CAN COATINGS FROM NITRILE COPOLYMER LATEXES

TRADUCTION NON-DISPONIBLE

English Abstract

CAN COATINGS FROM NITRILE COPOLYMER LATEXES
Abstract of the Disclosure
Metal surfaces such as steel, tin-plated steel,
and aluminum are coated and protected from corrosion by
means of an impermeable coating from a latex of a high
nitrile polymer.

Claims

THE EMBODIMENTS OF THE PRESENT INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A metal sheet coated on at least one side thereof
with an impermeable layer of a polymer produced by the poly-
merization of a major proportion of a monounsaturated nitrile
and a minor proportion selected from the group consisting of
another monovinyl monomer component copolymerizable with said
nitrile, and another monovinyl monomer component copolymerizable
with said nitrile in the presence of a preformed diene rubber.
2. The coated sheet of claim 1 wherein the polymer
is prepared by polymerization of 100 parts by weight of
(A) from 60 to 90% by weight of at least one nitrile
having the structure
<IMG>
wherein R is hydrogen, a lower alkyl group having
from 1 to 4 carbon atoms, or a halogen, and
(B) from 10 to 40% by weight based on the combined
weight of (A) and (B) of at least one member
selected from the group consisting of
(1) an ester having the structure
<IMG>
wherein R1 is hydrogen, an alkyl group
having from 1 to 4 carbon atoms, or a
halogen, and R2 is an alkyl group having
from 1 to 6 carbon atoms,
(2) an alpha-olefin having the structure
<IMG> wherein R' and R" are alkyl
groups having from 1 to 7 carbon atoms,
(3) a vinyl ether selected from the group con-
sisting of methyl vinyl ether, ethyl vinyl
ether, the propyl vinyl ethers, and the butyl
vinyl ethers,
13

(4) vinyl acetate, and
(5) styrene,
in the presence of from 0 to 40 parts by weight of
(C) a rubbery polymer of a conjugated diene monomer
selected from the group consisting of butadiene
and isoprene and a comonomer selected from the
group consisting of styrene, a monomer having the
structure <IMG> wherein R has the foregoing
designation, and an ester having the structure
<IMG> wherein R and R2 have the
foregoing respective designations, said rubbery
polymer containing from 50 to 100% by weight
of polymerized conjugated diene and from 0 to 50%
by weight of comonomer.
3. The coated sheet of claim 2 wherein (A) is acryloni-
trile.
4. The coated sheet of claim 3 wherein (B) is methyl
acrylate.
5. The coated sheet of claim 3 wherein (B) is styrene.
6. The process comprising coating at least one side of
a metal sheet with a layer of a latex of a polymer produced by
polymerization of a major proportion of a monounsaturated nitrile
and a minor proportion selected from the group consisting of
another monovinyl monomer component copolymerizable with said
nitrile, and another monovinyl monomer component copolymerizable
with said nitrile in the presence of a preformed diene rubber,
drying said layer and heating the thus-coated sheet for a short
time at a temperature in the range of from 200 to 300°C.
7. The process of claim 6 wherein the polymer is
prepared by polymerization in aqueous emulsion of 100 parts by
weight of
14

(A) from 60 to 90% by weight of at least one nitrile
having the structure <IMG>
wherein R is hydrogen, a lower alkyl group having
from 1 to 4 carbon atoms, or a halogen, and
(B) from 10 to 40% by weight based on the combined
weight of (A) and (B) of at least one member
selected from the group consisting of
(1) an ester having the structure <IMG>
wherein R1 is hydrogen, an alkyl group having
from 1 to 4 carbon atoms, or a halogen, and R2
is an alkyl group having from 1 to 6 carbon atoms,
(2) an alpha olefin having the structure
<IMG> wherein R' and R" are alkyl groups having
from 1 to 7 carbon atoms,
(3) a vinyl ether selected from the group
consisting of methyl vinyl ether, ethyl vinyl
ether, the propyl vinyl ethers, and the butyl
vinyl ethers,
(4) vinyl acetate, and
(5) styrene,
in the presence of from 0 to 40 parts by weight of
(C) a rubbery polymer of a conjugated diene monomer
selected from the group consisting of butadiene
and isoprene and a comonomer selected from the
group consisting of styrene, a monomer having
the structure <IMG> wherein R has the foregoing
designation, and an ester having the structure
<IMG> wherein R1 and R2 have the foregoing

