Coating solution for preventing adhesion of polymer scale and method for preventing scale adhesion during preparation of polymers

The present invention relates to a coating solution for preventing adhesion of polymer scale and a method for preventing scale adhesion during preparation of polymers which can provide polymers having high quality without coloring thereof while preventing adhesion of polymer scale to a polymerizer when a monomer having an ethylenically unsaturated double bond is polymerized. A coating solution for preventing adhesion of polymer scale which comprises anaphthoquinone natural dyestuffs, anthraquinone natural dyestuffs, tannin natural dyestuffs, xanthone natural dyestuffs, flavonoid natural dyestuffs, or/and benzoquinone natural dyestuffs and a polyvinyl alcohol having a degree of saponification of not less than 70 mole % was applied on at least a part of a polymerizer which comes in contact with a monomer having an ethylenically unsaturated double bond and was dried to give a coating film during polymerization thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a coating solution for preventing adhesion 
of polymer scale and a method for preventing adhesion of polymer scale to 
a polymerizer during polymerization of a monomer having an ethylenically 
unsaturated double bond, for instance, a vinyl ester or acrylic acid. 
There has been known a problem that, when a polymer is prepared by 
polymerizing a monomer in a polymerizer, the polymer adheres to the inner 
wall of the polymerizer in the form of scale. The adhesion of such scale 
results in the reduction of cooling capacity of the polymerizer and yield 
of intended polymers. Moreover, if the scale peeled off during the 
polymerization is mixed in the product, the resulting polymer becomes 
nonuniform and the quality thereof is hence impaired. For this reason, it 
is necessary to remove scale every two or three batches. This requires a 
great deal of labor and time. Furthermore, the scale contains poisonous 
unreacted monomers and thus sufficient care would be necessary for 
operations. 
In the polymerization of a monomer having an ethylenically unsaturated 
double bond, there have been known methods for preventing scale-adhesion 
which comprises, for instance, applying a variety of substances onto inner 
walls of polymerizers as scale-inhibiting agents. Examples of known 
substances suitable for use as scale-inhibiting agents are dyes and 
pigments such as those disclosed in Japanese Patent Application 
Publication Nos. 45-30835 and 52-24943; aromatic amine compounds such as 
those disclosed in Japanese Patent Provisional Publication No. 51-50887; 
and reaction products of phenolic compounds with aromatic aldehydes as 
disclosed in Japanese Patent Provisional Publication No. 55-54317. The 
scale-inhibiting methods which make use of these substances as 
scale-inhibiting agents are effective in polymerization of halogenated 
vinyl monomers such as vinyl chloride or mixtures comprising halogenated 
vinyl monomers, as principal components, and a small amount of other 
monomers copolymerizable therewith. 
However, most of the conventional scale-inhibiting agents represented by 
those disclosed in the foregoing patents are colored and hence the colored 
scale-inhibiting agents applied onto the inner walls of polymerizers are 
mixed in a polymerization system through dissolution or peeling off of the 
colored scale. This leads to coloring of the resulting polymer product and 
a reduction of quality thereof. 
In the foregoing scale adhesion-preventing methods, the scale 
adhesion-inhibitory effect of the foregoing scale-inhibiting agents varies 
depending on a variety of conditions such as the kinds of monomers and 
polymerization initiators (catalysts) used; manner of polymerization; and 
materials for the inner walls of polymerizers. Thus, it has been very 
difficult to effectively inhibit scale adhesion with certainty. 
Further, if a polymerization initiator having a strong oxidative effect is 
used, such as potassium peroxodisulfate, ammonium peroxodisulfate, acetyl 
cyclohexylsulfonyl peroxide or bis(2-ethoxyethyl)peroxy dicarbonate, a 
scale adhesion-inhibiting agent in the form of a coating is decomposed 
through oxidation and this results in the reduction of the scale 
adhesion-inhibitory effect. Moreover, polymer scale is easily adhered to 
the inner walls of polymerizers made of stainless steel or other steels as 
compared with the inner walls of polymerizers provided with glass lining. 
If monomers to be polymerized are those represented by the following 
general formula: 
EQU CH.sub.2.dbd.CR.sup.1 R.sup.2 
(wherein R.sup.1 represents a hydrogen atom or a methyl group and R.sup.2 
represents a hydrogen atom or a group --C.sub.n H.sub.2n+1, --COOH, --COOM 
in which M is an alkali metal or ammonium ion, --COOC.sub.n H.sub.2n+1, 
--CN, --C.sub.6 H.sub.5, --C.sub.6 H.sub.4 R.sup.2 in which R.sup.3 
represents a hydrogen atom, --OH, --CH.sub.3 or --CH.dbd.CH.sub.2 ; 
--OCOC.sub.n H.sub.2n+1, --OC.sub.n H.sub.2n+1 or --CH.dbd.CH.sub.2, and 
nis an integer), such as styrene, .alpha.-methylstyrene, acrylates and 
acrylonitrile, these monomers have high abilities of solubilizing the 
coating film formed according to the foregoing scale adhesion-inhibiting 
methods. For this reason, a part or whole of the coating film is dissolved 
away and thus effective inhibition of scale adhesion cannot be ensured. 
Among these, styrene, .alpha.-methylstyrene, acrylates and acrylonitrile 
have extremely high capacities of solubilizing the coating films of scale 
adhesion-inhibiting agents and thus, any desired scale adhesion-inhibitory 
effect cannot be obtained. The scale adhesion is a severe problem when a 
polymerizer of stainless steel is used. 
