Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-07
2001-11-20
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S233000
Reexamination Certificate
active
06320006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a suspending agent-containing slurry which not only has such an excellent suspending ability in suspension polymerization that it enables the production of vinyl polymer beads having a narrow bead size distribution, but also is capable of retaining this ability over long and of exhibiting the same ability even when it has a high concentration. The present invention also relates to a method for efficiently producing the suspending agent-containing slurry and a suspension polymerization process in which vinyl polymer beads having a narrow bead size distribution can be produced efficiently by use of the suspending agent-containing slurry.
BACKGROUND OF THE INVENTION
Generally employed suspending agents for suspension polymerization are in the form of a slurry comprising water and inorganic suspending agent particles. In most of such suspending agents, the inorganic suspending agent particles have a weight-average particle diameter of about from 2 to 3 &mgr;m and have a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is about from 20 to 30 &mgr;m.
However, the inorganic suspending agent particles contained in those suspending agent slurries are apt to aggregate into coarse particles with the lapse of time. Use of a suspending agent slurry containing coarse agglomerates of inorganic suspending agent particles in conducting suspension polymerization poses a problem that a polymer is; obtained as coarse beads or coagulates. Thus, the conventional suspending agents are less apt to retain their: ability over long.
Even when a conventional suspending agent slurry in which the inorganic suspending agent particles have not agglomerated is used to conduct suspension polymerization, there are problems that the polymer beads obtained tend to have a broad bead size distribution, and that an attempt to obtain polymer beads having a given bead diameter range results in a reduced yield.
On the other hand, an attempt has been made to obtain a narrower bead size distribution by adding various salts to an aqueous dispersion medium for use in polymerization or by regulating the hydrogen ion concentration of an aqueous dispersion medium at the initial stage of polymerization. However, use of these techniques poses a problem that the suspending agent particles, especially when having a small particle diameter, are apt to agglomerate into coarse particles which apparently have a far larger diameter than the primary particles of the suspending agent, whereby the polymer beads finally obtained have an increased bead diameter.
In general, it is preferred to finally obtain polymer beads having a bead diameter around 1 mm in high yield with a smaller suspending agent amount. Attempts are hence being made to reduce the particle diameter of suspending agent particles.
For example, a technique of synthesizing a specific inorganic suspending agent and a technique of grinding an inorganic suspending agent have been proposed (see JP-A-4-309504). (The term “JP-A” as used herein means an “unexamined published Japanese patent application.”) However, the former technique has a drawback that a special raw material is necessary. The latter technique is capable of yielding inorganic suspending agent particles having a reduced particle size. However, not only the reduced particle size is not sufficiently small, but also the heat generated by friction during grinding is apt to cause an increase in slurry viscosity and thermal agglomeration of suspending agent particles. Consequently, it is difficult with the latter technique to obtain a suspending agent having a desired particle diameter, and the slurry obtained has poor handleability due to its viscosity increase.
To mitigate the above-described problems, the grinding of a suspending agent should be performed in an extremely low suspending agent concentration, i.e., about 10% by weight or below. Although this technique is effective in mitigating the problems concerning the generation of heat in the suspending agent slurry and the viscosity increase caused by thermal agglomeration, industrial use thereof is still disadvantageous because large-scale treatment using this technique requires much time due to the low grinding efficiency thereof.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above-described problems of conventional techniques. An object of the present invention is to provide a suspending agent-containing slurry which not only has such an excellent suspending ability in suspension polymerization that it enables the production of vinyl polymer beads having a narrow bead size distribution, but also is capable of retaining this ability over long and of exhibiting the same ability even when it has a high concentration. Another object of the present invention is to provide a method for efficiently producing the suspending agent-containing slurry. Still another object of the present invention is to provide a suspension polymerization process in which vinyl polymer beads having a narrow bead size distribution can be efficiently produced by use of the suspending agent-containing slurry.
As a result of intensive studies made by the present inventors in order to eliminate the problems described above, it has been found that a slurry containing fine particles of an inorganic suspending agent dispersed with the aid of a dispersant has an excellent suspending ability and is capable of retaining this ability over long. The present invention has been achieved based on this finding.
The present invention provides a suspending agent-containing slurry comprising a particulate inorganic suspending agent, a dispersant, and an aqueous medium, said inorganic suspending agent having a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is 1 &mgr;m or smaller.
The present invention further provides a method of producing the suspending agent-containing slurry which comprises pulverizing a particulate inorganic suspending agent in an aqueous medium in the presence of a dispersant to such a degree that said inorganic suspending agent comes to have a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is 1 &mgr;m or smaller.
The present invention furthermore provides a process for suspension polymerization which comprises suspension-polymerizing a vinyl monomer in an aqueous medium containing an initiator, a suspending agent, and an anionic surfactant, said suspending agent being one supplied by using the above-described suspending agent-containing slurry in an amount of from 0.01 to 10 parts by weight on a solid basis in terms of the amount of the particulate inorganic suspending agent contained therein per 100 parts by weight of said monomer present in the suspension polymerization system.
DETAILED DESCRIPTION OF THE INVENTION
The suspending agent-containing slurry of the present invention comprises a particulate inorganic suspending agent, a dispersant and an aqueous medium.
Examples of the inorganic suspending agent for use in the present invention include aluminum hydroxide, ferric hydroxide, titanium hydroxide, the phosphates, carbonates, and sulfates of calcium, magnesium, and barium, and slightly water-soluble inorganic compounds such as talc, kaolin, and bentonite. Of these, phosphates such as tricalcium phosphate (hydroxy apatite) and magnesium pyrophosphate are preferred. In particular, a combination of a phosphate, e.g., tricalcium phosphate (hydroxy apatite) or magnesium pyrophosphate, and an anionic surfactant which will be described later is preferred, because a system containing this combination is capable of yielding polymer beads having an extremely narrow bead size distribution.
The particulate inorganic suspending agent should have a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size (hereinafter often referred to as d95), is
Kato Yukio
Murata Mitsushi
Takahashi Tsunenori
Henderson Christopher
Mitsubishi Chemical BASF Company Limited
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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