Process for producing vinyl chloride polymer

Details Process for producing vinyl chloride polymer Process for producing vinyl chloride polymer

1999-08-20

2001-10-16

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S062000, C526S227000, C526S291000

Reexamination Certificate

active

06303712

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing a vinyl chloride polymer by suspension polymerization of vinyl chloride monomers or a monomer mixture containing them.
2. Description of the Prior Art
The suspension polymerization of vinyl chloride monomers or a monomer mixture thereof in an aqueous medium are usually carried out in a polymerization vessel provided with a cooling/heating jacket, a stirrer, a material charging line, a baffle, a polymer draw-out line, an unreacted monomer recovery line and so forth. To polymerize the vinyl chloride monomers or monomer mixture in an aqueous medium in such a polymerization vessel, a process is employed in which the aqueous medium, a dispersant, the vinyl chloride monomers or monomer mixture, a polymerization initiator and optionally other additives are fed through the material charging line, provided at the gas-phase upper part of the polymerization vessel, into the polymerization vessel with stirring and thereafter these are heated to carry out polymerization.
In this polymerization process, polymer scales tend to adhere to the polymerization vessel inner wall, stirrers and so forth. Such polymer scales bring about problems that those having adhered thereto may cause a decrease in cooling capacity of the polymerization vessel, and also those having come off may mix in products, resulting in a low product quality. Much labor and time must be taken to remove such polymer scales having adhered. Also, since the polymer scales contain unreacted monomers, there is a problem of environmental hygiene.
Accordingly, in order to prevent polymer scales from adhering, a polymerization vessel is conventionally used whose inner wall and so forth have been coated with a polymer scale preventive agent to form its coating film.
Use of such a polymerization vessel, however, is still disadvantageous in that, with repetition of polymerization, the polymer scales tend to adhere to the polymerization vessel inner wall and especially to the baffle provided in the polymerization vessel, on its side facing the polymerization vessel inner wall at the interface between gas phase and liquid phase (hereinafter “gas/liquid interface”) and the vicinity thereof.
Once polymer scales have adhered to the baffle on its side facing the polymerization vessel inner wall at the gas/liquid interface and the vicinity thereof, the polymer scales grow gradually with repetition of polymerization, and the polymer scales having grown may come off and mix in the resulting polymer to cause fish eyes in a large number, resulting in a poor product quality. Such a problem has been involved.
In recent years, for the purpose of improving productivity, an oil-soluble polymerization initiator has been used whose temperature at which the half-life comes to be 10 hours in the state of a 0.1 mol/L benzene solution is 30 to 55° C., in order to shorten polymerization time (Japanese Laying-open Publication (kokai) Nos. 8-109203 and 8-225613). However, there is another problem that such an oil-soluble polymerization initiator is active at relatively low-temperature and hence the polymerization carried out using the oil-soluble polymerization initiator tends to result in a poor product quality, e.g., to cause fish eyes in a large number in the resulting polymer.
SUMMARY OF THE INVENTION
Accordingly, in a process for producing a vinyl chloride polymer by polymerizing vinyl chloride monomers or a monomer mixture thereof in an aqueous medium, an object of the present invention is to provide a vinyl chloride polymer production process that can effectively prevent polymer scales from adhering to the polymerization vessel inner wall of course and also to the baffle on its side facing the polymerization vessel inner wall at the gas/liquid interface and the vicinity thereof even with repetition of polymerization and may cause less fish eyes in the product polymer obtained.
To achieve the above object, the present invention provides a process for producing a vinyl chloride polymer, comprising subjecting vinyl chloride monomers or a vinyl-chloride-containing monomer mixture to suspension polymerization in the presence of a dispersant and a polymerization initiator in an aqueous medium in a polymerization vessel, wherein
a coating film of a polymer scale preventive agent has been formed on the inner wall of the polymerization vessel and other portions with which monomers come into contact during the polymerization;
the polymerization initiator is an oil-soluble polymerization initiator whose temperature at which the half-life comes to be 10 hours in the state of a benzene solution of 0.1 mol/L concentration is 30° C. to 55° C.; and
the process comprising the steps of:
charging materials including the vinyl chloride monomers or monomer mixture, the aqueous medium and the dispersant; and
initiating the polymerization by introducing the polymerization initiator at a position of the interior of the liquid phase comprising a mixture of the materials charged, the position satisfying the following expression:
H≦0.7H
0
wherein H represents a height from the bottom of the polymerization vessel to the position where the polymerization initiator is introduced, and H
0
represents a height from the bottom of the polymerization vessel to the liquid surface of the liquid phase comprising the mixture of the materials.


REFERENCES:
patent: 4256863 (1981-03-01), McOnie et al.
patent: 4431783 (1984-02-01), Walker et al.

Affiliated with

Also associated with

Rating

Process for producing vinyl chloride polymer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for producing vinyl chloride polymer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing vinyl chloride polymer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2606877