JPH09286825A - Production of fine powder, and fine powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process whereby a fine powder having an average primary particle size of 3μm or lower can be produced from a thermoplastic resin at a high productivity. SOLUTION: An emulsion of an acrylic copolymer formed from 70-97wt.% alkyl (meth)acrylate and 30-3wt.% unsatd. carboxylic acid is neutralized with an alkali metal compd. to neutralize 10-50% of carboxyl groups of the copolymer and is spray dried with a generally used spray drier. The emulsion can be produced by a usually used emulsion polymn. process. Thus obtd. fine powder is esp. suitable for a cement additive as a redispersible powder.

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 spherical fine particle powder made of a thermoplastic resin and a fine particle powder obtained by the method.

[0002]

2. Description of the Related Art Heretofore, as a method for producing a fine particle powder made of a thermoplastic resin, there has been known a method in which a resin obtained by various polymerization methods is pulverized by a pulverizer such as a jet mill and a fine particle having a desired particle size is obtained by a classifier. ing. However, this method requires an expensive pulverizer and a classifier, has a high running cost, has a low yield, and the obtained powder has an irregular particle shape and has a drawback of poor fluidity. is there. There is a method for obtaining bead-shaped particles by a suspension polymerization method for the purpose of making the particle shape of the powder spherical so as to improve the fluidity, but the obtained bead-shaped particles have an average particle diameter of at least 30 to 40 μm. And
It was essentially impossible to obtain fine particles of 10 μm or less.

As a method for obtaining spherical fine particle powder,
Japanese Patent Laid-Open No. 61-14201 proposes that spherical emulsion particles having an average primary particle size of 1 μm or less are obtained by emulsion polymerization and are made into powder by spray drying or the like. At this time, secondary agglomeration occurs, so the particles are pulverized by a jet mill and classified to obtain fine particles having a particle diameter of 1 μm or less. Also, in order to prevent secondary aggregation,
There is also known a method of copolymerizing a polyfunctional monomer to form particles having a crosslinked structure and improving the heat resistance of the fine particles, but the obtained fine particles are substantially not a thermoplastic resin.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a spherical fine particle powder made of a thermoplastic resin and having an average primary particle diameter of 3 μm or less with good productivity without using a crushing / classifying machine. Especially.

[0005]

The present invention provides an acrylic copolymer emulsion comprising 70 to 97% by weight of an alkyl (meth) acrylate and 30 to 3% by weight of an unsaturated carboxylic acid, and a carboxyl group of the acrylic copolymer. 10 to 10
After neutralizing with an alkaline metal compound to a degree of neutralization of 50%,
A method for producing a fine particle powder characterized by spray drying, and a true spherical fine particle powder having an average particle diameter of 3 μm or less obtained by the above method.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the alkyl (meth) acrylate constituting the acrylic copolymer of the acrylic copolymer emulsion in the present invention include alkyl acrylate and alkyl methacrylate having an alkyl group having 1 to 8 carbon atoms. , These single compounds or mixtures are used. Further, as the unsaturated carboxylic acid constituting the acrylic copolymer of the acrylic copolymer emulsion, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid and the like, a single compound or mixture of these. Is used.

The monomer composition of the copolymer in the acrylic copolymer emulsion is 70 to 97% by weight of alkyl (meth) acrylate and 30 to 3% by weight of unsaturated carboxylic acid.
It is. When the unsaturated carboxylic acid is less than 3% by weight, the particles are strongly blocked during spray drying in the subsequent step, and when the unsaturated carboxylic acid exceeds 30% by weight, the particles are not blocked on the particle surface in the subsequent neutralizing step. Swelling / dissolution occurs and fusion of primary particles occurs, and the viscosity of the emulsion increases, making spray drying difficult.

The method for producing the acrylic copolymer emulsion is not particularly limited as long as it is a method for forming primary particles of the acrylic copolymer, and a commonly used emulsion polymerization method or the like can be applied. However, it is not possible to obtain the desired primary particle level fine particles from the acrylic copolymer emulsion having the above-mentioned monomer composition by the emulsion polymerization method or the like.

In the present invention, the acrylic copolymer emulsion needs to be neutralized with an alkaline metal compound to a degree of neutralization of 10 to 50% of the amount of carboxyl groups of the acrylic copolymer present as particles. If the degree of neutralization is less than 10%, particles are blocked during spray drying in the subsequent step, and fine particles at the primary particle level cannot be obtained. If the degree of neutralization exceeds 50%, the surface of the primary particles is Swelling / dissolution occurs and fusion of primary particles occurs, and the viscosity of the emulsion increases, making spray drying difficult.