SUMMARY OF THE INVENTION 
An object of the present invention is generally to solve the foregoing 
problems and more specifically to provide a coating solution for 
preventing adhesion of polymer scale to a polymerizer during polymerizing 
a monomer having an ethylenically unsaturated double bond and which can 
provide a polymer having high quality without causing any severe 
coloration. 
According to the present invention, the foregoing object of the present 
invention can effectively be achieved by providing a coating solution 
which comprises a natural dyestuff and a polyvinyl alcohol having a degree 
of saponification of not less than 70 mole %. 
Another object of the present invention is generally to solve the foregoing 
problems and more specifically to provide a method for preventing adhesion 
of polymer scale to a polymerizer during polymerizing a monomer having an 
ethylenically unsaturated double bond and which can provide a polymer 
having high quality without causing any severe coloration. 
According to the present invention, the foregoing object of the present 
invention can effectively be achieved by providing a method for preventing 
scale adhesion during preparation of polymers which has a step of forming 
a coating film which comprises a natural dyestuff and a polyvinyl alcohol 
having a degree of saponification of not less than 70 mole %, on at least 
a part of a polymerizer which comes in contact with a monomer having an 
ethylenically unsaturated double bond during polymerization thereof. 
The polymerizing monomer having an ethylenically unsaturated double bond is 
represented by the following general formula: 
EQU CH.sub.2 .dbd.CR.sup.1 R.sup.2 
wherein R.sup.1 represents a hydrogen atom or a methyl group and R.sup.2 
represents a hydrogen atoms or a group --C.sub.n H.sub.2n+1, --COOH, 
--COOM in which M is an alkali metal or ammonium ion, --COOC.sub.n 
H.sub.2n+1, --CN, --C.sub.6 H.sub.5, --C.sub.6 H.sub.4 R.sup.3 in which 
R.sup.3 represents a hydrogen atom, --OH, --CH.sub.3 or --CH.dbd.CH.sub.2 
; --OCOC.sub.n H.sub.2n+1, --OC.sub.n H.sub.2n+1 or --CH.dbd.CH.sub.2, and 
n is an integer. 
The natural dyestuff may be selected from the group consisting of 
naphthoquinone type natural dyestuffs, anthraquinone type natural 
dyestuffs, tannin type natural dyestuffs, xanthone type natural dyestuffs, 
flavonoid type natural dyestuffs and benzoquinon type natural dyestuffs. 
Preferred are naphthoquinone type natural dyestuffs and anthraquinone type 
natural dyestuffs. The best type natural dyestuff is naphthoquinone. 
According to the method for preventing scale adhesion during preparation of 
polymers, the scale adhesion to the inner wall of a polymerizer can 
effectively be prevented during the polymerization of a monomer having an 
ethylenically unsaturated double bond irrespective of the kinds of 
materials for the inner walls of the polymerizers. 
In the invention, a coating solution for preventing adhesion of polymer 
scale which is applied onto, for instance, inner walls of polymerizers in 
the form of coating film comprises an anthraquinone type or naphthoquinone 
type natural dyestuff and a polyvinyl alcohol having a degree of 
saponification of not less than 70 mole %. The coating film does not have 
an ability of coloring and further i not dissolved in a polymerization 
system. Thus, the present invention can provide polymers which are not 
colored and hence have high brightness. For this reason, the present 
invention can effectively be applied to polymerization systems comprising 
monomers having high solubilizing abilities such as styrene, 
.alpha.-methylstyrene, acrylates and acrylonitrile. 
Moreover, when the polymerization is performed according to the method of 
this invention, it is sufficient to perform the operation for applying the 
coating solution of preventing adhesion of polymer scale every several to 
a dozen or so batches, in other words, it is not necessary to carry out 
the scale-removing operation every polymerization batches. This 
contributes much to the improvement of production efficiency.

DETAILED EXPLANATION OF THE INVENTION 
The coating solution and the method for inhibiting scale adhesion during 
preparation of polymers according to the present invention will 
hereinafter be described in more detail. 
Examples of naphthoquinone type natural dyestuffs used in the coating 
solution for the scale adhesion-inhibiting and the scale 
adhesion-inhibiting method during preparation of polymers are 
1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone, 
2-methyl-1,4-naphthoquinone, lawson, juglone, plumbagin, lapachol, 
alkannin, echinochrome A, spinochrome A, vitamin K.sub.1, vitamin K.sub.2, 
naphthazarin, 2,3-dihydroxynaphthazarin, 2-methyl-naphthazarin, 
2-hydroxynaphthazarin, 2-hydroxy-3-methylnaphthazarin, 
2-hydroxy-3-ethylnaphthazarin, 2-hydroxy-3-acetylnaphthazarin, 
2,7-dimethylnaphthazarin, alkannan, shikonin, acethylshikonin, 
isobutylshikonin, .beta., .beta.'-dimethylacrylshikonin, 
.beta.-hydroxyisovaleroshikonin, teracrylshikonin and derivatives thereof. 
These naphthoquinone type natural dyestuffs may be used alone or in any 
combination. 
Among these naphthoquinone type natural dyestuffs, particularly preferred 
are, for instance, shikonin, acetylshikonin, isobutylshikonin, .beta., 
.beta.'-dimethylacrylshikonin, .beta.-hydroxyisovaleroshikonin, and 
teracrylshikonin; and naphthazarins such as naphthazarin, 
2,3-dihydroxynaphthazarin, 2-methylnaphthazarin, 2-hydroxynaphthazarin, 
2-hydroxy-3-methylnaphthazarin, 2-hydroxy-3-ethylnaphthazarin, 
2-hydroxy-3-acethylnaphthazarin and 2,7-dimethylnaphthazarin. 
