KR970006669B1 - Method for manufacturing oxymethylene copolymer - Google Patents

Abstract

None.

Description

[Name of invention]

Process for preparing oxymethylene copolymer

Detailed description of the invention

The present invention relates to a process for preparing a stabilized oxymethylene copolymer.

Japanese Patent Laid-Open No. 61-152716 discloses a method for producing a coarse oxymethylene copolymer by copolymerizing formaldehyde gas and cyclic ether in the presence of a catalyst. Sub) 44-5234 discloses a process for preparing crude oxymethylene copolymers by copolymerizing trioxane and cyclic ethers in the presence of a catalyst. The coarse oxymethylene copolymers obtained by these methods have thermally labile moieties composed of oxymethylene repeating units at the main chain ends, so that the thermal labile moieties need to be decomposed and removed.

Various methods have also been proposed for the method of decomposing and removing the terminal heat labile portion of the coarse oxymethylene copolymer, but for example, coarse oxymethylene air as described in Japanese Patent Application Laid-Open No. 58-11450 The method of heat melting the coalescence is one of the preferred methods in view of operability and economy.

However, it is necessary to remove the activity of a copolymerization catalyst beforehand in order to heat-melt a coarse oxymethylene copolymer and remove terminal thermally stable part. This is because, when the coarse oxymethylene copolymer is heated and melted without removing the activity of the copolymerization catalyst, the copolymerization catalyst acts as a depolymerization catalyst, which significantly lowers the molecular weight of the copolymer.

Various methods are known also regarding the method of removing the activity of the copolymerization catalyst contained in a crude oxymethylene copolymer.

Japanese Laid-Open Patent Publication No. 61-151219 discloses a method of copolymerizing formaldehyde and 1,3,6-trioxocane with a boron trifluoride catalyst and removing ammonia by contacting ammonia gas. . In Japanese Patent Publications (SO) 55-45087 and (SO) 55-50485, trioxane and the like are polymerized with a boron trifluoride catalyst, and then trivalent phosphorus compounds are added to remove the activity of the catalyst. Japanese Laid-Open Patent Publication Nos. 62-267311, 63-12617 and 63-27519 are added to hindered amines to remove the activity of the catalyst. This is described.

In accordance with the teaching of Japanese Patent Laid-Open No. 61-151219, the coarse oxymethylene copolymer which has been contacted with ammonia gas to remove the activity of the catalyst is heated and melted in the presence of a stabilizer to decompose and remove the heat labile portion. The stable oxymethylene copolymer obtained has the drawback to be colored yellow. In the case of using a trivalent phosphorus compound, the copolymer may be heated to 140 to 260 ° C. and melt-decompose the terminal labile moiety, whereby the molecular weight may be lowered. In addition, even when a hindered amine is added to remove the activity of the catalyst, There is a problem that the copolymer is colored yellow.

The present inventors studied the cause of the yellowing of the copolymer obtained by heating and melting a coarse oxymethylene copolymer obtained by contacting with ammonia gas to remove the activity of the catalyst. It has been found that the reaction product of formaldehyde and ammonia gas generated when melt decomposing the unstable portion is a great cause of the coloration and has reached the present invention.

The present invention

(1) A coarse oxymethylene copolymer powder having a thermally labile moiety composed of oxymethylene repeating units at the main chain terminal and containing a copolymerization catalyst is contacted with an excess of ammonia gas to the catalyst to remove the activity of the copolymerization reaction. 1 step; A second step of blowing an inert gas into the coarse oxymethylene copolymer powder obtained in the first step to remove ammonia gas remaining in the copolymer; And dissolving and removing the coarse oxymethylene copolymer powder obtained in the second step by heating and melting in the presence of a stabilizer within a temperature range of 100 ° C. higher than the melting point or melting point of the copolymer. Method for producing a stabilized oxymethylene copolymer consisting of three steps and

(2) The coarse oxymethylene copolymer is formaldehyde copolymer, and before contacting the coarse formaldehyde copolymer powder with ammonia gas, an inert gas is blown into the copolymer powder to remove unreacted formaldehyde gas remaining in the copolymer. It relates to a method for producing a stabilized oxymethylene copolymer of the above (1).

Next, each process of this invention is demonstrated.

[Step 1]

Crude oxymethylene copolymers can be prepared by copolymerizing formaldehyde or trioxane with cyclic ethers in the presence of a copolymerization catalyst, according to methods known per se.

The cyclic ether used is, for example, a compound of the following general formula.

Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each a hydrogen atom, an alkyl group, an allyl group and a cycloalkyl group, l, m and n are each an integer of 1 to 6, l, At least one of m and n is an integer of 2 or more, and a, b and c are each 0 or 1, respectively.

