RUBBER MIX

Description

[0001] The invention relates to a rubber mixture which is particularly suitable for use in the drinking water and food sectors.

[0002] Most conventional crosslinking chemicals, such as sulfur accelerators or peroxides, produce decomposition products during vulcanization that are undesirable in the elastomer product and often cause negative organoleptic properties. Furthermore, most decomposition products have not yet been fully tested or evaluated for toxicological reasons.

[0003] These concerns have prompted the German Federal Environment Agency (UBA) to prohibit the use of classic cross-linking chemicals in the new elastomer guideline (German regulation for elastomers in contact with drinking water) after December 31, 2021, unless the safety of the substances is proven by extensive toxicological studies.

[0004] Therefore, alternative crosslinking chemicals are being sought that do not produce degradation products during vulcanization and thus do not cause odor and taste impairment. Furthermore, in accordance with the Elastomer Guidelines, they should also be approved after 2021.

[0005] It is known from the prior art that resins, preferably butylphenol-formaldehyde resins, can be used as crosslinking chemicals for certain elastomers.

[0006] The advantage of this type of crosslinking lies in the complete incorporation of the crosslinking chemical into the polymer chains, thus preventing the formation of accelerator degradation products. The negative organoleptic properties often associated with these degradation products and their potential migration into the medium, such as drinking water, are thus prevented.

[0007] Resin crosslinking has been known for some time in the field of bladder production for car tires, where butyl rubber or halogenated butyl rubber (CIIR and BIIR) is preferably used, see e.g. EP1016691A1.

[0008] EP2871212A1 describes how EPDM rubber, IIR rubber, CIIR rubber, BIIR rubber, or a mixture thereof can be crosslinked with 3 to 10 phr of butylphenol formaldehyde resin and an activation system consisting of 1 to 8 phr of ZnO, 2 to 6 phr of a C 6-24 carboxylic acid, and a chlorinated polymer, such as CIIR, CPE, chlorinated polyisoprene, or chlorinated NR. Such a composition is characterized by an optimized compression set (DVR), allowing the elastomer to be used as a sealing ring in drinking water applications.

[0009] Activated zeolites and / or metal halides can support the resin crosslinking reaction, see e.g. EP2441798A1.

[0010] According to new legal requirements, such as EN45545, products intended for drinking water applications must also meet the increased requirements regarding fire and flame protection. This has not been possible with the rubber compounds described above, which are currently known from the state of the art.

[0011] The object of the present invention is therefore to provide a rubber compound that can be readily crosslinked with at least one resin and that simultaneously meets the requirements for drinking water approval and the increased requirements regarding fire and flame protection. At the same time, the other physical properties of the rubber compound should not deteriorate further.

[0012] This object is achieved in that the rubber mixture contains at least one rubber and at least one filler and at least one resin as crosslinking agent and at least one flame retardant and at least one carboxylic acid, wherein the rubber is selected from the group consisting of nitrile rubber (NBR) and (partially) hydrogenated nitrile rubber (HNBR) and wherein Zn stearate or aluminum trihydrate or magnesium hydroxide or hydrotalcite or a halogen-free phosphate compound or expandable graphite is used as flame retardant, in each case alone or in a combination of at least two flame retardants.

[0013] According to the invention, the rubber is selected from the group consisting of nitrile rubber (NBR) and (partially) hydrogenated nitrile rubber (HNBR).

[0014] The rubbers mentioned can be used alone or in combination.

[0015] In addition, the rubber mixture may contain at least one thermoplastic elastomer (TPE) and / or one thermoplastic (TP). Preferred TPEs and / or TPs are: polyolefin, in particular polyethylene (PE) or polypropylene (PP), and / or polystyrene and / or polyamide (PA), for example PA6 or PA6.6, and / or polyester (PES) and / or polyvinyl chloride (PVC).

[0016] Essential to the invention is that the rubber mixture is crosslinked with at least one resin. Any resin known to the skilled person can be used, either alone or in a combination of at least two resins. Phenolic resin, alkylphenol resin, or alkylphenol-formaldehyde resin is preferred, particularly resins containing tert-butyl radicals or tert-octyl radicals on the phenol ring. The use of a para-tert-butylphenol-formaldehyde resin has proven particularly suitable, particularly a para-tert-butylphenol-formaldehyde resin with a preferred methylol content of 8 to 15% and a particularly preferred methylol content of 10 to 14%.

