JPH035409B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a transparent molding material with little coloring and a high heat distortion temperature by continuously polymerizing methyl methacrylate with maleic anhydride and styrene as the main copolymer components. A method for producing a highly heat-resistant molding material by copolymerizing maleic anhydride with styrene and methyl methacrylate is known, but in a production method based on conventional knowledge, the resulting polymer cannot be make use of
When molded at high temperatures of 250°C or higher, there were problems such as foaming, scratches called silver streaks, and a noticeable yellow discoloration. These silver streaks and coloring problems cause the loss of light transmittance, which is an important performance of methyl methacrylate and styrene polymers, and significantly reduce the commercial value. The present inventors have conducted intensive studies to investigate the causes of these problems, and as a result, we have found that oxygen dissolved in the raw materials and unreacted maleic anhydride introduced from the polymerization reaction process to the devolatilization process. However, it was discovered that this had a serious adverse effect, and the present invention was completed. That is, commonly used industrial raw materials such as methyl methacrylate, styrene, maleic anhydride,
The solvent is stored in the presence of air, and oxygen is dissolved in these raw materials at a concentration commensurate with the partial pressure of the air. These oxygens do not have much effect on coloring in the polymerization of polymethyl methacrylate or polystyrene, so they are used as they are in the synthesis of polymers for purposes other than optical applications. However, the situation is quite different when it comes to maleic anhydride-based polymers, and it has been found that polymerization in the presence of oxygen promotes significant discoloration. Oxygen can be removed by methods such as distillation, stripping by contact with nitrogen gas, and vacuum deaeration. was used. When measured with a dissolved oxygen analyzer and using the indicated value as a standard, the above method can easily reduce the amount to 1/10 to 1/20. Moreover, coloration is sufficiently improved with this oxygen content. On the other hand, coloring with maleic anhydride shows a more peculiar behavior. In continuous polymerization, the polymerization rate is 100.
% is possible only in extremely limited compositions, and 100% polymerization usually impairs the transparency of the polymer. Therefore, the polymerization rate is 60%
It is preferable to choose a range of ~90%. Moreover, the polymerization method used at this time is not to perform a flow-type reaction from the start to the end of the polymerization, but to maintain a constant temperature and a constant reaction composition in as much of the polymerization as possible to achieve a constant polymer composition. It is convenient to carry out the reaction in a homogeneous reactor in order to improve transparency and mechanical and heat-resistant properties. However, in such a reaction using only a homogeneous reactor, monomers for maintaining the copolymer composition are inevitably discharged together with the polymer. In particular, for maleic anhydride, which has an important effect on heat resistance, it is necessary to maintain a constant monomer concentration, so if the reaction mixture is introduced into the devolatilization equipment as it is, it will not be possible to Due to the thermal influence of this process, only a markedly yellow polymer can be obtained. Such polymers have a large degree of silver streaks during injection molding and are not of practical use. Maleic anhydride would be introduced by the remaining unreacted components, but the inventors of the present invention attempted to solve this problem by introducing a new idea. That is, after more than half of the reaction is carried out in the first reactor, which is reacting uniformly, the reaction is further carried out in the second reactor, which is a flow reactor, to consume maleic anhydride, and to complete the devolatilization step. This is to reduce the amount introduced into the system. Here, the reaction rate in the first reactor is 30 to 70% of the total number of monomer moles supplied to the first reactor, and in the second reactor, the polymerization rate is increased by 10 to 30%. You need to react accordingly. If the polymerization rate in the first reactor is lower than 30%, in addition to being economically unfavorable, only a polymer with a wide composition distribution can be obtained, and a polymer with excellent transparency and heat resistance can be obtained. Hateful. On the other hand, if it exceeds 70%, it becomes difficult to consume maleic anhydride in the second reactor, which is not preferable.

The polymerization rate in the second reactor is preferably increased as low as possible, such that the maleic anhydride remaining in the first reactor is consumed to a sufficiently low concentration. This is a mixture of a polymer with a uniform refractive index obtained by homogeneous polymerization and a polymer with a gradually different refractive index produced in a second reactor, which are mutually compatible, resulting in a completely transparent polymer. This is to form a Furthermore, the reason why the polymer exhibits the best performance in both heat resistance and mechanical properties is because the polymer has a nearly uniform composition distribution.

