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EP-3902855-B1 - PULVERULENT MIXTURE OF PRECROSSLINKED NITRILE RUBBERS

EP3902855B1EP 3902855 B1EP3902855 B1EP 3902855B1EP-3902855-B1

Inventors

  • BRANDAU, SVEN
  • STAEBER, ROBERT
  • RUENZI, THOMAS

Dates

Publication Date
20260506
Application Date
20191125

Claims (13)

  1. Pulverulent mixture comprising (1) at least one nitrile rubber containing repeat units - of at least one α,β-unsaturated nitrile monomer selected from the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof, - of at least one conjugated diene monomer selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, piperylene and mixtures thereof, and - of at least one free-radically polymerizable compound having at least three olefinic double bonds per molecule wherein the free-radically polymerizable compound containing at least three olefinic double bonds per molecule is trimethylolpropane tri(meth)acrylate, wherein the proportion of the free-radically polymerizable compounds having at least three olefinic double bonds per molecule is in the range from 0.5% to 5% by weight, based on the overall polymer, and (2) at least one separating agent, wherein the at least one separating agent is selected from the group consisting of - silicas having a specific BET surface area of more than 5 m 2 /g, which have especially been chemically modified, - silicates being talc, mica, bentonites or montmorillonites, - fatty acid salts being alkali metal and alkaline earth metal salts of fatty acids having more than 10 carbon atoms, - polymers having a high glass transition temperature of more than 60°C, and - mixtures of the aforementioned separating agents; wherein 0.25 to 45 phr of the at least one separating agent, based on the nitrile rubber, is used; wherein the pulverulent mixture has an average particle diameter D a in the range from 0.06 mm to 0.75 mm as described in the description; and the preparation of the pulverulent mixture comprises either a grinding step or else a spray drying step, in the course of each of which the contacting with the at least one separating agent is effected, in the case of the grinding step, the nitrile rubber is first produced by emulsion polymerization, the resultant latex of the nitrile rubber is subjected to coagulation, and the coagulated nitrile rubber is washed, dried and then subjected to grinding, where the at least one separating agent is added in one or more portions during the grinding operation, in the case of the spray drying step, the nitrile rubber is first produced by emulsion polymerization, the resultant latex of the nitrile rubber, for the purpose of removing the water, is subjected to spray drying in a spray tower, and the at least one separating agent is either supplied to the spray tower as dry powder or else metered directly into the latex prior to the spray drying.
  2. Pulverulent mixture according to Claim 1, wherein the silicas have especially been chemically modified.
  3. Pulverulent mixture according to Claim 1, wherein the nitrile rubber has been precrosslinked.
  4. Pulverulent mixture according to any one of Claims 1 to 3, wherein the pulverulent mixture has an average particle diameter D a in the range from 0.08 mm to 0.6 mm.
  5. Pulverulent mixture according to any one of Claims 1 to 3, wherein the α,β-unsaturated nitrile monomer is acrylonitrile, and the conjugated diene monomer is 1,3-butadiene.
  6. Process for producing the pulverulent mixture according to any one of Claims 1 to 5, wherein the nitrile rubber is contacted with the at least one separating agent.
  7. Process according to Claim 6, wherein the nitrile rubber is first produced by emulsion polymerization, the resultant latex of the nitrile rubber is subjected to coagulation, and the coagulated nitrile rubber is washed, dried and then subjected to grinding, where the at least one separating agent is added in one or more portions during the grinding operation.
  8. Process according to Claim 6, wherein the nitrile rubber is first produced by emulsion polymerization, the resultant latex of the nitrile rubber, for the purpose of removing the water, is subjected to spray drying in a spray tower, and the at least one separating agent is either supplied to the spray tower as dry powder or else metered directly into the latex prior to the spray drying.
  9. Vulcanizable mixture comprising a pulverulent mixture according to any one of Claims 1 to 5 and at least one crosslinker.
  10. Process for producing vulcanizable mixtures according to Claim 9, wherein the pulverulent mixture according to any one of Claims 1 to 5 is contacted with at least one crosslinker.
  11. Process for producing vulcanizates, wherein the vulcanizable mixture according to Claim 9 is subjected to vulcanization.
  12. Vulcanizates comprising crosslinked pulverulent mixtures, wherein the pulverulent mixtures are are as defined in claim 1.
  13. Use of the vulcanizates according to Claim 12 in tyre treads.

Description

Field of Invention The present invention relates to pulverulent mixtures based on specific nitrile rubbers and at least one separating agent, and also to a process for producing vulcanizable mixtures and vulcanizates from these pulverulent mixtures, and to the resultant vulcanizates and the use thereof, especially in tyre treads. Background of Invention Nitrile rubbers, also abbreviated to "NBR", are understood to mean rubbers which are co- or terpolymers of at least one α,β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers. Such nitrile rubbers and processes for producing such nitrile rubbers have been known for many decades. NBR is typically produced by emulsion polymerization, at first giving an NBR latex. The NBR solids are isolated from this latex by coagulation, usually using salts or acids. The solid rubbers thus obtained can be converted to powder form by grinding. In an alternative workup, the NBR powder is obtained directly from the latex by spray drying. The emulsion polymerization typically has to be conducted using molecular weight regulators in order to obtain polymers having good processing properties. Processes for producing nitrile rubbers have long been known; the polymerization is typically conducted as an emulsion polymerization and can be free-radically initiated by azo initiators, persulfates, organic peroxides or redox systems. The production of precrosslinked nitrile rubbers is typically effected in the latex state and can be achieved firstly during the polymerization by continuing the polymerization up to high conversions, and after the polymerization by crosslinking or by copolymerization with crosslinking polyfunctional compounds. It is also possible to prepare precrosslinked nitrile rubbers by polymerization in the absence of molecular weight regulators. DE19701487A1 describes the production of such precrosslinked nitrile rubbers by adding peroxides to an uncrosslinked copolymer latex of acrylonitrile and butadiene in an autoclave and then crosslinking the polymer at elevated temperature via the presence of the peroxide for several hours. It is not stated whether any pulverulent precrosslinked nitrile rubbers of this kind have a positive effect on wet skid resistance, dry grip or rolling resistance in the case of use in tyres. EP0842708A1 describes the production of precrosslinked nitrile rubbers by polymerization of acrylonitrile, butadiene and a polyfunctional monomer. A wide variety of different polyfunctional monomers that can be used for production of precrosslinked nitrile rubbers are listed, such as trimethylolpropane trimethacrylate (TMPTMA), divinylbenzene (DVB) or butane-1,4-diol dimethacrylate. These precrosslinked rubbers are processed together with various other constituents such as PVC and plasticizers to give a mixture which is used for the surface treatment of components. There is no description of use or production of pulverulent precrosslinked nitrile rubbers. Pulverulent nitrile rubbers are in principle used in various applications. They are utilized, for example, in the modification of phenolic resins in the production of brake components, linings or discs. In addition, they are used for modification of thermoplastics, especially for modification of polyvinyl chloride (PVC), owing to excellent compatibility with this widely used plastic. Such elasticized PVCs are used, for example, for production of profiles, cable sheaths or seals. Various components of this kind are used in the automotive sector. In principle, a number of rubbers are conceivable for production of elastomers in powder form, such as NBR, EPDM or SBR. Especially when a modification of PVC, polyurethanes or polyamides is desired (for example to increase impact resistance), nitrile rubbers are particularly suitable owing to excellent compatibility. Use in the form of rubber powders here enables better dosage and dispersion in the thermoplastic, and hence a more homogeneous profile of properties. CN104193907A describes the production of thermally stable pulverulent nitrile rubbers by the use of N-phenyl amides in the polymerization. The coagulated rubber is finally ground, but directly processed further without further separating agents. There is no description of production of precrosslinked pulverulent nitrile rubbers through the use of crosslinking polyfunctional compounds during the polymerization, or crosslinking by addition of peroxides. There is no disclosure of the use of the powders in tyre treads nor of the effect of the powders on wet skid resistance, dry grip or rolling resistance in tyres. CN101643528A describes the production of precrosslinked pulverulent nitrile rubbers by high conversions during the polymerization. No additional separating agents are added. The two acrylonitrile and butadiene monomers are polymerized in emulsion polymerizations up to conversions of 96% and the coagulation parameters are chosen such that f