JPH023410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyoxymethylene. More specifically, the present invention relates to an improvement in a method for continuously producing powdered polyoxymethylene using trioxane as a raw material.

Polyoxymethylene has excellent properties such as wear resistance and friction resistance, and is widely used as an engineering plastic in electrical parts, automobile parts, mechanical parts, etc.

This polyoxymethylene has been produced by homopolymerizing trioxane in the presence of a catalyst, converting trioxane into ethylene oxide or dioxolane,
It is produced by copolymerizing it with a cyclic formal such as dioxepane.

However, in such methods, the polymerization reaction usually progresses rapidly and the reaction product solidifies, making subsequent processing difficult or accompanied by side reactions and coloring, so such undesirable situations must be avoided. Various considerations need to be taken to avoid this. For this reason, for example, a so-called slurry polymerization method in which polymerization is carried out in the presence of a large amount of inert solvent has been proposed, but this method requires time and effort to recover the solvent after use, and causes a decrease in the molecular weight of the resulting polymer. Due to these drawbacks, it cannot be said to be necessarily satisfactory as an industrial manufacturing method.

Therefore, bulk polymerization is currently the mainstream method for producing polyoxymethylene, and many improvements in this regard and improvements in the production equipment have been proposed.

For example, the reaction chamber may consist of a long double-barreled case along the outer boundary of a pair of intermeshed parallel screw members, each having threads running in the same direction and having longitudinal axes. A method using a twin-screw extrusion type polymerization reactor with a structure that rotates in the same direction around the center (Japanese Patent Publication No. 47-629), a long twin-barrel type in which the reaction chamber substantially follows the outer boundary of a pair of shafts. A method using a self-cleaning polymerization reactor consisting of a case, and the shaft having a number of alternately interlocking oval plates, each of which has a flat end that engages with the long axis end of the plate so as to stroke the surface of the other plate ( Japanese Unexamined Patent Publication 1977-
84890) have been proposed.

However, in the first method using a twin-screw extrusion type polymerization reactor, the crushing force of the product is weak, so a large amount of horsepower is required to move the product, and the load is often increased to the extent that it becomes difficult to rotate the screw. It has the disadvantage that it cannot be extruded. In addition, in the second method of using a self-cleaning polymerization reactor, since the tip of the oval plate paddle is flat, the effect of scraping off scale adhering to the inner surface of the casing and the paddle surface is small, and scale accumulates inside the reactor. However, as a result, the heat transfer coefficient decreases, making it difficult to remove polymerization heat, and the shaft is stretched out, applying extra force, resulting in torque out, making continuous operation difficult. are doing.

In addition, two shafts are housed in parallel in a double cylindrical case, and each of the shafts has a convex lens-shaped cross section, and both ends in the long axis direction form sharp edges. It has a number of plate-shaped paddles with a plane of symmetry that includes the plane, and each paddle maintains a small gap between its sharp tip and the side surface of the opposing paddle at the other end and the inner surface of the body to which it belongs. A method using a self-cleaning polymerization reactor having a structure in which the paddle is rotated by a lens (Japanese Unexamined Patent Publication No. 56-3812), and a method in which the paddle is shaped like a lens or has a pseudopolygon inscribed in a virtual circle at the apex angle. , and a method using a twin-body self-cleaning polymerization reactor having a structure in which a sharp scraper with no symmetrical surface is provided at the top corner of its cross section (Japanese Patent Laid-Open No. 56-38313), etc. has also been proposed. These methods are characterized by the fact that the tip of the long axis of the paddle is sharp, and the gap between the casing and the paddle is small, and the effect of scraping scale on the inner surface of the casing and the surface of the paddle is strong, and the scale inside the reactor is removed. Accumulation is small. However, in this method, because the paddle tip is sharp and the gaps between the casing and the paddles and between the paddles are small, the tip of the long paddle shaft may wear out the mating material due to a slight deflection of the center shaft. However, the problem remains that they are easily damaged and therefore must be handled with great care.

