Note: Descriptions are shown in the official language in which they were submitted.
~3a ckE~n :1 o ~ t h_I n ~?n L I o~l
~wo-piece metal containers of tlle mulciple clrawn and d~awn and
ironed type are increaslngly seen in the ~arketplace for
such items as beer and beverages, foods, etc. Such con~ainers
are formed by forcing a metal blank into a die or series of the
same on a punch or mandrel while the blank is preven~ed from
wrinkling by pressure exerted orl a clamp plate. The ~orming
steps may vary in number and may include multiple dra.1ing
steps or a series of drawing and ironing steps depending on
the type of container being formed. In recent years, various
organic coatings have been used in drawing, multipLe drawLor
deep draw procedures wherein metal is precoated with various
substances and then formed. In many of said methods, the
coating is used primarily as a lubricant during the forming
steps with little or no coating remaining on the formed con-
tainer. In my U.S. Patent 3,206,848, dated September 21,
1~65 and commonly assigned herewith, deep drawn containers
are produced having an organic coating thereon from metal
stock precoated with an organic coating by a method of
essentially baking the coating, drawing the metal, rebaking
~`?~
= , , ,, ~ ~. -; ~j' :,
the coating at a temperature 10-30F below the initial
hardening temperature, redrawing the metal, etc. In this
method, it was necessary to relieve the stresses in the
coating between each forming step and thus reduce the
susceptibility of the coating to fracture during the forminy
steps. For example, to produce a container having a diameter
of about 2 1/2 inches and a depth of about 2 1/4 inches, a
precoated blank was forced through a die to form a shallow
cup having a diameter of approximately three inches and a
depth of less than two inches; the cup was removed from the
press~ heated to stress relieve the coating, the cup was
cooled and forced through a second die to the final depth
and d.iameter. Additional drawing operations are repeated as
desired with baking steps between each of the draws resulting
in coated containers in which the coating undergoes
substantial deformation without substantial fracture or
exfoliation.
In Canadian patent 1,058,454 issued July 17, 1979
in the names of Kenneth R. Rentmeester and Richard R. Bolt,
there is described a method for forming drawn and ironed
containers from metal sheet precoated with an organic coating
that can withstand the drawing and ironing steps without
substantial exfoliation or fracture and without actively
heating between the drawing and ironing steps. A similar
procedure for aluminum is also disclosed in UOS. patent
3,832,962 issued September 3, 1974 to Rolles.
Such methods as represented by the above referred to
disclosures produce containers in which the coating on the
finished container as formed is without substantial ex-
foliation. The coating in these methods are applied tothe metal and partially cured to build in sufficient
2 -
æ
16~
l flexibility (or other viscoelastic properties) to enable
it to withs tand the deformation imposed by the various forming
steps. While the containers resulting from such methods are
coated as formed and permit a substantial reduction'in the
number of subsequent operations necessary to produce a
commercial can, the performance of such containers is usually
directly proportional to the damage which the coating has
undergone during forming. Where highly acidic and/o~ corrosive
products are to be contained in steel cpntainers or where the
containers are filled and subjected to high humidity conditions
as in sterilizatlon or pasteurization processes, such factors
as corrosion, adhesion, metal ion dissolution, sulfide
staining or buildup, etc. are directly proportional to the
number of fractures in the coating. Because the coating has
been undercured to withstand the forming steps and its
maximum properties of adhesion, gloss, etc. have not been
realized, it is customary to view the "as drawn" coating as
a base coat and to apply one or several top coats to such
containers as formed to minimize exposure of the metal to
the contents and to improve the performance and appearance
of the container,
A method for providing containers from precoated metal
sheet wherein sufficient viscoelastic properties are built ' ' -
into the coating initially so that baking between forming
steps is not necessary and wherein the 1exible as formed
coating has improved adhesion, resistance to corrosion and
staining without the need for a top coat or other repair of
the container i5 a primary object of this invention.