These shikonins and naphthazarins can be obtained through extraction, with 
an organic solvent, of roots (Shikon) of Lithospermum officinale or have 
recently been mass-produced by the use of so-called biotechnology. 
As the polyvinyl alcohol component of the coating solution for the scale 
adhesion-inhibiting, those having a high degree of saponification and a 
high average degree of polymerization are used for enhancing the ability 
of remaining on the wall of a polymerizer and resistance to film-forming 
ability of monomers. 
The polyvinyl alcohol used in the invention must have a degree of 
saponification of not less than 70 mole %, preferably not less than 80 
mole %, more preferably not less than 90 mole % and particularly not less 
than 98 mole %. This is because, if the degree of saponification thereof 
is less than 70 mole %, the resulting the coating solution for the scale 
adhesion -inhibiting has low ability of remaining on the wall and 
resistance to film-forming ability of monomers. 
The polyvinyl alcohol should have an average degree of polymerization of 
not less than 1000, preferably not less than 1500 and in particular not 
less than 2000. Such polyvinyl alcohols may be used alone or in any 
combination of those having different degree of saponification and average 
degrees of polymerization. 
The weight ratio of the naphthoquinone type natural dyestuff to the 
polyvinyl alcohol generally ranges form 100:0.1 to 100:5000 and preferably 
100:1 to 100:1000. 
A naphthoquinone type natural dyestuff and a polyvinyl alcohol having a 
degree of saponification of not less than 70 mole % are practically used 
by dissolving in an appropriate solvent to give a coating solution for the 
scale adhesion-inhibiting, applying the resulting solution onto the inner 
wall or the like of a polymerizer and then drying the coated film. 
Typical examples of such solvents include water, alcoholic solvents such as 
methanol, ethanol, propanol, butanol, 2-butanol, 2-methyl-1-propanol, 
2-methyl-2-pentanol; ketone type solvents such as acetone, methyl ethyl 
ketone and methyl isobutyl ketone; ester type solvents such as methyl 
formate, ethyl formate, methyl acetate and methyl acetoacetate; ether type 
solvents such as 4-methyldioxolan and ethylene glycol diethyl ether; and 
aprotic solvents such as furans, dimethylformamide, dimethylsulfoxide and 
acetonitrile. These solvents may be used alone or in any combination. It 
is desirable that the concentration of the sum of the naphthoquinone type 
natural dyestuff and polyvinyl alcohol in the coating solution is adjusted 
to the range of the order of 0.001 to 20% by weight. 
Further, the coating solution for the scale adhesion-inhibiting may 
optionally comprise, for instance a hydrophilic polymer, a surfactant 
(anionic, cationic, amphoteric ones), an amine type compound, a phenolic 
hydroxyl group-coating compound and/or a quinone type compound for the 
purpose of enhancing the scale adhesion-inhibitory effect of the resulting 
coating film. 
The pH value for the coating solution for the scale adhesion-inhibiting is 
preferably more than 7.0. It may optionally comprise a pH adjusting agent. 
Specific examples of pH adjusting agents are sulfuric acid, boric acid, 
phosphoric acid, acetic acid, oxalic acid, tartaric acid, lactic acid, 
p-toluenesulfonic acid, phytic acid, thioglycollic acid, glycollic acid, 
sodium hydroxide, potassium hydroxide, aqueous ammonia and 
ethylenediamine. 
The coating solution for the scale adhesion-inhibiting thus prepared is 
applied onto various parts of a polymerizer which possibly comes in 
contact with monomers during polymerization such as the inner wall of the 
polymerizer, stirring blades, a stirring shaft, a condenser, a header, a 
search coil, a bolt and a nut and then dried to give a coating film 
thereon. In addition, it is likewise desirable to apply the coating 
solution onto various parts of unreacted monomer recovery systems to which 
scale may adhered such as a monomer distillation column, a condenser, a 
tank for storing the monomer and the inner walls of valves. Surfaces 
materials to be coated are not restricted to specific ones and include, 
for instance, stainless steel, other steels and surfaces provided with 
glass lining. 
The coating solution for the scale adhesion-inhibiting may be applied 
according to any manner such as brush coating and spray coating or a 
method comprising filling a polymerizer with the coating solution and then 
withdrawing the solution. The coating can be performed according to the 
method as disclosed in Japanese Patent Provisional Publication No. 
57-61001 which comprises automatically spray-coating through a nozzle 
positioned at the inner and upper portion of the polymerizer. It is also 
possible to apply the coating solution for the scale adhesion-inhibiting 
in the form of polka dots as disclosed in Japanese Patent Provisional 
Publication No. 59-11303. Further, an automatic coating method as 
disclosed in Japanese Patent Provisional Publication No. 5-36288 may 
likewise be used, which comprises the coating solution for the scale 
adhesion-inhibiting by spraying it together with water vapor as a carrier 
gas. The carrier gas may be vinyl chloride monomer (see Japanese Patent 
Provisional Publication No. 56-501116) or a low boiling point hydrocarbon 
gas (see Japanese Patent Provisional Publication No. 56-501117). 
The drying of the coated film is performed at a temperature ranging from 
room temperature to 100.degree. C. Alternatively, the drying may be 
performed by blowing hot air on the coated surface or previously heating 
the surface to be coated to a temperature ranging from 30 to 80 .degree. 
C. and then directly applying the coating solution onto the heated 
surface. After drying, the coating solution onto the heated surface. After 
drying, the coated surface is, if necessary, washed with water. The amount 
of the coating solution to be applied is not less than 0.001 g/m.sup.2, in 
particular 0.05 to 2 g/m.sup.2 (weighed after drying). The foregoing 
coating operation can be performed every polymerization batches, but it is 
sufficient to perform coating operation every several to dozen or so 
polymerization batches since the coated film once formed has substantial 
durability and a long-lasting scale adhesion-inhibitory effect. 
