JPH0226642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a methacrylic resin that has excellent heat decomposition resistance and fluidity, and has good molding processability. More specifically, the present invention relates to a method for producing a methacrylic resin that has excellent heat decomposition resistance and fluidity, and has good molding processability, using a bulk polymerization method. The present invention relates to a method for economically producing a methacrylic resin having the following properties. Molded products made of methacrylic polymer have transparency,
Due to its excellent physical properties such as weather resistance, mechanical strength, and resistance to heat deformation, it is widely used in automobile parts, electrical appliance parts, glazing, etc. Hitherto, most industrial methods for producing methyl methacrylate polymers have been suspension polymerization. The suspension polymerization method uses water as a medium, making it easy to control the polymerization, but since auxiliary agents such as dispersants are used, these remain in the resulting resin, resulting in a decrease in quality. In addition, significant expense and processing equipment are required to avoid drying the polymer and pollution problems due to the use of large amounts of water. On the other hand, the bulk polymerization method has the advantages of not leaving behind any impurities and improving quality as mentioned above, but also not requiring wastewater treatment as mentioned above and making it easy to make the process continuous. However, since the viscosity of the system increases rapidly when the polymerization rate is increased, it is difficult to remove the polymerization heat, transfer, and mix satisfactorily, leading to an increase in equipment costs. Particularly in the bulk polymerization of methyl methacrylate, an acceleration of the polymerization rate known as the "gel effect" is observed, and if the viscosity of the system is high, it becomes difficult to control the polymerization. To avoid this, it has been proposed to carry out bulk polymerization at high temperatures. When the polymerization temperature is raised in bulk polymerization, the increase in the viscosity of the polymerization system is suppressed, the problem of removing polymerization heat is also alleviated, and it becomes possible to maintain a higher polymerization rate. However, for example 160
Bulk polymerization at high temperatures such as ℃ or above generates by-products compared to bulk polymerization at low temperatures, and it is difficult to obtain methyl methacrylate polymers with excellent heat decomposition resistance due to depolymerization reactions, etc. It was hot.
When such polymers with poor thermal decomposition resistance are used, if the molding temperature is increased or the molding time is lengthened in order to obtain a molded product with large dimensions, scratches called silver streaks may occur on the molded product. However, foaming sometimes occurs, making it difficult to obtain the desired molded product. On the other hand, methods to improve the moldability of methacrylic polymers include lowering the molecular weight of the polymer, increasing the copolymerization rate, or adding large amounts of additives such as plasticizers to improve the fluidity of the resin at low temperatures and pressures. is being raised. However, although the polymers obtained in this way have good fluidity at low temperatures and low pressures and generally good moldability, on the other hand, when the molecular weight is lowered, there is a significant decrease in mechanical properties. Furthermore, when the copolymerization rate is increased or when a plasticizer is added, there is a drawback that physical properties, such as heat distortion temperature, are significantly lowered. Therefore, it has been difficult to produce a high-quality methacrylic resin with good moldability that has both excellent thermal decomposition resistance and fluidity using conventional methods. The present inventors have conducted intensive research in order to improve the drawbacks of conventional methacrylic resins, to obtain a methacrylic resin that exhibits excellent heat decomposition resistance and fluidity during processing, and has the desirable physical properties inherent to methacrylic resins. As a result of repeated efforts, we achieved the high productivity mentioned above.
We discovered that even in high-temperature bulk polymerization at 160°C or higher, the purpose could be achieved by polymerizing under specific conditions and forming a polymer with specific stereoregularity.