- It is another object of this invention to provide a 30 method of forming coated cup-shaped metal containers from
precoated metal in which it is not necessary to bake the
coating between successive forming steps.
~ 8
1 I~ is a fur~her object of this invention to provide a
n!ethod of maximizing the properties of precoa~ed me~al con-
tainers as formed.
Another object of this invention is to provide coated
metal containers from precoatecl metal that have improved
resistance to corrosion, sulfide staining and improved
adhesion.
It is another objec~ of this invention to provide a
method of producing formed metal containers from metal
precoated with an organic resin capable of withstanding the
forming steps without substantial exfoliation and wherein
~the ormed container is post-treated to improve the performance
thereof thereby eliminating the need for a top-coat and other
conventional post-repair steps.
These and other objects and advantages of the invent.ion
will be apparent as they are better understood from the
description which follows.
Detailed_Description of the Invention
In accordance with this invention the method of forming
containers broadly comprises the steps of:
a) applying an organic resin to the surface of flat
metal strip or sheet;
b) subjecting said sheet carrying said resin to an
ele~ated temperature for a period of time sufficient
to effect adhesion to the metal and a partial
curing of the resin to the extent that it is
capable of withstanding the subsequent forming steps
without exfoliation;
c) forming a workpiece from said organic-resin carrying
metal sheet;
,
1 d) forcing said workpiece through sui~able dies to
form a coated article without actively heating during
or between the forming steps and
e) subjecting said coated article to an elevated
temperature for a period of time sufficie~t to further
cure the coating and improve resistance properties
thereof,
As employed herein, curing is meant to indicate hardening
an~ is applicable to either thermosetting resins which are
cured usually through reaction with a suitable material with
crosslinking and/or further polymerization or to thermoplastic
resins which are cured or hardened usually by evaporation of
solvents.
More specifically, an organic resin is applied to metal
sheet or strip which may be steel including blackplate
tinplate, chemically treated steel such as TFS-CT, aluminum
including alodine or other conversion coated aluminum, etc.,
after which the resin-carrying metal is subjected to an
elevated temperature, for example as by baking in an oven,
for a time sufficient to cure the resin to the extent that
it is capable of withstanding the forming steps, which may
be drawing, multiple drawing including reverse drawing
- and/or drawing and ironing, without exfoliation during and
after the forming steps. A workpiece is then formed from
the treated metal sheet or strip and may be a circular blank
which is forced through one or more dies or a circular
blank which is first drawn to a shallow cup which is then
forced through one or more dies. The entire ~orming operation
is performed without actively heating the workpiece and/or
coating, i.e. no additional baking steps are performed during
or between the forming steps. The formed coated article is
-- 5 --
..
; 14 ~
l then stripped from the dies and p~mch an(l subjected to an
elevated temperature for a period of time sufficient ~o
further cure the coa~ing, to repair any frac~ures therein
and to improve the adhesion o the coating to the ~etal.
There are thus obtained ar~icles exhibiting improved
performance with highly corrosive materials and other improved
properties.
