JPH07138314A - Method for coagulating polymeric latex - Google Patents

Abstract

PURPOSE:To make it possible to control to an arbitrary particle diameter and obtain polymer particles having uniform diameter with minimized amount of fine particles by coagulating a polymeric latex at a specified coagulation temperature, at a specified concentration of a coagulant and under specified agitating conditions. CONSTITUTION:A polymeric latex consisting of a vinyl polymer and/or a rubber modified vinyl polymer and having a rubbery polymer content of 0 to below 60wt.% is coagulated under the following conditions. (i) The coagulation temperature satisfies the formula: (Tm - 20 deg.C) <= coagulation temperature <=(Tm+30 deg.C), wherein Tm is the softening point ( deg.C) of recovered polymer. (ii) The coagulant comprises a salt, and the coagulant concentration satisfies the formulas: C <= coagulant concentration (mmol/l)<=C+2000 when the cation of the coagulant is monovalent; and C <= coagulant concentration (mmol/l)<=C +30 when the cation of the coagulant is divalent. (iii) The polymeric latex contacts the coagulant by agitation under such conditions that the peripheral speed of the tips of agitating blades satisfies the formula: 10 <= the peripheral speed <= 500(cm/S).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coagulating a polymer for recovering the polymer from a polymer latex obtained by emulsion polymerization, and more specifically, it can be controlled to any particle size and fine powder. The present invention relates to a method for coagulating a polymer latex to obtain polymer particles having a small number of particles and a uniform particle size.

[0002]

2. Description of the Related Art Generally, in order to recover a powdery polymer from a polymer latex produced by an emulsion polymerization method, it is necessary to add a coagulating liquid to the polymer latex to coagulate the polymer latex. As the most general method for coagulating such a polymer latex, there is known a method in which the polymer latex and a coagulation liquid are continuously supplied to a coagulation tank for coagulation and aggregation. However, this method has a problem that fine powder is generated. If there is a lot of fine powder, there is a danger of dust explosion, there is a problem of safety such as a fire explosion due to deterioration of carbonization characteristics, and there is a problem of environmental deterioration due to dusting.
Further, there is a problem that productivity is lowered such that dehydration is lowered and handling is difficult.

As a second method, a method is known in which the polymer latex is fed to a twin-screw extruder having a dehydration slit together with a coagulating liquid (Japanese Patent Publication No. 59-37021). However, this method has a problem in that the recovered polymer cannot be sufficiently washed with water, so that the soap and the coagulant remain in the final product, thereby deteriorating the quality of the polymer.

As a third method, there is a method in which a coagulant is sprayed into a coagulation chamber in the form of gas or mist and brought into contact with droplets of a polymer latex in a space to coagulate it (Japanese Patent Laid-Open No. 5-596).
8-87102). However, in this method, it is necessary to coagulate the latex in the gas phase until the hardness becomes sufficient within a short time when the latex droplets drop, so that the tower height is high in order to obtain a relatively large particle size. A coagulation tower is required, the equipment cost becomes large, and the latex tends to adhere to the wall due to the drift of the gas in the tower during spraying, or when the coagulated particles fall into the gas phase and collide with the water phase. 300 μm because particles are easily broken by impact and fine powder is easily generated
There are drawbacks such as difficulty in obtaining the above particles.

As a fourth method, there is a method of slowly coagulating the polymer latex (Japanese Patent Publication No. 3-51728). However, this method has a drawback that the bulk density is low when applied to a rubber-modified polymer latex having a rubber-like polymer content of less than 60%. In addition, in any of these methods, the coagulated particle size cannot be controlled.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in the background of the above-mentioned prior art, in which there are few fine powders, the handling is easy, the productivity is excellent, and the quality of the polymer particles is arbitrary. It is an object of the present invention to provide a method for coagulating a polymer latex that can be controlled and recovered.

[0007]

Means and Actions for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the coagulant concentration, the coagulation temperature and the stirring conditions in the coagulation step are limited to specific ranges. The inventors have found that the solution to the problem can be achieved and arrived at the present invention.

