INNER LINERS COMPRISING LOW ACID NUMBER ROSIN ESTERS

Abstract

The instant invention relates to an inner liner formulation comprising a rosin ester with a low acid number and a butyl rubber, to a tire inner liner comprising said inner liner formulation, and to a method for providing an inner liner formulation, wherein the rosin ester has an acid number of at most 15 mgKOH/g.

Claims

1. An inner liner formulation comprising a rosin ester and a butyl rubber, wherein the rosin ester has an acid number of at most 15 mgKOH/g.

2. The formulation of claim 1 wherein the rosin ester has an acid number of at most 10 mgKOH/g, in particular of at most 7.5 mgKOH/g, more in particular of at most 5 mgKOH/g, and even more in particular at most 4.5 mgKOH/g.

3. The formulation of claim 1 wherein the rosin ester has a softening point from 70 to 150° C., in particular from 75 to 125° C. and more in particular from 80 to 105° C.

4. The formulation of any one of claim 1 comprising 1 to 20 phr of rosin ester, in particular 2 to 15 phr of rosin ester, more in particular 2.5 to 10 phr of rosin ester, and even more in particular from 5 to 7.5 phr.

5. The formulation of any one of claim 1 wherein the rosin ester is an ester of a polyhydric alcohol and rosin.

6. The formulation of claim 5 wherein the polyhydric alcohol is selected from glycerol and pentaerithrytol.

7. The formulation of claim 5 wherein the rosin is selected from wood rosin, gum rosin and tall oil rosin.

8. The formulation of any one of claim 1 wherein the butyl rubber is halobutyl rubber, and in particular is bromobutyl rubber.

9. The formulation of any one of claim 1 that does not comprise styreneisobutylene-styrene rubber, styrene-isoprene-styrene rubber, and/or polypropylene rubber.

10. The formulation of any one of claim 1 further comprising carbon black.

11. The formulation of any one of claim 1 having a total De Mattia crack growth cycles (L to L+10) of at least 1500 kcyles, in particular at least 2000 kcycles.

12. The formulation of any one of claim 1 having a green tack adhesion of at least 15 ounces, in particular at least 20 ounces.

13. The formulation of any one of claim 1 having a t90 from 5 to 10 min, in particular from 6 to 9 min as determined by (MDR).

14. A tire inner liner comprising the formulation of any one of claim 1.

15. A method for providing an inner liner formulation of any one of claim 1 comprising mixing a rosin ester with a butyl rubber, wherein the rosin ester has an acid number of at most 15 mgKOH/g.

Description

EXAMPLES

[0077] The performance of inner liner formulations was assessed comprising butyl rubber and a resin. The resins used were a low acid rosin esters according to the instant invention (resins A and B) and, as comparative examples, other resins including a rosin acid with a high acid number (resin C), and two homogenizer resins (resin D and E) commonly used in rubber formulations.

[0078] Resin A was a glycerol tall oil rosin ester having an acid number of 4.3 mgKOH/g, a MW of 893 g/mol and a softening point of 81.7° C. Resin A was obtained by esterification of tall oil rosin with a slight excess of glycerol in the presence of a suitable disproportionation catalyst (e.g. Lowinox™ TBM-6) and a suitable esterification catalyst (e.g. Zinc acetate or Magnesium acetate), as is known to a person skilled in the art. After completion of the esterification the ring & ball softening point was increased and acid number reduced by steam sparging until the desired values were obtained, as is known to person skilled in the art. Further reference on the art of rosin ester synthesis can be found in U.S. Pat. No. 5,969,092 and patent application WO2013/090283.

[0079] Resin B was a pentaerythritol rosin ester having an acid number of 14.8 mgKOH/g, a MW of 1043 g/mol and a softening point of 95.2° C. Resin B was obtained by esterification of tall oil rosin with a slight excess of pentaerythritol in the presence of a suitable disproportionation catalyst (e.g. Lowinox™ TBM-6) and a suitable esterification catalyst (e.g. Zinc acetate or Magnesium acetate), as is known to a person skilled in the art. After completion of the esterification the ring & ball softening point was increased and acid number reduced by steam sparging until the desired values were obtained, as is known to person skilled in the art. Further reference on the art of rosin ester synthesis can be found in U.S. Pat. No. 5,969,092 and patent application WO2013/090283.

[0080] Resin C was a tall oil rosin having an acid number of 161.4 mgKOH/g, a MW of 404 g/mol and a softening point of 70.6° C.

[0081] Resin D was dark aromatic hydrocarbon resin. Resin D was provided by Struktol under the name Struktol™ 40 MS flakes.

