Note: Descriptions are shown in the official language in which they were submitted.
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- COMPOSITIONS FOR TREATING ALUMINUM L
SURFACES FOR TARNISH RESISTANCE
Background of the Pr10r Art
This invention relates to novel and useful improvements in
5 chemical compositions that impart tarnish and corrosion resistance
to metal articles and, in particular, relates to compositions of
matter~and methods for their application for treating aluminum ~
containers to render them stain and corrosion resistant. r
As is known, when meta1 sur~aces are exposed to hot aqueous f
10 solutions, especially aluminum surfaces, for extended periods of
time there is a marked tendency ~for such surfaces to tarnish to a
brown or black coloration. Apparently, this coloration is a
~; ~ refractive effect of the~light as it passes throuyh amorphous
~ platelets of generally hydrated aluminum oxides that deposit and ~r;~ 15 build up on the sur~ace of the metal. This~problem becomes~acute
in certain industries. For example, it has been the general prac-
tice in breweries to pasteurize alcoholic bever~ages such as ale, ,
stout and beer in metal containers and this is generally done by
subjecting the cans to hot water ba-ths or sprays in the range of
20 about 140F to about 170F. In subiecting metal containers to hot
water there is a marked tendency for the metal surface, especially
aluminum, to stain upon exposure and this is especially noted on
the bottom portions of the containers. In practice, the severest
problem of staining or discoloration is encountered during pas-
25 teurizing of the package as no organic coating is applied to the
container bottom to protect it from corrosion and if left
untreated, it will discolor during pasteurization, turning
brownish. While seemingly this effect does not harm the contents
thereof, lt makes the product unappealing in its appearance to
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the consumer. Heretofore it has been a practice in the art
to apply a so-called conversion coating to metal containers
in order to suppress or passivate such metal and to prevent
tarnishing ~s well as to promote the adhesion of inner
lacquers and outer coatings of ink, paints and the like.
Various corrosion inhibitors have been used
commercially such as inorganic ions including chromates and
phosphates and are referred to as conversion coatings.
Generally, the surface to be treated is subjected to an
aqueous solution containing such ions. It is believed that
these inorganic ions or heavy metal ions have the ability
to bond or adhere in the form of insoluble oxides which resist
tarnishing and corrosion of the metal surface. In general,
the conversion coating solution is prepared and sprayed at
some elevated temperature for a short period of time. After
treating the metal surface with the solution, the surface is
thoroughly rinsed with water to remove unreacted coating
solution. However, in spite of the aclvantages of these
corrosion inhibiting solutions, these inorganic ions have
come under increasing scrutinization by environmental groups
and governmental agencies with the result that there has been
an increasing demand for compositions that do not have these
detrimental heavy metal ions.
According to an aspect of the .invention there is
provided a composition of matter consisting essentially of
about 0.01 to about 10 weight percent of a water-soluble
portion containing about 10 to about 95 weight percent of an
alkali metal silicate and about 5 to about 90 weight percent
of an organic polymer selected from the group consisting of
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poly(acrylic-co-acrylate), poly(vinyl alcohol), poly(acrylic
acid),t~bs~r~e~ poly(acrylamide), poly(maleic anhydride-
co-methylvinyl ether), and poly(styrene sulfonic acid), and
about 90 to about 99.99 weight percent water.
According to a further aspect of the invention
there is provided a method for treating aluminum with the
above described composition.
According to a still further aspect of the invention
there is provided an aluminum surface treated by the method
of the invention.
Metal surfaces treated by the process of this
invention remain stain and corrosion resistant over a long
period of time and do not have to be further treated or coated.
Furthermore, the compositions herein clo not present toxic
materials and do not have any disposal problems. Thus, the
subject compositions are free of chromium ions and of the
chromium subgroup of the Periodic Table and also materials
such as ferricyanide and ferrocyanide.
Description of the Invention
The particular group of silicates that have been
found to be effective herein are those aqueous silicates
such as sodium,
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potassium or lithium, or mixtures of such silicates. These sili-
cates are known generally as water glasses and are usually aqueous
solutions containing numerous varieties of alkali me-tal silicates,
e.g.,
M20 SiO2; ~120-2SiO2; M20 3SiO2;
M20-~Sio2; M20 SSiO2
and may be represented generally as
0 M
~.Si - O ~-- ~
x.
( ) M
where M is sodium, potassium or li-thium and x is an integer, generally
between l and lO~ ~.
In general these aqueous silicate solutions have a specific
gravi-ty range from about l.3 to about l.6 and comprise about 23 to
15 about ~8 percent by weight of the alkali metal silicate.
EfFective silica to metal oxide weight ratios range from about
l.87 to about lOØ
The useful polymers of the subject invention are organic,
polymeric substances having displaceable or displaced hydrogens
20 and are generally derived by polymerization of at least one mono-
ole~inic compound through an aliphatic unsaturated group to yield
a water-soluble synthetic polymer having a strOucture substantially
free of cross-linkage. In general, the polymers herein are those
water-soluble polymers having a linear polymeric structure of car-
25 bon or carbon with some other atom such as oxygen and contain in apendent side chain a hydrophilic group ~rom the class consisting
of hydroxyl, carboxylic acids, carboxylic acid amides, sul-Fonic
acids and phosphoric acids. It will be appreciated that in its
broadest aspect the aforementioned polymers Fa1l into two classes,
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(1) those consisting of polynleric organic substances which in an
aqueous medium will form organic anions haviny a substantial num-
ber of negative charges distributed at a mul-tiplicity of positions
on the polymer, and (2) those consistiny oF polymeric organic sub-
5 stances which in an aqueous medium will not form ions but nonethe-
less contain a sufficient number of hydrophilic groups to be ~
water-soluble. The first class of polymers may be referred to as _
anionic organic polymers and the second class may be called
non-ionic-organic polymers.
