USE OF SURFACTANTS WITH LOW MOLECULAR WEIGHT FOR IMPROVING THE FILTERABILITY IN HYDRAULIC LUBRICANTS

A hydraulic oil, a predominant amount of an oil having a viscosity suitable for lubrication and from 0.03% to 0.06% of an agent improving filterability, corresponding to the formula R—Z. Z represents a polar group containing one or more substituents chosen from phosphoric esters, amides, ethers, amino alcohols, ethoxylated amines, and mixtures thereof. R represents a lipophilic chain having 14 to 24 carbon atoms.

EXAMPLES 
 Comparative Example A formulation of basic additives containing functional quantities of zinc dithiophosphate, an ash-free dithiocarbamate, a detergent containing calcium, a phenolic antioxidant, anti-rust additives, demulsifying agents, a foam inhibitor based on a silicone polymer, were mixed in such a way that the basic formulation of additives (XOIE 303J) represents 0.80% by weight of the finished oil formulation. The finished oil formulation had a kinematic viscosity at 40° C. equal to about 46 cSt. 
 Comparative Example A The basic formulation of additives was mixed in a refined basic oil with a solvent “A” with the addition of a PPD (of the PMA type) in a quantity of 0.2% by weight. 
 Example 1 A quantity of 0.05% by weight of a commercial phosphoric ester “P1” (Rhodafac PA35 from Rhône Poulenc) was added to the finished oil of comparative example A. 
 Example 2 A quantity of 0.05% by weight of a commercial phosphoric ester “P2” (CRODAFOS N3A from Croda) was added to the finished oil of comparative example A. 
 Example 3 A quantity of 0.05% by weight of a commercial phosphoric ester “P3” (CRODAFOS N5A from Croda) was added to the finished oil of comparative example A. 
 Example 4 A quantity of 0.03% by weight of a commercial fatty amide “OL” (CRODAMIDE O from Croda or Armeed O from Akzo) was added to the finished oil of comparative example A. 
 Comparative Example B The basic formulation of additives was mixed in a refined basic oil with a solvent “B” with the addition of a PPD (of the PMA type) in a quantity of 0.2% by weight. 
 Example 5 A quantity of 0.05% by weight of a commercial phosphoric ester “P1” (Rhodafac P PA35 from Rhône Poulenc) was added to the finished oil of comparative example B. 
 Example 6 A quantity of 0.05% by weight of a commercial phosphoric ester “P2” (CRODAFOS N3A from Croda) was added to the finished oil of comparative example B. 
 Example 7 A quantity of 0.05% by weight of a commercial phosphoric ester “P3” (CRODAFOS N5A from Croda) was added to the finished oil of comparative example B. 
 Example 8 A quantity of 0.03% by weight of a commercial fatty amide “OL” (CRODAMIDE O from Croda or Armeed O from Akzo) was added to the finished oil of comparative example B. 
 Comparative Example C The basic formulation of additives was mixed in a refined basic oil with a solvent “C” with the addition of a PPD (of the PMA type) in a quantity of 0.2% by weight and the addition of a VI improver (of the PMA type) in a quantity of 4.65% by weight. 
 Example 9 A quantity of 0.05% by weight of a commercial phosphoric ester “P1” (Rhodafac PA 35 from Rhône Poulenc) was added to the finished oil of comparative example C. 
 Example 10 A quantity of 0.05% by weight of a commercial phosphoric ester P2” (CRODAFOS N3A from Croda) was added to the finished oil of comparative example C. 
 Example 11 A quantity of 0.05% by weight of a commercial phosphoric ester “P3” (CRODAFOS N5A from Croda) was added to the finished oil of comparative example C. 
 Example 12 A quantity of 0.03% by weight of a commercial fatty amide “OL” (CRODAMIDE O from Croda or Armeed O from Akzo) was added to the finished oil of comparative example C. 
 Comparative Example D The basic formulation of additives was mixed with a “basic formulation speciality” containing a certain quantity of a VI improver (of the PMA type). 
 Example 13 A quantity of 0.05% by weight of a commercial phosphoric ester “P1” (Rhodafac PA 35 from Rhône Poulenc) was added to the finished oil of comparative example D. 
 Example 14 A quantity of 0.05% by weight of a commercial phosphoric ester “P2” (CRODAFOS N3A from Croda) was added to the finished oil of comparative example D. 
 Example 15 A quantity of 0.05% by weight of a commercial phosphoric ester “P3” (CRODAFOS N5A from Croda) was added to the finished oil of comparative example D. 
 Example 16 A quantity of 0.03% by weight of a commercial fatty amide “OL” (CRODAMIDE O from Croda or Armeed O from Akzo) was added to the finished oil of comparative example D. The above-mentioned examples were evaluated in the filterability tests AFNOR NFE 48690 (A, B, C, D) and AFNOR NFE 48691 (A, B). Table 1 below summarised the test results. 1 TABLE 1 Filterability tests on formulations HM and HV in oil of grade ISO VG 46 (filterability index IF and IFE) Filterability AFNOR test NFE 48690 48691 48691 48690 48690 48690 Type of oil HM HM HM HM HV HV Basic oils A B A B C D Grade ISO VG46 VG46 VG46 VG46 VG46 VG46 Constituents Amount (wt. %) Reference XOIE 1.58 8.1 1.68 3.2 1.32 1.28 additives 303 J P1 0.05 1.13 1.11 1.31 1.14 1.21 1.12 P2 0.05 1.05 1.10 1.30 1.16 1.27 1.30 P3 0.05 1.10 1.11 1.16 1.11 1.23 1.26 OL 0.03 1.03 1.18 1.23 1.19 1.32 1.23