[0017] The amount of resin used or the total amount of resins used if more than one resin is used is preferably 0.01 to 25 phr, more preferably 0.1 to 10 phr and most preferably 0.1 to 5 phr and further most preferably 0.1 to 3 phr or 0.1 to 1 phr.

[0018] It is also essential to the invention that the rubber mixture contains at least one flame retardant.

[0019] According to the invention, Zn stearate or aluminum trihydrate or magnesium hydroxide or hydrotalcite or a halogen-free phosphate compound or expandable graphite are used as flame retardants, each alone or in a combination of at least two flame retardants.

[0020] The use of zinc stearate, aluminum trihydrate, magnesium hydroxide, hydrotalcite, a halogen-free phosphate compound, or expanded graphite has proven particularly suitable for drinking water applications. When using zinc stearate as a flame retardant, the rubber compound can, in a particularly preferred embodiment, be free of ZnO, i.e., the amount of ZnO in this case is 0 phr. This eliminates the need for additional, health-hazardous zinc compounds.

[0021] To support resin crosslinking, the rubber compound also contains at least one carboxylic acid. This can be a monocarboxylic acid, a dicarboxylic acid, or a mixture of monocarboxylic acid and dicarboxylic acid.

[0022] Monocarboxylic acids are acids that have a carboxyl group.

[0023] The monocarboxylic acid can be an acyclic aliphatic monocarboxylic acid, a cyclic aliphatic monocarboxylic acid, an aromatic monocarboxylic acid, or a heterocyclic monocarboxylic acid. They can be saturated or unsaturated.

[0024] Examples of saturated cyclic monocarboxylic acids are cyclobutanoic acid or cyclohexanecarboxylic acid.

[0025] Preferably, however, it is a saturated acyclic aliphatic monocarboxylic acid with the formula H(CH) m COOH, where m can assume values ​​between 0 and 40, preferably between 8 and 25. Examples of such saturated aliphatic monocarboxylic acids are formic acid (m=0), acetic acid (m=1), propionic acid (m=2), butyric acid (m=3), valeric acid (m=4), caproic acid (m=5), enanthic acid (m=6), caprylic acid (m=7), pelargonic acid (m=8), capric acid (m=9), undecanoic acid (m=10), lauric acid (m=11), tridecanoic acid (m=12), myristic acid (m=13), pentadecanedioic acid (m=14), palmitic acid (m=15), margaric acid (m=16), stearic acid (m=17), nonadecanoic acid (m=18), arachidic acid (m=19), heneicosanoic acid (m=20), behenic acid (m=21), lignoceric acid (m=22), etc.

[0026] Dibasic acids are carboxylic acids that have two carboxyl groups.

[0027] The dibasic acid can be an acyclic aliphatic dibasic acid, a cyclic aliphatic dibasic acid, an aromatic dibasic acid, or a heterocyclic dibasic acid. They can be saturated or unsaturated. Examples of aromatic dibasic acids include phthalic acid, terephthalic acid, or isophthalic acid.

[0028] Preferably, however, it is an aliphatic dibasic acid with the formula HOOC(CH) m COOH, where m can assume values ​​between 0 and 40, preferably between 6 and 22, particularly preferably between 6 and 12. Examples of such aliphatic dibasic acids are oxalic acid (m=0), malonic acid (m=1), succinic acid (m=2), glutaric acid (m=3), adipic acid (m=4), pimelic acid (m=5), suberic acid (m=6), azelaic acid (m=7), sebacic acid (m=8), undecanedioic acid (m=9), dodecanedioic acid (m=10), brassylic acid (m=11), tetradecanedioic acid (m=12), thapsic acid (m=14), heptadecanedioic acid (m=15), octadecanedioic acid (m=16), nonadecanedioic acid (m=17) and eicosanoic acid (m=18), etc.

[0029] All carboxylic acids can be used alone or in combination.

[0030] Particularly suitable acids are stearic acid and benzoic acid.

