ANTIOXIDANT BLEND FOR EMULSION POLYMERISATION RUBBERS

Abstract

The present invention relates to stabilising compositions, particularly stabilising compositions which can be used to stabilise elastomeric materials, such as rubbers and/or butadiene based elastomers. The stabilising composition comprises: a first stabilising component comprising at least one phosphite antioxidant; a second stabilising component comprising at least one aminic antioxidant; and a third stabilising component comprising at least one phenolic antioxidant. Also disclosed herein is use of the stabilising composition for stabilising elastomeric materials, a stabilised composition comprising an elastomeric material and the aforementioned stabilising composition and a useful article comprising the stabilising composition.

Claims

1. A stabilising composition for an elastomer, comprising: a. at least one phosphite antioxidant; b. at least one aminic antioxidant; and c. at least one phenolic antioxidant.

2. (canceled)

3. The stabilising composition according to claim 1, further comprising at least one sulphur-containing antioxidant.

4. The stabilising composition according to claim 1, wherein the phenolic antioxidant is a hindered phenolic antioxidant.

5. The stabilising composition according to claim 1, wherein the phenolic antioxidant is present in the stabilising composition in an amount of from about 20% to about 50% by weight of the stabilising composition.

6. The stabilising composition according to claim 1, wherein the phosphite antioxidant is a triaryl phosphite or a nonyl phenyl free antioxidant.

7. The stabilising composition according to claim 1, wherein the phosphite antioxidant is present in an amount from about 45% to about 70% by weight of the stabilising composition.

8. The stabilising composition according to claim 1, wherein the phosphite antioxidant is a liquid at a temperature of 50° C. or lower, at atmospheric pressure i.e. 101.325 kPa.

9. The stabilising composition according to claim 1, wherein the aminic antioxidant is a secondary amine.

10. The stabilising composition according to claim 1, wherein the aminic antioxidant comprises at least one aromatic group.

11. The stabilising composition according to claim 1, wherein the aminic antioxidant is 4,4′-bis(α,α-dimethylbenzyl) diphenylamine and/or mixed butylated, octylated diphenyl amine.

12. The stabilising composition according to claim 1, wherein the aminic antioxidant is present in the stabilising composition in an amount of from about 5% to about 25% by weight of the stabilising composition.

13. The stabilising composition according to claim 1, wherein the ratio of phosphite antioxidant to aminic antioxidant to phenolic antioxidant is: (from about 45 to about 65):(from about 5 to about 25):(from about 15 to about 30).

14. The stabilising composition according to claim 3, wherein the ratio of phosphite antioxidant to aminic antioxidant to phenolic antioxidant to sulphur-containing antioxidant in the stabilising composition is: (from about 45 to about 65):(from about 5 to about 25):(from about 15 to about 30):(from about 1 to about 15).

15. The stabilising composition according to claim 1, wherein the stabilising composition is a liquid composition at a temperature of 50° C. or lower, at atmospheric pressure i.e. 101.325 kPa.

16-18. (canceled)

19. A stabilised elastomeric composition, comprising: a. an elastomeric material; and b. the stabilising composition according to claim 1.

20. The stabilised elastomeric composition according to claim 19 wherein the elastomeric material comprises a natural rubber and/or synthetic rubber; and/or wherein the elastomeric material is a product of emulsion polymerisation.

21. The stabilised elastomeric composition according to claim 19 wherein the elastomeric material is a butadiene based elastomer.

22. The stabilised elastomeric composition according to claim 21, wherein the butadiene based elastomer is selected from the group consisting of styrene-butadiene, polybutadiene, nitrile rubber, polychloroprene, and mixtures thereof.

23. (canceled)

24. An article comprising the stabilised elastomeric composition of claim 19.

25. (canceled)

26. The stabilised elastomeric composition according to claim 19, wherein the Mooney viscosity of the elastomeric composition, measured in accordance with ASTM D1646, fluctuates less over a six day heat aging period at 100° C. than that of the same elastomeric composition containing an equivalent w/w amount of the same stabilising composition, absent any aminic component.

