Method of preventing polymer scale deposition

A method of preventing polymer scale deposition in a polymerization vessel during polymerization of a monomer having an ethylenically double bond, wherein said polymerization is carried out in a polymerization vessel of which the inner wall has a coating comprising a reaction product of a tannin and an acid halide. Polymer scale deposition on the inner wall, etc. of the polymerization vessel can be effectively prevented. The preventive agent used has neither risk of produced polymer being colored nor toxicity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of preventing polymer scale 
deposition on the inner wall and so forth of a polymerization vessel 
during polymerization of a monomer having an ethylenically double bond. 
2. Description of Prior Art 
In processes of preparing polymers by polymerizing a monomer in a 
polymerization vessel, the problem that polymers deposit on the inner wall 
and other parts which come into contact with the monomer such as stirring 
blades of the polymerization vessel 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 the cooling capacity of the 
polymerization vessel are lowered; that the polymer scale may peel and mix 
into manufactured polymer, thereby impairing the quality of the 
manufactured polymer; and that removal of such polymer scale is laborious 
and hence time-consuming. Further, since the polymer scale contains 
unreacted monomer, there is a danger that the workers may be exposed to 
the unreacted monomer, which may give them some physical disorders. 
Heretofore, there are known methods for preventing polymer scale deposition 
in which the inner wall and so forth are coated with various materials 
that act as polymer scale preventive agents, for example, particular polar 
compounds (Japanese Patent Publication (KOKOKU) No. 30343/1970); dyes or 
pigments (Japanese Patent Publication (KOKOKU) Nos. 30343/1970 and 
30835/1970); an aromatic amine compound (Japanese Pre-examination Patent 
Publication (KOKAI) No. 50887/1976); a reaction product of a phenolic 
compound with an aromatic aldehyde (Japanese Pre-examination Patent 
Publication (KOKAI) No. 54317/1980). 
These methods are effective in preventing polymer scale deposition, in the 
case where the monomer to be polymerized is vinyl halide such as vinyl 
chloride or a monomer mixture containing a large amount of vinyl halide 
and a small amount of other monomers copolymerizable therewith. However, 
the scale-preventing effect achieved varies depending on polymerization 
conditions such as the kind of monomers, the kind of a polymerization 
catalyst, form of polymerization system and the material of the inner wall 
of a polymerization vessel; it is difficult to prevent the scale 
deposition effectively and certainly. Specifically, when a polymerization 
catalyst with a strong oxidative effect such as potassium persulfate, 
acetylcyclohexylsulfonyl peroxide and di-2-ethoxyethyl peroxydicarbonate 
is used, the scale preventive agent forming the coating may be oxidized, 
so that the scale preventing effect is impaired. In the case of 
polymerization vessels with inner wall made of stainless steel or other 
steels, polymer scale deposition is liable to occur as compared with 
vessels lined with glass. Emulsion polymerization is liable to form 
polymer scale deposition as compared with suspension polymerization. 
Of the scale preventive agents used in the above methods, the dyes and 
pigments described in Japanese Patent Publication (KOKOKU) No. 30835/1970 
and 24953/1977, the aromatic amine compounds described in Japanese 
Pre-examination Patent Publication (KOKAI) No. 50887/1976, the reaction 
products of a phenolic compound with an aromatic aldehyde described in 
Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980 are 
colored and therefore possibly have a disadvantage of putting a color to 
product polymers. 
Aniline, nitrobenzene, formaldehyde, etc. of the polar organic compounds 
described in Japanese Patent Publication (KOKOKU) No. 30343/1970, and the 
pigments containing a heavy metal such as chromium and lead described in 
Japanese Patent Publication (KOKOKU) No. 30835/1970 are poisonous. The 
dyes described in Japanese Patent Publication (KOKOKU) Nos. 30835/1970 and 
24953/1977 include dyes that involve some concern about carcinogenesis. 
These substances may cause serious problems from viewpoint of safety in 
work operations. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
of preventing polymer scale deposition effectively and certainly under any 
conditions as to the kind of monomer, etc., with no concern about 
coloration of manufactured polymers or safety in work operations. 
The present inventors have discovered that the above object can be achieved 
by forming a coating comprising a particular compound on the inner wall of 
a polymerization vessel. 
Thus, the present invention provides, as a means of solving the prior art 
problems, a method of preventing polymer scale deposition in a 
polymerization vessel during polymerization of a monomer having an 
ethylenically double bond, wherein said polymerization is carried out in a 
polymerization vessel of which the inner wall has a coating comprising a 
reaction product of a tannin and an acid halide. 