In order to overcome the drawbacks of such conventional methods, especially the problems arising from the reaction equipment, the present inventors have conducted intensive research and have found that by adding innovation to the shape of the paddle attached to the rotating shaft. The inventors have discovered that the object can be achieved and have come up with the present invention.

That is, the present invention has a structure in which two parallel rotating shafts each having a large number of paddles are housed in a double cylindrical case having an inner wall surface along the rotational circumferential surface of each paddle. Using a reactor with In a method in which a reaction is carried out while stirring in a narrow gap formed between walls, and powdered polyoxymethylene is continuously collected from a discharge port provided at the other end, each paddle in the reactor is is plate-shaped with a convex lens-shaped cross section, and both ends of the circular arc circumferential surface are asymmetrical and diagonally intersect with the long axis of the paddle, leaving claw-like edges to form a sharp scraper. It is characterized by having a shape in which the paddle is notched, and the above-mentioned edge has a shape offset from the long axis of the paddle cross section.

As described above, in the reaction device used in the present invention, since the leading edge of the paddle is not flat, it has the effect of scraping off scale generated on the inner wall surface of the case and the surface of the paddle. Surprisingly, it was also found that although the paddle of the present invention has a scraper, it does not damage the inner wall surface of the case or the paddle surface. The reason for this is not clear, but the scraper is not on the plane that includes the long axis of the paddle, and there is an arcuate circumferential surface in front of the scraper, which allows the polymerization product to be constantly and more efficiently engulfed and This is thought to be due to the relaxation of deflection. In other words, it is considered that the powder scraped off by the scraper and rolled up onto the arcuate circumferential surface in front of the scraper is more likely to be deflected by supporting the paddle on the arcuate circumferential surface.

Note that the front here refers to the front in the rotational direction of the paddle, and the arc circumferential surface refers to the arc surface located in front of the scraper. In addition, the presence of this arcuate circumferential surface increases the amount of polymerization product that comes into contact with the scraper, resulting in excellent pulverization efficiency and finely pulverized polyoxymethylene.

Next, the reaction apparatus used in the method of the present invention will be explained with reference to the accompanying drawings. FIG. 1 is a partially sectional side view of one example of the reaction apparatus used in the method of the present invention, and FIG. 2 is a cross-sectional view thereof. It is.

This reactor consists of a double cylindrical case 1 having a pear-shaped cross section with eccentric centers and the same diameter communicating in the longitudinal direction at the center.
Two rotating shafts 2, 2' are housed inside, and one or more divided temperature control jackets 4 are provided on the outside of the body. A large number of paddles 3, 3' each having a convex lens-shaped cross section are fixed to the above two rotating shafts, and the tip of each paddle in the long axis direction is asymmetrical and diagonal with respect to the long axis of the paddle. The arcuate circumferential surface is cut out so as to have an intersecting cross section, leaving a claw-like edge, which forms a sharp scraper. Further, this scraper is formed to be offset from the long axis of the convex lens type cross section.

The radius of curvature of the circular arc circumferential surface of the tip in the longitudinal direction of the paddle of the present invention is usually between 1/2 of the major axis radius and the radius of curvature of the convex lens-shaped cross section, and the radius of curvature of this circular arc circumferential surface is as described above. The present invention also includes cases where the value continuously changes within the range of . These paddles come in two types: flat-sided and helical-sided.
The combination of paddles can be arbitrarily selected depending on the phase change of the reaction system.

The gap between the tip surface of the paddle and the inner wall surface of the case is 2% or less, particularly preferably 1% or less, of the long axis of the paddle, and the tip surface of one paddle is installed facing the rotation axis of the other. The gap between the paddle and the side surface is at most 5 times, preferably at most 2 times, the gap between the paddle and the inner wall surface of the case.

