RUBBER COMPOUND

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 purposes.

[0003] These concerns have prompted the German Federal Environment Agency (UBA) to prohibit the use of classic crosslinking 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 decomposition 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 eliminating the formation of accelerator degradation products. The negative organoleptic properties often associated with degradation products and potential migration of the degradation products 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 (CSD), 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] However, the amounts of carboxylic acid in the activation system described in EP2871212A1 can lead to either the resin and / or the carboxylic acid not being fully crosslinked and migrating. Such migration of crosslinking and / or activator chemicals is undesirable.

[0011] US 3 008 915 A deals with the topic of resin crosslinking, but does not disclose para-tert-butylphenol formaldehyde resin.

[0012] The object of the present invention is therefore to provide a rubber mixture which can be easily crosslinked with at least one resin and which, at the same time, shows no tendency for the crosslinking chemicals used to migrate.

[0013] This object is achieved in that the rubber mixture contains at least one rubber and at least one resin as a crosslinking agent and 0.1 to 1.5 phr of at least one carboxylic acid, wherein the resin is a para-tert-butylphenol formaldehyde resin. Surprisingly, it has been found that good crosslinking with resins can be achieved even when the concentration of carboxylic acids in the activator system is comparatively low. In particular, the rubber mixture shows significantly better dynamic suitability. This includes improved elongation properties of more than 450% with the same or even improved compression set.

[0014] The rubber is preferably selected from the group consisting of ethylene-propylene copolymer (EPM) and ethylene-propylene-diene copolymer (EPDM) and nitrile rubber (NBR) and (partially) hydrogenated nitrile rubber (HNBR) and natural rubber (NR) and styrene-butadiene rubber (SBR) and solution-polymerized styrene-butadiene rubber (SSBR) and emulsion-polymerized styrene-butadiene rubber (ESBR) and chloroprene rubber (CR) and isoprene rubber (IR) and butyl rubber (IIR) and bromobutyl rubber (BIIR) and chlorobutyl rubber (CIIR) and butadiene rubber (BR) and chlorinated polyethylene (CM) and chlorosulfonated polyethylene (CSM) and alkylated chlorosulfonated polyethylene (ACSM) and Polyepichlorohydrin (ECO) butadiene rubber (BR) and ethylene vinyl acetate rubber (EVA) and silicone rubber (MQ, VMQ, PVMQ,FVMQ) and polyurethane (PU) and polynorbene rubber (PNR) and trans-polyoctenamer rubber (TOR) and polyester urethane rubber (AU) and polyurethane ether rubber (EU).

[0015] The rubbers mentioned can be used alone or in a combination of at least two rubbers.

[0016] Particularly good results can be achieved when NBR, EPDM and / or IIR are used as rubber, either alone or in a combination of at least two rubbers.

[0017] 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).

[0018] In particular, the use of a combination of NBR and PVC (NBR / PVC) shows particularly good results.

[0019] It is essential to the invention that the rubber mixture is crosslinked with at least one resin.

[0020] This resin is para-tert-butylphenol formaldehyde resin with a preferred methylol content of 8 to 15% and a particularly preferred methylol content of 10 to 14%.

[0021] In a preferred embodiment, the amount of resin is between 0.1 and 3 phr, particularly preferably between 0.1 and 1 phr. This further reduces the tendency of the crosslinking chemicals to migrate, since even this small amount of resin is sufficient for complete crosslinking.

[0022] According to the invention, the rubber mixture also contains 0.1 to 1.5 phr, particularly preferably 0.1 to 1 phr, of at least one carboxylic acid. This can be at least one monocarboxylic acid or at least one dicarboxylic acid, or a mixture of monocarboxylic acid and dicarboxylic acid. If more than one carboxylic acid is used, the stated amount refers to the total amount of all carboxylic acids. Monocarboxylic acids are acids that contain one 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 blacks, graphite, CNTs and metals and their compounds, especially iron compounds, has proven to be particularly preferred.

[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, Zn stearate, Mg stearate, stearic acid, PE and / or PTFE powder, and plasticizers, such as white oils, esters, factice and waxes, and emulsifiers and dispersants and neutralizing agents and anti-aging agents and adhesion promoters, such as DBU or DBN and their salts, and ozonants and flame retardants and functional materials, such as antimicrobial additives, odor neutralizers, flavors, and lubricants and mold release agents and anti-rot agents and permeation-inhibiting substances, such as phyllosilicates. The additives mentioned can 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, in particular pressure equalization membranes, protective suits, printing blankets or bellows.

