Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-07-20
2001-06-05
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S331600, C525S358000
Reexamination Certificate
active
06242539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of chlorinated polyvinyl chloride resin. More particularly, it relates to a process for producing chlorinated polyvinyl chlorides which process prevents the formation of floating resin in the step of chlorination and yields a chlorinated polyvinyl chloride resin excellent free flow property and in further, which is superior in initial coloring as well as heat stability at a time of molding with application of heat.
2. Prior Art
A chlorinated polyvinyl chloride resin (hereinafter referred to as “CPVC”) can be obtained by chlorination of polyvinyl chloride resin (hereinafter referred to as “PVC”). Processes for chlorinating PVC suspended in an aqueous medium are known in the prior art and described, for example, in Japanese Laid Open Patent specifications Kokai Sho 58-103507 (1983) and Sho 64-6002 (1989).
When CPVC is chlorinated in aqueous suspension, the resins tend to float up, and because of this tendency, in the step of discharging the resins from the reaction vessel after completion of the reaction, the resins may partly remain in the vessel undischarged, or in the step of transportation of resin slurries, these may cause pump cavitation troubles. For these and other reasons, productivity is low.
On the other hand, CPVC is characterized by its higher heat resistance as compared with PVC, and therefore is used in manufacturing pipes, joints, industrial plates, sheets or the like where heat resistance is required.
However, CPVC is inferior in heat stability to PVC, and therefore, it easily undergoes scorching during molding processes, and hence is not suited for long time processing for molding. Discoloration troubles thus may be encountered in transparent moldings production, for instance.
Further, CPVC easily becomes electrified and therefore its free flow property is not good. For this reason, these resin tend to cause blocking of the hopper of an extruder, disturbing the intended constant extrusion, among other problems.
For these reasons, as a measure for resin floating, a technology was proposed in Japanese Laid Open Patent specification Kokai Hei 9-95513 (1997). The proposed method comprises chlorinating a PVC obtained by suspension polymerization in the presence of a specific amount of a specific polyvinyl alcohol as a suspending agent. This method indeed improves productivity since the floating resin problem can be avoided.
However, this proposed method is not yet free from the problems of heat stability in molding processes and/or discoloration of moldings, for transparent applications. In addition, the free flow property problem is still to be solved and, therefore, a constant extrusion operation is often difficult to achieve because of blocking of the hopper of the extruder, among other problems.
It is an object of the present invention to provide a novel process for the production of chlorinated polyvinyl chloride resin (CPVC), which prevents resin floating in the chlorination process and gives CPVC having excellent free flow property and further showing good resistance to initial discoloration as well as good heat stability at the time of heating and molding processing.
SUMMARY OF THE INVENTION
As a result of an intensive study made by the inventors of the present invention to solve the above-mentioned problems, the inventors found that in chlorinating PVC in aqueous suspension, if the PVC has a specific average particle diameter as well as specific porosity, the resin floating problem at the time of chlorination can be prevented, and the CPVC obtained by this process has excellent free flow property and that, in addition, the CPVC shows good resistance to initial discoloration and good heat stability in the heating and molding process, and they have now completed this invention.
More precisely, the process for the production of CPVC according to the present invention is characterized in that a PVC having an average particle diameter not less than 150 &mgr;m and porosity not less than 0.15 cc/g at 31-1,011 psi is suspended in an aqueous medium in a reaction vessel and the above-mentioned chlorination reaction of PVC is carried out in said aqueous suspension.
By this invention, a process for the production of CPVC can be provided, which prevents resin floating in the chlorination process and gives CPVC having excellent free flow property and further showing good resistance to initial discoloration as well as good heat stability in the heating and molding process.
DETAILED DESCRIPTION OF THE INVENTION
THE PVC in the present invention includes homo—and copolymers of vinyl chloride.
Monomers copolymerizable with vinyl chloride monomer are for example ethylene, propylene, vinyl acetate, allyl chloride, allyl glycidyl ether, acrylic acid esters, methacrylic acid esters, vinyl ethers and the like. These monomers may be used alone or in combination. The amount of these comonomers, when used, is about 0-20 parts by weight per 100 parts by weight of vinyl chloride monomer.
The average polymerization degree of PVC is not particularly limited. Since the obtained CPVC is mainly used in the production of pipes, joints, industrial plates, sheets or the like, the average polymerization degree of PVC is preferably in the range of 400-2,000. When the average polymerization degree is lower than 400, the impact strength of molded CPVC products is insufficient, and when it is over 2,000, the melt viscosity of CPVC is too high, rendering processing thereof very difficult.
The term “average particle diameter” as used herein means the value which is calculated from a cumulative distribution by using standard sieves of 42 mesh, 60 mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh and 200 mesh, according to the test method of JIS Z 8801.
The average particle diameter of PVC in this invention is limited to not less than 150 &mgr;m. When the average particle diameter is less than 150 &mgr;m, resin floating tends to occur at the time of chlorination, and the obtained CPVC may have low free flow property.
The use of a PVC having an average particle diameter of not less than 200 &mgr;m is more preferable since resin floating at the time of chlorination and the free flow property of the obtained CPVC can be further improved. The term “porosity at 31-1,011 psi” as used herein means the value obtained by dividing, by the resin weight, the total volume, measured with a mercury penetration method porosimeter at 31-1,011 psi, of porosity occurring in the vinyl chloride resin and having an average diameter of 5.9-0.17 &mgr;m.
In the present invention, the porosity of PVC at 31-1,011 psi is limited to not less than 0.15 cc/g. When the said porosity value is below 0.15 cc/g, the gelation property of CPVC is deteriorated and/or the resistance to initial discoloration and the heat stability become poor.
When the above-mentioned porosity value is not less than 0.19 cc/g and the bulk density is not less than 0.54 g/cc, the resin floating-preventing effect resulting from said average particle diameter, free flow property improving effect resulting from said bulk density and the initial discoloration resistance and heat stability improving effect in the heating and molding process as resulting from said porosity can preferably be increased.
The chlorination process for obtaining CPVC by chlorination of PVC is carried out in a conventional manner in aqueous suspension. There is no particular limitation imposed on this process. The process comprising blowing gaseous chlorine into PVC under irradiation with a mercury lamp, which is the simplest one from the equipment viewpoint, is preferred, however.
The temperature at the time of chlorination is preferably 40-90° C. from the plant's corrosion resistance viewpoint and also for improving the resistance to initial discoloration as well as the heat stability of the obtained CPVC.
Further, the chlorination is preferably conducted in a pressure range of 0-1.5 kg/cm
2
G from the viewpoint of plant's resistance to corrosion and pressure.
The prev
Isshiki Minoru
Suzuki Takeyuki
Tadokoro Tadashi
Jordan and Hamburg LLP
Kaneka Corporation
Lipman Bernard
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