The resins utilized herein may be any thermoplastic or
thermosetting resin or combinations thereo that are capable
of withstanding the forming steps without exfoliation, that
exhibit adequate elongation, compression and plastic flow
under the orming condi~ions, exhibit malleability with good
adhesion to metal without adhesion to tooling; that are
abrasion resistant; that will not impart off-flavor or odor
or other detrimental affects to comestibles contacted therewith
and that are capable of conversion to a corrosion and abuse-
resistant coating upon being subjected to an elevated
temperature af~er forming. It has been found tha~ vinyl
resins such as polyvinyl chloride organosols, solution
vinyls and combinations thereof are particularly effective as
inside coatings in the process and exhibit the optimum
requisite properties in accordance with the method of the
invention. Suitable vinyl organosols include known compositions
of polyvinyl chloride resins of relatively high molecular
weight, usually at least about 15,000, which resins are
substantially insoluble in the usual solvents and are
designed to be dispersed in the liquid ingredients of the
organosol. The high molecular weight resins are in a finely
divided state, generally of a particle size of less than
5 microns. The term "vinyl organosol" as employed herein
indicates dispersions of vinyl chloride resins including not
1 only the homopolymer bu~ also copolymers o~ vinyl chloride
~ith a vinyl carboxylate including vinyl acetate, vinyl
butyrate, etc. usually containing at least.50% vinyl chloride
in the vinyl copolymer structure. Dispersants for such
resins are well known and include any substance in~which
dispersions of the resins can be ~ormed and maintained with-
out solution and/or gelation. Suitable dispersants include
oxygen-containing polar solvents including water, ketones,
ether alcohols, glycol ethers, esters and hydrocarbons,
examples of which include dlisobutyl ketone, isophorone,
2-butoxy ethanol, ethylene glycol monobutyl ether, benzene,
toluene ar.d mixtures of such solvents.
Solution vinyls are also a well known class of resin
compositions and include vinyl chloride homopolymers as well
as copolymers thereof with vinyl carboxylates such as vinyl
acetate and terpolymers thereof with maleic acid or other
dicarboxylic acids. These resins may also be dissolved in
suitable solvents including those lis~ed above as dispersants
for the organosols and particularly ketones such as methyl
ethyl ketone, methyl isobutyl ketone and mixtures thereof
with suitable hydrocarbons such as toluene, xylene, etc.
The vinyl resins may advantageously be admixed with
` suitable adhesion promoting solution resins, if desired,
such as epoxy resins, melamines, acrylic acid resins, phenol
formaldehydes, urea formaldehydes, etc. A particularly
preferred composition may be illustrated by a composition
comprising about 80% polyvinyl chloride admixed with a
20% solution resin mixture comprising epoxy, polyester and
melamine resins. Other suitabLe resins may be illustrated
by vinyl chloride-vinyl acetate copolymers and mixtures
thereof, for example, copolymers comprising approximately
.. . .
~W '
l 85 to 90% vinyl chloride and about S ~o 15% vinyl acetate,
~lso including such resins containing interpolymerized maleic
acid. Such resins may also be admixed with other resins
including epoxy, acrylic, phenol ~ormaldehyde, etc.
The vinyl resins may be applied to one or both~ sides
of the metal sheet. In the instance where such resins are
applied to only one side, it is preerred that they be applied
to that surface of the metal that is to form the inside of
the container to convey the highly beneficial corrosion-
resistance and o~her properties when in contac~ wi~h thecontents of the container.
Other resins such as epoxy-urea formaldehydes and
epoxy-phenolics are also suitable for use as outside and
inside coatings. Such resins are well known in the art
and include reaction products of the classic epoxy resin
obtained by reaction of bisphenol A and epichlorohydrin,
known in the art as diglycidyl ethers of bisphenol A, also
referred to as DGEBA resins and other resins of this type
derived from reaction of polyhydric phenols and epichloro-
hydrins with phenol-formaldehyde resins. Preferred DGEBA
reactants are diglycidyl ethers of bisphenol A having average
molecular weights of from about 900 to 12,000 and epoxide
equivalents of from about 425 to about 6,000. Such resins
may be reacted with phenolic components such as methylol
ethers in which the hydrogen of the hydroxyl group attached
to the phenyl group is substituted by an alkyl, alkenyl or
cycloalkyl group or by an aralkyl or aralkenyl group as
well as the halogenated derivatives thereof. These resins
are A stage methylol phenol resins, i.e. soluble and fusible,
and are disclosed and described in U.S. Patent 2,579,330.
The preferred resin is l-allyloxy-2,4-trimethylol benzene.
.... .