Very small concentrations of the ingredients herein defined
have been found effecitve for improving the corrosion resistance.
The synthetic organic polymers containing only carboxylic acid,
sulfonic acid, phosphoric acid, as well as the salts thereof in a
side chain are anionic and those that contain hydroxy and carboxy- ~.
15 lic acid amide in the side chain are non-ionic. Natural carbohy-
drates have been found effective herein and included the highly
branched polymers of acacia gum. The invention herein contem-
plates polymers that contain either the anionic or non-ionic
groups as well as mixtures thereof.
The composition herein may be readily formulated in an aque-
ous media. The oryanic and inorganic ingredients may be Mixed in
any order into water. Preferably, the compositions are prepared
by mixing the components in a given amount of water with constant
stirring within ambient temperatures until the ingredients go
25 fully into solution. t
The preferred range for both the alkali nletal silicates and P'-
soluble polymers should be between about 0.05 and about 5 weight
percent. At its most preferred embodiment a mixture of the alkali
metal silicate and soluble polymer should be present at about 3
30 weight percent based on the total weight of the solution. Lower
concentrations do not produce an appreciable improvement in cor-
rosion characteristics, and higher concentrations do not increase
these characteristics, generally, any further. To these compos;-
tions may be readily added other various ingredients that are
35 compatible with the system. Such ingredients include wetting
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agents, dyes, pigments and germac;des. The compositions herein
described and claimed may be readily applied by various conven-
tional means known to the art and including dipping, spraying,
immersion, and roll-on techni~ues. It is believed that the compo-
5 sitions herein can be readily applied most economically andeffectively by spraying.
The following tabulation gives Examples comprising composi-
tions as defined herein that were prepared with the amount indi-
cated in grams per liter for the ingredients. To each of
10 Examples 8-2U were added about 0.01 grams of a commercial wetting
agent, Triton~X-100. Each formulation was placed in contact ~ith
an aluminum coupon for about two (2j minutes, at the ternperature
indicated and thereaFter rinsed and dried. The thus-treated
coupons were thereafter submerged for fifteen (15) minutes at
15 about 75C., in a standard solution comprising an aqueous solution
of 220 ppm NaHC03 and 83 ppm ,laCL. The processing conditions of
temperature, contact time, and contact me-thod are interdependent.
In general, app1ication of the cornpositions herein is conventionally
by spray technique and, considering normal plant operations, the
20 temperature of the solution will normally be from 30 to 90C.,
preferably about 35 to about 60C., and the contact time will be
between about 1~ and 90 seconds and usually less than 70 seconds.
Two commercial formulations were also tested as indicated in the
table. The ratings in the respective columns represent the amount
25 of discoloration for each example.
- It will be appreciated that is has been found in accordance
with the present invention that aqueous coating solutions con-
taining an alkali metal silicate and a water-soluble organic poly-
mer of the anionic, non-ionic type or mixtures thereof are
30 effective in protecting aluminum surfaces. The corrosion resis-
tant properties of the coating formed by applications of such
solutions within the scope of the present invention include the
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ability of the coating to withstand blackening or other discolor- r
ation when subjected to boiling water for a period of time of at
least two minutes or longer.
The particular compositions of the present invention can be
5 used to protect p~re aluminum or alloys of aluminum, for example,
aluminum alloys containing minor amounts of metals such as, for
example, magnesium, manganese, copper and silicon. Presently, two
of the most common alloys used in the aluminum container industry
are aluminum alloys 3003 and 3004.
After the coating compositions are applied the surfaces may be ~.
dried by conventional means such as an oven having forced circula- L
tion of hot air. After the coating has dried it can be readily
subjected to lacquering or to decorative operations which can
include applying to the surfaces inks, paints or other resin
15 coating. I~ith the methods and compositions of this invention very
excellent adhesion of these decorative finishes is realized.
A large number of water-soluble polymers of both the anionic
and non-ionic -type may be readily employed. Illustrative of the
non-ionic polymers are poly(vinyl alcohol), poly(acrylamide) and a
20 number of organic polymeric coagulants of vegetable and cellulosic
origin including Gum Arabic. Illustrative of the anionic types
are poly(acrylic-co-acrylate)j poly(acrylic acid), poly(maleic
anhydride-co-methylvinyl ether)g poly(styrene sulfonic acid),
sodium poly(acrylate), sodium poly(methacrylate), poly(itaconic-
25 co-vinyl acetate) and the like.
By poly(acrylic-co-acrylate) is meant those copolymers of
acrylic acid, methacrylic acid, methyl m~thacrylate, methylacry-
late and derivatives thereof.
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There has been disclosed herein a method oF and a composition F
for treating aluminum metal surfaces, and in particular those metal
surFaces that are subjected to hot water solutions and the like,
especially in pasteurization processes for aluminum can bodies. I
5 In view of the specifications, those skilled in the art may have
many modifications which fall within the true spirit and scope of
this invention. It is intended that all such modifications be .
within the scope Of the app~nded ~la~m.
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