Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
The process in forming deeply drawn containers
requires a lubricated sheet stock for proper forming. Such
lubricants include peanut oil, lanolin, petrolatum and castor
oil, and many others. It is possible to deeply draw a container
lubricated with any of the mentioned lubricants and others,
see for example United States Patent No. 4,042,515. Deep drawing
permits forming a two-piece drawn can which is a preferred con-
tainer in that the only seam is at the cover. The practice
lQ of heavily lubricating the sheet stock for a two-piece deeply
drawn can is necessary because of the stresses introduced during
forming. While certain chlorinated paraffins when used as
draw lubricants may be post coated without removal they are not
approved for such use in a food container by the Food and Drug
Administration without complete removal prior to post coating.
The lubricant of the present invention is approved when applied
as set forth and post baked. No other acceptable technique is
available to manufacture drawn and redrawn cans which will
permit direct post coating operations on the completed cans (on
either the inside or the outside surface). The most frequent
method of coating application is by post spraying the cans using
a typical can makers spray machine, where the cans are brought
into position in front of a stationary spray nozzle, are sprayed,
and are then carriedaway to a curing over. Prior to that operation,
all cans to be sprayed must be washed thoroughly to remove all
traces of lubricant used to allow forming of the original plate
into the container shape. This applies to cans made by draw/
redraw methods or by drawing and ironing techniques (see for
example RE 27,662). The problem in both cases with the cleaning
operation is that the lubricant has been forced into all available
pores, aberrations, interstices, etc. in the metal surface due
to the high pressure applied by the tooling to the metal
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in order to form it, in the presence of lubricant. The washing
must be done with the aid of chemical cleaners, the cans must be
rinsed with deionized water to remove all traces of the cleaner,
and the cans must then be oven dried in order to eliminate spot-
ting from residual rlnse water. The cost of this operation de-
pends to some extent on the size of the can, the number of cans
produced per year, and other factors (such as neutralization need-
ed in order to send the cleaning solution into a sanitary sewer
system, quality of the water available for the original wash
cycle~ etc.). Drawn containers of precoated metals are commercial
but it is recognized that a post sprayed container can have sup~
erior product resistance for certain hard to hold foods.
The three-piece container which had a body rolled into
a cylinder and side seamed and two double seamed ends and as such
are precoated and don't re~uire any luDricant. Thus, it was ea-
sier to process. Consequently, the need to remove the heavy lub-
rication on two-piece cans after deep drawing requires can washing
and drying energy, equipment and materials. Each is costly in
terms of capital investment, plant space and energy consumption.
In addition, the drying process was environmentally deleterious
in that vapors are driven off and in that fuel is consumed genera-
ting heat and leaves products of combustion.
The present invention essentially eliminates the need to
wash lubricants for deep drawing.
The present invention also provides a lubricant with
these properties which will also effectively permit the strip to
be deeply drawn without surface damage to the metal from which the
container is formed.
The present inventlon still further p~ovides a lubricant
which can be successfully overcoated during a post spraying opera-
tion and which will permit the post coating to form a strong bond
with the container.
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According to the present invention there is provided a
deep drawing and priming composition for precoating metallic stock
having a metal oxide surface prior to deeply drawing into food
containers consisting essentially of a com~ination of lubricant
compatible with aliphatic hydrocarbon type solvents being three
and two-tenths percent by volume of the composition, an air drying
type hydroxylated silicone resin sufficiently equipped with si-
lanol groups to bond with said metal oxides and to condense with
acid groups in said lubricant for uniform dispersion of said com-
position across ~he stock surface of said silicone resin beingeight-tenths percent by volume oE the composition and the remain-
ing ninety-six percent of the composition being solvents and said
precoated food container thereafter being receptive due to being
so primed to a further:protective postcoatingO
The present invention also provides a method of prepar-
ing thin metallic stock having an oxidized surface for deep draw-
ing into food containers and postcoating said container including
the steps of: a) applying a combination of lubricant compatible
with aliphatic hydrocarbon-type solvents and air drying type hy-
droxylated silicone resin sufficiently equipped with reactive hy-
droxyl groups to bond with said metal oxides and to consense with
acid groups in said lubricant for forming a uniform dispersion of
said composition across the stock surface said silicone resin in a
four-to-one mixture by volume dissolved in approximately 25 volumes
of solvent at a rate of about 20 mgs per square foot to the sur-
faces of a thin sheet of said oxidiged metal stock to be formed,
b) providing sufficient hydroxyl groups to bond with the metal
oxides and to condense with acid groups in said lubricant, c) per-
mitting sai.d combination and solvent to dry leaving an evenly de-
posited film over the surfaces of the thin sheet, d) progressivelyforming by deep drawing the film covered sheet into a deeply drawn
food container having a depth which is greater than its width, and
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e) spraying a post-coating to substantially seal over the film
covering the food container to the extent that negligible surface
areas remain uncovered by the postcoating.
