WO2005080493A1

WO2005080493A1 - Crosslinking of carboxylated nitrile polymers using compounds with at least two epoxy groups

Info

Publication number: WO2005080493A1
Application number: PCT/CA2005/000256
Authority: WO
Inventors: Frederic Guerin; Carl Walter Von Hellens
Original assignee: Lanxess Inc.
Priority date: 2004-02-23
Filing date: 2005-02-22
Publication date: 2005-09-01
Also published as: TW200540217A; CA2458752A1

Abstract

The present invention relates to a polymer compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler, a method of inducing curing in a compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, by addition of at least one epoxidized compound having at least two epoxide functions and subsequent curing.

Description

Crosslinking of carboxylated nitrile polymers using compounds with at least two epoxy groups

Field of the Invention. The present invention relates to a polymer compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler, a method of inducing curing in a compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, by addition of at least one epoxidized compound having at least two epoxide functions and subsequent curing.

Background of the Invention Carboxylated hydrogenated nitrile rubber (HXNBR), prepared by the selective hydrogenation of carboxylated acrylonitrile-butadiene rubber (nitrile rubber; XNBR, a co-polymer comprising at least one conjugated diene, at least one unsaturated nitrile, at least one carboxylated monomer and optionally further comonomers), is a specialty rubber which has very good heat resistance, excellent ozone and chemical resistance, and excellent oil resistance. Coupled with the high level of mechanical properties of the rubber (in particular the high resistance to abrasion) it is not surprising that XNBR and HXNBR have found widespread use in the automotive (seals, hoses, bearing pads) oil (stators, well head seals, valve plates), electrical (cable sheating), mechanical engineering (wheels, rollers) and shipbuilding (pipe seals, couplings) industries, amongst others.

Summary of the Invention In one of it's aspects, the present invention relates to a polymer compound comprising at least one carboxylated nitrile polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler. It is preferred that the XNBR is fully or partially hydrogenated ("HXNBR"). In particular, the invention relates to a polymer compound comprising at least one carboxylated nitrile polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler that comprises no further cross-linking agent, such as peroxides, sulphur, sulphur compounds, and the like.

Brief Description of the Drawings Fig 1. shows for the compounds of examples 1-3 the torque (S') in dN.m for the first hour of curing at 1 ° arc and 180°C.

Description of the Invention As used throughout this specification, the term "carboxylated nitrile polymer" or XNBR is intended to have a broad meaning and is meant to encompass an elastomer having repeating units derived from at least one conjugated diene, at least one alpha-beta-unsaturated nitrile, at least one monomer having a carboxylic group and optionally further one or more copolymerizable monomers. The conjugated diene may be any known conjugated diene, in particular a C4-C₆ conjugated diene. Preferred conjugated dienes are butadiene, isoprene, piperylene, 2,3-dimethyl butadiene and mixtures thereof. Even more preferred C₄-C₆ conjugated dienes are butadiene, isoprene and mixtures thereof. The most preferred C₄-C₆ conjugated diene is butadiene. The alpha-beta-unsaturated nitrile may be any known alpha-beta- unsaturated nitrile, in particular a C3-C5 alpha-beta-unsaturated nitrile. Preferred C₃-C₅ alpha-beta-unsaturated nitriles are acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof. The most preferred C₃- C₅ alpha-beta-unsaturated nitrile is acrylonitrile. The monomer having at least one carboxylic group may be any known monomer having at least one carboxylic group being copolymerizable with the nitrile and the diene. Preferred monomers having at least one carboxylic group are unsaturated carboxylic acids. Non-limiting examples of suitable unsaturated carboxylic acids are fumaric acid, maleic acid, acrylic acid, methacrylic acid and mixtures thereof. Preferably, the copolymer comprises in the range of from 40 to 85 weight percent of repeating units derived from one or more conjugated dienes, in the range of from 15 to 60 weight percent of repeating units derived from one or more unsaturated nitriles and in the range of from 0.1 to 15 weight percent of repeating units derived from one or more monomers having at least one carboxylic group. More preferably, the copolymer comprises in the range of from 55 to 75 weight percent of repeating units derived from one or more conjugated dienes, in the range of from 25 to 40 weight percent of repeating units derived from one or more unsaturated nitriles and in the range of from 1 to 7 weight percent of repeating units derived from one or more monomers having at least one carboxylic group. Optionally, the copolymer may further comprise repeating units derived from one or more copolymerizable monomers, such as alkylacrylate, styrene. Repeating units derived from one or more copolymerizable monomers will replace either the nitrile or the diene portion of the nitrile rubber and it will be apparent to the skilled in the art that the above mentioned figures will have to be adjusted to result in 100 weight percent. Hydrogenated in this invention is preferably understood by more than