The scale adhesion-inhibiting method of the present invention can be 
employed irrespective of the manner of polymerization. In other words, the 
method is effective in any of suspension polymerization, emulsion 
polymerization, solution polymerization, bulk polymerization and gas-phase 
polymerization. After forming the foregoing coating film on parts of a 
polymerizer which may come in contact with monomers to be polymerized such 
as the inner wall of the polymerizer, there are introduced, into the 
polymerizer, the monomer having an ethylenically unsaturated double bond 
represented by the general formula: CH.sub.2 .dbd.CR.sup.1 R.sup.2 and 
optional other monomers copolymerizable therewith to perform 
polymerization according to the usual manner. In this respect, it is also 
possible to simultaneously add, to the polymerizer, other additives 
currently used such as an optional catalyst and a dispersant for 
dispersing the monomers. 
More specifically, suspension and emulsion polymerization processes are 
generally carried out by charging water and a dispersant in a polymerizer, 
then introducing a polymerization initiator (catalyst) and a monomer (the 
internal pressure of the polymerizer usually reaches 0 to 10 
kgf/cm.sup.2), optionally adding one or more of water, a dispersant and a 
polymerization initiator to the polymerizer during the polymerization. It 
is in general judged that the polymerization is completed when a desired 
reaction rate is attained (at the time when the reaction rate reaches 80 
to 100%). In this case, the amounts of the water, dispersant and 
polymerization initiator range, respectively, from about 50 to 500 parts 
by weight, about 0.01 to 30 parts by weight and about 0.01 to 30 parts by 
weight and about 0.01 to 5 parts by weight per 100 parts by weight of the 
monomer. 
In case of solution polymerization, an organic solvent such as toluene, 
xylene or pyridine as the polymerization medium is substituted for water. 
A dispersant is optionally use 2. Other conditions for the solution 
polymerization are the same as those for the suspension and emulsion 
polymerization processes. 
Bulk polymerization is performed by replacing the atmosphere within a 
polymerizer with nitrogen gas or evacuating the interior of the 
polymerizer to a pressure of about 0.01 to 760 mmHg, then charging a 
monomer and a catalyst to perform polymerization at 10.degree. to 
250.degree. C. 
Examples of monomers to which the scale adhesion-inhibiting method of the 
invention can effectively be applied are vinyl esters such as vinyl 
acetate and vinyl propionate; acrylic acid, methacrylic acid and esters or 
salts thereof; diene monomers such as butadiene, chloroprene and isoprene; 
styrene, acrylonitrile, .alpha.-methylstyrene and vinyl ethers. 
The coating solution for the scale adhesion-inhibiting of the present 
invention is effective even if the polymerization system comprises a 
variety of additives conventionally used in preparation of vinyl chloride 
polymers, such as polymerization initiators, dispersants, solid 
dispersants, emulsifying agents, fillers, stabilizers, lubricants and 
chain transfer agents. Specific examples of these additives are as 
follows. 
Examples of polymerization initiators usable in the invention are t-butyl 
peroxy neodecanoate, bis(2-ethylhexyl) peroxy dicarbonate, 
3,5,5,-trimethylbexanoyl peroxide, .alpha.-cumyl peroxy neodecanoate, 
cumene hydroperoxide, cyclohexanone peroxide, t-butylperoxy pivalate, 
bis(2-ethoxyethyl)peroxy dicarbonate, benzoyl peroxide, lauroyl peroxide, 
2,4-dichlorobenzoyl peroxide, diisopropylperoxy dicarbonate, .alpha., 
.alpha.'-azobisisobutyronitrile, .alpha., 
.alpha.'-azobis-2,4-dimethylvaleronitrile, potassium peroxodisulfate, 
ammonium peroxodisulfate and p-menthane hydroperoxide. 
Examples of dispersants are natural and synthetic polymers such as 
partially saponified polyvinyl alcohol, polyacrylic acid, copolymer of 
vinyl acetate and maleic anhydride, cellulose derivatives such as 
hydroxypropyl methyl cellulose and gelatin. 
Examples of solid dispersants include calcium phosphate and hydroxy 
apatite. 
Examples of emulsifying agents include nonionic emulsifying agents such as 
sorbitan monolaurate, sorbitan trioleate and polyoxyethylene alkyl ether; 
and anionic emulsifying agents such as sodium laurylsulfate, sodium 
alkylbenzenesulfonates (for instance, sodium dodecylbenzenesulfonate) and 
sodium dioctylsulfosuccinate. 
Typical examples of fillers usable are calcium carbonate and titanium 
oxide. 
Examples of stabilizers which may be used in the invention are tribasic 
lead sulfate, calcium stearate, dibutyl tin dilaurate and dioctyl tin 
methylcaptide. 
Examples of lubricants include rice wax, stearic acid and cetyl alcohol. 
Examples of plasticizers include dioctyl phthalate and dibutyl phthalate. 
Examples of chain transfer agents are mercaptans such as t-dodecyl 
mercaptan; and trichloroethylene. 
The method of the present invention is likewise effective even in 
polymerization systems which comprise a pH adjusting agent. 
The scale adhesion-inhibiting method of the present invention can 
particularly effectively be applied to preparation of beads of latexes of 
polymers such as polystyrene, poly(methyl methacrylate) and 
polyacrylonitorile; preparation of synthetic rubbers, through emulsion 
polymerization, such as styrene-butadiene rubber (SBR), 
acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), isoprene 
rubber (IR) and isobutylene-isoprene rubber (IIR); and preparation of 
acrylonitrile-butadiene-styrene (ABS) resin. 
