GB2259303A - A process for the production of vulcanizable moulding compounds and to the moulding compounds produced by this process - Google Patents

Abstract

In a process for the production of vulcanizable moulding compounds consisting of one or more natural or synthetic rubbers or polymers the quantity of accelerators from the class of thiurams and/or dithiocarbamates is reduced to half the quantity originally required through the use of 3-thiocyanatopropyl trialkoxy silanes.

Description

A Process for the Production of Vulcanizable Moulciing Compounds and to

the Moulding Compounds Produced by this Process This invention relates to a process for the production of vulcanizable moulding compounds and to the moulding compounds produced by this process.

For some years now, the problems presented by the formation of volatile carcinogenic N-nitrosamines during the processing, vulcanization and storage of rubber arti cles have been of increasing concern in the rubber-proces sing industry. Initial legal regulations in the Federal Republic of Germany, such as for example the 11Technische Richtlinien filr Gefahrstoffell (TRGS 552), stipulate upper limits to the content of volatile N-nitrosamines in the working environment and prescribe significant limitations to the output of factories exceeding those limits. To avoid this. the rubber-processing industry is making increasing efforts to replace N-nitrosamine-forning agents in rubber mixtures and, where this is not possible, at least to reduce the quantities required.

As has meanwhile become known from various publica tions (see, for example, R.H. Schuster, F. Nabholz, M.

Gmfinder, "Kautschuk, Gummi, Kunststoffe 211 (1990) 95; W.

Hoffmann, "Zum Problem der Herstellung N-nitrosaminfreil!r Gummiartikelll, paper presented before the DKG-Bezirksgruppe Sild- u. SUdwestdeutschland, April 1990), nitrosamines are formed at the temperatures required for the compounding, processing and vulcanization of rubber mixtures through the decomposition of, in particular. mixture constituents which release secondary amines and reaction of those amines with the NO, omnipresent in nature.

One of the main sources of amines are the vulcaniza tion accelerators from the class of sulfenamides, thiurams and dithiocarbanates now mainly used in the rubber indus try. Accordingly, efforts are naturally being made in the rubber-processing industry to replace these toxic nitros amine-forming accelerators by safer compounds or at least to reduce the quantities required without,at the same is 2 is 91 185 KV time, giving rise to serious changes in the rubber properties.

The present invention relates to a process f or the production of vulcanizable moulding compounds consisting of one or more natural or synthetic rubbers or polymers vulcanized with sulfur or sulfur donors and accelerators, fillers and other typical constituents, at least one accelerator belonging to the class of thiurams and/or dithiocarbamates being used, characterized in that, where 3- thiocyanatopropyl trialkoxy silanes corresponding to the following general formula:

(R0) 3 S i (CH2) 3 S CN (I) in which R = Cl-8 alkyl, are simultaneously used, the quantity of accelerators from the class of thiurams and/or dithiocarbanates is reduced to at least half the quantity originally used in the vulcanizable moulding compound free from organosilicon compounds.

The invention also relates to the vulcanizates obtained by this process.

The accelerators in question include inter alia tetramethyl thiuram disulfide (TMTD), tetramethyl thiuram monosulf ide (TMTM), zinc-Ndimethyl dithiocarbamate (MDMC), zinc-N-diethyl dithiocarbamate (ZDEC), zinc-N-ethyl phenyl dithiocarbanate (ZEPC).

In the prior art, these accelerators are used in quantities of 0.2 to 10 phr (parts per hundred parts rubber).

The reduction preferably amounts to 20 to 50% of the original quantity and, in some cases, is even 100% (see Example 2).

It has been found that it is possible in accordance with the invention to reduce the quantity of the incriminated accelerators without having to accept reductions in the 3 91 185 KV range of customary rubber properties.

The moulding compounds are produced and vulcanized by known methods.

The other typical constituents, such as plasticizers, stabilizers, activators, pigments, antiagers and processing aids, are also known.

The moulding compounds generally contain the known light silicate fillers (for example clays, kaolins, precipitated and pyrogenic silicas, silicates, etc.) having BET surfaces of 1 to 1,000 M2 /g and preferably 5 to 300 M2/g, with the hydroxyl groups of which the trialkoxysilyl groups of the compounds according to the invention react with elimination of an alcohol, which leads to a chemical bond between filler and silane. However, the known carbon blacks are also used as fillers.

The thiocyanatosilane corresponding to general formula (I) is added to the vulcanizable moulding compound generally in quantities of 0.1 to 20 parts by weight and preferably in quantities of 0.1 to 10 parts by weight, based on 100 parts rubber or polymer, either directly or in a form in which it is already bound to the filler.