Particularly preferred compounds of the cyclic ethers are, for example, ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepan, 1,3,5-trioxepan, 1 , 3,6-trioxocane and epichlorohydrin.

The proportion of cyclic ethers in the crude oxymethylene copolymer is preferably in the range of 0.05 to 10 mol%, in particular 0.1 to 5 mol% relative to the oxymethylene unit. When the ratio is less than 0.05 mol%, the yield of the copolymer is low when the terminal unstable portion is decomposed and stabilized, and when the ratio is more than 10 mol%, the melting point and crystallinity of the copolymer are lowered and mechanical The nature and thermal properties deteriorate.

Specific examples of the copolymerization catalyst capable of removing the activity with ammonia include boron trifluoride, boron trifluoride-based hydrates, and organic compounds having oxygen or sulfur atoms and actor compounds of boron trifluoride. The copolymerization catalyst can be used as a solution of gaseous, liquid or organic solvent. Examples of organic compounds having oxygen or sulfur atoms which form coordination compounds with boron trifluoride are alcohols, ethers, phenols and sulfides. Particularly preferred copolymerization catalysts are boron trifluoride, boron trifluoride-diethyl etherate and boron trifluoride-dibutyl etherate.

Examples of the solvent for the copolymerization catalyst include aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane, heptane and cyclohexane, alcohols such as methanol and ethanol, halogenated hydrocarbons such as chloroform, dichloromethane and 1,2-dichloroethane and acetone. Ketones, such as methine ethyl ketone, are used. The amount of the polymerization catalyst added is in the range of 5 × 10 ⁻⁶ to 1 × 10 ⁻¹ mole with respect to 1 mole of formaldehyde or trioxane.

Apparatus for copolymerizing formaldehyde or trioxane with cyclic ethers are typically kneaders with well known Σ stir blades and reaction zones using cylindrical barrels, having coaxial and screw with a number of suspended acids in the barrel. A conventional screw extruder with a parallel screw such that a pair is mated with each other in a long case with a jacket for heating or cooling, a mixer operating to engage the gears protruding from the stop and the inner surface of the barrel; And a self-cleaning mixer that rotates while maintaining the slight spacing of the paddle surface and the inner surface of the opponent when the axes are simultaneously rotated in the same direction.

Particularly, in the bulk copolymerization with trioxane, rapid solidification and exotherm occur during polymerization, a device having strong stirring ability and controlled reaction temperature is preferable. It is also applicable to copolymerization in the presence of an organic solvent such as cyclohexane up to 10% by weight relative to trioxane.

The polymerization temperature is usually in the range of 40 to 80 ° C., near the boiling point, that is, 60 to 115 ° C., particularly preferably 60 to 90 ° C., when using formaldehyde gas.

The powdery crude oxymethylene copolymer obtained by copolymerizing formaldehyde or trioxane with cyclic ether in this manner is contacted with and substituted with ammonia gas.

As a method of making a powdery coarse oxymethylene copolymer contact ammonia gas, the following method can be employ | adopted, for example.

(1) A method of supplying and dropping a copolymer from the top of a cylindrical vessel, blowing ammonia gas from the bottom portion, and condensing the copolymer and ammonia gas.

(2) After introducing ammonia gas into a container containing a copolymer, vacuuming the inside of the container and repeating this operation several times.

(3) A method of introducing a copolymer into a vessel having a bottom funnel shape and blowing ammonia gas from the bottom.

When the coarse oxymethylene copolymer is a formaldehyde copolymer, it is preferable to blow an inert gas into the copolymer powder to remove the unreacted formaldehyde gas remaining in the copolymer before contacting the ammonia gas. This operation exerts a remarkable effect on lowering the molecular weight and preventing the coloring of the finally obtained stabilized oxymethylene copolymer.

The amount of ammonia used is excessively used relative to the number of moles of the catalyst contained in the copolymer, and is preferably at least 2 times mole, particularly at least 5 times mole of the mole number of the catalyst. Before contact with ammonia gas, the crude oxymethylene copolymer can be milled. The coarse oxymethylene copolymer obtained by the bulk polymerization of trioxane and cyclic ether is rapidly solidified at the beginning of the polymerization, and it is pulverized and taken out in the stirrer of the polymerization apparatus. .

[Step 2]

The crude oxymethylene copolymer powder obtained in the first step is introduced into the air stream of the inert gas to the copolymer, catalyst, ammonia and formaldehyde gas to replace the excess ammonia gas with the inert gas.

As the inert gas, inorganic gases such as nitrogen gas, air, carbon gas, helium and argon, organic gases such as methane, pentane and butane and mixed gas thereof can be used.

As the substitution method, the same method as that employed in the method of contacting the coarse oxymethylene copolymer and ammonia gas in the first step can be adopted, except that inert gas is used instead of ammonia gas.

