Note: Descriptions are shown in the official language in which they were submitted.
)5'7~43
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The present invention lies in improved corrosion
inhibitor compositions for internal combustion engines for auto-
mobiles. The pH is specially selected and adjusted (by alkaline
carbonates and hyd~oxides) for an alkaline in-use range of
between 10-12, preferably between 10-11, with the specific pre-
ferred range of 10.4-10.8.
The supplemental alkalinity in the present composition
serves to combat the thermal and chemical decomposition engendered
by the higher skin temperatures of heat transfer surfaces in
the passenger car engine and the normally higher temperatures
encountered in trucks. It is noted that J. I. Bregman in
Corrosion Inhibitors, MacMillan, 1963, states at pages 144-145
that conventionally the boron-nitrite inhibitors are used at
a pH range of 8.5-9.5 usually by a buffer combination of borax
and sodium nitrite. The supplemental alkalinity of these compo-
sitions also works to lncrease the time in use, making changes of
coolant fluid more infrequent despite the higher temperature ?
operating conditions.
The subject of satisfactory prevention of corrosion in
coolant systems of modern automobiles has been noted in recent
technic,al discussion. For example, in Chemical Week of ~uly 17,
1974, ~n an article entitled, "Auto Coolant Controversy Boils
Over," the need for more effective coolants has been highlighted
by the fact that today 72 percent of all U.S. built cars are
equipped with air conditioners and the operating temperatures of
the 1975 models are expected to be as high as 225F. The hotter
engines of the new cars require greater protection for the
coolant. This article further notes that in a current 1974
survey, a greater loss of reserve alk~linity (inhibitor capa-
30 ¦ ¦bil y) a= well as greater quantitiqs ~f rust and sed ment in
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the cooling system had occurred than in the same survey taken ten
years ago. The present invention contemplates a multicomponent
corrosion inhibitor of the following formulation, the liquid
version of which is:
FO~ULATION I
Necessary Percent
Soft Water 75-85
Alkali Metal Nitrite 1-3
Alkali Metal Silicate 1-5
~lkaliJ Metal Hydroxide (50% by wt. caustic) .25-3.5~.
Sulfur Containing Copper Inhibitor .5-1.5
Borax 1-10
Polymeric Suppressant .1-1.0
Polymeric Dispersant .1-.5
Optional
Sodium Oleate 1-3
Sodium Carbonate 1-3
Antifoam .05-.1
Dialkylaminoethanol .5-1
Dye . .05-.1
.. , . . _ . ,
.
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and the solid version of which is:
FORMULATION II
Necessary Percent
Alkali Metal Nitrite 10-20
Alkali Metal Sllicate 5-25
Alkali Metal Hydroxide (50% by wt. caustic) 7.5-17.5
Sulfur Containing Copper Inhibitor 2.5-7.5
Borax 5~50
Polymeric Suppressant .5~5.0
Polymeric Dispersant .5-2.5
Optional
Sodium Oleate 5-15
Sodium Carbonate 5-15
Antifoam .25-.5
Dialkylaminoethanol 2.5-5
Dye .25-.5
wherein the polymeric suppressant comprises a homopolymer of
maleic anhydride, or a copolymer of maleic anhydride with vinyl
acetate, styrene, ethylene, isobutylene or a vinyl ether, and
the polymRric dispersant is chosen from the group comprising
polyacrylates, methacrylate-acrylate copolymers, and carboxy-
methyll cellulose; is water soluble; and has an average molecular
weight in the range of from about 2,000 to about 50,000.
In the above Formulations I and II, the alkalinity in
use in the coolant is of prime importance and the composition of
the premix ingredients are adjusted chiefly by the alkali metal
hydroxide and carbonate content so that the pH in use is targeted
for a pH of 10-12 or preferably 10-11. The solid composition
(II above) may be incorporated into a pellet and placed in a
spin-on or cartridge-type filter which serves for unitary
replacemRnt in an engine cooling system.
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PRIOR ART
The prior patented art believed pertinent to this
application is as follows:
~ 2,723,956 ~ohnson (National Aluminate)
Styrene maleic anhydride (SMA) for reducing
scale in steam boilers.
2,815,328 Green et al (Nalco)
A basic corrosion inhibitor for diesel engine
cooling systems.
/ ~,877,188 Liddell (Hagan Chemicals) _~
Mercaptobenzothiazole as a copper inhibitor.
; 2,972,581 Johnson et al (Nalco)
A multicomponent corrosion inhibiting com-
position for diesel and auto cooling systems.
3,645,402 Alexander et al (Mack Trucks)
Disposable-type filter for an internal
combustion engine having a canister contain-
ing a chemical corrosion inhibitor in a
pallet preferably spun on to an adapter.
