JP2008155629A - Annealing apparatus for polyamide resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent problems such as occurrence of burned surface of a resin molding or occurrence of a fire or explosion in an annealing oven. <P>SOLUTION: An annealing apparatus for receiving cast polyamide resin moldings in the annealing oven, and heating and annealing them, is constituted by using a safety device which is for monitoring the concentration of oxygen in the oven and stopping the heating when the concentration of oxygen becomes a prescribed concentration or higher, a safety device which is equipped with a nitrogen gas flowmeter for nitrogen gas sent into the oven and for stopping the heating when the flow of nitrogen measured by the nitrogen flowmeter becomes a prescribed value or below, and furthermore, a control device which is for keeping the heater surface temperature in the oven within a prescribed temperature range. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an annealing for removing internal distortion of a molded product caused by stress generated by polymerization shrinkage, crystallization shrinkage, and shrinkage accompanying cooling during resin molding occurring in a cast molded product of polyamide that polymerizes lactam ( More specifically, the present invention relates to a technique for solving problems such as surface burning of a resin molded body, fire, and explosion in an annealing oven.

  Cast polyamide resin is the most representative engineering plastic, and has excellent mechanical strength, impact resistance, heat resistance, chemical resistance, and good workability, so it has many machine parts such as gears, rolls, and sliding materials. It is used as

  A polyamide cast product is often subjected to a heat treatment called annealing after the molding. This is because a cast molded product of polyamide resin undergoes shrinkage due to polymerization, shrinkage due to crystallization, and stress due to shrinkage due to cooling after molding, so that internal distortion occurs in the molded product. When the molded product is machined, such as by cutting, due to internal distortion, it may cause a resin crack even if the molded product is left unattended. In addition, since the strain is gradually released even at room temperature, there is a problem that even if it is processed to a predetermined size after molding, the size may change due to shrinkage after processing or warp may occur.

  Therefore, an operation called annealing is performed in which a molded article as described above is once heated to an appropriate temperature, held for a predetermined time, and then slowly cooled to lower the temperature to room temperature.

  By annealing the molded product, internal distortion of the molded product can be removed, cracking during machining can be prevented, and dimensional stability after processing can be ensured. Annealing is performed by heating the resin molding in an oven.

  On the other hand, in the cast molding of polyamide that polymerizes lactam, the monomer lactam does not completely polymerize into a polymer, and usually about several percent of lactam (monomer) is not yet present in the polymer molded article. The reaction remains.

  The remaining lactam remains in the molded product as it is, but it evaporates by heating for annealing, and is generated outside the molded product as a lactam gas.

  Lactam gas is a flammable gas and may ignite and explode if there is oxygen and an ignition source at temperatures above 375 ° C. Therefore, as a safety measure, a method of heating the inside of the oven while replacing the nitrogen by blowing nitrogen into the oven is employed, and the state is free of oxygen which is one of the causes of ignition.

  However, even if nitrogen replacement is performed, some oxygen remains, and oxygen concentration in the oven may increase due to oxygen entering from the outside, and the oxygen concentration must be checked. Therefore, a mechanism is provided to sample the gas in the oven, periodically check the oxygen concentration with an oximeter, and automatically turn off the oven heater if it exceeds a predetermined concentration ( Patent Document 1).

JP 2000-254929 A

  However, in the method of checking the oxygen concentration with an oximeter, it is difficult to continuously measure and monitor the oxygen concentration when the temperature of the gas in the oven exceeds 150 ° C. The gas is sampled and measured.

  Therefore, when the temperature in the oven is 150 ° C. or lower, the safety device works to prevent the resin molded product from being burned or exploded, but when the temperature exceeds 150 ° C., the oxygen concentration is measured. In this method, continuous monitoring was not possible, and there was anxiety in safety, and a system to prevent problems such as burning of resin products and explosions could not be taken.

  Therefore, in the present invention, the inside of the oven can be monitored even when the temperature of the oven becomes high, and the problem that the molded product is burnt to cause a defect and in some cases an explosion is prevented is prevented. Accordingly, an object of the present invention is to provide an annealing apparatus for a resin molded body capable of continuously monitoring the inside of an oven.

