Polymer Scale Preventive Agent, Polymerization Vessel Effective in Preventing Polymer Scale Deposition, and Process of Producing Polymer Using Said Vessel

1. Field of the Invention

The present invention relates to a polymer scale preventive agent in polymerization of a monomer having an ethylenically unsaturated double bond, a polymerization vessel effective in preventing polymer scale deposition, and a process of producing polymer using said vessel.

2. Description of the Prior Art

In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymer deposits on the inner wall surface and so forth in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality thereof; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer, operators may be exposed thereto, which may cause physical disorders in the operators.

Heretofore, as methods for preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel in polymerization of a monomer having an ethylenically unsaturated double bond, methods in which substances exemplified below are coated on the inner wall surface, etc. as a scale preventive agent, hate been known.

For example, particular polar organic compounds (Japanese Patent Publication (KOKOKU) No. 45-30343(1970)), a dye or pigment (Japanese Patent Publication (KOKOKU) Nos. 45-30835(1970) and 52-24953(1977)), an aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976)), a reaction product of a phenolic compound and an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 55-54317(1980)) and an electron-donating compound and/or an electron-accepting compound (Japanese Patent Publication (KOKOKU) No. 53-46235(1978) are disclosed.

According to the methods using these substances, one operation of forming a coating on the inner wall of a polymerization vessel enables repetition of polymerization runs without formation of scale deposition on the area of the liquid phase inside the polymerization vessel.

However, since scale deposition is generally liable to occur in the vicinity of the interface between the gas phase and liquid phase, which is located at an upper section in a polymerization vessel, scale deposition may take place on this area if a coating of a conventional polymer scale preventive agent mentioned above is formed. Once scale is deposited in the vicinity of the interface between the gas and liquid phases, the deposited scale will grow as polymerization runs are repeated, causing increase in fish eyes, one of the properties to be reduced from viewpoint of quality, of formed products.

That is, if polymer scale depositing on the vicinity of the interface between the gas and liquid phases has grown, it may be peeled and incorporated into a polymeric product. When the polymeric product containing the peeled scale is processed into formed products such as sheets or the like, the peeled scale causes many fish eyes in the formed products, lowering the quality thereof seriously.

An object of the present invention is to provide a polymer scale preventive agent which is capable of preventing polymer scale deposition effectively not only in the area of liquid phase but also in the vicinity of the interface between the gas and liquid phases, and producing a polymeric product of high quality and therefore reducing fish eyes in formed products to a markedly low level, a polymerization vessel capable of preventing polymer scale deposition using the same preventive agent, and a process of producing a polymer using the polymerization vessel.

Thus, the present invention provides, as a means of attaining said object, a polymer scale preventive agent for use in polymerization of a monomer having an ethylenically unsaturated double bond, comprising:

(A) a nitrogen-containing organic compound having at least five continuous conjugated .pi. bonds but containing neither a sulfonic acid group nor a carboxyl group,

(B) an anionic organic compound having at least one group selected from the group consisting of a sulfonic acid group and a carboxyl group and having at least five continuous conjugated .pi. bonds, and

(C) a water-soluble basic polysaccharide.

Further the present invention provides a polymerization vessel having on its inner wall surfaces a coating comprising said components (A), (B) and (C).

Furthermore, the present invention provides a process of producing a polymer by polymerization of a monomer having an ethylenically unsaturated double bond in a polymerization vessel, comprising the step of carrying out said polymerization in said polymerization vessel having the coating on the inner wall surfaces, whereby the deposition of polymer scale is prevented.

According to the present invention, deposition of polymer scale can be effectively prevented not only in the liquid phase area but also in the vicinity of the interface between the gas and liquid phases. In addition, the coating formed on the inner wall surfaces according to the present invention is hardly peeled or dissolved into a polymerization mass during polymerization; hence products formed from the resulting polymeric product have very few fish eyes.