Epoxy-urea formaldehycles are epoxy-amino resins derived by
reaction of DGEBA resins having epoxide equivalents of
425 to 6,000. An example of a suitable epoxy-phenolic resin
to be ùtilized herein may be illustrated by a ~ormulation
comprising about 50 to ~0%, preferably 70% Epon 1007
[trademark], a DGEBA resin having an epoxy equivalent weight
of about 2,000-2,500, about 5-50~ 1-allyloxy-2,4,6-trimethyl- ,
olbenzene and about l to 8% polyvinyl butyral. A preferred
epoxy-urea formaldehyde may be illustrated by a mixture o~
DER667, a DGEBA resin having an epoxy equivalent weight of
1,600-2,000 and Plaskon 3300 [trademark]~ urea-formaldehyde
resin.
Combinations of such resins may be employed as desired.
In a preferred embodiment, the inside coating is a vinyl
resin and the outside coating is an epoxy-phenolic. It is
also possible to apply a double coat system to either or hoth
sides of the metal sheet prior to forming including a base
coat and an overcoat of any of the above type resins and
combinations of the same.
The organic resins identified herein above may be formu-
lated in suitable solvents or dispersants with pigments and/or
fillers and/or internal lubricants and/or plasticizers as
desired, by means well known in the art. The particular
additives, whether solvents or dispersants, etc. are not
especially critical. It is necessary, however, that the
solvents or dispersants be volatile at the elevated tempera-
ture indicated and that they be compatible with all ingredients
of the composition in their useful concentration.
The coating may be applied by spraying, dipping, coil ~;
coating, electrocoating, roller coating or by other means well
known in the art.
Any suitable method may be used to heat the coated
_ g _
~ . ~
.
1 metal to the clesired telllperature both prior to forming and
subsequently. Hot air ovens as well as HTHV (high temperature-
high velocity) ovens have been used with success. Additionally,
the coated sheet may be heated by induction, flamè, or infra-
red means, etc.
The temperature and time to whicll the resin-carrying
sheet is subjected prior to forming will vary depending on
the particular resin and coating weight involved. Similarly,
the time-temperature relationship to which the coated formed
container is subjected after forming will likewise vary
depending on the particular resin and coating weight. Short-
high bakes in a high temperature-high velocity oven, for
example or lower bakes for longer periods may be used with
equivalent results. For the vinyl resins, conditions or the
initial bake of the coated metal may vary rom subiecting
the coated metal to a temperature of about 300F for about
20 minutes to subjecting the same in a high temperature-high
velocity oven at 600F for about 5 seconds. Optimum results
have been obtained with a sheet bake of about 390F for
6 to 8 minutes as well as with a coil bake in the HTHV oven
at 575F for about lS seconds. With the epoxy-phenolics and
epoxy-urea formaldehydes, the time-temperature relationship
may vary from a sheet bake of 270F for about 20 minutes to
a coil HTHY bake up to about 700F for about 5 seconds,
optimum results being obtained at 400F for 6 minutes as
well as 575F for 15 seconds. Post bakes varying from 300F
at 10 minutes to 675F for 2 seconds have been found to be
effective with all of the resins, with optimum results being
obtained with 400F for 5 minutes or at 500F for 6 seconds
in the HTHV oven. It is to be understood, however, that
other time and temperature relationships may be used to give
- 10 -
.
1 equivalent resul~s. It is essential that th~ po5t bake not
~e so high as to degrade the resin. Similarly, post baking
at too low a temperature leads to adhesi.on.loss and blistering
and will not improve the performance of the container. At
the same time, the initial bake temperature must be, suffi-
ciently high to partially cure the resin and effect adhesion
thereof to the metal but insuEicient to embrittle ~he r~sin
to the extent that it is deficient in flexibility and cannot
withstand the forces of deformation during formin~.
It is a particular feature of this invention that the
post-bake step given to the formed coated container results
in improved coating performance that is not seen when this
step is omitted and the improved performance is observed
regardless of the specific metal involved and regardless of
the number of forming steps that have been performed on the
coating as will be illustrated further hereinbelow.