[0082] Resin E was a light aliphatic hydrocarbon resin. Resin E was provided by Struktol under the name Struktol™ 60 NS flakes.

[0083] The selected resins were mixed into an innerliner formulation based on bromobutyl rubber. The resins were tested at different dosage levels of 2.5, 5 and 10 phr (exchanged against process oil). The control formulation with 10 phr of process oil was mixed in duplicate, leading to a total of 17 compounds. The bromobutyl rubber was Bromobutyl 2030, provided by Lanxess. The filler was Carbon black N-660, provided by Statex. As processing aid paraffin oil was used supplied by SUNOCO™ as Sunpar 2280. As curing agents sulfur was used in combination with zinc oxide, stearic acid and di(benzothiazol-2-yl) disulfide (MBTS) supplied by Lanxess as Vulkacit® DM/MG. The mixing was performed in a 1.6 L Banbury type internal mixer. The curing agents were mixed in on a two-roll mill.

[0084] The tested formulations used are displayed in Table 1. evaluated by the test methods displayed in Table 2.

[0085] The Mooney viscosity and Mooney scorch, the cure characteristics and the green tack were performed on the formulations of table 1 without further processing.

[0086] The inner liner formulations obtained were made into 2 mm thick sheets for assessing the tensile properties, into 0.51 mm thick samples for assessing the air permeability and into 6 mm De Mattia samples for assessing the crack resistance. All 2 mm thick tensile sheets and 0.51 mm thick air permeability samples were cured for 12 minutes at 160° C. The 6 mm thick De Mattia samples were cured for 18 minutes at 160° C.

TABLE-US-00001 TABLE 1 Formulation of the inner liner test compounds. Inner liner formulation 1 2 3 4 Amount (PHR) Butyl rubber 100 100 100 100 Carbon black 60 60 60 60 Paraffin Oil 10 7.5 5 0 Resin 0 2.5 5 10 Curing agents MBTS 1.3 1.3 1.3 1.3 Stearic acid 1 1 1 1 ZnO 3 3 3 3 Sulfur 0.5 0.5 0.5 0.5 Total PHR 175.8 175.8 175.8 175.8

TABLE-US-00002 TABLE 2 Test methods used for characterization of the inner liner compounds. Property Test method Mooney viscosity and Mooney scorch ISO 289 Cure characteristics (MDR) at 160° C. ISO 6502 Green tack Tel-Tak* Tensile properties (tensile strength, ISO 37, type 2 elongation at break, moduli) De Mattia crack growth ISO 132 Permeability to air at 60° C. ASTM D1434 *R. Beatty, Tel-Tak: A Mechanical Method for Estimating Both Tackiness and Stickiness of Rubber Compounds, Rubber Chemistry and Technology, 1969, Vol. 42, No. 4, p. 1040-1053

De Mattia Crack Growth

[0087] For the De Mattia crack growth test a 2 mm wide cut is made in the sample and the sample is pierced. The samples is flexed until the crack has increased by 2 mm in width (L+2) and the number of cycles is noted. The test is continued until the width has increased by 6 mm (L+6), followed by flexing until the width has increased by 10 mm (L+10). The test is stopped when 2750 kcycles or L+10 is reached.

[0088] The best crack results were obtained with formulations comprising low acid number rosin esters (Resin A & B) and rosin acid (Resin C). The results are displayed on table 3.

[0089] In particular, formulations with Resin C (and 10 phr of Resin B have superior crack resistance. For compounds with 5 & 10 phr Resin C the crack does not widen beyond L+2, for 2.5 phr Resin C the 2750 kcycles are reached just beyond L+2. Also the sample with 10 phr Resin B reaches 2750 kcycles before L+6 is reached. Formulations comprising 10 phr or even 5 phr of Resin A, did not reach the 2750 kcycles, but displayed a marked improvement with respect to compositions comprising no resin (with 10 phr paraffin oil) and to compositions comprising resins D and E.

Air Permeability

[0090] For each inner liner formulation 2 test sheets were made and tested for air permeability at 60° C.

[0091] The results from the air permeability testing are displayed on Table 4. Due to the semi-quantative nature of ASTM D1434, the air permeability test method has limited accuracy.

[0092] Based on the results displayed on Table 4 a trend can be identified towards lower air permeability with increasing dosage of homogenizer resin. However, when taking into account the error of the measurement, there appears, limited differentiation between the samples. Indicating that the presence of the resin does not significantly increase air permeability.