Further, according to the present invention, polymer scale deposition can be effectively prevented, irrespectively of polymerization conditions such as the kind of a monomer or a polymerization initiator, polymerization type, the kind of material constituting the inner wall of polymerization vessels, etc. That is, deposition of polymer scale can be effectively prevented in polymerizations in which polymer scale deposition has been difficult to prevent, e.g., in emulsion polymerization, polymerizations using a polymerization vessel made of stainless steel, or polymerizations using a polymerization initiator with a strong oxidizing action such as potassium peroxodisulfate and the like.

Therefore, if polymerization is carried out under application of the present invention, the operation of removing polymer scale is not necessarily conducted every polymerization run, thereby productivity being improved.

(A) Nitrogen-containing organic compound

The nitrogen-containing organic compound, component (A) of the polymer scale preventive agent of the present invention, needs to have at least five continuous conjugated .pi. bonds but must not contain a sulfonic acid group or a carboxyl group.

The nitrogen-containing organic compounds include, for example, nitrogen-containing benzene derivatives such as benzidine, 4-aminobiphenyl, 2,2'-diaminodiphenylacetylene, and Disperse Yellow 9 [i.e., N-(2,4-dinitrophenyl)-1,4-phenylenediamine]; nitrogen-containing naphthalene derivatives such as .alpha.-naphthylamine, .beta.-naphthylamine, 1,8-diaminonaphthalene, 1,5-diaminonaphthalene, etc.; nitrogen-containing polynuclear aromatic compounds such as 1-aminoanthracene, 1,4-diaminoanthracene, 9,10-diaminoanthracene, 1,6-diaminopyrene, etc.; nitrogen-containing quinones such as 2-aminoanthraquinone, 1,4-diaminoanthraquinone, 3,6-diamonophenanthrenequinone, etc.; nitrogen-containing heterocyclic compounds such as quinoline, 4-aminoacridine, 3,6-diaminoacridine, thionine, indophenol, methylviologen, 1,10-phenanthroline, phenothiazine, Methylene Blue, 2-aminofluorene, 9-aminofluorene, carbazole, methylcarbazole, 2,3-diaminophenazine, acriflavine, indigo, Safranine [C.I. No. 50240], Acridine Orange [C.I. No. 46005], Solvent Black 5 [C.I. No. 50415], etc.; alkaloids such as berberine; nitrogen-containing azo compounds such as azobenzene, p-hydroxyazobenzenes, p-aminoazobenzenes, 1,3-diphenyltriazene, 1-(phenylazo)-2-naphthalenol, Sudan I [i.e., C.I. Solvent Yellow 14], Sudan II [i.e., C.I. Solvent Orange 7], Sudan III [i.e., C.I. Solvent Red 23], Sudan IV [C.I. Solvent Red 24], Sudan Black B [C.I. Solvent Black 3], Oil Red O [i.e., C.I. Solvent Red 27], Disperse Orange 1 [i.e., 4-(4-nitrophenylazo) diphenylamine], Naphthyl Red [i.e., 4-phenylazo-l-naphthylamine], chrysoidine [C.I. No. 11270], C.I. Solvent Yellow 2 [C.I. No. 11020], C.I. Solvent Yellow 6 [C.I. No. 11390], Solvent Orange 1 [C.I. No. 11920], Solvent Orange 2 [C.I. No. 12100], Solvent Orange 14 [C.I. No. 20620], Solvent Red 1 [C.I. No. 12150], Solvent Red 3 [C.I. No. 12010], Solvent Brown 3 [C.I. No. 11360], etc. These may be used singly or in combination of two or more.

Among the compounds above, particularly preferred are Sudan Black B, 1,8-diaminonaphthalene, 3,6-diaminoacridine, .alpha.-naphtylamine, p-hydroxyazobenzene, Sudan III, Sudan IV, C.I. Solvent Black 5, C.I. Solvent Red 3, and C.I. Solvent Brown 3.

(B) Anionic organic compound

The anionic organic compound, component (B) of the polymer scale preventive agent of the present invention, has at least one group out of the sulfonic acid group and carboxyl group and has at least 5 continuous conjugated .pi. bonds.