The polymerization rate in the second reactor must be increased by at least 10% to lower the maleic anhydride concentration, and 30% or less to keep the composition distribution range within an acceptable value. In this way, as a means to maintain the reaction rate in the first reactor and the second reactor, the polymerization in the first reactor is mainly performed using a polymerization initiator, and the second reactor is Preferably, the polymerization utilizes a reaction using an initiator in the first reactor. Addition of a new polymerization initiator in the second reactor is also considered, but this is undesirable as it will cause a non-uniform reaction unless significant special measures are taken for mixing, and it is less desirable than adding such an additional catalyst. It is preferable to use catalysts of different stages together and add them as a composite catalyst before the first reactor. In the polymer systems of the present invention where styrene is present as a copolymer, the polymerization temperature is also important. That is, styrene can be polymerized by thermal polymerization in the absence of a polymerization initiator, but when carrying out a reaction based mainly on thermal polymerization, thermal decomposition resistance is unfavorable, and styrene is It is necessary to promote polymerization. From this point of view, the temperature of the polymerization reactor can be regulated, and it is particularly preferable to maintain the temperature in the first reactor within the range of 50 to 150°C. Setting the temperature below 50°C is not economical because the reaction rate and the amount of polymerization initiator used increase significantly.
Under conditions of 150°C or higher, the influence of thermal polymerization becomes significantly greater. More preferably, maintaining the temperature within the range of 70°C to 120°C gives good results. More preferably 70
℃~100℃. The temperature of the second reactor must be raised adiabatically or by heating from the temperature of the first reactor to achieve the desired increase in polymerization rate to a temperature of 150°C or lower, preferably 120°C or lower. There is. 150 while containing a large amount of maleic anhydride.
Exposure to high temperatures of .degree. C. or higher is not preferable from the viewpoint of yellowing, and it is necessary to keep the concentration of maleic anhydride sufficiently low. The concentration of such maleic anhydride is preferably 2.5% by weight or less, preferably 1.5% by weight or less as a proportion of volatile components such as residual monomers and solvents. For this purpose, it is necessary to make the ratio of styrene and maleic anhydride composition of the polymer produced in the second reactor to 1.8 or more. The higher this ratio, the more completely maleic anhydride can be consumed in the second reactor. However, this ratio must be kept below 3.5. This is because increasing the proportion of styrene weakens the strength of the polymer and further deteriorates its weather resistance.

In this way, maleic anhydride is consumed until the temperature is sufficiently low. In the polymerization process, recycling of volatile components has the important effect of not causing any deterioration in quality. From the viewpoint of a polymer that can satisfy weather resistance, the composition ratio of methyl methacrylate should be at least 40 parts by weight based on 100 parts of the total. As described above, the polymer mixture in which the concentration of maleic anhydride is sufficiently low relative to the total volatile components is sent to a devolatilization step to remove the volatile components without deteriorating the quality due to new coloring or decomposition. Maleic anhydride is less than 500ppm,
Preferably it should be 100pm. As a specific method of such a degassing method, for example, the reaction mixture is sent to a devolatilization step having a devolatilization zone consisting of two or more stages, and the temperature is lowered to 180°C or less in the first stage devolatilization zone, more preferably. In this method, most of the volatile components are removed under a temperature condition of 150° C. or lower, and the remaining volatile components are removed under reduced pressure at an even higher temperature in the second and subsequent devolatilization zones. It may be the first stage devolatilization zone of a devolatilization device consisting of two or more stages, the first stage of a multi-stage vented screw extruder, or a falling liquid column type evaporation devolatilization device. However, the important thing is to keep the devolatilization temperature conditions as low as possible. The temperature limit is 180
℃, and it is preferable to devolatilize at a temperature below this temperature. The final stage of the devolatilization step is preferably a screw extruder. Unless the remaining amount of maleic anhydride is less than 500 ppm, discoloration and foaming will occur during pellet molding. Under the conditions of the present invention, it is possible to easily reduce the content to 500 ppm or less.

Polymers polymerized under such polymerization conditions are sufficiently practical, but in the case of polymers with a large methyl methacrylate component, acrylates with 1 to 4 carbon atoms in ester groups such as methyl acrylate and ethyl acrylate, or acrylic acid It has been found that it is more effective to copolymerize within 2%.
If it exceeds 2%, the thermal decomposition resistance against heat will improve, but the thermal deformation resistance will decrease, which is not preferable.

This reaction gives better results when carried out using a solvent. This devolatilizes maleic anhydride efficiently, making the first stage devolatilization process particularly effective at low temperatures, and is suitable for stably performing low-temperature polymerization reactions. be. As the solvent, methyl isobutyrate, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethylbenzene, etc. can be used.

