JPH0582410B2 - - Google Patents

Description

[Detailed description of the invention]

<Field of Industrial Application> The present invention relates to a method for continuous melt polymerization of polyamide that rapidly increases the degree of polymerization of polyamide, prevents abnormal retention, and suppresses polymer decomposition and the formation of insoluble and infusible gel. . <Prior art> Due to its strong properties, polyamide is used for clothing,
It is used in large quantities as fiber for industrial materials and engineering plastics. Furthermore, these properties vary greatly depending on the degree of polymerization of the polyamide. Polyamide has a higher polymerization equilibrium than polyester.
Even molten polymers with water percentages in solubility equilibrium with water vapor at atmospheric pressure, on the highly water-rich end of the spectrum, will have a sufficient degree of polymerization for use in clothing fibers.
Therefore, in order to obtain a polymer used for clothing fibers, for example, in the case of nylon 66, an aqueous solution of hexamethylene diammonium adipate is reacted under pressure, and then the pressure is returned to normal pressure to ensure that no air is mixed in. A method has been adopted in which the polymer is introduced into a reactor that is open to the atmosphere, and excess moisture coexisting in the polymer is released to allow the polymerization reaction to proceed to an equilibrium state. However, in cases where a high degree of polymerization is required, such as in fibers for industrial materials or some engineering plastics, the molten polymer may be further heated in a reduced pressure gas phase, or in a gaseous atmosphere with a lower water vapor partial pressure using an inert gas such as nitrogen. It is necessary to contact the phase and lower the water content in the polymer. Generally, a method is employed in which the polymer is introduced into a large-capacity container and brought into contact with a gas phase under reduced pressure for a sufficient period of time. However, polyamide has the property of decomposing or changing into an insoluble gel when it remains in the melt for a long period of time, and this property is particularly important for adipic acid.
This is particularly the case with polymerized polyamides as components. This problem is noticeable when trying to obtain a polymer with a high degree of polymerization. A large-capacity container, ie, a reactor, itself becomes a part where polymer stays for a long period of time, and polymers adhering to the walls of the container or the surface of stirring blades stay there for an extremely long period of time, decomposing or turning into gel. This gel builds up slowly and occasionally flakes off, deteriorating the quality of the polymer. Further, the gas generated when the polymer decomposes causes yarn breakage during spinning, for example. U.S. Pat. No. 3,717,330 shows a method to improve these drawbacks by providing a self-cleaning property to the reactor, but this method is based on the function of co-rotating twin screws with three threads. The aim is to mechanically scrape off the polymer adhering to the inner wall of the container and the surface of the stirring blade by using it as a stirring blade. In this method, since there is a clearance, the polymer adhering to the gas phase region remains for a long period of time corresponding to the clearance, and decomposition and gelation progress. In addition, a polymerization method using a co-rotating twin-screw extruder is disclosed in Japanese Patent Publication No. 15275-1975 and US Patent No. 3040005.
It is stated in the number. This method using a co-rotating twin-screw extruder is also insufficient in terms of preventing polymer decomposition and gel formation caused by abnormal retention, as described below. That is, in a co-rotating twin-screw extruder, when the polymer filling rate becomes small, a portion that hardly contacts the polymer is formed on the back side of the screw flight. Due to flow rate fluctuations and scattering within the extruder, once the polymer adheres to this area, an amount corresponding to the clearance is not scraped off and remains for an abnormally long time, resulting in insoluble and infusible gel, etc. The polymer deteriorates and occasionally falls off, contaminating the polymer. <Purpose and Structure of the Invention> As a result of extensive research into a method for continuous melt polymerization of polyamide that eliminates the above-mentioned drawbacks, the present inventors have developed a twin-screw extruder that rotates in opposite directions and a screw structure for polymer retention. The present invention was achieved based on the knowledge