  In order to solve the above-mentioned problems, in claim 1 of the present invention, in an annealing apparatus for a polyamide resin molded body in which a cast polyamide resin molded body is accommodated in an oven and heated and annealed, the oxygen concentration in the oven A safety device that stops heating when the oxygen concentration exceeds a predetermined concentration and a nitrogen gas flow meter that is fed into the oven are provided, and heating is performed when the flow rate measured by the nitrogen gas flow meter falls below a predetermined value. A safety device for stopping and a control device for keeping the heater surface temperature in the oven within a predetermined temperature are used in combination.

  According to a second aspect of the present invention, there is provided the annealing apparatus for a polyamide resin molded body according to the first aspect, wherein the safety device is used in combination with a safety device that monitors the pressure in the oven and stops heating when the pressure falls below a predetermined value.

  In claim 3, the pressure in the bearing constituting the rotating shaft of the fan for circulating the gas in the oven is monitored and used together with a safety device that stops heating when the pressure falls below a predetermined value. Annealing equipment for polyamide resin.

  According to the first aspect of the present invention, the oxygen concentration in the oven of the annealing apparatus is monitored and a flow meter of nitrogen gas fed into the oven is provided, and a plurality of safety devices that stop heating according to each measured value are used in combination. Therefore, even if the temperature inside the oven becomes high and continuous monitoring with an oximeter is not possible, continuous monitoring can be performed by monitoring the flow rate of nitrogen gas, which is a substitute characteristic, with a flow meter. The oxygen concentration in the oven can be more reliably maintained at a problem-free level. Furthermore, since the control apparatus which maintains the heater surface temperature in oven within predetermined temperature is provided, generation | occurrence | production of the burning of the resin molding surface and explosion can be prevented.

  According to the second aspect of the present invention, it is possible to confirm whether or not nitrogen is sufficiently sent into the oven by attaching a pressure gauge for monitoring the pressure in the oven as a safety device. By setting so as to stop the oxygen concentration, the oxygen concentration in the oven of the annealing apparatus can be more reliably maintained at a level causing no problem.

  According to a third aspect of the present invention, the pressure in the bearing constituting the rotating shaft of the fan for circulating the gas in the oven is monitored, and a safety device that stops heating when the pressure falls below a predetermined value is also used. The apparatus for annealing a polyamide resin molded body described above can manage the oxygen concentration more reliably.

  FIG. 1 is a perspective view showing a state where an annealing oven door is opened in an annealing apparatus for a polyamide resin molded body, and FIG. 2 is a piping system diagram of a lactam vapor recovery apparatus in an oxygen concentration measurement system of the annealing oven.

  The annealing oven 1 removes strain at the time of molding the cast polyamide resin molded body and heats it in order to prevent cracking and damage during processing. It consists of a fan 22 for circulating gas.

  When annealing the resin molded product, there are problems such as the surface of the resin molded product being burnt black if the oxygen concentration in the annealing oven becomes too high, and safety issues such as heating the lactam and causing an explosion. Can happen. When heating the molded body in the oven, nitrogen is always sent to keep the oxygen concentration low. However, since this is a safety issue, an oxygen concentration meter is attached to measure the oxygen concentration in the annealing oven. The oxygen concentration was monitored. However, an oximeter cannot be constantly monitored because it periodically samples and measures.

  Therefore, the annealing apparatus of the present invention includes an oxygen concentration meter for periodically measuring the oxygen concentration in the annealing oven, and constantly monitoring the nitrogen fed into the oven with a flow meter, and a sufficient amount of nitrogen. A means of indirectly checking the oxygen concentration in the oven by checking whether the oxygen is being sent into the oven, and monitoring the heater surface temperature of the annealing oven and setting a predetermined temperature below the ignition temperature of the unreacted monomer The temperature can be controlled so as not to exceed.

  In some cases, a pressure gauge that constantly monitors the pressure in the annealing oven is attached to monitor whether the nitrogen gas is sufficiently flowing into the oven, and whether the oxygen concentration is sufficiently low. It becomes a means to confirm indirectly.

  For example, the oxygen concentration meter is attached as follows. In the annealing oven 1 having the lactam vapor recovery device S in the oxygen concentration measurement system of the annealing oven, the exhaust pipe 3 is connected to the exhaust hole 2 provided on the side wall, and the pressure for measuring the pressure inside the oven is measured from the exhaust pipe 3. A total of 4 branches. A lactam collection unit 6 made of a flexible hose curved downward is connected to the tip of the pressure gauge via an elbow 5.

