Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
1998-08-19
2002-05-21
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C252S073000, C252S075000, C252S076000, C252S077000, C252S079000, C252S392000, C252S394000, C252S396000
Reexamination Certificate
active
06391257
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to organic acid corrosion inhibitors for antifreeze compositions. More particularly, the present invention relates to mixtures comprising a carboxylic acid, or salt, isomer or mixture thereof, and a cyclohexenoic acid, or salt, isomer or mixture thereof, for use in antifreeze compositions as corrosion inhibitors to provide prolonged corrosion protection to the aluminum metal surfaces in cooling and/or heating systems, such as those found in internal combustion engines.
BACKGROUND OF THE INVENTION
Corrosion has long been a problem when certain metals or alloys are used in applications in which they come into contact with an aqueous medium. For example, in heat-transfer systems, such as those found in internal combustion engines, alcohol-based heat transfer fluids (i.e., antifreezes) can be very corrosive to the metal surfaces of the heat-transfer systems. Compounding this problem is the fact that the corrosion is accelerated under normal engine operating conditions (i.e., high temperatures and pressures).
Aluminum surfaces, are particularly susceptible to corrosion. See Darden et al., “Monobasic/Diacid Combination as Corrosion Inhibitors in Antifreeze Formulations,”
Worldwide Trends in Engine Coolants, Cooling System Materials and Testing
, SAE Int'l SP-811, Paper #900804, pp. 135-51 (1990) (“SAE SP-811”).
Indeed, aluminum surfaces are susceptible to several types of corrosion including general corrosion, pitting and crevice corrosion as well as cavitation-erosion corrosion. These types of corrosion, however, typically occur under different conditions and thus, affect different types of aluminum surfaces. For example, general corrosion usually occurs on aluminum surfaces which are readily susceptible to corrosion because they are poorly inhibited or because they are subject to “heat-rejecting” conditions (e.g., cylinder heads) or “heat-accepting” conditions (e.g., radiators and heater cores).
Pitting/crevice corrosion usually occurs on the thin aluminum sheets used in radiators or heater cores. Such corrosion generally results from localized penetration of the oxide film which would otherwise cover and protect the aluminum surfaces. See SAE SP-811.
Cavitation-erosion corrosion (“CE-type” corrosion), like pitting/crevice corrosion, attacks the protective oxide film which can result from implosion of bubbles on the aluminum surfaces. See SAE SP-811 at p. 136. CE-type corrosion can be accelerated by the formation of foam in the cooling system. Foam results from air bubbles which are entrapped and agitated in the cooling system. See, e.g., Nalco, “Cooling System Liner/Water Pump Pitting,” Technifax TF-159 (1988). Thus, aluminum water pumps, which are used to circulate antifreeze coolants throughout a vehicle's cooling and/or heating systems, are particularly susceptible to CE-type corrosion. This is so because bubbles are readily formed on the trailing sides of the water pump impeller blades due to locally reduced pressure and consequent boiling caused by the high rotation rate. When these bubbles collapse in higher pressure areas in the water pump, they can erode the metal in these areas. This process can eventually destroy the impeller causing loss of pumping performance and/or can perforate the pump body leading to loss of engine coolant. See, e.g., Oakes, “Observation on Aluminum Water Pump Cavitation Tests,” Second Symposium on Engine Coolants, ASTM STP 887, pp. 231-48 (1986).