that abnormal retention of polymer can be prevented by using the same piping. That is, an object of the present invention is to provide a continuous melt polymerization method for obtaining a polyamide with a high degree of polymerization, which is less likely to undergo deterioration into gel or the like caused by abnormally long retention of a polyamide melt polymer. In the polyamide polymerization method according to the present invention, the distance between one screw flight and the other screw flight of two screws that engage with each other and rotate in opposite directions is set to 1/15 or less of the screw diameter. A twin-screw extruder is used in which the distance between the top of one screw flight and the bottom of the other screw groove is set to 1/15 or less of the screw diameter, and the melting that is progressing inside the extruder is Gradually improves the degree of polymerization while continuously removing water contained in the polymer.
Furthermore, this polymer is supplied to a retention area connected to the exit side of the extruder, and while the molten polymer is advanced at an average flow velocity of 1 m/min or more, 2.0 m/min is added to the retention area.
This method is characterized in that the polymerization degree is improved by allowing the polymer to remain in the polymer for more than a minute to reach an equilibrium state with the water in the polymer, and then sequentially taken out of the system. <Means for solving the problems> The polymerization method of the present invention will be described in more detail.
The polymerization apparatus preferably used in the present invention is a twin-screw extruder that rotates in opposite directions and has openings, and the water contained in the polyamide polymer introduced into the extruder is adjusted to the polymerization degree and polymerization equilibrium of the polymer. The water content is reduced to below a certain level, and the polymerization reaction proceeds in a retention area in a pipe connected to the extruder. In order to remove sufficient moisture to achieve a high degree of polymerization, it is necessary to increase the contact time with a gas phase with a low moisture content or to increase the contact area with the gas phase per unit volume of passing polymer. However, in order to increase the contact time, the residence time in the extruder is generally increased, which necessitates a large-sized equipment for the production volume. Increasing the polymer temperature is also effective in increasing the degree of polymerization, but it is not preferable to rely on raising the polymer temperature because decomposition and gelation are significantly accelerated. In the present invention, in order to effectively contact the gas phase with a low moisture content, a twin-screw extruder rotating in opposite directions is used, which can transport the polymer while controlling the filling rate of the polymer in the extruder. Among twin-screw extruders, a co-rotating twin-screw extruder is not suitable for the present invention in terms of suppressing decomposition and gelation. It is true that in theory, a co-rotating twin-screw extruder can be designed to be completely self-cleaning, but in terms of manufacturing accuracy it will always have some clearance, and this clearance is a drawback for the following reasons. . In other words, in order to effectively remove water, the polymer filling rate in the extruder is controlled to be low to some extent, but in a co-rotating twin-screw extruder, at this time, the (on the opposite side), there is a part where the polymer hardly touches. Fluctuations in the flow rate of the polymer that occur during operation lead to fluctuations in the polymer filling rate in the extruder, causing it to adhere to the above-mentioned areas, or in rare cases, scattered polymer adheres to this area, but this polymer is difficult to maintain due to the lack of clearance in the screw. Because of this, it stays for a long time and decomposes or becomes an insoluble gel. This gel falls off due to extruder vibrations, screw shakes, etc. and mixes into the polymer, deteriorating the quality of the produced polymer. The present inventors have recognized that the above-mentioned phenomenon is unavoidable as long as a co-rotating twin-screw extruder is used, and have arrived at the fact that it can be solved by a special configuration of a counter-rotating twin-screw extruder. Theoretically, a counter-rotating twin-screw extruder cannot be designed to have perfect self-cleaning properties due to alternating screws. This is one of the reasons why co-rotating twin-screw extruders have been used more favorably than counter-rotating twin-screw extruders. However, it has been