Accelerator compositions and methods

Abstract

The invention provides a composition comprising a mixture or reaction mixture of a carbodithioic acid of formula: (I) or its internal salt; and at least one compound independently selected from a natural or synthetic rubber curing or vulcanization accelerator, activator or retarding agent. wherein R and R are independently selected from a C2-C18 aliphatic moiety; aromatic moiety; alicyclic moiety; aromatic heterocyclic moiety; and aliphatic heterocyclic moiety or R and R may together form part of an aromatic heterocyclic ring moiety or aliphatic heterocyclic ring moiety.

Claims

1. A composition comprising a mixture of a carbodithioic acid of formula ##STR00005## or its internal salt; wherein R and R together form a heterocyclic ring structure selected from the group consisting of piperazine, hexahydropyrimidine, hexahydropypridazine, imidazolidine, pyrazolidine, or a N-substituted or C-substituted derivative of any of the aforesaid moieties; a C.sub.6-C.sub.12 diazacycloalkane; oxazolidine; and thiazolidine, and at least one compound independently selected from the group consisting of a natural or synthetic rubber curing or vulcanization accelerator, activator or retarding agent.

2. The composition as claimed in claim 1 wherein each natural or synthetic rubber curing or vulcanisation accelerator is independently selected from the group consisting of a guanidine, an imidazole, a peroxide, a sulphenamide, a thiazole, benzothiazole, a thiourea, a triazine, a thiuram, a xanthate, a dithiophosphate, a dithiocarbamate, a dithiocaprolactam, an amine, a salt of an amine, an amine aldehyde, and amine-activated dithiocarbamate, an alkylphenyl polysulphide and an alkylphenyl disulphade.

3. The composition as claimed in claim 2, wherein each accelerator is independently selected from the group consisting of a thiuram, a thiazole, a benzothiazole, a dithiocarbamate, a dithiophosphate and a guanidine.

4. The composition as claimed in claim 1 wherein each activator is independently selected from the group consisting of a metal oxide, an amine, a salt of an amine, a thioamine, urea, a quaternary ammonium salt, an amine acid, a fatty acid and an amine complex capable of activating the carbodithioic acid on heating.

5. The composition as claimed in claim 1 wherein each activator is an amine or salt thereof.

6. The composition as claimed in claim 1 wherein each retarding agent is selected from the group consisting of an amine, a salt of an amine, cyclohexylthiophthalimide, phthalic anhydride, benzoic acid and salicylic acid.

7. The composition as claimed in claim 1 wherein at least one activator is an amine compound of formula:
H.sub.2NXNH.sub.2 or H.sub.2NYOH; wherein X is selected from a C.sub.2-C.sub.18 straight or branched, unsubstituted or substituted alkyl group; a straight or branched, unsubstituted or substituted C.sub.2-C.sub.18 aminoalkyl group; a disulphide bond; a straight or branched, unsubstituted or substituted C.sub.2-C.sub.18 hydroxyalkyl group, a straight or branched, unsubstituted or substituted C.sub.2-C.sub.18 aminohydroxyalkyl group, a ring moiety; and Y is selected from a C.sub.2-C.sub.18 straight or branched, unsubstituted or substituted alkyl, hydroxyalkyl or aminoalkyl group.

8. The composition as claimed in claim 4 wherein the amine is a C.sub.2-C.sub.18 diaminoalkane.

9. The composition as claimed in claim 8 wherein the diaminoalkane is diaminopropane or diaminohexane.

10. The composition as claimed in claim 8 wherein the diaminoalkane is 1,3-diaminopropane or 1,6-diaminohexane.

11. The composition as claimed in claim 1 wherein the carbodithioic acid is piperazine-1-carbodithioic acid.

12. The composition as claimed in claim 1 further comprising a liquid alkane in which the carbodithioic acid is suspended.

13. An additive masterbatch composition comprising the composition of claim 1, at least one binder, and at least one plasticiser.

14. The additive masterbatch composition as claimed in claim 13 further comprising at least one processing aid and/or at least one pH modifier.

15. A method of curing a natural or synthetic rubber compound, the method comprising the steps of mixing together a natural or synthetic rubber compound with the composition of claim 1 or the masterbatch of claim 13 and vulcanizing or curing the natural or synthetic rubber compound.