27. The stabilised elastomeric composition according to claim 19, wherein the Mooney viscosity of the elastomeric composition, measured in accordance with ASTM D1646, has a maximum % fluctuation of less than 25% over a six day period.

28. The stabilised elastomeric composition according to claim 19, wherein the elastomeric composition has a Yellowness Index value, measured in accordance with ASTM E313, to be less than 40, after a period of four days.

Description

EXAMPLES

[0135] Table 1 outlines details relating to different stabilising components that were used in the stabilising compositions. Hereinafter, the stabilising components will simply be referred to using the name given in the ‘shorthand’ column.

TABLE-US-00001 TABLE 1 Shorthand CAS No. Description Type W705 939402-02-5 WESTON ™ 705 - mixed 2,4- Component A bis(1,1-dimethylpropyl)phenyl and 4-(1,1-dimethylpropyl)phenyl phosphite WTNPP 26523-78-4 WESTON ™ TNPP - tris Component A (nonylphenyl) phosphite N445 10081-67-1 NAUGARD ™ 445 - 4,4′-bis(α,α- Component B dimethylbenzyl) diphenylamine NPS30 68411-46-1 NAUGARD ™ PS30 - mixed Component B butylated, octylated diphenylamine 5057 68411-46-1 IRGANOX ™ 5057 - benzamine, N- Component B phenyl-, reaction products with 2,4,4-trimethylpentene 438L 122-39-4 NAUGALUBE ™ 438L - Nonylated Component B diphenylamine 6PPD 793-24-8 SANTOFLEX ™ 6PPD - N-(1,3- Component B dimethylbutyl)-N′-phenyl-p- phenylenediamine A1315 171090-93-0 ANOX ™ 1315 - C13-C15 linear and Component C branched alkyl esters of 3-(3′,5′-di- t-butyl-4-hydroxyphenyl)propionate NPS48 125643-61-0 NAUGARD ™ PS48 - isooctyl 3- Component C (3′,5′-di-t-butyl-4- hydroxyphenyl)propionate NSP 61788-44-1 NAUGARD ™ SP - styrenated Component C phenol 1135 125643-61-0 IRGANOX ™ 1135 - benzene Component C propanoic acid, 3,5-bis(1,1- dimethyl-ethyl)-4-hydroxy-C7-C9 branched alkyl esters PP base 6386-38-5 Methyl 3-(3,5-di-tert-butyl-4- Component C hydroxyphenyl)propionate L520 110553-27-0 LOWINOX ™ 520 - 4,6- Component C bis(octylthiomethyl)-o-cresol and/or Component D DTDTDP 10595-72-9 NAUGARD ™ DTDTDP Component D ditridecylthiodipropionate Key to Table 1: Component A phosphite antioxidant Component B aminic antioxidant Component C phenolic antioxidant Component D sulphur-containing antioxidant

[0136] As will be apparent to the skilled person, certain materials (LOWINOX™ 520-CAS 110553-27-0, for example) may fall within one or more of the component categories A, B, C, D defined as necessary components of the invention. LOWINOX™ 520 therefore can be recognised as component C and/or component D according to the present invention.

[0137] Table 2 shows the various stabilising compositions that were prepared. The % amounts shown in the table are the % by weight of the overall stabilising composition, and the dosage of the stabilising composition in parts per hundred rubber (phr).

TABLE-US-00002 TABLE 2 Component C Component A Component B PP Component D Dosage/ Ex. W705 WTNPP N445 NPS30 5057 6PPD 438L A1315 PS48 NSP 1135 base L520 DTDTDP phr A 66.75 33.25 0.4 B 66.66 33.33 0.6 C 50 50 1.0 D 100 0.4 1 42.5 7.5 50 0.4 2 42.5 7.5 50 0.4 3 42.5 7.5 50 0.4 4 60 22.5 17.5 0.4 5 60 7.5 32.5 0.4 6 60 20 10 10 0.4 7 25 50 3.75 10 11.25 0.4 8 50 7.5 20 22.5 0.4 9 60 13.3 26.7 0.6 10 58.4 13.3 25 3.3 0.6 Examples A, B, C and D are comparative examples absent of any aminic component, with Example D representing the industrial benchmark. Examples 1 to 10 are in accordance with the invention.

Sample Preparation

[0138] Various mixtures of antioxidants were prepared according to the compositions summarised in Table 2. The antioxidant blends (ca 60 g) for each example were melted and mixed together. The mixture was then heated to 70° C. and dosed with oleic acid and mixed together. The mixture was then slowly dosed with KOH solution (13.3% w/w) (ca 48 g) and stirred at a high speed to ensure intimate mixing and the formation of an emulsion. The mixing speed was then reduced, and ca 152 g of hot deionised water was added. The resulting antioxidant emulsions had a solid content of about 20% w/w.

[0139] The Examples show the stability that can be attained by employing various stabilisation compositions in ESBR.

[0140] The ESBR latex was dosed with the antioxidant emulsion. After stirring, the ESBR latex samples were coagulated using a standard salt-acid coagulation system. More specifically, the samples were coagulated with a 2% calcium chloride. The latex was then dropped into the 2% calcium chloride solution and the rubber was transferred into fresh water. The rubber was washed 3 times with squeezing. The rubber was then dried in a vacuum oven for 16 hours at 50° C. A HAAKE™ Internal mixer was then used at 105° C. for 2 minutes to remove any remaining water. A two-roll mill was employed to make the elastomer more uniform.

[0141] The elastomers were oven aged at 100° C. and measurements were recorded every 24 hours for the duration of 4 days (Yellowness Index) and 6 days (Mooney viscosity).

Testing Conditions

Colour Stability

[0142] Samples were first placed in a compression mould at 100° C. for 5 minutes and the resulting ESBR sheet was 1 mm thick. The discolouration was measured in terms of Yellowness Index (YI) using a colourimeter. Approximately 4 g of the elastomer was taken for each YI measurement. YI values were taken at 0 hours and then every 24 hours and were measured as defined in ASTM E313. An average of 5 measurements were taken. The lower the YI value, the less discolouration of the composition. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Yellowness Index (YI) Ex. Day 0 Day 1 Day 2 Day 3 Day 4 A 12.57 20.87 31.69 36.24 43.34 B 13.28 18.87 31.08 39.04 42.78 D 20.60 28.26 38.37 45.11 53.75 1 15.32 21.40 32.46 46.65 50.57 2 14.31 21.15 34.27 45.88 48.33 3 7.09 14.63 25.09 32.44 36.04 4 6.66 14.29 20.99 29.23 37.16 5 8.83 15.58 23.94 30.38 35.83 6 7.34 14.33 20.55 26.14 27.87

[0143] Stabilising compositions A and B represent comparative examples which do not utilise an aminic antioxidant. Example D represents the industry benchmark, comprising L520.

[0144] From the results, it can be seen that the ESBR samples stabilised with stabilising compositions in accordance with the present invention (Examples 1-6) show less discolouration than the industry standard.

[0145] The ESBR samples stabilised with stabilising compositions in accordance with the present invention show a lower initial yellowness index at day 0 and a lower yellowness index value at day 4.

[0146] Therefore, the ESBR samples using the stabilising composition that is in accordance with the invention provide greater colour retention, allowing longer storage without change in colour.

Mooney Viscosity

[0147] Approximately 20 g of samples for each of the Examples were taken for Mooney viscosity testing. Mooney viscosity was measured using the standard method ASTM D1646 (1+4) T 100° C. Mooney viscosity values were taken at 0 hours and then every 24 hours.

