GB2035342A - A method for the preparation of polyvinyl chloride resins - Google Patents

Abstract

In the method for the preparation of a vinyl chloride-based resin by aqueous suspension polymerization of vinyl chloride monomer in which the polyvinyl chloride resin product is modified by a modifying resin or other agent having different properties from the resulting polyvinyl chloride resin, the modifying agent or resin is added to the polymerization mixture slurried in an aqueous medium together with a latex of a synthetic polymer at a time when the conversion of the monomer to polymer is in the range from 3 to 85%. It is also essential that the average particle diameter of the modifying agent or resin is in the range from 10 to 200 mu m and that of the polymer particles in the added latex is in the range from 0.01 to 5 mu m in order that good coalescence is obtained between the particles of the modifying agent or resin and the polyvinyl chloride resin.

Description

SPECIFICATION A method for the preparation of polyvinyl chloride resins The present invention relates to the preparation of polyvinyl chloride resins, more particularly, the preparation of polyvinyl chloride resins modified with certain modifying resins, the particles of which are in coalescence with the particles of the polyvinyl chloride formed by the suspension polymerization of vinyl chloride in an aqueous medium.

It may be too much to say that polyvinyl chloride resins belong to one of the most important classes of thermoplastic synthetic resins finding uses in a wide variety of applications owing to their excellent properties. Nevertheless, it is a common practice that various kinds of modifying agents are formulated with polyvinyl chloride resins in the fabrication thereof when further improvement of some of the properties is desired, for example, in the workability, anti-weathering resistance, anti-cold resistance, mechanical strengths, reduced electrostatic charging and other surface characteristics.

In formulating or adding a modifying agent with a polyvinyl chloride resin, the polyvinyl chloride resin and the modifying agent are combined in several different ways according to the type of the modifying agent and the object of the modification, including a method in which the modifying agent is admixed just before the polyvinyl chloride resin is subjected to fabrication, a method in which the modifying agent is added into the aqueous polymerizate slurry after completion of the suspension polymerization of vinyl chloride in an aqueous medium, a method in which the modifying agent is added or dissolved in the vinyl chloride monomer before polymerization so that the polymerization is performed in the presence of the modifying agent, and others.

It should be noted that the modification to be achieved by the addition of a modifying agent largely depends on the manner in which it is admixed with the vinyl chloride monomer or polymer. For example, when the modifying agent is added into the aqueous slurryofthe polymerizate, the most important parameter determining the properties of the resultant modified polyvinyl chloride resin is the particle size distribution of the modifying agent or the condition of its dispersion in the slurry which affects the degree or nature of the expected modification of the properties of the resultant resin product.

On the other hand, the method of dry blending of the modifying agent in powdery form with powdery polyvinyl chloride resin is accompanied by several problems such as the troublesome handling of powders as well as possible environmental contamination by the scattered powders not to mention that the desired improvement in the properties of the resin product is sometimes obtained only insufficiently due to the poor miscibility of the modifying agent and the polyvinyl chloride resin depending on the chemical or physical properties of the modifying agent.

In view of the above described difficult problems in the modification of a polyvinyl chloride resin with a modifying agent, e.g. a resin product which is different from the polyvinyl chloride to be modified, the inventors have conducted extensive investigations to develop a novel method by which the effect of modification is most effectively and reproducibly exhibited with a minimum amount of addition of the modifying agent regardless of the type of modifying agents.

The invention established as a result of the above investigations is based on the discovery that, in a method of adding a modifying agent into the polymerization mixture under polymerization reaction of vinyl chloride monomer in an aqueous medium, if the modifying agent is introduced in the form of an aqueous slurry together with an aqueous latex or emulsion of certain kinds of vinylic or dienic polymers at a moment when the conversion of the vinyl chloride monomer into polymer is within a specified range there may be obtained remarkably and unexpectedly enhanced modification effects in respect of powder characteristics and workability of the polyvinyl chloride resin product, mechanical strengths and surface properties, e.g.

electrostatic charging, of the articles shaped therefrom, presumably due to the coalescence of the particles of the modifying agent and the particles of of the polyvinyl chloride resin formed by the polymerization.

Thus, the method of the present invention for the preparation of a modified polyvinyl chloride resin comprises, in the suspension polymerization of vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium, introducing an aqueous slurry of a modifying agent having an average particle diameter in the range from 1 0Ftm to 200cm and an aqueous latex of a synethetic polymer of an ethylenically unsaturated monomer having an average particle diameter in the range from 0.01 lim to 5ym into the polymerization mixture during polymerization at a moment when the conversion of the vinyl chloride monomer or the monomer mixture into polymer is in the range from 3 to 85%.