Examples of anthraquinone-type natural dyestuffs used in the coating 
solution for inhibiting scale adhesion during polymerization according to 
the present invention are tectoquinone, 3-hydroxy-2-methylanthraquinone, 
2-hydroxyanthraquinone, alizarin, xanthopurpurin, rubiadin, munjistin, 
chrysophanic acid, carminic acid, kermesic acid and laccaic acid A as well 
as derivatives thereof. 
In this case, there may be used the same polyvinyl alcohols as those 
explained above in connection with the coating solution for the scale 
adhesion-inhibiting comprising naphthoquinone-type natural dyestuffs. The 
weight ratio of the anthraquinone-type natural dyestuff to the polyvinyl 
alcohol ranges form 100:0.1 to 100:5000 and preferably 100:1 to 100:1000. 
An anthraquinone-type natural dyestuff and a polyvinyl alcohol having a 
degree of saponification of not less than 70 mole % is dissolved in a 
proper solvent to give a coating solution for the scale 
adhesion-inhibiting, then applied onto, for instance, the inner wall of a 
polymerizer and dried. The same solvents used above may be employed. The 
concentration of the sum of the anthraquinone-type natural dyestuff and 
polyvinyl alcohol is adjusted to the range of the order of 0.001 to 20% by 
weight. 
Compounds added to the coating solution for improving the scale 
adhesion-inhibitory effect and pH of the coating solution are the same as 
those explained above in connection with the coating solution comprising 
naphthoquinone-type natural dyestuffs. 
Parts of the polymerizer to which the coating solution is applied, 
materials for the surface to be coated, methods for applying the coating 
solution and methods for drying the coated film are likewise identical to 
those discussed above in connection with the coating solution comprising 
naphthoquinone-type natural dyestuffs. Furthermore, manner of 
polymerization to which the method for preventing scale adhesion is 
applied, monomers to which the method can effectively be applied, a 
variety of additives use din preparation of polymers and polymerization 
reactions to which the method can be particularly preferably applied are 
identical to those discussed above in connection with the coating solution 
comprising naphthoquinone type natural dyestuffs. 
Examples of natural dyestuffs which may be used in the coating solution and 
the method for preventing scale adhesion during polymerization according 
to the present invention further include tannin type natural dyestuffs, 
xanthone type natural dyestuffs, flavonoid type natural dyestuffs and 
benzoquinone type natural dyestuffs in addition to the foregoing 
naphthoquinone type and anthraquinone type ones. 
Examples of tanning type natural dyestuffs are chlorogenic acids such as 
chlorogenic acid, isochlorogenic acid and theogallin as well as 
derivatives thereof; catechins such as catechin and gallocatechin as well 
as derivatives thereof; and leucoanthocyanins such as phlobaphene and 
derivatives thereof. 
Examples of xanthone type natural dyestuffs are gentisin, isogentisin, 
swertiamarin, euxanthone, jacareubin, mangostin, mangiferin, 
lichexanthone, asperxanthone and ravenerin as well as derivatives thereof. 
Examples of flavonoid type natural dyestuffs include flavones such as 
apigenin, primetin, baicalein, wogonin, scutellarin, luteolin, diosmetin 
and tricin as well as derivative thereof; flavonols such as galangin, 
datiscetin, kaempferol, fisetin, morin, quercetin, robinetin, 
calycopterin, gossypetin and syricetin as well as derivaties thereof; 
anthocyanins such as callistephin, pelargonin, fragarin, raphanin, 
salvianin, chrysanthemin, cyanin, keracyanin, shisonin, idaein, 
mecocyanin, rubrobrassicin, cyanidine-3-arabinoside, oxycoccicyanin, 
peonin, delphinin, delphin, nasumin, ciolanin, hyacin, awobanin, petunin, 
petunidin-5-xyloside, oenin, malvin, ensatin and uliginosin as well as 
derivatives thereof; flavonoid C-glycosides such as orientin and 
derivatives thereof; biflavonyls such as ginkgetin and derivatives 
thereof; chalcones such as carthamn, isocarthamin, pedicinin and butein as 
well as derivatives thereof; and aurones such as aureusidin, leptosidin 
and as well as derivatives thereof. Among the foregoing flavonoid natural 
dyestuffs, particularly preferred are flavones such as apigenin, primetin, 
baicalein and wogonin; flavonols such as galangin, datiscetin, kaempferol, 
fisetin, morin, quercetin, robinetin and myricetin; flavonoid C-glycosides 
such as orientin; and chalcones such as carthamin, isocarthamin, pedicinin 
and butein. 
Examples of benzoquinone type natural dyestuffs include o-benzoquinone, 
p-benzoquinone, tolu-p-quinone, o-xylo-p-quinone, thymoquinone, 
2-methoxybenzoquinone, gentisyl quinone, polyporic acid and ubiquinone n 
as well as derivatives thereof. 
When a monomer having an ethylenically unsaturated double bond is 
polymerized in a polymerizer, a coating film comprising a natural dyestuff 
and a polyvinyl alcohol having a degree of saponification of not less than 
70 mole % is previously applied onto parts of the polymerizer which 
possibly come in contact with the monomer. The resulting film serves to 
inhibit any physical and/or chemical adsorption of the monomer having an 
ethylenically unsaturated double bond, the initial condensates thereof and 
the resulting polymers present in the polymerizer onto the inner wall of 
the polymerizer and thus any formation of scale can be prevented. 
The present invention will hereinafter be explained in more detail with 
reference to the following non-limitative working Examples. 
Examples which make use of the coating solution for the scale 
adhesion-inhibiting comprising naphthoquinone type natural dyestuffs are 
as follows. 