In the present invention, a polymer latex (A) comprising a vinyl polymer and / or a rubber-modified vinyl polymer and having a rubber-like polymer content of 0 to less than 60% by weight is described below. (A), (b) and (c) Coagulation method of polymer latex characterized by being coagulated under the conditions (a) Coagulation temperature (° C) (Tm-20 ° C) ≤ coagulation temperature ≤ (Tm + 30 ° C) Tm; Softening point (° C.) of 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 + 2000, when the cation of the coagulant is divalent, C ≦ coagulant concentration (mmol / l) ≦ C + 30, when the cation of the coagulant is trivalent, C ≦ coagulant concentration (mmol / l) ≦ C + 10, when the coagulant is an acid, C ≦ coagulant concentration (m mol / l) ≦ C + 30 However, C; coagulation value (mmol / l) (c) The polymer latex and the coagulant are in contact with each other with stirring, and the peripheral speed of the tip of the stirring blade is 10 ≦ peripheral speed ≦ 500 (cm / S).

The present invention will be described in detail below. First, the method for obtaining the softening point (Tm) and the coagulation value shown in (a) and (b) of the present invention will be described. As for the softening point (Tm), the polymer is previously collected from the polymer latex used for coagulation, and the polymer after drying is used to measure JI.
The Vicat softening point is measured according to the method of SK7206, and this value is taken as the softening point (Tm) of the present invention. The coagulation value (C) was determined by the method shown below using the polymer latex used for coagulation and the coagulant used for coagulation. The polymer latex is diluted with water to a concentration of 0.20%. 10 cc of this polymer latex was placed in a test tube, 10 cc of coagulant aqueous solution of various concentrations was added, mixed well, and allowed to stand in a constant temperature bath at 30 ° C. The presence or absence of precipitate formation after 1 hour is checked, and the lowest concentration at which precipitation occurs (mm after mixing)
ol / l) was taken as the coagulation value.

The polymer latex (A) of the present invention comprises a vinyl-based polymer latex and / or a rubber-modified vinyl-based polymer latex, which are usually obtained by emulsion polymerization. It is obtained by polymerizing the vinyl monomer shown or a monomer copolymerizable therewith. The rubber-modified vinyl polymer latex is obtained by polymerizing the vinyl monomer shown below or a monomer copolymerizable therewith in the presence of the rubber polymer shown below.

The vinyl-based monomer is not particularly limited, and examples thereof include (meth) acrylic acid such as acrylic acid and methacrylic acid; acrylic acid alkyl ester-based monomers such as methyl acrylate, ethyl acrylate and butyl acrylate; Methacrylic acid alkyl ester monomers such as methyl methacrylate and ethyl methacrylate; vinyl cyan monomers such as acrylonitrile and methacrylonitrile; aromatic vinyl monomers such as styrene and α-methylstyrene; vinyl chloride, odor Various monomers such as vinyl halide-based monomers such as vinyl chloride may be mentioned, and these may 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.

Examples of other copolymerizable monomers include maleimide 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.

As the rubber-like polymer, polybutadiene,
Styrene-butadiene copolymer (styrene content 5-6
0% by weight is preferred. ), Styrene-isoprene-based copolymer, acrylonitrile-butadiene-based copolymer, ethylene-α-olefin-based copolymer, ethylene-α-olefin-polyene-based copolymer, acrylic rubber, butadiene-acrylic-based copolymer Examples thereof include polymer, polyisoprene, styrene-butadiene block copolymer, hydrogenated butadiene-based polymer, ethylene-based ionomer, and silicon-based rubber. These rubber-like polymers are used alone or in combination of two or more. 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 a latex-like one. Examples of the polymer of the polymer latex (A) include acrylic resins, polystyrene, styrene-acrylonitrile copolymers, (α-methyl) styrene- (acrylonitrile) -maleimide monomer-based copolymers, and ABS resins, Examples thereof include resinous polymers such as rubber-modified vinyl polymers such as MBS resin, AES resin, and AAS resin. The content of the rubber-like polymer in the polymer latex (A) is less than 60% by weight, preferably 55% by weight or less, more preferably 50% by weight or less. Especially 45
If the content is less than 40% by weight, especially 40% by weight, the objects and effects of the present invention will be further enhanced.

As the coagulant of the present invention, those generally used for coagulating latex can be used. Examples thereof include inorganic acids such as hydrochloric acid and sulfuric acid, organic acids such as acetic acid and formic acid, and metal salts of these acids. In addition, a polymer flocculant and the like can also be used in combination. Examples of the above metal salts include calcium chloride, calcium nitrate, aluminum chloride, aluminum sulfate, magnesium sulfate and the like. In the present invention, polyvalent metal salts and inorganic acids are preferred. More preferably, calcium chloride,
Examples thereof include magnesium sulfate and sulfuric acid. Examples of the polymer flocculant include polyacrylamide. Further, the salt and the acid can be used in combination.

