CURABLE RUBBER COMPOSITION

Abstract

A rubber composition containing based upon parts by weight per 100 parts by weight rubber (phr): (A) 20-50 phr of a copolymer of ethylene, at least one C3 to C23 -olefin and a least one polyene monomer, whereby the copolymer unit derived from the polyene is 1 to 5 wt. %, by weight of the copolymer (A) and has a Mooney viscosity ML (1+4) at 100 C. from 51 or greater, in particular from 55 to 90 at 100 C., (B) 50-80 phr of butyl-type rubber and (C) a resin-based curative, containing a phenol formaldehyde resin cross-linker as only curing agent and an activator package comprising of metal oxide and a halogen donor where a halogenated component (B) or halogenated cross-linker as part of component (C) not already present.

Claims

1-9. (canceled)

10. A method of providing an expandable tire curing bladder comprising (i) providing a curable rubber composition comprising based upon parts by weight per 100 parts by weight rubber (phr): (A) 20-50 phr of a copolymer of ethylene, at least one C3 to C23 -olefin and a least one polyene monomer, whereby the copolymer unit derived from the polyene is 1 to 5 wt. %, by weight of the copolymer (A) and has a Mooney viscosity ML (1+4) at 100 C. greater than or equal to 51, (B) 50-80 phr of butyl-type rubber and (C) a resin-based curative, comprising a phenol formaldehyde resin cross-linker as the only curing agent and an activator package comprising of a metal oxide and a halogen donor where a halogenated component (B) or halogenated cross-linker as part of component (C) is not already present, and (ii) curing the composition to provide an expandable tire curing bladder.

11. The method of claim 10 wherein the copolymer comprises 48 to 70 weight percent units derived from ethylene, 1 to 5 weight percent units derived from at least one non-conjugated diene and the balance is the C.sub.3 to C.sub.23 -olefin, preferably propylene.

12. The method of claim 10 wherein the butyl-type rubber is a butyl rubber comprising repeating units from isobutylene and 1 to 20 wt-% isoprene.

13. The method of claim 10 wherein the resin-based curative comprises a combination of a polychloroprene rubber and a phenol-formaldehyde resin.

14. The method of claim 10 wherein the resin-based curative comprises a combination of a polychloroprene rubber and a brominated phenolic resin.

15. The method of claim 10 further comprising at least one oil and/or wax.

16. The method of claim 10 wherein the curable rubber composition comprises from 20 to 100 phr of a filler.

17. An expandable tire curing bladder comprising a cured rubber composition obtained by curing a curable rubber composition based upon parts by weight per 100 parts by weight rubber (phr): (A) 20-50 phr of a copolymer of ethylene, at least one C3 to C23 -olefin and a least one polyene monomer, whereby the copolymer unit derived from the polyene is 1 to 5 wt. %, by weight of the copolymer (A) and has a Mooney viscosity ML (1+4) at 100 C. from 51 or greater, in particular from 55 to 90 at 100 C., (B) 50-80 phr of butyl-type rubber and (C) a resin-based curative, containing a phenol formaldehyde resin cross-linker as the only curing agent and an activator package comprising of a metal oxide and a halogen donor where a halogenated component (B) or halogenated cross-linker as part of component (C) is not already present.

18. A method of shaping and curing an uncured pneumatic rubber tire in a mold using an expandable tire curing bladder to shape and cure said uncured pneumatic rubber tire, comprising the sequential steps of: (A) inserting an uncured pneumatic rubber tire into a curing press comprising a rigid mold having an expandable tire curing bladder positioned therein, the rigid mold having at least one molding surface, (B) expanding the expandable tire curing bladder within the uncured pneumatic tire by filling an internal portion of the expandable tire curing bladder with a fluid to cause the expandable tire curing bladder to expand outwardly against an inner surface of the uncured pneumatic rubber tire to force the uncured pneumatic tire against the molding surface(s) of the mold; (C) curing the pneumatic rubber tire within the mold under conditions of heat and pressure, and (D) deflating the expandable tire curing bladder and removing said cured pneumatic rubber tire from the mold; wherein the expandable tire curing bladder is the expandable tire curing bladder of claim 17.