It has been thus found that the problems of the prior
techniques can be successfully ov~rcome by a lubricant that permits
direct overspray of the drawn can interior after forming but with-
out removal of the remaining lubricant thereby saving expense and
energy normally associated with the handling, the cleaning, the
washing and/or the drying processes. The lubricant is a combina-
tion of General ~lectric's silicone resin supplied under the trademark SR82 mixed in a toluene solution to a concentration of 60%
solids, and lanolin carried in a solvent such as Skelly C (a trade
mark) being heptane. The concentration of the combination contains
4% by volume of the lubricant materials or, expressed in another
way approximately 3.68~ of solids. A combination where one part
by volume SR82 and toluene ~60% solids) are mixed with four parts
by volume of 100% liquid lanolin, and the com~ination then dissol-
ved in toluene and heptane is preferred. The aromatic solvent tol-
uene is used to prevent precipitation of the SR~2 (a trade mark)
silicone resin and the aliphatic heptane fraction gives good sol-
vency to the lanolin. Tests of different concerltrations of lubri-
cant solids applied to bare tinplate stock by roller application
and felt-wipe have produced good results in that post spraying
without can washing produced an acceptable internal coverage with
good adherence. Different coating systems sprayed over the prefer-
red lubricant have been tried including solvent based coatings
such as an epoxy~phenolic type or a vinyl-organosol. The solvents
consisting of oxygenated, aromatic, and aliphatic hydrocarbon
types. Water based materials which are preferred for environmen-
tal reasons have also been tried with good results.
More particularly, the post sprayed container can bequickly tested by filling it with an electrolyte and checking the
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continuity or lack thereof between the outside of the container
body and an electrode in the center of the electrolyte. Such a
procedure is called quick testing and is common in the can manu-
facturing industry.
In order to perform a quick test a specified piece of
equipment is required. More particularly, a Model 1071 WACO (a
trade mark) Enamel Rater with a 0 to 1 milliamp attachment is used.
The apparatus has an electrode which is adapted to move vertically
in and out along the axis of a can positioned beneath it. The
electrode is positioned about 1" from the bottom of the can. The
can is held in position by a vise-lik~ device which clamps it
about the bottom holding it so that the open end of the can forces
up toward the electrode. The can is filled with 2~ solution oE
sodium sulfate and allowed to soak for at least 30 seconds be-
fore the electrode is dropped into the can. The solution tempera-
ture should be maintained between 72 to 78F, and the can should
be filled so that when the electrode is lowered into the test po-
sition the solution will reach approximately 1/8" below the top
flange radius. Care should be taken to avoid wetting the flange
since that will result in a false high reading. The milliamp me-
ter of the tester is connected to the vise-like device which holds
the bottom of the can. The electrode is connected to another lead
of the milliamp meter. A zeroiny of the instrument is required
and the operator adjusts the milliamp to read "T" on the scale.
Shortly after zeroing the meter a warning light comes on and the
reading should be taken immediately. When -this procedure was ap-
plied to the cans postcoated over the combined lubricant and sili-
cone resin, readings in the range of 0 to 3 milliamps were obtained
and such data is indicative of properly coated cans. The cans
were subsequently packed with -Yarious food and processed at temper-
atures of 240-270F. Tastetests and analytical studies have veri-
fied the efficacy of the coatings as applied over the combination.