Such anionic organic compounds include, for example, anionic benzene derivatives such as erythrosine [C.I. No. 45430], phloxine [C.I. No. 45410], Rose Bengal [C.I. No. 45440], Acid Red [C.I. No. 45100], Briliant Blue FCF [No. 42090], Fast Green FCF [C.I. No. 42053], etc.; anionic naphthalene derivatives such as sodium 1-naphthalenesulfonate, 3-hydroxy-2-naphthoic acid, 6,6'-oxybis(2-naphthalenesufonic acid), sodium 6-hydroxy-2-naphthalenesulfonate, etc.; anionic polynuclear aromatic compounds such as 9-anthracenecarboxylic acid, 1-pyrenebutylic acid, etc.; anionic quinones such as sodium anthraquinone-.beta.-sulfonate, sodium anthraquinone-2,6-disulfonate, Alizarine Red S [C.I. No. 58005], Alizarine Blue Black B [Mordant Black B], Alizarine Violet 3R [i.e., C.I. Acid Violet 34], etc.; anionic heterocyclic compounds such as Indigo Carmine [C.I. No. 73015], Acid Black 2, gallocyanine, etc.; anionic azo compounds such as sodium 4,4'-(1-triazene-1,3-diyl)-bis(benzenesulfonate), sodium 6-hydroxy-5-(phenylazo)-2-naphthalenesulfonate, sodium 4-[(2-hydroxy-1-naphthalene)azo]benzenesulfonate, sodium 3-hydroxy-4-[(4-sufophenyl)azo]-2,7-naphthalenesulfonate, Amaranth [C.I. No. 16185], New Coccine [i.e., C.I. No. 16255], Tartrazine [C.I. No. 19140], Tropaeoline O [i.e., C.I. Acid Orange 6], Orange I [Tropaeoline OOO No. 1; C.I. No. 14600], Ponceau SS [C.I. Acid Red 150], Metanil Yellow [i.e., C.I. Acid Yellow 36], C.I. Acid Blue 161, C.I. Acid Red 88, Alizarine Yellow R, C.I. Mordant Orange 10, C.I.Mordant Yellow 10, etc. These may be used singly or in combination of two or more.

Among the compounds above, preferred are C.I. Acid Black 2, C.I. Acid Blue 161, Alizarine Blue Black B, C.I. Acid Red 150, gallocyanine, Amaranth, Tropaeoline O and Orange I.

(C) Water-soluble basic polysaccharide

The water-soluble basic polysaccharide used in the present invention includes, for example, chitosans, water-soluble chitosan derivatives, polygalactosamines, water-soluble polygalactosamine derivatives and water-soluble chitin derivatives.

Chitosans are a straight chain polysaccharide, i.e., (poly-1,4-.beta.-glucosamine),formed by polymerization through .beta.-1,4 linkage of D-glucosamine. It can be obtained by deacetylization of chitin contained in the carapace of the Crustacea such as prawns, shrimps and crabs. Recently a chitosan can be produced by culturing a mold, and the chitosan thus produced can be used in the same manner as those naturally occurring. The chitosans are insoluble in water under the neutral conditions, but soluble under the acidic conditions; hence the chitosans are used under a pH of less than 7.

The water-soluble chitosan derivatives which may be used in the present invention include the following:

(1) Organic acid salts and inorganic acid salts of chitosans. The organic acid specifically includes, for example, acetic acid, glycollic acid, malic acid, citric acid, and ascorbic acid. The inorganic acid includes, for example, hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. Chitosans preferably have a deacetylization degree of 40 to 100%.

(2) Water-soluble low molecular products obtained by decomposition of chitosans, i.e., water-soluble glucosamine oligomers. Normally, 5 to 20-mers of glucosamine are preferred. Such oligomers can be produced by conventional depolymerization methods, for example, the hydrochloric acid hydrolysis method (Japanese pre-examination patent publication(KOKAI) No. 61-21102(1986), the nitrate decomposition method (Japanese pre-examination patent publication (KOKAI) No. 62-184002(1987), the chlorine decomposition method (Japanese pre-examination patent publication (KOKAI) No. 60-186504(1985), the phosphoric acid decomposition method and decomposition methods using an enzyme or microorganism.