found that this drawback of the counter-rotating twin-screw extruder can be solved as follows. That is, by filling the space between one screw with a polymer and applying sufficient shearing force to the polymer, it was possible to provide self-cleaning properties to a level that poses no practical problems. This method is not applicable in the case of a co-rotating twin screw extruder. This is because, in a co-rotating twin-screw extruder, there are portions between the screws where polymer cannot be filled. Furthermore, in order to achieve the above object, it is also necessary to specify the screws to be used in the counter-rotating twin-screw extruder. That is, the distance between one screw flight and the other screw flight is 1/15 or less of the screw diameter, and the distance between the screw flight and the other screw flight is 1/15 of the screw diameter. It is necessary to use a screw that is /15 or less. If a screw having a mesh gap outside this range is used, the polymer on the screw surface will not be renewed by the shearing force of the polymer, and decomposition and gel production cannot be suppressed. Further, by setting the distance between the screws within the range specified above, it is possible to sufficiently increase the polymer pressure at the tip of the extruder, and vent up from the opening can be prevented. This is a feature that cannot be obtained with a co-rotating twin-screw extruder or a single-screw pusher. As described above, a melt polymer with no gel contamination and a low water content can be obtained, but when rotated in the opposite direction 2
Since the residence time of the polymer in the shaft extruder is short, there is not enough time for the polymerization reaction to undergo an equilibrium shift corresponding to the water removed at the opening and to achieve a high degree of polymerization.
In order to effectively change the polymerization degree to a high degree, it is necessary to install a pipe that is connected to a twin-screw extruder rotating in opposite directions and where the polymer stays for at least 2 minutes, and to proceed with the polymerization reaction in this pipe until the polyamide polymer reaches an almost polymerization equilibrium state. There is. Only in this way can a highly polymerized polyamide without gel contamination be obtained. If the retention time is 2 minutes or less, the polymerization equilibrium state is far from being reached and the water removal effect is not effectively utilized. It is preferable that the diameter of the piping provided in the twin-screw extruder rotating in opposite directions be made small in order to suppress decomposition and gelation due to abnormal retention. The average linear velocity of the polymer is preferably 1 m/min or more, preferably 2 m/min or more. A facility for pelletizing, a spinning head, etc. can be provided in connection with this piping. On the other hand, methods for removing moisture from the polymer in the present invention include a method of reducing the pressure in the opening to prevent outside air from entering, or a method of introducing an inert gas such as nitrogen into the opening to lower the partial pressure of water vapor in the gas phase. etc. can be used. By using the apparatus described above, it is possible to quickly increase the degree of polymerization of polyamide and to suppress the formation of gel due to abnormal retention. <Examples> Next, the apparatus of the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Example 1 An example of implementation is shown in FIG. Screw 4 is a twin-screw extruder with two threads rotating in different directions (length L/D = 38) with a diameter D = 65 mm, a groove depth of 12 mm, a flight pitch of 55 mm, one screw flight and the other screw flight. The distance between 11' and 11' is 0.5
mm, the distance between the screw flight top and the other screw groove bottom is 0.5 mm, the length of opening 1 is L/D=3, the length of opening 2 is L/D=
6. The length from the screw tip to the opening 2 is L/D=5. The pipe 5 is a double pipe that can be heated by a heating medium, and the polymer flow path has an inner diameter of 25 mm and a length of 12 m. A polyhexamethylene adipamide melt polymer having a formic acid relative viscosity (hereinafter abbreviated as VP) VR = 34 was fed into the apparatus shown in Figure 1 from the supply port 3 while being metered with a gear pump, and the results shown in Table 1 were obtained. . The temperature inside the openings 1 and 2 was maintained at 70 torr, and the temperature of the heat medium in the extruder and piping was 285°C.
The polymer extracted from the nozzles 6 and 7 was passed through water in the form of a strand to solidify and form into pellets.

