JPH023409B2 - - 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 long axis 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 it is difficult to clean the inside of the reactor. Scale accumulates, which not only lowers the heat transfer coefficient and makes it difficult to remove polymerization heat, but also causes the shaft to expand and apply extra force, causing torque out and making continuous operation difficult. It has its drawbacks.

In addition, two shafts are housed in parallel in a double cylindrical case, and each of the shafts has a convex lens cross section, and both ends in the long axis direction form sharp edges, and the long axis is included. It has a large number of plate-shaped paddles with a plane of symmetry, and each paddle maintains a small gap between its sharp tip and the side surface of the opposing paddle on the other axis and the inner surface of the body to which it belongs. A method using a self-cleaning polymerization reactor having a rotating structure (Japanese Unexamined Patent Publication No. 56-3812), and a method in which the paddle is a lens shape or a pseudopolygon whose apex angle is inscribed in a virtual circle. There is also a method using a twin-body self-cleaning polymerization reactor (Japanese Patent Application Laid-open No. 38313/1983), which has a structure in which a sharp scraper with no symmetrical surface is provided at the top corner of the cross section. 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, the tip of the paddle is sharp and the gaps between the casing and the paddles and between the paddles are small, so 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. Trioxane or a mixture of it and other raw materials is introduced from a supply port provided at one end of the reactor, and each of the rotating shafts is rotated in the same direction, and each of the opposing paddle surfaces and the paddle surface and the inner wall surface of the case are In a method in which the reaction is carried out while stirring in a narrow gap formed between the paddles, and the powdered polyoxymethylene produced is continuously recovered from the discharge port provided at the other end, each paddle of the reaction device is It is characterized by having a plate shape with a convex lens-shaped cross section, and having a shape in which both ends thereof are cut out with an arcuate circumferential surface so that the cross section is asymmetrical and obliquely intersecting the long axis of the paddle. It is.

As described above, the feature of the reaction device used in the method of the present invention is that the paddle is plate-shaped with a convex lens-shaped cross section, and its both ends are arranged in an arcuate circumference so that the cross section is asymmetrical and diagonal to the long axis of the paddle. It has a cutout shape with no sharp tip or sharp scraper, and the tip has an appropriate angle to create a slight gap between the inner wall of the case and the facing paddle surface. It is important to maintain and interact with people.

In this reactor, 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. It was found that continuous operation for long periods of time is possible without damaging the surface, and that it can solve the problems of conventional reactors.

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

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 and 3' each having a convex lens-shaped cross section are fixed to the above two rotating shafts, and both ends of each paddle are asymmetrical and cross diagonally with respect to the long axis of the paddle. It has a shape cut out with an arc circumferential surface so as to form a 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 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 changes continuously within the range. These paddles include those with flat sides and those with helical sides, and the combination of these 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.The tip of paddle A, which has a convex lens-shaped cross section, is cut out by an arcuate circumferential surface a, and paddle B is It is attached at a 60° angle 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, and boron trifluoride ether coordination products. Boron diethyl ether coordination and boron trifluoride dibutyl ether coordination are preferred. Also,
Aliphatic, alicyclic, and aromatic hydrocarbons, such as anhydrous hexane, heptane, cyclohexane, and benzene, and halogenated hydrocarbons can also be used as inert organic solvents. 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 As shown in FIG. 1, a reaction apparatus equipped with a temperature control jacket around the outer periphery of the case 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. In addition, as shown in Figure 2, the tip of the paddle consists of an arcuate circumferential surface that is asymmetrical and diagonally intersects with the long axis of the paddle, and the radius of curvature of this arc is 3/5 times the length of the long axis. Also, one of the intersection lines between the circular arc circumferential surface and the convex lens type circumferential surface maintains a small gap with the inner surface of the case and the corresponding paddle surface of the other rotating shaft, and the gap between the tip of the paddle and the inner surface of the case is 2 mm or less, and the gap with the corresponding paddle surface of the other shaft is 4 mm or less. Furthermore, the paddles are sequentially moved in the direction of rotation following the feed screw.
They are installed offset by 45 degrees.

Liquid trioxane was added to the reactor at a rate of 40% per hour.
Kg, 800 g of ethylene oxide per hour, and 0.1 mmol and 1 mmol of boron trifluoride dibutyl ether coordination compound and methylal as solutions in cyclohexane per mole of trioxane, respectively. The polymerization temperature was 90°C, and the rotation speed of the paddle tip was 20 m/min. A fine particle polymer containing 8% of unreacted materials and passing through a 10-mesh sieve was obtained from the discharge port.

No abnormalities were observed during 500 hours of continuous operation, and when the inside of the reactor was inspected after the operation was completed, no abnormalities were observed on the inner surface of the shell, the side surface of the paddle, or the tip.

Comparative Example 1 A jacket capable of 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 located at the long axis end. A continuous mixer with a flat end that interlocked with the surface of the other oblong plate was used as the reactor. The inner diameter of the case of this device was 200 mm, and the L/D was 14.
The combination of multiple oblong plates installed inside the device was the same as in the paddle of 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 began to make 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 as shown in FIG. 1 was used. The inner diameter of the case of this device is 200 mm, the L/D is 14, and the paddle is plate-shaped with a convex lens-shaped cross section and a sharp tip. 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 rotation peripheral speed of the paddle tip at 20 m/min and the supply amounts of trioxane, ethylene oxide, polymerization catalyst, methylal, and polymerization temperature. A polymer containing 9% of unreacted substances was obtained from the discharge port. The polymer was generally fine particles, but 40% did not pass through a 10 mesh sieve. During 500 hours of continuous operation, it occasionally emitted a squeaking noise, and after the operation ended,
When I inspected the inside of the device, the L/D of the device was 7.
A scar was found on the lower part of the case in the center area, which appeared to be caused by contact with the tip of the paddle.

Comparative Example 3 A reaction apparatus as shown in FIG. 1 was used. The inner diameter of the case of this device is 200 mm, L/D is 14,
The paddle is shaped like a plate with a convex lens-shaped cross section and has a sharp scraper with no symmetrical plane at its apex.
It has the shape shown in the figure, and the combination of paddles and each gap are the same as in Example 1.

Operation was started under the same conditions as in Example 1, such as the rotation peripheral speed of the paddle tip at 20 m/min and the supply amounts of trioxane, ethylene oxide, polymerization catalyst, methylal, and polymerization temperature. A polymer containing 9% of unreacted substances was obtained from the discharge port. The polymer was generally fine particles, but 40% did not pass through a 10 mesh sieve. During 500 hours of continuous operation, it occasionally emitted a squeaking noise, and after the operation ended,
When I inspected the inside of the device, the L/D of the device was 7.
A scar was found on the lower part of the case in the center area, which appeared to be caused by contact with the paddle tip.

[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. Using a reaction device with a structure in which two parallel rotating shafts, each equipped with a large number of paddles, are housed in a twin cylindrical case with an inner wall surface along the rotational circumferential surface of each paddle. , introducing trioxane or a mixture of it and other raw materials from a supply port provided at one end thereof, and rotating each of the rotational shafts in the same direction, forming a shape 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 has a convex lens-shaped cross section, in which the reaction is carried out with stirring in a narrow space, and the powdered polyoxymethylene produced is continuously recovered from a discharge port provided at the other end. A method for producing polyoxymethylene, characterized in that it has a plate-like shape, and both ends thereof have a shape cut out with an arcuate circumferential surface so that the cross section is asymmetrical and diagonal to the long axis of the paddle. .