Cross-linking agents containing isocyanate groups for nitrile rubbers

Abstract

By the use of special cross-linkers that contain at least two isocyanate groups, hydroxyl group-containing optionally hydrogenated nitrile rubber polymers can be successfully cross-linked. Preferred cross-linkers contain allophanate, biuret, uretdione, uretonimine, bridged carbamate, carbodiimide, isocyanurate, iminooxadiazinedione or oxadiazinetrione structural elements.

Claims

1. Vulcanized molded articles produced by a process comprising cross-linking, with warming, a vulcanizable composition comprising: at least one hydroxyl group-containing (H)NBR rubber having a Mooney viscosity ML(1+4)100 C. of 15 to 160 Mooney units, and containing repeating units derived from at least one conjugated diene, at least one ,-unsaturated nitrile, and at least one copolymerizable hydroxyl group-containing monomer, wherein CC double bonds in the case of the HNBR are completely or partially hydrogenated; at least one compound of the general formula (I) as cross-linkers, ##STR00012## wherein R.sup.1 is O[M].sub.pR.sup.3 or NH[M].sub.pR.sup.3 R.sup.2 is H or R.sup.1 and R.sup.2 together yield a single bond or one of the following groups ##STR00013## R.sup.3, R.sup.4 and R.sup.5 are in each case identical or different and denote H or a radical that contains one or more of the following groups, a saturated, mono- or polyunsaturated carbo- or heterocyclyl radical, straight-chain or branched alkyl, aryl, heteroaryl, arylalkyl, heteroarylalkyl, alkoxy, aryloxy, heteroaryloxy, amino, amido, hydroxyimino, carbamoyl, alkoxycarbonyl, F, Cl, Br, I, hydroxyl, phosphonato, phosphinato, alkylthio, arylthio, thiocarboxy, sulphinyl, sulphono, sulphino, sulpheno, sulphonic acids, sulphamoyl, silyl, silyloxy, nitrile, sulphanyl, hydroperoxycarbonyl, hydroperoxy, thiocarboxy, dithiocarboxy, hydroxyimino, nitro, nitrosyl, carbonyl, carboxy, oxycarbonyl, oxysulphonyl, oxo, thioxo, borate, selenate, epoxy, cyanate, thiocyanate, isocyanate, thioisocyanate or isocyanide, M represents repeating units of one or more mono- or polyunsaturated monomers, selected from the group consisting of conjugated or non-conjugated dienes, alkynes, vinyl compounds, and a divalent structural element, which is derived from polymers selected from the group consisting of polyethers, polyalkylene oxides, polysiloxanes, polyols, polycarbonates, polyurethanes, polyisocyanates, polysaccharides, polyesters and polyamides, and p, q and r are identical or different and are 0 to 10,000; the compounds of the general formula (I) in each case contain at least two isocyanate groups; the composition contains either no solvents at all, or not more than 15% by weight solvents, based on the hydroxyl group-containing (H)NBR rubber, and the composition is not in liquid form; and the composition comprises at least one mold-release agent.

2. The vulcanized molded articles according to claim 1, wherein the compounds of the general formula (I) contain at least one allophanate, biuret, uretdione, uretonimine, bridged carbamate, carbodiimide, isocyanurate, iminooxadiazinedione or oxadiazinetrione structure.

3. The vulcanized molded articles according to claim 1, wherein the at least one compound of the general formula (I) comprises one or more compounds of the general formulae (I-1) to (I-6) as cross-linkers, ##STR00014## where, in the general formulae (I-1) to (I-6), the radicals R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and M and also p, q, r have the same meanings as in claim 1.

4. The vulcanized molded articles according to claim 1, wherein the compound of the general formula (I) is a dimer or trimer of diisocyanates.

5. The vulcanized molded articles according to claim 1, wherein, in the (H)NBR rubber, the copolymerizable hydroxyl group-containing monomer is selected from the group consisting of hydroxyalkyl (meth)acrylates.

6. The vulcanized molded articles according to claim 1, wherein the (H)NBR rubber additionally comprises repeating units of a copolymerizable cross-linking monomer.

7. The vulcanized molded articles according to claim 6, wherein the copolymerizable cross-linking monomer is a triacrylate.