As is mentioned above, the method of the present invention is applicable not only to the homopolymeriza tion of vinyl chloride monomer but also to the copolymerization of vinyl chloride monomer with one or more of copolymerizable ethylenically unsaturated monomers provided that the main component, say 50% by weight or more, of the monomer mixture is vinyl chloride. The monomers copolymerizable with vinyl chloride are well known in the art and exemplified by acrylic acid and esters thereof, methacrylic acid and esters thereof, acrylonitrile, vinyl ethers, vinyl esters such as vinyl acetate, vinyl halides other than vinyl chloride such as vinyl fluoride, aromatic vinyl compounds such as styrene, maleic acid and esters and anhydride thereof, olefins such as ethylene and propylene, vinylidene halide such as vinylidene chloride and the like.

The suspension polymerization of the vinyl chloride monomer or monomer mixture may be performed according to the conventional manner including the use of a suspending agent and a polymerization initiator under an ordinary pressure and at an ordinary polymerization temperature with no particular limitations. For example, the suspending agent may be exemplified by water-soluble polymeric substances such as partially saponified polyvinyl acetates, polyacrylic acids, water-soluble cellulose ethers, copolymers of vinyl acetate and maleic anhydride, polyvinyl pyrrolidones, copolymers of styrene and maleic anhydride, starch, gelatine and the like and the polymerization initiator may be selected from those soluble in the monomer phase e.g.

organic peroxide compounds such as lauroyl peroxide, benzoyl peroxide, di-isopropylperoxy dicarbonate, 2-ethylhexylperoxy dicarbonate, tert-butylperoxy pivalate, acetylcyclohexylsulfonyl peroxide and the like and azo compounds such as a,a'-azobisisobutyronitrile, a,a'-azobis-2,4-dimethylvaleronitrile, a, o'-azobis-4- m.ethoxy-2,4,-dimethylvaleronitrile and the like. It is of course possible that two kinds or more each of these suspending agents and polymerization initiators may be used in combination.

The kind of modifying agent to be introduced into the polymerization mixture in the course of the polymerization reaction naturally depends on the object of the modification of the polyvinyl chloride resin.

In some cases, for example, inorganic fillers, stabilizing agents and the like may be used as the modifying agent but the method of the present invention is particularly effective when the polyvinyl chloride resin is to be modified with a synthetic resin having different properties from the polyvinyl chloride resin to be formed by the polymerization.Such a synthetic resin is exemplified by polyolefin resins, e.g. polyethylene and polypropylene, polystyrene resins, acrylic resin, polyvinyl chloride resins, copolymeric resins of vinyl chloride and vinyl acetate, copolymeric resins of vinyl chloride and styrene, copolymeric resins of vinyl chloride and ethylene, copolymeric resins of vinyl chloride and propylene, copolymeric resins of vinyl chloride and vinylidene chloride, copolymeric resins of vi nyl acetate and ethylene, ternary copolymeric resins of vinyl chloride, vinyl acetate and ethylene, ternary copolymeric resins of methyl methacrylate, butadiene and styrene, ternary copolymeric resins of ethylene, propylene and vinyl chloride and the like.In particular, the use of a polyvinyl chloride resin having a rather small average degree of polymerization as the modifying agent is sometimes uniquely effective for improving the workability of a polyvinyl chloride resin of high molecular weight formed by the polymerization, which otherwise is fabricated with considerable difficulties in molding.

The above mentioned synthetic resins to be used as the modifying agent in the inventive method should desirably have an average particle diameter in the range from 10 ssm and 200 um in order that the desired modification effects be satisfactory. These modifying agents are necessarily introduced into the polymerization mixture as an aqueous slurry prepared in advance by a suitable mechanical dispersing means.The content of the modifying agent in the aqueous slurry is not limitative but, for example, it may be in the range from lotto 50% by weight; a too small content of the modifying agent in the aqueous slurry is undesirable since the introduction of a slurry of a too small solid content necessarily brings a considerable volume of water into the polymerizaton mixture so that the production capacity of the polymerization facilities is reduced.

The amount of the modifying agent to be added into the polymerization mixture in the form of an aqueous slurry is, of course, dependent on the kind of modifying agent and the object of the modification but it is usually in the range from 1 to 50% by weight of the solid in the aqueous slurry of the modifying agent based on the amount of the vinyl chloride monomer or the monomer mixture initially introduced into the polymerization reactor.