(3) Water-soluble derivatives of chitosans prepared by introducing a hydrophilic group thereinto. Examples are described in Japanese pre-examination patent publication (KOKAI) No. 63-14714(1988) and include polyoxyethylene chitosans, polyoxypropylene chitosans, phosphated chitosans, N-glycidyltrimethylammonium chitosans, and dihydropropylchitosans.

The polygalactosamines which may be used in the present invention are insoluble in water under neutral conditions, but soluble under a pH of 7 or less and therefore used under such conditions. Polygalactosamines can be produced by culturing a mold (APPLICATION OF CHITIN AND CHITOSAN pp.24-26, Edited by Society for Research of Chitin and Chitosan, 1990, published by Giho-do Shuppan).

The water-soluble polygalactosamines include the following:

(1) Organic acid salts and inorganic acid salts of polygalactosamines including salts of organic acids such as acetic acid, formic acid or the like, and salts of inorganic acids such as hydrochloric acid, nitric acid or the like:

(2) Water-soluble low molecular products obtained by decomposition of polygalactosamines. Normally, 5 to 20-mers of galactosamine are preferred. Such oligomers can be produced by decomposition methods using an enzyme or microorganism.

The water-soluble chitin derivatives which may be used in the present invention, include the following:

(1) Water-soluble N-acetylglucosamine oligomers obtained by decomposition of chitins. Normally, 5 to 20-mers are preferred. Such oligomers can be produced by conventional depolymerization methods, for example, the nitrous acid decomposition method, the formic acid decomposition method, the chlorine decomposition method (Japanese pre-examination patent publication (KOKAI) No. 62-186504(1987)) or decomposition methods using an enzyme (e.g., chittinase) or a microorganism.

(2) Water soluble derivatives of chitins prepared by introducing a hydrophilic group thereinto. Examples are described in Japanese pre-examination patent publication (KOKAI) No. 63-14714(1988) and include polyoxyethylene chitins, polyoxypropylene chitins, phosphated chitins and dihydropropylchitins.

Among the water-soluble basic polysaccharides described above, preferred are the inorganic acid salts and organic acid salts of chitosans, and more preferred are those having a deacetylization degree of 65% or more and a viscosity at 20.degree. C. in the form of an aqueous solution containing 1.0% by weight of the chitosan and 0.5% by weight of acetic acid of 30 cP or lower when measured with a B-type viscometer.

The water-soluble basic polysaccharides may be used singly or in combination of two or more.

The preferred combinations of the components (A), (B) and (C) include those specifically described in Examples later.

The amount of the water-soluble basic polysaccharide (C) in the polymer scale preventive agent of the present invention ranges normally from 0.1 to 1,000 parts by weight, preferably 1 to 600 parts by weight, per 100 parts by weight of the total amount of the nitrogen-containing organic compound (A) and the anionic organic compound (B). If the amount of the water-soluble basic polysaccharide is too small or too large, improvement in scale preventing effect due to the combined use of the component (C) with the components (A) and (B) is lowered.

The amount of component (B) is normally in the range of 0.1 to 1,000 parts by weight, preferably 5 to 400 parts by weight, per 100 parts by weight of the component (A). If the amount of component (B) is outside the range above, the scale preventing effect may be lowered.

The polymer scale preventive agent is used for forming a coating on the inner wall surfaces, and preferably the surfaces of parts with which monomer comes into contact during polymerization, e.g., a stirring shaft, stirring blades, baffles, condensing coils, etc. of a polymerization vessel, so that scale deposition in the vessel can be prevented. Normally, in forming said coating on the inner wall surfaces, etc. of a polymerization, the polymer scale preventive agent is used in a liquid state, i.e., as a coating liquid.

The coating liquid menthioned above is prepared by dissolving or dispersing said components (A), (B) and (C) in a solvent.

