JPH09286815A - Method for recovering polymer from latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering a polymer from a latex whereby a polymer contg. a small amt. of fine particles is recovered from a latex presubjected to a monomer removal treatment, etc., to reduce the residual monomer content by coagulating the latex under specified conditions. SOLUTION: A latex having a residual monomer content of 10,000ppm or lower (based on the polymer in the latex) is coagulated by bringing it into contact with a coagulant under stirring under such conditions that the coagulation temp. is higher than (Tv-15) deg.C but lower than (Tv+35) deg.C (wherein Tv is the Vicat softening point of the polymer); that when the coagulant is a salt with a mono-, di-, or trivalent cation, then the relation: C <= coagulant concn.(mmol/l)<=(C+2,000), C <= coagulant concn. <= (C+30), or C <= coagulant concn. <= (C+10) [wherein C is the coagulation value (mmol/l)] is satisfied, respectively; that when the coagulant is an acid, then the relation: C <= coagulant concn. <= (C+30) is satisifed; and that the peripheral speed at the end of the stirrer blade is 10-500cm/sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a polymer latex, and more particularly to a method for recovering a polymer having a small amount of particles after a polymer latex obtained by emulsion polymerization or the like is subjected to a monomer removal treatment. ..

[0002]

2. Description of the Related Art Latex obtained by polymerization usually contains 10,000 to 30,000 ppm of residual monomer, and therefore, when it is directly subjected to coagulation, it has a large fusion force and good coagulation property. However, from the viewpoint of environmental protection, it is desirable that the amount of residual monomer in the polymer is small. Generally, when a powdery polymer is coagulated and recovered from a polymer latex obtained by emulsion polymerization, the methods for reducing the residual monomer are a method of demonomerizing at the latex stage, and a method of removing the monomer after the powdery state. The present invention relates to the former, though there is a method for treating a monomer. However, in the latex which has been subjected to the demomer treatment, there is a problem that fine particles are generated because the cohesive force between the coagulated particles is small.

[0003]

SUMMARY OF THE INVENTION The present invention has been made against the background of the above-mentioned prior art, and a polymer having a small amount of fine particles is recovered from a polymer latex whose residual monomer concentration is reduced by a demonomer treatment or the like. The purpose is to provide a method.

[0004]

[However, Tv represents the Vicat softening point (° C.) of the recovered polymer. ]

(B) Coagulant concentration; When the coagulant is a salt and the cation of the coagulant is monovalent, C≦coagulant concentration (mmol/l)≦(C+2,000) The coagulant is a salt, When the cation of the coagulant is divalent, C≦coagulant concentration (mmol/l)≦(C+30) When the coagulant is a salt and the cation of the coagulant is trivalent, C≦coagulant concentration ( mmol/l)≦(C+10) When the coagulant is an acid C≦coagulant concentration (mmol/l)≦(C+30) [where C represents a coagulation value (mmol/l). ] (C) The polymer latex and the coagulant are contacted with stirring,
The peripheral speed of the tip of the stirring blade is 10≦the peripheral speed (cm/s) of the tip of the stirring blade≦500

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer latex applied to the present invention is a latex which is usually obtained by emulsion polymerization and comprises a vinyl polymer latex and/or a rubber-modified vinyl polymer latex. Of these, vinyl polymer latex is a vinyl monomer shown below,
Alternatively, it can be obtained by emulsion polymerization with another monomer copolymerizable therewith. Further, the rubber-modified vinyl-based polymer is obtained by emulsion-polymerizing a vinyl-based monomer shown below or another monomer copolymerizable therewith in the presence of the rubber-like polymer shown below. can get.

The vinyl monomer is not particularly limited, but includes (meth)acrylic acid such as acrylic acid and methacrylic acid; acrylic acid alkyl ester such as methyl acrylate, ethyl acrylate and butyl acrylate. System monomer; methyl methacrylate,
Methacrylic acid alkyl ester type monomers such as ethyl methacrylate; vinyl cyan type monomers such as acrylonitrile and methacrylonitrile; aromatic vinyl type monomers such as styrene and α-methylstyrene; vinyl chloride, vinyl bromide Various monomers such as halogenated vinyl-based monomers are listed, and these can be used in combination of two or more kinds. Examples of preferable vinyl monomers include (meth)acrylic acid alkyl esters, vinyl cyan monomers, and aromatic vinyl monomers.