While the exact reason for the improved performance is
not known, it has been found, for example, with double drawn
208 x 207 alum.inum cans by examination of samples of the
"as formed" and "post baked" coatings and metal by electron
microscopy that the top surface o the i'as formed" sample
has basically a very fine grained surface with portions of
what appear to be resin particles scattered randomly on the
surface while the post-baked sample differs in that sot
ridges are observed, the resin particles are reduced in size
and have a tendency to line up on the crests of the ridges.
The under surface of the "as formed" coating showed closely
spaced ridges and furrows while the post-baked sample
revealed more separation between ridges. The metal surface
as post-baked had ridging and in general resembled the
underside of the post-baked coating surface. These results
- 11 -
.
~ " ~ A
l are believed ~o inclica~e ~ha~ the post bake serves ~o
relieve the stresses built into the coating during ~orming
allowing the coating to relax and settle closer to the
surface of the metal resulting in increased adhesion of
coating and metal and improved resistance characteristics.
The following examples will serve to ~urther illustrate
the invention;
Example 1
r An epoxy-phenolic resin coating was applied as an
outside coating to TFS-CT ~tin free steel having a chrome-
chrome oxide sur~ace treatment) sheet at a coating weight
of 12 mg/4 in.2, baked for 6 minutes at a metal temperature
of 400 after which an aluminum pigmented polyvinyl chloride
organosol was applied as an inside coating at 30 mg./4 in.2
and baked for 6 minutes at a temperature of 390F. Both
sides of the coated sheet were lubricated with pe~rolatum.
The treated sheet was placed over an annular die, within a
hydraulic press and forced through a drawing die thereby
forming a cup having a diameter of approximately 5.312 inches
and a depth of 2.425 inches. Af ter the cup was formed by
the initial drawing operation, it was placed over a second
annular drawing die having a diameter less than the first.
A punch forced the coated metal cup through the die to
form a 404 x 307 inch elongated, cylindrical cup, ater
trimming. The cup is then subjected to a final bake step
in a hot air oven for approximately 5 minutes at 400F.
The final cup is a glossy, smooth, coated article having
improved adhesion and corrosion resistance.
Additional drawing operations may be performed after
the second drawing operation and before the post bake
~0
resulting in a deeper ar~icle of reduced diameter. Should
- 12 -
~ ~ ~ 6'~ ~
1 such additional draws be desired, ~he Eollowing average
reductions in diame~er for each draw is suggested where D
is the diameter: .
Circular blank D (diameter) Reduction in Diameter
First Operation cup-Dl 42V/o~D
Second Opera~ion cup-D2 25% Dl
Third Operation cup-D3 18% D2
To illustrate the effect of the post-bake on the
performance of the contai.ner, a number o~ experiments and
~ tests were performed.
Example 2
A. 404 x 309 double drawn'TFS cans were produced employing
the method and coatings of Example 1 but varying the
extent of the post-bake as indicated hereinbelow. The
- containers were filled with water and the filled
containers were contacted with steam at 250F for 130
minutes to simula~e the conditions present in a
sterilization procedure. The processed containers
were examined for condition of the,inside coating with
the results as listed in Table I which follows:
- 13 - '
l Table I
Con~ainer Pos~-Bake Observa~ion
. _ _
1. None Severe sca~tered blister-
i~g at sidewalls and
flange area.
2. 1 min. at 400F Moderate to severe
blistering`at side-
walls and flang~ area.
3. 2 min. at 400F Moderate scattered blister-
ing at side~alls and
flange area.
4. 3 min. at 400F Slight to moderate scat-
tered blistering at side-
walls and flange area.
5. 4 min. at 400F A trace of scattered
blistering at sidewalls
and flange area - Acceptable.
6. 5 min. a~ 400F No trace of blistering
at sidewalls or flange
area - coating in good
condition - acceptable.