The latex of a synthetic polymer to be introduced into the polymerization mixture in combination with the above described aqueous slurry of the modifying agent may be selected from a variety of latices of synthetic resins exemplified by acrylic ester resins, polyvinyl acetate resins, polymethyl methacrylate resins, polyvinyl chloride resins, vinyl acetate-acrylic ester copolymer resins, vinyl acetate-ethylene copolymer resins, acrylic ester-methyl methacrylate copolymer resins, acrylic ester-styrene copolymer resins, and vinyl chloride-vinyl acetate copolymer resins as well as latices of synthetic rubbers such as butadiene-styrene copolymer rubbers, butadiene-acrylonitrile copolymer rubbers, butadiene-isoprene copolymer rubbers and the like.

The polymer particles contained in the above mentioned latices should have an average particle diameter in the range from 0.01 Fm to 5 um or, preferably, from 0.05 um to 5 !lem. The content of the polymer in the latex is not limitative but it is usually in the range from 20 to 60% by weight.

The use of the latex is essential in the inventive method since the coalescence of the particles of the polyvinyl chloride resin formed by the polymerization and the particles of the modifying agent is effected only by the aid of the polymer particles contained in the latex which serve, so to say, as a binder between them. In order to obtain this bonding effect sufficiently, the amount of the latex to be added into the polymerization mixture is usually in the range from 0.01 to 10% by weight or, preferably, from 0.1 to 5% by weight of the solid polymer in the latex based on the amount of the vinyl chloride monomer or the monomer mixture initially charged into the polymerization reactor although the amount of the latex should be determined according to the kind and amount of the modifying agent. When the amount of the latex is smaller than that mentioned above, the coalescence of the particles is effected only insufficiently while too much latex added to the polymerization mixture results in inferior properties of the finally obtained polymer products not to mention the disadvantageously increased production cost arising from the use of an excessive amount of the relatively expensive latex.

The above described aqueous slurry of the modifying agent and the latex of the synthetic polymer are necessarily introduced into the polymerization mixture only at a time when the conversion of the vinyl chloride monomer or the monomer mixture into polymer is in the range from 3 to 85% or, preferably, from 10 to 85%. This is because with too early addition of the aqueous slurry and the latex into the polymerization mixture (before the conversion reaches 3%), the powder characteristics of the resultant polymer product cannot be satisfactory, while with delayed addition (after the conversion has exceeded 85%.) i.e. near the end of the polymerization, the expected coalescence of the particles of the polyvinyl chloride resin and the modifying agent can no longer be obtained to a satisfactory extent.

It may be possible to obtain sufficient coalescence of the particles even by the addition of the modifying agent and the latex at a too late stageof polymerization, e.g. after completion of the polymerization, by the combined addition of an organic solvent capable of dissolving vinylic resins such as methylene chloride, toluene, benzene, tetrahydrofuran and the like but the use of such an organic solvent is undesirable due to the necessity of subsequent recovery of the solvent with accompanying problems of environmental pollution.

In the following Examples, the procedures for the determination of the particle size distribution, gelation time and the average degree of polymerization of the polymer products were as follows.

Particle size distribution: according to the method specified in JIS (Japanese Industrial Standard) Z 8801.

Gelation time: 60 g of the resin composition composed of 100 parts by weight of the resin, 2 parts by weight of tribasic lead sulfate and 1 part by weight of lead stearate was subjected to the measurement by kneading in a Brabender plasticorder operated at 1700C with a velocity of 30 r.p;m. and the time in minutes to the maximum torque was recorded at the time of gelation. A shorter gelation time means better wokability in molding.

Average degree of polymerization: according to the method specified in JIS K 6721.

Example 1. (Experiments No. 1 to No. 8) Into an autoclave of 150 liter capacity made of stainless steel and equipped with a turbine blade stirrer were introduced 50 kg of deionized water and 25 g of a partially saponified polyvinyl acetate and, after evacuation by means of a vacuum pump, 25 kg of vinyl chloride monomer and 10 g of 2-ethylhexylperoxy dicarbonate were added thereinto. The polymerization was carried out at 51.5do.

At a time when the monomer conversion had reached 60%, a modifying agent slurried in water (solid content 30% by weight) as indicated in Table 1 below together with its particle size distribution and a latex of a synthetic polymer indicated in Table 2 below were added into the polymerization mixture in amounts shown in Table 3 in % by weight of the solids based on the amount of the vinyl chloride monomer, and the polymerization reaction was continued.