Preparation of Coating solution for Preventing Adhesion of Polymer Scale 
Coating solutions each having a composition as listed in the following 
Tables 1 to 3 were prepared by dissolving naphthoquinone type natural 
dyestuffs and polyvinyl alcohols in solvents and then adding pH adjusting 
agents. The kinds of naphthoquinone type natural dyestuffs, polyvinyl 
alcohols, weight ratios of the dyestuffs to the polyvinyl alcohols, 
solvents (compositions thereof), total concentration , pH adjusting agents 
and pH values of the resulting coating solutions employed in Examples and 
Comparative Examples are detailed in the following Tables 1 to 3. 
Polyvinyl alcohols used are those commercially available and listed in 
Table 4. In Comparative Example 5, C.I. Acid Black 2, an azine type 
synthetic dye, was substituted for the naphthoquinone type natural 
dyestuff. 
Polymerization 
Each resulting coating solution was applied to parts (such as a inner wall, 
a shaft for stirring, stirring blades or the like) of a polymerizer of 
stainless steel, having an inner volume of 1000l and provided with a 
stirring machine, which might come in contact with monomers used, using a 
spray coater, the temperature of a jacket was adjusted to 50.degree. C., 
followed by drying through heating for 10 minutes and washing with water 
to give a coating film. 
There were charged, to the polymerizer which had thus been subjected to 
scale adhesion-inhibiting treatment, 550 kg of water, 125 kg of styrene, 
120 kg of styrene-butadiene rubber latex (solid content=50%), 50 kg of 
acrylonitrile, 2.5 kg of an emulsifying agent for polymerizing synthetic 
rubbers (BANDIS T-100P, available from Harima Chemicals, Inc.), 0.1 kg of 
sodium hydroxide, 1.5 kg of t-dodecyl mercaptan and 0.3 kg of potassium 
peroxodisulfate and polymerization was performed at 70.degree. C. for 3 
hours with a stirring. 
Determination of Amount of Scale Adhered 
After the polymerization, the amount of the scale formed was determined by 
scraping off the polymer scale from the wall and it was expressed in terms 
of the weight of scale adhered per 1 m.sup.2 of the wall area. 
Determination of Brightness Index (L value) 
The brightness index of each polymer obtained in Examples and Comparative 
Examples was determined to evaluate whether the polymers were colored or 
not. The brightness index was determined in the following manner. 
An amount of a 2% magnesium sulfate solution was added to each resulting 
polymer latex (1kg) to coagulate and precipitate the polymer and the 
polymer precipitated was filtered off. The precipitates filtered off were 
washed with hot water of 80.degree. to 90.degree. C. two or three times, 
then dried at 40.degree. C. for 25 hours in a vacuum dryer to give a 
resin. 
The resulting resin was introduced into a frame of 9.times.9 cm (thickness 
0.1 cm) and press-molded under heating at 195.degree. C., 50 to 60 
kgf/cm.sup.2 to give a sample for testing. The brightness index L of the 
sample was determined according to Hunter's color difference equation as 
disclosed in JIS Z 8730 (1980). The greater the L value, the higher the 
brightness of the polymer. 
The L value was determined as follows. 
According to the description of JIS Z 8722, the stimulus value Y of the XYZ 
color system was determined by a stimulus value direct-reading method 
using the standard illuminant C and a photoelectric color meter (Z-1001DP 
Model, a colorimetric color difference meter; available from Nippon 
Denshoku Kogyo Co., Ltd.). The conditions described in the item 4.3.1 of 
JIS Z 8722 were adopted as geometrical conditions for illumination and 
light reception. The value L can be obtained by substituting the resulting 
stimulus value Y into the equation: L=10Y.sup.1/2. 
The amount of scale adhered and brightness indexes (L values) thus obtained 
are summarized in Tables 1 to 3. In these Tables, A represents a 
naphthoquinone type natural dyestuff and B represents a polyvinyl alcohol. 
TABLE 1 
__________________________________________________________________________ 
Naphthoquinone Total Amount 
Natural Polyvinyl 
Weight 
Solvent 
Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio Water/ 
(A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) CH.sub.3 OH 
(%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
1 Shikonin Kuraray PVA-140 
100/100 
50/50 0.3 KOH 7.0 1 84.5 
2 Shikonin Kuraray PVA-140 
100/10 
50/50 0.3 KOH 9.0 2 84.0 
3 Shikonin Kuraray PVA-140 
100/600 
50/50 0.3 KOH 9.0 0 84.7 
4 Shikonin Kuraray PVA-140 
100/100 
50/50 0.1 KOH 9.0 1 84.9 
5 Shikonin Kuraray PVA-140 
100/200 
50/50 0.3 Sulfuric 
4.5 4 84.6 
Acid 
6 Naphthazarin 
Shin-Etsu C-25 
100/200 
50/50 0.3 Boric Acid 
4.0 7 84.7 
7 Shikonin Shin-Etsu C-25 
100/200 
50/50 0.3 Phosphoric 
4.0 4 84.5 
Acid 
8 Shikonin Shin-Etsu C-25 
100/100 
80/20 0.3 KOH 8.5 1 84.5 
9 2,7-Dimethyl- 
Shin-Etsu C-17 
100/100 
80/20 0.3 KOH 8.5 1 84.4 
naphthazarin 
10 Acetylshikonin 
Shin-Etsu PA-18 
100/150 
80/20 0.3 KOH 8.5 1 83.7 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Naphthoquinone Total Amount 
Natural Polyvinyl 
Weight 
Solvent 
Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio Water/ 
(A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) CH.sub.3 OH 
(%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
11 2,3-dihydroxy- 
Gohsenol KP-08 
100/150 
80/20 0.3 KOH 8.5 6 84.5 
naphthazarin 
12 2-hydroxy- 
Gohsenol NH-26 
100/150 
80/20 0.5 NaOH 8.5 1 84.5 
naphthazarin 
13 .beta.,.beta.'-dimethyl- 
Gohsenol NH-26 
100/150 
80/20 0.5 NaOH 8.5 1 83.7 
acrylshikonin 
14 Isobutylshikonin 
Gohsenol NH-26 
100/150 
80/20 0.5 NaOH 8.5 0 83.4 
15 Naphthazarin 
Shin-Etsu C-20 
100/150 
80/20 0.5 NaOH 8.5 1 84.6 
16 Juglone Shin-Etsu C-20 
100/150 
80/20 0.5 NaOH 8.5 1 84.5 
17 Lawson Shin-Etsu C-20 
100/150 
80/20 0.5 KOH 8.5 2 84.6 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Naphthoquinone Total Amount 
Comp. 