The present invention also provides the polymerization vessel of which the 
inner wall has a coating comprising said reaction product of a tannin and 
an acid halide. 
Further, the present invention provides a polymer scale preventive agent 
comprising said reaction product of a tannin and an acid halide. 
According to the present invention, polymer scale deposition can be 
effectively and certainly prevented in the polymerization of monomers 
having an ethylenically double bond, irrespectively of the polymerization 
conditions such as the kind of monomers, the material of the inner wall of 
polymerization vessels, etc. For example, even in the case of polymerizing 
monomers by suspension polymerization, emulsion polymerization, bulk 
polymerization, solution polymerization or gas phase polymerization, or in 
the case of polymerizing in a stainless steel or glass-lined 
polymerization vessel, or in the case of using a polymerization catalyst 
having a strong oxidative effect, polymer scale deposition can be 
effectively and certainly prevented. Therefore, the operation of removing 
polymer scale is not required to be conducted every polymerization run; 
hence productivity is markedly improved. The reaction product of a tannin 
and an acid halide in general has no color; therefore there is no risk of 
manufactured polymers being colored. Accordingly, polymers of high quality 
can be produced stably. In addition, the scale-preventive agent used has 
no toxicity and therefore is safe in work operations. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Reaction product of a tannin and an acid halide 
The reaction product of a tannin and an acid halide used as the essential 
component of the scale preventive agent in the present invention is a 
reaction product obtained by reacting a tannin with an acid halide in an 
aqueous alkaline solution under heating. 
The tannin used includes, for example, hydrolyzable tannins such as tannic 
acid, Chinese gallotannin, nutgalls tannin, sumac tannin, tara tannin, 
valonia tannin, chestnut tannin, myrobalan tannin, oak tannin, divi-divi 
tannin, algarobillatannin and the like, and condensed tannins such as 
gambier tannin, quebrachotannin, mimosa tannin, mangrove tannin, hemlock 
tannin, spruce tannin, Burma cutch tannin, oak bark tannin, tannin of 
persimmon and the like. These can be used singly or in combination of two 
or more. Among the tannins, preferred are tannic acid, Chinese 
gallotannin, nutgalls tannin, quebracho-tannin, mimosa tannin, oak bark 
tannin and tannin of persimmon. 
The acid halide used in preparation of said reaction product includes, for 
example, the compounds represented by the formula: 
EQU RCOX 
wherein R represents a hydrogen atom, an alkyl group having 1 to 12 carbon 
atoms, an alkenyl group having 1-10 carbon atoms, and the phenyl group; 
and X represents a halogen atom such as fluorine, chlorine, bromine, and 
iodine. Such acid halides include, for example, formyl fluoride, formyl 
chloride, formyl bromide, formyl iodide, acetyl fluoride, acetyl chloride, 
propionyl chloride, n-butyryl chloride isbutyryl chloride, acryloyl 
chloride, crotonoyl chloride, methacryloyl chloride and benzoyl chloride. 
Among these, preferred are formyl chloride, acetyl chloride, isobutyl 
chloride, benzoyl chloride, and the like. These can be used singly or in 
combination of two or more. 
In the above reaction for preparation of the reaction product of a tannin 
and an acid halide, the tannin and the acid halide are normally used in a 
weight ratio of preferably from 95/5 to 10/90, more preferably from 90/10 
to 30/70. If the amount of the tannin is too large or too small, the 
reaction product may be obtained in a poor yield. 
As the aqueous alkaline solution, for example, aqueous solutions of an 
alkaline substance such as sodium hydroxide, potassium hydroxide and 
ammonia can be used. The aqueous alkaline solution normally contains the 
alkaline substance in a concentration of, preferably, from 1 to 50% by 
weight, more preferably from 5 to 30% by weight. 
The reaction is normally carried out at a temperature of from 10.degree. C. 
to 200.degree. C., preferably from 20.degree. C. to 100 .degree. C., 
normally for 0.1 to 24 hours, preferably from about 0.5 to 10 hours, 
preferably under stirring. 
Formation of the coating 
The coating comprising said reaction product can be formed, for example, by 
applying a coating solution comprising said reaction product on the inner 
wall of a polymerization vessel, followed by drying. 
The coating solution can be prepared by dissolving or dispersing the 
reaction product in a suitable solvent. The concentration of the reaction 
product may be normally from about 0.005% by weight to about 5% by weight, 
preferably from 0.05 to 2% by weight. However, the concentration is not 
particularly limited, as long as the desired coating weight is obtained. 