Further, as other copolymerizable monomers,
Examples thereof include maleimide-based monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide. When a maleimide-based monomer is used, heat resistance is improved and a polymer having excellent heat resistance can be obtained.

On the other hand, as the rubber-like polymer, polybutadiene, styrene-butadiene copolymer (styrene content is preferably 5 to 60% by weight), styrene-isoprene copolymer, acrylonitrile-butadiene copolymer,
Ethylene-α-olefin copolymer, ethylene-α-
Examples include olefin-polyene copolymers, acrylic rubbers, butadiene-acrylic copolymers, polyisoprene, styrene-butadiene block copolymers, hydrogenated butadiene polymers, ethylene ionomers, and silicone rubbers. These rubber-like polymers are used alone or in combination of two or more. Among these, preferred rubbery polymers include polybutadiene, styrene-butadiene copolymers, acrylic rubbers, and silicone rubbers (in particular, unsaturated group-containing silicone rubbers are preferable).
The rubber-like polymer used in the production of the rubber-modified vinyl polymer is latex.

Specific examples of the above polymer latex are usually
The polymer latex produced by emulsion polymerization is mentioned. For example, styrene-butadiene rubber (SBR),
Acrylonitrile-butadiene rubber (NBR), rubber-like polymer such as acrylic rubber, acrylic resin, polystyrene, styrene-acrylonitrile copolymer, α-methylstyrene-acrylonitrile-maleimide monomer copolymer, ABS resin, MBS resin , AES resin, AAS
Examples of the latex of these polymers include resinous polymers such as rubber-modified vinyl polymers such as resins.

The content of the rubber-like polymer in the polymer latex is preferably less than 60% by weight, more preferably 55% by weight or less, particularly preferably 50% by weight or less, and more preferably 45% by weight or less, 40% by weight
When it is below, the object and effect of the present invention will be further exerted.

The present invention is directed to a polymer latex which has been subjected to a demonomer treatment and has a residual monomer content of 10,000 ppm or less based on the polymer component. When the residual monomer content in the polymer latex is more than 10,000 ppm based on the polymer component,
Coagulation is good but environmentally problematic. On the other hand, 10,000
When it is 0 ppm or less, the coagulability is deteriorated and the amount of fine powder increases, but this problem can be solved by the method of the present invention. The residual monomer content in the polymer latex used in the present invention is 10,000 ppm or less, preferably 5,000 ppm or less, and particularly 1,000 ppm or less, based on the polymer component. The purpose and effect are further enhanced.

Here, the method for reducing the residual monomer content is not particularly limited, but it is carried out by a column tower type steam stripping, a vessel type reduced pressure steam stripping, a flash operation, or an air or inert gas blowing. A general method such as strip operation is adopted.

As the coagulant used in the present invention, those which are usually used for coagulating latex can be used. For example, it is an inorganic acid such as hydrochloric acid and sulfuric acid, an organic acid such as acetic acid and formic acid, or a metal salt of these acids, and in addition, a polymer flocculant and the like can be used together. Examples of the metal salt include calcium chloride,
Aluminum chloride, aluminum sulfate, magnesium sulfate, etc. may be mentioned. In the present invention, polyvalent metal salts and inorganic acids are preferred. More preferred are calcium chloride, magnesium sulfate and sulfuric acid. In addition, examples of the polymer flocculant include polyacrylamide. The salt and the acid can be used together.

In the recovery method of the present invention, the following (a),
The polymer latex is coagulated under the conditions of (b) and (c). That is, the coagulation condition of (a) is (Tv-1
5) <solidification temperature (°C) <(Tv+35), preferably (Tv-5) <solidification temperature (°C) <(Tv+25) [where Tv is the Vicat softening point (°C) of the recovered polymer.
Indicates. ]. If the coagulation temperature (°C) is lower than (Tv-15), fine powder is generated, while if it is higher than (Tv+35), dirt and lumps are generated on the inner wall of the coagulation tank and the long-term continuous operation becomes difficult.