In contrast to the prior art noted above, the present
formulations are constituted or made up so that a high pH is
obtained of from about 12-12.5 and a use level pH (in deionized
water) is obtained in the range 10-llj or more preferably 10.4-
10.8. What is meant by a use level pH is that pH obtained by
adding the equivalént of 4 fluid ounces of inhibitor composition
per gallon of coolant and measuring the resulting pH.
In a most preferred formulation, in order to better
protect copper, the present formulations substitute a
L'i ~
monoaryltria~ole such as benzotriazole and tolyl triazole for a
portion of the mercaptobenzothiazole formerly generally utilized.
Also, as an added facet there is added a polymeric
dispersant to assist in the dispersing of solid particles in the
coolant and such dispersant is selected from the group consisting
of polyacrylates, a methacrylate-acrylate copolymer, and
carboxymethyl cellulose, which are water soluble and have a
preferred molecular weight of between 2,000 and 50,000.
In providing corrosion protection designed specially
for automoti,ve engine systems, a composition must provide pro-
tection for multiple surfaces. For example, the following
metals are typical of those found in automotive systems:
aluminum, steel, copper, brass, cast iron, solder, and magnesium.
Additionally, in auto systems, the conventional use of so-called
"permanent" ethylene glycol antifreeze in the systems produces
by oxidation of the glycol a mixture of corrosive acids,
including formic, which, if-uninhibited~ will be more corrosive
than tap water to which no antifreeze had been added.
NECESSARY INGREDIENTS
2~ Alkali metal nitrite. Sodium nitrite and potassium
nitrite are utilized to inhibit corrosion of iron and other
metals.l These components are most efficient in the alkaline
range.
Alkali metal silicate. Potassium and sodium silicates
. .. ... . .
are preferred. The alkali silicates, such as sodium metasilicate,
also provide one source of buffering for the acids produced from
the glycol antifreeze in the system. Prime anti-corrosion
targets for the silicates utilized in the present compositions
are aluminum, iron, and solder, and here the silicate is believed
5'^~
~o operate by thin film protection best at the alkaline pH
targeted for the compositions of the present in~ention.
Alkali metal hydroxides and carbonates. These alkaline
components are used as pH regulators to produce the desired
working alkaline pH which is preferably about 10.4 to 10.8. The
carbonate is utilized optionally in these formulations to pro-
vide additional buffering action, together with borax, metaborate,
or tetraborate.
In this specification the term "alkali metal" is
limited to~the commercially feasible members comprising sodium
and potassium, and MeOH designates alkali metal hydroxide.
Borax. The use of borax and similar boron compounds of
l .
.j metaborate and tetraborate is helpful in a recirculating water
, system by inhibiting steel and zinc and additionally supplying
buffering capacity in alkaline pH's.
Sulfur containing copper inhibitor. The utilization
of compounds containing sulfur as an inhibitor for corrosion of ;
copper materials in automobile engines has been well described.
For example, -
2,198,151 Beekhuis et al describes potassium xanthate,
thio acetic acid, thiourea, and thio acetamide.
2,963,432 and 2,963,433 Little et al teach ~lkyldithio)
benzimidazole specifically as corrosion inhibitors for copper.
Both are nitrogen heterocycles which also contain divalent sulfur.
3,408,307 Troscinski et al describes tetrazoles.
3,598,756 Heit describes mixutres of mercaptobenzo-
thiazole and dibutylthiourea.
3,755,176 Kinney et al describes thiohydrocarbyl acid
or amine salts.
3,809,655 Williams describes dialkyl sulfides and di- -
alkyl sulfoxides.
11 ' I
l~S'~
Additionally, Bregman, ante, at pages 115-116,
recognizes that commercially the best corrosion inhibitor for
copper today is 2-mercaptobenzothiazole, which is not only
anodic inhibitor for copper but acts as a glycol oxidant
inhibitor to prevent or inhibit the oxidation of any glycol anti-
freeze normally present in auto systems. It has been theorized
that the presence of a ring sulfur and nitrogen and with an
ionizable sulfur in the formula
~ N ~
~,~ \ S
makes possible multiple sites for formation of coordinate bonds
with copper.
In the present invention a preferred substitution for
mercaptobenzothiazole is made by using a monoaryltriazole such
as benzotriazole or tolyltriazole. Due to the increased heat in
the automotive cooling system, it has been found that greater
stability is achieved by utilizing these more heat stable com-
pound,s in lieu of the more heat fragile mercaptobenzothiaæole. A
porti~n of the MBT is retained by a split dosage with one of the
monoaryltriazoles due to more rapid action of MBT in an optimum
formulation. A formulation of equiparts by weight of MBT and
a monoaryltriazole has been found especially useful. This group
of sulfur containing compounds are designated "sulfur containing
copper corrosion inhibitors" and in one preferred sense are
N-heterocycles containing sulfur.
