Abstract:
A filled insoluble polymer containing one or more corrosion inhibitors and a slightly water soluble polymer is utilized to automatically and continuously add a corrosion inhibitor to a coolant solution passing through a heat exchanger. The corrosion inhibitor is gradually leached from the filled polymer supplying inhibitor to the coolant to protect the metallic parts of the coolant system that are subject to corrosive conditions.

Description:
BACKGROUND OF THE INVENTION 
     Engine coolants for the cooling system of automotive vehicles usually contain ethylene glycol with a small percentage of diethylene glycol diluted with water to provide a 50% or lower concentration of glycol depending on the desired freezing point for the coolant system. Most companies that manufacture and/or distribute ethylene glycol for coolant systems add corrosion inhibitors to the solution to prevent corrosion of the copper-brass material traditionally used in the manufacture of vehicle radiators. 
     These inhibitors usually are a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates and/or arsenates, along with an organic compound, such as benzotriazole, tolyltriazole or mercaptobenzothiazole, to prevent copper corrosion. The solution is generally buffered to a pH in the range of 8-10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol. Most companies recommend only one or two years&#39; service for their antifreeze coolant, however, the average car owner does not follow the owner&#39;s instruction manual to maintain -20° F. protection for the coolant system and does not periodically check the coolant to determine if it is rusty or dirty. Vehicle owners will normally only add water where the antifreeze coolant is lost through leakage, hose breakage or overheating due to mechanical problems. 
     In normal passenger car service, 25% of the cars require coolant system servicing after one year and, after two years, this percentage rises to 50%. With a copper-brass radiator, it is extremely important that the coolant mixture contain 50-55% of the properly inhibited ethylene glycol. A reduction of 33% ethylene glycol and 67% water with a corresponding reduction in the inhibitor level will increase metal corrosion significantly. This is especially important in high temperature coolant systems which are becoming more common in view of the increased use of emission controls. Also, the corrosion inhibitor may lose its effectiveness with age and its use in a coolant system will result in an increase in corrosion of the metallic parts of the coolant system. 
     With the increasing emphasis on gas mileage of automobiles, cars are being downsized and reduced in weight by the substitution of lightweight metals or plastic for the traditional materials. In the coolant system, aluminum radiators are being substituted for previously used copper-brass radiators, and aluminum is more susceptible to the corrosive action of a coolant that is low in the percentage of ethylene glycol and/or corrosion inhibitor. In such a system, additional corrosion inhibitor must be added or the aluminum will begin to corrode by pitting at a rapid rate. The present invention overcomes this corrosion problem by providing for a substantially continuous automatic additon of corrosion inhibitor to the coolant. 
     SUMMARY OF THE INVENTION 
     The present invention relates to composition and device to automatically and continuously add a suitable corrosion inhibitor to a coolant solution in a cooling system for an automotive vehicle engine or other system utilizing a coolant circulating through a heat exchanger. The composition is a filled polymer containing one or more corrosion inhibitors for the metals commonly found in the coolant system. The composition in a suitable form is inserted into or incorporated as an integral part of the coolant system to be exposed to the circulating coolant so that the corrosion inhibitor would be leached out of the polymer into the coolant. 
     The present invention also comprehends the provision of a filled polymer including a suitable insoluble polymer material, a slightly water soluble polymer and a corrosion inhibitor. The components in powder form are ball milled and then compression molded to a suitable shape to be inserted into the coolant system. The slightly water soluble polymer prevents encapsulation of the corrosion inhibitor and slows solubility thereof. 
     Other objects and advantages of the invention will be apparent from the following detailed description of the preferred embodiments thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to a composition and method of automatically and continuously adding a corrosion inhibitor to a coolant solution for a coolant system having a heat exchanger therein; more specifically, an automobile engine coolant system with a radiator formed of a material that is subject to corrosion under corrosive conditions of the coolant solution due to the loss of ethylene glycol and inhibitor or to the loss of effectiveness of the inhibitor. 
     One suitable insoluble polymer for the filled polymeric composition is polypropylene, available as a fine powder, which was mixed with a slightly water soluble or water penetrable polymer, such as polyvinyl alcohol, and a corrosion inhibitor; ball milled for thirty minutes; and then compression molded at a temperature in the range of 400° to 450° F. for four minutes to form a plaque. Lithium phosphate (Li 3  PO 4 ) was chosen as the corrosion inhibitor because of its slow solubility in water and because phosphate has good corrosion inhibitor characteristics. For the slightly water soluble or water penetrable polymer, polyoxyethylene or a cellulose acetate could be substituted for the polyvinyl alcohol; the function of the slightly water soluble polymer being to slow the solubility of the inhibitor and to prevent encapsulation of the inorganic salt, lithium phosphate, by the insoluble polypropylene. 
     After the filled polymer plaques were formed, they were cut into strips and exposed to water or ethylene glycol solution to determine the amount of the corrosion inhibitor extracted as a function of time and temperature. Table I indicates the results of filled polymer strips in water at room temperature where the lithium phosphate gradually dissolved reaching a maximum solubility of approximately 400 parts per million after 48 days. After 105 days the water was replaced with new deionized water and the test continued. Analysis over the period of 112 to 150 days indicated that a filled polymer strip composed of 62.5% polypropylene, 25% lithium phosphate and 12.5% polyoxyethylene (test No. 73-15-3A) gave the greatest lithium phosphate solubility. At 160 days, the water was again changed, and the test continued for 362 days before replacing the water. At 369 days, the specimen was weighed showing a 17.8% weight loss. Assuming lithium phosphate and polyoxyethylene dissolve at rates equivalent to their initial concentration, then approximately one-half of the inhibitor is still available. After 537 days, the specimen showed an 18.7% weight loss and, after 675 days, the specimen showed a 19.1% weight loss. 
     
