Metal container coating compositions comprising stable emulsions of water resistant polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymers

A metal container coating composition comprising a crosslinking resin and an aqueous polyvinyl alcohol/vinyl chloride-ethylene copolymer emulsion, the copolymer having a Tg from 0.degree. to 50.degree. C., about 65 to 90 wt. % vinyl chloride, about 5 to 35 wt. % ethylene, 0 to 10 wt. % olefinically unsaturated copolymerizable monomer and prepared by emulsion polymerization of vinyl chloride, ethylene and, optionally, an olefinically unsaturated comonomer in the presence of 3 to 15 wt. % polyvinyl alcohol as the dispersing agent. Also a method for preparing such stable vinyl chloride based resin emulsions comprising PA0 (a) forming an aqueous emulsion reaction mixture containing substantially all the polyvinyl alcohol and a portion, preferably at least 5%, of the total vinyl chloride monomer, PA0 (b) pressurizing the reaction mixture with an ethylene pressure sufficient to provide the copolymer with a 5 to 35 wt. % ethylene content, PA0 (c) initiating the reaction mixture by the addition of a free radical generating source and continuing polymerization until the rate of polymerization begins to decrease to provide a prepolymer emulsion, and PA0 (d) adding the remaining vinyl chloride at a substantially uniform rate and continuing polymerization until the polymerization reaction is no longer self-sustaining, ethylene being neither withdrawn nor added during the polymerization in one embodiment.

TECHNICAL FIELD 
The present invention relates to vinyl chloride-ethylene copolymer 
emulsions and metal container coating compositions containing such 
emulsions. 
BACKGROUND OF THE INVENTION 
Emulsion polymerization processes employing polyvinyl alcohol or celluloses 
such as hydroxyethyl cellulose as the emulsifier, or protective colloid, 
yield emulsion polymer products widely used as adhesives, binders and 
coatings. Such products have historically been known to possess poor 
resistance to water, generally manifested as a loss of adhesive strength 
to the substrate on exposure to water or as an unattractive whitening 
characteristically known as "blushing". This poor water resistance 
property has inhibited the use of such polymers prepared in the presence 
of polyvinyl alcohol or celluloses as coatings coming in contact with 
water, for example, as interior can coatings. 
To overcome this water sensitivity, crosslinking agents have been added to 
react with the polyvinyl alcohol of the polymer coating to render it water 
insoluble. However, such coatings still demonstrate the unattractive 
blushing on exposure to water. U.S. Pat. No. 2,843,562 attempts to 
overcome the water sensitivity of graft copolymers of polyvinyl alcohol 
and vinyl chloride by incorporating a small amount of a cross-linking 
monomer containing at least two olefinic unsaturations. 
The inventor is aware that polymer emulsions which can deposit a polymer 
coating that has enhanced water resistance can be prepared by the aqueous 
emulsion polymerization of at least one ethylenically unsaturated monomer 
in a salt-free aqueous medium. The salt-free aqueous medium comprises a 
polyvinyl alcohol as the protective colloid and a redox system comprising 
hydrogen peroxide or an organic peroxy compound as the oxidant and an 
organic reductant. When this technology was applied to the preparation of 
vinyl chloride-ethylene copolymer emulsions using typical polymerization 
techniques including polyvinyl alcohol levels of 3 to 10 wt%, stable 
copolymer emulsions were not readily obtained. Another difficulty 
encountered is related to the solubility of the ethylene in that the 
ethylene pressure may rise uncontrollably during the polymerization 
reaction. 
U.S. Pat. No. 3,399,157 teaches improving the stability of ethylene/vinyl 
chloride latexes by adding only a portion of the desired amount of 
emulsifying agent to the reaction mixture prior to the initiation of 
polymerization and adding a second portion to the reaction mixture after 
the polymerization is completed. 
U.S. Pat. No. 3,501,440 discloses in Example 5 and reference Examples 5-6 
the use of polyvinyl alcohol as the protective colloid in the 
copolymerization of ethylene with vinyl chloride at a reaction temperature 
between the critical temperature of ethylene and 60.degree. C. and at an 
ethylene pressure which is maintained substantially constant by 
withdrawing excess ethylene out of the reaction vessel during the 
polymerization. 
U.S. Pat. No. 3,642,740 discloses that vinyl chloride homo- and copolymers 
can be prepared in aqueous emulsion using as the emulsifier system an 
alkali metal salt of a sulfated C.sub.8 -C.sub.18 fatty alcohol, a tallow 
fatty alcohol or an epoxidized unsaturated fatty acid oil, and a complex 
organic phosphate ester or salt derivative. Example 1 shows that the 
emulsion used in preparing the molding paste resin product involves the 
preparation of a polymer seed latex. 
U.S. Pat. No. 3,689,447 discloses that heat resistant copolymers of 
ethylene and vinyl chloride can be prepared by the use of a seed latex in 
the aqueous composition for emulsion polymerization, together with 
heat-activated initiation at between about 50.degree. and 85.degree. C. by 
water-soluble persulfates or peroxydiphosphates. The seed latex can be 
prepared by the emulsion polymerization of any polymerizable ethylenically 
unsaturated compound. The seed latex can be prepared beforehand in a 
separate vessel and a desired aliquot can then be introduced into the 
aqueous composition. Alternatively, the seed latex can be made in situ in 
all or part of the aqueous composition before the reactor is pressurized 
with ethylene. 
U.S. Pat. No. 3,725,367 describes a process for the preparation of polymers 
and copolymers having a vinyl base which comprises dispersing into the 
organic vinyl based monomeric system a seeding latex containing an excess 
amount of organo-soluble catalyst such that the seeding latex forms the 
dispersed phase and the organic monomeric system the continuous phase. 
U.S. Pat. No. 3,736,303 discloses a latex composition comprising a 
copolymer of vinylidene chloride, an ethylenically unsaturated sulfur acid 
having sulfur in a valent state of 6, optionally an ethylenically 
unsaturated carboxylic acid and another ethylenically unsaturated monomer 
prepared using a seed latex, an ascorbic acid-hydrogen peroxide redox 
system, and ionic buffers and surfactants. 
U.S. Pat. No. 3,875,130 discloses the preparation of homo- and copolymers 
of vinyl chloride in which the polymerization of the monomer composition 
is carried out in the presence of a seeding product prepared by the 
polymerization in emulsion or fine suspension. 
U.S. Pat. No. 4,150,210 discloses a one-step process for the emulsion 
polymerization of vinyl chloride and, optionally, comonomers using a 
water-soluble initiator or initiator system and a mixed emulsifier of (1) 
a C.sub.12 -C.sub.18 straight chain alkyl or alkenyl surfactant; (2) a 
C.sub.14 -C.sub.20 straight chain alkyl or alkenyl alcohol; and (3) a 
C.sub.5 -C.sub.8 straight alkyl chain sulfosuccinate emulsifier. The 
examples show the use of a hydrogen peroxide-ascorbic acid redox system. 
U.S. Pat. No. 4,189,415 discloses aqueous vinyl chloride-vinyl 
acetate-ethylene copolymer dispersions containing only polyvinyl alcohol 
as the protective colloid. All of the polyvinyl alcohol or only part of it 
can be introduced at the beginning, the ethylene pressure applied is kept 
constant and the polymerization temperature is 10.degree.-85.degree. C., 
preferably 20.degree.-50.degree. C. 
U.S. Pat. No. 4,331,577 discloses a method for preparing 
ethylene-containing copolymer emulsions by the selective addition of the 
monomers mixture to the reactor in response to pressure variation and the 
maintenance of a monomer unsaturated condition in the reactor. 
