Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/37—Thiols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
  • C08K5/3415—Five-membered rings
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/38—Thiocarbonic acids; Derivatives thereof, e.g. xanthates ; i.e. compounds containing -X-C(=X)- groups, X being oxygen or sulfur, at least one X being sulfur

Definitions

• This invention relates to a sulfur-vulcanized rubber composition having improved physical properties. More particularly, it relates to a sulfur-vulcanized rubber composition which is vulcanized in the presence of an anti -reversion coagent and an additive component comprising a thiol and an electron donor group.
• the invention also relates to a sulfur-vulcanization process which is carried out in the presence of an anti -reversion coagent and an additive component comprising a thiol and an electron donor group and the use of an anti-reversion coagent in combination with an additive component comprising a thiol and an electron donor group in the sulfur-vulcanization of rubber.
• the invention also relates to rubber products comprising rubber vulcanized with sulfur in the presence of an anti-reversion coagent and an additive component comprising a thiol and an electron donor group.
• Some articles relating to the sulfur-vulcanization of rubbers disclose the use of bismaleimides as coagents. Such articles include Chavchich, T.A., et al., Kauchuk i Rezina, vol. 4, pp. 20-3, 1981; Krasheninnikov, N.A., et al., Kauchuk i Rezina, vol. 3, pp. 10-12, 1974; Krasheninnikov, N.A., et al., Kauchuk i Rezina, vol. 3, pp. 16-19, 1975; Prashchikina, A.S., et al., Kauchuk i Rezina, No. 10, pp. 15-19, 1985. Even more recently, Japanese patent applications J6 3286-445 and J63312-333 disclosed the vulcanization of rubber with sulfur and an aliphatic bis-maleimide or N,N'-toluene bis-maleimide.
• patent publications which disclose sulfur-vulcanization systems wherein maleimides are used as coagents in combination with other components. Such patent publications include Japanese patent publication J6 1014-238, European patent applications 0 191931, 0345825 and 0410 152.
• the heat resistance is improved by the use of the anti-reversion coagent in combination with the additive components.
• a decrease of loss compliance (J) is established with the compositions of the present invention compared to the control and compositions comprising only anti-reversion coagent. This property leads to tires with a reduced rolling resistance. No detrimental effects on the properties have been established in using the combination of anti-reversion coagent and additive components.
• the present invention relates to a sulfur-vulcanized rubber composition which comprises the vulcanization reaction product of a composition containing at least:
• At least one anti-reversion coagent comprising at least two groups selected from citraconimide and/or itaconimide groups;
• n X is -N(R 4 )(R 5 ) or - (0-R 9 ) n ;
• R 4 , R 5 , R 8 , and R 9 are i ndependently sel ected from hydrogen
• C 1-18 cycl oal kyl groups optionally containi ng one or more hetero atoms; i n additi on R 9 may be -R 6 - (SH) m ; R 5 and R 7 are i ndependently sel ected from C 1-18 al kyl ene groups,
• R 4 and R 5 , R 4 and R 6 , or R 5 and R 6 may combine to form a ring or R 4 , R 5 and R 6 may combine to form a ring, in which case R 4 is nothing and R 5 is double bonded to the nitrogen, this double bond may be part of an aromatic structure; m and n are 1 or 2;
• R 7 and R 8 may combine to form a ring:
• Z 1 and Z 2 are independently selected from oxygen and sulfur; or the additive component is a composition of at least two compounds of which one contains the thiol group and the other the electron donor group, the electron donor group-containing compound being an amine or an ester compound.
• R 4 , R 5 , R 6 , R 7 , R 8 . and R 9 may be substituted by amino, nitroso, sulpho, oxygen, nitrogen, silicon, phosphorus, sulfur, polysulfide, sulphone, sulfoxy and boron, SiO 2 , amido, imino, azo, diazo, hydrazo, azoxy, alkoxy, hydroxy, iodine, fluorine, bromine, chlorine, carbonyl, carboxy, ester, carboxylate, SO 2 , SO 3 , sulphonamido, SiO 3 , nitro, imido, thiocarbonyl, cyano, and epoxy groups.
• the ring which may be formed by R 7 and R 8 may be, for example, lactone, lactam, or thiol actone.
• An example of the additive component being a composition of two compounds is the combination of 2-propanethiol and pi peri dine.