TABLE-US-00003 TABLE 3 De Mattia crack growth De Mattia crack cycles (kcycles) L + 2/ L + 6/ Total Sample L/L + 2 L + 6 L + 10 L to L + 10.  10 phr paraffin oil*  40 113 100 253 2.5 phr Resin A  83  46 270 399   5 phr Resin A  150 517 2 699  10 phr Resin A  333 833 750 1917 2.5 phr Resin B  200 467 417 1083   5 phr Resin B  500 583 667 1750  10 phr Resin B 2083 667** — 2750 2.5 phr Resin C 2500 250** — 2750   5 phr Resin C 2750** — — 2750  10 phr Resin C 2750** — — 2750 2.5 phr Resin D  100 300 433 833   5 phr Resin D  216 533 501 1250  10 phr Resin D  200 500 50 750 2.5 phr Resin E  50 100 100 250   5 phr Resin E  50  83 183 317  10 phr Resin E  67 127 107 300 *average of two samples **2750 kcycles reached, test stopped.

TABLE-US-00004 TABLE 4 Air permeability Permeability Sample (cm.sup.2/sec*atm)  10 phr paraffin oil* 2.57 × 10.sup.−8 2.5 phr Resin A 2.17 × 10.sup.−8   5 phr Resin A 2.37 × 10.sup.−8  10 phr Resin A 1.34 × 10.sup.−8 2.5 phr Resin B 2.02 × 10.sup.−8   5 phr Resin B 1.99 × 10.sup.−8  10 phr Resin B 1.08 × 10.sup.−8 2.5 phr Resin C 1.99 × 10.sup.−8   5 phr Resin C 1.82 × 10.sup.−8  10 phr Resin C 8.87 × 10.sup.−9 2.5 phr Resin D 1.99 × 10.sup.−8   5 phr Resin D 2.17 × 10.sup.−8  10 phr Resin D 1.31 × 10.sup.−8 2.5 phr Resin E 1.85 × 10.sup.−8   5 phr Resin E 2.52 × 10.sup.−8  10 phr Resin E 7.76 × 10.sup.−9 *average of two samples

Green Tack

[0093] The results of the green tack measurements are presented on Table 5.

[0094] As can be seen from Table 5, compounds with low acid number rosin esters (Resins A & B) show improved green tack when compared to formulations without resin or formulation with Resins D and E. The improvement has been found to be higher for the rosin ester with the lowest acid number Resin A).

TABLE-US-00005 TABLE 5 Green Tack Adhesion Sample (ounzes)  10 phr paraffin oil* 16 2.5 phr Resin A 22   5 phr Resin A 18  10 phr Resin A 23 2.5 phr Resin B 17   5 phr Resin B 18  10 phr Resin B 18 2.5 phr Resin C 23   5 phr Resin C 18  10 phr Resin C 14 2.5 phr Resin D 13   5 phr Resin D 17  10 phr Resin D 13 2.5 phr Resin E 18   5 phr Resin E 12  10 phr Resin E 10 *average of two samples

Mooney Viscosity and Mooney Scorch

[0095] The use of an increased amount of resin leaded to a slight increase in Mooney viscosity and a slight decrease in Mooney Scorch as can be seen in Table 6, for all samples tested except for Resin D. As can also be seen the use of low acid number rosin esters (resin A & B) does not detrimentally affect the Mooney Scorch properties with respect to the blank comprising paraffin oil, whereas rosin acid (resin C) significantly reduces the Mooney scorch. The strong reduction in Mooney scorch for resin C, indicates a limited scorch time; which might lead to premature curing of the compound during processing.

TABLE-US-00006 TABLE 6 Mooney properties Mooney viscosity Mooney Mooney Sample M.sub.L 1 + 4 Scorch t.sub.5 Scorch t.sub.35  10 phr paraffin oil* 55.0 22.6 29.6 2.5 phr Resin A 59.3 18.7 28.3   5 phr Resin A 57.0 19.3 27.2  10 phr Resin A 62.7 16.7 24.9 2.5 phr Resin B 61.9 17.6 26.2   5 phr Resin B 58.8 16.6 26.1  10 phr Resin B 62.5 15.8 23.1 2.5 phr Resin C 54.0 9.5 15.6   5 phr Resin C 55.8 8.2 13.1  10 phr Resin C 61.4 6.8 11.7 2.5 phr Resin D 61.6 22.2 33.7   5 phr Resin D 63.1 23.5 35.5  10 phr Resin D 71.7 20.0 32.7 2.5 phr Resin E 57.5 20.3 30.1   5 phr Resin E 59.9 23.2 30.3  10 phr Resin E 62.6 18.7 29.9 *average of two samples

Curing Characteristics

[0096] The curing characteristics where determined by the Moving Die Rheometer (MDR) method. The results are presented on Table 7.