                                           TABLE I__________________________________________________________________________Composition 73    9   15 - 5A*             22 - 1*                 15 - 1A                     15 - 2A                         15 - 3A                             8 - 4A*                                 8 - 3A*                                     22 - 2__________________________________________________________________________% Li.sub.3 PO.sub.4    100 25   25  25  25  25  25  25  25% Polypropylene        50   50  62.5                     62.5                         62.5                             75  75  --% CelluloseAcetate      25   25  12.5                     --  --  --  --  75% PolyvinylAlcohol  --  --   --  --  12.5                         --  --  --  --% Polyoxy-ethylene --  --   --  --  --  12.5                             --  --  --__________________________________________________________________________Time (days)    ←        ←             Litium Phosphate Analysis (PPM)                                 →                                     →__________________________________________________________________________1        59  --   --  --  --  --  28  22  --2        --  --   --  70  46  70  --  --  --4        --  131  --  --  --  --  --  --  --5        --  --   --  86  73  131 --  --  --7        --  --   39  --  --  --  --  --  1812       173 173  --  116 109 209 122 65  --15       --  --   72  --  --  --  --  --  2219       221 224  --  167 161 206 150 81  --26       262 278  --  --  --  --  156 80  --29       --  --   121 --  --  --  --  --  2634       339 --   --  230 247 247 206 106 --40       --  350  --  --  --  --  --  --  --48       420 304  127 221 254 254 193 79  2264       436 --   125 223 275 330 221 105 --74       --  330  --  --  --  --  --  --  --85       390 468  --  329 411 363 240 92  --105      377 --   --  --  --  --  380 150 --pH       10.0        8.5  --  10.2                     10.0                         10.3                             9.1 9.4 --    ←        ←             ←                 Replaced water                         →                             →                                 →                                     →112      221 36   12.5                 15  21  193 53  1.9 --__________________________________________________________________________      Composition 73               9   15 - 1A                        15 - 2A                            15 - 3A 15 - 5A*__________________________________________________________________________      % Li.sub.3 PO.sub.4               100 25   25  25      25      % Polypropylene               --  62.5 62.5                            62.5    50      % Cellulose      Acetate  --  12.5 --  --      25      % Polyvinyl      Alcohol  --  --   12.5                            --      --      % Polyoxy-      ethylene --  --   --  12.5    --__________________________________________________________________________      Time (days)               Lithium Phosphate Analysis (PPM)__________________________________________________________________________      112      221 15   21  193      36      126      220 25   30  171      66      141      253 29   40  207      78      150      384 44   78  311      147      160      ←                   Replace water                             →                                    →      170      12  1    1   14      3      175      12  1    2   16      4      180      ←                   Stop Test                        →                            --      Stop Test      189      --  --   --  22      --      202      --  --   --  166     --      228      --  --   --  280     --      362      --  --   --  461     --      362      --  --   --  Replace water                                    --      367                   6      % Specimen      Weight Loss      after 370 days               --  --   --  17.8    --      % Specimen      Weight Loss      after 537 days               --  --   --  18.7    --      % Specimen      Weight Loss      after 675 days               --  --   --  19.1    --__________________________________________________________________________ *Note: 15  5A Ball milled 22  1 Roll milled 8  4A Not milled 8  3A Ball milled 
    