As shown in Figure 2, the longitudinal tip of the paddle, which has a convex lens-shaped cross section, is machined into an arcuate circumferential surface with a claw-like edge; if desired, this tip can be welded with a particularly hard material. It can also be formed by Further, the thickness of the paddle is preferably about 1/20 to 1/5 of the long axis of the paddle. Furthermore, each adjacent paddle has an angle between its long axes.
They are installed with their directions shifted by 45°, 60°, or 90°.

FIG. 3 is a partial perspective view showing the shape of the paddle and its relationship with adjacent paddles. Paddle B is attached at an angle of 60° with paddle A.

To carry out the method of the present invention, trioxane is continuously supplied from the supply port 5 of the reactor shown in FIG. Adjust. The trioxane reacts while being stirred between the opposing paddles and between the paddles and the inner wall surface of the case, gradually moves as each paddle rotates, and is finally taken out from the discharge port 6 in the form of finely powdered polyoxymethylene. .

The method of the present invention is used for homopolymerization or copolymerization of trioxane, and when the purpose is to produce a copolymer, 0.1 to 20 mol% of oxyalkylene units having 2 or more carbon atoms in the oxymethylene main chain, preferably 0.4
Preferably, a mixture of trioxane and comonomer is used as the raw material in a proportion that yields a copolymer containing ~10 mol%. Comonomers include ethylene oxide, 1,3-dioxolane,
Examples include cyclic ethers or cyclic formals such as dioxepane and trioxokene.

As the polymerization catalyst, commonly used cationic polymerization catalysts can be used, but preferred are boron trifluoride, boron trifluoride hydrate,
Boron trifluoride ether coordination is particularly preferred, and boron trifluoride diethyl ether coordination and boron trifluoride dibutyl ether coordination are particularly preferred. Furthermore, aliphatic, alicyclic and aromatic hydrocarbons, such as anhydrous hexane, heptane, cyclohexane, and benzene, and halogenated hydrocarbons can also be used as the inert organic solvent. These may or may not dissolve the raw material monomer and catalyst.

Polymerization reaction temperature is 60-130℃, preferably 65-115℃
℃ range.

If the polymerization reaction apparatus in the method of the present invention is used,
A powdered oxymethylene polymer can be obtained efficiently and continuously, and continuous operation can be performed for a long period of time without any problems, and the reaction equipment will not be damaged.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A reactor equipped with a temperature control jacket around the outer periphery of the case as shown in FIG. 1 was used. This device has an inner diameter of 200 mm and a L/D (length/diameter) of 14
A feed screw with a length of 1D is attached directly below the raw material supply port. Also, as shown in Figure 2, the tip of the paddle is relative to the scraper and long axis.
It consists of an asymmetric circular arc circumferential surface, the radius of curvature of this arc is 3/5 of the major axis length, and the scraper has a gap of 2 mm or less with the inner surface of the case, and a gap of 4 mm or less with the corresponding paddle side of another rotating shaft. I'm keeping it. Paddles having such a shape are used following the feed screw and being sequentially shifted by 45 degrees in the direction of the rotation axis.

In this polymerization reactor, 40 kg of liquid trioxane was added per hour, 800 g of ethylene oxide was added per hour, and a solution of boron trifluoride dibutyl ether coordination compound and methylal in cyclohexane was added.
0.1 mmol and 1 mmol were fed per mole, respectively. The polymerization temperature was 90°C, and the rotational speed of the paddle tip was 20 m/min. A fine particle oxymethylene copolymer containing 9% of unreacted substances and passing through a 10-mesh sieve was obtained from the discharge port.

No abnormalities were observed even after 500 hours of continuous operation. Furthermore, after the operation was completed, the inside of the reactor was inspected, and no abnormalities were found on the inner surface of the case, the side surface of the paddle, or the tip.