50 % of the residual double bonds (RDB) present in the starting nitrile polymer/NBR being hydrogenated, preferably more than 90 % of the RDB are hydrogenated, more preferably more than 95 % of the RDB are hydrogenated and most preferably more than 99 % of the RDB are hydrogenated. The present invention is not restricted to a special process for preparing the hydrogenated carboxylated NBR. However, the HXNBR preferred in this invention is readily available as disclosed in WO-01/77185-A1. For jurisdictions allowing for this procedure, WO-01/77185-A1 is incorporated herein by reference. The XNBR as well as the HXNBR which forms a preferred component of the polymer compound of the invention can be characterized by standard techniques known in the art. For example, the molecular weight distribution of the polymer was determined by gel permeation chromatography (GPC) using a Waters 2690 Separation Module and a Waters 410 Differential Refractometer running Waters Millennium software version 3.05.01. Samples were dissolved in tetrahydrofuran (THF) stabilized with 0.025% BHT. The columns used for the determination were three sequential mixed-B gel columns from Polymer Labs. Reference Standards used were polystyrene standards from American Polymer Standards Corp. The inventive polymer compound further comprises at least one epoxidized compound having at least two or more epoxide functions. The epoxidized compound having at least two epoxide functions is not restricted and any known epoxidized compound having two or more epoxide functions that under the conditions typically used for rubber curing is capable of reacting with the carboxylic group(s) of the monomer having at least one carboxylic group is suitable. Non-limiting examples are epoxidized mineral oils, epoxidized fatty acids, epoxidized oils from natural sources, epoxidized derivatives of fatty acid glycerides which are prepared from the corresponding oils and fats by methods known in the art. Suitable epoxidized fatty acid glycerides include epoxidized soy bean oil (ESBO), epoxidized linseed oil, epoxidized corn oil, epoxidized coconut oil, epoxidized cottonzeed oil, epoxidized olive oil, epoxidized palm oil, epoxidized palm kernel oil, epoxidized peanut oil, epoxidized codliver oil, epoxidized tung oil, epoxidized beef tallow oil, epoxidized butter as well as epoxy resins, glycidyl epoxides, and non- glycidyl epoxides and mixtures thereof. Preferred are diglycidyl ethers of bisphenol-A (DGEBA). The inventive polymer compound further comprises at least one filler.

The filler may be an active or an inactive filler or a mixture thereof. The filler may be in particular: - highly dispersed silicas, prepared e.g. by the precipitation of silicate solutions or the flame hydrolysis of silicon halides, with specific surface areas of in the range of from 5 to 1000 m²/g, and with primary particle sizes of in the range of from 10 to 400 nm; the silicas can optionally also be present as mixed oxides with other metal oxides such as those of Al, Mg, Ca, Ba, Zn, Zr and Ti; - synthetic silicates, such as aluminum silicate and alkaline earth metal silicate like magnesium silicate or calcium silicate, with BET specific surface areas in the range of from 20 to 400 m²/g and primary particle diameters in the range of from 10 to 400 nm; - natural silicates, such as kaolin and other naturally occurring silica; - glass fibers and glass fiber products (matting, extrudates) or glass microspheres; - carbon blacks; the carbon blacks to be used here are prepared by the lamp black, furnace black or gas black process and have preferably BET (DIN 66 131) specific surface areas in the range of from 20 to 200 m²/g, e.g. SAF, ISAF, HAF, FEF or GPF carbon blacks; - rubber gels, especially those based on polybutadiene, butadiene/styrene copolymers, butadiene/acrylonitrile copolymers and polychloroprene; or mixtures thereof. Examples of preferred mineral fillers include silica, silicates, clay such as bentonite, gypsum, alumina, titanium dioxide, talc, mixtures of these, and the like. These mineral particles have hydroxyl groups on their surface, rendering them hydrophilic and oleophobic. This exacerbates the difficulty of achieving good interaction between the filler particles and the rubber. For many purposes, the preferred mineral is silica, especially silica made by carbon dioxide precipitation of sodium silicate. Dried amorphous silica particles suitable for use in accordance with the invention may have a mean agglomerate particle size in the range of from 1 to 100 microns, preferably between 10 and 50 microns and most preferably between 10 and 25 microns.