8. The vulcanized molded articles according to claim 1, wherein the composition is free of tin-containing compounds.

9. The vulcanized molded articles according to claim 1, wherein: the composition contains at least 33% by weight of the hydroxyl group-containing (H)NBR rubber, based on the weight of the total composition; the composition contains, based on the hydroxyl group-containing (H)NBR rubber, not more than 10% by weight of solvents during and after the mixing, and the (H)NBR rubber composition is produced by mixing the hydroxyl group-containing (H)NBR rubber with the compound of the general formula (I) in the presence of not more than 10% by weight of solvents, based on the hydroxyl group-containing (H)NBR rubber.

10. The vulcanized molded articles according to claim 1, wherein: the composition contains at least 40% by weight of the hydroxyl group-containing (H)NBR rubber, based on the weight of the total composition, and the Mooney viscosity ML(1+4)100 C. is 25 to 145 Mooney units, and the composition contains, based on the hydroxyl group-containing (H)NBR rubber, not more than 1% by weight of solvents during and after the mixing, and the (H)NBR rubber composition is produced by mixing the hydroxyl group-containing (H)NBR rubber with the compound of the general formula (I) in the presence of not more than 1% by weight of solvents, based on the hydroxyl group-containing (H)NBR rubber.

11. A process for the production of vulcanized molded articles according to claim 1, wherein the process comprises, without predissolving the (H)NBR in a solvent, mixing the (H)NBR rubber and the at least one cross-linker, as is defined in claim 1.

12. The vulcanized molded articles according to claim 1, wherein: the composition, during and after the mixing, contains not more than 5% by weight solvents, based on the hydroxyl group-containing (H)NBR rubber; and the HNBR rubber and crosslinker are mixed in the presence of not more than 5% by weight of solvents, based on the hydroxyl group-containing (H)NBR rubber.

13. The vulcanized molded articles according to claim 1, wherein: the composition, during and after the mixing, contains not more than 1% by weight solvents, based on the hydroxyl group-containing (H)NBR rubber; and the HNBR rubber and crosslinker are mixed in the presence of not more than 1% by weight of solvents, based on the hydroxyl group-containing (H)NBR rubber.

14. The vulcanized molded articles according to claim 1, wherein: the composition contains no solvents at all during and after the mixing; and the HNBR rubber and crosslinker are mixed in the presence of no solvents at all.

Description

EXAMPLES

(1) The nitrogen content for the determination of the acrylonitrile content (ACN content) is determined in the optionally hydrogenated hydroxyl group-containing nitrile rubbers according to the invention according to Kjeldahl in accordance with DIN 53 625. On account of the content of polar comonomers, the nitrile rubbers are customarily soluble to >85% by weight in methyl ethyl ketone at 20 C.

(2) The determination of the glass transition temperature, and its onset and offset points is carried out by means of dynamic differential calorimetry (Differential Scanning CalorimetryDSC) according to ASTM E 1356-03 or according to DIN 11357-2.

(3) The determination of the microstructure and the termonomer content of the individual polymers was carried out by means of .sup.1H NMR (apparatus: Bruker DPX400 with XWIN-NMR 3.1 software, measuring frequency 400 MHz, solvent CDCl.sub.3).

(4) The determination of the values for the Mooney viscosity (ML 1+4@ 100 C.) is in each case carried out by means of a shearing disc viscometer according to DIN 53523/3 or ASTM D 1646 at 100 C.

(5) The determination of the MSR (Mooney Stress Relaxation) is in each case carried out by means of a shearing disc viscometer according to ISO 289-4:2003(E) at 100 C.

(6) The course of vulcanization in the MDR and its analytical data were measured on a Monsanto rheometer MDR 2000 according to ASTM D5289-95.

(7) The compression set (CS) at the specified temperature was measured according to DIN 53517.

(8) The hardness according to Shore A was measured according to ASTM-D2240-81.

(9) The tensile tests for the determination of the tension as a function of the deformation were carried out according to DIN 53504 or ASTM D412-80.