Comparative Example 1 A jacket for heating the reaction mixture is provided around the outer periphery of the case, a pair of shafts are fixed horizontally within the case, each shaft has an oval plate that engages with the other, and the oval plate is elongated. A continuous mixer having a flat end that engaged with the surface of a mating oblong plate at the end of the shaft was used as the reactor. The inner diameter of the case of this device was 200 mm, and the L/D was 14. Further, the combination of a large number of oval plates attached to the inside of the device was the same as that of the paddle in Example 1, and the gaps were also the same. Operation was started under the same conditions as in Example 1, with the rotation peripheral speed of the flat end of the oblong plate tip being 20 m/min, and the conditions such as supply amounts of trioxane, ethylene oxide, polymerization catalyst, methylal, and polymerization temperature. After about 40 hours, the equipment made intermittent abnormal noises and the temperature began to rise, making it difficult to maintain it at a constant 90°C. After 150 hours had passed, the equipment's abnormal noises became louder and louder, and the shear pin suddenly broke and the shaft stopped rotating, so operation was halted. When the device was disassembled and inspected, large amounts of scale were found to have formed throughout the inside of the device.

Comparative Example 2 A reaction apparatus shown in FIG. 1 was used. The inner diameter of the case was 200 mm, and the L/D was 14. The paddle has a plate shape with a convex lens-shaped cross section with a sharp tip, and the tip is equipped with a sharply machined scraper. The same paddle combination as in Example 1 was used, and each gap was also the same. Operation was started using the same conditions as in Example 1, such as the supply amount of trioxane, ethylene oxide, polymerization catalyst, methylal, and polymerization temperature, with the rotation peripheral speed of the paddle tip being 20 m/min. A polymer containing 9% of unreacted substances was obtained from the discharge port. The polymers were generally fine particles, but 10
40% of the material did not pass through the mesh sieve.
During 500 hours of continuous operation, a squeaking-like noise was heard from time to time, and when the inside of the reactor was inspected after the operation was completed, the tip of the paddle was found at the bottom of the case in the center, where L/D of the reactor corresponds to 7. Scars were found that appeared to be caused by contact.

Comparative Example 3 A reaction apparatus shown in FIG. 1 was used. The inner diameter of the case was 200 mm, and the L/D was 14. Paddle is Tokukai Sho
No. 56-38313 It had a plate shape with a convex lens-shaped cross section as shown in FIGS. 2A and 3, and had a sharp scraper having no symmetry plane at its apex corner. The same paddle combination as in Example 1 was used, and each gap was also the same. Operation was started under the same conditions as in Example 1, such as the peripheral speed of rotation of the paddle tip at 20 m/min, trioxane, ethylene oxide, polymerization rate, methylal supply amount, and polymerization temperature. A polymer containing 9% of unreacted substances was obtained from the discharge port. The polymers were generally fine particles, but 10
40% of the material did not pass through the mesh sieve. During 500 hours of continuous operation, a squeaking-like noise was heard from time to time, and when the inside of the reactor was inspected after the operation was completed, the tip of the paddle was found at the bottom of the case in the center, where L/D of the reactor corresponds to 7. Scars were found that appeared to be caused by contact.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional side view of an example of a reactor used in the method of the present invention, FIG. 2 is a cross-sectional view thereof, and FIG. 3 is a partial oblique view showing the shape of a paddle and its relationship with adjacent paddles. . In the figure, 1 and 1' are the body, 2 and 2' are the central axis,
3 and 3' are paddles.

Claims (1)

[Claims] 1. A reaction device having a structure in which two parallel rotating shafts, each equipped with a large number of paddles, are housed in a double-bodied cylindrical case having an inner wall surface along the rotating circumferential surface of each paddle. Trioxane or a mixture of it and other raw materials is introduced from the supply port provided at one end, and each of the rotating shafts is rotated in the same direction, forming a space between each of the facing paddle surfaces and between the paddle surface and the inner wall surface of the case. In this method, each paddle in the reaction apparatus is made of a convex lens type. It has a plate shape with a cross section, and both ends are cut out on the arc circumferential surface so that the cross section is asymmetrical and diagonal to the long axis of the paddle, leaving claw-like edges to form a sharp scraper. , and the edge has a shape deviated from the long axis of the paddle cross section.