[0031] Furthermore, the rubber mixture contains at least one filler.

[0032] These can be any fillers known to the expert, such as carbon black, graphite, carbon nanotubes (CNT), silica, calcium and aluminum silicates, diatomaceous earth, kaolin, limestone, zeolites, cyclodextrins, feldspar and / or talc, chalk, alumina gel, fibers (short and long fibers, glass, carbon, aramid fibers), whiskers (aluminum oxide, silicon carbide), mica, magnetite, core / shell fillers, asphalt, hard rubber dust, chlorides, carbonates, sulfates, oxides and hydroxides of alkali and alkaline earth metals, Al(OH)3, PVC, polymer powders (e.g. PE or PTFE powder), factice, inorganic and organic pigments, organic or inorganic acids, glass beads, wood flour, nutshell flour, which can be used alone or in combination.

[0033] In order for the rubber compound to have good electrical conductivity, the use of conductive carbon black, graphite, CNT and metals and their compounds, especially iron compounds, has proven particularly preferable.

[0034] In a preferred embodiment, the rubber mixture contains further additives.

[0035] The other additives are selected from the group consisting of processing aids, such as ZnO, Mg stearate, stearic acid, PE and / or PTFE powder, and plasticizers, such as white oils, esters, factice, and waxes; and emulsifiers, dispersants, neutralizing agents, anti-aging agents, and adhesion promoters, such as DBU or DBN and their salts; and ozone protection agents and functional materials, such as antimicrobial additives, odor neutralizers, flavors; and lubricants, mold release agents, and anti-fouling agents and permeation-inhibiting substances, such as phyllosilicates. These additives may be present alone or in combination.

[0036] The rubber mixture according to the invention is preferably used in technical rubber articles, such as air springs, rubber spring elements, drive belts, conveyor belts, hoses, tires, sealing materials, multi-layer fabric webs for forming flexible containers, tents, tarpaulins, membranes, protective suits, printing blankets or bellows.

[0037] Hoses are primarily used for fuel pump hoses, manifold hoses, fuel hoses, offshore and marine hoses, bunker hoses, air conditioning hoses, paint spray hoses, heatable hoses, or low-permeation hoses. Due to the low toxicity of the rubber compound, which allows for use in the food and drinking water industries, the rubber compound is primarily used in drinking water and food hoses.

[0038] The rubber compound can also be used in covering films, tarpaulins, or linings for direct contact with drinking water. It can also be used in conveyor belts for transporting food or in drinking water applications.

[0039] The invention will now be explained in more detail using comparative and exemplary embodiments, which are summarized in Table 1. The mixture marked "E" is a mixture according to the invention, while the mixture marked "V" is a comparison mixture. Table 1 Components Unit V1 E1 NBR phr 100 100 Phenol-formaldehyde resin* phr 5 5 Aluminum trihydrate (ATH) phr 0 9 Test results Unit V1 E1 Hardness DIN 53505 Shore A 64 60 Tensile strength DIN 53504 S2 N / mm 2 23 19 Elongation at break DIN 53504 S2 % 567 639 Compression set, 25% yield, 100°C DIN ISO 815 % 33 40 Tear resistance DIN ISO 34-1A N / mm 12 15 Abrasion DIN ISO 4649 Method A mm 3< 105 109 *Para-tert-butylphenol formaldehyde resin; methylol content 8 to 12%

Claims

1. Rubber mixture, characterized in that it contains at least one rubber and at least one filler and at least one resin as a crosslinking agent and at least one flame retardant and at least one carboxylic acid, wherein the rubber is selected from the group consisting of nitrile rubber (NBR) and (partially) hydrogenated nitrile rubber (HNBR) and wherein the flame retardant employed is Zn stearate or aluminium trihydrate or magnesium hydroxide or hydrotalcite or a halogen-free phosphate compound or expandable graphite in each case alone or in a combination of at least two flame retardants.

2. Rubber mixture according to Claim 1, characterized in that the filler is silica and / or carbon black.

3. Rubber mixture according to either of Claims 1 to 2 for producing a covering film, a tarpaulin, a lining, a conveyor belt, a hose or a seal.