JPH07268017A - Production of thermoplastic polymer powder - Google Patents

Abstract

PURPOSE:To obtain a thermoplastic polymer powder having a sharp particle diameter distribution and a high bulk specific gravity by solidifying a latex of a thermoplastic polymer having a Tg of a specified temperature or higher under specified conditions to form a powder and heating the powder at a specified temperature. CONSTITUTION:A latex of a thermoplastic polymer having a Tg (A) of 40 deg.C or higher and obtained by emulsion polymerization is mixed with a coagulant to coagulate the polymer in an amount of 40-80wt.% based on the whole polymer in the latex, and the coagulant is further added to complete coagulation. The obtained coagulated slurry is solidified in a temperature range from Tg (A) -10 deg.C to Tg (A) +10 deg.C, dewatered and dried, and the dry polymer powder is heated at a temperature of Tgmax +(10 to 80 deg.C) to produce the objective powder. Tg (A) is represented by the formula [wherein (n) is the number of monomer species forming the polymer A; W1, W2..., Wn are each the weight fraction of each monomer (i) (i=1, 2, ..., n) in the polymer A; and Tg1, Tg2 ..., Tgn are each the glass transition temperature ( deg.C) of each monomer], and Tgmax is the highest glass transition temperature among those of the polymers obtained from the monomers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic polymer powder having a sharp particle size distribution and a high bulk specific gravity.

[0002]

2. Description of the Related Art Various methods for improving the powder characteristics of thermoplastic polymer powders have hitherto been studied. For example, a method in which a polymer latex is coagulated with a specific coagulant concentration as a method of devising a coagulation operation (Japanese Patent Laid-Open No. 217224/1985).
Japanese Unexamined Patent Publication No. 62-236829) and a method of adding a coagulant in two or more steps (Japanese Unexamined Patent Publication No. 59-91100), and a method of performing seed aggregation and then sintering (Japanese Unexamined Patent Publication No. 62-236829, Japanese Unexamined Patent Publication No. 63- 165438).

Further, as a procedure after solidification, a method for improving bulk specific gravity by adding a polymer for powder modification or an inorganic fine powder (Japanese Patent Laid-Open Nos. 55-90520 and 58-58).
-1742 and Japanese Patent Laid-Open No. 64-26663) have been proposed.

[0004]

However, the method of coagulating with a specific coagulant concentration is a method for a rubber-containing graft copolymer, and a hard polymer having a high glass transition temperature has a large bulk specific gravity. It cannot be improved. The same applies to the method in which the coagulant is added in two or more steps, and even if spherical particles are formed, it is not possible to obtain a granular material having a high bulk specific gravity. In addition, these two methods use the first stage precipitation amount and p
Even if H is controlled, depending on the type and amount of the surfactant present in the latex, if no coagulation occurs or the coagulation is locally completed, a good powdery polymer cannot be obtained. It has drawbacks.

The method of adding a polymer or inorganic fine powder for powder modification is a method of modifying the surface of the polymer powder to make the packing structure of the particle groups denser and increase the bulk specific gravity. . Therefore, no attention was paid to the voids inside the individual particles, and thus it was difficult to obtain a thermoplastic polymer powder having a sufficiently improved bulk specific gravity.

The method of sintering seeds after agglomeration has a problem that the solidification operation is complicated, and if the particle size is 1 mm or less, separation after solidification is difficult.

[0007]

Means for Solving the Problems As a result of intensive studies aimed at solving the above-mentioned problems, the present inventors have found that by controlling a specific process under a specific temperature condition, a sharp particle size distribution can be obtained. The present invention has been accomplished by finding that a thermoplastic polymer powder having a high bulk specific gravity can be obtained.

The gist of the present invention is to recover polymer powder from a latex of a thermoplastic polymer (A) having a glass transition temperature Tg (A) of 40 ° C. or higher obtained by emulsion polymerization, 1) coagulation 40% based on the total polymer in the latex
-80% by weight of the polymer is coagulated, 2) a coagulant is further added to complete the coagulation, and 3) the obtained coagulated slurry is (Tg (A) -10)-
(Tg (A) +40) ° C., solidified, dehydrated and dried in the temperature range shown in 4), and 4) the dried polymer powder is further added to (Tgmax + 10) to
It is a method for producing a thermoplastic polymer powder, which comprises heating within a temperature range indicated by (Tgmax + 80) ° C.