The object of the present invention is achieved by coagulating the polymer latex under the following conditions (a), (b) and (c). The solidification temperature of (a) is "(Tm-20 ° C)
≦ Freezing temperature ≦ (Tm + 30 ° C.) ”, preferably“ (Tm−10 ° C.) ≦ solidifying temperature ≦ (Tm + 10 ° C.) ”(softening point −20 ° C.). On the other hand, at a temperature higher than the temperature of (softening point + 30 ° C.), the coagulated particles are easily fused and coarse particles are generated, and the coagulated slurry concentration cannot be increased.

The coagulant concentration of (b) is such that when the coagulant is a salt and the coagulant cation is monovalent, C ≦ coagulant concentration ≦ C + 2000, preferably C ≦ coagulant concentration <C + 14.
00, more preferably C ≦ coagulant concentration <C + 700. When the coagulant cation is divalent, C ≦ coagulant concentration ≦
C + 30, preferably C ≦ coagulant concentration ≦ C + 20, more preferably C ≦ coagulant concentration ≦ C + 10. When the coagulant cation is trivalent, C ≦ coagulant concentration ≦ C + 10, preferably C ≦ coagulant concentration ≦ C + 5, more preferably C
≦ Coagulant concentration ≦ C + 3. When the coagulant concentration is less than the C value, coagulation does not sufficiently occur and the coagulation becomes uncoagulated. When the coagulant cation is monovalent, divalent, or trivalent, fine particles are generated when the coagulant concentrations (C + 2000), (C + 30), and (C + 10) are exceeded. When the coagulant is an acid, C ≦ coagulant concentration ≦ C + 30, preferably C ≦ coagulant concentration ≦ C +
20 and more preferably C ≦ coagulant concentration ≦ C + 10. When the coagulant concentration is less than the C value, coagulation does not sufficiently occur and the coagulation becomes uncoagulated. When the acid coagulant concentration exceeds (C + 30), fine particles are generated.

The preferred coagulant concentration when two or more coagulants containing a monovalent, divalent, or trivalent cation and an acid are mixed and used 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 trivalent cations is C ₃ (mmol / l), and 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 the equivalent coagulant concentration C converted to a divalent coagulant.
_{Expressed as CONV} . That is, C _CONV = A (C ₂ / C ₁ ) + B + C (C ₂ / C ₃ ) + D
(C ₂ / C ₄₎ using the terms of coagulant concentration, determine the析値(C _MIX) coagulation of the mixed coagulant to a predetermined ratio. And in this case, it solidifies on the following conditions. C _M ≤ reduced coagulant concentration ≤ C _M +30

The stirring condition (c) is such that the peripheral speed of the tip of the stirring blade is 10 ≦ peripheral speed ≦ 500 (cm / S), preferably 6
0 ≦ peripheral speed ≦ 360 (cm / S), more preferably 80
≤ peripheral speed ≤ 300 (cm / S), particularly preferably 100 ≤
Peripheral speed ≦ 250 (cm / S). Peripheral speed is 10 cm / S
If less than, a large lump will be generated. Further, if the peripheral speed exceeds 500 cm / S, fine powder is generated and the purpose cannot be achieved.

The solidified particles can be heat treated to improve the mechanical properties of the solidified particles and the powder properties such as the bulk density. This preferable heat treatment condition is Tm ≦ treatment temperature ≦ Tm + 50, and more preferably Tm.
m + 10 ≦ processing temperature ≦ Tm + 40. If it is lower than Tm, the effect of the heat treatment becomes small, and the effect of increasing the bulk density and reducing the water content in the recovered coagulated particles does not appear. Tm +
If the temperature exceeds 50 ° C., the solidified particles are fused with each other to form a clump, which makes stable operation impossible. Also, the slurry concentration cannot be increased. The heat treatment time is 5 minutes ≦ treatment time ≦ 1
20 minutes. Preferably, 10 minutes ≦ treatment time ≦ 60 minutes. If it is shorter than 5 minutes, the effect of the heat treatment is small, and the effects of increasing the bulk density and reducing the water content in the recovered coagulated particles do not appear. If it exceeds 120 minutes, the physical properties such as the hue of the resin will be impaired, and the equipment will be large, which is not economical.

