Tyre portions highly impermeable to oxygen

Abstract

A tire portion selected from the group including an innerliner, tread ply skim, TBR body ply skim, bead reinforcing skim, undertread, tie gum, squeegee, folded edge gum strip, belt edge gum strip and tread ply insert, and made from a compound including a polymer base and curing agents. The compound also includes a carbohydrate having 2 to 30 repetitive, possibly substituted, units.

Claims

1. A tyre portion made from a compound comprising a polymer base, curing agents and sucrose benzoate; wherein the tyre portion is selected from the group consisting of innerliner, tread ply skim, TBR body ply skim, bead reinforcing skim, undertread, tie gum, squeegee, folded edge gum strip, belt edge gum strip and tread ply insert.

2. A tyre portion as claimed in claim 1, wherein the compound comprises 0.05 to 10 phr of sucrose benzoate.

3. A tyre portion as claimed in claim 1, wherein the compound comprises 0.5 to 5 phr of sucrose benzoate.

4. A tyre comprising at least one portion as claimed in claim 1.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

Examples

(1) Two sets of examples were produced: a first set of compounds for producing innerliners; and a second set of compounds for producing belt skims.

(2) The compounds below were produced using a standard procedure not pertinent to the present invention.

(3) Compound Production

(4) (First Mixing Step)

(5) Before commencing the mixing stage, a 230-330-liter, tangential-rotor mixer was loaded with the polymer base and all the other ingredients, except for sulphur, zinc oxide and accelerants, to a fill factor of 66-72%.

(6) The mixer was operated at a speed of 40-60 rpm, and the resulting mix unloaded on reaching a temperature of 140-160 C.

(7) (Second Mixing Step)

(8) The mix from the first step was mixed again in the mixer operated at a speed of 40-60 rpm, and was unloaded on reaching a temperature of 130-150 C.

(9) (Third Mixing Step)

(10) The curing system, comprising sulphur, accelerants and zinc oxide, was added to the mix from the second step, to a fill factor of 63-67%.

(11) The mixer was operated at a speed of 20-40 rpm, and the resulting mix unloaded on reaching a temperature of 100-110 C.

First Set of Examples

(12) Two compounds were produced with typical innerliner compound compositions. One of the two compounds (Compound A) was produced in accordance with the present invention, and therefore containing a carbohydrate designed to react with molecular oxygen and prevent it from diffusing inside the compound.

(13) More specifically, the carbohydrate used was sucrose benzoate.

(14) The other compound (Compound B) was a control compound with the same composition as Compound A but containing no carbohydrate.

(15) Table I below shows the compositions in phr of the above innerliner compounds.

(16) TABLE-US-00001 TABLE I Compound A Compound B Halobutyl rubber 100 Carbon black 50 Clay 40 Stearic acid 1 Zinc oxide 2 Oil 10 Sulphur 1 Accelerant 2 Sucrose benzoate 1

(17) The carbon black used was N660.

(18) The accelerant used was dibenzothiazyl disulphide.

(19) As shown by the compositions in Table I, the control innerliner compound differs from the innerliner compound according to the invention simply by containing no carbohydrate.

(20) From the two compounds in Table I, respective cured-rubber specimens were made, each with the same characteristics as the innerliner made from the same compound.

(21) The specimens were tested for oxygen impermeability under different operating and material treatment conditions.

(22) More specifically, oxygen impermeability was measured on 0.7 mm thick materials, using a conventional apparatus such as a MOCON OX-TRA (model 2/61).

(23) The oxygen impermeability tests performed are shown below. Each test result is indexed to that of the control compound (Compound B) specimen. The higher the indexed value, the greater the impermeability to oxygen.

(24) A first set of oxygen impermeability measurements was performed by subjecting the Compound A and B specimens to different temperature conditions (25 C., 35 C., 45 C.). The results are shown in Table II.

