CA1195486A - Antifreeze compositions - Google Patents

Abstract

A B S T R A C T

ANTIFREEZE COMPOSITIONS

A single-phase glycol-based antifreeze composition having superior performance in multi-metal corrosion protection which contains certain silicate, phosphate, borate, nitrate, azole, and alkali compounds in specified proportions. Such compositions are of particular advantage in inhibiting the corrosion of aluminium surfaces at elevated antifreeze service temperatures.

Description

ANTIFREEZE COM2OSITIO~S

The present invention r21ates to glycol-based antifr~eze composi~ions~ par~icularly to corroslon-inhibl~ing compo~itlons useful in automotive service.
Current progress in automotive technol~gy is leading to the development of more efficient, smaller, light~r cars. In one aspect, this progress haR resul~ed 1~ the increased use of alu~ini~ in engl~e cylinder heads and ln componen~s of the engine cooling sys~em such as radiator cores and water pump housings and flttings. In ano~her aspect 9 ~his progress has resul~ed in engin~s d~slgned to opera~e at higher temperatures. Overalla these and other factors have recen~ly placed more stringen~ demands upon ~he performance o the aqueous glycol-based "antifreeze" solutions employed as engine coolants. An~lfreeze formulations must not only prevent the au~omo~ive engin~ cooling system from free ing and lS protect ~gain3t oYerhea~lng but must ~lso provide ~orro~ion protection of cooling syst~m ~urfaces with t~hich i~ is in contac~.
Conventional antifree2es which have been formulated with corrosion inhibitor3 satiqfactory for protec~ion o eng-lnes having cast iron, steel~ solder, copper and brass componen~ surfaces are generally not ~uieable i~ pre~entlng the corroslon of alu~inium and its alloy~. This ls partlculary true under increased opera~ing temperature3. In ~he cool~ng 3y5tem9 alum-lnlum ~orrosion produc~s, par~lcularly aluminiu~ oxide, typically c:lrcula~e ~o and deposi~
on lnternal rad~ator ~urface interfering with the hea~ ~ransfer nece~sary to keep the engine from overheating.
O course, various corroslon inhlbitors, particularly silicatc compound~, are knowm as components of arLtireeze formulations which aid in pro~ec~ing al~m-lnlu~. Lt has, how~er, b~en found dlfficult to formula~e uch aluminlu~ corroslon inhlbitors into a product whlch satlsfies all of the crlteria of ~' ~g~

antifreeze servlce. For instance, the silicates are often unstable, particularly in combinatlon wlth inhibitors necessary for protection of o~her metals. Instabill~y, as evidenced, for example, by precipi~ate formatlon or by loss of corrosion inhibiting activi~y, may be a problem ln terms of shelf life of an antifreeza concen~rate or in terms of use life in aqueous solutions under sen7ice conditlons ln the cooling syste~. In service 5 the inhibitors must remain s~able ln ~he presence of contaminant~, such as decompositlon p~oducts o~ ~he glycol upon which the antifreeze is based and substances such as carbon dioxide and exhaus~ gases which leak into the cooling system~ and must re~ain capable o coun~eractlng the corrosive tendencies of these con~aminants. Although stable and otherwise compa~ible inhibi~or c~mbina~ions have been developed, they are, as a rule, either unduly expensive, or ob~ertlonable from the s~andpoint of ~o~icology and environmental concerns, or ~nable to provid~ fully satisfac~ory ~ulti-me~al corrssion protection, or characterized by unacceptable physlcal properties.
Known antifree7 composi~ions comprising large proportions of phosphate do not have sa~isfac~ory performance wl~h respec~ to multl-metal corrosion protection. It has been sugges~ed (U.S.
4,242,214) that the presence of phosphate lons in antifree~e co~positions i9 a cau~e of the corrosion of alu~inium surfaces.
Moreover, an~ifreeze compositions comprising both phosphate and silicate components (e.g., ~hose disclosed ln U.S. 4,210,549 and U.S~ 3~1219692) do no~ contain the high level of phospha~e found to be critical for aluminium protectlon at hlgh ~emperature.
The present invention is directed to a particular comblnation of specific lngrediants in specifir proportions in a novel anti-3Q freeze composition which satisfies the needs o the progressing automo~ve technology. The co~pos-ltions shc~J a relatively high measure of ~tability in sen7ice and provlde unexpectedly superior p~QteC~ion of both aluminium and other metals under high ~empera~
ture service conditions.

