Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2000-09-19
2002-03-05
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S481000, C528S483000, C528S490000, C528S503000, C526S065000, C526S071000
Reexamination Certificate
active
06353088
ABSTRACT:
FIELD OF TECHNOLOGY
This invention relates to a method for removing volatile matters from polymer solution compositions and, more particularly, to a method for removing volatile matters such as monomers contained in aromatic vinyl polymers to an extremely low level.
BACKGROUND TECHNOLOGY
Polystyrene packaging containers have rapidly gained ground because of their handiness and versatility and found wide use as foamed polystyrene trays, containers for drinking water and the like. In recent years, however, there is a demand for as much reduction as possible of residual monomer and solvent in polystyrene. In general, volatile matters in styrenic resins manufactured by continuous mass polymerization or solution polymerization are removed by such procedures as flash devolitilization, extrusion devolitilization and membrane devolitilization.
Of the methods proposed so far for devolitilization, one is disclosed in Japan Tokyo Koho Sho 54-30428 (1979). The specification of this patent describes meticulous control of various operating conditions, for example, temperature and pressure at inlet, state and speed of feeding, residence time, heat exchange efficiency, temperature and pressure at outlet in the heating step and temperature and degree of pressure reduction during flash evaporation in the step for vapor-liquid separation under reduced pressure. According to this method, however, the operating conditions are difficult to set, which causes such problems as unstable operation and substantial difficulty of preventing the formation of low-molecular-weight substances and, likewise, the amount of volatile matters is not satisfactory.
A method disclosed in Japan Kokai Tokkyo Koho Sho 59-166506 (1984) effects the separation of volatile matters in three stages. This method comprises reducing the amount of volatile components in the polymer solution to 1% or less before introduction of the polymer solution to the third stage and adding a foaming agent under this condition. This method necessitates raising of the temperature of the resins to be transferred to the final devolitilizer and suffers not only from low operating efficiency but also from poor dispersion of polymer solution and foaming agent, thus lessening the effect of the added foaming agent and not reducing satisfactorily the amount of volatile matters.
Another method disclosed in Japan Tokkyo Koho Hei 6-827 (1994) is concerned with two-stage devolitilization consisting of devolatilizing vessels and heating devices connected directly to one another and describes meticulous control of the amounts of unreacted monomer and solvent, temperature for heating, degree of pressure reduction, residence time at the bottom of devolatilizing vessels and residence time extending from the first devolatilizing vessel to the second. However, even this method could not reduce the amount of volatile matters to a satisfactory level although it could prevent the formation of low-molecular-weight substances.
A method which employs a plate heat exchanger in the heating section in order to heat the resins at high efficiency is devised as a modification of flash devolitilization, but it cannot be said that the method sufficiently removes residual monomer and solvent. Further removal of residual monomer and solvent by this method is virtually difficult to realize as it would require a still greater pressure reduction, which would in turn require an enormous vacuum device.
Moreover, an example of removal of residual monomer and solvent to an extremely low level has been reported for a method utilizing an extruder, particularly a twin-screw extruder, as devolitilizer. This method, however, faces a number of problems such as high equipment and running costs, necessity for an enormous vacuum device, and operability, maintenance and inspection of equipment. Likewise, a membrane devolitilizer has an agitating device which requires high running cost and faces problems of operability, maintenance and inspection of equipment.
Under the circumstances mentioned above, an object of this invention is to provide a method for reducing the content of residual volatile matters in a relatively simple and economical manner in the devolitilization of aromatic vinyl resins.
The present inventors have conducted extensive studies in order to achieve the aforementioned object, found that the content of volatile matters such as residual monomer in the devolitilization of aromatic vinyl resins can be reduced to an extremely low level by multi-stage devolitilization while specifying the devolving conditions in the final stage, and completed this invention.
DISCLOSURE OF THE INVENTION
Accordingly, in a method for removing unreacted monomer and other volatile matters from a polymer solution composition obtained by continuous mass polymerization or continuous solution polymerization of an aromatic vinyl monomer alone or a mixture of an aromatic vinyl monomer and other monomers copolymerizable with said aromatic vinyl monomer in the presence or absence of rubbery polymers, this invention relates to a method for removing volatile matters from a polymer solution composition which comprises effecting the removal in multiple stages with the use of two or more flash devolatilizing vessels, adding 0.5-4 parts by weight of a foaming agent to the total polymer solution composition during its transfer from the outlet of the devolitilizer before the last-stage devolitilizer to the inlet of the last-stage devolitilizer while adjusting the solid content of the polymer solution composition to a level in excess of 97% at the outlet of the devolitilizer before the last-stage devolitilizer, passing the polymer solution composition through a step from the inlet of the last-stage devolitilizer to a pressure controller while maintaining the pressure of the polymer solution composition at 10 kg/cm
2
or more by means of the pressure controller provided either inside or at the inlet of the last-stage devolitilizer and the temperature in the range 190-260° C., introducing the polymer solution composition to a vapor-liquid separation vessel maintained at a vacuum of 20 Torr or less and allowing the composition to foam.
This invention will be described in detail below.
A polymer solution composition to which the method of this invention is applicable refers to a composition obtained by continuous mass or solution polymerization of an aromatic vinyl monomer alone or a mixture of an aromatic vinyl monomer and monomers copolymerizable with said aromatic vinyl monomer in the presence or absence of rubbery polymers. This polymer solution composition is obtained in the polymerization step in the manufacture of styrenic resins and contains volatile matters such as unreacted monomer and solvent added during the polymerization. Examples are polymer solutions obtained in the manufacture of styrenic resins by mass or solution polymerization, for example, polystyrene (GPPS), rubber-modified polystyrene (HIPS), styrene-acrylonitrile copolymers (SAN), acrylonitrile-butadiene-styrene copolymers (ABS), styrene-methyl methacrylate copolymers (MS) and methyl methacrylate-butadiene-styrene copolymers (MBS).
Aromatic vinyl monomers here include styrene, &agr;-methylstyrene, m-methylstyrene, p-methylstyrene, o-chlorostyrene and p-chlorostyrene and they may be used singly or as a mixture of two kinds or more.
Monomers copolymerizable with said aromatic vinyl monomers include acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate and they may be used singly or as a mixture of two kinds or more.
Rubbery polymers include polybutadiene, styrene-butadiene copolymers, polyisoprene and natural rubber and they may be used singly or as a mixture of two kinds of more.
In the continuous mass polymerization or continuous solution polymerization of this invention, the solution viscosity of polymer solution can be reduced, if necessary, by addition of inert hydrocarbon solvents, for example, aromatic hydrocarbons such as toluene, xylene and ethylbenzene, either singly or as a mixture of t
Fujitaka Toshihisa
Hayashi Keiichi
Hirashima Koji
Ono Hideki
Acquah Samuel A.
Birch & Stewart Kolasch & Birch, LLP
Nippon Steel Chemical Co. Ltd.
LandOfFree
Method for removing volatile matter from polymer solution... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing volatile matter from polymer solution..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing volatile matter from polymer solution... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2888639