The invention has been completed. The first object of the present invention is to provide a method for producing a methyl methacrylate polymer having excellent heat decomposition resistance and fluidity and good moldability by a high-temperature bulk polymerization method. . A second object of the present invention is to provide an economical and industrially advantageous method for producing a methyl methacrylate polymer with stable control of the polymerization reaction and constant quality. Thus, the present invention provides methyl methacrylate or
More than 80% by weight methyl methacrylate and 20% by weight
A monomer mixture of the following methyl methacrylate and other copolymerizable alkyl acrylate or alkyl methacrylate, 0.01 to 1.0 mol% mercaptan and the following formula 40≧A ^1/2・B ^-1/2 ×10 ³ 3≧ A・B×10 ⁵ and 2.0≧A ⁻¹・(B+10.3)×10 ⁻⁶ [In the formula, A is the number of moles of the polymerization initiator in 100 g of the feed monomer, and B is the polymerization of the radical polymerization initiator. A polymerization raw material containing an amount of radical polymerization initiator that satisfies the half-life (hours) at temperature is supplied to one reaction zone, and the reaction mixture in the reaction zone is
Polymerization is carried out at a temperature of 0.degree. C. with stirring and mixing substantially uniformly, and the viscosity of the reaction mixture is maintained at 10 to 500 poise at the reaction temperature of the reaction mixture, and then the reaction mixture is removed from the reaction zone, We also developed a method for producing a methacrylic resin with excellent heat decomposition resistance and fluidity, which is characterized by separating and removing volatile substances, mainly consisting of unreacted monomers, from a reaction mixture containing a polymer to obtain a methacrylic resin. provide. The method of the present invention can be roughly divided into two steps: polymerization and volatile matter separation step. The polymerization step is a step of bulk polymerizing a polymerization raw material consisting of a monomer mixture containing methyl methacrylate as a main component, a mercaptan, and a polymerization initiator. The volatile matter separation step is a step to obtain a methacrylic polymer by separating and removing volatile matter, which is mainly composed of unreacted monomers, from the reaction product containing the polymer produced in the polymerization step. In the polymerization step, methyl methacrylate containing a mercaptan and a radical polymerization initiator and a monomer as a main component are fed into one reaction zone. The monomer used in the method of the present invention is methyl methacrylate or a monomer mixture of 80% by weight or more of methyl methacrylate and 20% by weight or less of other alkyl methacrylate or alkyl acrylate copolymerizable with methyl methacrylate. be. The alkyl methacrylate used in the copolymerization with methyl methacrylate is selected from those having an alkyl group having 1 to 18 carbon atoms, such as methyl, ethyl, n-propyl, n-butyl, 2-ethylhexyl, dodecyl, and stearyl. Alkyl methacrylates having alkyl groups such as Further, the alkyl methacrylate which is a copolymerization component with methyl methacrylate is selected from those having an alkyl group having 2 to 18 carbon atoms. Particularly preferred in the present invention are methyl methacrylate and a monomer mixture of methyl methacrylate and an alkyl acrylate selected from methyl and ethyl. The mercaptan used in the present invention is a primary mercaptan having an alkyl group or a substituted alkyl group.
mercaptans such as n-butyl, isopropyl, n-octyl, n-dodecyl, sec-butyl, sec-dodecyl, tert-butyl mercaptan; aromatic mercaptans such as phenyl mercaptan, thiocresol , 4-tert-
Examples include mercaptans having 2 to 18 carbon atoms such as butyl-o-thiocresol; thioglycolic acid and its alkyl esters; β-mercaptopropionic acid and its alkyl esters; and ethylene thioglycol. These can be used alone or in combination of two or more. Among these mercaptans, tert-butyl, n-butyl, n-octyl and n-dodecyl mercaptan are preferred. The amount of mercaptan used ranges from 0.01 to 1.0 mol%. If the amount used is less than 0.01 mol %, the reaction rate becomes abnormally high and the polymerization reaction may not be controlled, making it difficult to obtain a polymer of constant quality and excellent heat decomposition resistance. Also
If it exceeds 1.0 mol%, the degree of polymerization will decrease and the mechanical properties of the product will decrease. The preferred amount used depends on the type of mercaptan, but is in the range of 0.05 to 0.5 mol%. Examples of the radical polymerization initiator used in the method of the present invention include di-tert.butyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, di-tert.butyl perphthalate, di-tert.butyl perbenzoate, and tert.・Butyl peracetate, 2,5-dimethyl-2,5-di-(tert/butylperoxy)
Organic peroxides such as hexane, di-tert-amyl peroxide, and 2,5-dimethyl-2,2-di(tert-butylperoxy)hexine, and azobisisobutanol diacetate, 1,
1-azobiscyclohexanecarbonitrile, 2
Examples include azo compounds such as -phenylazo-2,4-dimethyl-4-methoxyvaleronitrile and 2-cyano-2-propylazoformamide. These radical polymerization initiators can be used alone or in combination of two or more. The amount of radical polymerization initiator in the monomer mixture is A
= number of moles of radical polymerization initiator in 100 g of monomer feed, B = half-life (time) of radical polymerization initiator at polymerization temperature, then A and B are expressed by the following formulas (1), (2) and ( 3) must be controlled to satisfy. 40≧A ^1/2・B ^-1/2 ×10 ³ ...(1) 3≧A・B×10 ⁵ ......(2) and 2.0≧A ^-1・(B+10.3)×10 ^-5 ... ...(3) In the method of the present invention, if the concentration of the radical polymerization initiator used satisfies the above three equations, it is difficult to control the polymerization reaction in the polymerization reaction zone, and it is difficult to control the polymerization reaction in the polymerization reaction zone. A methacrylic polymer with excellent properties cannot be obtained. Here, "the half-life of a radical polymerization initiator at the polymerization temperature" means the half-life in a dilute benzene solution having the same temperature as the polymerization temperature, and this is described in Modern Plastics magazine, February 1952 issue, page 144. It can be easily measured according to the method. In the polymerization reaction zone, the reaction mixture in the reaction zone is stirred and mixed substantially uniformly at a temperature of 160 to 200°C, preferably 160 to 185°C, and the viscosity of the reaction mixture is adjusted to a temperature of 160 to 200°C, preferably 160 to 185°C. While maintaining the temperature within a certain range, the isotactic polymer content in the resulting polymer is at least 7.