Accordingly, the present lnventlon relates to a single pha~e gly~ol-based antifreeze composition which comprises one or more glycols and for every 100 parts by ~eigh~ of glycol. ~a) between 0.1 ~nd 500 parts by weigh~ of wa~er, (b) be~ween 0.05 and 0.30 parts by weight of 30dium meta~ilicate, (c) between 1.2 and about 4.0 parts by weight of a phosphate of po~assium, (d) be~ween 0O15 and 0~50 parts by we~ght of sodium metaborate and/or sodium tetrabora~e, (e) between OolO and 0.40 par~s by weigh~ of sodium nitrate 9 (f) an effective copper corrosion inhibi~ing amount of tolyltriazole and/or benzo~ria~ole and/or mercaptoben~othiazole, and (g~ a quan~ity of alkali sufficien~ to provide a pa for the compositlon of be~ween about 9 and 11.5.
The present inven~ion most particularly relates to ~lycol-based antifreeze composi~ions combinlng both a ~oderate amount of a silicate csmponent with a relatively large amount of a phosphate componen~ whlch provlde protec~ion of aluminium from corro~3ion under high temperature service condltion~ withou~
sacrificin~ the corrosion protection of o~her ~etals or the other propertie~ required of suitab~e anti~reeze formulatlons.
Sultable glycolq, whlch, of course, i~part to aqueou~
solutions the desired freezlng poin~ depression and boillng poi~t elevation inolude those commonly applied in conven~ional antifreeze compo~itions. Specific reference i9 made to the lower alkylene glycols, suc~, as e~hylene glycol and propylene glycol, ~he polyalkylene glycol~3, ~uch as dle~hyl~ne glycol, triethylene glycol, and dipropyle~e glycol, and polyhydroxy compounds3 such a-3 glycerol. MLxture~ of glycols are equally suitable. Preference l~
gi~en to the use of alkylene glycols and polyalkylene glycols ~ in partLcular ethylene glycol 9 die~hylene glycol and propylene glycol~ Mo~t preferred is ethylene ~lycol, which, a3 i~ is typ~cally commercially avaLlablc~ con~ai~s up ~o abou~ lO pe~ce~
by weight o other glycols.
The compo~i~lons according ~o the inven~ion op~ionally contai~ wa~erO For reasons relatlng to convellience in handllng and s~orage, the antifreeze composi~:Lons may be formulated a~ concen-trates containing little or no water. Typically, such concentrates con~aln be~ween 0.1 and 10 parts by weight of water per 100 parts by weight of glycol, while a water content of between 1 and 5 part~ by weight per 100 parts by welght of glycol is particularly preferred. The present inven~ion comprises both such concentrates as well as dilu~ions made wi~h wa~er for us~ in automotive cooling syst~ms and other heat ~ransfer services. For typical service 9 the concentrate is diluted to a solution containlng up to 400 pares by ~elght o water per 100 parts by weight of glycol, preferably from 40 to 200 par~s by weight of wa~er per 100 parts by we1ght of glycol, and most preferably from 65 to 150 par~s by weight of water par 100 par~s by weigh~ of glycol. The relative a~oun~ of water and glycol in such service solutions iR, of cour~e 9 varied to provide the desired combination of heat transfer, freezing point and boiling point propertles, aud corrosion protection.
The compositio~ according to the invention necessarily contains odlum m@~asilicate in a quanti~y sultably bstween 0~05 and 0.30 part~ by w~ight per 100 parts by w~igh~ o glycol, preferably between 0.06 and 0.25 part6 by ~ei~ht per 100 parts by weight of glycol, more preferably between 0.07 and 0~20 part~ by weight per 100 par~s by ~elght of glycol, and most preferably about 0~10 parts by weight per 100 parts by welght of glycol~ The hydrate for~ of the sod$um metasilicatP may be utilized in formulating the composition~ in whlch case the quantities indicated ~re excluslve of ~he water of hydration. I~ appears that the presence of the ~ilicate pro~ides benefit in aluminiu~
corrosion protec~ion, without suffering disadvantages of instability recognized in the art.
3Q A combinatlon of the speclied silicate compound and a phospha~e co~pound is ~hought ~o be primarily responsible for the hot alu~lnium 3urface corro~ion pro~ction p~-o~lded by ~he anti-freeze co~posi~ion accordlng to the pre~ent inven~ion~ The phosphate also aids in preventing cavitation ero~lon of aluminiu~
pu~p parts.