In addition to the reduction in the quantity of accelerator obtained in accordance with the invention, the use of the organosilicon compound corresponding to formula (I) also leads to a reduction in the viscosity of the vulcanizable moulding compounds and hence to an improvement in their processability.

Suitable rubbers and polymers for the process according to the invention are, in particular, rubbers low in double bonds, such as EPDM and EVA, but also NBR, NR and SBR.

The following Examples illustrate the advantages of the compounds according to the invention over the prior art and show that it is possible to manage without at least a large part of toxic nitrosamine-forming accelerators and 4 91 185 KV still to achieve at least the customary rubber properties.

Test Standands for Evaluation Test Method Unit Mooney viscosity DIN 53 523/524 MPa Tensile strength DIN 53 504 MPa Modulus DIN 53 504 MPa Shore hardness DIN 53 505 compression set ASTM D 395 The names and abbreviations used in the Examples have the following meanings:

Keltan 578 N 765 N 660 Ultrasil VN 3 Suprex Clay 20 Omya chalk Sunpar 150 Si 264 DEG CBS T= Rhenocure CUT ZDBC -3.

EPDM manufactured by DSM Furnace black, surface 34 m2/g Furnace black, surface 36 M2/g Precipitated silica, BET surface 175 M2/g Sodium silicate Calcium carbonate Paraffinic plasticizer 3-Thiocyanatopropyl triethoxy silane Diethylene glycol Benzothiazy1-2-cyclohexyl sulfenamide Tetramethyl thiuram disulfide Copper dialkyl dithiophosphate Zinc dibutyl dithiocarbamate 91 185 KV Example 1 Reduction of TMTD by using Si 264 in an EPDM cable sheath mixture 1 2 Keltan 578 100 100 Ultrasil VN 3 25 25 Omya chalk 50 50 Suprex Clay 125 125 ZnO RS 5 5 Stearic acid 2 2 Sunpar 150 30 30 DEG 2 2 Si 264 - 2 CBS 2 2 TMTD 1 0.5 Rhenocure CUT 2.5 2.5 Sulfur 1.5 1.5 Rheometer: 160C D.ax - Dmin (Nm) 10.63 t902 - t10z 4.0 Mooney viscosity ML 4 (100C) (MU) 78 11.27 3.3 58 Vulcanizate data: 160C, t95% Tensile strength MPa 10.3 11.1 Modulus 300% MPa 3.2 6.0 Shore hardness 74 78 compression set 22h/70C % 26.3 19.4 70h/10O.C % 73.2 67.5 This Example shows that, despite the 50% reduction in the quantity of thiuram, the state of the art (mixture 1) can at least be equalled and, in some cases, even surpassed by the use of Si 264 (mixture 2).' 6 91 185 KV Example 2 Replacement of T= by Si 264 in an EPDM hydraulic hose cover 1 2 Keltan 578 100 100 765 75 75 660 100 100 Suprex Clay 90 90 ZnO RS 5 5 Stearic acid 1 1 Sunpar 150 100 100 Si 264 - 1 MBT 1.5 1.5 WBC 0.8 0.8 T= 0.7 - Rhenocure CUT 0.7 0.7 Sulfur 4 4 Rheometer: 160&C Dm. - Dmi. (Nm) 9.93 13.05 Vulcanizate data: 1609C, tgsz Tensile strength MPa 10.1 10.8 Modulus 100% MPa 7.5 9.6 Shore hardness 86 86 Storage in ASTM oil 2 (70 h/160OC) Tensile strength MPa 3.4 4.3 Modulus 100% MPa 2.9 4.3 Elongation at break % 110 110 In Example 2, the TMTD can be omitted altogether through the use of Si 264 without any deterioration in the rubber porperties.

7 91 185 KV

Claims (2)

1. A process for the production of vulcanizable moulding compounds consisting of one or more natural or synthetic rubbers or polymers vulcanized with sulfur or sulfur donors and accelerators, fillers and other typical constituents, at least one accelerator belonging to the class of thiurams and/or dithiocarbamates being used, characterized in that, where 3-thiocyanatopropyl trialkoxy silanes corresponding to the following general formula:

(R0) 3 S' (CH2) 3 S CN (I) in which R = Cl-, alkyl, are simultaneously used, the quantity of accelerators from the class of thiurams and/or dithiocarbamates is reduced to at least half the quantity originally used in the vulcanizable moulding compound free from organosilicon compounds.

2. Vulcanizable moulding compounds produced by the process claimed in claim 1.