B. 300 x 402 containers were produced by the procedure of
example 1 employing an aluminum pigm~nted vinyl organosol
comprising about 60% polyvinyl chloride dispersion admixed
with about 40% solution resins (Tests 1 and 2) and a vinyl
~ organosol containing about 60% of a polyvinyl chloride
dispersion admixed with about 40% vinyl chloride-vinyl
acetate copolymers containing titanium dioxide and
lanolin (Tests 2 and.3) as the respective inside coatings.
Metal was coated and treate~ as indicated below, where
the bake time (6' ~ 3'~ employed indicates that the
coating was baked for 6 minutes after allowing 3 minutes
for the oven to reach the indicated temperature.
Finished containers were water-packed, double seamed
and processed in steam at 250F for 60 minutes after
which the coating condition was evaluated. The results
were as follows:
- 14 -
l Test l ~ 300 x 402 c~ns from coa~ed TlS at
30 mg/4 in. , initially baked 6' ~ 3'
a~ 400F.
After processing, poor coating adhesion and
- low gloss.
Test 2 - Same a,s Test 1 but given an 8' bake at 400
after can fabrication.
Excellen~ process resistance with improved
gloss and coating continuity.
Test 3 - 211 x 300 cans from coated TFS at
45 m~,/4 in.2, 575O coil bake for 15 seconds.
, Poor coating adhesion after process.
Test 4 - Same as Tes~ 3 but given a 6' bake at
400F after can fabrication.
After processing, improved adhesion of coating.
The above findings clearly illustrate a general correlation
between post-bake and coating performance on the finished
containers illustrating that for the coatings util'ized a
5-minute bake at 400F'or equivalent time-temperature re--
lationship gives a markedly improved container.
,
' Example 3
i~ To illustrate the ef~ect of the initial bake and post-
bake temperatures on the finished container, ~75 lb. TFS-CT
was coated with the polyvinyl chloride organosol resin of
Example 1 as the inside coating and an 'epo~y-phenolic coating
as the outside coating. The vinyl resin applied to the inside
surface included a variety of weighti~ and time-temperature
relationships as indicated in Table II which ollows. Double
drawn 404 x 307 cans were fabricated by the procedure of
Example 1. Samples of cans from each coating variable
were 1) given no post-bake treatment or 2) treated for
3 5 minutes at ~00F or 3) treated in the HTHV oven at 625F
- 15 -
1 for 8 seconds. The cans thus treated werc filled wi~h water,
~ouble seamed, subjected to a hot wa~er process ~or 60 mi.nutes
at 240F, cut open,scotch tapcd to evaluate adhesiorl of the
coating and painted with an indicator for iron which makes
visible fractures or imperfections in the coating. ~The
results were as indicated in Table II. In the Table, the
coa~ing weights are ~he semi-wet weights excep~ ~or con~ainers
9 and 10 where the dry coating weight is used. Redraw refers
to the portions of the container subjected to the mos~ defor-
mation while bottom refers to the bottom end.
.
. 20
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_ _ _ _ _
1 The effect o.E ~he time-~emperature relationship of the
initial bake as it affects the adhesion properties and con-
tinuity of the "as formed" coating as well as the ef~ect of
the post-treatment on adhesion and continuity may be readily
. seen from the results illustrated ln Table II. Thus, container
numbers 1,2,3,7 and 8 were initially baked at 400F for 9 to
- 13 minutes and exhibited the best properties on ~he "as ormed"
coating under severe condi.tions of heat and humidity while
. containers 5,6,9 and 10, ini.tially baked at 3~0-390 for 9 to
11 minutes or in the HTHV oven for approximately 15 seconds
exhibited the worse properties initially under these conditions.
All of such containers however, were improved in both adhesion
and coating continuity after the 400F post-bake treatment
while the HTHV treatment resulted in improved adhesion in all
cases except the 400F - 10'+3' relationship. That overbaking
initially is to be avoided is evidenced by container 4 where
baking at 415F for 6'~3' showed adhesion loss and discontinuity
which could not be improved by ei.ther of the treatments.