Examples of the alkaline metal compound used for neutralizing the carboxyl group of the acrylic copolymer include hydroxides or ammonium salts of lithium, sodium, potassium, beryllium, magnesium, calcium, barium, aluminum and the like. By such neutralization, particles of the acrylic copolymer in the emulsion become a metal salt by neutralizing the carboxyl groups on the particle surface, in particular, the heat resistance of the particle surface is significantly improved, and the thermosetting property having a crosslinked structure is obtained. It is possible to obtain heat resistance equivalent to that of resin.

Spray drying after the neutralization step is carried out using a conventional spray dryer. As the atomization method, a general method such as a rotary disk system, a two-fluid nozzle, a pressure type high pressure nozzle, or the like is used. The size of the mist at the time of atomization can be arbitrarily set according to the size of the spray dryer used, the atomization method, and the processing amount. The drying temperature may be a generally used temperature as long as both the hot air inlet temperature and the exhaust temperature are in a range in which particles do not cause blocking or thermal decomposition of the acrylic copolymer forming the particles. Conventionally, in the case of spray-drying a thermoplastic resin, when the exhaust temperature is set to the glass transition temperature (Tg) or higher of the resin, the particles are thermally fused, but the particles after the neutralization step in the present invention have a significantly improved heat resistance. Therefore, the exhaust temperature can be set to a temperature 30 to 40 ° C. higher than Tg.

The control of the particle size of the fine particle powder is as follows.
It can be performed by the concentration of the acrylic copolymer in the acrylic copolymer emulsion used and the atomizer rotation speed of the spray dryer.The higher the acrylic copolymer concentration, the larger the particle size, and the particle size with the large atomizer rotation speed. Therefore, the atomizer rotation speed of the spray dryer is preferably set in consideration of the acrylic copolymer concentration in the acrylic copolymer emulsion used.

The fine particle powder immediately after spray-drying exhibits an extremely weak form of secondary agglomeration, and this secondary agglomerate is easily disintegrated into a state of primary particles during transportation by a pipe from a spray dryer and pulverized. -Primary particle level powder can be obtained without using a classifier.

According to the present invention, although it is a thermoplastic resin, the heat resistance can be improved, the exhaust temperature at the time of spray drying can be made higher than the Tg of the resin, and at the time of atomization at the time of spray drying. Without any special consideration, the primary particles of the emulsion obtained by an existing method such as emulsion polymerization are powdered as they are, and a spherical fine particle powder having an average primary particle diameter of 3 μm or less can be easily obtained.

Further, the fine particle powder having an average particle diameter of 3 μm or less according to the present invention is used in a wide range of applications. As a form of use, the powder may be used as it is, or may be used by being redispersed or dissolved in water or a solvent. Applications include, for example, (1) paint resins, fillers, (2) sol paints, (3) molding materials, (4) cosmetics,
(5) Medical or medical drug carrier, (6) Liquid crystal display spacer, (7) Toner, (8) Cement admixture, etc., and particularly suitable as a cement dispersion admixture as a redispersible powder. To be

[0016]

The present invention will be described below in more detail with reference to examples. In the examples, "parts" means "parts by weight", and the evaluation was based on the following methods.

<Powder particle size> Laser diffraction / scattering particle size distribution analyzer LA-900 manufactured by Horiba, Ltd., relative refractive index 1.
Measured at 1. <Acid value> Amount of potassium hydroxide required to neutralize 1 g of resin (mg) <Spray drying continuous productivity> ◯: Continuous operation for 8 hours or more Δ: Continuous operation for 1 hour or more and less than 8 hours ×: Continuous operation Less than 1 hour

<Particle Shape> Primary: Primary Particles Secondary: Secondary Aggregate Particles <Observation of Powder Particles> The shape of particles is observed with a scanning electron microscope JSM-5200 (magnification: 7500 times) manufactured by JEOL Ltd.

(Example 1) Production of acrylic copolymer emulsion: Polyoxyethylene nonylphenyl was added to 2600 parts of pure water in which a dissolved oxygen was removed by sufficiently bubbling nitrogen gas in a 5-liter four-necked flask. 30 parts of ether (Emulgen 910, manufactured by Kao Corporation) and 1.5 parts of potassium persulfate were added, and the temperature was raised to 70 ° C. with stirring at 130 rpm in a nitrogen atmosphere. Next, a monomer mixture prepared by mixing 770 parts of methyl methacrylate, 350 parts of n-butyl acrylate, 280 parts of methacrylic acid, and 12 parts of sodium dialkylsulfosuccinate (Perecules OTP manufactured by Kao Corporation) was prepared in a flask. Drop 1/4 of it over 30 minutes,
The remaining 3/4 was dropped over 90 minutes and then maintained for 1 hour. After further raising the temperature to 80 ° C. and maintaining it for 1 hour, emulsion polymerization was completed. The resulting acrylic copolymer emulsion had a solid content of 35% by weight (polymerization rate 98.6%, acid value 120 g KOH
/ Mg), and a milky white emulsion containing particles having a volume average particle diameter of 0.3 μm.