~35~

A phospha~e of po~assium is necessary for the purposes of the invention. Other phosphates sultable for antifreeze service do not possess ~he solubili~y characteristics required in this compo-sition. ~urthermore, obser~ion has been m~de of a perfor~ance adYantage, in corrosion 2rotection, associated with the potassium ion. Although any of the known pho3phate salts of po~assium can be suitably applied9 dipotassium phospha~e (KzHPO43 is part~cular-ly preferred.
The coneen~ratlon ae which the pho~phate is applied i5 necessarily a~ least 1.2 parts by weight, and preferahly 1~9s than abou~ 4.0 par~s by weight, per 100 parts by weight of glycol.
Lower concen~rations~ e.g., one percent by welght on glycol or less, (as have been known in compo~itions described in the ar~) appear to function by a differe~t mechanism ~han the hlgher concentra~ions now specifled and, in any even~, do not provlde an acceptable level of aluminiu~ protec~ion in the presence of other components .~n compositions according ~o the inven~ion. Quant~ eie5 between 1.3 and 3.0 par~s by weight per 100 part~ by welght of ~lycol are preferred, ~hile those bet~een 1.4 and 2.5 parts by 2a weight per 100 part3 by weight of gly~ol are considered ~ore preferred9 and ~hose between 1.6 and 2.2 pares by weight per 100 parts by weight of glycol are considered most preferred. Again, ~he hydra~e form~ of ~he phospha~e~ may be e~ployed~ i~ whlch case the q~antities indicated are exclusive of the wa~er of hydration.
The composition accordillg to ~he lnventlon also nece~sarily contain~ sodium metaborate and/or sodlu~ tetrabora~e in a quantity ~ufficlent to provide protection agains~ corrosion of iron-contai~ing materlals. The level of borate must, howeverg be limlted in the interests of aluminium pro~ection. A conce~tra~io~
of ~he borate compound betwee~ 0015 and 0.50 par~s by welght ~exclusive ~f any water of hydrati~n) per lOQ par~s by weight of glycol is generslly s~itable~ whlle a co~cen,ratlon between 0020 and 0.45 par~ by we-lght per 100 par~ by we~ght glycol ls preferred and a conoentration between 0.25 and 0.~0 parts by ~eight per 100 par~s by weight of glycol ls more preferred. A~ou~