It is preferred that less than 10 percent by volume of the agglomerate particles are below 5 microns or over 50 microns in size. A suitable amorphous dried silica moreover usually has a BET surface area, measured in accordance with

DIN (Deutsche Industrie Norm) 66131, of in the range of from 50 and 450 square meters per gram and a DBP absorption, as measured in accordance with DIN 53601 , of in the range of from 150 and 400 grams per 100 grams of silica, and a drying loss, as measured according to DIN ISO 787/11 , of in the range of from 0 to 10 percent by weight. Suitable silica fillers are available under the trademarks HiSil® 210, HiSil® 233 and HiSil® 243 from PPG Industries Inc. Also suitable are Vulkasil® S and Vulkasil® N, from Bayer AG. Often, use of carbon black as a filler is advantageous. Usually, carbon black is present in the polymer composite in an amount of in the range of from 20 to 200 parts by weight, preferably 30 to 150 parts by weight, more preferably 40 to 100 parts by weight. Further, it might be advantageous to use a combination of carbon black and mineral filler in the inventive polymer composite. In this combination the ratio of mineral fillers to carbon black is usually in the range of from 0.05 to 20, preferably 0.1 to 10. The rubber composition according to the invention can contain further auxiliary products for rubbers, such as reaction accelerators, vulcanizing accelerators, vulcanizing acceleration auxiliaries, antioxidants, foaming agents, anti-aging agents, heat stabilizers, light stabilizers, ozone stabilizers, processing aids, plasticizers, tackifiers, blowing agents, dyestuffs, pigments, waxes, extenders, organic acids, inhibitors, metal oxides, and activators such as triethanolamine, polyethylene glycol, hexanetriol, etc., which are known to the rubber industry. The rubber aids are used in conventional amounts, which depend inter alia on the intended use. Conventional amounts are e.g. from 0.1 to 50 wt.%, based on rubber. Preferably the composition comprises in the range of 0.1 to 20 phr of an organic fatty acid as an auxiliary product, preferably a unsaturated fatty acid having one, two or more carbon double bonds in the molecule which more preferably includes 10% by weight or more of a conjugated diene acid having at least one conjugated carbon-carbon double bond in its molecule. Preferably those fatty acids have in the range of from 8-22 carbon atoms, more preferably 12-18. Examples include stearic acid, palmitic acid and oleic acid and their calcium-, zinc-, magnesium-, potassium- and ammonium salts. Preferably the composition comprises in the range of 5 to 50 phr of an acrylate as an auxiliary product. Suitable acrylates are known from EP-A1-0 319 320, in particular p. 3, I. 16 to 35, from US- 5 208 294, in particular Col. 2, I. 25 to 40, and from US-4 983 678, in particular Col. 2, I. 45 to 62. Particular reference is made to zinc acrylate, zinc diacrylate or zinc dimethacrylate or a liquid acrylate, such as trimethylolpropanetrimethacrylate (TRIM), butanedioldimethacrylate (BDMA) and ethylenglycoldimethacrylate (EDMA). It might be advantageous to use a combination of different acrylates and/or metal salts thereof. Of particular advantage is often to use metal acrylates in combination with a Scorch-retarder such as sterically hindered phenols (e.g. methyl-substituted aminoalkylphenols, in particular 2,6-di-tert.-butyl-4-dimethylaminomethylphenol). The ingredients of the final polymer composite are mixed together, suitably at an elevated temperature that may range from 25 °C to 200 °C. Normally the mixing time does not exceed one hour and a time in the range from 2 to 30 minutes is usually adequate. The mixing is suitably carried out in an internal mixer such as a Banbury mixer, or a Haake or Brabender miniature internal mixer. A two-roll mill mixer also provides a good dispersion of the additives within the elastomer. An extruder also provides good mixing, and permits shorter mixing times. It is possible to carry out the mixing in two or more stages, and the mixing can be done in different apparatus, for example one stage in an internal mixer and one stage in an extruder. However, it should be taken care that no unwanted pre-crosslinking (= scorch) occurs during the mixing stage, but that the conditions are suitable for the reaction between epoxidised compound and carboxylic groups. For compounding and vulcanization see also: Encyclopedia of Polymer Science and Engineering, Vol. 4, p. 66 et seq. (Compounding) and Vol. 17, p. 666 et seq. (Vulcanization). This process provides thermally resistant flexible cross-linking between the polymer chains. Thus, the invention provides a composition comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler. Furthermore, the inventive polymer compound may be used in the manufacture of a shaped article comprising said inventive polymer compound. Preferred shaped articles are a seal, hose, bearing pad, stator, well head seal, valve plate, cable sheating, wheel roller, pipe seal, in place gaskets or footwear component prepared by injection molding technology. Furthermore, the inventive polymer composite is very well suited for wire and cable production.