Neutralization of acrylic copolymer emulsion: 4,000 parts of the obtained acrylic copolymer emulsion was placed in a 5 liter four-necked flask and 280 rpm at room temperature.
With stirring. 25% potassium hydroxide 1% by weight aqueous solution
20 parts was added dropwise over 2 hours and stirred for 3 hours to complete the neutralization step. The amount of potassium hydroxide used for this neutralization corresponds to the amount that neutralizes 15% of the total amount of carboxyl groups of the acrylic copolymer.

Spray-drying of acrylic copolymer emulsion: The neutralized acrylic copolymer emulsion was subjected to a chamber inlet temperature of 140 ° C., a chamber outlet temperature of 90 ° C. and an atomizer rotation speed using an L-8 type spray dryer manufactured by Okawara Kakohki. Spray drying was performed at 35,000 rpm. The obtained powder has a volume average particle diameter of 0.
The particle size was 35 μm, and the particle size was a spherical particle having a primary particle level. Table 1 shows the evaluation results of the monomer composition ratio, the degree of neutralization, the spray-drying continuous productivity, the powder average particle diameter, and the particle shape. The monomer composition ratio in Table 1 is shown by wt%.

(Examples 2-3, Comparative Examples 1-5) Example 1
In the same manner as in Example 1, except that the monomer composition ratio and the degree of neutralization as shown in Table 1 were respectively changed, a powder was obtained by the production, neutralization and spray drying of the acrylic copolymer emulsion. The powders obtained in Examples 2 to 3 all have a volume average particle size of 0.33 to 0.31 μm.
It was a true spherical particle powder of the primary particle level.
Table 1 shows the evaluation results of the continuous spray-drying productivity of the obtained powder, the average particle diameter of the powder, and the particle shape.

Example 4 In Example 1, sodium dialkyl sulfosuccinate in the monomer mixture was added to polyoxyethylene nonylphenyl ether with a neutralization degree of 15
A powder was obtained by producing an acrylic copolymer emulsion, neutralizing, and spray-drying in the same manner as in Example 1 except that the respective percentages were changed to 20%. The particles of the obtained acrylic copolymer emulsion had a volume average particle diameter of 0.6 μm.
Further, the obtained powder had a volume average particle diameter of 0.62 μm and was a fine spherical particle powder having a primary particle level. Table 1 shows the monomer composition ratio, the degree of neutralization,
The results of evaluation of continuous spray-drying productivity, powder average particle diameter, and particle shape are shown.

[0024]

[Table 1]

In Table 1, Example 2 is a case where the degree of neutralization with potassium hydroxide is 30%, and Example 3 is a case where methacrylic acid which is an unsaturated carboxylic acid is 10% by weight. In Comparative Example 1, since the amount of methacrylic acid was as small as 1 wt%, the heat resistance due to neutralization with potassium hydroxide was insufficient,
Secondary agglomerated powder was obtained. In Comparative Example 2, since the amount of methacrylic acid was as high as 45 wt%, the emulsion viscosity increased due to neutralization with potassium hydroxide, the continuous productivity of spray drying became poor, and the powder was also secondary agglomerated. It became what was done. In Comparative Example 3, the degree of neutralization with potassium hydroxide is 8
%, The heat resistance due to the potassium salt was insufficient, resulting in secondary agglomerated powder, and Comparative Example 4 was a case where the degree of neutralization with potassium hydroxide was 60% and excessive, and the emulsion viscosity increased. As a result, atomization by spray drying became unstable, and fusion of particles was caused by swelling / dissolution of the copolymer, so that a fine particle powder could not be obtained. Further, Comparative Example 5 is a case where spray drying was performed without performing neutralization with potassium hydroxide, and there was no heat resistance due to the potassium salt, and a secondary agglomerated powder was obtained.

[0026]

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a spherical fine particle powder having an average particle diameter of 3 μm or less at the primary particle level, which is made of an acrylic copolymer of a thermoplastic resin, without using a crushing / classifying machine with good productivity. Can be obtained.

Claims (2)

[Claims] 1. Alkyl (meth) acrylate 70-9
After neutralizing an acrylic copolymer emulsion consisting of 7% by weight and 30 to 3% by weight of unsaturated carboxylic acid with an alkaline metal compound to a neutralization degree of 10 to 50% of the amount of carboxyl groups of the acrylic copolymer. A method for producing a fine particle powder, characterized by spray drying. 2. Alkyl (meth) acrylate 70-9
After neutralizing an acrylic copolymer emulsion consisting of 7% by weight and 30 to 3% by weight of unsaturated carboxylic acid with an alkaline metal compound to a neutralization degree of 10 to 50% of the amount of carboxyl groups of the acrylic copolymer. A spherical fine particle powder having an average particle diameter of 3 μm or less obtained by spray drying.