Polymerization is performed by adjusting the amount to be at least 7.5% by weight, preferably at least 7.5% by weight. If this condition is not met, a methacrylic resin with excellent heat decomposition resistance and fluidity, which is the object of the present invention, cannot be obtained.
If the temperature of the reaction mixture in the reaction zone is less than 160°C, the content of isotactics in the polymer tacticity will be low, resulting in poor fluidity. On the other hand, raising the temperature of the polymerization reaction mixture to 200°C or higher is advantageous in terms of productivity, but it also reduces the heat decomposition resistance of the resulting polymer, worsens its moldability, and produces side reaction products. The amount increases. Therefore, the polymerization temperature of the present invention is 160°C or higher and 200°C.
The temperature is less than 0.degree. C., preferably from 160.degree. C. to 185.degree. C., more preferably from 170.degree. C. to 180.degree. In the reaction zone, the viscosity of the reaction mixture is adjusted to 10 to 500 poise, preferably 10 to 300 poise at the reaction temperature.
Control the viscosity within the poise range. The viscosity in the reaction zone is
If it is less than 10 poise, the heat decomposition resistance of the obtained polymer will decrease. On the other hand, when the viscosity exceeds 500 poise, the resulting polymer has excellent thermal decomposition resistance, but it becomes difficult to mix and remove the heat of polymerization, making stable control difficult. In the reaction zone, the isotactic polymer must be contained in the reaction mixture in an amount of 7% by weight or more in the polymer obtained by polymerization. If the content of this isotactic polymer is less than 7% by weight, the effect of improving the fluidity of the obtained polymer cannot be expected, although the exact reason is unknown. On the other hand, if the content is too large, fluidity can be improved, but other physical properties are affected. Therefore, the preferred range of isotactic polymer content in the polymer of the present invention is 7 to 10% by weight. The content of other syndiotactic polymers and heterotactic polymers associated with this is 47 to 54, respectively.
% by weight and 39-43% by weight. The manufacturing equipment used in carrying out the present invention is not particularly limited as long as it does not impede the purpose of the present invention, but for example, Japanese Patent Publication No. 56-15641,
A tank-type reactor described in Utility Model Publication No. 54-38625 and the like, which has a function of sufficiently mixing the entire inside of the tank, is preferable. The reaction mixture that has been polymerized to a predetermined viscosity in the reaction zone is sent to a volatile matter separation step, where the reaction mixture is heated to 200-290°C under reduced pressure to remove volatiles mainly composed of unreacted monomers. Separate and remove most of it. Monomer content in the final resin is 1% by weight or less, preferably
The content shall be 0.3% by weight or less. The device used for volatile matter separation is a general vent extruder or a devolatizer. Preferably, those described in Japanese Patent Publication No. 52-17555, Utility Model Publication No. 55-30987, etc. are preferred. The polymer from which volatiles have been separated is extruded in the molten state through a die to form the desired shape. Plasticizers and lubricants such as dioctyl phthalate, dioctyl sebacate, stearyl alcohol, stearic acid, and lauryl alcohol; Tinuvin-P
(Ciba Geigy), ultraviolet absorbers such as methyl salicylate, phenyl salicylate, and additives such as colorants and pigments may be added within a range that does not impede the object of the present invention. These can be added during or after the polymerization step or volatile separation step. The methacrylic polymer obtained by the present invention has excellent heat decomposition resistance despite the high-temperature bulk polymerization method, and also has good fluidity, so it is particularly characterized by excellent moldability. The quality of moldability can be determined by the temperature range that allows molding, and the larger the range, the better. The upper limit temperature of this temperature range depends on the thermal decomposition resistance and volatile matter content of the molding material. However, the volatile content can be reduced by using good deaerators, so