  The lactam collection unit 6 curved downward by the flexible hose is immersed in a water tank 7 in which room temperature water is stored, and the inside of the lactam collection unit 6 is maintained at less than 69 ° C., which is the lactam solidification temperature.

  An ordinary exhaust pipe 9 is connected again via the elbow 8, and the exhaust pipe 9 is connected to the valve 10. Here, the valve 10 is set to be normally closed and open at the time of measurement. Further, the service valve 11 for confirming the closure of the flexible hose and the manometer 12 are branched in the middle of the exhaust pipe 9, and the manometer 12 knows from the instrumentation that the inside of the building is not blocked and is surely exhausted. Can do.

  A filter 13 is attached to the tip of the valve 10, and further to the oximeter 14. The filter 13 is provided for the sake of safety so as not to send a gas containing lactam to the oximeter 14.

  The oxygen concentration meter 14 includes a pump 15 (for example, a diaphragm pump), an oxygen sensor 16, and a signal generator 17. The pump 15 sucks gas into the oxygen sensor 16, and the oxygen concentration in the gas becomes a constant level. When it exceeds, a predetermined signal is generated by the signal generator 17, and the signal is sent to a control device (not shown) of the oven.

  The operation of this apparatus when actually performing annealing in the oven 1 will be described. First, annealing of the cast polyamide molded product itself is a very simple process, and the cast polyamide molded product (not shown) after molding is placed in the oven 1, the door is closed, and the inside of the oven is sealed. The switch is turned on and heating is started and the temperature is gradually raised. After heating at a temperature of about 180 to 200 ° C. for 4 to 100 hours, the temperature is gradually lowered.

  In the process, the oxygen concentration in the oven 1 is measured at a rate of about once / 30 to 200 min. When it is time to measure, the valve 10 is first opened, and the oxygen concentration meter 14 is connected from the oven 1 through the waste hole 2, the exhaust pipe 3, the lactam collection unit 6, the exhaust pipe 9, and the filter 13.

  Then, the gas in the oven 1 is sucked by operating the pump 15 of the oximeter 14. The gas may contain lactam gas, but the lactam having a high solidification temperature that is cooled when passing through the lactam recovery unit 6 adheres to the inner wall of the lactam recovery unit 6.

  The gas after a considerable amount of lactam is removed by the lactam collection unit 6 passes through the exhaust pipe 9 and the valve 10 and enters the filter 13. Here, as a precaution, the filter 13 is applied again to remove the lactam and other solids, and then the pump 15 is sent to the oxygen sensor 16.

  After the oxygen concentration is measured in the oxygen sensor 16, the gas is released to the outside air. When the oxygen concentration measured by the oxygen sensor 16 exceeds a predetermined concentration set in advance, a signal generated by the signal generator 17 is sent to the heater control device of the annealing oven and the heater is automatically turned off. By doing so, it is a safety device. In addition to turning off the heater, it is possible to raise an alarm. If the oxygen concentration exceeds 1.0%, the possibility of burning or explosion of the molded body increases. Therefore, the predetermined concentration in this case is preferably set to about 0.1 to 1.0%.

  The lactam recovery unit 6 passes through a water tank in which water is stored, and recovers the lactam by solidifying the lactam by lowering the temperature of the gas passing through the lactam recovery unit 6 to about 40 ° C. which is lower than the solidification temperature of the lactam, 69 ° C. However, depending on the flexible hose used in the lactam collection unit 6, the water in the water tank may be circulated as necessary.

  Although the cooling method using a water tank is shown above as the cooling means, it is not limited to this, and it is not limited to this. Anything can be used as long as it can cool below the temperature at which lactam is solidified, such as by creating a water channel and flowing water.

  Next, regarding nitrogen, nitrogen is fed into the oven through a nitrogen tube and exhausted through an exhaust tube installed on the opposite side so that the oven is filled with nitrogen. It will be installed in the middle of the nitrogen pipe that feeds in nitrogen. The nitrogen flow meter is attached to a nitrogen pipe that feeds nitrogen and measures the flow rate. It can be assumed that if the flow rate of nitrogen is sufficient, the oxygen concentration in the annealing oven will be a sufficiently low value indirectly. An oxygen concentration meter that cannot be constantly monitored can be complemented indirectly to monitor the oxygen concentration in the annealing oven to provide a safety device.