[0097] The use of Resin C (rosin acid) had a strong influence on the curing behavior of the compound, strongly reducing the t.sub.90 and lead to a much softer final compound, as can be derived from the maximum torque (MH) (Table 7). This indicates interference with the curing package, resulting in an acceleration of the cure rate and a limitation of the degree of curing. The accelerated curing could result in premature curing during processing. The limited degree of curing could have a undesired effect on the mechanical properties of the compound. Further, Resin D (Struktol 40 MS) showed an increase of the MDR t.sub.90, that means that the cure rate of the compound is reduced, which is also undesirable. The reduced cure rate could result in undercured products or an extended cure time; reducing rate of production. On the other hand low acid rosin esters (resins A & B) did not significantly affect the MDR t.sub.90 and resulted in stiffer compounds compared to compounds containing Resin C.

TABLE-US-00007 TABLE 7 Curing characteristics Maximum Delta S Sample t.sub.90 (min) Torque (Nm) (Nm)  10 phr paraffin oil* 9.22 0.68 0.51 2.5 phr Resin A 8.13 0.68 0.50   5 phr Resin A 7.62 0.59 0.42  10 phr Resin A 6.65 0.54 0.36 2.5 phr Resin B 7.90 0.63 0.45   5 phr Resin B 7.53 0.56 0.39  10 phr Resin B 6.48 0.47 0.30 2.5 phr Resin C 4.56 0.46 0.31   5 phr Resin C 3.33 0.38 0.22  10 phr Resin C 2.31 0.31 0.14 2.5 phr Resin D 10.94 0.63 0.46   5 phr Resin D 12.15 0.63 0.46  10 phr Resin D 13.58 0.69 0.49 2.5 phr Resin E 8.77 0.65 0.48   5 phr Resin E 8.73 0.65 0.48  10 phr Resin E 8.76 0.66 0.48 *average of two samples

[0098] In view of these results the effect interfering with the cure package has been found to be stronger as the acid number (AN) of the resin increases. The effect follows the order Resin C>Resin B>Resin A as do the AN of these resins 161.4>14.8>4.3. This suggests that the rosin acids in the products interfere with the curing process, leading to a lower crosslink density and therefore a softer compound.

Tensile Properties

[0099] To maintain an equal thermal history all tensile sheets were cured for 12 min. at 160° C.

[0100] As can be seen in Table 8 compounds with Resin C were softer, having a higher maximum elongation.

[0101] The softer compounds have a reduced tensile strength as can also be seen in Table 8. Compounds containing 5 & 10 phr of Resin A and 5 phr of Resin B have only a slightly reduced tensile strength.

[0102] The increased softness of the compounds also results in a lower modulus at 200%, 300% and 500% elongation (Table 8), the effects are most visible at 300% and 500% elongation.

TABLE-US-00008 TABLE 8 Tensile properties Modulus (MPa) at a Elonga- Tensile given elongation tion at strength 25 50 100 200 300 500 Sample break (%) (MPa) % % % % % % 10 phr 605 11.4 0.6 0.8 1.3 3.1 5.5 9.9 paraffin oil* 2.5 phr 667 11.9 0.6 0.8 1.3 3.0 5.3 9.7 Resin A 5 phr 694 11.3 0.6 0.8 1.2 2.6 4.6 8.6 Resin A 10 phr 690 11.2 0.6 0.8 1.2 2.6 4.5 8.7 Resin A 2.5 phr 660 11.6 0.6 0.9 1.3 3.0 5.2 9.5 Resin B 5 phr 720 11.3 0.6 0.8 1.2 2.8 4.9 8.7 Resin B 10 phr 833 10.7 0.7 0.8 1.1 2.1 3.6 6.9 Resin B 2.5 phr 823 10.5 0.7 0.9 1.3 2.5 4.0 6.8 Resin C 5 phr 822 10.1 0.7 0.9 1.4 2.6 4.2 7.0 Resin C 10 phr 857 10.6 0.8 1.1 1.5 2.9 4.7 7.7 Resin C 2.5 phr 685 11.6 0.6 0.8 1.3 3.1 5.5 9.6 Resin D 5 phr 749 11.4 0.6 0.8 1.3 2.9 4.9 8.3 Resin D 10 phr 831 11.1 0.6 0.9 1.4 2.8 4.5 7.4 Resin D 2.5 phr 621 12.2 0.6 0.8 1.4 3.5 6.1 10.6 Resin E 5 phr 622 12.1 0.6 0.8 1.4 3.6 6.3 10.7 Resin E 10 phr 667 12.6 0.6 0.9 1.4 3.3 5.9 10.5 Resin E *average of two samples