[0037] Hoses are preferably used for fuel pump hoses, manifold hoses, fuel hoses, offshore and marine hoses, bunker hoses, air conditioning hoses and paint spray hoses, heatable hoses or low-permeation hoses.

[0038] Due to the low toxicity of the rubber compound, which allows for application in the food and drinking water sector, the rubber compound is preferably used in drinking water hoses and food hoses.

[0039] 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.

[0040] The invention will now be explained in more detail using comparative and working examples, which are summarized in the two tables. The mixtures marked with "E" are mixtures according to the invention, while the mixtures marked with "V" are comparison mixtures.

[0041] A para-tert-butylphenol formaldehyde resin with a methylol content of 10 to 15% was used as the phenol-formaldehyde resin. Table 1 Components Unit V1 V2 E1 E2 Chlorobutyl rubber phr 100 100 100 100 Phenol-formaldehyde resin *< phr 0,9 0,9 0,9 0,9 Benzoic acid phr 0 1,6 0,8 1,2 Stearic acid phr 0 0 0 0 Test results Unit V1 V2 E1 E2 Hardness DIN 53505 Shore A 45 51 48 48 Tensile strength DIN 53504 S2 N / mm 2 10,4 12,4 13,1 13,9 Elongation at break DIN 53504 S2 % 557 461 521 508 Compression set, 25% yield, 70°C DIN ISO 815 % 24 12 14 14 Tear resistance DIN ISO 34-1A N / mm 9,3 6,2 8,4 8,3 Abrasion DIN ISO 4649 Process A mm 3< 580 467 515 509 Rheometer data according to DIN 53 529 Unit V1 V2 E1 E2 Smin 1,40 1,51 1,43 1,45 Smax 9,10 9,76 9,68 9,70 T10 min 4,80 1,89 3,19 2,41 T50 min 10,60 6,95 8,16 7,12 T90 min 19,99 17,92 19,37 18,95 Table 2 Components Unit V1 V3 E3 E4 Chlorobutyl rubber phr 100 100 100 100 Phenol-formaldehyde resin phr 0,9 0,9 0,9 0,9 Benzoic acid phr 0 0 0 0 Stearic acid phr 0 2 1 1,5 Test results Unit V1 V3 E3 E4 hardness Shore A 45 48 46 46 DIN 53505 Tensile strength DIN 53504 S2 N / mm 2 10,4 11,5 11,1 10,9 Elongation at break DIN 53504 S2 % 557 499 522 525 Compression set, 25% yield, 70°C DIN ISO 815 % 24 16 18 18 Tear resistance DIN ISO 34-1A N / mm 9,3 8,6 8,8 8,6 Abrasion DIN ISO 4649 Process A mm 3< 580 503 515 514 Rheometer data according to DIN 53 529 V1 V3 E3 E4 Smin 1,40 1,47 1,44 1,46 Smax 9,10 9,51 9,38 9,48 T10 min 4,80 4,06 4,60 4,23 T50 min 10,60 8,11 9,76 8,78 T90 min 19,99 19,99 19,99 19,99

Claims

1. Rubber mixture, characterized in that it contains at least one rubber and at least one resin as crosslinking agent and 0.1 to 1.5 phr of at least one carboxylic acid, wherein the resin is a para-tert-butylphenol formaldehyde resin.

2. Rubber mixture according to Claim 1, characterized in that the rubber is selected from the group consisting of ethylene-propylene copolymer (EPM) and ethylene-propylene-diene copolymer (EPDM) and nitrile rubber (NBR) and (partially) hydrogenated nitrile rubber (HNBR) and natural rubber (NR) and styrene-butadiene rubber (SBR) and solution-polymerized styrene-butadiene rubber (SSBR) and emulsion-polymerized styrene-butadiene rubber (ESBR) and isoprene rubber (IR) and butyl rubber (IIR) and butadiene rubber (BR) and ethylene-vinyl acetate rubber (EVA) and silicone rubber (MQ, VMQ, PVMQ, FVMQ) and polyurethane (PU) and polynorbornene rubber (PNR) and trans-polyoctenamer rubber (TOR) and polyester-urethane rubber (AU) and polyurethane rubber (EU).

3. Rubber mixture according to Claim 1 or 2, characterized in that it contains NBR as rubber and also PVC.

4. Rubber mixture according to any of Claims 1 to 3, characterized in that the filler is silica and / or carbon black.

5. Rubber mixture according to any of Claims 1 to 4, characterized in that it contains 0.1 to 3 phr of resin.

6. Rubber mixture according to any of Claims 1 to 5 for producing a covering film, a tarpaulin, a lining, a conveyor belt, a hose or a seal.