In the present invention, the amount of the coagulant is smaller than that in the conventional method, so that the uncoagulated latex may remain slightly, resulting in the generation of fine powder and the clogging of the spinneret of the dehydrator in the subsequent process. There are cases where it is not preferable in respect of. In this case, it is preferable to add an additional coagulant between the coagulation tank and the heat treatment tank to complete the coagulation completely. When the coagulant is a salt and the cation of the coagulant is monovalent, the concentration in the system is 200 mmo.
When the value is 1 / l or more, the concentration in the system is 5 mmol / l or more, when it is trivalent, the concentration in the system is 2 mmol / l or more, and when the coagulant is an acid, the concentration in the system is 5 mmol / l or more. Thus, it is preferred to add a coagulant.

The process of the method for coagulating the polymer latex of the present invention is not particularly limited, and a commonly used method can be used. An example of the coagulation method will be shown. The polymer latex, the coagulant (aqueous solution), and optionally water are continuously or batchwise supplied so as to satisfy the condition (b) of the present invention to obtain a coagulated slurry. The mixing and stirring of (c) of the present invention when obtaining this solidified slurry is performed at the time of and after the supply of the respective components. The solidified slurry is heated at the solidifying temperature of (a) of the present invention, and this heating is performed during and after the supply of each of the above components. During heating, the solidified slurry is stirred so that the polymerized components of the solidified slurry are well dispersed. By this heating, the polymer particles are aggregated to form aggregated polymer particles. The shape of the stirring blade used for this stirring is not particularly limited, and generally used blades such as a paddle blade, a turbine blade, a propeller blade, and a gate type blade can be used.

In the present invention, the above-mentioned aggregated polymer particles in the coagulated slurry can be separated, and if necessary, washed with water and dried to obtain dried polymer particles. Examples of the separation method include the following methods. That is, it can be dehydrated, washed and separated by a horizontal belt filter, a centrifugal dehydrator and the like. Further, it can be dried by a flash dryer or a fluid dryer and collected as dried polymer particles. Further, the coagulated slurry can be dried as it is or after being dehydrated with a horizontal belt filter, a centrifugal dehydrator or the like, and then dried with a twin-screw extruder with a dehydration slit. Since the agglomerated polymer particles according to the present invention have few fine powder particles, there are problems that usually occur in the above-mentioned method, namely, horizontal belt filter, clogging of filter cloth of centrifugal dehydrator, and bite at the inlet of twin-screw extruder. It is possible to perform dehydration and drying without causing a low discharge rate due to defects and without causing leakage of agglomerated particles from the dehydration slit of the twin-screw extruder.

[0024]

EXAMPLES The method of the present invention will be specifically described below with reference to examples, but these do not limit the scope of the present invention.

Powder characteristic measuring method Bulk density: Measured according to JIS-K-6721.
(Unit: g / ml) Average particle size; Up to a particle size of 1000 μm, the particle size distribution is determined by a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba Ltd.) For those exceeding 1000 μm, it is determined by image analysis. The average particle diameter d ₅₀ is the particle diameter of 50% cumulative value obtained from the cumulative distribution curve of this particle size distribution. Presence of fine particles; determined by the amount of resin passing through the 200 mesh gold net.

Example 1 As a polymer latex, a graft copolymer comprising 20% by weight of butadiene obtained by graft copolymerizing styrene, methyl methacrylate and acrylonitrile on polybutadiene, 18% by weight of styrene, 5% by weight of acrylonitrile and 57% by weight of methyl methacrylate. The combined latex was used as a raw material. The solid content concentration of this graft copolymer latex was 30% by weight, the coagulation value measured using an aqueous solution of calcium chloride (coagulant) was 11 mmol / l, and the Vicat softening point was 90 ° C. A 2% calcium chloride aqueous solution was used as a coagulant. In a coagulation tank (two-stage inclined paddle blade, blade diameter 7.5 cm) equipped with a stirrer with an internal volume of 2 liters, the above latex was continuously mixed at 50 ml / min and 2% at a place where the tip peripheral speed of the blade was 160 cm / S. An aqueous solution of calcium chloride was added at 13.3 ml / min, and ion-exchanged water was added at 134.5 ml / min. The coagulant concentration in the coagulation tank was 12 mmol / l. The temperature of the coagulation tank is controlled to 95 ° C. by heating the jacket, and the coagulated slurry continuously discharged from the coagulation tank that has been continuously coagulated is heated at 110 ° C. for 40 minutes, and then the centrifuge is used. The polymer component was separated, washed with water and dehydrated to obtain a wet powder. The wet powder was dried to obtain dry polymer particles. The results are shown in Table 1.

Example 2 Example 2 was repeated except that the coagulant concentration in the coagulation tank was 30 mmol / l.

Example 3 Example 3 was repeated except that the solidification temperature was 105 ° C.

