JPH0139444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coagulation method for recovering thermoplastic resin from thermoplastic resin latex, and more specifically, the present invention relates to a coagulation method for recovering thermoplastic resin from thermoplastic resin latex. Regarding efficient collection methods. Conventionally, the following method has been generally used to recover polymers from thermoplastic resin latex. That is, the stabilized thermoplastic latex is treated with inorganic salts (Al ₂ (SO ₄ ) ₃ , CaCl _{2 ,} etc.), inorganic acids (HCl, H ₂ SO ₄ , etc.), organic acids (acetic acid, etc.) or hydrophilic polar solvents. The polymer latex is first creamed in the first tank, and then in the second tank, the creamed particles are heated to a coagulation temperature higher than the heat distortion temperature of the polymer while stirring in the second tank. The polymer powder is collected by coagulation and enlargement. If an inorganic acid is used as a coagulant, the recovered polymer particles will have fewer fine particles, a uniform particle size, and a high bulk specific gravity, but in terms of quality, especially heat resistance, those coagulated with inorganic salts The result is inferior to that of This is because the emulsifier used during polymerization is converted into an organic acid by the inorganic acid of the coagulant and remains in the polymer, reducing heat resistance. Therefore, if the heat resistance of the resulting resin is important, it is appropriate to use an inorganic salt as a coagulant. However, when inorganic salts are used as a coagulant in the conventional coagulation method described above, the resulting coagulated particles are unsatisfactory, with a large number of fine particles, a wide particle size distribution, and a low bulk specific gravity. For coagulated particles with many fine particles, washing with water,
Even after the dehydration process, only wet powder with a high moisture content is obtained, and therefore the residual rate of coagulant is high. It also causes clogging of the cloth in the centrifuge during the dehydration process, resulting in poor dehydration. Further, in the drying process, various problems occur such as scattering of fine powder, reduction in recovery rate, and failure to penetrate the powder into the ruder when pelletizing the obtained powder. Therefore, it has good heat resistance, has few fine particles, and has a particle size of 10 mesh or more.
There was a desire for a method to efficiently recover relatively large coagulated thermoplastic resin particles with a size of 200 mesh and a bulk specific gravity of 0.25 or more. The present inventors have arrived at the present invention as a result of various studies to solve such problems.
Using one or more compounds selected from CaCl ₂ , BaCl ₂ , MgCl ₂ , ZnCl ₂ and MgSO ₄ , the thermoplastic resin latex is brought into contact with a coagulation liquid in a temperature range equal to or higher than the heat distortion temperature of the thermoplastic resin. The thermoplastic resin latex is placed at an angle of 90° ± 45° with respect to the stirring shaft and with respect to the flow direction in the stirring system in a stirring system under high shear conditions where the shear rate of the coagulated liquid at ^a point is 100 sec -1 or more. The present invention provides a method for coagulating a thermoplastic resin latex, characterized in that the thermoplastic resin latex is supplied at an angle of 90°±45°. The coagulant used in the present invention is CaCl ₂ ,
A compound selected from BaCl ₂ , MgCl ₂ , ZnCl ₂ and MgSO ₄ or a mixture thereof. NaCl has unsatisfactory coagulation performance, and Al ₂ (SO ₄ ) ₃ causes sulfate radicals to remain in the resin, not only discoloring the resin but also worsening the thermal stability of the resin. The amount of coagulant is determined by the type and amount of emulsifier used during polymerization of the thermoplastic resin, but is generally 0.5 to 5.0% by weight, preferably 1.0 to 3.0% by weight based on the thermoplastic resin. . If the amount used is less than 0.5% by weight, the coagulation of the latex will be insufficient, and if the amount used exceeds 5.0% by weight, a large amount of washing water will be required to wash away the excess amount of coagulant, which is uneconomical. It is. The coagulation temperature needs to be higher than the heat distortion temperature of the thermoplastic resin in order to enlarge the coagulated particles. When the coagulation temperature is lower than the heat distortion temperature of the thermoplastic resin, the average particle size of coagulated particles becomes small and a large amount of fine particles are generated. In addition, in order to perform solidification operation stably, it is appropriate that the upper limit of the solidification temperature is the heat distortion temperature + 40°C. If coagulation operation is performed at a temperature higher than this, a large amount of large particles will be generated, which will cause solidification blockage in the coagulation tank and clogging in the slurry transfer piping. The coagulation in the present invention is characterized in that the thermoplastic resin latex is supplied into a coagulation liquid in a high shear state at a temperature higher than the thermal deformation temperature of the thermoplastic resin, and the coagulated particle size is enlarged in one step. A high shear state when thermoplastic resin latex is supplied into a coagulating liquid means that the shear rate of the coagulating liquid at the point of contact between the thermoplastic resin latex and the coagulating liquid is
It means to maintain a condition of 100sec ^-1 or more. That is, one of the features of the present invention is that it has been found that the stirring effect at the local point where the thermoplastic resin latex is introduced is important, rather than the stirring effect throughout the coagulation tank. In the present invention, the shear rate of the coagulating liquid at the point of contact between the thermoplastic resin latex and the coagulating liquid is taken as a measure of this local stirring effect, and when the shear rate of the coagulating liquid becomes less than 100 sec ^-1 , the coagulating liquid is introduced into the coagulating tank. It was confirmed that the generation of giant particles is unavoidable because the shear force on the latex is weak and non-uniform. In addition, in order to achieve the effects of the present invention, the latex is fed into the stirring system at an angle of 90°±45° with respect to the stirring shaft and with respect to the flow direction within the stirring system.
