Abstract:
A method of producing suspension polymerized vinyl chloride polymers or copolymers of improved flowability by polymerizing vinyl chloride monomers alone, or in a mixture with other monomers, in an aqueous medium, to form a slurry of polymer suspended in said aqueous medium. After removing unreacted monomers, a polyhydric alcohol is added to the slurry containing the suspension polymerized polymer or to a product obtained after the dewatering of the slurry, in an amount of 0.001 to 0.5 parts by weight based on 100 parts by weight of the vinyl chloride polymer or copolymer suspended in the slurry.

Description:
This application is a file wrapper continuation of Ser. No. 08/155770 filed Nov. 23, 1993, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of producing vinyl chloride polymer or copolymer through the suspension polymerization process. In particular, it relates to a production method of vinyl chloride polymer or copolymer having excellent fluidity. 
     The vinyl chloride polymer or copolymer is usually produced through the suspension polymerization process and, after the refinements such as separation from slurry and drying, it is conveyed by the pneumatic transportation for storage or bag-filling. 
     However, the vinyl chloride polymer or copolymer thus obtained carries the static electricity through the frictions by itself and with other materials in the processes of conveyance and bag-filling to reduce the fluidity and to decrease the bulk density over the vinyl chloride polymer or copolymer just after the production. Hence, it becomes remarkably difficult in handling, posing a problem of serious obstacles in operation. As the methods of alleviating the adverse effect due to such electrification of polymer, a method to add a nonionic surfactant, cationic surfactant or the like being an antistatic agent to vinyl chloride polymer or copolymer and a method to adjust the humidity by blowing the steam into vinyl chloride polymer or copolymer have been employed so far. 
     Said method to add the surfactant, however, has such drawbacks that it cannot enough prevent the decrease in bulk specific gravity of polymer and, in addition, it adversely affects the thermal stability and the initial coloring property of product. Moreover, the method to blow the steam has drawbacks of increased labor requirement, complicated equipment and the like. 
     SUMMARY OF THE INVENTION 
     This invention has as its objective the production of vinyl chloride polymers or copolymers of improved flowability and antistatic performance when dry. The polymers or copolymers are produced via a suspension polymerization process. The process includes polymerizing, in an aqueous medium, a vinyl chloride monomer or a mixture of vinyl chloride monomer and other monomers polymerizable therewith wherein vinyl chloride is a major component of the mixture. The polymerization is conducted to completion using a suspension polymerization process, thereby forming an aqueous slurry containing the vinyl chloride polymer or copolymer. A polyhydric alcohol is added to the aqueous slurry, or to a product formed after dewatering of the slurry. The polyhydric alcohol is added as an aqueous solution having a concentration of 5 to 90 percent, the amount of polyhydric alcohol added being from 0.001 to 0.5 parts by weight based on 100 parts by weight of the vinyl chloride polymer or copolymer. The dewatered slurry containing the polymer treated with polyol may be dried using a fluidized drying technique. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the method of the invention, the vinyl chloride polymer or copolymer is first synthesized through the suspension polymerization process. As the vinyl chloride polymers, homopolymer of vinyl chloride and copolymers of vinyl chloride with other copolymerizable vinyl monomers can be mentioned. As the vinyl type monomers copolymerizable with vinyl chloride, for example, alkyl vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, α-monoolefinic monomers such as ethylene and propylene, acrylic alkyl esters such as methyl acrylate and methacrylic alkyl esters such as methyl methacrylate are mentioned. 
     The suspension polymerization of vinyl chloride polymer or copolymer is well known and vinyl chloride monomer or vinyl chloride monomer and other polymerizable vinyl monomers are polymerized in an aqueous medium in the presence of suspending agent and polymerization initiator. In this way, a slurry containing vinyl chloride polymer or copolymer can be obtained through the suspension polymerization process. 
     Next, according to the inventive method, a polyhydric alcohol is added to the slurry containing vinyl chloride polymer, polymer or copolymer cake obtainable after the dewatering of said slurry or powder of vinyl chloride polymer or copolymer after the drying of said polymer cake as an aqueous solution of concentration of 5 to 90%. Such polyhydric alcohols include ethylene glycol, propylene glycol, glycerine, pentaerythritol and their polycondensates and water-soluble polyhydric alcohols having these as major components. The addition level of said polyhydric alcohol is preferable to be 0.001 to 0.5 parts by weight to 100 parts by weight of vinyl chloride polymer or copolymer. If the addition level is under 0.001 parts by weight, the extreme decrease in bulk density due to electrification cannot be prevented. Even if the addition level may exceed 0.5 parts by weight, the effect of addition is not enhanced beyond, which is uneconomical. 
    