respective designations, said rubbery polymer
containing from 50 to 100% by weight of polymer-
ized conjugated diene and from 0 to 50% by weight
of comonomer.
8. The process of claim 7 wherein (A) is acrylonitrile.
9. The process of claim 8 wherein (B) is methyl
acrylate.
10. The process of claim 8 wherein (B) is styrene.
16

Description

1~3~
CAN COATINGS FROM NITRILE COPOLYMER LATEXES
This invention relates to can coatings based on high
nitrile copolymer resins, and more particularly pertains to a
process for coating with an impervious coating cans and similar
materials with a latex of a high nitrile copolymer. --
Prior to our invention, it was not practical to use a
polymer latex, per se, as a can-coating agent. Cans made of
metal, such as tin-plated steel and aluminum, are normally coated
with a corrision-resistant coating to protect the contents on
long storage. This is particularly true when foods and bever-
ages are to be stored in the cans. Because the coatings which
usually result from use of polymer latexes as the coating agent
are not continuous coatings free of pinholes, and the like,
polymer coatings are usually applied to cans by means of organic
solvents. The use of organic solvents is both expensive and
hazardous.
We have discovered that continuous protective films
having good chemical resistance can be made from latexes of
certain nitrile copolymer latexes which are more fully described
below.
The polymer latexes most useful in the present invention
are those which result from the polymerization in emulsion of a
major proportion of an olefinically unsaturated nitrile, another
monomer component copolymerizable therewith and optionally a
preformed rubber component.
Usually the latex (or blend of latexes) used in this
invention will contain from about 20 to 45~ solids and will
have average particle sizes ranging from 500 to 3000 angstroms.
Thus, In accordance with the present teachings, there is
provided a metal sheet coated on at least one side thereof with
--1--
,~
fC

~3~
an i.mpermeable layer of a polymer produced by the polymeriza-
tion of a major proportion of a monounsaturated nitrile and a
minor proportion selected from the group consisting of another
monovinyl monomer component copolymerizable with the nitrile,
and another monovinyl monomer component copolymerizable with the
nitrile in the presence of a preformed diene rubber.
In accordance with a further embodiment a process is
provided which comprises coating at least one side of a metal
sheet with a layer of a latex of a polymer produced by polymer-
ization of a major proportion of a monounsaturated nitrile anda minor proportion selected from the group consisting of another
vinyl monomer component copolymerizable with the nitrile and an-
other monovinyl monomer component copolymerizable with the nitrile
in the presence of a preformed diene rubber, drying the layer
and heating the thus coated sheet for a short time at a tempera-
ture in the range of from 200 to 300C.
The polymers which are most useful in the process of
this invention include those produced by polymerizing a major
proportion of a monounsaturated nitrile, such as acrylonitrile,
and a minor proportion of another monovinyl monomer component
copolymerizable with said nitrile in aqueous emulsion, optionally
in the presence of a preformed diene rubber which may be a homo-
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'~