The higher the thermal decomposition resistance of the molding material, the higher the upper limit temperature can be obtained. On the other hand, the above-mentioned lower limit temperature is determined mainly depending on the fluidity of the molding material, and can be controlled relatively easily by changing the average degree of polymerization, the amount of copolymerization component, and the amount of plasticizer. However, in practice, it is difficult to lower the temperature to the lower limit because increasing the fluidity and lowering the lower limit temperature also leads to a decrease in physical properties. However, the methacrylic polymer obtained according to the present invention can improve fluidity, that is, lower the lower limit temperature, compared to conventional products without changing the degree of polymerization, amount of copolymerization, or plasticity. Therefore, according to the present invention, a resin with improved thermal decomposition resistance and a high upper limit temperature and an increased fluidity and a lower lower limit temperature can be obtained, and therefore the molding temperature range is widened. As a result, during molding, the incidence of defective products is reduced, the yield is further improved, and not only small molded products but also large molded products can be molded. The resin obtained by the present invention can be used for various molded products, such as extruded plates, and as a molding material, and particularly when used as a molding material, it can exhibit excellent molding properties. Although the present invention can be carried out both in batch mode and continuous mode, it is preferable to carry out in continuous mode from the viewpoint of quality stability and productivity. Examples are shown below. These examples are not intended to limit the invention. All parts and percentages used below are by weight. The apparatus used in the examples had the following specifications, and the reaction tank and volatile matter separator were directly connected to carry out a continuous process. Reaction tank: A reaction tank equipped with a spiral ribbon type stirrer and a jacket with an internal volume of 300. Volatile separator; twin screw vent extruder
Screw 90mmφ×2 Total length 1200mm Bent part: 600mm length Evaluations in Examples were conducted using the following method. (1) Molding processability (A) Resistance to thermal decomposition of the polymer The polymer was repeatedly operated under the injection molding machine and injection conditions shown below while varying the barrel temperature of the injection molding machine, resulting in a phenomenon known as silver streak or flashing. The upper limit barrel temperature (hereinafter abbreviated as _T2 ) at which the appearance rate of molded products with visible defects is 20% or less was determined. Molding machine: H-35A plunger type manufactured by Kakaki Seisakusho Mold capacity: 130 mm x 130 mm x 2 mm 2 holes Injection pressure: 1200 Kg/cm ² G cycle: 65 seconds (B) Polymer fluidity ASTM-D1238-65T Flow rate value measured according to the specified method (displayed as the amount of polymer extruded in 10 minutes (g) when the barrel temperature is 230°C and the load is 10 kg.Hereinafter, this is referred to as the FR value) Measured by. (2) Heat distortion temperature Measured in accordance with ASTM D-648-56 at a fiber stress of 264psi and a heating rate of 3.6〓/min. (3) Tactility of polymer Measuring device: JEOL FT-NMR JNM-FX90Q Measuring method: Tactility was determined by measuring the NMR spectrum and analyzing the triad chain from the quaternary carbon signal. (4) Measurement of [η] Dissolve the sample in chloroform and add 0.5% by weight.
This solution was kept at 25° C., and the number of seconds t of flow between the marks of an Ostwald viscometer and the number of seconds t ₀ of flow of chloroform were measured, and the intrinsic viscosity [η] was calculated using the following formula. [η] = 3 {(t/t ₀ ) ^1/3 -1}/C where C is the sample concentration (g/) Example 1 90 parts of methyl methacrylate, 10 parts of methyl acrylate, 0.2 parts of n-octyl mercaptan, G-
A monomer mixture consisting of 0.0017 parts of t-butyl peroxide was fed continuously to the reactor at 25/hour under nitrogen. Nitrogen was injected into the reaction tank to increase the internal pressure to 8Kgcm ²
G, and the polymerization temperature was adjusted to 170°C. After about 8 hours, steady operation was reached, the rotational speed of the stirring blade was set at 90 rpm to ensure sufficient mixing, the residence time was about 4.5 hours, and the viscosity in the reaction tank was 30 poise. The viscosity in the reaction tank was measured using a rotary process viscometer attached to a pipe provided at the bottom of the reaction tank and continuously sending the reaction mixture to the devolatilizer (the same applies hereinafter).