16. The method as claimed in claim 15 wherein the natural or synthetic rubber compound is selected from the group consisting of polychloroprene rubber, natural rubber, polyisoprene, nitrile rubber, natural latex, butadiene rubber, styrenebutadiene rubber, ethylene propylene diene monomer rubber, polyisobutylene rubber, ethylene acrylic rubber, isobutylene-isoprene rubber, brominated isobutylene-isoprene rubber, chlorinated isobutylene-isoprene rubber, epichlorhydrin, acrylonitrile butadiene, or mixtures thereof.

17. The method as claimed in claim 16 wherein the mixing step is performed at a temperature of up to 45 C.

18. The method as claimed in claim 16 wherein the curing or vulcanizing step is performed at a temperature of between 15 C. and 350 C.

19. The method as claimed in claim 15, wherein the natural or synthetic rubber compound is natural rubber latex or synthetic rubber latex and the vulcanization or curing step is performed at a temperature of up to 150 C.

20. The method as claimed in claim 15 wherein the natural or synthetic rubber compound is not latex and the vulcanization or curing step is performed at a temperature of up to 275 C.

21. The composition as claimed in claim 1, wherein the composition is in the form of a dispersion.

22. The additive masterbatch composition as claimed in claim 13, wherein the additive masterbatch composition is in the form of a dispersion.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) In order that the invention may be more clearly understood an embodiment/embodiments thereof will now be described, by way of example only with reference to the following Figures, in which:

(2) FIG. 1 is a table showing the results of rheometer tests on the cured polychloroprene rubber of Example 3;

(3) FIG. 2 is a table showing the results of rheometer tests on the cured polychloroprene rubber of Example 4;

(4) FIG. 3 is a table setting out the formulations of Example 5; and

(5) FIG. 4 is a table setting out the rheometer data from testing of the formulations of Example 5.

(6) FIG. 5 is a table setting out rheometer data from testing of the formulations of Example 6.

EXAMPLES

Example 1Preparation of a Composition Comprising a Mixture of Carbodithioic Acid and an Amine of the Invention

(7) A solution of NaOH (128.0 g, 3.20 mol, 1.161 equiv.) in water (250 mL) was added to a solution of piperazine (250.0 g, 2.90 mol, 1.052 equiv.) in CH.sub.2Cl.sub.2 (2.5 L). The resulting biphasic system was gently cooled (internal temperature: 5-10 C.) and vigorously stirred with mechanical stirrer and a solution of CS.sub.2 (166.5 mL, 210 g, 2.757 mol, 1 equiv. in CH.sub.2Cl.sub.2 (300 mL) was added drop-wise in 65-75 min with such a speed that the internal temperature of the reaction mixture was between 10 C. and 15 C. The resulting suspension was stirred for 10-20 min, filtered and washed on the filter with CH.sub.2Cl.sub.2 (250 mL). The crude betaine sodium salt was dried in the air at ambient temperature for 24 h. Yield: 778 g (>100%). This salt was dissolved in dist. water (4.0 L) and acidified with 50% aqueous solution of acetic acid until pH 5.5-6.5 while vigorously stirred by mechanical stirrer. The resulting precipitate was filtered and washed on the filter with dist. water (42 L) and twice with methanol (1:750 mL; 2:200 mL) to yield the betaine (internal salt) of piperazine-1-carbodithioic acid (hereinafter PCA).

(8) The PCA (814 g, 5.02 mol) was placed into 6 L flask from rotary evaporator Buchi-200. The flask was equipped with mechanical stirrer and hexanes (2 L) was added. Neat 1,3-diaminopropane (186 g, 2.51 mol) was added to the resulting suspension under vigorous stirring in a thin spout in 20-30 min with such a speed that internal temperature of the reaction mixture keeps in the range of 20-25 C. The reaction flask containing the suspension of PCA and 1,3-diaminopropane in hexanes was mounted on rotary evaporator and the solvent was evaporated under reduced pressure (200 mbar, bath temperature 40 C.) in 1.5 h. The resulting free flying powder was placed in vacuum cabinet and dried for additional 30 min at 20-50 mbar until the weight reached the theoretically calculated value (10005 g). The resultant composition comprised a mixture of PCA and 1,3-diaminopropane (Yield: 1004 g (quant.)), according to the invention.

