Abstract:
A coolant containing 35-65 wt. % polyethylene glycol and 65-35 wt. % ethylene glycol, which is especially useful for cooling motor vehicle engines.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cooling mediums at elevated temperatures, such as 130° C. 
     2. Description of the Prior Art 
     Heat-stabilized, glass-fibre-reinforced polyamide (PA) 66 is successfully used throughout the world in motor vehicle coolant systems. The economical and efficient manufacture of cooling water tanks, water pipes and thermostatic valve housings in addition to high dynamic loading capacity and resistance to the cooling medium at 108° C. predestines PA 66 for this field of application. Development work to increase the efficiency of internal combustion engines expects higher temperature stresses in the cooling medium. Demands on mechanical properties following contact with the cooling medium at 130° C. are increasing. 
     A mixture comprising ethylene glycol:water in the ratio 1:1 is described as cooling medium in the motor vehicle field. The mixture solidifies at −30° C. and boils at 108° C. Azeotropic distillation is not involved. First of all, the water distils off at 108° C. The temperature of the boiling material increases as the ethylene glycol content increases, until pure glycol distils at 197.4° C. 
     If the temperature of the cooling medium in the closed cooling system rises to 130° C., the internal pressure rises to 2 bars. With the increase in the operating temperature of the cooling medium, in addition to very good tightness, high mechanical strength values at 130° C. in the state saturated with cooling medium are a prerequisite for the operation of the cooling system. If part of the cooling medium escapes as steam, the ethylene glycol content in the cooling medium increases. Components made of polyamide may partially dissolve if glycol content and temperature increase perceptibly. 
     The object of the invention was therefore to develop a cooling medium which operates at the desired temperatures (approx. 130° C.) without pressure increase and does not perceptibly impair the mechanical properties of polyamide. 
     The invention provides a cooling medium containing 
     A) 35-65, preferably 45 to 55 wt. % of polyethylene glycol 
     B) 35-65, preferably 45 to 55 wt. % of ethylene glycol. 
     The cooling medium is suitable for cooling motor vehicle engines. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Polyethylene glycols of the formula HO—(CH 2 —CH 2 —O) n —H, with an average molar mass between 285 and 420 g/mol, a hydrolysis value between 271-315 and a density between 1.12-1.15 g/cm 3  are suitable as polyethylene glycol (A) of the mixture according to the invention. 
     Technical ethylene glycols of the formula HO—CH 2 —CH 2 —OH, a molar weight of 60.05 g/mol and a density of 1.10 to 1.13 g/cm 3  are suitable as ethylene glycol (B) of the mixture according to the invention. 
     Stabilizers may additionally be added to the mixture. 
     Metal deactivators, phosphites and anti-oxidants, such as are conventionally used in the stabilization of a cooling medium, are suitable as stabilizer. The stabilizer is conventionally added in quantities up to 2 wt. %, related to 100 wt. % of mixture comprising A) and B). 
     It has surprisingly been found that glass-fibre-reinforced PA 6 is also resistant to this cooling medium at 130° C. PA 6 can therefore also be used for the manufacture of components in the cooling system, such as cooling water tanks, thermostatic valve housings, cooling water pipes. 
     The glass fibre content is generally 25-45 wt. %, preferably 30-35 wt. % (related to the total moulding compound). 
    
    
     EXAMPLES 
     The following products are used in the examples: 
     PA 66 GF 30=Durethane AKV 30 HR H 2.0 9005/0, Bayer AG 
     PA 6 GF 30=Durethane BKV 30 H 2.0 9005/0, Bayer AG Pseudoplastic 
     PA 6 GF 30=Durethane KU 2-2140/30 H 2.0 9005/0, Bayer AG 
     Polyglycol 300=Polyethylene glycol 300, e.g. Hoechst or Merck 
     Polyglycol 400=Polyethylene glycol 400, e.g. Hoechst or Merck 
     Ethylene glycol=Ethanediol 
     Example 1 (Comparison) 
     Test bodies made of Durethane AKV 30 HR H 2.0 9005/0 (Bayer AG) are stored in a cooling medium, consisting of ethanediol:water in the weight ratio 1:1, in an autoclave. 
     The autoclave is half-filled with cooling medium (ethanediol:water in the ratio 1:1) as tempering fluid. The test bodies are stored separately in the cooling medium in special steel containers. At 130° C. the pressure gauge gives a pressure reading of 2 bars. The heating is switched off after 10, 21 and 40 days. After a cooling time of 16 hours, the test bodies are removed, washed with water, dried, weighed and tested within three hours. The results obtained are summarized in Table 1. 
     Example 2 
     Test bodies made of Durethane AKV 30 HR H 2.0 9005/0 (Bayer AG) are stored in a flask with reflux condenser, in a cooling medium consisting of ethanediol:polyglycol 300 (1:1). The flask is heated by means of an oil bath at 137° C. The temperature of the cooling medium is constantly kept at 130° C. The test bodies are removed after 10, 21 and 40 days, cooled in cold cooling medium, washed with water, dried, weighed and tested within three hours. The results obtained are summarized in Table 1. 
     Example 3 
     The tests in Example 2 are repeated. The storage tests take place at a cooling medium temperature of 150° C. The results obtained are summarized in Table 1. 
     Examples 4 and 5 
     Example 1 is repeated with test bodies made of Durethane KU 2-2140/30 instead of AKV 30 HR at 130 and 120° C. The results obtained are summarized in Table 2. 
     Example 6 
     Example 2 is repeated with test bodies made of Durethane KU 2-2140/30 H 2.0 and BKV 30 H 2.0 9005/0 instead of AKV 30 HR at 130° C. The results obtained are summarized in Table 2. 
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Mechanical properties of AKV 30 HR H 2.0 9005/0 after storage in 
               
               
                 various cooling media at 130° C. and 150° C. 
               