[Step 3]

The coarse oxymethylene copolymer obtained in the second step is heated and melted according to a method known per se and the terminal heat labile portion is decomposed and removed to obtain a stabilized oxymethylene copolymer.

Examples of stabilizers include hindered amines, phenolic antioxidants and formaldehyde absorbents.

As a hindered amine, the thing of Unexamined-Japanese-Patent No. 62-257922 is contained, The content of this publication comprises a part of this specification. Specific examples of hindered amines are bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate.

As phenolic antioxidant and a formaldehyde absorbent, the thing of Unexamined-Japanese-Patent No. 63-75019 is contained, The content of this publication comprises a part of this specification. Specific examples of the phenolic antioxidant include triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], and a specific example of formaldehyde absorbent is melamine. have.

The amount of the stabilizer added is 0.01 to 10% by weight, preferably 0.02 to 5.0% by weight, more preferably 0.05 to 3.0% by weight based on the crude oxymethylene copolymer, and less than 0.01% by weight is not sufficient to improve the heat resistance. However, if the content exceeds 10% by weight, the stabilizer is precipitated in the form of white powder on the surface of the oxymethylene copolymer, which is not preferable because the product price is lowered.

In addition to the stabilizer, the thermally labile portion is quickly decomposed and removed by using a decomposition accelerator for the terminal thermally labile portion. Examples of terminal decomposition accelerators include those described in JP-A-63-75019, and specific examples thereof include calcium hydroxide and magnesium hydroxide.

Crude oxymethylene copolymers are generally hot melted in a degasser. As the apparatus, a well-known apparatus can be generally used, and examples thereof include a single vent vent extruder having a hole, a twin screw vent extruder having a hole, and a continuous mixed heating degassing apparatus suitable for other high viscosity materials. In the apparatus, it is important to have a vent hole or a degassing vent hole, and the inside of the apparatus is sucked out of the hole so as to be vacuum or reduced pressure to promote the exhaust of gas generated from the copolymer or water which is already added by addition. It is preferable. In addition, it is desirable to increase the surface renewal and the degassing effective area by sufficient kneading.

The heat-melting temperature of the coarse oxymethylene copolymer is at least the melting point of the copolymer, preferably in a range up to a temperature of 100 ° C. above the melting point. The melt treatment time depends on the amount of the terminal unstable portion of the copolymer and the melt treatment temperature, but is 1 to 120 minutes, preferably 10 to 90 minutes.

Before melt stabilization, final products such as lubricants, nucleating agents, mold release agents, colorants, antistatic agents, light stabilizers, glass fibers, carbon fibers, potassium titanate fibrous reinforcements, inorganic reinforcing agents such as talc, calcium carbonate, mica, polymers or low molecular organic modifiers As an additive, all necessary additives may be added, kneaded and treated, followed by pelletization and stabilization, and at the same time, it may be made into an oxymethylene composition product. It can also be

Reference Example

Next, reference examples of the present invention are shown.

Reference Example 1

In many elliptical shapes, two horizontal stirring shafts with mixing stirring blades are housed in the outer case, and when the stirring blades are rotated, there is a slight gap between the surfaces of the mixing stirring blades and the inner wall of the case. 1,3,6-trioxokane in a polymerization apparatus (described in Japanese Laid-Open Patent Publication No. 59-115318) consisting of a biaxial mixing stirrer with a hopper and an external circulation cooler connected thereto. Hereinafter, 50 kg of an oxymethylene copolymer composed of formaldehyde (hereinafter referred to as FA) and TOC containing about 2 mol%) is introduced, and this is circulated at 600 kg / h. Gas phase FA having a water content of 50 to 80 ppm at 6 kg / h, gaseous TOC at 480 g / h, toluene at 142 g / h, and gaseous boron trifluoride at 18.0 mmol / h, respectively. do. The amount of cooling water introduced into the jacket of the biaxial mixing stirrer and the cooler is controlled such that the temperature of the biaxial mixing stirrer outlet of the copolymer is maintained at 60 ° C. The resulting crude oxymethylene copolymer is withdrawn from the overflow line of the hopper. The crude coarse oxymethylene copolymer obtained is η _r = 1.755.

Reference Example 2

A 3-liter kneader with two Σ type stirring blades was heated to 60 ° C., 3.0 kg of trioxane, 66 g of ethylene oxide and catalyst boron trifluoride-diethyl etherate in an amount of 200 ppm by weight of trioxane by weight It is added as a benzene solution and stirred at 30 rpm. The contents solidify in a few minutes, and the temperature inside the system rises due to the heat of reaction and friction, so that cooling is caused by passing a cold air inside the Σ stir blade, and the rotation speed is lowered to 10 rpm and the maximum temperature is adjusted to 80 ° C. Stirring is continued as it is, and after 60 minutes, the crude oxymethylene copolymer is taken out. The crude coarse oxymethylene copolymer is η _r = 1.685.