(10) The abbreviations indicated in the following tables have the following meanings: RT Room temperature (232 C.) TS Tensile strength, measured at RT EB Elongation at break, measured at RT M50 Modulus at 50% extension, measured at RT M100 Modulus at 100% extension, measured at RT M300 Modulus at 300% extension, measured at RT S min is the minimum moment of rotation of the cross-linkage isotherm S max is the maximum moment of rotation of the cross-linkage isotherm Delta S is equal to S maxS min t.sub.10 is the time when 10% of S max is achieved t.sub.50 is the time when 50% of S max is achieved t.sub.90 is the time when 90% of S max is achieved t.sub.95 is the time when 95% of S max is achieved TS2 denotes the time until the Mooney viscosity has increased by two units in comparison to the starting point
The Following Substances were Employed in the Examples:

(11) The following chemicals were obtained as commercial products of the firms indicated in each case or originate from production plants of the firms indicated. Addolink TT dimeric tolylene diisocyanate with uretdione structure (commercial product of Rheinchemie Rheinau GmbH) Corax N550/30 carbon black (commercial product of Evonik Degussa) Desmodu N3300 trimeric hexamethylene diisocyanate with cyanurate structures (commercial product of Bayer Material Science AG) Diplast TM 8-10/ST trioctyl mellitate (commercial product of Lonza SpA) TAIC 70 triallyl isocyanurate (commercial product of Kettlitz Chemie GmbH & Co.) Luvomaxx CDPA p-dicumyldiphenylamine (commercial product of Lehmann & Voss) Maglite DE magnesium oxide (commercial product of HallStar Company) Winstay 29/Naugawhite mixture: mixture of 25 g of Sorbilene Mix (mixture of sorbitan esters and ethoxylated sorbitan esters) from Lamberti, 38 g of Naughawhite (2,2-methylenebis(6-nonyl-p-cresol)) from Chemtura, 125 g of Wingstay 29 (styrenized diphenylamine) from the company Eliokem and 63 g of water PERKADOX 14-40 di(tert-butylperoxyisopropyl)benzene supported on silica& whiting (40% active ingredient) (commercial product of Akzo Nobel Chemicals GmbH) Premix solution Fe(II)SO.sub.4 contains 0.986 g of Fe(II)SO.sub.4.7 H.sub.2O and 2.0 g of RongalitC in 400 g of water Rongalit C sodium salt of a sulphinic acid derivative (commercial product of BASF SE) t-DDM: tertiary dodecylmercaptan; LANXESS Deutschland GmbH Texapon K-12: sodium laurylsulphate (commercial product of Cognis GmbH) Trigonox NT 50 p-menthane hydroperoxide (commercial product of Akzo-Degussa) Vulcanox ZMB2/C5: zinc salt of 4- and 5-methyl-2-mercaptobenzimidazole (commercial product of LANXESS Deutschland GmbH)
I Production of the Nitrile Rubbers A, B, C (Examples According to the Invention)

(12) The production of the nitrile rubbers A, B, C employed in the following example series was carried out according to the basic recipe indicated in Table 1, where all materials used are indicated in parts by weight based on 100 parts by weight of the monomer mixture. Table 1 also mentions the respective polymerization conditions.

(13) TABLE-US-00001 TABLE 1 Nitrile rubber A B C Butadiene 59.0 56.5 56.1 Acrylonitrile 36.0 36.0 35.5 2-Hydroxethyl methacrylate (HEMA) 5 7.5 2-Hydroxethyl acrylate (HEA) 8.4 Total amount of water 220 220 220 Texapon K-12 3.0 3.0 3.0 Na.sub.2SO.sub.4 0.12 0.12 0.12 pH 7 7 7 t-DDM 0.54 0.52 0.56 Trigonox NT 50 0.02 0.02 0.02 Premix solution FeSO.sub.4 0.03 0.03 0.07 Diethylhydroxylamine 0.2 0.2 0.2 Mixture Winstay 29/Naugawhite 0.18 0.18 0.18 Polymerization temperature [ C.] 8.0 0.5 8.0 0.5 8.0 0.5 Polymerization conversion [%] 85 84 83 Polymerization time [h] 6.0 5.5 10.0

(14) The production of the nitrile rubbers was carried out batchwise in a 5 l autoclave having a stirrer. In each case 1.25 kg of the monomer mixture and a total amount of water of 2.1 kg and EDTA in an equimolar amount based on the Fe-II were used in the autoclave batches. Of this amount of water, 1.9 kg were initially introduced into the autoclave with the emulsifier and flushed with a stream of nitrogen. The destabilized monomers and the amount of the molecular weight regulator t-DDM indicated in Table 1 were then added, and the reactor was closed. After thermostatting the reactor contents, the polymerizations were started by the addition of the premix solutions and of para-menthane hydroperoxide (TrigonoxNT50).