~ 6 --0.30 to 0035 par~s by weight sodlum tetrabora~e ~par~icularly abou~ 0.50 parts by weight sodium tetrabora~e pentahydrate, inclusive of water of hydration~ is most preferred.
Sodium nitrate is also necessarily present in ~he composition according to the invention in a~ amoun~ between 0.10 and n ~ 40 parts by weigh~ per 100 parts by weight of glycol. The nitrate concentratlon is preferably between 0.15 and 0.309 most preferably between 0.20 and 0.25, par~s by weight per 100 parts by weigh~ of glycol.
lQ In order ~o protec~ agalnst corrosio~ of brass and copper, the antifreeze of the inven~ion necessarily contains an effec~ve amount of ~olyltriazole and/or benzotr~azole and/or sodium mercaptobenzothlazole. For the tolyltriazole or benzotrlazole9 such an effective a~ount is sui~ably a~ leas~ about 0.05, preferably between 0007 and 0.20, and mose preferably abou~ 0.10 par~s by weigh~ per 100 parts by weight of glycol~ ~or the mercaptobenzothiazole9 an effective a~ount is at least abou~ 0.107 preferably between 0015 and 0.50, and most preferably about 0028 par~s by weight per 100 par~ by weight of glyco~. Mos~ preference 2Q is given to the use of toly:Ltriazole.
The p~ of the compo~ition according to ~he inven~ion, whether an an~ifreeze co~ce1ltrate or a diluted service solution, must also be controlled for purposes of corroslon protec~ion. As prepared, the an~ifreeze ~hould generally have a pH in the range from about 9 to 11.5, measured7 for example9 on a sa7~ple dilu~ed with 100 to 900 parts by volllme water per 100 parts by volume of antifreeze and de~eI~lined with a standardized p~ meter according to ASTM
me~hod D 1287. (In servlce, p~ often decreases from s~ch a level to about 8 to 9.) A p~ be~ween 9.5 and 11 is preferred7 while a p~
3Q between 10 and 10.8 i9 consldered most preferredO To provide ~he desired p~ level 7 it is ge~rally nece~sary to add ~o ~he composl~io~ any of the alkali know~ to be ~uitable for antifraeze services, preferably one or a mixture of alkqli me~al hydroxide~
mor~ preferably sodium or pot~ssium ~s~

hydroxide, and most preferably sodium hydroxide in a quantity9 for instance9 of about 0.12 part~ by weight per 100 parts by weigh~ of glycol.
If desired, the antifreeze composition according ~o the invention may contain small amoun~s of further, optional ingredlents and/or mi~tures of ingredients, compatible wi~h those hereinabove specified~ which are designed to impart speclal proper~ies. For lllus~ra~lon, mention may be made of dyes, anti-foam agents, additional corrosion inhibitors, glycol oxidatlon inhibitor~, and sealants. In some C2Se8, such ingredients may be responsible for the presence of a second phase in the otherwise single-phase solution of the composieion according ~o the inventio~.
The invention will now be illus~raeed by means of the following E~amples.
E~MPLE 1 An antifreeze conce~trate in accordance with ehe inven~ion was formulaeed to a cO~po~ieion containing about 93.870w e~hylene glycol, 3~2~/ow water3 0.1670w sodium meeasilicate pentahydrate, 2a l~90~ow dipotassium phospha~e, 0.50%~ b3rax pentahydra~e, 0.2S70w sodium ni~rate~ 0.1070w eolyltriazole, and 0.137OW sodium hydroxide.
Multi-metal corrosion protection of ~he formulation was evaluated in ~he standard ~lassware Corrosion Test ASTM D 1384.
~esults of the performance of the an~ifreeze concentrate9 after 25 tilu~ion in one case to 33% volume concentraee in watPr and in another case to 25% volu~ concsn~ra~e in water; are presented in Table I. Also shown in ehis Table9 for csmpari~on9 are generally recognized standards for maximu~ acceptable levels oE corrosion with a 33% volu~e sslution of concen~rate in water. Entries in the 3Q table are in terms of milligrams per square inch of metal surface lost during a 14 day test a~ 88C, and represe~t average results for four tests.

. ~ _ _ _.

volume carbon cast dilution copper solder brass steel iron aluminlum _, _ . .
formu- 33 0.2 0.5 0.6 0.8 0.3 0.0 latlon 25 0.1 0.8 0.1 0.2 1.7 2.0 cording to in~
vention __ _ _ , _ ~ .
standard 33 2 4 2 2 2 _ 5 .