    
     In following, the invention will be illustrated concretely based on the examples, but the invention is not confined thereto. 
     EXAMPLE 1 
     Into a stainless steel polymerization reactor were charged 100 parts by weight of vinyl chloride monomer, 150 parts by weight of deionized water, 0.1 part by weight of partially saponified poly(vinyl alcohol) and 0.04 parts by weight of 2-ethylhexyl peroxydicarbonate, and the polymerization was conducted at a temperature of 57° C. When the pressure inside the polymerization reactor reached kg/cm 2  (gauge), the unreacted vinyl chloride monomer was recovered to obtain a slurry of vinyl chloride polymer. Tetraglycerine a tetramer of glycerine having the structural formula HO CH 2  CH(OH)CH 2  O(CH 2  CH(OH)CH 2  O) 2  CH 2  CH(OH) CH 2  OH was added to the polymer slurry thus obtained as 30% aqueous solution in an amount of 0.1 part by weight based on polymer. Thereafter, the polymer was separated from said slurry and submitted to fluidized drying for 2 hours at 70° C. to obtain vinyl chloride polymer. 
     EXAMPLES 2 THROUGH 4 
     Similarly to Example 1, vinyl chloride polymers were obtained, except that the type of polyhydric alcohol, addition level and concentration of aqueous solution in Example 1 were varied as the conditions shown in table 1. 
     EXAMPLE 5 
     Into a stainless steel polymerization reactor were charged 100 parts by weight of vinyl chloride monomer, 150 parts by weight of deionized water, 0.1 part by weight of partially saponified poly(vinyl alcohol) and 0.04 parts by weight Of 2-ethylhexyl peroxydicarbonate, and the polymerization was conducted at a temperature of 57° C. When the pressure inside the polymerization reactor reached 6.0 kg/cm 2  (gauge), the unreacted vinyl chloride monomer was recovered and the slurry was dewatered to obtain a cake of vinyl chloride polymer containing 20% by weight of water. Ethylene glycol was added to the polymer cake thus obtained, as 30% aqueous solution in an amount of 0.1 part by weight based on polymer, which was then submitted to fluidized drying for 2 hours at 70° C. to obtain vinyl chloride polymer. 
     EXAMPLE 6 
     Into a stainless steel polymerization reactor were charged 100 parts by weight of vinyl chloride monomer, 150 parts by weight of deionized water, 0.1 part by weight of partially saponified poly(vinyl alcohol) and 0.04 parts by weight of 2-ethylhexyl peroxydicarbonate, and the polymerization was conducted at a temperature of 57° C. When the pressure inside the polymerization reactor reached 6.0 kg/cm 2  (gauge), the unreacted vinyl chloride monomer was recovered and the slurry was dewatered and then submitted to fluidized drying for 2 hours at 70° C. to obtain vinyl chloride polymer. Ethylene glycol was added to the vinyl chloride polymer obtained as 50% aqueous solution in amounts of 0.05 parts by weight based on polymer under fluidized state. 
     EXAMPLES 7 THROUGH 9 
     Similarly to Example 6, vinyl chloride polymers were obtained, except that the type of polyhydric alcohol, addition level and concentration of aqueous solution in Example 6 were varied as the conditions shown in Table 2. 
     COMPARATIVE EXAMPLE 1 
     Similarly to Example 1, vinyl chloride polymer was obtained, except that tetraglycerine in Example was not added. 
     COMPARATIVE EXAMPLE 2 
     Similarly to Example 1, vinyl chloride polymer was obtained, except that 50% aqueous solution of polyoxyethylene sorbitan monolaurate were used in place of tetraglycerine in Example 1. 
     With the vinyl chloride polymers obtained in Examples 1 through 9 and Comparative examples 1 and 2 aforementioned, measurement test of bulk density and test of thermal stability were performed. The results are shown in Tables 1 and 2. 
     1. Measurement Test of Bulk Density 
     After the vinyl chloride polymer was allowed to stand for 48 hours in a thermohygrostatic room of temperature of 23° C. and relative humidity of 50%, the bulk density was measured according to the method of JIS K-6721. 
     Moreover, after the vinyl chloride polymer allowed to stand for 48 hours under the same conditions as above was stirred for 2 minutes at 60 rpm with Brabender planetary mixer, the bulk density was compared by the same method as above. 
     2. Thermal Stability 
     To 100 parts by weight of vinyl chloride polymer, 
     tribasic lead sulfate 1.0 part by weight 
     lead stearate 1.5 part by weight 
     calcium stearate 0.5 part by weight 
     were formulated and, after kneading for 5 minutes on rolls of 190° C., 1 mm thick sheet was fabricated. This sheet was placed in an oven of 190° C. and the time required for blackening was measured. 
     
                                           TABLE 1__________________________________________________________________________        Example 1               Example 2                      Example 3                             Example 4__________________________________________________________________________AdditiveType    Tetraglycerine               Hexaglycerine                      Tetraethylene                             Ethylene glycol                      glycolConcentration of        30     30     30     30aqueous solution(%)Addition level        0.1    0.1    0.1    0.1(part by weight)Adding condition        Addition to               Addition to                      Addition to                             Addition to        polymer slurry               polymer slurry                      polymer slurry                             polymer slurryBulk No mixing        0.552  0.551  0.551  0.555DensityMixing  0.549  0.550  0.551  0.553(g/cc)Thermal stability (min)        60     60     60     60__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________                                            Comparative                                                   Comparative         Example 5                Example 6                       Example 7                              Example 8                                     Example 9                                            example                                                   example__________________________________________________________________________                                                   2Additive Type    Ethylene                Ethylene                       Glycerine                              Propylene                                     Tetraglycerine                                            --     Polyoxyethylen         glycol glycol        glycol               sorbitan                                                   monolaurate Concentration of         30     50     50     50     50     --     50 aqueous solution (%) Addition level         0.1    0.05   0.05   0.05   0.05   --     0.1 (part by weight) Adding condition         Addition to                Addition to                       Addition to                              Addition to                                     Addition to                                            --     Addition to         polymer cake                dried powder                       dried powder                              dried powder                                     dried powder  polymer slurry                of polymer                       of polymer                              of polymer                                     of polymerBulk Density No mixing         0.556  0.554  0.554  0.555  0.553  0.555  0.553(g/cc) Mixing  0.553  0.552  0.554  0.552  0.552  0.510  0.540Thermal stability (min)         60     60     60     60     60     60     50__________________________________________________________________________