SUMMARY OF THE INVENTION 
The present invention provides stable polyvinyl alcohol/vinyl 
chloride-ethylene copolymer emulsions which can deposit a polyvinyl 
alcohol-containing polymeric coating on a substrate that demonstrates 
surprisingly enhanced water resistance and adhesion to the substrate. 
The stable resin emulsion comprises from 20 to 70 wt%, especially about 40 
to 60 wt%, of a copolymer colloidally dispersed in an aqueous medium, the 
copolymer comprising about 65 to 90 wt% vinyl chloride, about 5 to 35 wt% 
ethylene, and 0 to about 10 wt% olefinically unsaturated copolymerizable 
monomer and having a Tg from about 0.degree. to 50.degree. C. The 
copolymer is prepared by emulsion polymerization, preferably in a 
substantially salt-free aqueous medium, in the presence of about 3 to 15 
wt% polyvinyl alcohol which is 70 to 91 mole % hydrolyzed as the 
dispersing, or emulsifying agent. The wt% values are based on monomers 
incorporated into the copolymer. 
With regard to the invention, "salt-free" means the substantial absence of 
ionic materials, that is to say the presence of ionic materials at less 
than about 0.1 wt% based on solids. Accordingly, the free radical 
generating source for initiating and sustaining the polymerization process 
would be a redox system comprising hydrogen peroxide or an organic peroxy 
compound as the oxidant and an organic reductant. 
According to the invention the polymerization process comprises 
(a) forming an aqueous emulsion reaction mixture containing substantially 
all the polyvinyl alcohol and a portion, preferably at least 5%, of the 
total vinyl chloride monomer, 
(b) pressurizing the reaction mixture with an ethylene pressure sufficient 
to provide the copolymer with about 5 to 35 wt% ethylene content, 
(c) initiating the reaction mixture by the addition of a free radical 
forming source and continuing polymerization until the rate of 
polymerization begins to decrease, 
(d) adding the remaining vinyl chloride, preferably at a substantially 
uniform rate over a period of time, while continuing polymerization until 
the reaction is no longer self sustaining, and 
(e) removing the unreacted ethylene and reducing the vinyl chloride free 
monomer content, preferably to less than 10 ppm. 
Particular embodiments of the invention in addition to the resin emulsions, 
are a metal container, such as a metal can, coated with a polymeric film 
deposited from the polyvinyl alcohol-stabilized vinyl chloride-ethylene 
copolymer emulsions and metal container coating compositions containing 
such emulsions and crosslinking agents or resins. 
As an advantage of the invention, the emulsion polymerization process 
provides polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymer 
emulsions possessing enhanced stability compared to copolymers prepared 
using conventional copolymerization techniques. 
As another advantage the vinyl chloride-ethylene copolymer emulsions 
deposit polymeric films of dramatically improved water resistance, 
especially if prepared in a salt-free medium. It is not necessary to use 
crosslinking agents to provide a high degree of water resistance although 
such agents can be used. In addition, compared to standard vinyl 
chloride-ethylene products the copolymers of this invention show improved 
dry film tensile hardness and improved adhesion to various substrates 
including wood, glass and metals such as steel and aluminum. 
DETAILED DESCRIPTION OF THE INVENTION 
The vinyl chloride-ethylene copolymers of the stable emulsions according to 
the invention contain about 65 to 90 wt% vinyl chloride, preferably about 
75 to 80 wt%. The copolymerization reaction is performed under an ethylene 
pressure which is sufficient to provide the copolymer with about 5 to 35 
wt% ethylene content, preferably about 20 to 25 wt%. Pressures of about 50 
to 100 atm are generally used to afford such ethylene content. When the 
vinyl chloride content is less than about 65 wt%, the requisite ethylene 
pressures are difficult to handle and at greater than about 90 wt% vinyl 
chloride stability becomes a problem. 
The vinyl chloride-ethylene copolymers may also contain up to about 10 wt%, 
preferably about 1 to less than 5 wt%, of other olefinically unsaturated 
monomers copolymerizable with vinyl chloride and ethylene. By way of 
illustration, other suitable olefinically unsaturated co-monomers for 
making the stable copolymer emulsions and water resistant copolymers of 
the invention include vinyl esters of C.sub.1 -C.sub.12 alkanoic acids, 
such as vinyl formate, vinyl propionate, and especially vinyl acetate; 
C.sub.3 -C.sub.10 alkenoic acids, such as acrylic acid and methacrylic 
acid, and alpha,beta-unsaturated C.sub.4 -C.sub.10 alkanoic acids, such as 
crotonic acid, isocrotonic acid, and their esters with C.sub.1 -C.sub.18 
alkanols such as methanol, ethanol, propanol and butanol, as well as 
2-ethylhexyl alcohol, cyclohexyl alcohol and lauryl alcohol; vinylidene 
halides, such as vinylidene chloride; styrene; alpha,beta-unsaturated 
C.sub.4 -C.sub.10 alkenedioic acids such as maleic acid, fumaric acid and 
itaconic acid and their monoesters and diesters of C.sub.1 -C.sub.18 
alkanols; and nitrogen containing monoolefinically unsaturated monomers, 
particularly nitrides, amides, N-methylol amides, lower alkanoic acid 
esters of N-methylol amides, lower alkyl ethers of N-methylol amides and 
allyl carbamates, such as acrylonitrile, acrylamide, methacrylamide, 
N-methylolacrylamide, N-methylol methacrylamide, N-methylol allyl 
carbamate or N-methylol lower alkyl ethers or N-methylol lower alkanoic 
acid esters of N-methylolacrylamide, N-methylol methacrylamide and 
N-methylol allyl carbamate such as N-isobutoxymethylacrylamide. The 
preferred comonomers for the vinyl chloride-ethylene polymers are the 
C.sub.3 -C.sub.10 alkenoic acids and nitrogen-containing monomers, such as 
acrylic acid, acrylamide, N-methylolacrylamide and 
N-isobutoxymethylacrylamide, preferably in about 1 to 5 wt%. 
The dispersing agent, or protective colloid, used in preparing the stable 
emulsions is at least one polyvinyl alcohol. A single polyvinyl alcohol 
may be used alone or mixtures of different polyvinyl alcohols can be used. 
The amount of polyvinyl alcohol used in the polymerization reaction is 
about 3 to 15 wt%, preferably 4 to 10 wt%, based on monomers, 
substantially all of which is added initially to the aqueous medium, i.e. 
prior to initiation of polymerization. Less than about 3 wt% polyvinyl 
alcohol is unsuitable for providing stable copolymer emulsions because of 
emulsion coagulum while greater than 15% polyvinyl alcohol is generally 
unsuitable because of high viscosity at commercially acceptable solids. 
Additional amounts of polyvinyl alcohol can be added to the reaction 
mixture during polymerization provided that at least about 3 wt%, 
preferably at least about 4 wt%, polyvinyl alcohol is present in the 
reaction mixture upon initiation. 
The polyvinyl alcohols which are suitable for use in the invention are, in 
general, 70 to 91 mole% hydrolyzed, preferably 85 to 89 mole% hydrolyzed, 
and most preferably 87 to 89 mole% hydrolyzed, and have a degree of 
polymerization (DPn) ranging from 200 to 4,000, preferably 500 to 2,500. A 
polyvinyl alcohol having a DPn at the lower end of the range, e.g. from 
200 to about 400, should be used in combination with a polyvinyl alcohol 
having a higher DPn of about 500 or more. For example, Vinol.RTM. 203 
polyvinyl alcohol (DPn about 250) when used alone did not afford a stable 
product, but in a 1:2 weight ratio with Vinol 205 polyvinyl alcohol (DPn 
about 550) stable emulsions were readily obtained if the Vinol 203 
polyvinyl alcohol was added during the polymerization reaction (delay 
addition). 