1 ~5~156
Although post sprayed coatings generally yield quick
test readings in the range of 1 to 3 milliamps, there can be an
occasional small area of metal exposure resulting from a piece of
dirt on the surface as it is being sprayed, or dirt from particles
in the air during oven curing, and those areas are sometimes attac-
ked by the product packed in the can. By choice of the proper
metal substrate (electrolytic tin plate of various tin weights,
or tin free steel - CT~ various foods can be packed and properly
held. Possible metal exposure is the reason for different metal
substrates being used for different products, even though the post
spray coating is the same. In the event of exposure, tin coat-
ings on the substrate will reduce the amount of attack by the more
active foods. For example, coated TFS-CT is adequate for beef
stew, but probably not for green beans, which may require coated
#25 or #50 ETP, and certainly not for blueberries or red sour pit-
ted cherries, which normal~y require coated #75 or #100 ETP pounds
per base box which is the industry convention for amount of elec-
trolytically deposited tin on steel. Similarly, peanut oil has
also heen mixed with General Electric's SR82, and has upon check-
0 ing with quick test, after post spraying, performed successfully.Explanation of the Invention
Certain silicone resins such as General Electric's SR82
are known for their ability to modify coatings and thereby enhance
their bond with a metal substrate to which they are applied. More
particularly, the addition of silicone resin such as General Elec-
tric's SR~2 (a trade mark) to lanolin acts to permit subsequently
applied coatings(after forming) to cover the surface of the metal
substrate completely. That is to say that, without the addition
of silicone resin to the lanolin it would prevent complete coverage
of portions of metal substrates by coatings applied after forming
leaving eye holes, discontinuities in the coverage or even tenden-
cies for the coating to bead up. The affect is much like water on
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freshly waxed surfaces. The addition of silicone resin permits a
wettin~ action and alters the surface tension of ~he lanolin sur-
face tension of the lanolin sufficiently to allow the coatings as
applied to spread evenly and completely over the lubricated (lano-
lin and silicone resin combination) metal substrate and to form a
good bond across the entire surface~ The proposed combination of
silicone resin and lanolin when preapplied to coils or panels of
tin free steel plate, electrolytic tinplate or other materials
for deep drawing containers or cup-like objects which are intended
to be post sprayed or post decorated performs successfully because
of the bonding and good adherence of the wettable combination to
the lubricated metal surface. If lubrication is the only require-
ment, a complete coverage of the metal surface is not necessary
since the drawing tools ~end to spread whatever lubricant is avail-
able and a coating of lubricant huilds on the tools to the extent
that sufficient lubrication is available for the forming process
even on material which is slightly under lubricated. The wetting
is necessary to provide sufficient adherence to the metallic sub-
strate.
The lubricant and silicone resin combination is applied
as a solvent solution such that the co~ination remains as a film
on the surface of the metal after the solvent has evapoxated.
Consequently, the lubricant may be applied to the plate to be drawn
several days prior to use (so long as the surface so coated is pro-
tected from settling dust impurities)~ The evaporation time for the
solvents at normal room temperature when applied in the concentra-
tions preferred is approximately 20 seconds, i.f a roller type ap-
plicator is used in combination with a felt wiper to remove the
excess.
Example 1
A 4~ mixture may be made by dissolving 24 milliliters of
SR82 (a trade mark~ as received from General Elec~ric (a toluene
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solution of a specific pure silicone resin with 60~ solids) in
sufficient toluene to make 1550 ml total solution. To this was
added a solution of 96 ml of liquid lanolin (Ritalan (a trade
mark) 100% pure, from R.I.T.A. Chemical Company) in sufficient
Skelly (a trade mark) "C" (Heptane) to make 1450 ml of total solu-
tion. The combination gives approximately 3000 ml containing 4%
by volume or 120 ml of the lubricant materials such that the solids
concentration would be about 3.68%. The combination was applied
to coil stock feed to the press and in the actual operation suffi-
cient time to permit evaporation of the solvents was available when
the distance bet~Yeen the felt wiper and the centerline of the press
tools was 17 feet. The stock 50/100 ETP as received from the steel
mill was fed at a rate of 8 1/2" per second and the combined lub-
ricant and resin were applied at a rate o~ 15 to 25 mgs per square
foot. The best lubricant in solvent concentration was found to
be approximately 4% by volume or more particularly 4.5% - .5%.