Solutions containing the nitrogen-containing organic compound (A) and the anionic organic compound (B) in a solvent may be stabilized at a basic side (pH 8 to 13), so that they can be stored for a long time. From viewpoint of scale preventing effects, the pH of the coating liquid ranges preferably from 7 to 13, more preferably from 9 to 12. Thus, in preparation of the coating liquid above, after the addition of the components (A), (B) and (C) to a solvent, a basic substance is desirably added, if necessary (where the solution is not basic), to make the solution basic. Basic substances to be added include, for example, sodium hydroxide, sodium carbonate, sodium phosphate, ethylenediamine, ethanolamine and triethanolamine.

Solvents suitably used for preparation of the coating solution include, for example, water; alcohols such as methanol, ethanol, propanol, butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 2-pentanol, etc.; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.; esters such as methyl formate, ethyl formate, methyl acetate, methyl acetoacetate, etc.; ethers such as 4-methyldioxolane, ethylene glycol diethyl ether, etc.; furans; and aprotic solvents such as dimethylformamide, dimethyl sulfoxide, acetonitrile, etc. These solvents may be used singly or as a mixed solvent of two or more thereof as appropriate.

The total concentration of components (A), (B) and (C) in the coating liquid is not particularly limited as long as the total coating weight described later is obtained, and normally may range from 0.001 to 15% by weight, preferably from 0.01 to 1% by weight.

To the coating liquid, for example, a cationic surfactant, a nonionic surfactant, an anionic surfactant, and so forth can be added as long as the scale preventing effect is not impaired.

Further, inorganic compounds can be optionally added to the coating liquid as long as the scale preventing effect is not impaired. The inorganic compounds which may be added include, for example, silicic acids or silicates such as orthosilicic acid, metasilicic acid, mesodisilicic acid, mesotrisilicic acid, mesotetrasilicic acid, sodium metasilicate, sodium orthosilicate, sodium disilicate, sodium tetrasilicate and water glass; metallic salts such as oxygen acid salts, acetates, nitrates, hydroxides or halides of a metal selected from alkali earth metals such as magnesium, calcium, and barium, zinc family metals such as zinc, aluminum family metals such as aluminum, and platinum family metals such as platinum; and inorganic colloids such as ferric hydroxide colloid, colloid of silicic acid, colloid of barium sulfate, and colloid of aluminum hydroxide. The above-mentioned inorganic colloids may be those prepared, for example, by mechanical crushing, irradiation with ultrasonic wave, electrical dispersion or chemical methods.

When the coating liquid prepared as described above is used for forming a coating on the inner wall surface of a polymerization vessel, first, the coating liquid is applied to the inner wall surface and then dried sufficiently, followed by washing with water if necessary. A coating is formed by these operations on the inner wall surface of the polymerization vessel; hence the polymer scale deposition thereon can be prevented.

The above-mentioned coating is preferably formed on not only the inner wall surfaces of a polymerization vessel but also other parts with which the monomer comes into contact during polymerization. For example, it is preferred to form the coating by applying said coating liquid on a stirring shaft, stirring blades, condensers, headers, search coil, bolts, nuts, etc.

More preferably, the coating is formed on not only the parts with which the monomer comes into contact during polymerization but also other parts on which polymer scale may deposit, for example, such as the inner surfaces of equipment and tubes of recovery system for unreacted monomer. These parts, more specifically, are exemplified by the inner wall surfaces of monomer distillation columns, condensers, monomer stock tanks and valves, etc. in said recovery system.

The method of applying the coating liquid on the inner wall surface, etc. of a polymerization vessel is not particularly limited, and includes, for example, the brush coating, spray coating, the method of filing the polymerization vessel, etc. with the coating liquid followed by withdrawal thereof, and automatic coating methods as disclosed in Japanese Pre-examination Patent Publication (KOKAI) Nos. 57-61001(1982) and 55-36288(1980), and Japanese Patent Publication (KOHYO) Nos. 56-501116(1981) and 56-501117(1981), and Japanese Pre-examination Publication (KOKAI) No. 59-11303(1984), etc.

The method of drying wet coated surface provided by application of the coating liquid, is not limited, either. The drying is conducted preferably at a temperature within the range from room temperature to 100.degree. C. Specifically, a method in which, after the liquid is applied, hot air with a suitable elevated temperature is blown to the coated surface, and a method in which the inner wall surface of a polymerization vessel and the surfaces of other parts to be coated are previously heated at, e.g., 30.degree.-80.degree. C. and the coating liquid is directly applied to the heated surfaces, etc. After dried, the coated surfaces are washed with water if necessary.

The coating thus formed has normally a coating weight of 0.001 g/m.sup.2 or more, preferably from 0.05 to 2 g/m.sup.2.

The above coating operation may be conducted every 1 to ten-odd batches of polymerization. The formed coating has fairly good durability and retains the polymer scale-preventing action; therefore the coating operation is not necessarily performed for every batch of polymerization. Hence, the productivity of the manufactured polymer is improved.

After forming the coating on the inner wall surfaces of a polymerization vessel and other parts with which monomer may come into contact by application of the coating liquid, polymerization is carried out in accordance with conventional procedures therein. That is, a monomer having an ethylenically unsaturated double bond and a polymerization initiator (catalyst) are charged, and then, a polymerization medium such as water, etc. and, optionally, a dispersing agent such as suspension agents, solid dispersing agents, and nonionic and anionic emulsifying agents, etc. are charged, followed by carrying out polymerization according to conventional methods.

The monomer having an ethylenically unsaturated double bond to which the method of this invention can be applied includes, for example, vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, and esters and salts thereof; maleic acid, fumaric acid, and esters and anhydrides thereof; and diene monomers such as butadiene, chloroprene and isoprene; aromatic vinyl compounds such as styrene; as well as acrylonitrile, halogenated vinylidenes, and vinyl ethers.

There are no particular limitations on the type of polymerization to which the method of this invention can be applied. The present invention is effective in any types of polymerization such as suspension polymerization, emulsion polymerization, solution polymerization, bulk polymerization, and gas phase polymerization. Particularly, the present method is suitable to polymerizations in an aqueous medium such as suspension or emulsion polymerization.

Specifically, in the case of suspension polymerization and emulsion polymerization, polymerization is generally performed as follows, for instance.

First, water and a dispersing agent are charged into a polymerization vessel, and thereafter a polymerization initiator is charged. Subsequently, the inside of the polymerization vessel is evacuated to a pressure of from about 0.1 to about 760 mmHg, and a monomer is then charged (whereupon the pressure inside the polymerization vessel usually becomes from 0.5 to 30 kgf/cm.sup.2.G). Then, the polymerization is normally carried out at a temperature of from 30.degree. to 150.degree. C. During the polymerization, one or more of water, a dispersing agent and a polymerization initiator may be added, if necessary. Reaction temperature during the polymerization is different depending on the kind of monomer to by polymerized. For example, in the case of polymerizing vinyl chloride, polymerization may be carried out at 30.degree. to 80.degree. C.; in the case of polymerizing styrene, polymerization may be carried out at 50.degree. to 150.degree. C. The polymerization may be judged to be completed when the pressure inside the polymerization vessel falls to from about 0 to 7 kgf/cm.sup.2.G or when cooling water which passes through a jacket provided around the polymerization vessel indicates almost the same temperature at the inlet where it is charged and at the outlet where it is discharged (i.e., when liberation of heat due to polymerization reaction has been completed). The water, dispersing agent and polymerization initiator charged for the polymerization are used in amounts of about 20 to 500 parts by weight, about 0.01 to 30 parts by weight, and about 0.01 to 5 parts by weight, respectively, per 100 parts by weight of the monomer.

In the case of solution polymerization, an organic solution such as toluene, xylene, pyridine and the like is used as a polymerization medium in place of water. The dispersing agent is optionally used. The other conditions are generally the same as those described for suspension and emulsion polymerization.