The solvent used for preparation of the coating solution includes, for 
example, water; alcohols such as methanol, ethanol, propanol, 1-butanol, 
2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 3-methyl butanol, 
2-methyl-2-butanol, and 2-pentanol; ketones such as acetone, methyl ethyl 
ketone, and methyl isobutyl ketone; esters such as methyl formate, ethyl 
formate, methyl acetate, and methyl acetoacetate; ethers such as 4-methyl 
dioxolan, ethylene glycol diethyl ether and 1,4-dioxane; furans such as 
tetrahydrofuran; aprotic solvents such as dimethylformamide, dimethyl 
sulfoxide, and acetonitrile; aliphatic hydrocarbon solvents such as 
n-hexane and n-pentane; aromatic hydrocarbon solvents such as toluene and 
xylene; and halogenated hydrocarbon solvents such as 
1,1,1-trichloroethylene and 1,1,1,2-tetrachloroethylene. These solvents 
are appropriately used singly or as a mixed solvent of two or more. 
The coating solution is applied to the inner wall surface of the 
polymerization vessel, thoroughly dried, and optionally washed with water 
as required, to form the coating having scale preventing effect. The 
drying of the solution applied on the inner wall may be conducted, for 
example, at a temperature of from room temperature to 100.degree. C. 
Preferably, the coating comprising said reaction product is also previously 
formed on other parts of the polymerization vessel with which the monomer 
comes into contact during polymerization, in addition to the inner wall. 
Such parts include, for example, stirring blades, a stirring shaft, a 
condenser, a header, baffles, search coils, bolts, nuts, etc. The coating 
on these parts can be formed in the same manner as described above. 
Particularly, stirring blades, stirring shaft, and baffles should be 
coated. 
Moreover, preferably, the coating solution is also applied to parts of 
recovery system for an unreacted monomer with which the unreacted monomer 
may come into contact, for example, the inner surfaces of monomer 
distillation columns, condensers, monomer stock tanks and valves. Scale 
formation can be thereby prevented at these parts due to a coating thus 
formed. 
The method of applying the coating solution is not particularly limited, 
and includes typically the brush coating, spray coating, the method of 
filing the polymerization vessel with the coating solution followed by 
withdrawal thereof, and automatic coating methods as disclosed in Japanese 
Pre-examination Patent Publication (KOKAI) Nos. 61001/1982, 36288/1980 and 
11303/1984, Japanese Pre-examination Publication (KOHYO) Nos. 501116/1981 
and 501117/1981. The method of drying wet coated surfaces is not limited, 
either. Following methods can be used. For example, a method in which, 
after the solution is applied, hot air with an suitable elevated 
temperature is blown to the coated surface, and a method in which the 
inner wall surface of a polymerization vessel and other parts to be coated 
are previously heated, and the coating solution is directly applied on the 
heated inner wall surface, etc. After dried, the coated surfaces are 
washed with water if necessary. 
The coating thus formed has normally a coating weight of 0.005 g/m.sup.2 or 
more, preferably from 0.005 to 5 g/m.sup.2, more preferably from 0.05 to 2 
g/m.sup.2 in the dried state. 
The coating operation may be conducted every 1 to ten-odd polymerization 
runs. The formed coating has considerably good durability and retains the 
scale-preventing effect; therefore the coating operation is not 
necessarily performed every polymerization run. 
Polymerization 
After the formation of the coating on the inner wall surface of a 
polymerization vessel, etc., polymerization is carried out in accordance 
with conventional procedures. That is, a monomer having an ethylenically 
double bond, a polymerization initiator, and other necessary additives 
such as a dispersing agent for the monomer, and optionally a 
polymerization medium are charged into the polymerization vessel, followed 
by carrying out polymerization. 
The monomer having an ethylenically double bond to which the method of this 
invention can be applied may include, for example, vinyl halides such as 
vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; 
acrylic acid and methacrylic acid, or esters or salts of these; maleic 
acid or fumaric acid, and esters or anhydrides thereof; and diene monomers 
such as butadiene, chloroprene and isoprene; as well as styrene, 
.alpha.-methylstyrene, acrylates, acrylonitrile, halogenated vinylidenes, 
and vinyl ethers. 