• additive components of formula (I) in accordance with the present invention include, but are not limited to, the following:
• 2-aminothiophenol 2-amino-ethanethiol (cysteamine); 3-amino-propanethiol; 2-amino-propanethiol; 4-amino-butanethiol; 2-amino-butanethiol; 5-amino-pentanethiol; 2-amino-pentanethiol; 6-amino-hexanethiol; 2-amino-hexanethiol; 7-amino-heptanethiol; 2-amino-heptanethiol; 8-amino-octanethiol; 2-amino-octanethiol; 2-amino-nonanethiol; 2-amino-3-phenyl-propanethiol; 2-amino-2-phenyl-ethanethiol; 2-pyridinethiol; 3-pyridinethiol; 4-pyridinethiol; 3-chloro-2-
• (II) in accordance with the present invention i nclude, but are not l imited to, the fol lowing: methyl-3-mercaptopropionate; ethyleneglycol -bi s-mercaptoacetate; dimethyl -mercaptosuccinate; methyl -thioglycolate; ethyl -thioglycolate; octyl -thioglycol ate; ethyl -2-mercaptopropionate; ethyl -thiosali cate; and ethyl -2-mercapto-dithiopropionate.
• Japanese application J63182-355 discloses a sulfur-vulcanized rubber composition comprising bismaleimide and a triazine type compound.
• a sulfur-vulcanized rubber composition comprising bismaleimide and a triazine type compound.
• such a composition exhibits a pronounced reversion effect during vulcanization and, when vulcanized, exhibits several disadvantages regarding certain properties of the composition.
• Thioglycolic acid derivatives are known as accelerators in rubber vul canization from JP 7314 777, J4 8094-743, and EP 0 041 742.
• JP 7314 777, J4 8094-743, and EP 0 041 742 are known as accelerators in rubber vul canization from JP 7314 777, J4 8094-743, and EP 0 041 742.
• a citraconimide- or itaconimide-containing anti-reversion agent nor to any influence which the thioglycolic acid derivatives might have when used in combination with such compounds in the sulfur-vulcanization of rubber.
• the present invention is applicable to all natural and synthetic rubbers.
• rubbers include, but are not limited to, natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, isoprene-isobutylene rubber, brominated isoprene-isobutylene rubber, chlorinated isoprene-isobutylene rubber, ethyl ene-propylene-di ene ter-polymers, as well as combinations of two or more of these rubbers and combinations of one or more of these rubbers with other rubbers and/or thermoplastics.
• sulfur examples include various types of sulfur such as powdered sulfur, precipitated sulfur and insoluble sulfur.
• sulfur donors may be used in place of, or in addition to sulfur in order to provide the required level of sulfur during the vulcanization process.
• sulfur donors include, but are not limited to, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylene thiuram hexasulfide, dipentamethylene thiuram tetrasulfide, dithiodimorpholine, caprolactam disulfide, dialkylthiophosphoryl disulfide, and mixtures thereof.
• references to sulfur shall include sulfur donors and mixtures of sulfur and sulfur donors. Further, references to the quantity of sulfur employed in the vulcanization, when applied to sulfur donors, refer to a quantity of sulfur donor which is required to provide the equivalent amount of sulfur that is specified.
• the anti-reversion coagents of the present invention are characterized by the fact that they must be capable of forming cross-links bonded to the rubber by a carbon-carbon linkage.
• This type of cross-link is known in the rubber literature from, for example, Krasheninnikov, N.A., et al., Kauchuk i Rezina, No. 3, pp. 16-20, 1975.
• Such cross-links bonded to the rubber by a carbon-carbon linkage are highly desirable in rubbers, and particularly sulfur-vulcanized rubbers since such cross-links are thermally stable.
• Anti-reversion coagents of the present invention include, but are not limited to compounds represented by the general formula A:
• D optionally containing one or more heteroatoms selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone, sulphoxy, and sulfur, is a monomeric or oligomeric divalent, trivalent or tetravalent group
• p is an integer selected from 1, 2 or 3
• Q 1 and Q 2 are independently selected from the formulas III and IV: and
• R 1 , R 2 and R 3 are independently selected from hydrogen, C 1 -C 18 alkyl groups, C 3 -C 18 cycloalkyl groups, C 1 -C 18 aryl groups, C 7 -C 30 aralkyl groups and C 7 -C 30 alkaryl groups and R 2 and R 3 may combine to form a ring when R 1 is hydrogen;
• B and B 1 are independently selected from the following hetero atoms: oxygen and sulfur.
• the imides of the present invention are, in general, known compounds and may be prepared by the methods disclosed in, Galanti, A.V. et al., J. Pol. Sc.: Pol. Chem. Ed., Vol. 19, pp. 451-475, (1981); Galanti, A.V. et al., J. Pol. Sc: Pol. Chem. Ed., Vol. 20, pp. 233-239 (1982); and Hartford, S.L. et al., J. Pol. Sc: Pol. Chem. Ed., Vol. 16, pp. 137-153, 1978, the disclosures of which are hereby incorporated by reference.