For polymerization recipes containing up to about 8 wt% polyvinyl alcohol, 
a polyvinyl alcohol resin having a degree of polymerization of less than 
about 2500 should be used, and at about 8 to 15 wt% a polyvinyl alcohol of 
less than about 1000 degree of polymerization should be used. 
The water solubility of polyvinyl alcohols which are less than 70 mole% 
hydrolyzed has diminished to the point where it adversely affects emulsion 
polymerization. 
It has also been discovered that the use of fully hydrolyzed polyvinyl 
alcohols, i.e. 98 to 99+ mole% hydrolyzed, in combination with a partially 
hydrolyzed polyvinyl alcohol in a 1:1 weight ratio did not afford stable 
emulsions. It should be possible to use a stabilizing system comprising 
predominantly a partially hydrolyzed polyvinyl alcohol and a minor amount 
of a fully hydrolyzed polyvinyl alcohol and it is believed that such 
stabilizing system should contain at least about 75 wt% partially 
hydrolyzed polyvinyl alcohol. In other words, it is believed that when 
such a stabilizing system contains more than 25 wt% fully hydrolyzed 
polyvinyl alcohol, gritty unsuitable polyvinyl alcohol/vinyl 
chloride-ethylene products will result. Solely using a fully hydrolyzed 
polyvinyl alcohol would yield a suspension resin. 
Other protective colloids, such as the celluloses or hydroxyalkyl 
celluloses, or typical emulsifying agents such as ionic or nonionic 
surfactants in combination with the polyvinyl alcohol may be used in 
amounts up to about equal proportions, preferably less than 50%, based on 
weight of polyvinyl alcohol, although water resistance may be impaired. 
Free radical sources, for example redox systems, used in the practice of 
this invention are conventional and used in conventional amounts. The 
polymerization is generally performed with quantities of redox system 
ranging from 0.03 to 3 wt% based on monomers. Typically, the entire 
quantity of either the oxidant or reductant component of the redox system, 
or a substantial portion, is introduced at the beginning and 
polymerization is initiated and controlled by metering in the other 
component. Obviously, the polymerization may be controlled by the 
simultaneous metering in of both components. Examples of the oxidizing 
component are ammonium persulfate, potassium persulfate, hydrogen peroxide 
and t-butyl hydroperoxide. Examples of the reducing component are sodium 
sulfite, sodium metabisulfite and zinc or sodium formaldehyde sulfoxylate. 
Although the use of such conventional redox systems affords stable 
emulsions and vinyl chloride-ethylene copolymer coatings having improved 
water resistance, adhesion and tensile hardness, the resistance to water 
can be further enhanced by polymerization in a salt-free aqueous 
environment. Accordingly, the redox system must be salt-free, that is to 
say, nonionic as far as the oxidant and reductant are concerned. 
For the salt-free system suitable oxidizing agents, or initiators, include 
hydrogen peroxide and organic peroxy compounds. Illustrative of the 
organic peroxides that can be used are alkylhydroperoxides such as t-butyl 
hydroperoxide, dialkyl peroxides such as di-t-butyl peroxide, peroxy acids 
such as peracetic acid and perbenzoic acid, diacyl peroxides such as 
diacetyl peroxide and dilauroyl peroxide, and peroxy esters such as 
t-butyl peracetate and t-butyl perbenzoate. The preferred oxidant for use 
in the invention is hydrogen peroxide. 
The reductant component of the redox system used in the practice of the 
invention is a nonionic organic material such as a reducing sugar or other 
easily oxidizable polyhydroxy compound. Compounds frequently employed in 
this capacity are glucose, levulose, sorbose, invert sugar, ascorbic acid 
and its enantiomer erythorbic acid which are the preferred reductants, 
citric acid and the like. Other useful organic reductants include hydroxyl 
amines, thiols, pentamines and tartaric acid. 
The preferred redox catalyst system for making stable vinyl 
chloride-ethylene copolymer emulsions comprises hydrogen peroxide and 
ascorbic acid or erythorbic acid. 
The oxidizing agent is generally employed in an amount from about 0.01 to 
1.0%, preferably 0.05 to 0.5%, based on the weight of monomers introduced 
into the polymerization system. The reductant is ordinarily added in an 
aqueous solution in the necessary equivalent amount. It is important that 
a reductant be present in the polymerization recipe because the oxidant, 
in most cases, does not furnish free radicals rapidly enough at 
temperatures below about 80.degree. C. to expeditiously effect 
polymerization of the monomers. 
The salt-free redox catalyst system may contain promoters such as ferrous 
sulfate in typically minor amounts. Such minor amounts of ionic materials 
would not adversely affect the water resistance of the emulsion polymers. 
Needless to say, the requirement of a salt-free aqueous medium rules out 
the use of ionic buffering agents as is so often used in many 
polymerization recipes for maintaining a particular pH range. However, it 
has been found that buffers are not required to make the emulsions whether 
or not salt-free conditions are used. Buffers may thus be used if desired. 
A key to providing the stable vinyl chloride-ethylene copolymer emulsions 
of the invention is the particular emulsion polymerization procedure 
employed. The reaction temperature of the polymerization can be controlled 
by the rate of free radical source addition and by the rate of the heat 
removal. Generally, it is advantageous to maintain a mean temperature of 
about 55.degree. C. during the polymerization of the monomers and to avoid 
temperatures much in excess of 80.degree. C. While temperatures as low as 
0.degree. can be used, economically the lower temperature limit is about 
30.degree. C. 
The reaction time will vary depending upon other variables such as the 
temperature, free radical source, and the desired rate of the 
polymerization and reactor heat removal capacity. It is generally 
desirable to continue the reaction until the heat generation due to 
polymerization has subsided, i.e. the polymerization reaction is no longer 
self-sustaining. 
In carrying out the polymerization, substantially all the polyvinyl alcohol 
and a portion of the vinyl chloride is initially charged to the 
polymerization vessel which is then pressurized with ethylene. Most 
advantageously, at least about 5% of the total vinyl chloride to be 
polymerized is initially charged, preferably at least about 15%. The 
remainder of the vinyl chloride is added, desirably at a substantially 
uniform rate, during the course of the polymerization after the initially 
charged vinyl chloride monomer content has been substantially reduced, as 
evidenced by a decrease in the rate of polymerization, to avoid 
overpressurization of the reactor. No more than about 60% of the vinyl 
chloride should be charged initially since it is necessary to generate a 
prepolymer in situ in order to obtain the stable emulsions. 
The quantity of ethylene entering into the copolymer is influenced by the 
pressure, the mixing, and the addition rate and amount of free radical 
generating source. Thus, to increase the ethylene content of the copolymer 
higher pressures, greater mixing and higher free radical source rate and 
amount are employed. 
By way of example, at a polymerization temperature of about 55.degree. C. 
an ethylene pressure in the range of 750 psig to 1000 psig is required to 
provide a copolymer with about 20-30 wt% ethylene. Above about 1000 psig 
an undesirable pressure rise occurs while an ethylene pressure below 750 
psig yields an unstable emulsion product. It appears that certain amounts 
of ethylene are needed to be polymerized with the initial vinyl chloride 
charge to yield a stable emulsion. Needless to say, the 750 to 1000 psig 
ethylene pressure range for 55.degree. C. polymerization would vary with 
the reaction temperature employed. Higher pressures can be used in 
suitable pressure reactors. 