Further, the concentration of the coagulant (b) (mmol/
l) is C≦coagulant concentration≦(C+2,000), preferably C≦coagulant concentration≦(C+1,400), when the coagulant is a salt and the cation of the coagulant is monovalent. More preferably, C≦coagulant concentration≦(C+700). When the cation of the coagulant is divalent, C≦coagulant concentration≦
(C+30), preferably C≦coagulant concentration≦(C+2
0), more preferably C≦coagulant concentration≦(C+10)
Is. Furthermore, when the cation of the coagulant is trivalent, C≦
Coagulant concentration≦(C+10), preferably C≦coagulant concentration≦(C+5), more preferably C≦coagulant concentration≦(C
+3). Here, when the coagulant concentration is less than C (coagulation value), coagulation does not sufficiently occur and the state is uncoagulated. on the other hand,
When the cations of the coagulant are monovalent, divalent, and trivalent, the respective coagulant concentrations (C+2,000), (C+30), (C
When it exceeds +10), fine particles are generated.

On the other hand, when the coagulant is an acid, C≦coagulant concentration≦(C+30), preferably C≦coagulant concentration≦(C+
20), more preferably C≦coagulant concentration≦(C+1
0). Here, when the coagulant concentration is less than C (coagulation value), coagulation does not sufficiently occur and the state is uncoagulated. On the other hand, when the acid coagulant concentration exceeds (C+30), fine particles are generated.

A preferred coagulant concentration when two or more coagulants containing a monovalent, divalent, or trivalent cation and an acid are used as a mixture is determined by the following method. The coagulation value of the coagulant containing a monovalent cation is C ₁ (mmol/l), the concentration used is A (mmol/l); the coagulation value of the coagulant containing a divalent cation is C ₂ (mmol/l). l), the concentration used is B (mmol/l); the coagulation value of the coagulant containing a trivalent cation is C ₃ (mmol/l), the concentration used is C (m
mol/l); the coagulant is an acid and the coagulation value is C ₄ (mmo
l/l), when the concentration used is D (mmol/l),
The coagulant concentration is represented by the following converted coagulant concentration C _CONV converted into the coagulant containing divalent cations. _{C CONV = A (C 2 /} C 1) + B + C (C 2 / C 3) + D
(C ₂ / C ₄₎

Using this converted coagulant concentration, the coagulation value C _MIX of the coagulant mixed in a predetermined ratio is determined. And
In this case, it solidifies under the following conditions. C _MIX ≤ converted coagulant concentration ≤ (C _MIX +30)

Next, the stirring condition of (c) is 10≦peripheral speed (cm/s)≦500, preferably 60≦peripheral speed (cm/s).
s)≦360, more preferably 80≦peripheral speed (cm/
s) ≤ 300, particularly preferably 100 ≤ peripheral speed (cm/
s)≦250. If the peripheral speed is less than 10 cm/s, large lumps will be generated. On the other hand, the peripheral speed is 500 cm/s
If it exceeds, fine powder is generated and there is a problem in handling.

In the present invention, the solidified slurry (solidified particles) is heat-treated to improve properties such as an increase in bulk density and a reduction in water content in the recovered solidified particles. The heat treatment condition is (Tv-25)≦heat treatment temperature (° C.)≦(Tv+50), preferably (Tv-20)≦
Heat treatment temperature (° C.)≦(Tv+40), more preferably (Tv−15)≦heat treatment temperature (° C.)≦(Tv+3
0) [However, Tv represents the Vicat softening point (° C.) of the recovered polymer. ]. The heat treatment temperature is (Tv-
When the temperature is lower than 25) (°C), the effect of heat treatment is small, and the effects of increasing bulk density and reducing the water content in the recovered coagulated particles do not appear. On the other hand, when the temperature exceeds (Tv+50) (° C.), the solidified particles are fused with each other to form a lump, which prevents stable operation. Moreover, the slurry concentration cannot be increased to a practical range.