Example 4 The procedure of Example 1 was repeated, except that the rotation of the stirrer was lowered and the peripheral speed of the tip was 80 cm / S.

Example 5 The procedure of Example 1 was repeated, except that the heat treatment after completion of solidification was carried out at 130 ° C. for 40 minutes.

Example 6 Using sulfuric acid as a coagulant, the coagulant concentration was 4 mmol.
It carried out like Example 1 except having carried out by / l.
The coagulation value was 2 mmol / l.

Example 7 As a polymer latex, a material obtained by copolymerizing 22% by weight of acrylonitrile, 1% by weight of styrene, 76% by weight of α-methylstyrene and 1% by weight of methyl methacrylate was used as a raw material. The solid content of this polymer latex is 3
It was 0% by weight. The coagulation value measured using calcium chloride (coagulant) was 3 mmol / l. The Vicat softening point was 115 ° C. Using this polymer latex, the coagulation temperature is 98 ° C., the coagulant concentration is 4 mmol / l,
Coagulation was carried out by the apparatus used in Example 1 so that the peripheral speed of the stirring blade was 200 cm / S. The heat treatment was carried out at 135 ° C. for 60 minutes. The results are shown in Table 1.

Example 8 The same procedure as in Example 1 was carried out except that tonalium chloride was used as the coagulant and the coagulant concentration was 300 mmol / l. The coagulation value was 260 mmol / l.

Example 9 The procedure of Example 1 was repeated, except that aluminum chloride was used as the coagulant and the concentration of the coagulant was 0.75 mmol / l. The coagulation value is 0.68 mmol / l
Met.

Examples 1 to 9 are examples carried out within the scope of the present invention, and the object of the present invention was achieved without fine powder. On the other hand, Comparative Example 1 has a solidification temperature below the range of the present invention and contains a large amount of fine powder. In Comparative Example 2, the solidification temperature exceeds the range of the present invention, the fusion of the polymer particles is vigorous, and the operation is impossible. In Comparative Example 3, the coagulant concentration is less than the range of the present invention, and coagulation hardly occurs. Comparative Example 4 is an example in which the coagulant concentration exceeds the range of the present invention, and contains a large amount of fine powder. In Comparative Example 5, the peripheral speed of the stirring blade is less than the range of the present invention, and a large lump is generated. In Comparative Example 6, the peripheral speed of the stirring blade exceeds the range of the present invention, and fine powder is produced. Comparative Example 7 has a low heat treatment temperature and a low bulk density. In Comparative Example 8, the heat treatment time is short and the bulk density is low. Comparative Example 9 has a low solidification temperature and a large amount of fine powder.

[0036]

[Table 1]

[0037]

As a conventional method for recovering a polymer from a polymer latex, a coagulant is generally added to the polymer latex to agglomerate the polymer, which is then heated to enlarge the polymer particles. Although it was separated by a separator to obtain a powdery polymer, since it contains many fine powder particles, various problems occur. The present invention suppresses the generation of fine powder particles by controlling the particle size by coagulating at a coagulant concentration lower than the conventionally generally used coagulant concentration, and at a coagulant concentration in a specific range, a coagulating temperature in a specific range, and stirring conditions. It is a thing. It is completely novel to control the particle size to a desired particle size for coagulation under the conditions of the coagulant concentration range, stirring conditions and coagulation temperature range of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teizo Fukuda 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. A vinyl-based polymer and / or a rubber-modified vinyl-based polymer, wherein the content of the rubber-like polymer is 0.
A method for coagulating a polymer latex, which comprises coagulating the polymer latex (A) in an amount of ˜60% by weight under the following conditions (a), (b) and (c). (A) Coagulation temperature (° C) (Tm-20 ° C) ≤ coagulation temperature ≤ (Tm + 30 ° C) where Tm; softening point (° C) of recovered polymer (b) coagulant concentration where the coagulant is a salt When the cation of the coagulant is monovalent, C ≦ coagulant concentration (mmol / l) ≦ C + 2000, when the cation of the coagulant is divalent, C ≦ coagulant concentration (mmol / l) ≦ C + 30 When the cation of the coagulant is trivalent, C ≦ coagulant concentration (mmol / l) ≦ C + 10, when the coagulant is acid, C ≦ coagulant concentration (mmol / l) ≦ C + 30 where C; Deposition value (mmol / l) (c) The polymer latex and the coagulant are in contact with each other with stirring, and the peripheral speed of the tip of the stirring blade is 10 ≦ peripheral speed ≦ 500 (cm / S)