Natural Polyvinyl 
Weight 
Solvent 
Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio Water/ 
(A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) CH.sub.3 OH 
(%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
1 None None -- -- -- -- -- 550 85.2 
2 Shikonin None 100/0 50/50 0.5 KOH 9.0 110 82.5 
3 None Kuraray PVA-140 
0/100 
50/50 0.5 KOH 9.0 530 85.0 
4 Shikonin Gohsenol L-5407 
100/100 
50/50 0.5 KOH 9.0 25 84.5 
5 C.I. Acid 
Kuraray PVA-140 
100/100 
50/50 0.5 Sulfuric 
2.5 5 77.2 
Black 2 Acid 
__________________________________________________________________________ 
TABLE 4 
______________________________________ 
Degree of Average 
Saponification 
Degree of 
Polyvinyl Alcohol 
(mole %) Polymerization P 
______________________________________ 
Kuraray PVA-140 99.0 .+-. 0.5 
4000 
(Available from 
Kuraray Co., Ltd.) 
Gohsenol NH-26 99.0 or more 
2600 
(Available from The Nippon 
Synthetic Chemical 
Industry, Co., Ltd.) 
Shin-Etsu Poval C-20 
99.0 or more 
2000 
(Available from Shin-Etsu 
Chemical Co., Ltd.) 
Shin-Etsu Poval C-25 
99.0 or more 
2500 
(Available from Shin-Etsu 
Chemical Co., Ltd.) 
Shin-Etsu Poval C-17 
98.5 .+-. 0.5 
1700 
(Available from Shin-Etsu 
Chemical Co., Ltd.) 
Shin-Etsu Poval PA-18 
88 .+-. 1 1800 
(Available from Shin-Etsu 
Chemical Co., Ltd.) 
Gohsenol KP-08 73 .+-. 2 800 
(Available from The Nippon 
Synthetic Chemical 
Industry, Co., Ltd.) 
Gohsenol C-5407 40 .+-. 1 390 
(Available from The Nippon 
Synthetic Chemical 
Industry, Co., Ltd.) 
______________________________________ 
Examples which make use of the coating solution for the scale 
adhesion-inhibiting comprising anthraquinone type natural dyestuffs are as 
follows. 
Preparation of Coating Solution for Preventing Adhesion of Polymer Scale 
Coating solutions each having a composition as listed in the following 
Tables 5 and 8 were prepared by dissolving anthraquinone type natural 
dyestuffs and polyvinyl alcohols in solvents and then adding pH adjusting 
agents. The kinds of anthraquinone type natural dyestuffs, polyvinyl 
alcohols, weight ratios of the dyestuffs to the polyvinyl alcohols, 
solvents (compositions thereof), total concentrations, pH adjusting agents 
and pH values of the resulting coating solutions employed in these 
Examples and Comparative Examples are detailed in the following Tables 5 
to 8. Polyvinyl alcohols used are those commercially available and listed 
in the foregoing Table 4. In Comparative Example 10, C.I. Acid Black 2, an 
azine type synthetic dye, was substituted for the anthraquinone type 
natural dyestuff. 
Polymerization, determination of the amount of scale adhered and 
determination of the brightness index (L value) were performed in the same 
manner used in the foregoing Examples in which naphthoquinone type natural 
dyestuffs were used. The amount of scale adhered and the brightness 
indexes (L values) thus obtained are summarized in Table 5 to 7. In these 
Tables, A represents a anthraquinone type natural dyestuff and B 
represents a polyvinyl alcohol. 