EXAMPL~ 2 A 25% volume dilution of the an~lfreeze concen~ra~e (in accordance wi~h the invention) described in Example 1 was evalua~ed in a "hot surface aluminium" corroslon tes~ for performance in proeectlng against the corrosion nf aluminium at eleva~ed temperature. ~nder ~he standard test procedures of Wiggle et al ~SAE 810038), the corrosion of aluminitlm coupon surfaces in the 25% volume solutlon of ehe s~oncentra~e in wa~er was deterMined in a 7 day te~ at 135C.
As a result of this test9 aluminlum corrosion was decermined for the formulatio~ iu accordance with the in~ention at a level of 0.3 milligrams per square centimetre of alumin~um coupon surface.
Thl9 level compares favourably to a generally recognl2ed standard for ma~i~u~ accep~able corrosion in ~he ho~ ~rface aluminium tes~
of 1.0 milligrams per square centimetre.
Durlng ~he test, p~ o the antifreeze solutlon dropped fro~
abou~ 10.0 to 8.7, whlle reser~e alkalinity ~aln~alned about 92 ~s~
_ 9 _ of its initial valu~. Following ~he tes~, the antifreeze solution was ob~erved ~o be clear and the coupon surface to be clean, i~e., without noeiceable depDsi~ or discoloration.
EXAMPL~ 3 S A second antifreeze concen~rate, in ascordance with the invention, was formulated as described in Example 1, but in this case having 1.47w dipo~assium phosphate (and 94.0%w ethylene gly~ol).
A third concentrate, not in accordance with the inven~ion, wa~ also formulated as de~crlbed in Example 1, but in this caRe having only 1.0%w dipotassium phosphate ( nd 94.470w e~hylene glycol)0 The critical influence of ~he dipotassium phosphate (K2HP04) concen~ratlon level upon aluminium corrosion pro-tectlon of ~he overall composition is illustrated by comparison of hot surface aluminium ~2stq conducted with the three orm~1a~ions.
~ith regard to aluminium corro~ion, the test of the 1, 47w R2~P04 formula~ion resul~ed in a slight gain in coupon weight of 0.2 mg/cm , which compares favourably with the 0.3 mg/cm 2Q loss shown in Example 2 Por the test of the 1.97w K~HP04 formulation and ~he ~tandard of l.0 mglcm . The for~ulation containing only l~O~/ow K2HP04, however~ was tested wi~h an unacceptable weight loss of 13.5 mg/cm2. Wlth both the 1.970w and 1.4% ~2HP04 fo~mulations the antifreeze solution was clear and the coupon surface clear at the conclusion of the test. Followingthe test of the 1.070~ K2HPO~ formulation, the solution qhowed a whlte precipitate and the coupon surface was black.

The stabili~y o the antlfreeze formula~ion described in Example 1 and its continued perfo~mance with respece to corroslon inhibltlon in antomotive coDling ~ys~ems were evaluated under typical service conditions in ten 1981 model au~omobiles, se~en of which had alu~inlum cylinder heads.

5~

The cooling system of each of ~he tast cars was charged wi~h a 40-50% volume mixture of the antifreeze concentrate in waterO
During the tes-ts, ehe individual automobiles were opera~ed between appro~imately 3 ~o 6 months, attaining between lQ,000 ~nd 40,000 service miles. Radiator ~amples following the test were clear to slightly hazy with ~o precipitation, no solids, and no visual indication of inhlbitor breakdown or corrosi~n products.
The pH of ~he an~ifreeze declined early ln the servlce test~
from about 10 to about 8.5 to 9 but maintained ~he lower level thereafter. ~uffer capacity remained e~cellent - reserve alkalinity averaged 94% of the original value after 10,000 to 15,000 mlles, 90% af~er 209000-25,000 miles and 84% after 35~0~0 ~iles.
- Silica~e content in solution in the antifreaze was found to maintain a level of about 50% of ori~i~al in the atltomobiles reaching 20~000 to 35,000 miles. The aluminlum content of radi~tor antifreeze samples after 35,000 miles was less than 4 par~s per million (ppm), no more than the level f~und in fre3h radiator samples sub~ected to very fe~ miles of service. The level~ of iron 2Q and lead in radiator samples at the end of the ~eqt were generally less ~han 5 ppm, w~ile sopper levels normally averaged le~s than 10 ppm.