(15) The course of the polymerization was monitored by gravimetric conversion determinations. On achieving the conversions indicated in Table 1, the polymerization was halted by addition of an aqueous solution of diethylhydroxylamine. Unreacted monomers and other volatile constituents were removed by means of steam distillation.

(16) The dried NBR rubbers were characterized by the Mooney viscosity, their MSR, the ACN content and the glass transition temperature and the content of the hydroxyl group-containing termonomer was determined by .sup.1H-NMR analysis (Table 2).

(17) TABLE-US-00002 TABLE 2 Nitrile rubbers A, B, C; properties Nitrile rubber A B C ACN content (%) 34.1 34.1 35.3 Mooney viscosity ML(1 + 4 at 100 C.) (Mu) 27 30 28 MSR (Mu/s) 0.653 0.626 0.591 Termonomer HEMA HEMA HEA Incorporation of Terrnonomer (% by weight) 2.9 4.8 2.0 Glass transition temperature T.sub.g ( C.) 21.6 20.3 23.4
II Production of Vulcanizates V1 to V9 of the Nitrile Rubbers A, B, C (Examples According to the Invention)

(18) The vulcanizates V1 to V9 were prepared from the nitrile rubbers A, B and C as described below. The constituents of the mixtures are related to 100 parts of nitrile rubber and indicated in the Tables 3, 7 and 11.

(19) The mixtures were prepared in a Banbury mixer. For this, the rubber and all additives mentioned in Table 3, 7 or 11 were mixed for a total of 4 minutes at a maximum temperature of up to 120 C. The rubber was introduced into the mixer for this, after 1 minute all other additives were added and after a further 2 minutes a reverse direction step was carried out. After a total of 4 minutes, the rubber was discharged from the mixer. The compound was vulcanized at a temperature of 170 C. for 30 min.

(20) TABLE-US-00003 TABLE 3 Vulcanizates V1-V3; composition Mixture V1 V2 V3 Polymer A 100 Polymer B 100 Polymer C 100 LUVOMAXX CDPA 1 1 1 VULKANOX ZMB2/C5 0.4 0.4 0.4 MAGLITE DE 2 2 2 CORAX N 550/30 50 50 50 DIPLAST TM 8-10/ST 5 5 5 ADDOLINK TT 8 8 8 Total phr 166.4 166.4 166.4 Density g/ccm 1.162 1.162 1.162

(21) The vulcanizates obtained had the properties indicated in Tables 4 to 6:

(22) TABLE-US-00004 TABLE 4 Vulcanizates V1-V3; vulcanization course in the MDR (170 C./30 min) Mixture V1 V2 V3 S max (dNm) 30.5 41.9 23.5 t.sub.10 (min) 1.0 1.0 1.0 t.sub.95 (min) 11.7 14.2 13.5

(23) The level of the respective maximum torque is according to the proportions of hydroxyl-containing monomers in the polymers A-C. All cross-linkage were carried out without the addition of heavy metal compounds as catalyst, such as, for example, organic tin compounds.

(24) TABLE-US-00005 TABLE 5 Vulcanizates V1-V3; vulcanizate properties Mixture V1 V2 V3 Cross-linkage temperature C. 170 Cross-linkage time min 12 13 13 TS MPa 24.7 23 14.5 EB % 259 171 144 M50 MPa 3.3 4.4 3.4 M100 MPa 8.5 12 9 M300 MPa Hardness Shore A 74 78 75

(25) The polymers according to the invention are distinguished in their vulcanizates by a high tensile strength and very high modulus values at 100% extension.

(26) TABLE-US-00006 TABLE 6 Vulcanizates V1-V3; compression set measured at RT and 100 C. Mixture V1 V2 V3 Temperature and time: RT and 24 hours CS % 4 3 6 Temperature and time: 100 C. and 24 hours CS % 30 160 32

(27) As a result of the relationship between cross-linker and hydroxyl-containing termonomer, elongation at break and maximum torque in the vulcanizate can be adjusted without problem with a simultaneously good compression set.