The heat treatment time is 10≦heat treatment time (minutes)≦180, preferably 20≦heat treatment time (minutes)≦120. When the heat treatment time is shorter than 10 minutes, the effect of heat treatment does not appear. On the other hand, if it exceeds 180 minutes, the physical properties such as the hue of the resin are impaired, and the apparatus becomes too large, which is not economical.

The heat treatment is preferably carried out while stirring the polymer slurry composed of the coagulated particles, and particularly preferably so as to achieve uniform mixing. The stirring speed is
The peripheral speed of the stirring blade is preferably 20 to 1,000 m/s, more preferably 50 to 800 cm/s.

The pH condition for the heat treatment is 3≦pH.
≦8, preferably 4≦pH≦6. This is due to the charged state of the particle surface, and the effect of pH is small even if the pH is lower than 3 or higher than 8. The pH may be adjusted before the heat treatment, that is, at the time of coagulation, but in this case, the coagulant is limited to the organic acid salt and/or the inorganic metal salt, and in other cases, the pH is adjusted after the coagulation treatment. Preferably. Note that p
For H adjustment, hydrochloric acid, sulfuric acid, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or the like can be used.

As the process of the method for recovering the polymer latex of the present invention, the polymer latex and the coagulant (aqueous solution) are used.
And, if necessary, each of the water is continuously supplied so as to satisfy the conditions (a), (b), and (c) of the present invention to obtain a solidified slurry.

In order to prevent the polymer from adhering to the coagulation tank during solidification, the following surface finish may be applied as a measure for preventing the adhesion. That is, it is preferable that the inner wall of the coagulation tank and the surface of the stirring blade have a buff number of 400 or more. More preferably, buff #800 or more, and more preferably, electrolytic polishing is performed. Most preferably, buffing #400 or more is performed, and then electrolytic polishing is performed. The shape of the stirring blade used for mixing and stirring when obtaining this solidified slurry is not particularly limited, and commonly used blades such as paddle blades, turbine blades, propeller blades, gate blades, ribbon blades are used. it can.

In the present invention, the above-mentioned coagulated polymer particles in the coagulated slurry can be separated, washed with water if necessary, and dried to obtain dried polymer particles. As a separation method, a horizontal belt filter, a centrifugal dehydrator, a vertical pressure filter or the like can be used for dehydration. Further, the dehydrated coagulated particles can be dried with a twin-screw extruder equipped with a dehydration slit.

Since the polymer particles obtained by the present invention have few fine powder particles, the problems that usually occur in the above method can be improved. The clogging of the horizontal belt filter and the filter cloth of the centrifugal dehydrator can be eliminated. A low discharge amount due to defective biting at the entrance of the twin-screw extruder is eliminated. It is possible to dehydrate and dry without causing leakage of coagulated particles from the dehydration slit of the twin-screw extruder.

[0028]

EXAMPLES The method of the present invention will be described in detail below with reference to examples, but these do not limit the scope of the present invention. The parts and% in the examples are by weight unless otherwise specified. Moreover, the measuring method of each physical property in an Example is as follows.

Coagulation value Polymer latex was diluted with water so that the solid content concentration was 0.2%, 10 cc of this diluted polymer latex was put in a test tube, and 10 cc of coagulant aqueous solution of various concentrations was added thereto, and well. After mixing, the mixture was allowed to stand in a constant temperature bath at 30° C., and after 1 hour, the presence or absence of precipitate formation was examined, and the lowest concentration of the coagulant causing precipitation (mmol/l after mixing) was taken as the coagulation value. Vicat softening point The Vicat softening point is measured according to JIS K72 by previously collecting and drying the polymer from the polymer latex used for coagulation.
It was measured according to the method of 06. The load used for measurement is 1 Kgf.

[0030] to an average particle diameter of particle diameter 1000μm called for particle size distribution by laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba). Further, those having a thickness of more than 1,000 μm were obtained by image processing. The average particle diameter d ₅₀ is a particle diameter having a cumulative value of 50% obtained from the cumulative distribution curve of the above particle size distribution. Bulk density Measured according to JIS-K-6721 (unit: g/
ml). The amount of fine particles was determined by the amount of resin passing through a 200 mesh wire mesh.