EXAMPLE

Next, the Example of this invention is shown.

Example 1

50 g of the coarse oxymethylene copolymer obtained in Reference Example 1 was transferred to a rod-shaped cylindrical container with a lower portion and contacted with 5 times molar amount of ammonia gas of the catalyst. Thereafter, nitrogen gas is blown and the excess ammonia gas is replaced with nitrogen gas. 0.1 wt% of calcium hydroxide as a stabilizer in the coarse oxymethylene copolymer, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] (Shiba-Geigy Co., Ltd.) : 0.5% by weight of Irganox 245) and 0.2% by weight of melamine are mixed well with a high speed rotary mixer. The mixture is then degassed by melt kneading at 220 ° C. and 20 rpm for 30 minutes in a melt training degassing apparatus having two Σ stir blades under a vacuum of 30 mmHg.

In this invention, relative viscosity and coloring degree are evaluated as follows.

[Relative viscosity η _r ]

0.40 g of oxymethylene copolymer is dissolved in 100 ml of p-chlorophenol containing 2% α pinene and measured at 60 ° C.

[Coloring degree]

The oxymethylene copolymer is placed in a colorless tube made of Pyrex having a diameter of 28 mm and a length of 250 mm, melted and cooled at 210 ° C. in a nitrogen stream, and ranked in the order of 1,2,3 in the order of the strongest coloring. The results are shown in Table 1.

Example 2

Before the coarse oxymethylene copolymer obtained in Reference Example 1 is contacted with ammonia gas, the unreacted formaldehyde gas of the copolymer is replaced with nitrogen gas, and then stabilized in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1

After coarse oxymethylene copolymer obtained in Reference Example 1 was contacted with ammonia gas, stabilization treatment was carried out in the same manner as in Example 1 except that the substitution operation was not performed with nitrogen gas. The results are shown in the first table.

[Comparative Example 2]

The stabilization treatment is carried out in the same manner as in Example 1, except that a benzene solution of triphenylphosphine in twice the molar amount of the catalyst is added without performing a substitution operation with nitrogen gas. The results are shown in the first table.

Comparative Example 3

Use of bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate (trade name: Sanol LS 770; manufactured by Sangyo Kogyo Co., Ltd.) as a hindered amine without performing a substitution operation with nitrogen gas. The benzene solution was stabilized in the same manner as in Example 1 except that the amount of the hindered amine was 0.3% by weight based on the copolymer. The results are shown in Table 1.

Example 3

The coarse oxymethylene copolymer obtained in Reference Example 2 is placed in a rod-shaped cylindrical container with a lower portion thereof, and a 5-fold molar amount of ammonia gas of the catalyst is brought into contact. Next, nitrogen gas is blown in and the excess ammonia gas is replaced with nitrogen gas. Triethyleneglycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] as a stabilizer in a coarse oxymethylene copolymer (available from Ciba-Geigy Company: Irganox 245 0.5% by weight and 0.2% by weight of melamine are added and mixed well with a high speed rotary mixer. The mixture was then degassed by melt kneading at 210 ° C. and 20 rpm for 60 minutes in a melt training degassing apparatus having two Σ stir blades under a vacuum of 30 mm Hg. The results are shown in Table 1.

Comparative Example 4

After the coarse oxymethylene copolymer obtained in Reference Example 2 was contacted with ammonia gas, stabilization treatment was carried out in the same manner as in Example 3 except that the substitution operation was not performed with nitrogen gas. The results are shown in Table 1.

It can be seen from the first table that the oxymethylene copolymer produced by the present invention has a small decrease in molecular weight and coloration is prevented.

Claims (2)

A first step having a coarse oxymethylene copolymer powder having a thermally labile portion composed of oxymethylene repeating units at the main chain terminal and containing a copolymerization reaction catalyst with excess ammonia gas to the catalyst to remove activity of the copolymerization reaction; A second step of blowing an inert gas into the coarse oxymethylene copolymer powder obtained in the first step to remove ammonia gas remaining in the copolymer; And dissolving and removing the coarse oxymethylene copolymer powder obtained in the second step by heating and melting in the presence of a stabilizer within a temperature range of 100 ° C. higher than the melting point or melting point of the copolymer. A process for producing a stabilized oxymethylene copolymer consisting of three steps. The unreacted formaldehyde of claim 1, wherein the coarse oxymethylene copolymer is a formaldehyde copolymer, and before the coarse formaldehyde copolymer powder is contacted with ammonia gas, an inert gas is blown into the copolymer powder to remain in the copolymer. Process for producing a stabilized oxymethylene copolymer, characterized in that the gas is removed.