on trioxane) and methyla were used at a jacket temperature of 80 ° C. -(0.3 mol% with respect to trioxane) and boron trifluoride dibutyl etherate as a polymerization catalyst were continuously supplied so as to be 0.60 × 10 ^-2 mol% with respect to trioxane to carry out polymerization. . The concentration of trace impurities (water, methanol, formic acid) in the raw material monomer was the concentration shown in Table 2 in terms of water.

The polymerized polymer discharged from the polymerization machine was taken out in an aqueous solution containing 1% of triethylamine under a nitrogen atmosphere and subjected to a stirring deactivation treatment for 1 hour. The obtained polymer was filtered and dried to obtain a crude oxymethylene copolymer. The unstable terminal portion of the obtained oxymethylene copolymer had the values shown in Table 2. Then the polymer 2,2
After adding 0.3 part by weight of -methylenebis- (4methyl-6-t-butylphenol), terminal stabilization was performed by the twin-screw extruder used in Example 1. The end stabilization conditions were exactly the same as in Example 1 except that the end stabilizers shown in Table 4 were used to obtain pellets. Measurement results of the unstable terminal portion before and after terminal stabilization and measurement results of MI and color tone (Comparative Example 5
Is the result) is shown in Table 4.

Comparative Example 6 to Comparative Example 7 The same as Example 2 except that the crude oxymethylene copolymer obtained in Example 2 was used and the terminal stabilizer and the amount of the terminal stabilizer shown in Table 4 were used. The ends were stabilized.
Table 4 shows the measurement results of the unstable terminal portion of the polymer before and after the terminal stabilization, and the measurement results of MI and color tone.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

Claims (3)

[Claims] 1. Stabilization of an oxymethylene copolymer having an unstable terminal, an oxymethylene copolymer having an unstable terminal portion of 300 to 3000 ppm of the oxymethylene copolymer is used as a raw material, and an alkali metal hydroxide is added to the oxymethylene copolymer. 5 to 500 pp of at least one alkaline earth metal hydroxide or alkaline earth metal hydroxide
m, 0.01 to 5 wt% of aliphatic amine, 0.1 to 0.1% of water or alcohol having a boiling point of 50 to 150 ° C.
A method for producing an oxymethylene copolymer, which comprises co-existing with 5 wt% of the oxymethylene copolymer, melt-hydrolyzing the oxymethylene copolymer, and then degassing under reduced pressure in a molten state. 2. The oxymethylene copolymer before stabilization contains trioxane and 1,3 with respect to 1 mol of trioxane.
0.001 to 0.75 mol of dioxolane or / and 1,3,5 triioxepane and 1 m of trioxane
The method for producing an oxymethylene copolymer according to claim 1, wherein the oxymethylene copolymer is obtained by polymerizing in the presence of 0.1 × 10 ^{−5 to} 5 × 10 ⁻⁵ mol of an acid catalyst with respect to ol. 3. The 1,3 dioxolane or / and 1,3,5 tritoxepane to be subjected to the polymerization is used to convert the sterically hindered phenols into 1,3 dioxolane or / and 1,
10 to 500 ppm for 3,5 trioxepane
The method for producing an oxymethylene copolymer according to claim 2, which comprises: