Transmission lubricant

Abstract

The present invention relates to a transmission lubricant comprising at least 30% by weight of polyalkyl (meth)acrylate. The present invention further describes polyalkyl (meth)acrylates for use in lubricants and also processes for preparing them and their use. The present lubricants can be used particularly in wind turbine transmissions.

Claims

1. A lubricant, comprising at least 30% by weight of a polyalkyl(meth)acrylate, wherein the polyalkyl(meth)acrylate comprises: a) 0 to 0.5% by weight of repeat units derived from (meth)acrylates of the formula (I): ##STR00008## wherein R is hydrogen or methyl, and R.sup.1 is an alkyl radical having 1 to 5 carbon atoms; b) 50 to 100% by weight of repeat units derived from (meth)acrylates of the formula (II): ##STR00009## wherein R is hydrogen or methyl, and R.sup.2 is an alkyl radical having 6 to 15 carbon atoms; and c) 0 to 50% by weight of repeat units derived from (meth)acrylates of the formula (III): ##STR00010## wherein R is hydrogen or methyl, and R.sup.3 is an alkyl radical having 16 to 40 carbon atoms; and wherein the polyalkyl(meth)acrylate comprises n-dodecyl thioether and t-dodecylthioether terminal groups, the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that 5 to 80% of the R.sup.2 radicals are branched, based on the weight of the repeat units of the formula (II), the polyalkyl(meth)acrylate is obtained by copolymerization of the component monomers in the presence of 2 to 6% by weight relative to a total weight of the component monomers of a combination of n-dodecylmercaptan and t-dodecyl mercaptan, and a weight average molecular weight of the polyalkyl(meth)acrylate is from 3000 to 25,000 g/mol and a polydispersity of the polyalkyl(meth)acrylate is from 1.1 to 2.5.

2. The lubricant of claim 1, further comprising a polyalphaolefin (PAO) having a kinematic viscosity KV.sub.100 in the range from 3 to mm.sup.2/s, measured at 100 C. according to ASTM D 445.

3. The lubricant of claim 1, further comprising a pour point improver and a group III mineral oil having a kinematic viscosity KV.sub.100 in the range from 3 to 10 mm.sup.2/s, measured at 100 C. according to ASTM D 445.

4. The lubricant of claim 1, wherein a weight-average molecular weight of the polyalkyl(meth)acrylate is from 10,000 to 18,000 g/mol.

5. The lubricant of claim 1, wherein a kinematic viscosity KV.sub.100 of the lubricant is at least 30 mm.sup.2/s, measured at 100 C. according to ASTM D 445.

6. The lubricant of claim 1, wherein a proportion of repeat units derived from (meth)acrylates of the formula (II) is at least 70% by weight.

7. The lubricant of claim 1, wherein the polyalkyl(meth)acrylate further comprises repeat units derived from dispersing monomers.

8. A polyalkyl(meth)acrylate, comprising: a) 0 to 0.5% by weight of repeat units derived from (meth)acrylates of the formula (I): ##STR00011## wherein R is hydrogen or methyl, and R.sup.1 is an alkyl radical having 1 to 5 carbon atoms; b) 50 to 100% by weight of repeat units derived from (meth)acrylates of the formula (II): ##STR00012## wherein R is hydrogen or methyl, and R.sup.2 is an alkyl radical having 6 to 15 carbon atoms; and c) 0 to 50% by weight of repeat units derived from (meth)acrylates of the formula (III): ##STR00013## wherein R is hydrogen or methyl, and R.sup.3 is an alkyl radical having 16 to 40 carbon atoms, wherein: the polyalkyl(meth)acrylate comprises n-dodecyl thioether and t-dodecylthioether terminal groups, the polyalkyl(meth)acrylate has a weigh-average molecular weight in the range from 3000 to 25,000 g/mol and a polydispersity in the range from 1.1 to 2.5; the polyalkyl(meth)acrylate is obtained by copolymerization of the component monomers in the presence of 2 to 6% by weight relative to a total weight of the component monomers of a combination of n-dodecylmercaptan and t-dodecyl mercaptan, and the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that 5 to 80% of the R.sup.2 radicals are branched, based on the weight of the repeat units of the formula (II).

9. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that 10 to 65% of the R.sup.2 radicals are branched, based on the weight of the repeat units of the formula (II).

10. The polyalkyl(meth)acrylate of claim 8, wherein the weight-average molecular weight is from 5000 to 15 000 g/mol.

11. The polyalkyl(meth)acrylate of claim 8, wherein the polydispersity is from 1.4 to 1.9.

12. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that a proportion by weight of the branched R.sup.2 radicals having 9 to 11 carbon atoms is higher than a proportion by weight of the linear R.sup.2 radicals having 9 to 11 carbon atoms.

13. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that a proportion by weight of the linear R.sup.2 radicals having 12 to 15 carbon atoms is higher than a proportion by weight of the branched R.sup.2 radicals having 12 to 15 carbon atoms.

14. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of branched and linear radicals such that a weight ratio of branched to linear R.sup.2 radicals is in the range from 60:40 to 20:80.

15. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of R.sup.2 radicals having a different number of carbon atoms, such that a proportion by weight of R.sup.2 radicals having 12 to 15 carbon atoms is greater than a proportion by weight of R.sup.2 radicals having 7 to 11 carbon atoms.

16. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of linear and branched radicals such that at least 50% by weight of the repeat units of the formula (II) comprise a branched R.sup.2 radical having a branch at the 2 position.

17. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of repeat units comprising methyl branches and ethyl branches.

18. The polyalkyl(meth)acrylate of claim 8, wherein the repeat units of the formula (II) comprise a mixture of repeat units comprising propyl branches and longer-chain branches.

19. A process for preparing the polyalkyl(meth)acrylate of claim 8, the process comprising polymerizing a composition comprising a (meth)acrylate of the formula (II) by a free-radical polymerization in the presence of 2 to 6% by weight relative to a total weight of the component monomers of a combination of n-dodecyl mercaptan and t-dodecyl mercaptan.

20. The process of claim 19, wherein the composition comprises 2 to 4.5% by weight of the combination of n-dodecylmercaptan and t-dodecyl mercaptan, based on the weight of monomers.

21. The process of claim 19, wherein at least 60% by weight of monomers are initially charged.

22. The process of claim 19, further comprising adding an initiator in at least two steps, such that less of the initiator is added in a first step than in subsequent steps.

23. The process of claim 19, wherein a proportion of solvent present during the polymerization is from 0.5 to 10% by weight.

24. The process of claim 19, wherein the polymerization occurs at a temperature in a range from 0 to 30 C. above an initiator temperature at which the half-life of the initiator is 30 minutes.

25. A process of lubricating a transmission system, the process comprising contacting the transmission system with the lubricant of claim 1.

26. A wind power plant, comprising a transmission system having the lubricant of claim 1.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

General Method for Preparation of the Polymers

(1) A 1 liter 4-neck round-bottom flask equipped with a precision glass stirrer (in saber form) and precision glass stirrer sleeve (operated at 150 revolutions per minute), thermometer and reflux condenser was initially charged with 760.0 g of a monomer mixture whose composition is shown in table 1, for example consisting of C12-C15-alkyl methacrylates for example 2, together with 14.06 g of dodecyl mercaptan and 14.06 g of tert-dodecyl mercaptan and 32.4 g of the mineral oil Nexbase 3020 as a solvent. The temperature was adjusted to 110 C. Thereafter, 1.9 g of tert-butyl per-2-ethylhexanoate dissolved in 7.60 g of Nexbase 3020 (20% solution) were metered in within three hours, with addition of 5% of the amount specified within the first hour, 25% within the second hour and 70% within the third hour. 120 minutes and 180 minutes thereafter, another 1.52 g each time of tert-butyl per-2-ethylhexanoate are added. The total reaction time is 6 hours.

(2) The weight-average molecular weight M.sub.w and the polydispersity index PDI of the polymers were determined by GPC. The measurements were effected in tetrahydrofuran at 35 C. against a polymethylmethacrylate calibration curve from a set of standards (Polymer Standards Service or Polymer Laboratories), the M.sub.peak of which had a homogeneous logarithmic distribution over the range from 5.Math.10.sup.6 to 2.Math.10.sup.2 g/mol. A combination of six columns (Polymer Standards Service SDV 100 /2SDV LXL/2SDV 100 /Shodex KF-800D) was used. To record the signal, an RI detector (Agilent 1100 Series) was used.

(3) TABLE-US-00001 TABLE 1 Properties of the polymers used Monomer composition Mw PDI Polymer (weight ratio) [g/mol] (Mw/Mn) Example 1 LIMA 13400 1.66 100 Example 2 LIMA - LMA 14400 1.68 20 - 80 Example 3 LIMA - LMA 14200 1.68 40 - 60 Example 4 IDMA - LMA 14500 1.70 20 - 80 Example 5 iC.sub.13MA - LMA 14300 1.69 20 - 80 Example 6 IDMA - C.sub.13-C.sub.15MA 13700 1.68 20 - 80 LMA: alkyl methacrylate having 12 to 14 carbon atoms in the alkyl radical, the alkyl radical being a mixture comprising predominantly linear radicals (proportion of linear radicals approx. 98% by weight; proportion of C.sub.12 approx. 73% by weight; proportion of C.sub.14 approx. 25% by weight) IDMA: alkyl methacrylate having about 10 carbon atoms in the alkyl radical, the alkyl radical being a mixture comprising predominantly branched radicals (proportion of branched radicals approx. 98% by weight; proportion of C.sub.10 approx. 89.9% by weight; proportion of C.sub.11 approx. 4.6% by weight) LIMA: alkyl methacrylate having 12 to 15 carbon atoms in the alkyl radical, the alkyl radical being a mixture comprising branched and linear radicals (proportion of C.sub.12 branched: approx. 12% by weight and C.sub.12 linear: approx. 11.3% by weight; proportion of C.sub.13 branched: approx. 17.3% by weight and C.sub.13 linear: approx. 13.5% by weight; proportion of C.sub.14 branched: approx. 15.7% by weight and C.sub.14 linear: approx. 11.9% by weight; proportion of C.sub.15 branched: approx. 9.8% by weight and C.sub.15 linear: approx. 6.2% by weight; proportion of methyl branching approx. 14%, proportion of ethyl branching approx. 10%, proportion of propyl branching approx. 10%, proportion of longer-chain branching, especially butyl and higher, approx. 17%, based on the sum of linear and branched radicals) iC.sub.13MA alkyl methacrylate having about 13 carbon atoms in the alkyl radical, the alkyl radical being predominantly branched (proportion of C.sub.13 branched: approx. 99% by weight) C.sub.13-C.sub.15MA alkyl methacrylate having 13 to 15 carbon atoms in the alkyl radical, the alkyl radical being a mixture comprising branched and linear radicals (proportion of C.sub.13 branched: approx. 35.6% by weight and C.sub.13 linear: approx. 30.7% by weight; proportion of C.sub.15 branched: approx. 16.9% by weight and C.sub.15 linear: approx. 13.9% by weight)

(4) The proportions of linear and branched radicals were determined by means of GC and .sup.13C and .sup.1H NMR. The .sup.13C spectra were conducted at 30 C. using standard pulse sequences for quantitative determination of .sup.13C signals, more particularly with selection of a relaxation time of 10s and use of broadband decoupling to suppress nuclear Overhauser effects. To improve the signal-noise ratio (S/N ratio), at least 1000 scans were conducted.

(5) The .sup.13C NMR data obtained were processed by mathematical methods in order to optimize the S/N ratio (line broadening of 3 Hz). The .sup.13C NMR signals were assigned by 2D NMR experiments, taking into account the influences of the incremental chemical shifts of the .sup.13C signals. The integrals of the following .sup.13C signal areas were used to calculate the isomer distribution:

(6) TABLE-US-00002 Substructure Chemical shift of the .sup.13C signal unbranched n-alkanol 62.93 ppm (C1) 2-methyl-1-alkanol 69.30 ppm (C1), 16.68 ppm (C1, side chain) 2-ethyl-1-alkanol 65.23 ppm (C1), 42.12 ppm (C2) 2-propyl-1-alkanol 20.10 ppm (C2, side chain), 40.43 ppm (C2) 2-butyl+*-1-alkanol 65.61 ppm (C1) includes 2-propyl *butyl and >C4 chains (C1), 40.64 ppm (C2)

(7) The signal areas were normalized to 100% in order to obtain the isomer distribution of the alcohols in percent.

(8) The results were checked by means of .sup.1H NMR:

(9) TABLE-US-00003 Substructure Chemical shift of the .sup.1H signal unbranched n-alkanol 3.61 ppm (2H, t) 2-methyl-1-alkanol 3.37 ppm (1H, B component of the ABX system) all other branched alkanols 3.50 ppm (2H, d)

(10) In addition, the degree of branching was checked via by evaluation of the signal areas of the -methyl groups (0.88 ppm) and of the -CH.sub.2 groups (3.3-3.7 ppm).

(11) Application Studies

(12) The properties of the polymers obtained were tested using lubricant compositions which comprised 2.65% by weight of additive (Hitec 307) and a polyalphaolefin (PAO 8). The amounts of PAO and of polymer added up to 97.35% by weight. Table 1 reports only the proportion of polymer, and the lubricants were adjusted to a kinematic viscosity of 320 mm.sup.2/s at 40 C. (KV.sub.40). The kinematic viscosities KV.sub.40 and KV.sub.100 measured at 40 C. and 100 C. respectively were determined according to ASTM D 445. The viscosity index VI was found according to ASTM D 2270. The pour point was measured according to ASTM D97. The low-temperature flowability at 26 C. was determined according to ASTM D2983 (Brookfield; BF). The results obtained are shown in table 2. The Brookfield viscosity was determined by two measurements, and the arithmetic mean is reported.