Tg (A) = W ₁ × Tg ₁ + W ₂ × Tg ₂ + ... + W _n × Tg _n- (X) [where n is a unit amount forming the thermoplastic polymer (A)] Is the number of the body, and W ₁ , W ₂ ... W _n are each monomer i (i =
1, 2, represents the polymer (A) weight fraction in _{n), Tg 1, Tg 2} ···, Tg n is the glass transition temperature of the polymer composed of the monomer i (° C. ) Represents. ] Tgmax: Glass transition temperature showing the highest temperature among the polymers obtained from the monomers forming the thermoplastic polymer (A).

The present invention will be described in more detail below.

As the monomer forming the thermoplastic polymer (A) in the present invention, for example, a diene-based monomer such as butadiene, isopropylene or chloropropylene; an acrylic acid alkyl ester-based such as butyl acrylate or octyl acrylate. Monomers; methacrylic acid alkyl ester-based monomers such as methyl methacrylate and ethyl methacrylate; vinyl cyanide-based monomers such as acrylonitrile and methacrylonitrile; styrene, dichlorostyrene,
Aromatic vinyl monomers such as α-methylstyrene; Vinyl halide monomers such as vinyl chloride and vinyl bromide; Glycol monomers such as ethylene glycol; Various copolymerizable monomers such as dimethylsiloxane And these are 2
It is also possible to use more than one type.

As the thermoplastic polymer (A) in the present invention, one having Tg (A) represented by the formula (X) of 40 ° C. or higher is used.

The emulsion polymerization method in the present invention may be a commonly used method, and the initiator and other polymerization aids are not particularly limited, and may be those usually used.

In the present invention, coagulation of the polymer latex is carried out under the above-mentioned first stage coagulation condition, whereby the acid-stable surface active agent maintains the emulsified state and destroys the emulsified state. It can be adjusted, and a powdery granular polymer having a sharp particle size distribution can be obtained. When a coagulant is added to the thermoplastic polymer latex, the emulsion state of the latex is destroyed, and the fine polymer particles that have been emulsified and dispersed in the latex aggregate to aggregate particles (hereinafter referred to as coagulated particles). To form.

Examples of the coagulant used include inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid, and organic acids such as formic acid and acetic acid, which may be used alone or in combination.

As the first stage coagulation, it is necessary to coagulate 40 to 80% by weight of the total polymer in the latex. The amount of polymer coagulated here was obtained by comparing the coagulated slurry with Toyo Filter Paper No. It was filtered through 131 (JIS P3801, Type 3), and the polymer concentration in the filtrate was measured and converted from the amount of uncoagulated polymer obtained. 40% by weight of coagulated polymer
If the amount is less than the above, many polymer latices will be coagulated in the state where the emulsion state breaking action is strong when the coagulation is completed, and it will be difficult to obtain a powdery granular polymer having a sharp particle size distribution, which is not preferable. On the other hand, if it exceeds 80% by weight, the effect of destroying the emulsion state is too strong, and it is difficult to obtain a powdery polymer having a sharp particle size distribution.

In the practice of the present invention, in order to stably control the precipitation state of coagulated particles, if necessary, a sulfuric acid ester-based and / or sulfonic acid-based anionic surfactant is added to the polymer latex in the thermoplastic polymer. It is preferably present in an amount of 0.05 to 0.2 parts by weight per 100 parts by weight of the coalescence. Among the surfactants, examples of the sulfate ester type anionic surfactant include higher alcohol sulfate ester salts,
Examples thereof include polyoxyethylene alkyl sulfate ester salts, and examples of the sulfonic acid type anionic surfactant include alkyl sulfonates, alkylbenzene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether sulfonates, and the like. The surfactant may be added before the polymerization, during the polymerization, or at any time after the polymerization.

In the second stage coagulation, coagulated particles are completely precipitated. At this time, the pH of the coagulated slurry is preferably set to 2 or more. When the pH of the coagulation slurry is less than 2, it is not preferable because the thermal stability of the product powder is deteriorated, and it is desirable to neutralize the pH to about 2 to 4 with an alkaline chemical or the like.