(9) In other examples the 1,3-diaminopropane may be replaced with other accelerators or activators as detailed herein.

Example 2Preparation of a Polymer Masterbatch Containing the Composition Prepared in Example 1

(10) The following ingredients in Table 1 below were mixed on a 2-roll mill and the resultant polymer masterbatch containing 50% active (PCA and 1,3-diaminopropane) was then allowed to cool.

(11) TABLE-US-00001 TABLE 1 Polymer masterbatch composition of Example 2 the invention. Ingredient Function Amount Mixture of PCA and 1,3- Accelerator 120.0 g diaminopropane (prepared as hereinabove) Ethylene Propylene Diene Polymer binder 35.0 g monomer (Vistalon (RTM) 404, supplied by Du Pont, USA) Ethylene vinyl acetate Polymer binder 35.0 g co-polymer Dioctyl adipate Plasticiser 12.0 g Stearic acid Processing aid 12.0 g Calcium Oxide pH modifier 26.0 g Total: 240.0 g

Example 3Use of the Composition of Example 1 in Curing Polychloroprene Rubber Gumstock

(12) Polychloroprene rubber gumstock (unfilled) was prepared by mixing and compounding the following ingredients at between 20 C. and 70 C. for 10 to 15 minutes. All amounts are listed as parts per hundred rubber (phr):

(13) Polychloroprene granules100 phr

(14) Stearic acid0.6 phr

(15) Accelerator composition of Example 1 2.5 phr

(16) The rubber was compounded using a 30 cm 2-roll roller from David Bridge & Co with the nip between the rollers set at 80.sup.th and the guides set at 15 cm apart.

(17) After compounding the rubber was removed and allowed to cool for 3 hours before testing for rheological properties.

(18) A moving die rheometer (MDR) was used for testing rheological properties. The test was performed at 160 C. for 15 minutes in a Monsanto Rheometer MDR 2000E. Approximately 5 g of each sample material was used for each rheological test and each sample was tested at least 3 hours but less than 24 hours after compounding.

(19) Following the rheological testing, the rubber was cured at 160 C. for 1.5T90 on a 12 inch diameter hydraulic press from Bradley and Turton Ltd. 100 tonnes was applied to approximately 70 g material within a 15150.2 cm mould.

(20) The resultant cured rubber sheet was tested for the following parametersmodulus of elasticity, ultimate tensile strength, elongation at break point (all at time 0 and after 7 days incubation at 70 C.) and hardness. The results of the rheology and physical parameter testing are set out in Table 2 of FIG. 1.

Example 4Use of Accelerator Systems Incorporating the Composition of Example 1 in Curing Polychloroprene Rubber Masterbatch

(21) A polychloroprene masterbatch formulation was prepared using the following ingredients which were all mixed between 20 C. and 70 C. from 10 to 15 minutes.

(22) Polychloroprene rubber100 phr

(23) Carbon black (FEF N550supplied by Cabot Corporation)70 phr

(24) Citrofol (a citrade plasticizer supplied by Jungbunzlaver Suisse AG)10 phr

(25) ODPA (octylated diphenylamine antioxidant supplied by Duslo, Slovak Republic)2 phr

(26) WS180 (a processing aid supplied by Struktol)1 phr

(27) The resultant polychloroprene masterbatch was then compounded with a number of accelerator systems incorporating the composition of Example 1, which included secondary accelerators such as tetrabenzyldithiuram disulphide (TBzTD) and activators (metal oxides ZnO or MgO, multi-functional additive (1,4DAB.SA (1,4-diaminobutane/stearic acid)) as shown in Table 3 of FIG. 2. A control accelerator system which did not include the composition of Example 1, but instead used a known ethylene thiourea system (ETU) was also used. Compounding of the polychloroprene masterbatch with each accelerator systems was done at between 20 C. and 70 C., and subsequent vulcanization/curing was undertaken using the process described in Example 3.

(28) The rubber was compounded using a 30 cm 2-roll roller from David Bridge & Co with the nip between the rollers set at 80.sup.th and the guides set at 15 cm apart.

(29) After compounding the rubber was removed and allowed to cool for 3 hours before testing for rheological properties.

(30) A moving die rheometer (MDR) was used for testing rheological properties. The test was performed at 160 C. for 15 minutes in a Monsanto Rheometer MDR 2000E. Approximately 5 g of each sample material was used for each rheological test and each sample was tested at least 3 hours but less than 24 hours after compounding.

(31) Following the rheological testing, the rubber was cured at 160 C. for 1.5T90 on a 12 inch diameter hydraulic press from Bradley and Turton Ltd. 100 tonnes was applied to approximately 70 g material within a 15150.2 cm mould.

(32) The resultant sheet cured rubber was tested for the following parametersmodulus of elasticity, ultimate tensile strength, elongation at break point (all at time 0 and after 7 days incubation at 70 C.) and hardness. The results of the rheology and physical parameter testing are set out in Table 3 of FIG. 2.

(33) From the results it can be seen that the polychloroprene cured using systems employing the accelerator compositions of Example 1 of the invention, as primary accelerators, match or improve on many of the rheological and physical properties of the rubber, as compared to rubber cured using traditional systems employing ETU. In addition the use of compositions of Example 1, which comprises piperazine-1-carbodithioic acid and 1,3-diaminopropane as an accelerator mixture, is less environmentally harmful than ETU-based systems.

Example 5Use of Accelerator Systems Incorporating the Composition of Example 1 in Curing Non-Polychloroprene Rubber Compositions

(34) Fifteen (15) rubber formulations, each incorporating one of five different non-polychloroprene rubber compounds, were prepared and which incorporated the accelerator composition of Example 1, using a similar process to that described for Example 3.

(35) Representative example formulations are set out in Table 4 of FIG. 3. All ingredient concentrations are in phr (parts per hundred rubber)

(36) Each formulation was mixed between the rollers of a 30 cm, 2-roll roller with a nip of 80.sup.th for all formulations bar those containing EDPM and NBR, where the nip was 20.sup.th. All formulations were processed with the roller guidelines at 15 cm, apart from those containing EDPM and NBR where the guides were opened to the maximum. The formulations were mixed with the rollers set at 63 C. except for those containing NBR which were mixed at ambient temperature. Following curing, the cured rubber formulations were cooled for 3 hours at room temperature prior to testing for rheological and physical properties.

(37) A moving die rheometer (MDR) was used from testing rheological properties. The test was performed at 160 C. for 15 minutes except for Formulations 3, 4 and 5 which extended to 30 minutes in a Monsanto Rheometer MDR 2000E. Approximately 5 g of each sample material was used for each rheological test, and each sample was tested at least 3 hours but less than 24 hours after compounding.

(38) Following the rheological testing the rubber formulation were cured at 160 C. for 1.5T90 on a 12 inch diameter hydraulic press from Bradley and Turton Ltd. 100 tonnes was applied to approximately 70 g of material within a 15150.2 cm mould.

(39) The results of the rheological testing are given in Table 5 of FIG. 4.

(40) The results of the rheological tests show that diene-based rubbers can be effectively and efficiently cured using the compositions of Example 1, whether alone or in combination with secondary accelerators and activators.

Example 6Use of Further Accelerator Systems Incorporating Compositions of the Invention in Curing Polychloroprene Rubber Compositions

(41) Five further compositions of the invention were prepared comprising the following mixtures:

(42) TABLE-US-00002 Ref Carbodithioic acid Accelerator or Activator 401 PCA Butylamine 402 PCA Multi-functional additive - the reaction product of butylamine and stearic acid 403 PCA Tetramethylthiuram Disulfide (TMTD) 404 PCA Diphenylguanidine (DPG) 405 PCA Salicylic acid

(43) A polychloroprene rubber masterbach formulation was prepared according to the method described in Example 4 and the five compositions compounded with the masterbach according to the method described in Example 4, with the concentration of PCA in each resultant mixture being 0.5 phr, and the concentration of the accelerator or activator being 1 phr.

(44) The rheological properties of the resultant rubber, as tested according to the process described in Example 4, and the results, are shown in Table 6 of FIG. 5.

(45) The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.