Process and apparatus for the preparation of crosslinkable rubber mixtures
The invention relates to a process and an apparatus for the preparation of a crosslinkable rubber mixture for vehicle tires, lines, drive belts and other industrial rubber articles, which can be carried out at least semicontinuously. The present invention is based on the discovery that the experiments known from the prior art to carry out the batchwise process usually used at least partly continuously have failed in particular because of the problem that the crosslinking agents have to be mixed rapidly and homogeneously with the base mixture, also referred to as rubber base mixture, without the mixture consisting of the base mixture and the crosslinking agents heating up too strongly. According to the invention, attention was therefore focussed on reliably mixing the base mixture homogeneously with the crosslinking agents and minimizing the mixing time. A first measure for achieving the desired aim consists in first mixing the crosslinking agents with one another before they are mixed with the base mixture. The mixture of crosslinking agents is in particular first packed in a container which is used for feeding the crosslinking agents into a base mixture.
1. A process for the preparation of a crosslinkable rubber mixture, comprising: mixing a first crosslinking agent with a second crosslinking agent, wherein the first crosslinking agent and the second crosslinking agent are coated with a polymer; thereby forming a homogenous mixture of crosslinking agents, whereby a melting point depression of less than 120° C. is achieved for the mixture of crosslinking agents, and continuously admixing the homogenous mixture of crosslinking agents with a discontinuously produced base mixture, said base mixture comprising at least one rubber.
2. The process according to claim 1 , wherein the first crosslinking agent and the second crosslinking agent each melt at a temperature of below 100° C. and wherein the step of admixing the mixture of crosslinking agents with the base mixture is performed at a temperature of between 100° C. and 150° C.
3. The process according to claim 1 , wherein prior to the step of admixing the homogenous mixture of crosslinking agents with the base mixture, the mixture of crosslinking agents is pumped at high pressure into contact with the base mixture.
4. The process according to claim 1 , further comprising:
placing, prior to the step of admixing the mixture of crosslinking agents with a base mixture, the mixture of crosslinking agents into a container,
thereafter closing the container, thereby providing a closed container,
connecting the closed container to an apparatus capable of admixing the base mixture with the crosslinking agents,
opening the closed container, and
transferring the mixture of crosslinking agents to the apparatus capable of admixing the crosslinking agents with the base mixture.
5. The process according to claim 1 , wherein the first crosslinking agent and the second crosslinking agent mixture contains an element or compound selected from the group consisting of sulphur, a peroxide, a metal oxide, a fatty acid, a dithiocarbamate, tetramethylthiuram disulphide, tetramethylthiuram monosulphide, tetraethylthiuram disulphide, bis(pentamethylene)thiuram tetrasulphide, ethylenethiourea, N,N,N′N′-tetramethylthiourea, diethylthiourea, dibutylthiourea, 2-mercaptobenzothiazole, mercaptobenzothiazyl, zinc mercaptobenzothiazole, N′-cyclohexylbenzothiazole-2-sulphenamide, N-tert-butyl-2-benzothiazolesulphenamide, 2-morpholinebenzothiazolesulphenamide, dithiophosphates, diphenylguanidine, N′N-di-ortho-tolylguanidine, a discolouring anti-ageing agent, a non-discolouring anti-ageing agent, a paraphenylenediamine, isopropylphenylparaphenylenediamine, paraphenylenediamine, N,N-ditoly-p-phenylenediamine, trimethyl-1,2-dihydroquinoline, [(phenyl)amine]-1,4-naphthalenedione, bis(4-octylphenyl)amine, styrenated diphenylamine, mono-bisphenol, bisphenol, mercaptobenzimidazole, 2-mercaptobenzimidazole, 2-mercaptomethyl-benzimidazoles, zinc 4-methyl-2-mercaptobenzimidazole, zinc 5-methyl-2-mercaptobenzimidazole, an olefin, a paraffinic plasticizer, an aromatic plasticizer, and mixtures thereof.
6. The process according to claim 1 , further comprising:
marking the first crosslinking agent and the second crosslinking agent with a marking substance, and
monitoring the distribution of the first crosslinking agent and the second crosslinking agent continuously while the remaining steps are performed.
7. The process according to claim 6 , wherein the proportion of the marking substance present is less than 50% by weight based on the total amount of the first crosslinking agent and second crosslinking agent used.
8. The process according to claim 1 , wherein the first crosslinking agent and the second crosslinking agent each melt at a temperature of below 100° C. and wherein the step of admixing the mixture of crosslinking agents with the base mixture is performed at a temperature of below 120° C.
9. The process according to claim 3 , wherein said high pressure is at least 50 bar.
10. The process according to claim 6 , wherein the proportion of the marking substance present is less than 5% by weight based on the total amount of the first crosslinking agent and second crosslinking agent used.
11. A process for the preparation of a crosslinkable rubber mixture, comprising:
mixing a first crosslinking agent with a second crosslinking agent, thereby forming a homogenous mixture of crosslinking agents, whereby a melting point depression of less than 120° C. is achieved for the mixture of crosslinking agents, and
admixing the homogenous mixture of crosslinking agents with a discontinuously produced base mixture, said base mixture comprising at least one rubber,
wherein, the first crosslinking agent and the second crosslinking agent are marked with a marking substance, and
monitoring the distribution of the first crosslinking agent and the second crosslinking agent continuously while the remaining steps are performed.
12. The process according to claim 11 , wherein the proportion of the marking substance present is less than 50% by weight based on the total amount of the first crosslinking agent and second crosslinking agent used.