The process of forming the vinyl chloride-ethylene copolymer emulsions 
generally comprises the preparation of an aqueous solution containing 
substantially all the polyvinyl alcohol dispersing agent. This aqueous 
solution and the initial charge of vinyl chloride are added to the 
polymerization vessel and ethylene pressure is applied to the desired 
value. As previously mentioned, the mixture is thoroughly mixed to 
dissolve ethylene in the vinyl chloride and in the water phase. 
Conveniently, the charge is brought to polymerization temperature during 
this mixing period. Mixing can be effected by shaking, by means of an 
agitator or other known mechanism. 
The polymerization is then initiated by introducing initial amounts of a 
free radical generating source. For example, either the oxidant or 
reductant component of a redox system could be initially added to the 
aqueous medium with the polyvinyl alcohol and vinyl chloride with the 
other redox component subsequently added to initiate the reaction. With 
the commencement of initiation, the addition of any third monomer, i.e. 
olefinically unsaturated copolymerizable monomer, is also begun 
incrementally. After polymerization has started, delay addition of the 
free radical generating source is used to continue polymerization until 
the prepolymer reaction is essentially completed as evidenced by a 
reduction in the rate of the polymerization. As is well known in the art 
the rate of polymerization can be followed by plotting the temperature 
difference (.DELTA.T) between the reaction mixture and the reaction vessel 
jacket. The point at which .DELTA.T begins to decrease corresponds to a 
reduction in the rate of polymerization. At this point, the remaining 
vinyl chloride is incrementally added along with additional free radical 
generating source and the remaining olefinically unsaturated monomer as 
delays to continue the polymerization. By "delay" addition is meant the 
addition of a component in a continuous or intermittent and, preferably, a 
substantially uniform rate. 
When preparing a vinyl chloride copolymer having a Tg of about 20.degree. 
to 50.degree. C., the ethylene pressure during the polymerization reaction 
is neither decreased by venting nor maintained at a substantially steady 
pressure by the addition of make-up ethylene for that consumed, i.e. 
ethylene being neither withdrawn nor added during polymerization. Rather 
the ethylene pressure is permitted to increase, decrease or remain 
constant, i.e. float, and eventually to reduce gradually as ethylene in 
the sealed polymerization vessel is copolymerized. Once the requisite 
ethylene pressure is set in the reactor, it will rise for a short period 
of time with initiation of polymerization as the vinyl chloride in which 
it is soluble is reacted to give the polymer in which it is less soluble. 
After the initially charged vinyl chloride has been reacted and the vinyl 
chloride delay begun, the pressure essentially stabilizes over the 
remaining polymerization period and eventually decays. This procedure 
avoids uncontrollable ethylene pressure rises. 
For preparing copolymers having a Tg of about 0.degree. to 20.degree. C., 
make-up ethylene may be used in suitable pressure reactors. Make-up 
ethylene is usually that amount needed to maintain the initial pressure. 
It is preferred to make such copolymers (Tg=0.degree.-20.degree. C.) by 
increasing the initial vinyl chloride monomer charge and increasing 
ethylene pressure, for example to 1000 psig. 
As mentioned, the reaction is generally continued until the polymerization 
reaction is no longer self-sustaining, desirably until the residual vinyl 
chloride content is below 0.5%. The completed reaction product is removed 
from the presence of ethylene and then maintained at a temperature above 
the Tg of copolymer while sealed from the atmosphere. The reaction mixture 
can also be transferred to a degasser with removal of ethylene. The 
unreacted vinyl chloride monomer content is reduced by its reaction with a 
vinyl acetate addition. 
Another method for producing the vinyl chloride-ethylene copolymers 
comprises first forming an aqueous emulsion of vinyl chloride and the 
polyvinyl alcohol stabilizing agent. The reactor is pressurized with 
ethylene and the resulting reaction mixture is adjusted to a temperature 
from about 10.degree. to 30.degree. C. Polymerization is initiated by the 
addition of a free radical source at a rate such that the reaction mixture 
is brought to a temperature from 45.degree. to 85.degree. C., preferably 
50.degree. to 60.degree. C., within a period of 1 hour or less, preferably 
30 minutes. The polymerization is continued until the rate of the 
polymerization begins to reduce. The major portion of the vinyl chloride 
is then added to the reaction vessel as a delay. 
Although the water resistance of the vinyl chloride-ethylene copolymer 
emulsions of this invention is surprisingly enhanced and unexpected since 
polyvinyl alcohol is present as the stabilizing agent, the water 
resistance can be further increased by crosslinking the hydroxyl sites on 
the polyvinyl alcohol polymer, which is believed to be incorporated into 
the copolymer, with crosslinking agents. There are many known agents for 
crosslinking polyvinyl alcohol and these include formaldehyde and other 
aldehydes, in particular dialdehydes such as glutaraldehyde and glyoxal; 
dimethylol urea, tetrabutyl titanate, bis-3-methoxyl propylidene, 
pentaerythritol; diazonium and tetrazonium salts, boric acid. Polyvinyl 
alcohol may also be crosslinked by radiation. Other agents which might be 
used are those known to crosslink cellulose, for example N-methylol and 
N-methylol ether derivatives of amines, amides and ureas, such as 
dimethylol dihydroxy ethylene urea and ethyl-N,N-dimethylol carbamate; 
diepoxides such as diglycidyl ether; ethyleneamine derivatives; divinyl 
sulphone and bis-(2-hydroxyethyl)sulphone; epichlorohydrin; phosgene and 
diacid-dichlorides; and 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone. 
Such crosslinking agents typically are added to the polymer emulsion just 
prior to the coating step in a 1 to 10 wt% range, based on emulsion 
solids. Acid catalysts such as phosphoric acid, hydrochloric acid, 
p-toluenesulfonic acid, and oxalic acid are often added to catalyze the 
crosslinking reaction upon heating of the polymer films or coatings. 
The polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymer 
emulsions may be used to prepare container coating compositions which, 
when applied to a metal substrate and cured, provide a polymer coating 
possessing surprising and enhanced water resistance. Such container 
coating compositions generally involve admixing the copolymer emulsions 
with crosslinking resins, coalescing agents and acid components all well 
known in the metal container coating art such as melamine formaldehydes, 
epoxies, dialdehydes, amines, diols, acid catalysts and organic 
co-solvents. A general can coating composition would comprise (a) about 45 
to 95 wt% copolymer emulsion, (b) about 5 to 40 wt% crosslinking resin, 
based on solids, (c) up to 10 wt% organic cosolvent (coalescing agent) 
and, optionally, (d) up to 5 wt% acid catalyst. An illustrative container 
coating composition would be a vinyl chloride-ethylene copolymer emulsion 
according to the invention and Cymel 303 melamine formaldehyde, 90/10 wt%, 
40 wt% solids in water/diethylene glycol monoethylether acetate (90/10 
wt%). These compositions are then applied to metal substrates such as 
steel or aluminum by spraying, dipping, roll coating or other application 
methods well known in the can coating art and cured by heating. 
The polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymer 
emulsions of the invention exhibit interesting rheological properties 
which are evident under conditions of moderate to high shear. Data 
obtained using a Haake Rotoviscometer, Model RV100, with shear rates from 
0-20,000 sec.sup.-1, suggests that such emulsions would have useful flow 
and leveling characteristics. It also suggests that coating compositions 
containing such emulsions could be applied with a direct and/or indirect 
roll coater. High speed, coil applied roll coatings impart shear rates of 
several thousand seconds.sup.-1.

The following examples are provided to illustrate the invention and are not 
intended to restrict the scope thereof. Test procedures used in evaluating 
the vinyl chloride copolymer resins for can coatings: 
Blushing: 
Blushing (film whitening) is observed immediately following removal of 
coated aluminum panel from test solution and rated using the following 
scale: 
Rating scale 10-0 (10 excellent or not change) 
10=No Blush 
8=Faint Blush 
6=Moderate Blush 
4=Definite 
2=Very White 
0=Terrible, Film Lifts 
Inpact Resistance: 
ASTM D 2794-69 
Pencil Hardness: 
ASTM D 3363-74 
Metal Adhesion: 
ASTM D 3359-78 using Ericsen Type 295 Adhesion tester 
MEK Resistance: 
A cotton swab saturated with MEK is rubbed back and forth across coated 
panel until coating is removed or until 100 rubs is reached. One back and 
forward movement across test panel constitutes one rub. 
EXAMPLE 1 
The polymerization of various vinyl chloride-ethylene copolymer emulsions 
of Runs 1-26 was carried out in a pressure vessel equipped with a jacket 
and an agitation system involving turbine blades. 
In preparing the copolymer emulsion of Run 1 the following initial charge 
was introduced into the reaction vessel: 
______________________________________ 
INITIAL CHARGE 
______________________________________ 
Distilled water 555 g 
Ferrous ammonium sulfate 
0.9 g 
Sequestrine 30A.sup.a 2.7 g 
Vinol .RTM. 205.sup.b PVOH (12% solution) 
854 g 
______________________________________ 
.sup.a Ethylenediamine tetraacetic acid sodium salt marketed by CibaGeigy 
as a 30% aqueous solution. 
.sup.b An 87 to 89 mole % hydrolyzed PVOH marketed by Air Products and 
Chemicals, Inc. 
The pH of the above charge was adjusted between 4.0 and 4.5 with acetic 
acid. 
The vessel contents were agitated at 200 rpm and purged three times with 
ethylene (25 psig). Vinyl chloride monomer (240 g) was then added and the 
reactor was heated to 55.degree. C. and pressurized with ethylene (875 
psig). The agitation was increased to 900 rpm and 7 ml of 10% aqueous 
solution of erythorbic acid (pH 4.5) was pumped into the reactor. After 
the temperature and pressure had been equilibrated, the polymerization was 
initiated with a 1% aqueous hydrogen peroxide solution. After the rate of 
polymerization began to decrease (substantially all the vinyl chloride had 
polymerized with ethylene), the remaining vinyl chloride monomer (1,415 g) 
was added over a 4 hr period maintaining the polymerization temperature of 
55.degree. C. using approximately 1.2 g hydrogen peroxide as a 1% solution 
and 2.7 g erythorbic acid as the activator. Additional oxidant and 
reductant were used after the vinyl chloride monomer had been added to 
complete polymerization. A total of 1.67 g hydrogen peroxide as a 1% 
solution and 5.0 g erythorbic acid were used for the entire 
polymerization. The ethylene pressure was allowed to "float" during the 
polymerization without makeup or withdrawal. The emulsion was transferred 
to a degasser and the unreacted vinyl chloride monomer reduced to less 
than 10 ppm by the addition of vinyl acetate (15 g) followed by t-butyl 
hydroperoxide (4 g) and erythorbic acid (3 g), ferrous ammonium sulfate 
(0.2 g ) and sequestrine 30A (0.8 g) in water (50 g). The vinyl 
chloride-ethylene copolymer of Run 1 was 83 wt% vinyl chloride, 17 wt% 
ethylene and had a Tg of about 30.degree. C. Emulsion solids were about 
55%. 
Table 1 shows the amounts of the various monomers and other polymerization 
components for Runs 2-26 as well as physical data for the resulting 
emulsions. 
In general, for runs 2-26 the above procedure was modified as follows: 
The polymerization was initiated at 52.degree. C. and the desired ethylene 
pressure, usually 875 psig to afford a copolymer having a Tg of about 
20.degree. to 35.degree. C. and suitable for can coating formulations. 
Upon initiation by the addition of the oxidant (H.sub.2 O.sub.2) at a 
fixed rate, the temperature of the polymerization reaction mixture was 
allowed to rise to 55.degree. C. where it was maintained automatically by 
the heat exchange function of the reaction vessel jacket as is well known 
in the art. Concomitantly, the pressure would rise, for example from 875 
psig to almost 950 psig. The jacket temperature began to drop after 
initiation and, usually, after about one half hour would reach a minimum, 
namely about 40.degree. C. In approximately 5 to 10 minutes the jacket 
temperature usually began to rise corresponding to the time when the rate 
of polymerization began to decrease. When the jacket temperature 
approached 45.degree. to 50.degree. C., the amount of oxidant consumed was 
recorded and the vinyl chloride delay commenced. Again, this initial, or 
prepolymerization, step avoids the build up of excess unreacted vinyl 
chloride monomer in the sealed reaction vessel and reduces the possibility 
of the ethylene vessel pressure approaching the upper pressure limitation 
of the vessel. If the vinyl chloride monomer delay were commenced at 
polymerization initiation, an amount of cooling ability, which may be in 
excess of that of the reactor, would be required to permit reaction of 
sufficient vinyl chloride and ethylene monomer so as to prevent excessive 
pressure rise which could exceed the limits of the vessel. Typical plant 
reactors are not designed to withstand such conditions. 
In those Runs in which a terpolymer was made, the olefinically unsaturated 
comonomer was added in the delay mode upon initiation of the 
polymerization reaction. 