There are no particular limitations on the form of polymerization to which 
the method of this invention can be applied. The present invention is 
effective in any forms of polymerization such as suspension 
polymerization, emulsion polymerization, solution polymerization, bulk 
polymerization, and gas phase polymerization. 
More specifically, in the case of suspension or emulsion polymerization, 
polymerization is generally carried out by a process comprising the steps 
of charging water and a dispersing agent into a polymerization vessel, 
charging a polymerization initiator, evacuating the inside of the 
polymerization vessel to a pressure of from about 0.1 mmHg to about 760 
mmHg, charging a monomer (whereupon the pressure inside the polymerization 
vessel usually becomes from 0.5 to 30 kg.cm.sup.-2), polymerizing the 
monomer at a temperature of from about -10.degree. C. to 150.degree. C., 
and optionally adding at least one of water, a dispersing agent and 
polymerization initiator during polymerization. The polymerization may be 
judged to be completed when the pressure inside the vessel falls to from 
about 0 to about 7 kg.cm.sup.-2 G The water, dispersing agent and 
polymerization initiator are used in amounts of about 20 to about 300 
parts by weight, about 0.01 to about 30 parts by weight, and about 0.01 to 
about 5 parts by weight, respectively, per 100 parts by weight of the 
monomer. 
In the case of solution polymerization, an organic solvent such as toluene, 
xylene and pyridine is used as the polymerization medium in place of 
water. The dispersing agent is optionally used. The other conditions are 
generally the same as those as described for suspension or emulsion 
polymerization. 
In the case of bulk polymerization, the process typically comprises the 
steps of evacuating the inside of a polymerization vessel to a pressure of 
from about 0.01 mmHg to about 760 mmHg, charging a monomer, and then 
charging a polymerization initiator, and then carrying out polymerization 
at -10.degree. C. to 250.degree. C. 
The method of this invention is effective regardless of the materials 
constituting the inner wall, etc. of a polymerization vessel. That is, 
this method is effective for any type of polymerization vessels having 
inner wall made of stainless steel or lined with glass. 
Accordingly, any additive materials that are conventionally added in a 
polymerization system can be used without any limitation. More 
specifically, the method of this invention can effectively prevent 
polymers from depositing, even in polymerization systems containing the 
following additives: for example, polymerization catalysts such as t-butyl 
peroxyneodecanoate, di-2-ethylhexyl peroxydicarbonate, 
3,5,5-trimethylhexanoyl peroxide, .alpha.-cumyl peroxyneodecanoate, cumene 
hydroperoxide, cyclohexanone peroxide, t-butyl peroxypivalate, 
di-2-ethoxyethyl peroxydicarbonate, benzoyl peroxide, lauroyl peroxide, 
2,4-dichlorobenzoyl peroxide, diisopropyl peroxydicarbonate, 
acetylcyclohexylsulfonyl peroxide, 
.alpha.,.alpha.'-azobisisobutyronitrile, .alpha.,.alpha.'-azobis-2,4-dimet 
hylvaleronitrile, potassium persulfate, ammonium persulfate, p-menthane 
hydroperoxide; suspension agents comprised of natural or synthetic 
polymers such as partially oxidized polyvinyl acetates, polyacrylic acids, 
vinyl acetate/maleic anhydride copolymer, cellulose derivatives such as 
hydroxypropyl cellulose, and gelatin; solid dispersants 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 
dodecylbenzenesulfonate and sodium dioctylsulfosuccinate; fillers such as 
calcium carbonate and titanium oxide; stabilizers such as tribasic lead 
sulfate, calcium stearate, dibutyltin dilaurate and dibutyltin mercaptide; 
lubricants such as rice wax and stearic acid; plasticizers such as DOP and 
DBP; chain transfer agents such as trichloroethylene and mercaptans; pH 
adjusters.

EXAMPLES 
The method of the present invention is now described by way of working 
examples and comparative examples. In each of the tables below, Experiment 
Nos. marked with * indicate comparative examples, and the other Experiment 
Nos., working examples of the present invention. 
Production of reaction products 
(1) Production of Reaction Product No. 1 
In 300 g of water was dissolved 30 g of tannic acid, and 30 g of benzoyl 
chloride was then added. After 25 g of a 20% aqueous sodium hydroxide 
solution was added thereto, the mixture was allowed to react at 30.degree. 
C. for 1 hour under stirring. 
The resulting reaction mixture was filtered, and the residue obtained was 
washed with water 5 to 6 times, followed by drying to give 45 g of a 
desired compound (hereinafter called Reaction Product No.1). 