The corrosion of aluminum surfaces has become a significant concern in the automotive industry because of the increasing use of such lightweight materials. See, e.g.,
Ward's Auto World
, p. 22 (September, 1996);
Ward's
1996
Automotive Yearbook
, p. 27 (58th ed. 1996). For example, heat exchangers in cars and light duty trucks are now being constructed using aluminum components including the water pumps. See Hudgens et al., “Test Methods for the Development of Supplemental Additives for Heavy-Duty Diesel Engine Coolants,” Engine Coolant Testing: Second Volume, ASTM STP 887, Beal, Ed., ASTM, Philadelphia, 1986, pp. 189-215; Oakes “Observations on Aluminum Water Pump Cavitation Tests,” Engine Coolant Testing: Second Volume, ASTM STP 887, Beal, Ed., ASTM, Philadelphia, 1986, pp. 231-248; Beynon et al., “Cooling System Corrosion in Relation to Design and Materials,” Engine Coolant Testing: State of the Art, ASTM STP 705, Ailor, Ed., ASTM, Philadelphia, 1980, pp. 310-326. In particular, CE-type corrosion has become a significant concern because, aside from mechanical seal failures caused by high thermal stresses and inadequate lubrication, CE-type corrosion is one of the leading causes of water pump failures. See, e.g., Beynon, supra at pp. 310-326 (1980).
In general, corrosion inhibitors have been used to protect the metal surfaces used in heat transfer systems. For example, triazoles, thiazoles, borates, silicates, phosphates, benzoates, nitrates, nitrites and molybdates have been used in antifreeze formulations. See, e.g., U.S. Pat. No. 4,873,011; see also, SAE SP-811 at pp. 135-138, 145-46. However, such corrosion inhibitors have several problems, including expense, and inadequate long-term protection. See U.S. Pat. No. 4,946,616, col. 1, lines 31-45; U.S. Pat. No. 4,588,513, col. 1, lines 55-64; SAE SP-811, pp. 137-38. Accordingly, automobile manufacturers have begun using, and several now require, organic acid based (or extended life) corrosion inhibitors such as mono- and/or di-carboxylic acids. A number of carboxylic acid corrosion inhibitors have been described. See, e.g., U.S. Pat. Nos. 4,382,008, 4,448,702 and 4,946,616; see also U.S. Pat. No. 5,741,436, incorporated herein by reference.
However, carboxylic acid corrosion inhibitors, while effective at protecting against general and pitting/crevice types of aluminum corrosion, are generally ineffective as CE-type corrosion inhibitors. See, e.g., D. E. Turcotte, “Engine Coolant Technology, Performance and Life for Light Duty Application,” Fourth Symposium on Engine Coolants (1997). Indeed, many of the known aluminum corrosion inhibitors, while effective at protecting against one or more types of aluminum corrosion, are generally not known to be effective at inhibiting all types of aluminum corrosion. For example, silicates and phosphate salts known to be effective at inhibiting general corrosion and CE-type corrosion, are not known to inhibit pitting/crevice corrosion. Also, nitrates which are known to be effective pitting/crevice corrosion inhibitors, are not known to inhibit general or CE-type corrosion. Certain carboxylic acid based compositions comprising polymerizable-acid graft polymers useful as cavitation-erosion corrosion inhibitors are also disclosed in co-pending U.S. patent application Ser. No. 08/999,098, filed Dec. 29, 1997, and incorporated by reference herein.
Certain cyclohexenoic acids are known and used primarily in the preparation of water-soluble surfactants. See, e.g., U.S. Pat. Nos. 3,931,029 and 4,476,055. Other cyclohexenoic acids have been used as corrosion inhibitors in metal working applications and as corrosion inhibitors in antifreeze compositions for inhibiting the corrosion of metals other than aluminum (e.g., solder alloys). See, e.g., U.S. Pat. No. 3,931,029. However, such corrosion inhibitors were not known to be effective as aluminum corrosion inhibitors and in particular, CE-type corrosion inhibitors.
Thus, there remains a need for a composition which provides improved CE-type corrosion inhibition of aluminum surfaces and which provides acceptable overall corrosion inhibition of aluminum surfaces.
SUMMARY OF THE INVENTION
The present invention provides antifreeze concentrates comprising:
(a) from about 90% to about 99.89% by weight of a liquid alcohol which functions as a freezing point depressant, or mixture thereof;
(b) from about 0.1% to about 5.5% by weight of a carboxylic acid selected from the group consisting of saturated and unsaturated aliphatic, and aromatic, mono-, di- and tri-carboxylic acids, and salts and iso
McKane Elizabeth
Prestone Products Corporation
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