TABLE 1 
__________________________________________________________________________ 
RUN 
1 2 3 4 5 6 7 8 9 10 11 12 13 
__________________________________________________________________________ 
VINYL CHLORIDE 83 83 83 81 78 80 85 
81 83 78 81 93 85 
ETHYLENE 17 17 17 19 21 20 15 
19 17 22 18 6 15 
COMONOMER (%) -- 3% AAm 
-- -- -- -- -- 
-- -- -- 1% 1% 1% 
AA AA AA 
POLYVINYL ALCOHOL (%) 
5 SLS 5 5 6 6 6 10 10.sup.A 
10.sup.A 
5 5 5 
REDOX SYSTEM H.sub.2 O.sub.2 
NH.sub.4 S.sub.2 O.sub.4 
NH.sub.4 S.sub.2 O.sub.4 
H.sub.2 O.sub.2 
(SAME FOR RUNS 4-13) 
EA SFS SFS EA 
ACCELERATED -- -- -- 8 6 7 4 1 2 1 6 3.5 15 
SEDIMENTATION (%) 
Tg (.degree.C.) 30 30 27 21.5 
22.5 
29 34 
34 33.5 
25 26.5 
25 30 
SOLIDS (wt %) -- 50 55 55 46 51 52 
50 51.5 
49 52 52 49 
DRY FILM 
PENCIL HARDNESS -- 2H 5H 4H 5H 5H 5H 
4H 4H 5H 4H 4H 5H 
MEK RUBS -- 6 3 3 1 2 4 3 3 1 3 3 2 
BOILING WATER (2 min) 
BLUSH RESISTANCE 
-- 7 6 8+ 9 9 7 9+ 9 7+ 9+ 10 9 
AL ADHESION -- 0 9 10 10 10 10 
10 10 10 10 10 10 
PENCIL HARDNESS -- 5B 4B H 2B -- B H H H 2B HB F 
WATER SOAK 
BLUSH RESISTANCE 
-- 10 10 10 10 10 10 
10 10 10 10 10 10 
PENCIL HARDNESS -- B HB 4H 2H 4H F HB 5H 3H 3H -- 5H 
__________________________________________________________________________ 
RUN 
14 15 16 17 18 19 20 21 22 23 24 25 26 
__________________________________________________________________________ 
VINYL CHLORIDE 80 78 78 77 -- 79 81 -- -- -- -- 74 -- 
ETHYLENE 18 19 21 22 -- 20 18 -- (750 
(700 
(650 
26 (1200 psi 
psig) 
psig) 
psig) 
(1100 
& 
psig) 
make-up 
COMONOMER (%) 2% AA 
3% 1% 3% 3% 1% 1% -- -- -- -- -- -- 
AA AA AA AA AAm 
N--i-BMA 
POLYVINYL ALCOHOL (%) 
5 5 6 6 6 5 5 4.4 4 4 4 5 
partial 
delay 
REDOX SYSTEM H.sub.2 O.sub.2 
(SAME FOR RUNS 14-26) 
ACCELERATED 10 20 1 1 -- 9 7 Extreme- 
13 20 30 4 Aborted 
SEDIMENTATION (%) ly gritty 
Tg (.degree.C.) 23 27.5 
25.5 
34 -- 27.5 
38.5 discard 
26 29 -- 6 Pressure 
-- -- -- 48 Rose 
&lt;1400 
psi 
SOLIDS (wt %) 53.7 
53 49.5 
49 -- 53 45.6 
DRY FILM 
PENCIL HARDNESS 4H 4H 4H 4H 5H 4H 5H 
MEK RUBS 3 3 3 3 3 3 20 
BOILING WATER (2 min) 
BLUSH RESISTANCE 
8+ 7+ 10 10 8 9+ 10 
AL ADHESION 10 8 10 10 10 10 10 
PENCIL HARDNESS 2B 2B HB H H 2B 5H 
WATER SOAK 
BLUSH RESISTANCE 
9+ 10 10 10 10 10 10 
PENCIL HARDNESS H 3H -- -- F 3H 5H 
__________________________________________________________________________ 
##STR1## 
AA = acrylic acid 
AAm = acrylamide 
N--i-BMA = N--ibutoxymethylacrylamide 
EA = erythorbic acid 
SFS = sodium formaldehyde sulfoxylate 
SLS = sodium lauryl sulfate 
The comparison of Run 2 with Run 3 shows the effect of polyvinyl alcohol in 
place of an ionic surfactant in the ethylene-vinyl chloride polymerization 
recipe. The dry film tensile hardness is improved and the adhesion of the 
film to aluminum is improved significantly as shown by its ability to 
withstand boiling water. When Run 3 was repeated using a salt-free system 
in Run 4 (erythorbic acid instead of sodium formaldehyde sulfoxylate as 
reductant), the blush resistance was improved and the hardness retention 
of the film after exposure to water was significantly better. 
Runs 5-7 demonstrate the effect of increasing the polyvinyl alcohol content 
to about 6 wt%. An improvement in blush resistance was attained over Run 
3. A slight improvement in blush resistance was obtained in Run 8 by the 
addition of 4 wt% more polyvinyl alcohol to a 10 wt% total polyvinyl 
alcohol level. 
Runs 11-15 show the effect of adding one, two and three percent acrylic 
acid to a five percent polyvinyl alcohol containing ethylene-vinyl 
chloride polymerization recipe. Here the blush resistance and the hardness 
of the film has been improved. Runs 16-18 show the effect of increasing 
the polyvinyl alcohol content to 6 wt% at one and three percent acrylic 
acid levels. Outstanding blush resistance and improvement in boiling water 
film hardness were demonstrated. 
Runs 19 and 20 show the five percent polyvinyl alcohol stabilized vinyl 
chloride-ethylene copolymers also comprising a nitrogen-containing 
monomer, namely acrylamide and N-isobutoxymethylacrylamide, respectively. 
Run 19 showed good blush resistance and Run 20 showed excellent blush 
resistance and hardness. In addition, a substantial improvement in MEK 
rubs was obtained in Run 20 due to the self-crosslinking nature of 
N-isobutoxymethylacrylamide. 
Run 21 used a partial delay of polyvinyl alcohol to the polymerization 
recipe. Initially 15% (0.66 g) of the total polyvinyl alcohol (4.4 g) was 
added prior to initiation and the remainder added by delay addition to the 
reaction mixture with the vinyl chloride monomer. A suspension-type 
polymer was obtained (extremely gritty). This Run demonstrates the need 
for at least 3 wt%, preferably 4 wt%, polyvinyl alcohol in the reaction 
medium when forming the prepolymer. 
Runs 22-24 were performed at ethylene pressure of 750, 700 and 650 psig, 
respectively, without ethylene makeup and yielded product which, although 
low in grits, showed unacceptably high unaccelerated sedimentation values. 
The maximum acceptable accelerated sedimentation was set as 10%. These 
Runs show that with no ethylene make up, ethylene pressures of greater 
than about 750 psig are required to provide the stable vinyl 
chloride-ethylene copolymer emulsion according to the procedure set forth 
for Run 2. 
Runs 25 and 26 showed that 1100 psig and no ethylene make up provided an 
acceptable emulsion even though a large amount of redox system was used, 
while 1200 psig and make up ethylene resulted in aborting the run due to 
uncontrollable pressure rise. 
EXAMPLE 2 
In this example several vinyl chloride-ethylene-acrylic acid copolymer 
emulsions from Example 1 were tested with and without external 
cross-linkers as films deposited by a #8 wire rod onto aluminum panels and 
cured for 10 minutes at 380.degree. F. The resultant data are set forth in 
Table 2. It is apparent from the data that combining the polyvinyl 
alcohol/vinyl chloride-ethylene copolymers of the invention with 
cross-linking agents provide a container coating formulation which can 
deposit a resin film having good water resistance and hardness. 