     A similar extraction test was run in a 50--50  solution of Prestone II and water at room temperature. The results of this test are shown in Table II. During this test, the specimens were taken out after 42 days, placed in 100% water and the test continued for 253 days. Then the specimens were dried and weighed. Again, the specimen composed of 62.5% of polypropylene, 25% lithium phosphate and 12.5% polyoxyethylene showed the greatest solubility by weight loss. 
     
                       TABLE II______________________________________Composition73       54 - 1  54 - 2  54 - 3                          54 - 4                                54 - 5                                      54 - 6______________________________________% Li.sub.3 PO.sub.4    100     25      25    25    25    15% Polypropy-lene     --      50      62.5  62.5  62.5  30% CelluloseAcetate  --      25      12.5  --    --    55% PolyvinylAlcohol  --      --      --    12.5  --    --% Polyoxy-ethylene --      --      --    --    12.5  --______________________________________Time (Days)    Lithium Phosphate Analysis (PPM)______________________________________5        55      137     110   83    111   13312       119     168     141   114   141   16219       176     220     164   156   202   24526       219     266     196   196   237   30542       226     286     224   191   146   31242       ← Take all samples out and let dry →                            Stop                            Test55       ←  Put all samples in water                            →56       14      6       3     2     7     --66       29      27      21    27    30    --98       247     247     163   169   228   --112      348     371     264   359   289   --246      406     745     411   550   539   --246      ←  Replace water                        →                              →251      21      3       1     11    22% SpecimenWeight Lossafter 253 days    --      13.6    5.4   4.2   20.0% SpecimenWeight Lossafter 420 days    --      15.0    5.8   6.1   25.8% SpecimenWeight Lossafter 608 days    --      17.1    6.9   7.1   28.3______________________________________ 
    
     Some of the data from Tables I and II has been tabulated in Table III to compare the extraction rates in water with that in Prestone II. 
     
                                           TABLE III__________________________________________________________________________Composition:    1       2       3       4       5__________________________________________________________________________% Li.sub.3 PO.sub.4    100     25      25      25      25% Polypropylene    --      50      62.5    62.5    62.5% CelluloseAcetate  --      25      12.5    --      --% PolyvinylAlcohol  --      --      --      12.5    --% Polyoxy-ethylene --      --      --      --      12.5__________________________________________________________________________    Lithium Phosphate Analysis (PPM)       50%     50%     50%     50%     50%       Prestone               Prestone                       Prestone                               Prestone                                       PrestoneTime (days)    H.sub.2 O       50% H.sub.2 O            H.sub.2 O               50% H.sub.2 O                    H.sub.2 O                       50% H.sub.2 O                            H.sub.2 O                               50% H.sub.2 O                                    H.sub.2 O                                       50% H.sub.2 O__________________________________________________________________________ 1        59       --   -- --   -- --   -- --   -- -- 5       --  55  131               137   86                       110   73                                83  131                                       11112       173       119  173               168  116                       141  109                               114  209                                       14119       221       176  224               220  167                       164  161                               156  206                                       20227       262       219  278               266  -- 196  -- 196  -- 23748-42    420       226  350               286  221                       224  254                               191  254                                       146__________________________________________________________________________ 
    
     From Tables I, II and III, it can be concluded that at room temperature lithium phosphate gradually leaches from filled polypropylene plastics containing water soluble or penetrable polymers; this continuing over more than a one year period with water replaced three times (test No. 73-15-3A). Lithium phosphate is also extracted from a 50--50 Prestone II-water mixture, but at a slightly slower rate. Also, approximately 50% of the filler of lithium phosphate-polyoxyethylene is extracted in approximately one year&#39;s time. 
     Extraction tests were also run in refluxing solution simulating actual use in an automobile radiator. The extraction tests in water at 100° C. are shown in Table IV and in a 50--50 solution of Prestone II and water at 107° C. are shown in Table V. 
     