In the styrene used for the main polymerization, it is better to keep the amount of tert-butylcatechol, which is generally added at about 15 ppm as a polymerization inhibitor, as low as possible. This is because it affects the coloring of the polymer, and it is preferable to use it at 5 ppm or less. To this end, it is necessary to remove it with an adsorbent or the like immediately before use, or by distillation.

The present invention will be explained in detail below with reference to Examples.

In the examples, % indicates weight %, and the heat resistance evaluation is
VSP defined in ASTM D-1525 was measured.
Melt flow index is ASTM-D-1238
(Conditions).

Example 1 A first reactor consisting of a uniformly stirred tank with a reaction volume of 10, followed by a plug flow second reactor with a reaction volume of 1.5 and L/D = 20, and 3 as a devolatilization device.
The polymer was obtained using an apparatus consisting of a stage vented extruder.

Raw materials include monomers consisting of 72 methyl methacrylate, 18 styrene containing 1 ppm of tert-butylcatechol, 9 maleic anhydride, and 1 methyl acrylate, a catalyst consisting of 0.45 lauryl peroxide, 0.11 octyl mercaptan, and 42.9 parts by weight of methyl ethyl ketone. The mixture was brought into countercurrent contact with nitrogen gas in a deoxidizing tower.

The removal rate of dissolved oxygen in this mixture was measured using a universal oxygen analyzer manufactured by Orital Electric (the sensor is for organic solvents).
When the oxygen concentration was measured based on the movement of the needle of the sample in equilibrium with air at 20°C and atmospheric pressure, it was less than 1/20 of that.

This raw material was continuously fed to the first reactor. The first reactor is operated at 78°C with a residence time of 4 hours. The inside is pressurized with nitrogen gas to 6Kg/cm ² G,
Prevents air from entering. Continued, entrance 78
The reaction was carried out in a plug flow second reactor whose temperature was gradually raised to 110°C at the outlet for a residence time of 0.6 hours. After 20 hours of reaction time, the reaction mixture was sampled from the outlet of the first reactor and the second reactor, and the composition analysis was performed. As a result, the polymerization reaction rate was 55% and 80%.
It was %. The composition ratio of the polymer components was determined by infrared absorption spectrum, acid drop method, and pyrolysis gas chromatography, and found that in the first reactor, 64.4% by weight of methyl methacrylate, 22.8% by weight of styrene, 11.9% by weight of maleic anhydride, and 0.9% by weight of methyl acrylate. At the outlet of the second reactor, the contents were 67.2% by weight of methyl methacrylate, 21.3% by weight of styrene, 10.6% by weight of maleic anhydride, and 0.9% by weight of methylacrylate.

On the other hand, regarding volatile components, in the first reactor, methyl methacrylate 41.6, styrene 6.2,
The contents were 2.8% by weight of maleic anhydride, 0.6% by weight of methyl acrylate, and 48.8% by weight of methyl ethyl ketone. At the outlet of the second reactor, methyl methacrylate 29.0, styrene
1.5, maleic anhydride 0.8, methyl acrylate
0.5, and 68.2% by weight of methyl ethyl ketone.
These polymerization reactants at the outlet of the second reactor are continuously heated at 120°C under atmospheric pressure at the first stage vent, at 220°C 20 Torr at the second stage vent, and at 220°C 4 Torr at the third stage vent.
The pressure was reduced to 1,000 ml, and devolatilization was performed.

The resulting polymer is methyl methacrylate
67.2, styrene 21.3, maleic anhydride 10.6, and methyl acrylate 0.9% by weight.
Regarding residual monomers, methyl methacrylate was detected at 300 ppm, and styrene and maleic anhydride were below the detection limit of 100 ppm.

Using the obtained pellets, press at 270℃ for 10 minutes.
Pressure molding was performed for a minute to obtain a test piece measuring 50 x 100 x 4 mm.
No air bubbles were detected anywhere in this test piece, and almost no coloration was observed. Furthermore, in order to investigate the pyrolysis loss, we used a thermogravimetric measuring device manufactured by Daini Seikosha.
The amount of thermal decomposition measured at 275℃ with SSC/560GH is 0.8
%/10 minutes. This resulted in a thermal decomposition level comparable to that of commercially available polymethyl methacrylate. The VSP value of this specimen is 128℃, and the MI value is 230℃.
The load was 3.8 kg and the speed was 1.5 g/10 minutes.

Comparative Example 1 Polymerization was carried out using the same apparatus as in Example 1, but the deoxidation treatment of the reaction raw material was omitted.

The residual maleic anhydride content of the obtained polymer is
Although the concentration was less than 100 ppm, the pellets were colored yellow.