The coagulated slurry thus obtained enhances the shape-retaining power of coagulated particles and makes it hard to break in the subsequent steps (Tg
Heat treatment is performed in a temperature range of (A) -10) to (Tg (A) +40) ° C., and then dehydration / drying is performed. When the solidification temperature is raised to around the glass transition temperature Tg (A) of the thermoplastic polymer or more, the coagulated particles are fused and can be recovered as solid particles. Also, if the heat treatment time etc. is lengthened, fusion will proceed,
The water content during dehydration can be further reduced.

In the case of a thermoplastic polymer having a glass transition temperature Tg (A) of 40 ° C. or higher, it is difficult to fuse the coagulated particles themselves which can achieve a sufficient bulk specific gravity only by solidification treatment. On the other hand, this dried polymer powder (Tgmax + 10)
By further heating in the temperature range of to (Tgmax + 80) ° C, a thermoplastic polymer powder having a high bulk specific gravity can be obtained. As a temperature condition for applying heat to the coagulated particles after drying to promote fusion, the glass transition temperature (Tgmax of the component showing the highest temperature among the polymers obtained from the monomers constituting the thermoplastic polymer) ) Or more is preferable.
If it is lower than (Tgmax + 10) ° C., the fusion of the fine particles constituting the coagulated particles is not sufficient and a satisfactory bulk specific gravity cannot be obtained. In addition, heating at a temperature exceeding (Tgmax + 80) ° C. is not preferable, because the cohesive force is too strong and the coagulated particles are integrated with each other. It is considered that the reason why the heating range is preferably Tgmax or more is that all the components constituting the thermoplastic polymer must be rubbery in order to fuse the dried coagulated particles.

When the fusion of the thermoplastic polymer is promoted by heating, the coagulated particles are also fused, so that the polymer powder becomes a block. This block-like material is easily crushed to the original coagulated particle unit, but if the heating conditions are too strong, the crushing may become difficult although the bulk specific gravity increases. In this case, an inorganic compound for powder modification may be added in advance in order to prevent fusion of the coagulated particles. As the inorganic compound for powder modification, oxides, chlorides, hydroxides, carbonates of one or more elements selected from the group consisting of Si, Mg, Al, Ca, Ba, Zn and Ti are used. Examples thereof include salts and sulfates, or a mixture thereof. Specific examples thereof include SiO ₂ , MgO, Mg (OH) ₂ , MgCO ₃ ,
Al ₂ O ₃ , Al (OH) ₃ , Al ₂ (CO ₃ ) ₃ , CaO,
Examples thereof include CaCO ₃ , TiO ₂ , talc, clay, diatomaceous earth, and calcium metasilicate. These inorganic compounds preferably have an average particle size of 10 μm or less, and may be added in a step after coagulation and before the step of heat-drying the dry powder.

A representative apparatus used to practice the present invention will be described with reference to FIG. Polymer latex from metering pump (1), coagulant from metering pump (2)
It is sent to the tank (4). The coagulant added to increase the recovery rate of the polymer is sent from the metering pump (3) to the second tank (5). After the slurry is heat-treated in the third tank (6), it is further washed with water, dehydrated and dried, although not shown, to obtain a powdery polymer.

[0023]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by these examples. In the examples, the apparatus shown in FIG. 1 was used for coagulation.

Example 1 Methyl methacrylate 85% and butyl acrylate 15
Emulsion-polymerized copolymer latex (solid content 28%)
Got The average particle size of the obtained latex is 0.105μ.
m and PH are 8.0, and the type and amount of the surfactant present in the latex are as shown in Table 1. The latex had a Tg (A) of 81 ° C and a Tgmax of 105 ° C.

The above latex and the acid of the type shown in Table 1 were fed so that the pH and the amount (%) of the polymer coagulated in the first tank would be the values shown in Table 1. Acids of the types shown in Table 1 were supplied to the second tank so that the pH values were as shown in Table 1. In the third tank, the coagulated slurry was solidified under the heat treatment conditions shown in Table 1. Third
The slurry discharged from the tank was washed with water, dehydrated and dried to obtain a powdery polymer. When this polymer was allowed to stand still in a hot air dryer at 150 ° C. for 10 minutes, the polymer powder became a fragile block. This block-like material was taken out and crushed to obtain a polymer powder.

The particle size distribution of the obtained powdery granular polymer was measured by the sieving method. Further, the uniformity of the particles was obtained from the formula shown below.

