Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-06-06
1997-04-08
Zemel, Irina S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525302, 525308, 525309, 525312, C08F28500, C08F 222, C08J 928
Patent
active
056188889
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing emulsion polymers having a hollow structure. More specifically, the present invention relates to a process for preparing emulsion polymers which comprises forming an internal layer with an alkali-swellable resin, carrying out a subsequential emulsion polymerization by means of a continuous variation in composition and a kinetic steric barrier to form a hard polymer layer outside the internal layer, swelling the internal layer with an alkali and then drying to remove water contained in the alkali-swellable resin, thereby forming a closed internal pore in the center of the polymer particle.
BACKGROUND ART
Emulsion polymers having a hollow structure have been widely used as a plastic pigment in the field of water-soluble paints, paper coating agents, information recording papers, synthethic resins and the like.
In the prior art, numerous methods for preparing plastic pigments having a hollow structure have been proposed as follows: polymerizing a mixture of monomers containing a blowing agent to prepare a plastic bead which is then blown under heating (see U.S. Pat. No. 3,615,972); of 1 to 25 micron which comprises mechanically stirring a solution of polyester dissolved in styrene to prepare an emulsion of water/oil/water which is then polymerized (see U.S. Pat. No. 3,891,577); material to a polymer and then gasifying the volatile material to swell the polymer (see Japanese Patent No. 252635/1985); polymer and then blowing a gas such as air, etc., therein; and polymer particle having a glass transition temperature of -10.degree. C. or more with hot air in the spray dryer and then immediately cooling the swollen polymer to normal temperature (see Japanese Laid-open Patent Publication No. (Hei) 4-145131).
Although the polymer beads prepared according to the prior methods as mentioned above have a self-hiding property and therefore can serve as a pigment, these prior methods have some disadvantages in that the particle size cannot be uniformly controlled, and these methods cannot properly play the role of a dispersing agent of titanium oxide; they contribute poorly to the critical surface porosity and tend to precipitate during the storage; and further the pore size and shell thickness are difficult to control.
In addition, Japanese Patent Publication No. 44282/88 discloses a method for preparing a hollow particle by phase separation and polymerization shrinkage. However, this method also has disadvantages that the hollow portion is not smooth and the method cannot be practically used on an industrial scale because of the high material cost resulting from the massive use of a cross-linking agent.
In order to improve the disadvantages in such prior methods for preparing plastic pigments having hollow particles, a method for producing hollow particles by preparing a core-shell polymer having an alkali-swellable resin inside the particles via a multi-step continuous polymerization and then subjecting the polymer to alkali swelling and drying has; been developed. This multi-step continuous polymerization process is influenced by the composition and glass transition temperature of monomers used in each polymerization step, the kind and concentration of the emulsifying agent, and the kind and concentration of the polymerization initiator, reaction temperature, etc. Further, the method using alkali-swelling procedures tends to produce a reverse core-shell polymer or a confetti-like abnormal structure due to the hydrophilicity of the polymers present inside the particles, which is far greater than that of polymers present on the outer shell of particles. Accordingly, numerous methods have been proposed for inhibiting the formation of such abnormal particle structures.
For example, U.S. Pat. Specification No. 4,427,836 discloses a method which comprises polymerizing carboxylic acid-containing hydrophilic polymers in which the volume can be swollen two times or more with an aqueous solution of a volatile base at a first emulsion polym
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Choi Su B.
Jang Tae H.
Lee Chan H.
Yoo Jin N.
LG Cehmical Ltd.
Zemel Irina S.
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