~1~}31~t~
polymer or a copolymer of a conjugated diene monomer~
The conjugated diene monomers useful in the present in-
vention include butadiene-1,3, isoprene, chloroprene, bromoprene,
cyanoprene, 2,3-dimethyl butadiene-1,3, 2-ethyl butadiene-1,3
2,3-diethyl butadiene-1,3, and the like. Most preferred for the r
purpose of this invention are butadiene-1,3 and isoprene because
of their ready availability and their excellent polymerization
properties.
The olefinically unsaturated nitriles useful in the
present invention are the alpha,beta-olefinically unsaturated
mononitriles having the structure CH2=C-CN
wherein R is hydrogen, a lower alkyl group having from 1 to 4
carbon atoms, or a halogen. Such compounds include acrylonitrile,
alpha-chloracrylonitrile, alpha-fluoroacrylonitrile, methacryloni-
trile, ethacrylonitrile, and the like. The most preferred olefini-
cally unsaturated nitriles in the present invention are acryloni-
trile and methacrylonitrile and mixtures thereof.
The other monovinyl monomer component copolymerizable
with the olefinically unsaturated nitriles and conjugated dienes
includes one or more of the esters of olefinically unsaturated
carboxylic acids, vinyl esters, vinyl ethers, alpha-olefins, vinyl
aromatic monomers, and others.
The esters of olefinically unsaturated carboxylic acids
include those having the structure CH2=1-COOR2
wherein Rl is hydrogen, an alkyl group having from 1 to 4 carbon
atoms, or a halogen, and R2 is an alkyl group having from 1 to 6
carbon atoms. Compounds of this type include methyl acrylate,
ethyl acrylate, the propyl acrylates~ the butyl acrylates, the amyl
acrylates, the hexyl acrylates; methyl methacrylate, ethyl
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methacrylate, the propyl methacrylates, the butyl methacrylates,
the amyl methacrylates, and the hexyl methacrylates; methyl
alpha-chloroacrylate, ethyl alpha~chloroacrylate, and the like.
Most: preferred in the present invention are methyl acrylate,
ethyl acrylate, methyl methacrylate, and ethyl methacrylate.
The alpha-olefins useful in the present invention are
those having at least 4 and as many as 10 carbon atoms having
the structure R~ wherein R' and R" are alkyl groups hav-
CH2=C
R"
ing from 1 to 7 carbon atoms, and more specially isobutylene,
2-methyl butene-l, 2-methyl pentene-l, 2-methyl hexene-l, 2-methyl
heptene-l, 2-methyl octene-l, 2-ethyl butene-l, 2-propyl pentene-l
and the like. Most preferred is isobutylene.
The vinyl ethers include methyl vinyl ether, ethyl vinyl
ether, the propyl vinyl ethers, the butyl vinyl ethers, methyl
isopropenyl ether, ethyl isopropenyl ether, and the like. Most
preferred as methyl vinyl ether, ethyl vinyl ether, the propyl
vinyl ethers, and the butyl vinyl ethers.
The vinyl esters include vinyl acetate, vinyl propionate,
the vinyl butyrates, and the like. Most preferred is vinyl acetate.
The vinyl aromatic monomers include styrene, alpha-methyl
styrene, the vinyl toluenes, the vinyl xylenes, and the like. Most
preferred is styrene.
Specific polymers useful in this invention are those
prepared by the polymerization of 100 parts by weight of (A) from
60 to 90% by weight of at least one nitrile having the structure
CH2=C-CN wherein R has the foregoing designation, and (B) from
R
10 to 40% by weight based on the combined weight of (A) and (B)
of at least one member selected from the group consisting of (1)
an ester having the structure CH2=f-COOR2 wherein Rl and R2 have
R
~ -3-
.