Description

EXAMPLES

[0065] Compounds described in the examples were mixed in a Harburg Freudenberger 1.5 litre internal mixer having an intermeshing rotor configuration, and using a fill factor of 68%. To achieve the best possible dispersion, while controlling cure safety, a two-step mixing process was employed. In the first mixing step the polymers, (butyl rubber, EPDM and if used polychloroprene as part of the curing package), were introduced to the mixer at an initial mixer body temperature of 40 C. and blended together for 30 seconds using a rotor speed of 45 rpm. Fillers and optionally oil were then added, and the rotor speed was increased after a further 30 seconds in a stepwise manner, first to 70 rpm, then after a further 20 seconds to 150 rpm. Mixing was allowed to proceed until a batch temperature of 170 C. was achieved, taking approximately 2 minutes, when the batches were removed from the mixer and transferred to a two roll mill (Troester WNU 2) for cooling and sheeting off.

[0066] After the batches had cooled to 23 C. (room temperature), they were returned to the internal mixer and mixed using a rotor speed of 45 rpm until a temperature of 70 C. was reached, when the curing resin optionally as masterbatch with some additional butyl rubber like Rhenogran PCZ-70/IIR was added. Mixing continued until the batches reached a temperature of 100 C., when stearic acid was added. The rotor speed was then reduced (approximately 30 rpm) to maintain a batch temperature of 100 C. for a further minute before the batches were removed and transferred to the two roll mill for cooling and sheeting off.

[0067] Analysis of cure rheology was carried out using a moving die rheometer (MDR2000E) with test conditions of 60 minutes at 180 C., according to ISO 6502:1999. The rheometer data was used to establish cure times to produce moulded 2 mm tensile test sheets from each batch, being equivalent to 2tc(90) at 180 C.

[0068] Resistance to the formation of cracks due to flex fatigue was measured using a DeMattia Flexing Machine according to ASTM D430-06, Method B. In accordance with the standard, the number of cycles were recorded at progressive levels of crack severity as described by the standard, i.e.

[0069] Grade 0 No cracking has occurred.

[0070] Grade 1 Cracks at this stage appear as pin pricks to the naked eye. Grade as 1 if the pin pricks are less than 10 in number and less than 0.5 mm in length.

[0071] Grade 2 Assess as Grade 2 If either of the following applies:

[0072] (1) The pin pricks are in excess of 10 In number, or

[0073] (2) The number of cracks is less than 10 but one or more cracks have developed beyond the pin prick stage, that is, they have perceptible length without much depth, but their length is still less than 0.5 mm.

[0074] Grade 3 Assess as Grade 3 if one or more of the pin pricks have become obvious cracks with a length greater than 0.5 mm but not greater than 1.0 mm.

[0075] Grade 4 The length of the largest crack is greater than 1.0 mm but not greater than 1.5 mm (0.06 in.).

[0076] Grade 5 The length of the largest crack is greater than 1.5 mm but not greater than 3.0 mm (0.12 in.).

[0077] Grade 6 The length of the largest crack is greater than 3.0 mm but not greater than 5.0 mm (0.20 in.).

[0078] Grade 7 The length of the largest crack is greater than 5.0 mm but not greater than 8.0 mm (0.31 in.).

[0079] Grade 8 The length of the largest crack is greater than 8.0 mm but not greater than 12.0 mm (0.47 in.).

[0080] Grade 9 The length of the largest crack is greater than 12.0 mm but not greater than 15.0 mm (0.60 in.).

[0081] Grade 10 The length of the largest crack is greater than 15.0 mm. This indicates complete failure of the specimen.

[0082] The lower the grade observed, the more curing cycles in the operation of the curing bladders can be expected.

Example 1

[0083] Table 1 shows Comparative Experiment A, a typical resin cured butyl formulation being representative of the type of formulation used in the manufacture of tire curing bladders. Examples 1, 3 and 5 as well as Comparison Examples 2, 4 and 6 introduce EPDM 1 and EPDM 2 (see table 2) respectively by replacing Butyl 1 at different levels.

TABLE-US-00001 TABLE 1 Example/Comparative Experiment Comp. Comp. Comp. Comp. Exp. A Expl. 1 Expl. 2 Expl. 3 Expl. 4 Expl. 5 Expl. 6 EPDM 1 20 30 40 EPDM 2 20 30 40 WRT Neoprene* 5.5 5.5 5.5 5.5 5.5 5.5 5.5 Butyl1* 89 69 69 59 59 49 49 Butyl1 (as 6.4 6.4 6.4 6.4 6.4 6.4 6.4 part of resin masterbatch) ZnO 6.4 6.4 6.4 6.4 6.4 6.4 6.4 Carbon black 55 55 55 55 55 55 55 N-339* Castor oil 5 5 5 5 5 5 5 Tudalen B-8014* Resin* 8.6 8.6 8.6 8.6 8.6 8.6 8.6 Stearic acid 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Total phr 177.4 177.4 177.4 177.4 177.4 177.4 177.4 *Ingredient Details; EPDM 1 and EPDM 2 see table 2

TABLE-US-00002 WRT Neoprene Supplied by DuPont; Mercaptan modified polychloroprene; Viscosity ML(1 + 4)@100 C. = 46 Butyl 1 IIR butyl 301, Supplied by Lanxess; Butyl rubber; viscosity ML(1 + 8)@125 C. = 51, 1.85 mol % isoprene content 2.24 wt. % Tudalen B-8014 Supplied by Hansen & Rosenthal; Paraffinic processing oil resin alkylphenol resin Carbon black N-339 Supplied by Cabot; High Abrasion Furnace Black

[0084] Table 2 polymer specifications for EPDM 1 and EPDM 2;

TABLE-US-00003 TABLE 2 Units EPDM 1 EPDM 2 Test Method Mooney viscosity ML MU 33 67 ISO 289 (1 + 4) 125 C. Mooney viscosity ML MU 57.3 100 ISO 289 (1 + 4) 100 C. Ethylene content wt % 55 65 ASTM D 3900 Third monomer type ENB ENB Third Monomer wt % 2.3 2.8 ASTM D 6047 content Molecular weight Kg/mol 195 270 GPC (Mw) Molecular weight 2.9 2.8 GPC distribution (Mw/Mn)

[0085] Table 3 Shows the results of DeMattia flex fatigue testing. It can be seen that Comparative Experiment A starts to show Grade 2 damage after 2000 kcycles and complete failure after 4000 kcycles, whereas the Examples 1, 3, and 5 display no signs of flex fatigue damage after 8000 kcycles, when the test was stopped.

TABLE-US-00004 TABLE 3 DeMattia Comp. Comp. Comp. Comp. Flex Fatigue Exp. A Expl. 1 Expl. 2 Expl. 3 Expl. 4 Expl. 5 Expl. 6 Grade 1 [kcycles] 0 0 0 0 0 0 Grade 2 [kcycles] 2000 0 0 0 0 0 0 Grade 3 [kcycles] 2250 0 0 0 0 0 0 Grade 4 [kcycles] 2500 0 0 0 0 0 0 Grade 5 [kcycles] 0 0 0 0 0 0 Grade 6 [kcycles] 3024 0 0 0 0 0 0 Stopped [kcycles] 4000 8000 8000 8000 8000 8000 8000 Condition Grade 10 No No No No No No cracks cracks cracks cracks cracks cracks

[0086] Table 4 Shows the original tensile strength and the tensile strength after heat aging for 24 hours at 180 C. It can be seen from all of the examples that the presence of EPDM, regardless of the EPDM viscosity, always improves the retention of tensile strength after heat aging when compared with Comparative experiment A. It can also be seen by comparing Comparative experiment A with the other examples that the lower viscosity EPDM 1 gives a better retention of tensile strength than that achieved by using the same amount of the higher molecular weight EPDM 2. It can further be seen by comparing Comparative experiment A and comparison examples 2, 4 and 6 that as the level of EPDM increases, the percentage loss of tensile strength is much higher than for examples 1, 3 and 5 after aging for 24 hours

TABLE-US-00005 TABLE 4 Examples/Comparative Experiment Comp. Comp. Comp. Comp. Exp. A Expl. 1 Expl. 2 Expl. 3 Expl. 4 Expl. 5 Expl. 6 Cure 2xT90 MDR @ 180 C. T.S.* [MPa] 13.5 14.1 15.9 14.1 16.4 13.7 18.4 Aged 24 hours @ 180 C. T.S.* [MPa] 8.5 11.9 11.5 12.7 11.6 13.1 13.3 Change [%] 37.04 15.60 27.67 9.93 29.27 4.38 27.72 *T.S. = tensile strength

Example 2

[0087] Table 5 shows again the recipe of Comparative Experiment A, representing a typical resin cured butyl formulation as used for tire curing bladders. Also shown are Examples 7 and 8, which incorporate 30 and 40 phr respectively of EPDM 1, and Comparison Examples 9 and 10, which incorporate respectively 30 and 40 phr of EPDM 3 with a high amount of ENB. EPDM 3 has a similar molecular weight, molecular weight distribution and ethylene content as EPDM 1, but has a significantly higher level of ENB unsaturation. Details of EPDM can be seen in Table 6.