Dewatering property The water content (weight basis) after centrifugal dehydration (rotation speed 1,800 rpm, 5 minutes) was evaluated. The fluidity of the fluid polymer particles is described in “Chemical Engineering” (19
Measured four values of "angle of repose", "compression degree", "spatula angle" and "uniformity (or cohesion degree)" by the method described on pages 163-168, issued on January 18, 1965. Then, a score was given from the values according to the conversion table, and the liquidity index represented by the sum thereof was evaluated.

Example 1 As a polymer latex, a graft copolymer latex consisting of 10 parts of butadiene obtained by graft copolymerizing styrene, methyl methacrylate and acrylonitrile on polybutadiene, 23 parts of styrene, 10 parts of acrylonitrile and 57 parts of methyl methacrylate was used as a raw material. And The residual monomer content of this graft copolymer latex was 15,
It was 000 ppm. This latex was placed in a closed tank, the pressure was reduced to 150 Torr by a vacuum pump, and steam was blown into the latex to heat it to 70° C. to perform a monomer removal treatment. The residual monomer content after demonomerization was 200 ppm. The solid content concentration of this graft copolymer latex is 30%, and the coagulation value measured using an aqueous solution of calcium chloride (coagulant) is 15 mmol.
/L, the Vicat softening point was 90°C.

Next, using a coagulation tank with an internal volume of 10 liters equipped with a stirrer (two-stage inclined paddle blade, blade diameter = 14.5 cm, inner surface is mirror-finished by electrolytic polishing), stirring was performed at a tip speed of the stirring blade of 100 cm/s. Then, 333 ml/min of the above latex and 666 ml/min of 0.35% calcium chloride aqueous solution were continuously added. At this time, the coagulant concentration in the coagulation tank was 20 mmol/l. Further, the temperature of the coagulation tank was controlled at 90° C. by adjusting the amount of steam blown in. The continuously discharged coagulated slurry was subjected to heat treatment at pH 5 at 110° C. for 40 minutes. Then, using a centrifuge, the polymer component was separated, washed with water, and dehydrated to obtain a wet powder. The wet powder was dried with hot air (70° C.×7 Hr) to obtain dry polymer particles.
The results are shown in Table 1.

Example 2 The procedure of Example 1 was repeated except that the concentration of the coagulant in the coagulation tank was 30 mmol/l. The results are shown in Table 1. Example 3 Example 1 was repeated except that the solidification temperature was 85°C. The results are shown in Table 1. Example 4 Example 4 was repeated except that the stirrer was rotated at a peripheral speed of 150 cm/s. The results are shown in Table 1.

Example 5 As a polymer latex, a graft copolymer latex comprising 16 parts of butadiene obtained by graft copolymerizing styrene, methyl methacrylate and acrylonitrile onto polybutadiene, 15 parts of styrene, 26 parts of acrylonitrile and 43 parts of α-methylstyrene. Was used as a raw material. The residual monomer amount of this graft copolymer latex was 17,000.
It was 0 ppm. When the monomer removal treatment was carried out in the same manner as in Example 1, the residual monomer content was 380 ppm. The solid content concentration of this polymer latex was 30%, the coagulation value measured using sulfuric acid was 1 mmol/l, and the Vicat softening point was 112°C. Using this polymer latex, coagulation temperature 105° C., coagulant concentration 2 mmol/
l, and the peripheral speed of the stirring blade was 200 cm/s, and solidification was performed by the solidification device with a stirrer used in Example 1. Also,
The heat treatment is performed at 120° C. for 9 hours at pH 5 of the solidified slurry.
It was carried out for 0 minutes. The results are shown in Table 2.

Example 6 As a polymer latex, a copolymer of 22% acrylonitrile, 1% styrene, 76% α-methylstyrene and 1% methyl methacrylate was used as a raw material. The residual monomer amount of this polymer latex is 23,000 pp
It was m. When the monomer removal treatment was carried out in the same manner as in Example 1, the residual monomer content was 520 ppm. The solid content concentration of this polymer latex was 30%, the coagulation value measured using calcium chloride was 3 mmol/l, and the Vicat softening point was 115°C. Using this polymer latex, coagulation temperature 110°C, coagulant concentration 4 mmol
/L and a stirring blade peripheral speed of 200 cm/s were solidified by the solidification device with a stirrer used in Example 1. Also, the heat treatment is performed at 135° C. under the pH 5 of the solidified slurry.
Was carried out for 60 minutes. The results are shown in Table 2.