             
          
           
               
                   
                 Example No. 
               
             
          
           
               
                   
                 1 (comparison) 
                 2 
                 3 
               
               
                   
                   
               
             
          
           
               
                 Cooling 
                   
                 Days 
                 Glycol:water 
                 Polyglycol: 
                 Polyglycol: 
               
               
                 medium 
                   
                 (d) 
                 (1:1) 
                 glycol 
                 glycol 
               
               
                   
                   
                   
                   
                 (1:1) 
                 (1:1) 
               
               
                 Temp./ 
                 ° C./ 
                   
                 130/2 
                 130/1 
                 150/1 
               
               
                 pressure 
                 bars 
               
               
                 Weight 
                 % 
                 0 d 
                 11 
                 8 
                 9 
               
               
                 increase 
                   
                 21 d 
                 11  
                 8 
                 9 
               
               
                   
                   
                 42 d 
                 11 
                 8 
                 9 
               
               
                 Impact 
                 kJ/m 2   
                 0 d 
                 61 
                 61 
                 61 
               
               
                 strength 
                   
                 10 d 
                 57 
                 100 
                 88 
               
               
                 ISO 180 1C 
                   
                 21 d 
                 54 
                 83 
                 59 
               
               
                   
                   
                 42 d 
                 17 
                 61 
                 25 
               
               
                 Tear strength 
                 MPa 
                 0 d 
                 181 
                 181 
                 181 
               
               
                 ISO 527 
                   
                 10 d 
                 75 
                 104 
                 99 
               
               
                   
                   
                 21 d 
                 66 
                 101 
                 95 
               
               
                   
                   
                 42 d 
                 32 
                 98 
                 54 
               
               
                 Elongation 
                 % 
                 0 d 
                 3.9 
                 3.9 
                 3.9 
               
               
                 at tear 
                   
                 10 d 
                 4.8 
                 7.3 
                 6.0 
               
               
                 ISO 527 
                   
                 21 d 
                 3.2 
                 5.4 
                 5.0 
               
               
                   
                   
                 42 d 
                 1.1 
                 4.2 
                 1.8 
               
               
                 Tensile E 
                 MPa 
                 0 d 
                 9330 
                 9330 
                 9330 
               
               
                 modulus 
                   
                 10 d 
                 3790 
                 4490 
                 4500 
               
               
                 DIN 53457-1 
                   
                 21 d 
                 3870 
                 4500 
                 4500 
               
               
                   
                   
                 42 d 
                 3670 
                 4780 
                 4270 
               
               
                 Bending 
                 MPa 
                 0 d 
                 281 
                 281 
                 281 
               
               
                 strength 
                   
                 10 d 
                 107 
                 145 
                 139 
               
               
                 ISO 178 
                   
                 21 d 
                 84 
                 147 
                 109 
               
               
                   
                   
                 42 d 
                 36 
                 136 
                 58 
               
               
                 Outer fibre 
                 % 
                 0 d 
                 4.8 
                 4.8 
                 4.8 
               
               
                 strain 
                   
                 10 d 
                 5.7 
                 7.6 
                 7.3 
               
               
                 ISO 178 
                   
                 21 d 
                 3.7 
                 7.4 
                 4.5 
               
               
                   
                   
                 42 d 
                 1.5 
                 5.7 
                 2.6 
               
               
                 Bending E 
                 MPa 
                 0 d 
                 8590 
                 8590 
                 8590 
               
               
                 modulus 
                   
                 10 d 
                 3300 
                 3980 
                 3810 
               
               
                 ISO 178 
                   
                 21 d 
                 3340 
                 4000 
                 3750 
               
               
                   
                   
                 42 d 
                 3110 
                 4120 
                 3310 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Mechanical properties of BKV 30 H 2.0 9005/0 and KU 2-2140/30 
               
               
                 H 2.0 9005/0 after storage in various cooling media at 120° C. and 
               
               
                 130° C. 
               