                                           TABLE IV__________________________________________________________________________Composition 73    15 - 6          15 - 5B                15 - 1B                    15 - 2B                        15 - 3B                            8 - 4B*                                 8 - 3B*                                      15 - 4B*__________________________________________________________________________% Li.sub.3 PO.sub.4    100   25    25  25  25  25   25   25% Polypropylene    --    50    62.5                    62.5                        62.5                            75   75   75% CelluloseAcetate  --    25    12.5                    --  --  --   --   --% PolyvinylAlcohol  --    --    --  12.5                        --  --   --   --% Polyoxy-ethylene --    --    --  --  12.5                            --   --   --__________________________________________________________________________Time (days)    Lithium Phosphate Analysis (PPM)__________________________________________________________________________1        --    --    --  --  --  160  50   --2        363   --    138 228 216 182  69   76                            ←Replace water→4        --    448   --  --  --  --   --   --          New water5        400   --    221 284 294 84   11   128                            ←Replace water→12       481   395   329 329 358 62   16   21120       483   766   517 578 334 --   --   261    New water   ← Replace water →                                      New water26       --    1180  --  --  --  --   --   --    --    New water                --  --  --  --   --   --34       607   --    121 320 325 --   --   8240       --    411   --  --  --  --   --   --48       690   --    171 337 309 --   --   8352       New water   ← Replace water →                                      New water54       --    580   --  --  --  --   --   --60       --    New water                --  --  --  --   --   --66       298   --    39  223 200 --   --   674       --    83    --  --  --  --   --   --89       418   258   117 409 369 --   --   12pH       9.7   6.9   6.2 9.6 9.5 --   --   8.4                ← Replace water →112      66    46    21  282 237 --   --   3.0__________________________________________________________________________ *Note: 8  4B Not ball milled 8  3B Ball milled 15  4B Ball milled 
    
     
                                           TABLE V__________________________________________________________________________Composition 73    55 - 1         55 - 2              55 - 3                   55 - 4                        55 - 5                             55 - 6__________________________________________________________________________% Li.sub.3 PO.sub.4    100  25   25   25   25   15% Polypropylene    --   50   62.5 62.5 62.5 30% CelluloseAcetate  --   25   12.5 --   --   55% PolyvinylAlcohol  --   --   --   12.5 --   --% Polyoxy-ethylene --   --   --   --   12.5 0__________________________________________________________________________Time (days)    Lithium Phosphate Analysis (PPM)__________________________________________________________________________ 5       161  264  209  139  115  52812       158  371  275  147  133  31718       206  980  334  176  144  103218       ← Solution replaced with new 50% Prestone II - 50% H.sub.2    O →26       213  194  99   193  153  15142       228  228  201  177  141  23542       ←Take out all samples. Dry specimens and weigh.→                             Stop test55       ←Place all specimens in H.sub. 2 O (100° C.)→    4                   →56       32   11   6    18   19   --66       46   37   24   44   42   --70       44   39   23   46   44   --70       Stop all Tests% SpecimenWeight Lossafter 42 days 5.7  2.9  4.4  5.2__________________________________________________________________________ 
    
     The data for both solutions are compared in Table VI. 
     
                                           TABLE VI__________________________________________________________________________Composition    1       2       3       4       5__________________________________________________________________________% Li.sub.3 PO.sub.4    100     25      25      25      25% Polypropylene    --      50      62.5    62.5    62.5% CelluloseAcetate  --      25      12.5    --      --% Polyvinylalcohol  --      --      --      12.5    --% Polyoxy-ethylene --      --      --      --      12.5__________________________________________________________________________    Lithium Phosphate Analysis (PPM)       50%     50%     50%     50%     50%       Prestone               Prestone                       Prestone                               Prestone                                       PrestoneTime (days)    H.sub.2 O       50% H.sub.2 O            H.sub.2 O               50% H.sub.2 O                    H.sub.2 O                       50% H.sub.2 O                            H.sub.2 O                               50% H.sub.2 O                                    H.sub.2 O                                       50% H.sub.2 O__________________________________________________________________________ 5       400       161  448               264  221                       209  284                               139  294                                       11512       481       158  395               371  329                       275  329                               147  358                                       13320-18    483       206  766               480  517                       334  578                               176  334                                       14420-18    ←       ← Solution replaced with new H.sub.2 O or Prestone II -       H.sub.2 O →              →34-26    607       213  -- 194  121                        99  320                               193  325                                       15348-42    690       228  -- 228  171                       201  337                               177  309                                       141__________________________________________________________________________ 
    