It is necessary to do this at an angle within the range of 90°±45°. If the supply of latex to the stirring system deviates from the above angle, the stirring effect of the stirring system on the supplied latex will not be sufficient, the latex will become unevenly dispersed, large particles will be generated, and the slurry discharge pipe This will block the pipes, making continuous operation difficult. As the coagulation apparatus of the present invention, commonly used stirring tanks, screw extruders, centrifugal pumps, dynamic mixing devices, etc. are designed to satisfy the above-mentioned conditions of shear rate of coagulation liquid and feeding direction of latex. used. Latexes applicable to the present invention include polymer latexes of alkenyl aromatic monomers such as styrene and α-methylstyrene polymerized by a general emulsion polymerization method; acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate; Polymer latex of acrylic monomers such as butyl methacrylate; Copolymer latex consisting of a mixture of two or more of the above monomers; At least one of the above monomers and polybutadiene or butadiene and monoolefin monomer graft polymer latex with a butadiene copolymer;
A graft polymer latex of at least one of the above monomers and a mixture of polybutadiene and a butadiene copolymer; a mixed latex of two or more of the above polymer latexes, copolymer latexes and graft polymer latexes. In carrying out the coagulation of the present invention, the solid content concentration of the thermoplastic resin in the coagulation liquid is 5 to 25% by weight, preferably 10 to 20% by weight. If the solid content concentration is less than 5% by weight, it is difficult to increase the particle size, and the amount of steam required for heating per unit weight of thermoplastic resin increases, which is uneconomical. On the other hand, the solid content concentration is 25% by weight.
If it exceeds this amount, large particles in the shape of a smudge will be generated, causing blockage in the coagulation tank and the coagulation slurry transfer pipe, which is not desirable for stable operation. According to the method of the present invention, since the thermoplastic resin latex is fed into the coagulation liquid under high shear conditions and coagulation and particle size enlargement are performed in one step, the average residence time in the coagulation tank is It is sufficient if it is within about 10 seconds, and compared to conventional coagulation methods (average residence time of 40 minutes or more), a shorter residence time is required and the coagulation tank can be made smaller. Furthermore, compared to the conventional two-stage solidification method, the solidification temperature can be lowered, which is economically advantageous. The present invention will be explained in detail below using Examples and Comparative Examples. Note that parts and % in the following examples mean parts by weight and % by weight unless otherwise specified. Example 1 (Production of thermoplastic resin latex) Polybutadiene latex 16 parts (solid content), α
- 50 parts of methylstyrene (hereinafter abbreviated as AMS),
10 parts of styrene (hereinafter abbreviated as ST), 24 parts of acrylonitrile (hereinafter abbreviated as AN), distilled water
Emulsion polymerization was carried out using 200 parts of disproportionated potassium rosin acid and 3 parts of disproportionated potassium rosin acid at 70° C. for 5 hours under a nitrogen stream using a catalytic amount of a radical polymerization catalyst. A thermoplastic resin latex with a polymerization conversion rate of 95% and a solids content of 32% was obtained. The heat distortion temperature (ASTM D-648, test piece 1/8" bar, no annealing, load 264 psi) of this latex coagulated with CaCl ₂ was 90°C. (Coagulation equipment) The coagulation tank used had an internal volume of 7 This is a pressure-resistant stirring tank shown in Fig. 1.The stirring blades 2 are three paddle blades with a diameter of 110 mm and an angle of 45 degrees, and are installed in three stages.The stirring shaft is operated at a speed of 1200 rpm by a continuously variable transmission 9. A horizontal pipe 4 at the bottom of the coagulation tank was placed 40 mm from the stirring blade, and latex was supplied to the coagulation tank through this pipe.