In the case of bulk polymerization, after the inside of a polymerization vessel is evacuated to a pressure of from about 0.01 mmHg to about 760 mmHg, a monomer and a polymerization initiator are charged, and then polymerization is carried out at a temperature of from -10.degree. C. to 250.degree. C. For example, in the case of polymerizing vinyl chloride, polymerization is carried out at a temperature of from 30.degree. C. to 80.degree. C.; and in the case of polymerizing styrene, polymerization may be carried out at 50.degree. C. to 150.degree. C.

The method of the present invention is effective in preventing polymer scale from depositing, independent of materials constituting the inner wall, etc. of a polymerization vessel. For example, this method is effective in preventing polymer scale from depositing in polymerization vessels made of a stainless steel or other steels or vessels lined with glass.

Any additive materials that have been added in a polymerization system can be used without any limitation. More specifically, the method of this invention can effectively prevent polymer scale from depositing, even in polymerization systems containing the following additives: for example, polymerization initiators such as t-butyl peroxyneodecanoate, bis(2-ethylhexyl) peroxydicarbonate, 3,5,5-trimethylhexanoyl peroxide, .alpha.-cumyl peroxyneodecanoate, cumene hydroperoxide, cyclohexanone peroxide, t-butyl peroxypivalate, bis(2-ethylhexyl) peroxydicarbonate, benzoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide, diisopropyl peroxydicarbonate, .alpha.,.alpha.'-azobisisobutyronitrile, .alpha.,.alpha.'-azobis-2,4-dimethylvaleronitrile, potassium peroxodisulfate, ammonium peroxodisulfate, p-methane hydroperoxide; suspension agents comprised of natural or synthetic polymeric compounds such as partially saponified polyvinyl alcohols, polyacrylic acids, vinyl acetate/maleic anhydride copolymer, cellulose derivatives such as hydroxypropylmethyl cellulose, and gelatin; solid dispersing agents such as calcium phosphate and hydroxyapatite; nonionic emulsifying agents such as sorbitan monolaurate, sorbitan trioleate and polyoxyethylene alkyl ether; anionic emulsifying agents such as sodium lauryl sulfate, sodium alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dioctylsulfosuccinate; fillers such as calcium carbonate and titanium oxide; stabilizers such as tribasic lead sulfate, calcium stearate, dibutyltin dilaurate and dioctyltin mercaptide; lubricants such as rice wax, stearic acid and cetyl alcohol; plasticizers such as DOP and DBP; chain transfer agents such as trichloroethylene and mercaptans as exemplified by t-dodecyl mercaptans; and pH adjusters.

The polymer scale preventive agent of the present invention may be added into a polymerization medium in addition to the formation of the coating, so that the scale preventing effect is further improved. The amount of the polymer scale preventive agent to be added into the polymerization medium, preferably ranges from about 10 ppm to 1,000 ppm based on the whole weight of the monomer charged. The addition should be conducted so that it may not affect the quality of polymeric product to be obtained with respect to fish eyes, bulk density, particle size distribution, etc.

The present invention is now described in detail by way of working examples and comparative examples. In each of the tables below, Experiments of Nos. marked with * are comparative examples, and the other Experiments working examples of the present invention. Chitosans used as the component (A) in Examples 1 and 2 below are those described in Table 1.

Polymerization was carried out in the following manner using a polymerization vessel with an inner capacity of 1,000 liters and having a stirrer.

In each experiment, first, a component (A) (nitrogen-containing organic compound), a component (B) (anionic organic compound) and a component (C) (water-soluble basic polysaccharide) and optionally a pH adjuster were dissolved in a solvent so that the total concentration thereof might become the value given in Table 2, to prepare a coating liquid. The coating liquid was applied to the inner wall and other parts with which a monomer comes into contact including the stirring shaft, stirring blades and baffles, followed by drying under heating at 40.degree. C. for 15 min. to form a coating, which was then washed with water.

Experiments of Nos. 101-108 are comparative examples in which no coating liquid was applied or a coating liquid containing only one or two of components (A), (B) and (C) was applied. Experiments of Nos. 109-115 are comparative examples whose coating liquids contains a polymeric compound other than a water-soluble polysaccharide as the component (C).