     From these three tables, it can be concluded that, at boiling temperatures, lithium phosphate dissolves at a faster rate than at room temperature, except for the polypropylene, polyoxyethylene, lithium phosphate composition. This may result from the tendency of polyoxyethylene to gel or precipitate at boiling temperatures. Also, the rate of extraction of lithium phosphate is greater in water than in a 50--50 mixture of Prestone II and water. 
     In additional tests, the lithium phosphate was replaced by a more soluble commercially available corrosion inhibitor which was analyzed to be a mixture of sodium and/or potassium salts of nitrite, nitrate, borate and silicate. These tests as shown in Table VII showed very little difference in extraction rates in either water or a Prestone II-water mixture under room temperature or boiling temperature conditions. 
     
                                           TABLE VII__________________________________________________________________________Composition: 98     21-1 21-2 21-3 21-1W                        21-4 21-2W                                 22-1 22-2 22-3 22-4__________________________________________________________________________% Inhibitor     1    5    12.5 12.5                        25   25  1.0  5.0  12.5 25% Polypropylene     86.5 82.5 75   75  62.5 62.5                                 86.5 83.5 75   62.5% Polyoxy-ethylene  12.5 12.5 12.5 12.5                        12.5 12.5                                 12.5 12.5 12.5 12.5     50%  50%  50%      50%      50%  50%  50%  50%Solution  Prestone          Prestone               Prestone                    H.sub.2 O                        Prestone                             H.sub.2 O                                 Prestone                                      Prestone                                           Prestone                                                Prestone     50% H.sub.2 O          50% H.sub.2 O               50% H.sub.2 O                        50% H.sub.2 O                                 50% H.sub.2 O                                      50% H.sub.2 O                                           50% H.sub.2 O                                                50% H.sub.2 OTemperature °C.     107  107  107  100 107  100 ← Room Temperature__________________________________________________________________________                                 →Time (Days)     ←          ←               ←                    ←Analysis for Sodium (PPM)→                                      →                                           →                                                →__________________________________________________________________________  10      200  150  70   152 250  292 0    60   0    0 50       0    85   237  234 0    358 16   199  356  225 50       Changed to Room Temperature --   --   --   -- 70       91   244  188  211 391  325 0    71   97   0184       320  480  660  245 540  395 170  190  170  360184       ←          ←               ←                    Solution changed to water in all                                      →                                           →                                                →189       85   123  150  9   10   2   42   12   13   24% Specimen WeightLoss After 191Days      12.1 14.7 17.1 18.7                        22.3 21.4                                 5.0  6.3  13.8 15.8% Specimen WeightLoss After 358Days      13.3 16.0 19.7 22.0                        24.0 25.8                                 8.4  9.9  15.8 18.4% Specimen WeightLoss After 496Days      13.4 16.2 20.5 22.3                        24.5 26.3                                 10.5 12.0 18.1 21.1__________________________________________________________________________ 
    
     All of the filled polymers retained their integrity over the test periods. Other polymeric materials which may be utilized for this composition include the following insoluble thermoplastics: polyethylene, ABS, fluorocarbons, nylon, polyamides, polycarbonates, polyethylene oxide, polyesters, polyphenylene sulfide, polyphenyl sulfone, polysulfone, polystyrene, styrene acrylonitrile and polyvinyl choloride. Insoluble thermosetting materials include phenolics and epoxys. With respect to the slightly water soluble or water penetrable polymers, these can include natural materials, such as corn starch, dextrin, animal glue, gelatin and alginates, and synthetics falling into the catagories of cellulose derivatives, acrylates and miscellaneous. The cellulose derivatives include carboxymethyl cellulose, hydroxyethyl cellulose and carboxymethyl hydroxyethyl cellulose. The acrylates include polyacrylic acid salts and polyacrylamide, while the miscellaneous materials include polyvinyl alcohol, polyoxyethylene and polyvinyl pyrrolidone.