When the internal pressure of the polymerization reactor dropped to 5.5 kg/cm2G, the polymerization reaction was terminated by cooling and the polymerization mixture discharged out of the reactor was dehydrated and dried to give a polyvinyl chloride resin product. The particle size distribution and gelation time of the resin products are set out in Table 3. In each ofthe Experiments No. 1 to No. 6 and No. 8, microscopic examination of the resin product showed that smaller particles were bonded around larger particles and, in particular, the smaller particles bonded to the larger particles in Experiment No. 6, where the modifying agent was a polystyrene resin, were transparent indicating that the smaller particles were the polystyrene resin particles.

The polyvinyl chloride resin obtained in Experiment No. 7, in which no modifying agent and latex were added to the polymerization mixture in the course of polymerization, had an average degree of polymerization of about 1300.

TABLE 1 (Modifying agent) Particle size distribution, % passing through screen of No. Type 60 mesh 80 mesh 100 mesh 150 mesh 200 mesh Polyvinyl chloride resin having an 100 100 92.5 65.7 53.1 average degree of polymerization 700 II Vinyl chloride-vinyl acetate copolymer 100 100 90.1 63.2 50.1 resin Ill Polystyrene resin 100 100 89.5 60.2 45.0 TABLE 2 (Latex of synthetic polymer) No.Type Solid content, Average particle % by weight diameter, um I 2-Ethylhexyl acrylate resin 35 1.0 II Copolymer of vinyl acetate and ethylene (5:1) 40 1.5 Ill Copolymer of methyl acrylate and vinyl acetate (1:1) 40 3.0 IV Methyl methacrylate resin 40 5.0 V Copolymer of vinyl chloride and vinyl acetate (8::2) 35 3.5 VI Copolymer of butadiene and styrene (1 1) 35 2.0 TABLE 3 Modifying Latex Properties of product Ex- agent Particle size distribution, % peri- passing through screen of Gelation ment No. % by No. % by time, No. weight weight 60 80 100 150 200 minutes as solid as solid mesh mesh mesh mesh mesh 1 1 30 1 2 100 90.5 50.6 10.1 0.2 7 2 1 40 11 3 100 90.3 55.5 15.2 0.5 7.1 3 1 50 V 5 100 92.0 53.3 12.0 0.3 7.2 4 11 10 Ill 2 100 95.5 60.1 17.3 0.7 6.3 5 11 20 VI 3 100 91.1 53.1 11.7 0.3 6.2 6 Ill 30 IV 2 100 92.3 60.7 11.8 0.3 6.5 7 None - None - 100 91.1 52.3 13.1 0.2 10.5 8 1 30 None - 100 96.0 85.5 47.9 16.2 7.3 16 IV 20 1 2 100 90.3 52.5 11.0 0.3 14.0 17 V 25 IV 3 100 92.5 53.6 10.5 0.3 13.9 18 VI 30 1 2 100 92.6 50.2 13.5 0.4 14.6 19 None - None - 100 87.5 48.5 9.6 0.1 18.3 20 VI 30 None - 100 95.3 86.2 47.9 18.3 15.0 Example 2. (Experiments No. 9 to No. 12) The same experimental procedure as in Example 1 was repeated except that the modifying agent and the latex were modifying agent Ill and latex I in all of the experiments and the amount of the modifying agent was 7.5 kg as solid, the modifying agent and the latex being introduced into the polymerization mixture at a time when the monomer conversion was 30%. The amount of the added latex was varied, 0.005%, 0.1%, 1% and 5% by weight as solid, in Experiments No.9 to No. 12, respectively.

The microscopic examination of the resultant resin products revealed that substantially all of the transparent polystyrene particles were found to be in coalescence with the particles of the polyvinyl chloride resin and not free in Experiments No. 11 and No. 12 while a considerable proportion of the polystyrene particles was free with little coalescence with the polyvinyl chloride particles in Experiment No. 10 and substantially no coalescence was found in Experiment No. 9.

Example 3. (Experiments No. 13 to No. 15) The procedure was substantially the same as in Example 1 except that 25 kg of vinyl chloride monomer was replaced with a monomer mixture composed of 20 kg of vinyl chloride and 3 kg of vinyl acetate, sec-butylperoxy dicarbonate was used as the polymerization initiator in place of 2-ethylhexylperoxy dicarbonate and the polymerization temperature was increased to 580C.

