DE4129023A1 - Non-nitrosamine-toxic, non-corrosive age-resistant vulcanising system - contg. rubber, carbon black, fillers, bis-ammine zinc di:isocyanate, 2-mercapto:benzothiazole, etc. - Google Patents

Abstract

A non-nitrosamine-toxic crosslinking system with reduced aggressivity to metal and improved heat ageing stability, contains 100 pts. wt. rubber, 50-150 pts. wt. carbon black, 0-200 pts. wt. inactive filler, 0-120 pts. wt. rubber plasticiser, 0-10 pts. wt. CaO, 0-20 pts. wt. ZnO, 0.5-6.5 pts. wt. 2-mercaptobenzeno-thiazole (MBT) or salts thereof and/or -thiazyl disulphide (MBTS) and/or other suitable combined crosslinkers (e.g. sulphenamides) (II) 0.5-10 pts. wt. bis-(ammoniato)-Zn(NCO)2 (III) or analogues thereof (also with other central atoms) 0.1-6 pts. wt. N, N'-bis-(caprolactam)-monosulphide or poly-sulphide (IV), 0-3 pts. wt. sulphur and up to 100 pts. wt. rubber additives. USE/ADVANTAGE - Provides rubber vulcanising system with no nitrosamine toxicity which gives vulcanised rubber with low metal corrosion and increased resistance to thermal ageing (as required esp. for combined metal/rubber parts for use in motor vehicle engine compartments etc). (8pp Dwg.No.0/4)

Description

The difficulties, with the existing ones, not nitrosamintoxic rubber crosslinking agents the state of Technology to manufacture equivalent rubber products, especially those with above-average networking density, are known. These vulcanizing agents are in all previously known cases significantly weaker networking as z. B. the previously considered indispensable low molecular thiurams or dithiocarbamates, d. H. you are equimolecular not interchangeable and even in higher dose not technically equivalent. Only by the Use of certain synergistic combinations with - in usually individually the weaker - non-nitrosamintoxic Covulcanization agents have managed to overcome this deficiency and thus a practically equivalent, new, to establish non-nitrosamintoxic combination class (DE-A-40 27 114, DE-A-40 36 420, DE-A-40 38 946).

This is of particular importance for the only moderately reactive EPDM Rubber, because for this even the potentially superior classic crosslinkers in both a larger number also in a very high total dosage (up to 10 times compared with other diene rubbers) must be used. This alone highlights the difficulty of solving it this problem.

A disadvantage, however, which is also the new, non-nitrosamine attached to toxic systems, is the unwanted contact corrosivity of the rubber products concerned towards metals, a factor especially in the automotive industry plays significant role and usually the aggressiveness of free and / or primary bound sulfur is.

Accordingly, it is a new objective, not a goal nitrosamintoxic crosslinker or a non-nitrosamine to invent a toxic combination that is capable of this To eliminate shortage. For a concretization, the Idea that new ones in question should be used Crosslinker or reactant a kind of moderating function assume a reduction at the same degree of cross-linking of the free, to be released and / or in any form provisionally bound (labile) sulfur, by the fact that these

• 1) even little or no releasable sulfur contained and yet directly a high rubber have reactivity,
• 2) simultaneously or alternatively to the still needed sulfur-containing co-crosslinkers and the free sulfur activating, so that you are able to the number and quantity of the latter or the amount of available sulfur due to relatively higher Limit crosslinking yield.

In addition, with regard to a required universal Application of such a rubber material on a decisive improvement of heat aging resistance particular value is placed on it, in particular in the Use in engine combination parts is severely lacking. Such weaknesses are becoming more noticeable today as the engine compartment temperatures due to more and more in the fore The reason for this is that there is always a trend towards noise reduction measures continue to rise. When realizing the postulated Mechanism should also have a suitable networking structure can occur.  

Such a key agent to this invention provides the sulfur-free compound of the following basic structure,

wherein NH₃ by primary amines and / or non-nitrosamintoxic secondary amines in whole or in part and zinc through another divalent metal atom, in particular nickel, cobalt and manganese, is substitutable. To solve the problem is this Compound according to the invention in combination with

• a) 2-mercapto-benzothiazole or its salts and / or thiazyl disulfide and / or other suitable combinations crosslinkers (eg sulfenamides) as well as
• b) N, N'-bis (caprolactam) monosulfide or polysulfide,

optionally together with sulfur used.

In the context of the experimental part, the effect of the substance in a pattern mixture is shown in the graphs (FIGS . 1 to 4).

The diagram ( Fig. 1) describes the positive influence of the bis (ammoniakato) zinc diisocyanate (abscissa: amount in phr) on the surface change (ordinate: degree of corrosion) of a copper sheet.

The diagram ( Fig. 2) shows in principle the same favorable trend with respect to a metal-containing PVC decorative strip (abscissa as in Fig. 1, ordinate: degree of discoloration).

In the diagram ( Figure 3), the quantitative change in tensile elongation (ordinate: Δ tensile elongation in%) due to hot air aging (168 h, 100 ° C) as a function of increasing concentration of bis (ammoniakato) diisocyanate in phr ( Abscissa) shown graphically. It turns out that an increase in the amount of this substance reduces the waste and thus increases the aging resistance. The drop in tensile strength (ordinate: Δ tensile strength in%) according to the diagram ( Fig. 4) also decreases and even develops from about 3 phr of the bis (ammoniacato) diisocyanate (abscissa) even to positive values (increase in tensile strength) ,

The diagrams ( FIGS. 1 to 4) are based on the following basic formula (in phr):

EPDM rubber (oil-extended) 150 Rubber molding (N 550) 100 chalk 100 Paraffinic-naphthenic rubber softener 40 Calcium oxide dispersion (80%) 6 zinc oxide 5 2-mercaptobenzothiazole 3.8 Bis (Ammoniakato-) zinc-diisocyanate variable N, N'-bis- (caprolactam) disulfide 1.8-3.0 1.8 (curve a) 3.0 (curve b) 2.4 (curve c) sulfur 0.95

Concrete applications (invention examples) are in the Tables 1a, 1b (example: profile) and 2a, 2b (example: Heat-resistant hose) demonstrated. The under A and D up led to represent nitrosamintoxic compositions Prior art blends, while B and C respectively E and F in each case according to the invention, non-nitrosamintoxic Represent compositions. The latter do not just meet one wall-free those contained in the right columns for intuition, often exceptionally high physical power limit requirements (Tables 1b, 2b) of industrial engineering, but in a surprising way also make it clear overall improved versions of their - to date, at the expense of "Weaknesses" often only explicitly tolerated - mission statements This is reflected in particular in the stabilization of Properties after drastic heat aging processes.  

Table 1a

Table 1b

Table 2a

Table 2b

Claims (1)

Non-nitrosamine-toxic crosslinking system with reduced metal aggressiveness and improved heat aging resistance, characterized by the following composition (in phr): rubber 100 rubber black 50-150 Fillers (inactive) 0-200 rubber plasticizers 0-120 calcium oxide 0-10 zinc oxide 0-20 2-mercaptobenzothiazole or its salts and / or thiazyl disulfide and / or other suitable combination crosslinkers (eg sulfenamides) 0.5-6.5 Bis (ammoniacato) zinc diisocyanate and analogues (also with other central atom) 0.5-10 N, N'-bis (caprolactam) monosulfide or polysulfide 0.1-6 sulfur 0-3 Rubber additives until 100