N = D ₇₅ / D ₂₅ (where D ₇₅ is the particle diameter (μm) at 75% of the cumulative weight distribution curve, and D ₂₅ is the particle diameter (μm at 25% of the cumulative weight distribution curve of the particle group). In addition, the bulk specific gravity of the obtained powdery granular polymer is determined according to JIS K-67.
21.

The evaluation results are shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

Example 2 A powdery granular polymer was obtained in the same manner as in Example 1 except that the drying temperature in the latter stage was changed to 170 ° C. The particle size distribution at this time was almost the same as in Example 1, and the bulk specific gravity was 0.50.

Example 3 Using the thermoplastic polymer latex of Example 1, Aerosil R972 (Nippon Aerosil Co., Ltd.) was used after the first-stage drying.
0.5 part by weight was added to 100 parts by weight of the thermoplastic polymer and dry blended. This powdery polymer is
The treatment was performed in the same manner as in Example 1 except that the drying temperature at the first stage was changed to 170 ° C. The block after drying could be easily disintegrated. The particle size distribution at this time was almost the same as in Example 1, and the bulk specific gravity was 0.50.

Comparative Example 1 A treatment was carried out in the same manner as in Example 1 except that the second stage drying temperature was set to 200 ° C. However, after the drying, the block was too hard to be crushed and a powdery granular polymer was obtained. I couldn't.

Comparative Example 2 A powdery granular polymer was obtained by the same treatment as in Example 1 except that the second stage drying temperature was changed to 100 ° C. for 60 minutes. The particle size distribution at this time was almost the same as in Example 1, but the bulk specific gravity was 0.38.

Example 4 A powdery polymer was obtained by the same procedure as in Example 1 except that the solidifying temperature was changed to 98 ° C. The particle size distribution at this time was almost the same as in Example 1, but the water content after dehydration was reduced to 35%, and the bulk specific gravity was 0.39 after the first-stage drying and after the second-stage drying. Was 0.47.

Comparative Example 3 A powdery polymer was obtained by treating in the same manner as in Example 1 except that the solidification temperature was changed to 70 ° C. Particles collapsed after dehydration and generation of fine powder was observed. As a result of measuring the particle size distribution after drying the first step, the proportion of 105 μm or less was increased to 22.3%.

[0037]

According to the present invention, the glass transition temperature is 40.
A powdery granular polymer having a sharp particle size distribution and a high bulk specific gravity can be obtained by coagulating a thermoplastic polymer latex having a temperature of not less than 0 ° C. under specific conditions and drying at a temperature higher than usual.

[Brief description of drawings]

FIG. 1 is an example of a device used in the present invention.

[Explanation of symbols]

 1 metering pump 2 metering pump 3 metering pump 4 1st tank 5 2nd tank 6 3rd tank

Claims (2)

[Claims] 1. When recovering a polymer powder from a latex of a thermoplastic polymer (A) having a glass transition temperature Tg (A) of 40 ° C. or higher obtained by emulsion polymerization, 1) a coagulant is used. 40 to 80% by weight of the polymer in the latex is coagulated, 2) a coagulant is further added to complete the coagulation, and 3) the resulting coagulated slurry is treated with (Tg (A ) -10) ~
(Tg (A) +40) ° C., solidified, dehydrated and dried in the temperature range shown in 4), and 4) the dried polymer powder is further added to (Tgmax + 10) to
A method for producing a thermoplastic polymer powder, which comprises heating within a temperature range of (Tgmax + 80) ° C. Tg (A) = W ₁ × Tg ₁ + W ₂ × Tg ₂ + ... + W _n × Tg _n −− (X) [where n is the number of monomers forming the thermoplastic polymer (A)] And W ₁ , W ₂ ... W _n are each monomer i (i =
1, 2, represents the polymer (A) weight fraction in _{n), Tg 1, Tg 2} ···, Tg n is the glass transition temperature of the polymer composed of the monomer i (° C. ) Represents. ] Tgmax: Glass transition temperature showing the highest temperature among the polymers obtained from the monomers forming the thermoplastic polymer (A). 2. (Tgmax + 10) to (Tgmax + 80)
The method for producing a thermoplastic polymer powder according to claim 1, wherein the inorganic compound is added in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the polymer powder before heating in the temperature range shown in ° C.