The nitrogen-containing organic compound (A), the anionic organic compound (B), the water-soluble basic polysaccharide (C), the total concentration of the components (A), (B) and (C), the weight ratios of (B)/(A) and (C)/[(A)+(B)], the solvent used and pH of the coating liquid in each experiment are given in Table 2. For cases where a pH adjustor was used, it is indicated.

In preparation of the coating liquids containing a basic polysaccharide above, the water-soluble basic polysaccharide was first dissolved in an aqueous ascorbic acid solution with a pH of 4, and the resulting aqueous solution was mixed with the solutions of the components (A) and (B) each in a solvent.

Subsequently, in the polymerization vessel in which a coating had been formed by the coating operation as above, were charged 400 kg of water, 200 kg of vinyl chloride, 250 g of a partially saponified polyvinyl alcohol, 25 g of hydroxypropylmethyl cellulose and 70 g of 3,5,5-trimethylhexanoyl peroxide. Then, polymerization was carried out at 66.degree. C. with stirring for 6 hours. After the completion of the polymerization, polymeric product and unreacted monomer were taken out of the vessel and then the inside of the vessel was washed with water and residual resin was removed.

Thereafter, the batch of operations from applying a coating liquid through carrying out polymerization to cleaning the vessel with water was repeated. After repetition of 10 batches of polymerization run, the amount of polymer scale depositing on the inner wall was measured at an area in the liquid phase and in the vicinity of the interface between the gas and liquid phases, in accordance with the method below. The results are given in Table 3, provided that for Experiments of Nos. 101 to 115 (comparative examples), the results after the second batch were given.

The polymeric products obtained were tested for fish eyes in accordance with the method below. The results are given in Table 3.

Measurement of the amount of polymer scale

The scale depositing on the inner wall surface in the area of 100 cm.sup.2 were scraped off with a stainless steel spatula as completely as possible to be confirmed with naked eyes, and then the scraped scale was weighted on a balance. Thereafter, the amount of the deposited scale per area of 1 m.sup.2 was obtained by multiplying the measured value by 100.

Measurement of fish eyes

A hundred parts by weight of a polymer, 50 parts by weight of DOP, 1 part by weight of dibutyltin dilaurate, 1 part by weight of cetyl alcohol, 0.25 part by weight of titanium oxide and 0.05 part by weight of carbon black were formulated to prepare a mixture. The mixture was kneaded at 150.degree. C. for 7 min. with a twin roll mill, and then formed into a sheet 0.2 mm thick. The sheet was examined for number of fish eyes per 100 cm.sup.2 by light transmission.

In each experiment, the coating procedure of Example 1 was repeated for a stainless steel polymerization vessel having an inner capacity of 20 liters and equipped with a stirrer, except that a coating liquid in which the nitrogen-containing organic compound (A), the anionic organic compound (B), the water-soluble basic polysaccharide (C), the total concentration of the components (A)+(B)+(C), the weight ratios of (B)/(A) and (C)/[(A)+(B)], the solvent and pH of the coating liquid in each experiment are as given in Table 4, was used. Experiments of Nos. 201 to 208 are comparative experiments in which no coating liquid was applied or a coating liquid containing only one or two of the component (A), (B) and (C) was applied.

In preparation of the coating liquids containing a water-soluble basic polysaccharide above, the water-soluble basic polysaccharide was first dissolved is an aqueous glycolic acid solution with a pH of 4.0, and the resulting aqueous solution was mixed with the solutions of the components (A) and (B) each in a solvent.

In the polymerization vessel in which the coating was thus formed, were charged 9 kg of water, 225 g of sodium dodecylbenzenesulfonate, 12 g of t-dodecyl mercaptan, and 13 g of potassium peroxodisulfate. After the inner atmosphere was replaced with a nitrogen gas, 1.3 kg of styrene and 3.8 kg of butadiene were charged, followed by polymerization at 50.degree. C. for 20 hours.

After completion of the polymerization, the amount of polymer scale depositing on the inner wall surface was measured at an area which had been located in the liquid phase during polymerization and in the vicinity of the interface between the gas and liquid phases.

The results are given in Table 4.