(25) TABLE-US-00002 TABLE II Specimen from Specimen from T ( C.) compound A compound B 25 124 100 35 116 100 45 110 100

(26) A second set of measurements was performed on the Compound A and B specimens subjected first to a first ageing process, in which the specimens were kept in an oven at 70 C. for three and seven days. The measurements of the aged specimens were made at a temperature of 25 C. The results are shown in Table III.

(27) TABLE-US-00003 TABLE III Specimen from Specimen from compound A compound B 3 days 126 100 7 days 120 100

(28) A third set of measurements was performed on the Compound A and B specimens subjected first to a second, more stringent, ageing process, in which the specimens were kept in an oven at 70 C. for one, three, and seven days in the presence of 70% relative humidity and 0.45 bar partial oxygen pressure. These conditions serve to simulate more critical markets in terms of environment. The measurements were made at a temperature of 25 C.

(29) The results are shown in Table IV.

(30) TABLE-US-00004 TABLE IV Specimen from Specimen from compound A compound B 1 days 115 100 3 days 114 100 7 days 110 100

(31) As shown clearly in Tables II, III and IV, the innerliner specimen according to the present invention shows a far greater impermeability to oxygen than the control innerliner specimen, which only differs by having no oxygen-reacting chemical compound. The impermeability test results therefore confirm the ability of chemical compounds, designed to react with molecular oxygen, to make the innerliner more impermeable to oxygen.

(32) It is important to note how the improvement in impermeability to oxygen persists even under high-temperature and ageing conditions.

(33) By making it more impermeable to oxygen, the innerliner may therefore be made thinner, with all the advantages this affords in terms of material saving and reducing tyre weight and rolling resistance.

Second Set of Examples

(34) Two belt skim compounds were produced: a compound (Compound C) in accordance with the invention and comprising sucrose benzoate as the oxygen-reacting chemical compound; and a control compound (Compound D) with no oxygen-reacting sucrose benzoate.

(35) Table V shows the compositions in phr of Compounds C and D, which were made using the same process, not pertinent to the present invention.

(36) TABLE-US-00005 TABLE V Compound C Compound D Natural rubber 100.00 Carbon black 60.00 Stearic acid 2.00 Zinc oxide 10.00 Antioxidant 2.00 Cobalt salt 0.90 Sulphur 9.00 Accelerant 2.00 Sucrose benzoate 1.00

(37) The following are ingredient specifications not shown in the Table.

(38) Carbon black: N330.

(39) Antioxidant: N-1,3-dimethylbutyl-N-phenyl-paraphenylenediamine (6PPD)

(40) Cobalt salt: cobalt neocaprate

(41) Accelerant: benzothiazyl-2-dicyclohexyl sulphonamide (DCBS)

(42) Respective cured-rubber specimens with embedded metal cords were made from Compounds C and D in Table V.

(43) The cord-rubber specimens were aged in an oven at 60 C., in the presence of 85% relative humidity and 0.2 bar partial oxygen pressure, to simulate critical cord-compound adhesion conditions in terms of environment.

(44) Compound-to-cord adhesion was assessed by quantifying the cord percentage still covered with rubber after the two parts of the cord-rubber composite were separated by applying a load. The measurements were made at a temperature of 25 C.

(45) More specifically, rubber-to-cord adhesion was calculated according to the number of days the specific cord-rubber composite was aged. More specifically, the number of days' ageing necessary to bring about a 50% reduction in rubber-to-cord adhesion was calculated.

(46) The findings showed that reducing rubber-to-cord adhesion by 50% took 4.2 days for the Compound D specimen, as compared with 5.0 days for the Compound C specimen.

(47) The findings confirm a 20% increase in rubber-to-cord adhesion due to the presence of sucrose benzoate.

(48) This demonstrates how the presence of a carbohydrate is capable of preventing oxygen diffusion and, therefore, rubber degradation and consequent rubber detachment from the cords.

(49) Finally, achieving a tyre portion guaranteeing very little oxygen diffusion makes it possible to reduce the thickness of the portion and the presence of chemical compounds such as adhesion promoters, with obvious advantages in terms of rolling resistance and manufacturing cost.