Example 7 Example 1 was repeated except that sodium chloride was used as the coagulant and the coagulant concentration was 1,000 mmol/l. The coagulation value is 900 mmol/l.
Met. The results are shown in Table 2. Example 8 The procedure of Example 1 was repeated, except that aluminum chloride was used as the coagulant and the concentration of the coagulant was 2 mmol/l. The coagulation value was 1.4 mmol/l. The results are shown in Table 2.

Comparative Example 1 The same treatment as in Example 1 was carried out except that the solidification temperature was changed to 140° C. The results are shown in Table 3. Comparative Example 2 Treatment was carried out in the same manner as in Example 1 except that the solidification temperature was changed to 70°C. The results are shown in Table 3. Comparative Example 3 The treatment was performed in the same manner as in Example 1 except that the coagulant concentration was changed to 10 mmol/l. The results are shown in Table 3.

Comparative Example 4 Treatment was carried out in the same manner as in Example 1 except that the coagulant concentration was changed to 60 mmol/l. The results are shown in Table 3. Comparative Example 5 Example 1 except that the peripheral speed of the stirring blade was changed to 5 cm/s.
Was processed in the same manner as. The results are shown in Table 3. Comparative Example 6 Processing was performed in the same manner as in Example 1 except that the peripheral speed of the stirring blade was changed to 600 cm/s. The results are shown in Table 3.

Examples 1 to 8 are examples carried out within the scope of the present invention, and the number of fine particles was small, and the object of the present invention was achieved. On the other hand, in Comparative Example 1, the solidification temperature was high, the amount of the polymer attached was large, and lumps were formed in the solidification tank, which made the operation impossible. In Comparative Example 2, the solidification temperature was low and the amount of fine particles was large.
In Comparative Example 3, the coagulant concentration was less than the range of the present invention, and almost no coagulation occurred. Comparative Example 4 is an example in which the coagulant concentration exceeded the range of the present invention, and many fine particles were generated. In Comparative Example 5, the peripheral speed of the stirring blade was less than the range of the present invention, large lumps were formed, and operation became impossible. Comparative Example 6
Is an example in which the peripheral speed of the stirring blade exceeded the range of the present invention, and fine particles were generated.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

In the past, as the most general method for coagulating a polymer latex, there is known a method in which a polymer latex and a coagulant are continuously supplied to a coagulation tank for coagulation and aggregation. There is. However, the polymer latex that has been subjected to the demonomer treatment has a poor coagulability and produces ultrafine powder, which is a problem in handling. The present invention performs demomerization treatment,
When coagulating with the residual monomer content kept below a certain value, the coagulation temperature, coagulant concentration and agitation speed are limited to suppress the generation of fine particles and to recover the polymer.

Claims (1)

[Claims] 1. A method for recovering a polymer latex, which comprises coagulating a polymer latex having a residual monomer content of 10,000 ppm or less with respect to a polymer component under the following conditions (a) to (c): .. (A) Solidification temperature (°C); (Tv-15) <solidification temperature (°C) <(Tv+35) [where Tv represents the Vicat softening point (°C) of the recovered polymer. (B) Coagulant concentration; when the coagulant is a salt and the cation of the coagulant is monovalent, C≦coagulant concentration (mmol/l)≦(C+2,000) the coagulant is a salt , When the cation of the coagulant is divalent C≦coagulant concentration (mmol/l)≦(C+30) When the coagulant is a salt and the cation of the coagulant is trivalent C≦coagulant concentration (Mmol/l)≦(C+10) When the coagulant is an acid C≦coagulant concentration (mmol/l)≦(C+30) [where C represents a coagulation value (mmol/l). ] (C) The polymer latex and the coagulant are contacted with stirring,
The peripheral speed of the tip of the stirring blade is 10≦the peripheral speed (cm/s) of the tip of the stirring blade≦500