TABLE 2 
__________________________________________________________________________ 
EMULSION RUN 
2 2 3 3 9 9 11 11 11 
__________________________________________________________________________ 
CROSS-LINKER -- 
10% -- 
10% -- 
10% -- 10% 10% 
(% solids/solids) CYMEL303 CYMEL303 CYMEL303 DER732 
CYMEL303 
pH -- 
4.3 -- 
4.6 -- 
8.0 5.3 
-- -- 
DRY FILM 
PENCIL HARDNESS 2H 
5H 5H 
5H 4H 
5H 4H 4H 5H 
MEK DBL RUB 6 10 3 4 3 17 3 3 3 
BOILING WATER 
BLUSH RESISTANCE (2 min) 
7 -- 6 -- 9 10 9+ 8 -- 
BLUSH RESISTANCE (30 min) 
-- 
1 0 0 8 10 9 -- 7 
AL ADHESION (2 min) 
0 -- 9 -- 10 
-- 10 9+ -- 
AL ADHESION (30 min) 
-- 
10 10 
0 10 
10 10 -- 4 
PENCIL HARDNESS (2 min) 
5B 
-- 4B 
-- 5H 
-- 2B 4B -- 
PENCIL HARDNESS (30 min) 
-- 
4B 6B 
5B H 3H F -- 3B 
24 HOUR SOAK (ACID/WATER) 
BLUSH RESISTANCE (ACID) 
-- 
10 -- 
5 10 
10 10 -- 10 
BLUSH RESISTANCE (WATER) 
10 
10 10 
10 10 
10 10 10 -- 
AL ADHESION (ACID) 
-- 
7 -- 
10 6 10 10 -- 10 
AL ADHESION (WATER) 
-- 
4 -- 
10 10 
10 10 9 -- 
PENCIL HARDNESS (ACID) 
-- 
B -- 
F 3H 
4H H -- 2H 
PENCIL HARDNESS (WATER) 
B B HB 
H 5H 
4H 3H HB -- 
__________________________________________________________________________ 
EMULSION RUN 
11 11 12 
12 15 15 15 
15 
__________________________________________________________________________ 
CROSS-LINKER 10% 10% -- 
10% -- 10% -- 
10% 
(% solids/solids) CYMEL303 
RESIMENE CYMEL303 CYMEL303 RESIMENE 
MC 730 730 
pH -- -- -- 5.8 
-- 5.8 
5.7 
DRY FILM 
PENCIL HARDNESS 5H 5H 4H 
4H 4H 5H 5H 
5H 
MEK DBL RUB 10 3 3 4 3 20 3 12 
BOILING WATER 
BLUSH RESISTANCE (2 min) 
-- -- 10 
-- 7+ -- 8 6 
BLUSH RESISTANCE (30 min) 
9 6 10 
9 6 10 -- 
-- 
AL ADHESION (2 min) 
-- -- -- 
-- 8 -- 10 
6 
AL ADHESION (30 min) 
10 7 10 
10 10 10 -- 
-- 
PENCIL HARDNESS (2 min) 
-- -- -- 
-- 2B -- HB 
5B 
PENCIL HARDNESS (30 min) 
2B 6B H F 4B H -- 
-- 
24 HOUR SOAK (ACID/WATER) 
BLUSH RESISTANCE (ACID) 
10 -- 10 
10 9 10 -- 
-- 
BLUSH RESISTANCE (WATER) 
-- -- 10 
10 10 10 10 
10 
AL ADHESION (ACID) 
10 -- 10 
10 5 10 -- 
-- 
AL ADHESION (WATER) 
-- -- 10 
10 10 10 10 
7 
PENCIL HARDNESS (ACID) 
4H -- H H 5B H -- 
-- 
PENCIL HARDNESS (WATER) 
-- -- 4H 
3H 3H 4H H 3B 
__________________________________________________________________________ 
EMULSION RUN 
15 16 
17 
17 19 19 
__________________________________________________________________________ 
CROSS-LINKER 5% -- 
-- 
10% -- 10% 
(% solids/solids) DER732 CYMEL303 CYMEL303 
MC 
pH 4.7 -- 
-- 
-- -- 4.6 
DRY FILM 
PENCIL HARDNESS 5H 4H 
4H 
5H 4H 5H 
MEK DBL RUB 2 3 3 18 3 3 
BOILING WATER 
BLUSH RESISTANCE (2 min) 
10 10 
10 
10 9+ -- 
BLUSH RESISTANCE (30 min) 
-- 10 
10 
10 -- 4 
AL ADHESION (2 min) 
10 -- 
10 
-- 10 -- 
AL ADHESION (30 min) 
-- 10 
10 
10 -- 10 
PENCIL HARDNESS (2 min) 
4B -- 
H -- 2B -- 
PENCIL HARDNESS (30 min) 
-- HB 
H H -- H 
24 HOUR SOAK (ACID/WATER) 
BLUSH RESISTANCE (ACID) 
-- 10 
10 
10 -- 10 
BLUSH RESISTANCE (WATER) 
10 10 
10 
10 10 10 
AL ADHESION (ACID) 
-- 10 
10 
10 -- 10 
AL ADHESION (WATER) 
10 10 
10 
10 10 10 
PENCIL HARDNESS (ACID) 
-- H -- 
4H -- 2H 
PENCIL HARDNESS (WATER) 
H 4H 
3H 
5H 3H 4H 
__________________________________________________________________________ 
DER 732 is a water based epoxy resin marketed by Dow Chemical. 
CYMEL 303 is a melamine formaldehyde marketed by American Cyanamid. 
RESIMENE 730 is a melamine formaldehyde marketed by Monsanto. 
MC is methyl cellosolve. 
EXAMPLE 3 
In this example experimental runs for the preparation of vinyl 
chloride-ethylene copolymer emulsions set forth as Runs 27-36 in Table 3 
were conducted using substantially the same procedure for preparing 
polyvinyl alcohol-stabilized vinyl chloride-ethylene copolymer emulsions 
as described under Example 1. The major difference was the emulsifying 
system and its mode of addition to the polymerization reaction medium. The 
emulsifying system were among those taught in U.S. Pat. No. 3,689,447 as 
being functionally equivalent. Run 37 is a polyvinyl alcohol/vinyl 
chloride-ethylene copolymer emulsion according to the present invention. 
TABLE 3 
__________________________________________________________________________ 
ETHYL- 
ENE 
EMUL- 
EMULSIFYING 
MODE OF PRES- 
OXI- 
REDUC- 
% GRITS ACCELERATED 
SION SYSTEM ADDITION SEED 
SURE DANT 
TANT SOLIDS 
100 MESH 
SEDIMENTATION 
__________________________________________________________________________ 
27 SLS (3%) Batch Yes 900 H.sub.2 O.sub.2 
EA run coagulated 
28 SLS (3%) Batch Yes 900 APS SFS run coagulated 
29 DS-10 (3%) 
Batch Yes 900 APS SFS run coagulated 
30 DS-10 (3%) 
Delay No 850 APS SFS run coagulated 
31 POLYSTEP Delay No 850 APS SFS run coagulated 
B-27 (3%) 
32 Nat.250LR (2%) 
Nat.250LR-Batch 
No 850 APS SFS run coagulated 
Igepal CO 990 
Igepal CO 990- 
(0.5%) Delay 
33 Nat.250LR (2%) 
Nat.250LR-Batch 
No 900 H.sub.2 O.sub.2 
EA 46.8 74 0.7 
SLS (0.5%) 
SLS-Delay 
34 Nat.250LR (2%) 
Nat.250LR-Batch 
No 900 APS SFS 51.7 1470 2.1 
SLS (0.5%) 
SLS-Delay 
35 SLS (2.0) 
Delay No 800 APS SFS 50 1 g. amt. 
0.1 
36 Nat.250LR (2.0%) 
Nat.250LR-Batch 
No 900 APS SFS 48 79 1.0 
Igepal CO990 
Igepal CO 990 
(1.5%) Delay 
37 Vinol 205 (6%) 
Batch Yes H.sub.2 O.sub.2 
EA 
__________________________________________________________________________ 
SLS = sodium lauryl sulfate 
DS-10 = dodecyl benzene sulfonate, sodium salt 
Igepal CO990 = nonyl phenoxy poly(ethyleneoxy)ethanol 
Polystep B27 = octyl phenoxy poly(ethyleneoxy)ethanol sulfate ester, 
sodium salt 
SFS = sodium formaldehyde sulfoxylate 
APS = ammonium persulfate 
EA = erythorbic acid 
Natrosol 250LR = hydroxyethyl cellulose 
As can be seen from Table 3, the indicated anionic, nonionic and colloid 
stabilizers were used alone and in combination in attempting to prepare 
stable vinyl chloride-ethylene copolymer emulsions. Each of the common 
techniques used in the art to prepare stable polymer emulsions were tried, 
i.e. the surfactants were batch-added all at once or delayed into the 
reaction medium along with emulsion seeding being used in several runs. 