[Table] After 7 days of operation, the extruder was stopped and the screws were taken out, but no gel was observed on the screw surface in any of the cases No. 1 to No. 6 in Table 1. Furthermore, as shown in the section of formic acid relative viscosity in Table 1, a polymer with a high degree of polymerization was obtained. Measurement of formic acid relative viscosity was performed according to ASTM D-789. Comparative Example 1 Polyamide was continuously polymerized under the same conditions as in Example 1, except that the polymer was extracted from the nozzle 8 in FIG. 1 and passed through water in the form of a strand to solidify and pelletize it. The results obtained are shown in Table 2.

[Table] When the polymer is extracted from the nozzle 8, as shown in Table 2, the residence time of the polymer in the pipe is short (within 1 minute), so the relative viscosity of formic acid is low, and a polymer with a sufficiently high degree of polymerization can be obtained. do not have. Example 2, Comparative Example 2 The screw in the apparatus used in Example 1 was replaced with the screw shown below and the apparatus was operated. The newly installed screw is a type that rotates in different directions.
The groove depth was 16 mm, the distances 11 and 11' between the screw flight top and the other screw flight were 4 mm (Example 2) and 8 mm (Comparative Example 2), respectively. The distance between the groove bottoms 12 is 4 mm, and the others are as in Example 1.
It is similar to Operating conditions are polymer flow rate 50Kg/hour,
The screw rotation speed is 50 rpm, the opening pressure is 70 torr, and the extruder and piping temperature is 285°C. The supplied polyhexamethylene adipamide had a VR of 34, and the VR of the polymer obtained from nozzle 6 was 86, indicating that a high degree of polymerization was successfully achieved. However, from the third day after the start of operation, black gel appeared in the pellets. began to be recognized. Therefore, when the screw was stopped and the screw was pulled out, black gel was observed here and there on the side where the distance between the screw flight and the other screw flight was 8 mm (Comparative Example 2). No abnormality was observed on the 4 mm side (Example 2) and the bottom of the groove. Comparative Example 3 3 with a pellet melting section and two supply sections
Using a co-rotating twin-screw extruder with a screw diameter of 84 mm, polyhexamethylene adipamide pellets with a VR = 34 moisture content of 0.14% were supplied at a flow rate of 90 kg/hour, and extrusion was performed at a temperature of 285 °C. . Initially, the piping used in Example 1 was connected to the extruder outlet, and when the opening was sealed and the operation was started, venting occurred from the opening near the tip of the extruder, so the piping was removed and the opening pressure was reduced to 70°C.
I changed the conditions to Tor and continued driving for the fourth day. The screw rotation speed is 80 rpm. When the screw was pulled out after the screw was stopped, there was a band of black gel attached to the back side of the screw flight. <Effects of the Invention> By using the polyamide polymerization method according to the present invention, it is possible to suppress gelation, etc., so that the continuous operation period of the polymerization equipment can be extended, and the obtained high degree of polymerization polyamide polymer is also free from gel contamination. In the spinning process, the spinneret exchange cycle can be extended and yarn breakage can be reduced. In the field of engineering plastics, it is expected to improve yields by reducing contamination of molded products and improve physical properties such as strength. When polyamides containing adipic acid as one component, such as polyhexamethylene diamide, remain for a long time and continue to receive heat, the adipic acid component decomposes at a fairly rapid rate while generating carbon dioxide, resulting in gelation. The effects of using the polymerization method of the present invention are significant.

[Brief explanation of the drawing]

FIG. 1 is an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is an enlarged partial view of a cross section taken in a plane including the central axes of two screws in mesh, seen from vertically above. 1 and 2...opening, 3...polymer supply port, 4
... Screw, 5 ... Piping, 6 ... Polymer nozzle, 7 and 8 ... Sampling nozzle, 9 ... Vacuum pump, 11 and 11' ... Between the screw flight and the other screw flight, 12 ...
...The distance between the top of the screw flight and the bottom of the other screw groove, 13...Polymer traveling direction.

Claims (1)

[Claims] 1. The distance between one screw flight and the other screw flight of two screws that engage with each other and rotate in opposite directions is 1/15 of the screw diameter.
A twin-screw extruder is used with the following settings and the distance between the top of one screw flight and the bottom of the other screw groove is set to 1/15 or less of the screw diameter, and the extruder moves through the extruder. The degree of polymerization is gradually increased while continuously removing water contained in the molten polymer, and this polymer is further supplied to a retention area connected to the exit side of the extruder, and the molten polymer is moved at a linear speed of 1 m/ The polyamide is allowed to remain in the retention area for 2 minutes or more while advancing at an average flow rate of 1 minute or more to improve the degree of polymerization until it reaches an equilibrium state with the water in the polymer, and then sequentially taken out of the system. Continuous polymerization method. 2. The polymerization method according to claim 1, wherein the polyamide is a polyamide containing adipic acid as one component.