Example 4
208 x 207 double drawn aluminum cans were produced using
the procedure of Example 1. Both plain and alodine treated
aluminum sheet and strip were coated with an epoxy-urea
formaldehyde resin coating as the outside coating, with the
sheet being baked at 300F for 8 minutes and the strip being
baked in an oven for 60 seconds at 650F. To each of the
sheets and strip thus coated, an epoxy-phenolic coating
containing about 1% lanolin was applied as the inside coating,
the sheet being baked for 8 minutes at 370 and the strip for
60 seconds at about 600 to 650F. Containers were fabricated
from each of the variables and were beaded and post-baked at
- 18
l 380F for S minutes or beaded with no post-bake. 'IAs
formed" containers were also evaluated as controls. Adhesion
of the inside coating on each of the variables was evaluated
before and after processing ~or 30 minu~es with 250.F steam.
The results were as given in Table III.
Table III
Metal Coatin~ Before Process Coating A.f~er Process
As Beaded As Beaded
Drawn Beaded Post-Baked Drawn Beaded Post-Baked
Al Sheet S S S , B U S
Al + Alodine
Sheet S S S . B- S S
Al Strip
(650) S S S B U S
Al + Alodine
Strip (650~ S S S B- B- S
Al Strip
(600) S S S S U S
Al + Alodine
Strip (600) S S S S B- S
In the table, S indicates sat.isfactory coating conditions;
B indicates a borderline,condition with traces of blush and/or
loss of adhesion and U indicates unsatisfactory condition
with blisters and/or loss of adhesion making the container
unacceptable~ It will be seen from the above that while
all containers were satisfactory before processing, only the
post-baked containers were consistently satisfactory even
after beading which further deforms the coating.
Example 5
3o 307 x 113 single draw containers were produced by the
procedure of Example,l from tinplate coated with epoxy-phenolic
- 19 - .
'
1 coatings. Bo~h coatings were applied as inside coatings at
16~ mgs. and baked Eor 8 minutcs at 400F. Containers thus
produced were post-baked for 8 minutes at 380~ retaining some
"as formed" containers without a post-bake treatment as controls,
The post-baked and "as formed" containers were pack~ed with
tuna, stored or several days after which they were opened,
evaluated for sulfide staining and rated on a scale of 10 to
0 with 10 indicating severest staining. The results were as
~ollows:
10 Test 1 Ratin~
Container As Drawn: Severe staining 9
Container (1) Post-baked: Slight staining 3
Container (2) Post-baked: Slight staining 4
Test 2
Container As Drawn: Severe s~aining 7
Container ~1) Post-baked: Trace of staining 2
Container (1) Post-baked: Trace of staining
Example 6
211 x 400 triple drawn containers were produced from
75 lb. TFS-CT with each of various coatings by the procedure
of Example 1 after which containers from each variable were
post-baked at 400F for 5 minutes. The containers were hot
filled with 180F water, double seamed and processed for 50
minutes at 250F af~er which adhesion was evaluated with
Scotch Tape. The coatings and results were as follows in
Table IV.
In the table, the outside coating on all variables was
an epoxy-phenolic resin. For purposes of comparison, an equal
3 number of containers not post-treated were filled, processed
and evaluated under the same conditions.
- 20 -
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1 It will be evident ~rom the above that containers
produced by the instant method and subjected ~o the post
bake as described herein have improved resistance to corrosion
under severe conditions of heat and humidity, are of improved
gloss, coating continuity and adhesion.
It will be evident from the aforegoing that although the
method has primarily been described in terms of drawing and
multiple drawing steps, other steps may be used including
drawing and ironing, flanging, beading~ curling, erimping, etc.
It is thought that the invention and many of its attendant
advantages will be understood from the foregoing description
and it will be apparent that various changes may be made in
the steps of the method described and their order of accom-
plishment without departing from the spirit and scope of the
invention, the form hereinbefore described being merely a
preferred embodiment thereof.
,
- 23 -