This concentration was necessary for lubricating in a continuous
draw/redraw process, with a total of three drawing stations. If
it is merely a drawing operation with only one step forming the
lubricant concentration can be low~red to 2~ by volume, and applied
at ~ to 12 mgs per square foot. Ten thousand cans were deeply
drawn in three stations and post coated with an epoxy phenolic sol
vent based coating. The coating was applied by spray at a rate
sufficient to giv~ a weight of about 25 mg per 4 square inches
and then baked at 400F for seven minutes in a continuous oven.
Quick test results on randomly sampled containers gave readings of
0-3 ma.
Example 2
The combination of silicone resin and lanolin was the
same as in Example 1, however, the metal stoc]c was strip fed, TFS-
CT precoated on both sides with an expoxy-vinyl coating at a level
of 13 mg per 4 square inches. Felt wipers were saturated with the
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1 ~57~16
combination and the surfaces wiped across the wet wipers to coat
the strips. Five thousand containers were drawn and redrawn in a
three step operation and subsequently post coated as set forth in
Example 1. Quick test results were extremely good in that read-
ings were between 0-1 ma.
Example 3
One part of petrolatum by volume was mixed with 1.66
parts by volume of SR82 (a trade mark) as received from General
Electric. The mixture was thinned with about 50 parts of toluene
to give a 4% by weight solution. The combination was applied by
the procedure of Example 2 to the metal materials of Examples 1 and
2 and containers were drawn and redrawn in three operations as be-
fore. The post coating in this Example was an epoxy water base
material applied by spraying at a rate of about 20 mg per 4 square
inches and cured in continuous operation at 380F for 2 minutes.
Quick test results have readings of 5 to 25 ma.
Example 4
The combination of silicone resin and lanolin of Exam-
ples 1 and 2 applied as in Example 2 on the ma-terial of Example 2
and post coated with the water base epoxy of Example 3. Quick
test results gave readings o 1 - 4 ma for material Example 1 and
0 ma for the other.
Example S
This was identical to Example 1 except that peanut
oil was used in place o~ lanolin as the lubricant i.n the combina-
tion. The quick test results gave r~adings of 5 to 9 ma which
was not as good but for some foods would be acceptable.
A typical container as formed by the draw/redraw process
using the l.ubricant combination of this invention is a 303 x 406
two-piece s-teel can. The inside diameter of the triple drawn fi-
nished container is 3.060", the height is 4.375", and the bottom
and sidewall thickness are approximately 0. 0083", when the feed
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stock was 75 #T-~ plate; either TFS-CT tin free steel or elec-
trolytic tinplate having various tin weights deposited on both
sides of the plate will perform acceptably.
The combination of lanolin and General Electric's SR82
can be applied as described previously from a solvent solution us-
ing a roller applicator and suitable doctor blades or felt wi-
pers to remove the excess so as to yield about 20 mgs per square
foot of the combination on each side of the plate to be treated,
after the solvents are removed. The combination can also be ap-
plied from a solvent dissolved system where the combination is at
concentrations as high as about 60% (in toluene as the solvent)
by spraying onto the plate to be lubricated. A typical installa-
tion for applying lubricants to strips of plate in this manner em-
ploys a continuous conveyor belt which brings the strips past an
air atomizing nozzle which is spraying the combination downward
onto the pla~e. Through adjustments to the nozzle flow rate, and
by varying the speed of the belt, a coverage of about 20 mgs per
square foot is readily attained. Similarly, such a spray or atom-
iæing system could be used to lubricate a precoated TFS~CT coil
on a coil coating line, or to lubricate a coil of uncoated elec-
trolytic tinplate which is to be converted to containers suitablefor post coating without further washing or cleaning treatment.
While the preceeding has dealt with various e~amples
and various materials, the invention in its braodest aspect is
considered to include any type of silicone resin with the appro-
priate drawing lubricant which permits a subsequently applied coat-
ing to spread evenly over the remaining combination after a deep
drawing operation and results in a good bond to the metal sbustrate
after curing o~ the coating. For specific applications which re-
quire moresevere draws and/or thinner post coatings, the amounts
of the various constituents in the combination can be varied in
order to maintain low costs with a lubricant which will perform
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successfully. In addition, post coating of all ranges of tin
coverage on steel will work successfully with this type of lub-r~
cant combina-tion. Lightly precoated tin free steels (TFS-CT)
will also succeed in processing into post coatable containers
using this combination.
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