DE4038946A1 - Highly crosslinked roll-ring vulcanisates without nitrosamine toxicity - comprises mixt. of SBR stearic acid, rubber plasticiser, antioxidant and zinc oxide and vulcanisate additive - Google Patents

Abstract

Highly crosslinked rollring-vulcanisates without nitrosaminetoxicity comprise (in phr); (A) (i) 100 natural rubber and blends esp based on styrex butadiene rubber (SBR), (2) 10-150 rubber, (3) 0-3 stearic acid, (4) 10-100 rubber plasticiser, (5) 0.5-6 antioxidant, (6) 3-20 zinc oxide; and B) vulcanisate additive of compsn: (1) 0.5-6 vulcanising agent of formula (I) and/or (II), 0.5-4 phr 2-mercapto-benzothiazyldisulphide (MBTS) and/or 2-mercapto-benzothiazol (MBT) and/or chemical equivs of MBT salts, 0.3-5 vulcanising agent (III), 0.1-2.5 S, up to 50 other additives; (2) 0.5-8 phr vulcanising agent (I) and/or (II), 0.5-5 MBTs and/or MBT and/or MBT-salts, 0.3-6 vulcanising agent (III); (3) 0.5-7 vulcanising agent (I) and/or (II) 0-4 MBTS and/or MBT and/or MBT salts, 0.4-4 sulphenamide, 1-4 vulcanising agent (III), 0.1-2.5 phfs; (4) 0.7-8 vulcanising agent (I) and/or (II), 0-4 MBTS and/or MBT and/or MBT-salts, 0.4-4 sulphenamide, 1-4 vulcanising agent (III), 0.1-2.5S or (5) 0.1-4 vulcnaising agent (I) and/or (II), 0.5-5 MBTS and/or MBT and/or MBT-salts, 1-6 xanthogenate-polysulphide, 0.5-5 vulcanising agent (III), 0.1-2.5 phr s. (In (I) sum of R1, R2, R3, R4 is at least 16C; and n is at least 1). (In (II), sum of R1, R2, is at least 8C; n is at least 1, esp at least 2; and M = metal.) In (III), sum of R1, (R2, R3, R4 is at least 4C; and is at least 1. ADVANTAGE - Vulcanisates contain no nitrosamine-toxic cross-linking agents.

Description

Roll rings (and generally gaskets) made of rubber material, whether solid or with pore structure, are used to ensure a lasting Sealing performance determined and under conditions of use required sealing properties. They manifest themselves especially in a low compressive stress relaxation and low Residual deformation after pressure relief. Furthermore, there are strict requirements after a limitation of the restoring force and good ozone, aging and Swelling resistance properties.

Further difficult requirements arise from the processing practice of the preferably used for the production continuous (because economical) LCM process: foaming and precipitation phenomena (formation insoluble stearates) in the cooling bath enforce the absence of stearic acid as Blend component, a measure that lower the pursuit of attainment Compressive stress relaxation and residual deformation values (high or highest Crosslink density) is diametrically opposite.

The sum of these requirements could so far exclusively with specific, highly reactive vulcanizing agents, such as TMTD (tetramethyl thiuram disulfide) or TMTM (tetramethylthiuram monosulfide) or the corresponding dithiocarbamate, are met; Substances for the Production of short-chain sulfur bridges in high concentration verant are verbal.

In order to achieve the above-mentioned technical goals, moreover, had to highly reactive elastomer partner with special elasticity disposition such as NR, CR, SBR or BR rubber, among which  z. B. NR has the disadvantage unfavorable aging behavior. on the other hand aged NR vulcanizates often show strong tack and CR vulcanizates Over time, the tendency to lose soft elasticity harden. The most suitable materials under such aspects are SBR and its blends with No. SBR and NR can also individually through BR replaced or used in a 3-fold blending together with BR.

Despite such merits, SBR (unlike NR, CR, and BR) can only do so exploit its advantage, if it succeeds, its structural deficit to compensate for basic elasticity, which is the rolling ring products of Prior art only by the above, extremely efficient low molecular weight crosslinker of thiuram dithiocarbamate class is possible. However, these are the ones that generate - as a result of their type and not least of all here necessary abnormal large amount of use of up to 5 phr - in the course of the Vulkanisationsprozesses and during storage and use the rubber part comparatively extremely high doses of emitted carcinogenic Nitrosamines as reaction by-products.

As the danger to humans by inhalation is still essential increasing proves the fact that according to the usual technique Rolling ring vulcanizate preferably in continuous salt bath (LCM) Process can be prepared in a nitrate / nitrite melt; a process the unfavorable addition, a high-grade potential of nitroso groups which provides nitrosamines from the amines supplied by the gum in still significantly increased quantities.

The object of the invention is the above-mentioned nitrosamintoxic To eliminate crosslinking agents and non-polluting by the environment to replace.