the foregoing respective designations, (2) an alpha-olefin havîng
the structure R~ wherein Rl` and Rl' have the foregoing
CH2=
R~
respective designations, (3) a vinyl ether selected from the
group consisting of methyl vinyl etherr ethyl vinyl ether, the
propyl vinyl ethers, and the butyl vinyl ethers, (4) vinyl ace-
tate, and (5) styrene, in the presence of from 0 to 40 parts by
weight of (C) a rubbery polymer of a conjugated diene monomer
selected from the group consisting of butadiene and isoprene and
optionally a comonomer selected from the group consisting of sty-
rene, a nitrile monomer having the structure CH2=C-CN wherein R
R
has the foregoing designation, and an ester having the structure
CH2-f-COOR wherein Rl and R2 have the foregoing respective
Rl
designations, said rubbery polymer containing from 50 to 100%
by weight of polymerized conjugated diene and from 0 to 50% by
weight of comonomer.
The polymer latexes useful in the present invention
can be prepared in aqueous emulsion by polymerization techniques
involving batch, continuous or intermittent addition of monomers
and other components. The polymerization is preferably carried
out in aqueous medium in the presence of an emulsifier and a
free radical generating polymerization initiator at a temperature
of from about 0 to 100C in the substantial absence of molecular
oxygen. The preparation of typical latexes useful in the present
invention are more fully described in U. S. Patents Nos. 3,426,102,
3,586,737 and 3,763,278.
The latexes of this invention are applied to the
degreased metal of the can to be coated by means of a doctor
knife or wire bar, a roller coater, a spray gun, by dipping the
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11~33~)8
metal into the latex, by flow coating, or by other means known
to lhose skilled in the coating art.
After the latex coating has been dried, the polymer
coating is dried at a temperature in the range of from 200 to
300C. Any of the usual metal sheet used for making cans
may be used including steel, tin-plated steel and aluminum.
This invention will be further illustrated in the
fGllowing examples wherein the amounts of ingredients are given
in parts by weight unless otherwise indicated.
Example l
A. A rubber latex was prepared by polymerizing with
continuous agitation at 45C in the substantial absence of
oxygen a mixture of the following ingredients:
_ngredient Parts
acrylonitrile 40
butadiene-1,3 60
Gafac RE-610* (emulsifier) 2.4
azobisisobutyronitrile 0.3
t-dodecyl mercaptan 0.5
water 200
*A mixture of R-O-(CH2CH2O-)nPO3M2
and [R-o-(cH2cH2o-)n]2po2M wherein
n is a number from l to 40, R is an
alkyl or alkaryl group and preferably
a nonyl phenyl group, and M is
hydrogen, ammonia or an alkali
metal, which composition is a trademark
of and sold by GAF Corporation.
Before the reaction was started, the pH of the mixture
was adjusted to about ~3 with KOH. The polymerization was carried
out for 22 and l/2 hours to a conversion of 92% and a total
solids of 33.1%.
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11(13~
B. A high impact, gas barrier resin was prepared by
polymerization of a mixture of the followin~ ingredients;
Ingredient Parts
acrylonitrile 75
methyl acrylate 25
latex A (above) 31.9
potassium persulfate 0~06
Gafac RE-610 3
n-dodecyl mercaptan
ethylene diamine tetraacetic acid 0.05
water 200
The pH was adjusted to about 7 with KOH. The polymerization was
carried out in the substantial absence of molecular oxygen at
60C for 20 hours to produce a conversion of 97~ of a latex hav-
ing 33% solids.
Example 2
The procedure of Example lB was repeated excluding
the latex A ingredient. A latex of the copolymer of acrylo-
nitrile and methyl acrylate resulted.
Example 3