When the flow rate is less than a predetermined amount, it can be considered that nitrogen is not sent to keep the oxygen concentration in the oven sufficiently low, and an alarm is issued and heating is stopped. Although it depends on other conditions, it can be considered that a flow rate sufficient to keep the oxygen concentration sufficiently low is secured if there is a flow rate of 0.5 Nm ³ / h or more.

  A temperature sensor is attached to the surface of the oven heater, and the temperature is constantly monitored. Even if the oxygen concentration is unexpectedly increased by setting the temperature to 375 ° C. or lower, for example, about 300 ° C., which is the temperature at which the monomer gas of caprolactam ignites, and adjusting the temperature not to exceed that temperature The risk of explosion can be avoided.

  In addition to these safety devices, a pressure gauge may be attached to the oven to constantly monitor the pressure in the oven. As described above, nitrogen gas is constantly fed into the oven, and a constant pressure higher than one atmosphere is maintained. When the pressure in the oven decreases, it is possible to indirectly detect that nitrogen is not sufficiently fed and the oxygen concentration is increased. When the pressure in the oven becomes lower than a predetermined value, a safety device can be obtained by also issuing an alarm and stopping the heating.

  Further, a pressure gauge connected to the inside of the bearing is provided in the bearing portion of the rotating shaft of the fan 22 that circulates the expectation in the oven so that the internal pressure of the bearing seal cap can be measured. Is provided. If the sealing performance of the bearing portion of the bearing shaft in the rotating shaft of the circulation fan is deteriorated, outside air is drawn into the oven, and the oxygen concentration in the oven becomes high. However, as described above, the pressure inside the bearing bearing of the circulation fan rotating shaft is measured, and when the pressure inside the bearing becomes lower than a predetermined pressure, an alarm is issued and the oven heater is stopped. By adopting a mechanism, it is possible to prevent the problem that the surface of the resin molded body is burned. The predetermined pressure for generating the alarm is set to 0.1 kPa or less, for example, so that normal annealing can be performed and a good molded body can be obtained.

  The cast polyamide resin referred to in the present invention is obtained by anionic polymerization in a mold of a polymerizable lactam solution obtained by adding an anionic polymerization catalyst and an anionic polymerization initiator to substantially anhydrous ω-lactam.

  The ω-lactam is α-piperidone, ε-caprolactam, ω-laurolactam alone, or a mixture of two or more of these. Industrially advantageous lactams are ε-caprolactam and ω-laurolactam.

  Examples of the anionic polymerization catalyst include known ω-lactam polymerization catalysts such as sodium hydride, lithium hydride, sodium, potassium, etc. The addition amount is usually 0.1 to 0. It is about 02 mol%.

  Examples of the anionic polymerization initiator include N-acetyl-ε-caprolactam, isocyanate, diisocyanate, urea derivative, urethane, isocyanurate derivative, and the addition amount is usually 0.05 to 0 with respect to ω-lactam. About 1 mol%.

  As a method for producing a cast polyamide resin molded article, an anionic polymerization catalyst is added to ω-lactam and dissolved, and then an anionic polymerization initiator is added at the time of casting or after casting, or ω containing an anionic polymerization catalyst. Molding by mixing lactam and ω-lactam containing an anionic polymerization initiator at the time of casting or after casting, and heating in the mold at a temperature of about 100 to 210 ° C., preferably about 130 to 180 ° C. for a predetermined time. Goods are obtained.

  Thereafter, annealing is performed in an annealing oven in order to remove internal distortion of the molded product and prevent cracking during machining or to ensure dimensional stability after processing.

  In addition, oils that do not inhibit polymerization, waxes, zinc stearate, calcium stearate and other lubricants, carbon fibers, wollastonite and other reinforcing materials, and polyvinylidene chloride and other colorants can be added as other compounding agents. Is possible.

(Example)
For the purpose of removing internal strain of 20 monomer cast nylon plate-shaped molded articles having a thickness of 10 to 50 mm, a width of 1050 mm, and a length of 2050 mm, an oxygen concentration meter, an oven pressure gauge, and a nitrogen gas flow meter as shown in FIG. These three alarm devices and an annealing device with a heater output limit were used, and annealing treatment was performed under the program operation conditions shown in FIG.