The difficulty here lies in the fact that

• 1. all known, non-nitrosamintoxic in theory Crosslinkers are less reactive, d. H. a lower networking potential not only those of their chemical constitution own  Networking weakness, but in addition to that loss share has to be compensated for by the density of interconnectedness Working without or with limited amounts of stearic acid arises;
• 2. in the fact that the "most-known" highly reactive (low molecular weight) crosslinker of thiuram dithiocarbamate class (so-called ultra accelerators) as well as the nitrosamintoxic sulfur donors, as measured by the standard rubber practice, to obtain the required crosslink density already in abnormal overdoses must be used;
• 3. in the fact that the incubation phase of the crosslinking in the new crosslinkers is so small that the production of rubber compounds and their production to rubber parts impossible or at least with intolerably high manufacturing risks (committee); such as
• 4. in the above-described lack of sufficient basic elasticity of favoring SBR rubbers.

The situation outlined here clearly shows that a solution of the upcoming Problems, if at all, only via suitable so-called synergistic Interaction combinations can be enabled.

This problem is solved by the characteristic composition Claim 1, wherein the alternative use of the component systems A to E essential is:

A component system

Vulcanizing agent (I) and / or (II)
MBTS and / or MBT and / or chemical equivalents of MBT salts
- vulcanizing agent (III)
- sulfur

Component system B

Vulcanizing agent (I) and / or (II)
MBTS and / or MBT and / or chemical equivalents of MBT salts
- vulcanizing agent (III)

Component System C

Vulcanizing agent (I) and / or (II)
- CBS and / or other non-nitrosamintoxic sulfenamides
- vulcanizing agent (III)
- sulfur

Component system D

Vulcanizing agent (I) and / or (II)
MBTS and / or MBT and / or chemical equivalents of MBT salts
- sulfur

Component system E

Vulcanizing agent (I) and / or (II)
MBTS and / or MBT and / or chemical equivalents of MBT salts
- xanthogenate polysulfide
- vulcanizing agent (III)
- sulfur

The abbreviations used here mean:
MBT 2-mercaptobenzothiazole
MBTS 2-mercapto-benzothiazyl disulfide
CBS N-cyclohexyl-N-benzothiazyl sulfenamide

As an additional component of the component system C may optionally MBTS and / or MBT and / or equivalents of the MBT salts.

Within the following experimental part, recipes and physical properties of compact, non-driven vulcanizates of Pororoll ring mixtures (Examples 1 to 6, Table 1, 2) recorded. 2 to 6 formulations according to the invention represent while Figure 1 includes a conventional rolling ring formulation (prior art).  

Table 1

Table 2

Claims (9)

1. Highly crosslinked rolling ring vulcanizates without nitrosamine toxicity, characterized by the following composition (in phr): Rubber and its blends (in particular based on SBR) 100 rubber black 10-150 stearic acid 0-3 rubber plasticizers 10-100 Ozone and / or anti-aging agents 0.5-6 zinc oxide 3-20 wherein the vulcanizing agents (I, II, III) have the following basic structures: (Σ R₁, R₂, R₃, R₄ is 16 C atoms; n 1) (Σ R₁, R₂, C atoms 8; n 1, in particular n 2;
M = metal atoms) (Σ R₁, R₂, R₃, R₄ 4 C atoms; n 1) 2. vulcanizates according to claim 1, characterized in that the substituents R₁ to R₄ are the same or different. 3. vulcanizates according to claim 2, characterized in that the substituents aliphatic, aromatic or mixed aliphatic-aromatic hydrocarbons are. 4. vulcanizates according to claim 2 or 3, characterized in that with respect to the vulcanizing agent (I, II) the following structural parameters apply:

• (I) R₁ = R₂ = R₃ = R₄ = benzyl; n = 2
  [Tetrabenzyl-thiuram-disulfide]
• (II) R₁ = R₂ = benzyl; n = 2; M = zinc
  [Zinc N, N-dibenzyl-dithio-carbamate]

5. vulcanizates according to claim 2, characterized in that the substituents hetero and / or halogen atoms. 6. vulcanizates according to any one of claims 2, 3 or 5, characterized in that the substituents R₁, R₂ or R₃, R₄ are annularly connected to each other. 7. vulcanizates according to claim 6, characterized in that with respect to the vulcanizing agent (I, II) the following structural parameters apply:

• (I) R₁, R₂ = R₃, R₄ = (CH₂-CH₂) ₂NCH₃; n = 2
  [Bis (4-methyl-piperazino) thiuram disulfide]
• (II) R₁, R₂ = (CH₂-CH₂) ₂NCH₃; n = 2; M = zinc
  [Zinc-bis (4-methyl-piperazino) dithio-carbamate]

8. vulcanizates according to claim 6, characterized in that with respect to the vulcanizing agent (III) the following structural parameters apply:
R₁, R₂ = R₃, R₄ = (CH₂) ₅; n = 2
[N, N'-bis- (caprolactam) disulfide]