Example 2 Using the same equipment as in Example 1, methyl methacrylate 62.5, trrr styrene containing 1 ppm of butylcatechol 28.4, maleic anhydride 8.1, methyl acrylate 1.0, lauryl peroxide 0.45, octyl mercaptan 0.11, methyl ethyl ketone 42.9
The reaction raw material was brought into countercurrent contact with nitrogen gas in a deoxidizing tower to reduce the oxygen removal rate to 1/20 or less, and was continuously supplied to the first reactor.

The residence time and temperature of the first reactor and second reactor were the same as in Example 1.

The polymerization rate in the first reactor was 55%, and the polymerization rate in the second reactor was 80%. The composition of volatile components in the polymerization reaction mixture leaving the second reactor is methyl methacrylate.
26.4, styrene 4.8, maleic anhydride 0.16, methyl acrylate 0.4, and methyl ethyl ketone 68.2% by weight.

Subsequently, devolatilization was carried out under the same conditions as in Example 1 using a devolatilization device consisting of a three-stage vent. The recovered liquid recovered from this first stage vent was mixed with new raw materials without any special treatment such as distillation, passed through a deoxidation process, and was operated continuously for 10 days, but the operation and quality remained stable. A polymer with excellent chromaticity was obtained.

The resulting polymer composition was methyl methacrylate
57.4%, styrene 31.7%, maleic anhydride 10.0%,
A polymer consisting of 0.9% methyl methacrylate,
Regarding remaining monomers, methyl methacrylate was detected at 0.05%, and styrene and maleic anhydride were also detected.
It was below the detection limit of 100ppm. Using this pellet, dumbbells were made using an injection molding machine at 250 and 270°C, but there was very little discoloration due to temperature and no silver streaks were observed. Regarding the heat resistance of this resin, the VSP130°C MI value was 1.4.

Comparative Example 2 Methyl methacrylate 81.3, styrene 7.3, maleic anhydride 11.4, and lauryl peroxide
After deoxidizing the raw material consisting of 0.45, octyl mercaptan 0.11 and methyl ethyl ketone 42.9, 10
Continuously introduced into a homogeneous reactor with a residence time of 4 hours, the polymerization rate was 55%, and the polymer composition was methyl methacrylate.
80.1, styrene 9.9, maleic anhydride 10.4 and methyl methacrylate 42.4 as volatile components.
A mixture containing 2.1% by weight of styrene, 6.7% by weight of maleic anhydride, and 48.8% by weight of methyl ethyl ketone was obtained. This mixture was introduced into a devolatilization device consisting of a three-stage vent, and the volatile components recovered from the first vent were reused without purification. When molding was attempted at 270°C, a marked increase in black-yellow coloring was observed as the molding temperature increased, and severe silver streaks were observed during molding at 270°C.

Claims (1)

[Scope of Claims] 1. A method for producing a heat-resistant thermoplastic resin by continuously polymerizing methyl methacrylate, maleic anhydride, styrene, or an alkyl acrylate having an alkyl group having 1 to 4 carbon atoms. In the first reactor, a polymerization reaction is carried out in the range of 50℃ to 150℃ using a raw material mixture in which dissolved oxygen has been removed to at least 1/10 of the oxygen dissolved in equilibrium at 20℃ in the atmosphere. The polymerization reaction was carried out to a polymerization rate of ~70% by weight, and then the polymerization rate was further increased by 10 to 30% by weight in a second reactor consisting of a flow reactor, so that the composition of the resulting polymer mixture became maleic anhydride 5. ~20 wt%, styrene 10-40 wt%, and the weight ratio of styrene to maleic anhydride is
1.8 to 3.5, further polymerized so that the methyl methacrylate composition exceeds 40% by weight, and the alkyl acrylate content is 0 to 20% by weight,
Moreover, after reacting until the concentration ratio of maleic anhydride among volatile components such as monomers and solvents remaining in the polymer mixture exiting the second reactor is 2.5% by weight or less, the devolatilization step is carried out. A method for continuously polymerizing and producing a transparent heat-resistant polymer with little coloration, characterized by devolatilizing the maleic anhydride to a concentration of 0.05% by weight or less. 2 The first reactor is 70-100℃, the second reactor is 70-100℃
The method according to claim 1, wherein the temperature is 120°C. 3. Claim 1, wherein the devolatilization step consists of a step operated under at least two stages of devolatilization conditions, and the temperature of the first stage devolatilization zone is 180°C or less.
The method described in Sections 1 and 2. 4 5 weight of polymerization inhibitor contained in styrene
The method according to any one of claims 1 to 3, wherein the polymerization is carried out at less than ppm.