(28) TABLE-US-00007 TABLE 7 Vulcanizates V4-V7; composition Mixture V4 V5 V6 V7 Polymer A 100 100 Polymer B 100 100 LUVOMAXX CDPA 1 1 1 1 VULKANOX ZMB2/C5 0.4 0.4 0.4 0.4 MAGLITE DE 2 2 2 2 CORAX N 550/30 50 50 50 50 DIPLAST TM 8-10/ST 5 5 5 5 ADDOLINK TT 4 6 4 6 Total phr 162.4 164.4 162.4 164.4 Density g/ccm 1.156 1.159 1.156 1.159

(29) The vulcanizates obtained had the properties indicated in the Tables 8 to 10:

(30) TABLE-US-00008 TABLE 8 Vulcanizates V4-V7M; vulcanization course in the MDR (170 C./30 min) Mixture V4 V5 V6 V7 S max (dNm) 17.6 29.4 21.5 32.8 t.sub.10 (min) 1.2 1.2 1.1 1.0 t.sub.95 (min) 14.1 17.9 12.6 12.3

(31) The level of the respective maximum torque is according to the proportion of the hydroxyl-containing monomer in the polymers to the ratio of the dimeric diisocyanate. All cross-linkages were carried out without the addition of heavy metal compounds as catalyst, such as, for example, organic tin compounds.

(32) TABLE-US-00009 TABLE 9 Vulcanizates V4-V7; properties Mixture V4 V5 V6 V7 Cross-linkage temperature C. 170 Cross-linkage time min 20 20 20 20 TS MPa 20.5 19.8 20 19.5 EB % 417 271 336 220 M50 MPa 2.8 4 3.3 4.6 M100 MPa 5.3 7.9 6.4 9.5 M300 MPa 15.8 21.3 18.4 Hardness Shore A 71 75 72 78

(33) The polymers according to the invention lead to vulcanizates having high tensile strength and very high modulus values at 100% extension relative to elongation at break.

(34) TABLE-US-00010 TABLE 10 Vulcanizates V4-V7; compressive deformation at RT and 100 C. Mixture V4 V5 V6 V7 Temperature and time: RT and 24 hours CS % 9 6 6 5 Temperature and time: 100 C. and 24 hours CS % 20 23 15 15

(35) In addition to cross-linkages by means of dimeric diisocyanates with uretdione structure, cross-linkages were also carried out with trimeric hexamethylene diisocyanates having cyanurate structures.

(36) TABLE-US-00011 TABLE 11 Vulcanizates V8-V9; composition Mixture V8 V9 Polymer B 100 100 LUVOMAXX CDPA 1 1 VULKANOX ZMB2/C5 0.4 0.4 MAGLITE DE 2 2 CORAX N 550/30 50 50 DIPLAST TM 8-10/ST 5 5 Desmodur N3300 4 6 Total phr 162.4 164.4 Density g/ccm 1.15 1.15

(37) The vulcanizates obtained had the properties indicated in Tables 12 to 14:

(38) TABLE-US-00012 TABLE 12 Vulcanizates V8 and V9; Vulcanization course in the MDR (170 C./40 min) Mixture V8 V9 S max (dNm) 15.6 23.3 t.sub.10 (min) 0.5 0.5 t.sub.95 (min) 6.2 6.9

(39) The level of the respective maximum torque is according to the proportions of a cross-linker. All cross-linkages were carried out without the addition of heavy metals as a catalyst, such as, for example, organic tin compounds.

(40) TABLE-US-00013 TABLE 13 Vulcanizates V8 and V9; properties Mixture V8 V9 Cross-linkage temperature C. 170 Cross-linkage time min 8 9 TS MPa 16.3 17.5 EB % 359 238 M50 MPa 2.1 3.1 M100 MPa 4.6 7.7 M300 MPa 14.4 Hardness Shore A 74 69

(41) TABLE-US-00014 TABLE 14 Vulcanizates V8 and V9; compression set at RT, 100 C., 150 C. Mixture V8 V9 Temperature and time: RT and 24 hours CS % 10 6 Temperature and time: 100 C. and 24 hours CS % 17 15 Temperature and time: 150 C. and 24 hours CS % 57 49

(42) The vulcanizates are distinguished by a very low compression set even at unusually high temperatures of 150 C. for NBR.