(13) TABLE-US-00004 TABLE 2 Amount of Pour BF 26 polymer KV.sub.40 KV.sub.100 point C. Application [% by wt.] [mm.sup.2/s] [mm.sup.2/s] VI [ C.] [mPas] 1 Example 1 321.1 36.90 163 39 62000 48.1 2 Example 2 319.1 37.08 165 33 62000 48.2 3 Example 3 316.2 36.87 165 36 57500 48.2 4 Example 4 319.4 36.38 162 39 67000 46.0 5 Example 5 320.7 36.53 162 39 65000 47.1 6 Example 6 321.0 36.06 159 42 70000 46.2

(14) In addition, tests were conducted to show the influence of the second base oil. For this purpose, various lubricants were produced, the composition and properties of which are described in table 3. The test methods were detailed above, and all proportions are based on % by weight.

(15) TABLE-US-00005 TABLE 3 Lubricant 7 8 9 10 Constituents Polymer 61.0 51.0 according to Example 1 Polymer 57.0 47.0 according to Example 2 Hitec 307 2.65 2.65 2.65 2.65 PAO 4 36.35 40.35 PAO 8 46.35 50.35 Test results KV.sub.40 [ C.] 318.2 315.4 316.3 323.9 KV.sub.100 [ C.] 38.44 36.78 37.45 36.27 VI 172 165 168 159 Pour point 45 45 33 39 [ C.] BF 26 C. 60000 62000 57000 71000 [mPas]

(16) To study seal compatibility, the lubricant composition detailed in application 8 comprising about 51% by weight of polymer according to example 1 and 46.35% by weight of PAO 8 was used. The test data were obtained according to DIN 53521 and DIN 53505. The data obtained are shown in table 4.

(17) TABLE-US-00006 TABLE 4 Seal compatibility of the lubricant detailed in application 8 Tensile Hardness Change in Time Temp. strength Strain [Shore A volume [h] [ C.] Elastomer [%] [%] points] [%] 168 100 SRE NBR 3.6 21 2 +3.6 28/SX 168 100 72 NBR +0.8 +1.6 +1 1.5 902 168 100 75 FKM 6.9 +5.3 0 +0.3 585 168 130 75 FKM 12 +5.3 0 +1.5 170055 1000 100 SRE NBR 23 67 +6 +8.3 28/SX 1000 100 72 NBR 13 57 +4 +5.8 902 1000 100 75 FKM 10 0.9 0 +0.7 585 1000 130 75 FKM 13 +3.2 0 +3.3 170055

(18) In addition, the improvement in wear through an inventive composition was studied. For this purpose, a lubricant comprising about 51.2% by weight of polymer according to example 1, 2.65% by weight of Hitec 307 and 46.15% by weight of PAO 8 was produced and subjected to an SVR test according to DIN 51834-4. In the case of a measurement at 60 C., the lubricant had a wear factor of 987 at a wear diameter of 608 m (60 C., 300N, 1200, 50 Hz, 3 h). In the case of a measurement at 110 C., the wear factor was 472 at a wear diameter of 655 m (110 C., 300N, 1200, 50 Hz, 3 h). The coefficient of friction was 0.072.

(19) In addition, a test of formation of gray staining was conducted with an instrument from PCS Instruments (PCS Micropitting rig). This involved operating three rollers against one another with different loads using a lubricant. The speed on the contact surfaces is approx. 3.5 m/s, and three load stages are typically selected. For instance, the rollers are run first at 1.1 GPa for one hour, then at 1.4 GPa for one hour and finally at 1.7 GPa for two hours. The roller wear caused by the load is determined after each stage. The test was conducted at 60 C. and 90 C. with the lubricant detailed above in application 4 (46.0 by weight of polymer according to Example 4, 51.35 PAO 8). The comparative example selected was a customary formulation composed of different PAOs which are used in wind power plants.

(20) TABLE-US-00007 TABLE 5 Results of the micropitting test Time [h] 1 2 4 Weight loss of the rollers [mg] at 90 C. Comparative lubricant 1 0.5 5.7 6 Lubricant according to 0.6 1.1 2.1 application 4 Weight loss of the rollers [mg] at 60 C. Comparative lubricant 1 0.2 1.4 1.4 Lubricant according to 0.1 0.2 0.6 application 4