The coagulant solution and heating steam are supplied from piping at the bottoms 5 and 6 of the coagulation tank, and the solidified slurry is discharged from a horizontal pipe 7 at the top of the coagulation tank. When a coagulation temperature of 100° C. or higher was required, a pressure regulating valve was installed in the coagulation slurry discharge pipe 7 to keep the internal pressure of the coagulation tank constant. The temperature of the liquid in the coagulation tank is detected by a thermometer 8, and can be adjusted to a predetermined temperature by adjusting the water vapor flow rate. (Coagulation) The rotation of the coagulation tank stirring shaft was adjusted to 1200 rpm and started, and the following components were introduced into the coagulation tank 1 using a metering pump. At this time, the shear rate of the coagulating liquid at the point where the latex was introduced was 170 sec ^-1 . Thermoplastic resin latex 1.0 ^{M 3} /hr 0.5% CaCl ₂ aqueous solution 1.2 M ³ /hr At the same time, water vapor at a pressure of 3 Kg/cm ² G was introduced into the coagulation tank, and the liquid temperature in the coagulation tank was adjusted to 105°C. In addition, in order to adjust the internal pressure of the coagulation tank to 0.5 kg/cm ² G, the slurry discharge pipe pressure regulating valve was operated. Thirty minutes after the start of the coagulation operation, the slurry discharged from the discharge pipe was sampled, filtered with a centrifuge, washed with water, dehydrated, and dried overnight in an aerated dryer. Regarding the dry powder, particle size distribution and bulk specific gravity were measured according to JIS Z8801 and JIS K6721. The results are shown in Table 1. Example 2 (Manufacture of thermoplastic resin latex) 1 part of sodium stearate, 200 parts of distilled water, and a catalytic amount of radical polymerization catalyst were mixed with 18 parts of polybutadiene latex (solid content), and styrene was added to the mixture.
A mixture of 60 parts of acrylonitrile and 22 parts of acrylonitrile was added dropwise, and the solid content was determined by emulsion polymerization.
A 32% thermoplastic latex was obtained. This latex was solidified with CaCl ₂ and had a heat distortion temperature of 78°C. (Coagulation) Using the same coagulation apparatus as in Example 1, the following components were introduced into the coagulation tank using a metering pump. Thermoplastic resin latex 1.0 ^{M 3} /hr 0.5% CaCl ₂ aqueous solution 1.2 M ³ /hr At the same time, water vapor at a pressure of 3 Kg/cm ² G was introduced into the coagulation tank, and the liquid temperature in the coagulation tank was adjusted to 95°C. Thirty minutes after the start of coagulation, the slurry discharged from the slurry discharge pipe was sampled and treated in the same manner as in Example 1 to obtain a dry powder. Table 1 shows the results of measuring the particle size distribution and bulk specific gravity of this dry powder. Example 3 (Production of thermoplastic resin latex) 60 parts of AMS, 10 parts of MMA (methyl methacrylate)
part, 30 parts of AN, 4 parts of potassium oleate, 250 parts of water
The mixture was emulsified in a 50° C. portion and emulsion polymerized for 5 hours at 50° C. using a catalytic amount of a radical polymerization catalyst. A thermoplastic resin latex with a polymerization conversion rate of 97% and a solids content of 28% was obtained. This latex was solidified with CaCl ₂ and had a heat distortion temperature of 98°C. (Coagulation) Using the same coagulation apparatus as in Example 1, the following components were introduced into the coagulation tank using a metering pump. Thermoplastic resin latex 1.0 ^{M 3} /hr 0.5% CaCl ₂ aqueous solution 1.2 M ³ /hr At the same time, water vapor at a pressure of 3 Kg/cm ² G was introduced into the coagulation tank, and the liquid temperature in the coagulation tank was adjusted to 115°C. Thirty minutes after the start of coagulation, the slurry discharged from the slurry discharge pipe was sampled and treated in the same manner as in Example 1 to obtain a dry powder. Particle size distribution for this dry powder,
The results of measuring the bulk specific gravity are shown in Table 1. Example 4 Coagulation was performed in exactly the same manner as in Example 2, except that the coagulant was changed from CaCl ₂ to MgSO ₄ , and the properties of the dry powder were evaluated. The results are shown in Table 1. Example 5 The coagulation process and dry powder evaluation were carried out in the same manner as in Example 1, except that the latex supply pipe 4 at the bottom of the coagulation tank was placed 10 mm from the stirring blade. At this time, the shear rate of the coagulating liquid at the point of introduction of the latex was 690 sec ^-1 . The characteristics evaluation results of the dry powder are shown in Table 1. Comparative Example 1 Coagulation and coagulation particles were evaluated in the same manner as in Example 1, except that in the coagulation apparatus of Example 1, the latex supply was changed from the latex supply pipe 4 to the latex supply pipe 3 at the top of the coagulation tank. The shear rate of the coagulating liquid at the latex supply port during this coagulation was 30 sec ^-1 . Slurry sampling was performed 10 minutes after the start of coagulation. Ten minutes after the coagulation operation started, the slurry discharge pipe became clogged with coarse particles, making it impossible to discharge the slurry, making it impossible to continue the coagulation operation. Table 1 shows the results of coagulated particle powder characteristics for the slurry 8 minutes after the start of coagulation operation, and there were a significant number of coarse particles on the 10th mesh, making stable operation difficult.