The temperature of the vent extruder is 230℃ at the vent section and at the die section.
The temperature was 225°C, and the vent vacuum level was 9 mmHg abs. 1/
The polymer was extruded into strands through a die having four 8" diameter circular holes, water cooled and cut into 1/4" lengths to form pellets. It was operated continuously for 180 hours under these conditions. The FR value of the obtained molding material was 28-32, and the residual monomer measured by gas chromatography was 0.2-32.
0.4%, and _T2 showed a high value of 300-305°C. The heat distortion temperature and [η] were 85° C. and 0.058/g, respectively, and the material had high mechanical strength and excellent transparency, and had good quality as a molding material. The molding material also contained a high isotactic polymer content of 8.5% isotactic polymer, 52.0% syndiotactic polymer and 39.5% heterotactic polymer. Example 2 99.5 parts of methyl methacrylate, 0.29 parts of t-butyl mercaptan per 0.5 parts of methyl acrylate,
A monomer mixture consisting of 0.002 parts of di-t-butyl peroxide was polymerized in the same manner as in Example 1. However, the polymerization temperature was 175°C and the residence time was 4.1 hours. The viscosity in the reaction tank at this time was 140 poise. The temperature of the vent extruder is 260℃ at the vent part.
The extrusion part was set at 240°C, the die part was set at 235°C, and the degree of vacuum at the vent part was set at 9 mmHg. A molding material was obtained by continuous operation for 150 hours under these conditions. This molding material
The FR value was 7.5-8.5, the residual monomer was 0.2-0.4%, and the _T2 was as high as 300-305°C. The heat distortion temperature and [η] are 102℃ and 0.057, respectively.
/g. This molding material also contains 9.0% isotactic polymer and syndiotactic polymer.
It had a high isotactic polymer content of 50.0% and 41.0% heterotactic polymer. of the molding materials obtained in Examples 1 and 2 above.
_T2 is generally about 310-340℃ for methacrylic polymers
Considering that it is said that thermal decomposition begins rapidly at For comparison, T ₂ values measured for currently commercially available methacrylic polymer materials are shown in Table 1 below.

[Table] Examples 3 to 12, Comparative Examples 1 to 4 The same method as in Example 1 was used. The feeding rate of the monomer mixture was 25/hour, and the temperature of the vent extruder was 230 to 260℃ at the vent section and 230 to 250℃ at the extrusion section.
℃, the die part was 225 to 240°C, and the vent part vacuum degree was 9 mmHg abs. Table 2 shows the polymerization conditions and the physical properties of the obtained polymer.

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Claims (1)

[Claims] 1. Methyl methacrylate or a monomer mixture of 80% by weight or more of methyl methacrylate and 20% by weight or less of methyl methacrylate and other alkyl acrylate or alkyl methacrylate copolymerizable with 0.01 to 1.0 mol% Mercaptan and the following formula 40≧A ^1/2・B ^-1/2 ×10 ³ 3≧A・B×10 ⁵ and 2.0≧A ^-1・(B+10.3)×10 ^-6 [In the formula, A is feed Polymerization raw materials containing an amount of radical polymerization initiator that satisfies the number of moles of polymerization initiator in 100 g of monomer, B is the half-life (time) of the radical polymerization initiator at the polymerization temperature are placed in one reaction zone. feed the reaction mixture in the reaction zone to 160-200
The polymerization is carried out with substantially uniform stirring and mixing at a temperature of 0.degree. Production of a methacrylic resin with excellent heat decomposition resistance and fluidity, which is characterized by obtaining a methacrylic resin by extracting and separating and removing volatile substances mainly composed of unreacted monomers from a reaction mixture containing a polymer. Law. 2. The method for producing a methacrylic resin having excellent heat decomposition resistance and fluidity according to claim 1, wherein the content of the isotactic polymer in the methacrylic resin is 7% by weight or more. 3. The content of isotactic polymer in the methacrylic resin is 7 to 10% by weight, the content of syndiotactic polymer is 47 to 54% by weight, and the content of heterotactic polymer is 39 to 43% by weight. A method for producing a methacrylic resin having excellent heat decomposition resistance and fluidity according to claim 1.