Claims (12)

C L A I M S

1. A single-phase glycol-based antifreeze composition which comprises one or more glycols and for every 100 parts by weight of glycol: (a) between 0.1 and 500 parts by weight of water, (b) between 0.05 and 0.30 parts by weight of sodium metasilicate, (c) between 1.2 and about 4.0 parts by weight of a phosphate of potassium, (d) between 0.15 and 0.50 parts by weight of sodium metaborate and/or sodium tetraborate, (e) between 0.10 and 0.40 parts by weight of sodium nitrate, (f) an effective copper corrosion inhibiting amount of tolyltriazole and/or benzotriazole and/or mercaptobenzothiazole, and (g) a quantity of alkali sufficient to provide a pH for the composition of between about 9 and 11.5.

2. A composition according to claim 1, comprising for every 100 parts by weight of glycol up to 400 parts by weight of water, between 0.06 and 0.25 parts by weight of sodium metasilicate, between 1.3 and 3.0 parts by weight of a phosphate of potassium, between 0.20 and 0.45 parts by weight of sodium metaborate or sodium tetraborate, between 0.15 and 0.30 parts by weight of sodium nitrate, and a quantity of alkali sufficient to provide a pH for the composition of between about 9.5 and 11.

3. A composition according to claim 2, comprising for every 100 parts by weight of glycol between 40 and 200 parts by weight of water, between 0.07 and 0.20 parts by weight of sodium metasilicate, between 1.4 and 2.5 parts by weight of a phosphate of potassium, between 0.25 and 0.40 parts by weight of sodium metaborate or sodium tetraborate, and between 0.20 and 0.25 parts by weight of sodium nitrate.

4. A composition according to claim 3, comprising for every 100 parts by weight of glycol, between 0.07 and 2.0 parts by weight of tolyltriazole or benzotriazole.

5. A composition according to claim 3, comprising for every 100 parts by weight of glycol, between 0.15 and 0.50 parts by weight of mercaptobenzothiazole.

6. A composition according to claim 1 wherein the glycol comprises ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol or glycerol.

7. A composition according to claim 1 wherein the phosphate of potassium is dipotassium phosphate.

8. A single-phase glycol-based antifreeze concentrate according to claim 1, which comprises for every 100 parts by weight of glycol, between 1 and 5 parts by weight of water, about 0.10 parts by weight of sodium metasilicate, between 1.6 and 2.2 parts by weight of a phosphate of potassium, between 0.30 and 0.35 parts by weight of sodium metaborate or sodium tetraborate, between 0.20 and 0.25 parts by weight of sodium nitrate, an effective copper corrosion inhibiting amount of tolyltriazole and/or benzotriazole and/or mercaptobenzothiazole, and a quantity of alkali sufficient to provide a pH for the composition of between about 10 and 10.8.

9. A concentrate according to claim 8, comprising for every 100 parts by weight of glycol, between 0.07 and 2.0 parts by weight of tolyltriazole or benzotriazole.

10. A concentrate according to claim 8, comprising for every 100 parts by weight of glycol, between 0.15 and 0.50 parts by weight of mercaptobenzothiazole.

11. A concentrate according to claim 8 wherein the glycol comprises ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol or glycerol.

12. A concentrate according to claim 8 wherein the phosphate of potassium is dipotassium phosphate.