Also, the number of microparticles that passed through 200 meshes was significantly higher.
This is problematic because it causes trouble in the slurry separation, drying process, and ruder process. Comparative Example 2 Coagulation and coagulation particles were evaluated in the same manner as in Example 1 except that the temperature of the internal liquid in the coagulation tank was changed to 88°C. The results of the coagulated particle powder characteristics are shown in Table 1. Comparative Example 3 A conventional two-stage coagulation apparatus shown in FIG. 2 was used. First, the following ingredients were introduced into the 100 coagulation tank (with a stirrer) 11 using a metering pump, and at the same time the pressure was 3Kg/cm ²
Steam G was also introduced into the coagulation tank, and the liquid temperature in the coagulation tank was adjusted to 80°C. Thermoplastic resin latex 300/hr 0.5% CaCl ₂ aqueous solution 400/hr This solidified cream liquid was supplied to the second aging tank (500 capacity) 13 at a rate of 800/hr using a gear pump 12, and at the same time the pressure was 3 kg/hr. cm ² G of water vapor was introduced to adjust the liquid temperature in the aging tank to 125°C. The coagulated slurry discharged from the slurry discharge pipe 14 was sampled two hours after the start of the coagulation operation and treated in the same manner as in Example 1 to obtain a dry powder. The powder property results are shown in Table 1. Comparative Example 4 A coagulation operation was carried out in exactly the same manner as in Comparative Example 3, except that the temperature of the liquid in the aging tank was raised to 130°C. As a result, the resin solidified in the aging tank, making it impossible to operate. Comparative Example 5 The coagulation operation was carried out in exactly the same manner as in Comparative Example 1, except that the type of latex supplied in Comparative Example 1 was changed to thermoplastic resin latex, and the liquid temperature in the coagulation tank was changed to 115°C. Table 1 shows the powder properties of the dry powder obtained from the sampled slurry. Comparative Example 6 In Example 2, the coagulant type was changed to H ₂ SO ₄ ,
The coagulation process and dry powder characteristics were evaluated in exactly the same manner as in Example 2, except that the liquid temperature in the coagulation tank was changed to 90°C. The heat distortion temperature of the resin obtained here (ASTM D
−648, specimen 1/8″ bar, no annealing, load
264psi) is 72℃, which is significantly lower than the heat distortion temperature of the resin obtained in Example 2, which was 78℃, and it is clear that using an acid as a coagulant reduces the heat resistance of the resin obtained. Is recognized. Table 1 shows the results of powder characteristic evaluation of the obtained dry powder. Even when an acid is used, good coagulated particles can be obtained by employing the coagulation method of the present invention. 【table】

[Brief explanation of drawings]

FIG. 1 shows a longitudinal cross-sectional view of one embodiment of a coagulation tank used in the method of the present invention, and FIG. 2 shows a flow sheet of a conventional two-stage coagulation apparatus system. 1... Coagulation tank, 2... Stirring blade, 3, 4... Latex supply pipe, 5... Coagulant supply pipe, 6...
Steam supply piping, 7... Slurry discharge piping, 8...
...Thermometer, 9...Continuously variable transmission, 11...Coagulation tank,
12...Gear pump, 13...Aging tank, 14...
Slurry discharge pipe.

Claims (1)

[Claims] 1 When coagulating thermoplastic resin latex, CaCl ₂ , BaCl ₂ , MgCl ₂ , ZnCl ₂ is used as a coagulant.
Using one or ^more compounds selected _from ¹
The thermoplastic resin latex is fed into the stirring system under the above high shear condition at an angle of 90° ± 45° to the stirring shaft and at an angle of 90° ± 45° to the flow direction within the stirring system. A method for coagulating thermoplastic resin latex, characterized by: