PROCESS FOR OBTAINING NATURAL RUBBER, RUBBER COMPOSITION CONTAINING NATURAL RUBBER AND USE THEREOF

Abstract

The present invention relates to a process for obtaining aging-resistant natural rubber, to a rubber composition comprising the thus-obtained natural rubber and to the use of this composition for producing consumer goods.

Claims

1-13. (canceled)

14. A method for obtaining aging-resistant natural rubber, the method comprising: (I) providing a plant material comprising a polymer-containing sap, wherein the polymer-containing sap contains at least natural polyisoprenes, (II) treating the plant/the plant material in such a way that the sap and/or its ingredients is separated from the remaining plant tissue, (III) contacting the plant material/the polymer-containing sap and/or its ingredients with at least one aging stabilizer, (IV) coagulating and/or agglomerating the natural polyisoprenes to afford natural rubber flakes, (V) optionally washing the natural rubber flakes, (VI) obtaining the natural rubber flakes from the extract/the washing solution, (VII) optionally drying the natural rubber (VIII) optionally incorporating the aging stabilizer into the natural rubber, wherein the contacting of the aging stabilizer according to step (III) is carried out before or at the latest during the drying of the natural rubber.

15. The method of claim 14, wherein the method is carried out with fresh and or stored but not separately dried plant material.

16. The method of claim 14, wherein (III) is carried out before, during or after step (II), before, during or after step (IV), and/or before or during step (V), but in any case before or at the latest during step (VII).

17. The method of claim 14, wherein the polymer-containing sap and/or its ingredients is/are extracted from at least one plant material selected from a Taraxacum sp. or Scorzonera sp., especially from Russian dandelion, such as Taraxacum kok-saghyz, Taraxacum krim-saghyz, Taraxacum bicorne, Taraxacum brevicorniculatum, or from Scorzonera tau-saghyz, Scorzonera uzbekistanica, Scorzonera taka-saghyz, Scorzonera hispanica, Scorzonera tau-saghyz, or mixtures of these plants, preferably from Taraxacum kok-saghyz, Scorzonera tau-saghyz, Scorzonera uzbekistanica, Scorzonera teke-saghyz or mixtures or natural or cultivated hybrids thereof, further preferably at least from Taraxacum kok-saghyz, Taraxacum krim-saghyz or mixtures thereof or hybrids with involvement thereof, particularly preferably at least from Taraxacum kok-saghyz.

18. The method of claim 14, wherein the aging stabilizer is selected from butylated hydroxytoluene (BHT), vitamin E in at least one stereoisomeric form or a derivative thereof, an N—C.sub.1-12-alkyl-N′-phenyl-p-phenylenediamine, such as N-isopropyl-N′-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N′-phenyl-p-phenylenediamine (7PPD) or N,N′-bis-1,4-(1,4-dimethylpentyl)-p-phenylenediamine (77PD), diaryl-p-phenylenediamine (DTPD), 4,4′-bis(C.sub.1-12-alkylamino)triphenylamine, 7,8-dimethylisoalloxazine or a compound containing 7,8-dimethylisoalloxazine as a structural building block, such as riboflavin, p-phenylenediamine, p-di(nitroso)arenes, such as poly-p-di(nitroso)benzene, oligomerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), styrenated diphenylamine (DDA), cumylated diphenylamine, zinc salt of 4- and 5-methylmercaptobenzimidazole, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,2′-methylenebis(6-tert-butyl)-p-cresol, poly(dicyclopentadiene-co-p-cresol), n-octadecyl beta-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (BPH), 2-methyl-4,6-bis(octylsulfanylmethyl)phenol, thiobisphenols, 4,4′-bis(1,1-dimethylbenzyl)diphenylamine (CDPA), octylated diphenylamine (ODPA), phenyl-a-naphthylamine (PAN), phenyl-beta-naphthylamine (PBN), tris(nonylphenyl)phosphite, sodium hypophosphite, 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 2-mercaptobenzimidazole (MBI), methyl-2-mercaptobenzimidazole (MMBI), or any combination of the foregoing, preference being given to the aging stabilizers selected from butylated hydroxytoluene (BHT), vitamin E in the form of a tocopherol or a tocotrienol, the zinc salt of di-n-butyldithiocarbamic acid, and a mixture of butylated reaction products of p-cresol and dicyclopentadiene according to formula (I) with n=1, 2, 3, 4, 5, 6, 7, 8 or 9, ##STR00002## particular preference being given to using at least butylated hydroxytoluene (BHT) as aging stabilizer.

19. The method of claim 14, wherein the plant material comprises at least Russian dandelion, in particular Taraxacum kok-saghyz, and at least one aging stabilizer is selected from BHT, vitamin E or a derivative thereof and a compound according to formula (I) with n=1, 2, 3, 4, 5, 6, 7, 8 or 9.

20. The method of claim 14, wherein the aging stabilizer(s) is/are added to the plant material/the polymer-containing sap and/or its ingredients in an amount such that it is/they are present in the natural rubber obtained in a total amount of at least 0.01 phr, preferably in an amount of from 0.05 to 5 phr, further preferably from 0.10 to 3.5 phr, particularly preferably from 0.25 to 2 phr, most preferably from 0.4 to 1 phr.

21. The method of claim 14, wherein the aging stabilizer is added in the form of a powder, a suspension, a liquid or a solution to the plant material/the polymer-containing sap and/or its—optionally purified—ingredients.

22. The method of claim 14, wherein the contacting of the aging stabilizer into the natural rubber occurs under at least one of the following conditions: (i) at a temperature of from −25° C. to 100° C., preferably in the range from 0° C. to 90° C., particularly preferably from 10° C. to 80° C. (ii) by mechanical agitation, preferably stirring, rolling, milling or kneading or a combination thereof, or by diffusion in a suspension of rubber and aging stabilizer in water (iii) for a period of at least 10 min, preferably at least 30 min, further preferably at least 1 hour.

23. The method of claim 14, further producing a rubber composition containing the natural rubber.

24. The method of claim 23, wherein the rubber composition additionally comprises at least one of the following additives: (i) further types of rubber selected from natural rubber or synthetic rubber (ii) fillers, preferably carbon black and/or silica (iii) plasticizers (iv) activators (v) adhesives (vi) pigments (vii) vulcanization accelerators (viii) vulcanization retarders (ix) further crosslinking agents (x) other admixtures.

25. The method of claim 24 further comprising producing rubber articles using the rubber composition.

26. The method of claim 25, wherein the rubber article is selected from tires, in particular vehicle tires, or tire parts, bellows, conveyor belts, air springs, belts, drive belts, such as V-belts, toothed belts, flat belts, V-ribbed belts, hoses, footwear soles, rubber rings, medical articles or tubing.

Description

EXAMPLE 1: ADDITION OF VARIOUS AGING STABILIZERS

[0073] Various aging stabilizers, as shown in Table 1, were contacted with the natural rubber over an incubation time of 8 hours. The rubber produced was stored at 70° C. for up to 14 days. Stabilization against aging was determined in the rubber obtained by determining, by means of gel permeation chromatography, the number-average (M.sub.n) and the weight-average (M.sub.w) molecular weights of the natural rubber polymers, from which the polydispersity factor can be calculated. Comparing these values over time gives a measure of the aging of the rubber.

TABLE-US-00001 TABLE 1 1 2 LNR (2) without aging LNR (2) without aging stabilization stabilization Aging fresh 14 days/70° C. Mn 565 000 222 000 Mw 1 953 000   678 000 PD (1)     3.45     3.06 Mn fresh/Mn 14     2.55 days/70° C. 3 4 LNR (2) with BHT LNR (2) with BHT Aging fresh 14 days/70° C. Mn 616 000 303 000 Mw 2 250 000   885 000 PD (1)     3.65     2.92 Mn fresh/Mn 14     2.03 days/70° C. 5 6 LNR (2) with Wingstay LNR (2) with Wingstay Aging fresh 14 days/70° C. Mn 452 000 260 000 Mw 1 942 000   771 000 PD (1)     4.29     2.97 Mn fresh/Mn 14     1.74 days/70° C. 7 8 IR (3) IR (3) Aging fresh 14 days/70° C. Mn 328 000 225 000 Mw 1 241 000   861 000 PD (1)     3.79     3.82 Mn fresh/Mn 14     1.46 days/70° C. 9 10 NR (4) NR (4) Aging fresh 14 days/70° C. Mn 332 000 323 000     Mw 1 260 000   1 177 000      PD (1)     3.80 3.65 Mn fresh/Mn 14 1.03 days/70° C. (1) polydispersity factor (M.sub.w/Mn) (2) LNR = natural rubber from dandelion, in this case Taraxacum kok-saghyz (3) IR: synthetic rubber (4) NR: natural rubber from Hevea brasiliensis

[0074] The degree of stabilization against aging was determined via the number-average molecular weight ratio Mn fresh/Mn 14 days at 70° C.:

Results:

[0075] LNR without aging stabilization: 2.55: decrease in molecular weight, aging [0076] LNR with BHT: 2.0: average aging [0077] LNR with Wingstay®: 1.7: average aging [0078] IR: 1.46: little aging [0079] NR: 1.03: virtually no decrease in molecular weight, hardly any material aging

EXAMPLE 2: QUALITY FEATURES OF AGING-RESISTANT NATURAL RUBBER COMPOSITIONS

[0080] The further ingredients shown in Table 3 were incorporated into the natural rubber compositions 1 to 6 produced according to Example 1 and into a natural rubber likewise admixed with a vitamin E derivative according to batches 11 and 12, in order to produce rubber compositions suitable for tire production. To this end, 100 parts by weight of each of the rubber compositions 1 to 6 and 11 and 12 (see Table 2) were admixed with the further constituents indicated in Table 3 (in parts by weight) and processed to form a rubber material:

TABLE-US-00002 TABLE 2 Batch No. 1. LNR without aging stabilization, fresh 2. LNR without aging stabilization, aged for 14 days/70° C. 3. LNR with BHT, fresh 4. LNR with BHT, aged for 14 days/70° C. 5. LNR with Wingstay ®, fresh 6. LNR with Wingstay ®, aged for 14 days/70° C. 11. LNR with DMT3, fresh 12. LNR with DMT3, aged for 14 days/70° C. LNR = natural rubber from dandelion, in this case Taraxacum kok-saghyz

TABLE-US-00003 TABLE 3 Further ingredients of the rubber compositions, each in (parts by weight) Carbon black (N 121) 48.50 DTPD 1.00 6PPD 1.50 TMQ 1.00 Antiozonant wax 2.50 ZnO 3.00 Stearic acid 2.00 TBBS 1.00 Sulfur 1.65

[0081] The results of the quality test and load test for the rubber compositions produced are shown in Table 4.

TABLE-US-00004 TABLE 4 Evaluation of the properties of the rubber compositions Batch No. Unit 1 2 3 4 5 6 11 12 Evaluation Vulcanization min 5 5 5 5 5 5 5 5 time Vulcanization Celsius 160 160 160 160 160 160 160 160 temperature Shore A hardness Shore A Shore 72.1 74.3 69.5 73.1 71 75.2 72 69.7 hardness (RT) A Δ Shore A 2.2 3.6 4.2 −2.3 hardness after aging (RT) Shore A Shore 66 67 63.2 66.5 65.4 67.1 63.9 63.3 hardness A (70° C.) Δ Shore A 1 3.3 1.7 −0.6 hardness after aging (70° C.) Rebound elasticity (resilience) Resilience (RT) % 32.4 31 34.8 30.6 33.8 31.3 31.5 33.2 Resilience % 48.3 44.5 51.1 45.6 49.3 46.7 46.3 48.4 (70° C.) Δ resilience −3.8 −5.5 −2.6 2.1 after aging (70° C.) Diff(Rb 70° C. − % 15.9 13.5 16.3 15.1 15.5 15.4 14.9 15.1 (A) Rb RT) Stress value (modulus) RT (S3) M100 (RT) (S3) MPa 3 3 3 3.6 2.9 3 2.8 2.5 M200 (RT) (S3) MPa 7.9 7.3 7.4 8.7 7.8 7.4 7 6.4 M300 (RT) (S3) MPa 14 12.6 12.9 14.1 13.5 12.5 11.7 11.2 M300/M100 4.67 4.20 4.30 3.92 4.66 4.17 4.18 4.48 Δ after aging −0.47 −0.38 −0.49 0.30 (RT) Tensile MPa 21.2 18.9 21.5 20.4 21.3 19.1 18.9 17.4 strength (RT) (S3) length Δ tensile −2.3 −1.1 −2.2 −1.5 (B) strength after aging (RT) Elongation at % 440 438 466 430 458 445 462 442 break (RT) (S3) length Δ elongation at −2 −36 −13 −20 break after aging (RT) Fracture J/cm.sup.3 42.7 38.5 45.8 42.3 45.2 39.9 40.9 34.8 energy density (S3) length Δ fracture −4.2 −3.5 −5.3 −6.1 (C) energy density after aging (RT) Abrasion Abrasion (RT) mm.sup.3 182 198 171 187 196 190 184 190 Δ abrasion after (D) aging (RT) 16 16 −6 6 Table data: methods of determination Shore A hardness at room temperature and 70° C. using a durometer in accordance with DIN ISO 7619-1 [Shore A] Rebound elasticity at room temperature and 70° C. in accordance with DIN 53 512 or ISO 4662 or ASTM D 1054 [%] Stress value (modulus) at 100%, 200% and 300% elongation at room temperature in accordance with DIN 53 504 [MPa] Tensile strength at room temperature in accordance with DIN 53 504 [MPa] Elongation at break at room temperature in accordance with DIN 53504 [%] Fracture energy density determined in a tensile test in accordance with DIN 53 504, the fracture energy density being the work required for fracture, based on the volume of the specimen [J/cm.sup.3] Abrasion at room temperature in accordance with DIN 53 516 or new DIN/ISO 4649 [mm.sup.3]

[0082] The results of the quality test show that the addition of aging stabilizers to the natural rubber composition has a positive influence not only on the aging of the natural rubber, but also on the properties of the rubber produced from this material.

[0083] Regarding the evaluation in Table 4: [0084] (A) a smaller drop in difference in rebound elasticity provides advantages in the trade-off between rolling resistance and wet grip of a vehicle tire [0085] (B) the smaller the drop in tensile strength after aging, the better the durability [0086] (C) the smaller the drop in fracture energy density after aging, the better the durability [0087] (D) the lower the DIN abrasion after aging, the longer the life of a tire.