TABLE 5 
__________________________________________________________________________ 
Anthraquinone Total Amount 
Natural Polyvinyl 
Weight Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio (A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) 
Solvent (%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
18 Carminic Acid 
Shin-Etsu C-25 
100/100 
Water/CH.sub.3 OH 
1.0 KOH 9.0 1 83.7 
50/50 
19 Carminic Acid 
Shin-Etsu C-25 
100/10 
Water/CH.sub.3 OH 
0.3 KOH 9.0 1 84.2 
50/50 
20 Carminic Acid 
Shin-Etsu C-25 
100/100 
Water/CH.sub.3 OH 
0.1 KOH 9.0 1 84.4 
50/50 
21 Carminic Acid 
Shin-Etsu C-25 
100/100 
Water/CH.sub.3 OH 
0.01 
KOH 9.0 4 84.9 
50/50 
22 Carminic Acid 
Shin-Etsu C-25 
100/800 
Water/CH.sub.3 OH 
0.5 KOH 9.0 1 84.3 
50/50 
23 Alizarin Kuraray PVA-140 
100/100 
Water/CH.sub.3 CH.sub.2 OH 
0.5 Ethylene- 
9.5 1 84.2 
50/50 diamine 
24 2-hydroxy- 
Kuraray PVA-140 
100/100 
Water/CH.sub.3 CH.sub.2 OH 
0.5 Ethylene- 
9.5 2 84.1 
anthraquinone 50/50 diamine 
__________________________________________________________________________ 
TABLE 6 
__________________________________________________________________________ 
Anthraquinone Total Amount 
Natural Polyvinyl 
Weight Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio (A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) 
Solvent (%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
25 Laccaic Acid A 
Kuraray PVA-140 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.5 Ethylene- 
9.0 1 84.2 
50/50 diamine 
26 Munjistin 
Gohsenol NH-26 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.5 Ethylene- 
9.0 2 84.1 
50/50 diamine 
27 Tectoquinone 
Shin-Etsu C-20 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.3 Ethylene- 
9.0 2 84.3 
50/50 diamine 
28 Chrysophanic 
Shin-Etsu C-17 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.3 Ethylene- 
9.0 6 84.2 
Acid 50/50 diamine 
29 3-hydroxy-2- 
Shin-Etsu PA-18 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.3 Ethylene- 
9.0 7 84.2 
methyl- 50/50 diamine 
anthraquinone 
30 Alizarin Gohsenol KP-08 
100/250 
Water/CH.sub.3 CH.sub.2 OH 
0.3 Ethylene- 
9.0 6 84.3 
50/50 diamine 
31 Rubiadin Gohsenol NH-26 
100/400 
Water/CH.sub.3 OH 
0.3 Aqueous 
10.0 
1 84.2 
90/10 Ammonia 
32 Xanthopurpurin 
Gohsenol NH-26 
100/400 
Water/CH.sub.3 OH 
0.3 Aqueous 
10.0 
2 84.1 
90/10 Ammonia 
33 Kermesic Acid 
Gohsenol NH-26 
100/400 
Water/CH.sub.3 OH 
0.3 Aqueous 
10.0 
1 84.1 
90/10 Ammonia 
34 Chrysophanic 
Shin-Etsu C-20 
100/400 
Water/CH.sub.3 OH 
0.3 Sulfuric 
3.0 5 84.4 
Acid 90/10 Acid 
35 2-Hydroxy- 
Shin-Etsu C-20 
100/400 
Water/CH.sub.3 OH 
0.3 Phosphoric 
4.0 7 84.3 
anthraquinone 90/10 Acid 
__________________________________________________________________________ 
These test results indicate that the vinyl chloride polymer obtained in 
each Example has a brightness index of not less than 80, i.e., high 
brightness and is not colored at all. 
Furthermore, coating solution each having a composition as listed in the 
following Table 9 were prepared by dissolving naphthoquinone type natural 
dyestuffs or anthraquinone type natural dyestuffs, and polyvinyl alcohols 
in solvents and then adding pH adjusting agents. Then, polymerizations 
were performed in the same manner used in the foregoing Examples. 
After the polymerization, the amount of the scale formed was determined by 
scraping off the polymer scale from the wall and it was expressed in terms 
of the weight of scale adhered per 1 m.sup.2 of the wall area. 
The foregoing polymerization was performed repeatedly till the amount of 
scale adhered was over 10 g/m.sup.2. Preventing scale times was determined 
as the time of polymerization of which amount of scale adhered was over 10 
g/m.sup.2. 
Preventing scale times thus obtained are summarized in Table 8. 
TABLE 7 
__________________________________________________________________________ 
Anthraquinone Total Amount 
Comp. 
Natural Polyvinyl 
Weight Concn. 
pH of Scale 
Ex. Dyestuff Alcohol Ratio (A + B) 
Adjust Adhered 
Brightness 
Nos. 
(Component A) 
(Component B) 
(A/B) 
Solvent (%) Agent pH (g/m.sup.2) 
Index 
__________________________________________________________________________ 
6 None None -- -- -- -- -- 550 85.2 
7 Carminic Acid 
None 100/0 
Water/CH.sub.3 OH 
0.3 KOH 9.0 130 82.2 
50/50 
8 None Shin-Etsu C-25 
0/100 
Water/CH.sub.3 OH 
0.3 KOH 9.0 530 85.0 
50/50 
9 Carminic Acid 
Gohsenol L-5407 
100/100 
Water/CH.sub.3 OH 
0.3 KOH 9.0 24 84.2 
50/50 
10 C.I. Acid 
Shin-Etsu C-25 
100/100 
Water/CH.sub.3 OH 
0.3 Phosphoric 
2.0 6 78.5 
Black 2 50/50 Acid 
__________________________________________________________________________ 
TABLE 8 
__________________________________________________________________________ 
Total Preventing 
Natural Polyvinyl Weight Concn. 
pH Scale 
Ex. Dyestuff Alcohol Ratio (A + B) 
Adjust Times 
Nos. 
(Component A) 
(Component B) 
(A/B) Solvent (%) Agent pH (batch) 
__________________________________________________________________________ 
36 Carminic Acid 
Kuraray PVA-140 
100/200 
Water/CH.sub.3 OH 
0.3 NaOH 8.5 28 
80/20 
37 Chrysophanic 
Gohsenol NH-26 
100/200 
Water/acetone 
1.3 KOH 8.0 26 
Acid 90/10 
38 Acetylshikonin 
Gohsenol NH-26 
100/200 
Water/CH.sub.3 OH 
0.3 KOH 8.5 39 
50/50 
39 Shikonin Kuraray PVA-140 
100/200 
Water/CH.sub.3 OH 
0.3 NaOH 9.5 41 
80/20 
__________________________________________________________________________