Runs 27-31 using three different anionic surfactants, namely sodium lauryl 
sulfate, sodium dodecyl benzene sulfonate and the sodium salt of 
nonylphenoxy poly(ethyleneoxy)ethanol sulfate ester did not afford a 
stable emulsion product when added to the initial charge and a seed 
emulsion was prepared. Rather the reaction medium coagulated during the 
polymerization process. Likewise for Run 32 which used a surfactant system 
comprising hydroxyethyl cellulose and a nonylphenoxy(polyethoxy)ethanol. 
Each of the polymerization runs that coagulated was attempted several 
times with the same result. 
However, four relatively stable vinyl chloride-ethylene copolymer emulsions 
were prepared. Runs 33, 34 and 36 which used stabilizer systems comprising 
a protective colloid (hydroxyethyl cellulose) and a nonionic or anionic 
surfactant successfully yielded an emulsion when the colloid was added all 
up front to the reaction medium and the surfactant was delayed in during 
the polymerization process. Runs 33 and 34 were identical except for the 
use of two different redox systems, namely hydrogen peroxide/erythorbic 
acid in Run 33 and ammonium persulfate/sodium formaldehyde sulfoxylate in 
the Run 34. These emulsions were suitable for can coating composition 
testing. 
Run 35 was prepared using sodium lauryl sulfate as the sole surfactant in a 
delay surfactant procedure and starting the vinyl chloride monomer delay 
shortly after polymerization initiation. Run 35 had a very large amount of 
grit and would not be sufficiently stable to be commercially acceptable. 
It was, nevertheless, tested in the can coating composition. 
TABLE 4 
__________________________________________________________________________ 
EMULSION ONLY* FORMULATED EMULSION** 
DRY BOILING WATER 
24 HOUR DRY BOILING WATER 
24 HOUR 
FILM (2 min.) WATER SOAK FILM (2 min.) WATER SOAK 
RUN PENCIL 
BLUSH 
ADH. 
pH BLUSH 
ADH. 
pH PENCIL 
BLUSH 
ADH. 
pH BLUSH 
ADH. 
pH 
__________________________________________________________________________ 
33 2H 6 0 B 8 0 2H 2H 7 10 H 10 10 2H 
34 2H 1 0 &lt;2B 
7 0 HB 2H 1 10 B 9 10 2H 
35 F 4 0 2B 7 -- HB 2H 1 2 &lt;2B 
4 0 HB 
36 H 1 0 &lt;2B 
6 0 &lt;2B 
2H 3 10 HB 10 10 2H 
37 2H 8 0 F 8 0 2H 4H 9 10 2H 10 10 2H 
__________________________________________________________________________ 
*Dried 2 min. at 380.degree. F. over aluminum 
**Formulation: 
Emulsion 82 wt % solids or solids 
Celanese 5003 Dispersion 9 wt % 
Cymel 303 malamine formaldehyde 9 wt % 
n-Butanol:Butyl Cellosolve (1:1) 
Benzene sulfonic acid salt 4 wt % based on Cymel 303 solids 
Formulation coating was baked 4 min at 380.degree. F. 
Pencil Hardness: H &gt; F &gt; B 
The emulsions of Runs 33-36 and the emulsion of Run 37 which was a 6% 
polyvinyl alcohol stabilized vinyl chloride-ethylene copolymer emulsion 
according to the invention made in a pilot plant reactor were evaluated, 
both as is and in a can coating composition containing epoxy and melamine 
resins, for blushing, metal adhesion and tensile hardness after exposure 
to (1) boiling water for 2 min. and (2) a 24 hr. water soak. The results 
of the testing are set forth in Table 4. 
The most critical test with regard to the water resistant property of the 
emulsion copolymer, both as is and in the can coating composition, is the 
blush test. Blushing is an inherent characteristic of the polymer exposed 
to water. For the most part, such blushing of the copolymer cannot be 
reduced by can coating formulating. On the other hand, loss of adhesion to 
the aluminum substrate can be countered by appropriate formulating. The 
aluminum substrate used in the comparative runs of this Example 3 was a 
commercial aluminum substrate which is used in the can manufacturing 
industry as opposed to the aluminum substrate used with the tests in 
Example 2 which was a specially treated non-commercial substrate. 
It can be see from the data in Table 4 that the polyvinyl alcohol 
stabilized vinyl chloride-ethylene emulsion copolymer showed unexpectedly 
superior water resistance according to the sensitive blush test in boiling 
water and the water soak compared to vinyl chloride-ethylene emulsion 
copolymers stabilized with other protective colloids and surfactants. This 
superior water resistance is even more surprising in view of the fact 
that, according to the prior art, polyvinyl alcohol stabilized emulsion 
copolymers are notoriously water sensitive. 
When films of the emulsion copolymers themselves were tested, the emulsions 
of Runs 34 and 36 which used the hydroxyethyl cellulose in combination 
with an anionic and nonionic surfactant, respectively, showed exceedingly 
poor water resistance. The emulsion of Run 35, using solely an anionic 
surfactant stabilizing system, showed very poor water resistance. The 
emulsion of Run 33, which used the same stabilizing system as the emulsion 
of Run 34 but used a nonionic redox system, demonstrated better water 
resistance according to the blush tests. However, it was still inferior to 
that of the polyvinyl alcohol stabilized emulsion of Run 37. 
When the emulsions were formulated in a can coating composition and tested, 
the emulsions of Runs 34, 35 and 36 again showed poor blushing 
characteristics in boiling water compared to the emulsions of Runs 33 and 
37. Again, in spite of the presence of polyvinyl alcohol in the copolymer 
emulsion, the water resistance of the can coating composition containing 
the emulsion of Run 37 was surprisingly superior to the other vinyl 
chloride-ethylene copolymer emulsions. 
EXAMPLE 4 
This Example 4 demonstrates that the use of a fully hydrolyzed polyvinyl 
alcohol in combination with a partially hydrolyzed polyvinyl alcohol did 
not result in stable polyvinyl alcohol/vinyl chloride-ethylene copolymer 
emulsions. Runs 38-41 used a combination of Vinol 107 fully hydrolyzed 
polyvinyl alcohol and Vinol 205 partially hydrolyzed polyvinyl alcohol and 
an erythorbic acid-hydrogen peroxide redox system generally following the 
procedure of Example 1. It can be seen from Table 5 that Runs 38-41 all 
yielded unsuitable product. 
TABLE 5 
______________________________________ 
Vinol 107* Vinol 205 
(wt %) (wt %) Reaction Product 
______________________________________ 
Run 38 
4.15 5 Extremely viscous and dilatant 
Run 39 
5 5 Extremely viscous, dilatant 
gritty emulsion 
Run 40 
5 5 Extremely gritty emulsion 
Run 41 
2.5 5 Run aborted; extremely gritty 
emulsion 
______________________________________ 
*A 98 to 98.8 mole % hydrolyzed PVOH marketed by Air Products and 
Chemicals, Inc. 
STATEMENT OF INDUSTRIAL APPLICATION 
The stable polyvinyl alcohol/vinyl chloride-ethylene copolymer emulsions 
according to the invention are useful in container coating compositions in 
that they provide a polymer coating on a metal surface possessing enhanced 
water resistance, improved dry coating tensile hardness and improved 
adhesion of the coating to the surface even after exposure to water.