An acrylonitrile-stryene copolymer was prepared in
the presence of a latex of a rubbery butadiene-styrene copolymer
(72% by weight of butadiene, 28~ by weight of styrene) using
the following recipe:
Ingredient Parts
water 419
Gafac RE-610 6.3
t~dodecyl mercaptan 0.6
azobisisobutyronitrile 0,5
acrylonitrile 91.Q5
styrene 8.95
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Ingredient Parts
styrene-butadiene
latex (solids basis) 10.8
The polymerization was carried out at 60C in a nitro-
gen atmosphere. The molar ratio of acrylonitrile/styrene as
charged was 20/1. The polymerization time was 130 minutes,
and during this time an additional 53 parts of styrene were fed
to the reaction mixture. A 73% yield of polymer was obtained.
A sample of the polymer solid was found to have a nitrogen content
of 11.19~ by weight which corresponds to an acrylonitrile/styrene
mole ratio in the polymer of 1.44/1.
Example 4
A latex of an acrylonitrile-styrene copolymer was pre-
pared according to the procedure of Example 3 except that the
butadiene-styrene latex was excluded from the recipe.
Example 5
A. A sample of the polymer latex described in Example
lB was carefully filtered through coarse filter paper (or
cheesecloth) to remove any small particles of polymer ("pre-
flock") which might be present. The latex was then thinned by
adding from 0 to 3 parts by weight of distilled water per each
part by weight of filtered latex. Commonly- 3 parts of water
per part of latex were used. The diluted latex was then placed
in a spray gun (Binks, Model No. 26). Steel sheet, tin-coated
steel sheet and aluminum sheet were all coated by spraying
latex on the sheet. In each case, the surface of the flat metal
sheet was first cleaned of any oil or grease film that may have
been left on it from the metal rolling fabrication. Carbon
tetrachloride, or a similar solvent, was used to clean the metal
surface.
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The resulting clean, dry, metal surfaces were then
spray coated with the latex~ The spray gun was set to give a
fairly light, fine spray. One to five thin, even coatings of
latex on a metal surface were made allowing each successive
coating to air dry for about 1 minute before the next coating
was applied. After the top most layer had air dried, the coated
metal sheet was placed in a circulating air oven maintained
about about 200 to 220C for 1 or 2 minutes. The coated metal
sheet was then removed from the oven and allowed to cool to room
temperature. Care must be taken to avoid overheating of the
coating because polymer degradation might occur on prolonged
exposure to high temperature.
The thickness of the final coating was about 0.5 mil,
+ 0.1 mil. In most cases, the thickness of the coatings thus
applied was in the range of 0.1 to 1 mil. Although the coated
metal can have any desired dimensions, for testing purposes
metal sheets from 4 to 7 mils thick in 5" x 8" rectangles were
used.
B. The toughness of the polymer coating as applied
to the test metal sheets according to A above as well as the
adhesion of the coating to the metal surface were determined
by a bending test.
In the bending test, the polymer-coated metal sheet
was placed in a vise. The sheet was bènt away from the coated
side, it was then removed from the vise and bent all the way in
the same direction so that it doubled back on itself. Thus,
the coated side was bent 180 and sharply creased. At this
point, the crease on the coated side was inspected for chipping
or flaking of the polymer coating from the metal surface.
Next, the polymer~coated metal sheet was placed back
in the vise and bent at a different place. This time the coated
surface was bent toward itself. Again, a 180 bend was made in