(2) Production of Reaction Product No. 2 
In 300 g of water was dissolved 40 g of tannin of persimmon, and 10 g of 
acetyl chloride was then added. After 20 g of a 20% aqueous potassium 
hydroxide solution was added thereto, the mixture was allowed to react at 
30.degree. C. for 1 hour under stirring. 
The resulting reaction mixture was filtered, and the residue obtained was 
washed with water 5 to 6 times, followed by drying to give 47 g of a 
desired compound (hereinafter called Reaction Product No.2). 
(3) Production of Reaction Product No. 3 
In 300 g of water was dissolved 30 g of nutgalls tannin, and 20 g of 
benzoyl chloride was then added. After 20 g of a 20% aqueous sodium 
hydroxide solution was added thereto, the mixture was allowed to react at 
50.degree. C. for 0.5 hour under stirring. 
The resulting reaction mixture was filtered, and the residue obtained was 
washed with water 5 to 6 times, followed by drying to give 40 g of a 
desired compound (hereinafter called Reaction Product No.3). 
EXAMPLE 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 reaction product as prepared above was 
dissolved in a solvent as shown in Table 1 to prepare a coating solution. 
The coating solution was applied to the inner wall and other parts with 
which monomers come into contact during polymerization, such as the 
stirring shaft, stirring blades and baffles. Then, the wet coated surfaces 
were dried by heating at 50.degree. C. for 15 min., followed by washing 
with water. However, Experiment Nos. 101 to 103 are comparative examples 
in which no coating solution was applied, or a coating solution containing 
a tannin was applied. The reaction product of a tannin and an acid halide 
used, its concentration, and the solvent used in each experiment are given 
in Table 1. 
Subsequently, in the polymerization vessel thus coated, were charged 400 kg 
of water, 200 kg of vinyl chloride, 250 g of partially saponified 
polyvinyl alcohol, 25 g of hydroxypropylmethyl cellulose and 75 g of 
diisopropyl peroxydicarbonate. Then, polymerization was carried out at 
75.degree. C. with stirring for 6 hours. After the completion of the 
polymerization, the amount of polymer scale depositing on the inner wall 
of the polymerization vessel was measured. The results are given in Table 
1. 
TABLE 1 
______________________________________ 
Ex- Coating solution Amount 
peri- Concen- 
of 
ment Compound Solvent tration 
scale, 
No. dissolved (wt. ratio) wt. % g/m.sup.2 
______________________________________ 
101* -- -- -- 1,300 
102* Tannic acid Water/methanol 
0.5 1,200 
(50/50) 
103* Tannin of Water/methanol 
0.5 1,200 
persimmon (50/50) 
104 R.Product No.1 
Water/methanol 
0.5 10 
(50/50) 
105 R.Product No.2 
Water/methanol 
0.5 16 
(50/50) 
106 R.Product No.3 
Water/methanol 
0.5 12 
(50/50) 
107 R.Product No.1 
Water/methanol 
1.0 7 
(50/50) 
108 R.Product No.2 
Water/methanol 
1.0 11 
(70/30) 
109 R.Product No.3 
Water/methanol 
1.0 8 
(50/50) 
110 R.Product No.1 
Methanol 0.5 7 
111 R.Product No.2 
Methanol 0.5 14 
112 R.Product No.3 
Methanol 0.5 10 
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EXAMPLE 2 
In each experiment, a polymerization vessel with an inner capacity of 20 
liters and having a stirrer was coated with the coating solution of 
Experiment No. in Example 1 as shown in Table 2, followed by drying in the 
same manner as in Example 1. However, Experiment No. 201 is a comparative 
example in which no coating solution was coated. 
Subsequently, in the polymerization vessel thus coated, were charged 9 kg 
of water, 225 g of sodium dodecylbenzenesulfonate, 12 g of t-dodecyl 
mercaptan, and 13 g of potassium persulfate. 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 
deposition on the inner wall of the polymerization vessel was measured. 
The results are given in Table 2. 
TABLE 2 
______________________________________ 
Experi- 
ment Amount of scale 
No. Coating solution 
g/m.sup.2 
______________________________________ 
201* -- 400 
202* Experiment No. 102 
390 
203* Experiment No. 103 
390 
204 Experiment No. 104 
7 
205 Experiment No. 106 
10 
206 Experiment No. 107 
7 
207 Experiment No. 108 
14 
208 Experiment No. 109 
8 
209 Experiment No. 110 
8 
210 Experiment No. 112 
7 
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