TABLE-US-00004 Mooney Viscosity Max % Day Day Day Day Day Day Day Fluc- Ex. 0 1 2 3 4 5 6 tuation A 56.30 50.52 36.33 61.02* 67.64 72.19 82.58 46.68 B 53.52 49.62 39.99 37.08 44.66* 54.54 60.81 30.72 C 50.93 37.03 62.09* 64.50 76.22 73.42 — 49.66 D 52.98 42.76 36.01 31.04 37.51* 42.32 50.50 41.41 1 53.22 52.37 46.44 42.26 41.41 42.98* 43.76 22.19 2 52.03 53.08 48.17 44.78 46.29* 44.02 53.17 15.39 3 48.06 51.21 50.51 48.60 46.94 46.85 48.45 6.55 4 49.08 52.60 50.51 48.60 46.94 46.85 48.45 7.17 5 49.52 50.69 46.59 44.69 42.30 42.16 41.68 15.83 6 48.02 51.08 49.58 47.13 46.23 45.49 47.18 6.37 7 55.69 54.72 53.02 52.96 51.16 54.2 54.7 5.94 8 54.14 49.13 43.49 40.09 35.63 37.75 35.78 34.19 *The day ESBR began to cross-link. An overall increase in Mooney viscosity is expected when degradation via crosslinking predominates over chain scission. Degradation of ESBR is dominated by crosslinking.

[0148] Elastomeric structures primarily degrade by two different mechanisms of degradation; chain scission and crosslinking. The act of chain scission generally takes place earlier on in the degradation process and can result in the lowering of Mooney viscosity. Cross linking generally occurs later in the process and results in an increase in Mooney viscosity. It is theorised that Example 8 Exhibits rather higher initial chain scission than other Examples, but subsequently exhibits relatively low fluctuation in Mooney viscosity, as witnessed between days 2 and 6, compared with the Comparative Examples.

[0149] The less fluctuation in Mooney viscosity values over time demonstrates the structural integrity of the elastomer and shows minimal degradation.

[0150] The Examples according to the invention show superior Mooney viscosity to the comparative examples at equivalent loading and are equivalent or superior to the comparative examples at lower loading level.

[0151] Therefore, the Examples which comprise the stabilising composition in accordance with the present invention clearly exhibit superior Mooney viscosity retention and outperform comparative Examples A to D. These stabilising compositions will have better storage stability capabilities with greater retention of physical properties.

[0152] The Examples according to the invention show a lower degree of fluctuation of Mooney viscosity between day 0 and day 6. As can be seen from the results, the maximum % fluctuation of the Examples according to the present invention are significantly lower that the comparative examples.

[0153] Therefore, the Examples which comprise the stabilising composition in accordance with the invention clearly display greater retention and less drift of Mooney viscosity and outperform comparative Examples A to D.

[0154] Samples of Examples 9 and 10 were taken for Mooney viscosity testing. Mooney viscosity values are measured using the standard method ASTM D1646 (1+4) T 100° C. Mooney viscosity values are taken at 0 hours and then at 12, 24, 36 and 72 hours.

TABLE-US-00005 Mooney Viscosity 0 12 24 36 72 Max % Ex. hours hours hours hours hours Fluctuation 9 57.2 56.2 55.0 55.5 57.6 3.89 10 56.3 56.5 55.8 56.4 56.8 0.89

[0155] Examples 9 and 10 both comprise the stabilising composition in accordance with the invention. Example 10 shows a considerably lower degree of fluctuation of Mooney viscosity between 0 and 72 hours.

[0156] As can be seen from the results, the addition of Component D to the stabilising composition significantly increases stabilisation and reduces fluctuation in Mooney viscosity. Therefore, the Example which comprises a 4-component stabilising composition in accordance with the invention (Example 10) clearly displays greater retention and less drift of Mooney viscosity. This stabilising composition will have better storage stability capabilities with greater retention of physical properties.

[0157] Elastomer converters typically standardise the processing conditions of elastomers for mass production, therefore a drift in Mooney viscosity will result in the fluctuation of final article properties and result in quality inconsistency. This is undesirable.

[0158] The accelerated heat aging test simulates changes in Mooney viscosity during various storage and transportation conditions. This gives elastomer producers an indication of how stabile their elastomer will be.

[0159] The increased stabilisation and reduced fluctuation in Mooney viscosity when using the stabilising compositions in accordance with the invention is therefore beneficial to the customer and results in greater consistency of product quality.