~C 3~8

the metal sheet with the coated surface on the inside of the
sheet. Again, the crease area was inspected for chipping or
flaking of polymer. In the case of all three types of coated
met:al sheet, steel, tin-coated steel, and aluminum, described
above, no chipping or flaking of the coating was detected in
the bending test.
C. A "punched-hole" test was devised which is a
relatively high speed and more severe test than the bending
test described in B above.
In the punched-hole test, a coated metal sheet from
B above was placed flat over a partly opened vise or over a
metal plate with a hole in it. In either case a hard, solid
surface was placed under the coated sheet except for one small
area, which was an open space directly beneath the sheet.
Directly over this unsupported area in the sheet, a punch was
placed and the punch was driven through the sheet by a sharp
blow from a hammer. The polymer coating in the area around
the resulting jagged hole was inspected for chipping or flaking.
The absence of chipping or flaking means the coating is a good
one. Poor coatings will show chipping, flaking and cracking
of the surface extensively around the punch hole and even back
as far as 1/8 to 1/4 of an inch from the edge of the hole.
The punch-hole test was run both ways, the coated side
of the sheet on top first, then the coated side on the bottom
of the sheet second. In the first part of the test, the punch
goes down through the coating, the second part the punch is
actually coming up through the coating. The coated metal sheet
samples prepared in B above all showed essentially no chipping,
flaking or cracking and thus demonstrated that they had good
coatings in this test.
D. A test, called the pinhole test, was devised to
determine whether the polymer coatings on the test sheets described
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~3~38
in E above were continuous and free of pinholes and ~oids in
the surface of the coating.
A 2% by weight solution of CuSO4.5H2O in distilled
water was prepared. The pH of this solution was adjusted to
1 with a small amount of H2SO4. The coated metal test sheet
was then immersed in this solution and in a short time the un-
coated side of the metal sheet (steel or tin-coated steel)
became coated with copper metal. On the coated side, however,
if there were no pinholes, voids or scratches in the polymer
coating there was no deposition of copper metal. If the polymer-
coated side had pinholes, scratches or voids in the plastic
coating, a tiny surface of the metal surface was exposed and
copper metal deposited on this exposed surface. When fine
scratches were deliberately put in good polymer coatings and
the sheets were immersed in the copper sulfate solution,
invariably the scratches quickly showed up as fine, dark red
lines on the coated side of the steel or tin-plated steel sheets.
A modification of the pinhole test was necessary for
samples of polymer-coated aluminum sheet. The copper sulfate
solution described above was adjusted to pH 1 with hydrochloric
acid rather than sulfuric acid. With this modification, it was
found that copper plates out better on aluminum when it is
immersed in the solution.
The copper sulfate pinhole test can also be used on
polymer-coated sheets which have undergone the bending and
punch-hole tests described above. The polymer-coated metal
sheets described in B above all were found to have excellent
continuous coatings in the copper sulfate pinhole tests.
Example 6
A sample of the polymer latex described in Example lB
was carefully filtered through coarse filter paper and used
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31~8
undiluted. Dip coating was done using aluminum sheet and the
filtered latex.
The clean, oil-and-grease~free aluminum sheets were
dipped down into the latex at room temperature and were held
in t:he down position for from about 5 to 10 seconds. The sheets
were then pulled up out of the latex an~ suspended to drain off
excess latex for from about 5 to 15 seconds and to air dry for
about 5 minutes. The resulting coated sheets were placed in a
circulating air oven for from about 1 to 2 minutes at 200 to
220C.
In dip coating, both sides of the aluminum sheet were
coated, instead of just one side as described for spray coating
in Example 5A. The thickness of the coating was determined with
a micrometer.
Coatings with an average thickness on one side of 0.3
to 0.4 mil over most of the sheet surface were made.
With dip coating, the coating thickness tends to vary,
being thinnest at the upper end of the sheet and thickest at
the lower end of the sheet (where draining latex tends to collect).
In order to get a more uniform thickness on a sheet, it is
recommended that the sheet be rotated during the air-draying step.
The dip-coated aluminum sheet prepared in this manner was found
to have an excellent coating in the tests described in Example 5B-D.
Example 7
A latex sample described in Example lB was filtered
and diluted as described in Example 5A. The latex was coated
by roller coating onto clean steel and tin-plated steel sheet.
~he sheet was placed on a flat, leYel surface and was taped
down at both ends. The dilution factor of distilled water
to filtered latex was 1:1 by weight. The latex can also be used
undiluted after filtering. A small amount of the diluted latex

1~33~8
was poured out across one end of the flat metal sheet. Then a
rubber roller was slowly rolled across the sheet, always push-
ing a tiny wave of the latex before it. A thin layer of the
lalex adhered to the metal surface after the roller has passed
over it. This coating was allowed to air dry for several
minutes at room temperature. The coated sheet was then heated
at 200 to 220C in a circulating air oven.
Example 8
The procedures of Example 1 were repeated using the
latex described in Example 2. Excellent coatings were achieved
on steel, tin-plated steel and aluminum sheets.
Example 9
The procedures of Example 1 were repeated using the
latex described in Example 3. Excellent coatings were obtained
on steel, tin-plated steel and aluminum sheets.
Example 10
The procedures of Example 1 were repeated using the
latex described in Example 4. Excellent coatings were obtained
on steel, tin-plated steel and aluminum sheets.
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