EXAMPLES

Examples 1 - 3 Polymer composites were mixed in a brabender miniature internal mixer in a single mixing step (8min/30°C/80 rpm). Composites can also be prepared by mill mixing. The formulations used in this assessment are based on a recipe according to Table 1. Example 3 is comparative. Table 1. Compounding Recipe. Example 1 Example 2 Comp. 3

ARMEEN 18D 0.5 0.5 0.5

THERBAN XT 8889 100 100 100

CARBON BLACK, N 660 STERLING-V 50 50 50

NAUGARD 445 1 1 1

PLASTHALL TOTM 5 5 5

DIAK #7 1.5

EPON RESIN 828 5 10

STRUKTOL ZP 1014 7

VULCUP 40KE 7

Armeen™ 18D is an octadecylamine available from AkzoNobel and is used to reduce compound stickiness to metal.

THERBAN™ XT™ 8889 is HXNBR from Bayer AG.

Naugard™ 445 (p-dicumyl diphenyl amine) is a stabilizer from Uniroyal.

Plasthall TOTM™ (Trioctyl Trimellitate) is a plasticizer from C.P. Hall.

Diak™ 7 (Triallyl isocyanurate) is a coagent from DuPont. Struktol™ ZP 1014 (zinc peroxide 50% on inert carrier).

Vulcup 40 KE (α, α-bis(t-butylperoxy)diisopropylbenzene), 40% peroxide. The epoxidized molecule used as curing agent is EPON™ 828, a liquid epoxy resin produced from bisphenol-A and epichlorohydrin and is available from Resolution Performance Products. Polymer Composites Properties Table 2 shows a summary of the properties of polymer composites of Exp. 1-3. MDR Cure Properties (180°C, 1° arc, 1.7 Hz, 60 minutes)

Table 2. MDR Cure Properties. Example 1 Example 2 Comp. 3 Maximum Torque (MH, dN.m) 44.19 57.50 35.29 Minimum Torque (ML, dN.m) 1.10 0.83 1.62 Delta MH-ML (dN.m) 43.09 56.67 33.67

The Delta MH-ML gives an indication of the crosslinking density and it increases as a function of epoxy resin content.

Claims

1. A polymer compound comprising at least one carboxylated nitrile polymer, that is optionally hydrogenated, at least one epoxidized compound having at least two epoxide functions and at least one filler.

2. A compound according to claim 1 wherein the carboxylated nitrile polymer is a hydrogenated carboxylated nitrile rubber.

3. A compound according to claim 1 or 2 wherein the compound does not comprise any further cross-linking or curing agent.

4. A compound according to any of claims 1-3 wherein the epoxidized compound is a glycidyl epoxy compound.

5. A compound according to any of claims 1-4 wherein the epoxidized compound is present in an amount of from 0.1 to 20 phr, more preferably in an amount of from 5 to 20 phr.

6. In a method of inducing curing in a compound comprising at least one carboxylated nitrile rubber polymer, that is optionally hydrogenated, by addition of at least one epoxidized compound having at least two epoxide functions and subsequent curing.

7. Use of a polymer compound comprising at least one carboxylated nitrile polymer, that is optionally hydrogenated, at least one epoxidised compound having at least two epoxide functions and at least one filler in the manufacture of a shaped article.

8. Use according to claim 7 in the manufacture of a seal, hose, bearing pad, stator, well head seal, valve plate, cable sheating, wheel roller, pipe seal, belt, in place gaskets or footwear component prepared by injection molding technology, wire and cable production.