(43) III Production of Hydrogenated Nitrile Rubbers HNBR 1 and HNBR 2 by Hydrogenation

(44) The nitrile rubber NBR used as a starting material for the hydrogenation contained repeating units of acrylonitrile, butadiene and with (NBR 1) or without (NBR 2; comparison experiment) a hydroxyl group-containing monomer in the amounts indicated in Table 15 below. It had a Mooney viscosity as indicated in Table 15.

(45) TABLE-US-00015 TABLE 15 NBR 1 employed for the hydrogenation (according to the invention) and NBR 2 (comparison) Butadiene Mooney content Termonomer ACN viscosity [% by content content (ML 1 + 4 NBR weight] Termonomer [% by wt] [% by wt] at 100 C.) NBR 58.3 Hydroxy- 5.3 36.4 34 1 ethylene glycol methacrylate NBR 65.5 0 34.5 27.4 2

(46) A solution of the NBR 1 or NBR 2 having a solids content of 12% in monochlorobenzene (MCB) as a solvent was introduced into a high-pressure reactor and heated to 138 C. with stirring at 600 rpm. After adjusting a stable temperature, a solution of 0.06 phr of Wilkinson catalyst and 1.0 phr of triphenylphosphine (TPP) in MCB was introduced as co-catalyst and hydrogen was introduced into the reactor up to a pressure of 85 bar. The reaction mixture was stirred for 4 hours, whereupon the hydrogen pressure was let off and the reactor was cooled to approximately 22 C. The polymer solution was then discharged from the reactor and coagulated according to known processes using steam. The isolated polymer was subsequently dried.

(47) IV Production of the Vulcanizable Compositions

(48) The components of the vulcanizable composition indicated in Table 16 were mixed in a Banbury mixer by conventional mixing as already described above. The polymer composition was then vulcanized at 180 C. for 20 minutes and temperature-controlled at 175 C. for 4 hours.

(49) The properties of the HNBR vulcanizates, as are reproduced in Tables 17 and 18 and shown in FIG. 1, show the superiority with regard to the cross-linkage density, an increased modulus 100 and the increased tensile strength of HNBR 1 in comparison to HNBR 2. This leads to significant practical advantages in different dynamic applications, such as conveyor belt and sealing applications, where increased dynamic properties of the vulcanizates are demanded.

(50) TABLE-US-00016 TABLE 16 Formulation of the vulcanizable compositions, Examples Q1-2 Example Q1 Q2 Rubber component Parts Parts HNBR 1 100 HNBR 2 100 Other components phr* phr* CORAX N550 50 50 MAGLITE DE 2 2 VULKANOX ZMB2/C5 0.4 0.4 DIPLAST TM 8-10/ST 5 5 LUVOMAXX CDPA 1 1 ADDOLINK TT 8 TAIC 70 2.1 PERKADOX 14-40 7 In Table 16, the amounts of all other components are specified in phr, i.e. parts by weight per 100 parts of rubber component.

(51) TABLE-US-00017 TABLE 17 HNBR vulcanizates Q1 and Q2; physical properties Example Q1 Q2 Hardness ShA [Shore A] 77 68 M10 MPa 0.9 0.6 M25 MPa 1.8 1.1 M50 MPa 3.8 1.9 M100 MPa 12.1 5.0 EB % 199 236 TS MPa 27.6 21.4

(52) TABLE-US-00018 TABLE 18 HNBR vulcanizates Q1 and Q2; MDR values at 180 C. MDR 180 C. Q1 Q2 S min [dNm] 5.05 1.49 S max [dNm] 25.69 23.08 Delta S dNm 20.64 21.59 TS2 s 57.6 36 t50 s 160.35 118.13 t90 s 393.36 329.43 t95 s 494.28 424.22

(53) FIG. 1 shows the MDR at 180 C. for the HNBR vulcanizates of Examples Q1 and Q2. HNBR 1 is the curve running at the top in FIG. 1, the curve of HNBR 2 runs below.