             
          
           
               
                   
                 Example 
               
             
          
           
               
                   
                 4 
                 5 
                 6 
                 7 
               
               
                   
                   
               
             
          
           
               
                 Polyamide 
                   
                   
                 KU-2 
                 KU 2- 
                 KU 2- 
                 BKV 30 
               
               
                   
                   
                   
                 2140/30 
                 2140/30 
                 2140/30 
               
               
                 Cooling 
                   
                 Days 
                 Glycol: 
                 Glycol: 
                 Polyglycol: 
                 Polyglycol: 
               
               
                 medium 
                   
                 (d) 
                 water 
                 water 
                 glycol 
                 glycol 
               
               
                   
                   
                   
                 (1:1) 
                 (1:1) 
                 (1:1) 
                 (1:1) 
               
               
                 Temp./ 
                 ° C./ 
                   
                 120/1.6 
                 130/2 
                 130/1 
                 130/1 
               
               
                 pressure 
                 bars 
               
               
                 Weight 
                 % 
                 10 d 
                 12 
                 11 
                 10 
                 10 
               
               
                 increase 
                   
                 21 d 
                 11 
                 11 
                 10 
                 10 
               
               
                   
                   
                 42 d 
                 12 
                 11 
                 10 
                 10 
               
               
                 Impact 
                 kJ/m 2   
                 0 d 
                 67 
                 67 
                 67 
                 65 
               
               
                 strength 
                   
                 10 d 
                 67 
                 35 
                 80  
                 84 
               
               
                 ISO 180 
                   
                 21 d 
                 51 
                 13 
                 67 
                 69 
               
               
                 IC 
                   
                 42 d 
                 19 
                 — 
                 49 
                 50 
               
               
                 Tear 
                 MPa 
                 0 d 
                 176 
                 176 
                 176 
                 170 
               
               
                 strength 
                   
                 10 d 
                 69 
                 52 
                 86 
                 87 
               
               
                 ISO 527 
                   
                 21 d 
                 66 
                 26 
                 87 
                 84 
               
               
                   
                   
                 42 d 
                 33 
                 — 
                 83 
                 80 
               
               
                 Elongation 
                 % 
                 0 d 
                 3 
                 3 
                 3 
                 3.3 
               
               
                 at tear 
                   
                 10 d 
                 5.6 
                 3.1 
                 6.2 
                 7.2 
               
               
                 ISO 527 
                   
                 21 d 
                 4.6 
                 0.9 
                 5.8 
                 6.1 
               
               
                   
                   
                 42 d 
                 1.2 
                 — 
                 4.7 
                 4.2 
               
               
                 Tensile E 
                 MPa 
                 0 d 
                 10710 
                 10710 
                 10710 
                 9580 
               
               
                 modulus 
                   
                 10 d 
                 3670 
                 3830 
                 4190 
                 4000 
               
               
                 DIN 
                   
                 21 d 
                 3920 
                 3670 
                 4340 
                 4140 
               
               
                 53457-1 
                   
                 42 d 
                 3790 
                 — 
                 4430 
                 4190 
               
               
                 Bending 
                 MPa 
                 0 d 
                 262 
                 262 
                 262 
                 260 
               
               
                 strength 
                   
                 10 d 
                 97 
                 72 
                 118 
                 123 
               
               
                 ISO 178 
                   
                 21 d 
                 93 
                 35 
                 115 
                 120 
               
               
                   
                   
                 42 d 
                 40 
                 — 
                 90 
                 95 
               
               
                 Outer 
                 % 
                 0 d 
                 4.1 
                 4.1 
                 4.1 
                 4 
               
               
                 fibre 
                   
                 10 d 
                 6.8 
                 4 
                 7.5 
                 7.3 
               
               
                 strain 
                   
                 21 d 
                 5.6 
                 1.4 
                 6.5 
                 6.3 
               
               
                 ISO 178 
                   
                 42 d 
                 1.7 
                 — 
                 4.2 
                 4.7 
               
               
                 Bending E 
                 MPa 
                 0 d 
                 8610 
                 8610 
                 8610 
                 8410 
               
               
                 modulus 
                   
                 10 d 
                 3180 
                 3170 
                 3530 
                 3630 
               
               
                 ISO 178 
                   
                 21 d 
                 3400 
                 3125 
                 390 
                 3670 
               
               
                   
                   
                 42 d 
                 3220 
                 — 
                 3660 
                 3670 
               
               
                   
               
             
          
         
       
     
     From Example 1 (comparative test) in Table 1 it can be seen that: 
     1) the internal pressure in the cooling system rises to 2 bars; 
     2) impact strength, tear strength and bending strength decrease steadily with the storage period; 
     3) the modulus values drop in the course of saturation with cooling medium and remain at the level reached; 
     4) the elongation values rise only through saturation with cooling medium and then drop as a result of surface decomposition. 
     Examples 2 and 3 show that: 
     1) the weight increase on storage in the cooling medium claimed is lower than in the comparative test (Example 1) at both 130° C. and 150° C.; 
     2) there is no pressure increase at temperatures up to 150° C.; 
     3) the properties after storage at 130° C. are distinctly higher than in the comparative test and still perceptibly higher at 150° C. 
     From Table 2 it can be seen that: 
     1) when stored in the standard cooling medium Durethane KU 2-2140/30/pseudoplastic PA 6 GF 30 can only be used up to 120° C. (pressure rise to 1.6 bars); 
     2) for both Durethane KU 2-2140/30 and the standard PA 6 GF 30 (Durethane BKV 30), the properties after storage at 130° C. in the cooling medium claimed are at a distinctly higher level than in the comparative test (Example 1 in Table 1).