In all annealing processes, the oxygen concentration meter (whether it is less than 1.0% or not in the temperature rising, heating holding and cooling I processes in which the gas temperature inside the annealing apparatus reaches a high temperature of 150 to 200 ° C. is determined. Measurement monitoring every hour), pressure gauge in the oven (continuously monitoring whether the increase relative to normal pressure is less than 0.1 kPa) and nitrogen gas flow meter (not less than 1.0 Nm ³ / h) (Continuous monitoring) was installed and linked with the alarm device. Subsequent cooling II requires cooling from 150 ° C. or lower to room temperature while forcibly taking in and out the oven, but the heater surface temperature is 300 ° C. below the ignition temperature (375 ° C.) of the combustible caprolactam monomer gas. The heater output limit that controls the heater was set at 55%.

  During the annealing process, the pressure gauge in the oven became less than 0.1 kPa and an alarm was issued. Therefore, when the sealing performance of the annealing oven was investigated, a leak of nitrogen gas was found from the door packing, and the packing was replaced. As a result, there was no leakage, the operation was resumed, and the annealing process was completed normally.

  By combining the above three alarm devices and heater output limits, abnormalities during annealing could be found, and the quality of the molded product and safety during annealing could be ensured.

(Comparative Example 1)
Annealing apparatus was used to remove 20 internal cast nylon sheet-shaped molded bodies to remove internal strains, except that an oven pressure gauge with an alarm device and a nitrogen gas flow meter were not installed. Processing was carried out. Since an alarm of oxygen concentration abnormality was given on the way, when the molded product in the annealing oven was examined, the surface was oxidized black and the appearance was poor. This is because the detection of the oxygen concentration abnormality was delayed because the oxygen concentration was detected every 3 hours.

(Comparative Example 2)
No internal pressure gauge and nitrogen gas flow meter with an alarm device were installed, and the internal strain of 20 monomer cast nylon sheet-like molded bodies was the same as in the examples except that the oxygen concentration was continuously detected. Annealing treatment was performed to remove. Although it has a mechanism for removing caprolactam monomer gas from the gas, it continuously detects oxygen concentration, so two hours after the start of heating and holding the oven, caprolactam monomer is connected to the oximeter piping. Stuck and solidified, causing clogging, making it impossible to detect the oxygen concentration, and the quality and safety could not be ensured.

  From these results, when performing the annealing process, the flow rate of the nitrogen gas supplied to the oven and the pressure inside the oven are measured together with the measurement of the oxygen concentration, and an alarm is issued when it is out of the predetermined range. It was found that the annealing process can be carried out by securing the apparatus while ensuring safety and without causing defects.

    The present invention is an annealing for removing internal distortion of a molded product caused by stress generated by polymerization shrinkage, crystallization shrinkage, and shrinkage accompanying cooling during resin molding occurring in a cast molded product of polyamide that polymerizes lactam ( By monitoring the oxygen concentration in the annealing oven in which annealing is performed, it is possible to prevent the occurrence of explosion due to burning of the molded body or heating of the lactam.

It is a perspective view which shows the place which opened the door of annealing furnace. It is a piping system diagram of a lactam vapor recovery device in an oxygen concentration measurement system of an annealing oven. It is a schematic diagram explaining the mechanism of the annealing apparatus of this invention. It is a figure which shows the operating condition program of an annealing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Annealing oven 2 Exhaust hole 3 Exhaust pipe 4 Pressure gauge 5 Elbow 6 Lactam collection part 7 Elbow 8 Water tank 9 Exhaust pipe 10 Valve 11 Valve 12 Manometer 13 Filter 14 Oxygen meter 15 Pump 16 Oxygen sensor 17 Signal generator

Claims (3)

  An annealing apparatus for a resin molded body in which a cast polyamide resin molded body is accommodated in an oven and heated and annealed, and a safety device that monitors the oxygen concentration in the oven and stops heating when the oxygen concentration exceeds a predetermined concentration; , Equipped with a nitrogen gas flow meter that feeds into the oven, a safety device that stops heating when the flow rate measured by the nitrogen gas flow meter falls below a predetermined value, and further maintains the heater surface temperature in the oven within the predetermined temperature An annealing apparatus for a polyamide resin molded body, characterized by being used in combination with a control apparatus.   The polyamide resin molded body annealing apparatus according to claim 1, wherein a safety apparatus is used in combination with a safety apparatus that monitors the pressure in the oven and stops heating when the pressure falls below a predetermined value.   2. The polyamide resin molded body according to claim 1, wherein the pressure in the bearing constituting the rotating shaft of the fan for circulating the gas in the oven is monitored, and a safety device that stops heating when the pressure falls below a predetermined value is also used. Annealing equipment.

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