At a time when the monomer conversion was 80%, 7.5 kg of modifying agent Ill as slurried and 1 kg of a polymethyl acrylate latex containing 40% by weight of solids having an average particle diameter of about 2 um were added to the polymerization mixture and the polymerization reaction was continued.

When the internal pressure of the polymerization reactor dropped to 2.0 kg/cm2G, the polymerization was terminated and the copolymer resin product was obtained in the same manner as in Example 1. The microscopic examination of the resin product revealed that the transparent particles of the polystyrene resin were bonded to and around the opaque particles of the copolymer resin with coalescence.

For comparison, the addition of the latex was omitted (Experiment No. 15) to give a polymer product which was a mere mixture of transparent polystyrene particles and opaque particles of the copolymer resin as shown by microscopic examination. In Experiment No. 14, the addition of both the modifying agent and the latex was omitted to give an ordinary copolymer resin having an average particle diameter of about 120 um.

Example 4. (Experiments No. 16 to No. 20) Into the same autoclave as used in Example 1 were introduced 50 kg of deionized water and 25 g of a partially saponified polyvinyl acetate and, after evacuation with a vacuum pump, 25 kg of vinyl chloride monomer and 25 g of 2-ethylhexylperoxy dicarbonate were further added thereinto followed by the polymerization carried out at 300C.

At a time when the conversion of the vinyl chloride monomer had reached 60%, one of the polyvinyl chloride resins indicated as modifying agents, IV, V and VI in Table 4 below in an amount shown in Table 3 and latex I or IV as used in Example 1 in an amount also shown in Table 3 were added to the polymerization mixture and the polymerization reaction was continued.

For comparison, the addition of both the modifyir.g agent and the latex was omitted (Experiment No. 19) or the modifying agent alone was added with omission of the latex (Experiment No. 20).

The polymerization reaction was terminated when the internal pressure of the polymerization reactor dropped to TABLE 4 (Modifying agent) Average degree of Particle size distribution, % No. polymerization of passing through screen of polyvinyl chloride resin 60 80 100 150 200 mesh mesh mesh mesh mesh IV 700 100 100 90.2 61.3 53.2 V 1000 100 100 93.2 63.3 50.2 VI 1300 100 100 89.3 60.2 50.1 3.5 kg/cm2G and the aqueous slurry of the polymerizate was processed in the same manner as in Example 1 to give a polyvinyl chloride resin product. The particle size distribution and the gelation time of the thus obtained resin products were as shown in Table 3.

The polyvinyl chloride resin product obtained in Experiment No. 19, in which no modifying agent and latex were added to the polymerization mixture, the other polymerization conditions being the same as in the other experiments, had an average degree of polymerization of about 3800.

The microscopic examination of the resin products obtained in Experiments No. to No.18 revealed that smaller particles were bonded to and around larger particles with coalescence while, in the resin product obtained in Experiment No. 20, no smaller particles were bonded to the larger prticles but were found free.

Claims (8)

1. A method for the preparation of a vinyl chloride-based resin modified with a modifying agent by suspension polymerization of vinyl chloride monomer or a monomer mixture mainly composed of vinyl chloride in an aqueous medium in the presence of a suspending agent and a polymerization initiator soluble in the monomer phase which comprises admixing the polymerization mixture with an aqueous slurry of a modifying agent having an average particle diameter in the range from 10 um to 200 um and a latex of a synthetic polymer having an average particle diameter in the range from 0.01 um to 5 um at a time when the conversion of the monomer or monomers into polymer is in the range from 3% to 85%.

2. The method as claimed in claim 1 wherein the modifying agent is a synthetic resin having properties different from the vinyl chloride-based resin formed by the suspension polymerization.

3. The method as claimed in claim 2 wherein the synthetic resin having properties different from the vinyl chloride-based resin is a polyvinyl chloride resin having an average degree of polymerization smaller than that of the vinyl chloride-based resin formed by the suspension polymerization.

4. The method as claimed in claim 1,2 or 3 wherein the amount of the modifying agent is in the range from 1% to 50% by weight based on the amount of the vinyl chloride monomer or the monomer mixture initially introduced into the polymerization reactor.

5. The method as claimed in any preceeding claim vvherein the amount of the latex of the synthetic polymer is in the range from 0.01% to 10% by weight as solid based on the amount of the vinyl chloride monomer or the monomer mixture initially introduced into the polymerization reactor.

6. The method as claimed in claim 1, substantially as described in any of the Experiments.

7. Avinyl-chloride based resin when prepared by a method as claimed in any preceding claim.

8. A shaped article formed from a resin as claimed in Claim 7.