Suppressant. Preferred suppressants are maleic
anhydride polymers. Especially useful maleic anhydride polymers
are selected from the group consisting of homopolymers of maleic
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anhydride, and copolymers of maleic anhydride with vinyl acetate, styrene,
ethylene, isobutylene, and vinyl ethers. These polymers can be easily pre-
pared according to standard methods of polymerization. In addition to
synthetic polymers, natural polymers could also be useful, such as tannins
and modified tannins, lignins and lignosulfonates, and water-soluble gums
and starches.
Dispersant. The dispersant can be selected from the group
consisting of polyacrylates, methacrylate-acrylate copolymers, and
carboxymethyl cellulose which are water-soluble and have an average
molecular weight in the range of about 2,000 to 50,000.
OPTIONAL INGREDIENTS
The optional ingredients of the present formulations include
an antifoam agent, dialkylaminoethanol, sodium oleate, alkali metal
carbonates such as discussed above under "Hydroxides" as well as a small
amount of an identifying dye.
The antifoam utilized is preferably a polyoxyalkylene glycol
or diether thereof or a polypropylene glycol-ethyleneoxide condensate or
other conventional commercial antifoams. Such a suitable antifoam is
Ucon 50 B 5100*, a polyalkylene glycol (Union Carbide).
As a specific inhibitor targeted to protect solder, a minor
perce~tage of a dialkylaminoethanol is optionally utilized. In this
case ~he alkyl group is lower alkyl (Cl - C6) and specific examples of
the solder protector are diethylaminoethanol, dipropylaminoethanol,
dibutylaminoethanol, dimethylaminoethanol, etc.
The function of sodium oleate as an optional ingredient is
also to protect solder.
*Trade r~ark
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1I~5~3
FO~ AND DOSAGE
The format for including the corrosion inhibitor in
the automobile coolant system is either liquid or solid and the
composition is utilized in a dosage of 2-4 fluid ounces per gallon
of coolant with a preferred dosage of about 4 fluid ounces per
gallon. For shipping and installation, a compact unit together
with a solids filter is preferred and an example where the
chemical container is spun on to a ratchet in the filter is noted
in 3,645,402 Alexander, noted ante. Such a compact unit solves
many o~ the~problems arising in current cooling systems by ~
raising the pH to at least 10.4-10.8, supplying more inhibitor
and re~oving suspended precipitates from antifreeze by means of
a filter.
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EXAMPLE 1
A liquid corrosion inhibitor which exhibited a broad
pH of 12-12.5 and a use pH of about 10.6 was prepared by utilizing
the components below in the order o addition noted to produce
a liquid product:
Water (preferably soft or deionized water~ 81.2~-%
Antifoam (Ucon 50 HB 5100--polyalkylene
glycol) 0.1 %
Alkali~metal hydroxide (50% by wt. caustic) 2.7 %
Benzotriazole as copper inhibitor0.5 %
Mercaptobenzothiazole as copper inhibitor 0.5 %
Borax 6.0 %
Sodium metasilicate 3~5 %
Sodium nitrite 3.0 %
Styrene maleic anhydride 0.5 %
Dye .08%
Sodium polyacrylate 0.3 %
An additional experiment utilized tolyltriazole for benzo-
triazole in the above formulation and further experiments added
2 percent of sodium oleate as a solder protector and 1 percent
of dia1kylaminoethanol also as a solder protector. The necessary
ingred~ents were varied within the limits set out in Formulation I
ante.-
~ 2-'
¦ A solid corrosion inhibitor formulation was prepared
utilizing the same ~rder of addition of ingredients as Exam~le 1
but deleting water as follows:
Antifoam (Ucon 50 ~B 5100--polyalkylene 0 5
glycol~
Alkali metal hydroxide (50% by wt, caustic) 13.5 %
~enzo~iazale as copper inhibitor 2.5 %
Nercapt~be~zothiazole as copper inhibitor 2.5
Borax ~ 30.0 %
lU Sodium metasilicate 17.5 %
Sod,ium nitrite 15.0 ~ ,
Styrene maleic anhydride ' ' 2.5 %
Dye '4 %
Sodium polyacrylate 1.5 % '
In this case the final product had a pH of about 12.3.
This formulation was varied within the limits of Formulation II.
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EXAMoeLE 3
Twelve ounces of the preparation of Example 2 were made
up into a chemical package or pallet and placed into a disposable'
type filter particularly adapted for use in the cooling systems
of automlobile engines. The filter was inserted into the cooling
system of a 1968 standard Thunderbird (Ford Motor Company) and
the filter was changed every six months to observe'preci~itate
and general condition of the coolant which proved satisfactory.
The filter is available commercial,ly from Mack Trucks, Inc.,
and is further described in 3,645,402 Alexander.
