Agitating – Having specified feed means – Pump forces material through restriction
Reexamination Certificate
1993-12-27
2001-07-24
Teskin, Fred (Department: 1713)
Agitating
Having specified feed means
Pump forces material through restriction
C366S303000, C366S304000
Reexamination Certificate
active
06264357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing particles of polymerization products, particularly those having controlled particle sizes and size distributions, that are suitable for use in the powder making industry. Examples of the products include gap retainers, slip imparting agents, functional carriers, monodispersed particles having surface activity, standard particles, toners, and functional fillers that control the fluidity and gloss characteristics of paints. More particularly, the present invention relates to an improved process for producing particles having a size of 5-50 &mgr;m by suspension polymerization.
2. Background of Related Art
The importance of powder making technology which takes advantage of the various functions of particles per se is increasingly recognized these days. Among the particles produced by this technology are gap retainers, slip imparting agents, functional carriers, monodispersed particles having surface activity, standard particles, toners, and functional fillers that control the fluidity and gloss characteristics of paints. In order to produce these particles by polymerization, emulsion polymerization is used most commonly today. In speciality applications, other methods of polymerization are employed, such as soap-free polymerization, dispersion polymerization, seed polymerization and swelling polymerization.
However, these methods of polymerization have several defects. For example, considerable difficulty is involved in removing non-negligible impurities such as emulsifiers. Second, the size of particles that can be produced is limited. Third, the production cost is exorbitant. Fourth, these methods are too complex to be suitable for large-scale production. Particles having a narrow size distribution are in most cases produced by emulsion polymerization but the size of particles that can be produced by this method is only about 1 &mgr;m at maximum and producing larger particles is extremely difficult.
Suspension polymerization is also capable of producing particles, however, the only products obtained so far are nonuniform in particle size and have a broad particle size distribution. Since particle size and size distribution are closely related to the performance of polymer products in such aspects as mechanical strength, chemical resistance, color, transparency and moldability, improvements in those factors are desired. In suspension polymerization, the liquid droplets dispersed under agitation have various sizes and during dispersion they are subjected to repeated breadkup and coalescence to produce particles having an extremely broad size distribution. For this reason, it is very difficult to produce by suspension polymerization those particles which have as narrow a size distribution as monodispersed particles. Under these circumstances, one of the objectives in the powder making industry is to establish a simple technique of suspension polymerization that is capable of producing homogeneous particles.
The mechanism by which particles are produced by suspension polymerization is as follows. A disperse phase and a continuous phase are broken up by applied energy, such as agitation, to form droplets that are dispersed in the continuous phase. The droplets, if they are left as they are, are generally unstable and undergo repeated breadkup and coalescence, but eventually they are supplied with energy, such as heat, to be polymerized to form rigid and stable particles that are no longer capable of breadkup and coalescence. Therefore, in order to control the size of particles produced by suspension polymerization, one may control in some way the size of the droplets and the process of their breadkup and coalescence. In fact, however, there are many factors that relate to the size of the droplets, such as the characteristics of a disperser (which is hereinafter referred to as a “granulator”), its construction, shape, rotational speed, size, or the size and shape of the reaction vessel, the amount in which the reaction solution is charged, or the ratio between disperse and continuous phases in the reaction solution, its viscosity, as well as the type and amount of a dispersant used, and it is practically impossible to control all of these factors in a desired way. Therefore, in practice, some of these factors have to be fixed so that suitable conditions for producing desired particles are determined with the other factors being varied.
However, this approach depends so much upon a trial-and-error basis that it is not readily adaptable to design changes such as scale-up of the process. This is a serious obstacle to the production of desired particles and the process lacks flexibility, particularly for the purpose of producing particles that are to be used in powder form.
The present invention has been accomplished under these circumstances and an object of providing a method of suspension polymerization that is capable of producing smaller particles having a size distribution being controlled in an easy way.
SUMMARY OF THE INVENTION
As a result of the intensive studies conducted in order to solve the aforementioned problems of the prior art, the present inventors found a new method of production that solves those problems in a simple way.
The present invention relates generally to a method of suspension polymerization comprising the step in which a disperse phase composed of an addition polymerizable monomeric composition and a continuous phase containing a suspension stabilizer and other necessary dispersive aids are respectively retained in independent vessels and are supplied continuously into a granulator in controlled proportions through associated independent passageways to form a suspension having a group of polymerizable droplets of a desired size, and the step of recovering the suspension from the granulator and supplying it into a polymerization vessel in which a polymerization reaction is completed to produce a polymer. The method is characterized in that the disperse and continuous phases are supplied independently into a shear force generating field within the granulator, where a suspension is formed by shear force and allowed to leave the shear force generating field through a clearance of a specified size provided in that field, whereby the suspension having a group of polymerizable droplets of a desired size is produced.
In the method described above, the granulator generates shear force with a rotating part that preferably rotates at a speed of 3,000-50,000 rpm, more preferably at 10,000-30,000 rpm. The rotating part that generates shear force in the granulator is spaced from the stationary part by a gap of preferably 0.01-5.0 mm, more preferably 0.05-2.0 mm.
In order to control the size of particles produced by suspension polymerization, it is important to control the size of droplets undergoing polymerization reaction. The droplets are broken up by turbulent energy due to the agitation of the reaction solution. On the other hand, the droplets coalesce upon mutual contact. The final size of droplets is determined by the balance between these processes of breadkup and coalescence. As regards breadkup, the present inventors studied various methods for producing droplets having a size range not greater than 50 &mgr;m and found that the impact (shear force) created by blades in the dispersing apparatus was a predominant factor in controlling the size of droplets. The size of droplets formed by breadkup under the impact of blades depends on such factors as the state of droplets before breadkup, the intensity of shear force and the number of shear cycles. Droplets are subjected to shear force of the same strength irrespective of their size, so large droplets are broken up into smaller sizes under shear force but even if small droplets are supplied into an area where shear force is applied, they are further broken up into even smaller sizes until they are eventually emulsified. The emulsified components can no longer coalesce to form large particles and they are simp
Kamiyama Masafumi
O'Shima Eiji
Tsuchida Minoru
Yano Haruhiko
Pillsbury & Winthrop LLP
Teskin Fred
Tomoegawa Paper Co. Ltd.
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