TABLE-US-00006 TABLE 5 Example/Comparative Experiment Comp. Comp. Comp. Exp. A Expl. 7 Expl. 8 Expl. 9 Expl. 10 EPDM 1 30 40 EPDM 3 30 40 BAYPREN 210* 5.5 5.5 5.5 5.5 5.5 Butyl 1 89 59 49 59 49 Butyl 1 (as part of 6.4 6.4 6.4 6.4 6.4 resin masterbatch) Carbon black N-339 55 55 55 55 55 SUNPAR 2280 10 10 10 10 ZnO 6.4 6.4 6.4 6.4 6.4 CASTOR OIL 5 Resin 8.6 8.6 8.6 8.6 8.6 Stearic acid 1.5 1.5 1.5 1.5 1.5 Total phr 177.4 182.4 182.4 182.4 182.4 *Ingredient Details; BAYPREN 210: Supplied by LANXESS; Mercaptan modified polychloroprene; Viscosity ML(1 + 4)@100 C. = 48 +/ 4

TABLE-US-00007 TABLE 6 Units EPDM 3 Test Method Mooney viscosity ML MU 33 ISO 289 (1 + 4) 125 C. Mooney viscosity ML MU 55 ISO 289 (1 + 4) 100 C. Ethylene content wt % 56 ASTM D 3900 Third monomer type ENB Third Monomer wt % 11 ASTM D 6047 content Molecular weight Kg/mol 175 GPC (Mw) Molecular weight 2.6 GPC distribution (Mw/Mn)

[0088] Results in Table 7 show that the presence of EPDM 3 at a level of 40 phr gives the best result in higher original (unaged) tensile strength than was achieved with Comparative Experiments. This is associated with a higher cross-link density as expressed by delta S (AS), which is the difference between the minimum and maximum torque values of a cure curve obtained from a curemeter. In the case of this study, cure curves were produced using a moving die rheometer (MDR) manufactured by Alpha Technologies and operated in accordance with ASTM D 5289, using a cure temperature of 200 C. and a test duration of 60 minutes. Data obtained from the cure curves of Comparative Experiment A, example 7 and example 8 and Comparison Examples 9 and 10 inclusive can be seen in Table 8.

[0089] It can also be seen from Table 7 that the aged tensile strength of Example 8 that contain 40 phr of EPDM 1 respectively, show a significantly lower % change from their original tensile strength results after aging 24 hours at 180 C., when compared with the changes experienced by Comparative Experiments.

TABLE-US-00008 TABLE 7 Examples/Comparative Experiment Comp. Comp. Comp. Exp. A Expl. 7 Expl. 8 Expl. 9 Expl. 10 Cure 2 T90 MDR @ 200 C. T.S.* 12.2 14.3 13.5 16.1 16.8 (original) [MPa] Aged 24 hours @ 180 C. T.S.* [MPa] 8.5 11.9 12.6 10.6 10.6 Change [%] 32 16.8 6.7 34.2 36.9 *T.S. = tensile strength

TABLE-US-00009 TABLE 8 Examples/Comparative Experiment Comp. Comp. Comp. Exp. A Expl. 7 Expl. 8 Expl. 9 Expl. 10 MDR 60 minutes @ 200 C. Min. Torque [dNm] 2.58 2.17 2.11 2.13 2.26 Max. Torque [dNm] 12.55 11.66 11.4 14.71 15.09 S [dNm] 9.97 9.49 9.29 12.58 12.83

[0090] In Table 9 the De Mattia flex fatigue life is shown for Comparative Experiment A and Examples 7 and 8 as well as Comparison examples 9 and 10. Examples 7 and 8, which contain respectively 30 and 40 phr EPDM 1, which has a low ENB level of 2.3 wt %, have significantly greater flex fatigue resistance than Comparison Examples 9 and 10, containing 30 and 40 phr respectively of EPDM 3, which has a high ENB level of 11 wt % but similar molecular weight and molecular weight distribution.

TABLE-US-00010 TABLE 9 DeMattia Flex Comp. Comp. Comp. Fatigue Exp. A Expl. 7 Expl. 8 Expl. 9 Expl. 10 Cure 1.5 t90 @ 200 C Grade 1 [kcycles] 200 1000 2000 Grade 2 [kcycles] 3000 3000 100 Grade 3 [kcycles] 367 250 Grade 4 [kcycles] 400 Grade 5 [kcycles] Grade 6 [kcycles] Stopped [kcycles] 400 4000 4000 300 100 Condition Grade Grade Grade Grade Grade 4 2 2 7 7