• the group D mentioned in the formula A can be a monomeric divalent, trivalent or tetravalent linear or branched radical chosen from a C 1 -C 18 alkyl, C 2 -C 18 alkenyl, C 2 -C 18 alkynyl, C 3 -C 18 cycloalkyl, C 3 -C 18 polycycloalkyl, C 6 -C 18 aryl, C 6 -C 30 polyaryl, C 7 -C 30 aralkyl, C 7 -C 30 alkaryl, oligomers of one or more of these radicals, and which radicals may optionally contain one or more of oxygen, nitrogen, silicon, phosphorus, sulfur, polysulfide, sul phone, sulfoxy and boron, all of which radicals may also be optionally substituted at one or more of the atoms in the radical with a substituent selected from oxygen, nitrogen, silicon, SiO 2 , sulfoxy, boron, sulfur, phosphorus,
• imide compounds useful in the present invention include, but are not limited to, the following: bis(2-citraconimidoethyl) sulfide; bis(2-citraconimidoethyl) disulfide; bis(2-citraconimidoethyl) polysulfide; bis(3-citraconimidopropyl) disulfide; bis(4-citraconimido-2-methyl butyl) disulfide; bis(2-citraconimidocyclohexyl) disulfide;
• N,N',N"-(2,4,6-trihexamethylene-isocyanuratetriyl)-tris-citraconic imide TCI-AA33
• N,N'-(3,5-benzoic aciddiyl)-bis-citraconic imide TCI-AA33
• N,N'-(4-(N-methylene-citraconic imide)-octamethylene-bis-citraconic imide TCI-C9v
• N,N'-nonamethylene-bis-citraconic imide TCI-C9v
• N,N'-polytetrahydrofuryl-bis-citraconic imide N,N'-(Jeffamine D230 ® )-bis-citraconic imide
• N,N'-(Jeffamine ED600 ® )-bis-citraconic imide N,N'-polytetrahydrofuryl-bis-citraconic imide
• N,N'-(Jeffamine D230 ® )-bis-citraconic imide N,N'-(Jeffamine D2000 ® )-bis-citraconic imide
• N,N'-(Jeffamine ED600 ® )-bis-citraconic imide N,N'-polytetrahydrofuryl-bis-citraconic imide
• Jef famine D230 ® , Jef famine D2000 ® and Jef famine ED600 ® are registered tradenames of the Texaco company.
• the biscitraconic imides based on these amines have the following general structure:
• Q 1 and Q 2 are as defined above, q represents from 1 up to 1000.
• the bis-, tris- and tetra-itaconimides of the present invention may be the same as mentioned above, except that all citraconimide groups are exchanged for itaconimide groups.
• the same materials as mentioned above may be mixed imides if some of the citraconimide groups are exchanged for itaconimide groups.
• the amount of sulfur to be compounded with the rubber is, based on 100 parts of rubber, usually 0.1 to 25 parts by weight, and more preferably 0.2 to 8 parts by weight.
• the amount of sulfur donor to be compounded with the rubber is an amount sufficient to provide an equivalent amount of sulfur which is the same as if sulfur itself were used.
• the amount of anti-reversion coagent to be compounded with the rubber is, based on 100 parts of rubber, 0.1 to 5 parts by weight, and more preferably 0.2 to 3 parts by weight. These ingredients may be employed as a pre-mix, or added simultaneously or separately, and they may be added together with other rubber compounding ingredients as well.
• the amount of additive component to be compounded with the rubber is, based on 100 parts of rubber, 0.1 to 8 parts. More preferably, 0.2 to 2 parts of additive component per 100 parts of rubber are employed.
• a vulcanization accelerator in the rubber compound.
• Conventional, known vulcanization accelerators may be employed.
• the preferred vulcanization accelerators include mercaptobenzothiazole, 2,2'-mercaptobenzothiazole disulfide, sulfenamide accelerators including N-cyclohexyl-2-benzothiazole sulfenamide, N-tertiary-butyl-2-benzothiazole sulfenamide, N,N'-dicyclohexyl-2-benzothiazole sulfenamide, and
• 2-(morpholinothio)benzothiazole 2-(morpholinothio)benzothiazole; thiophosphoric acid derivative accelerators, thiurams, dithiocarbamates, diphenyl guanidine, diortho- tolyl guanidine, dithiocarbamyl sul fenamides, xanthates, triazine accelerators and mixtures thereof.
• the vulcanization accelerator When the vulcanization accelerator is employed, quantities of from 0.1 to 8 parts by weight, based on 100 parts by weight of rubber composition, are used. More preferably, the vulcanization accelerator comprises 0.3 to 4 parts by weight, based on 100 parts by weight of rubber.
• rubber additives may also be employed in their usual amounts.
• reinforcing agents such as carbon black, silica, clay, whiting and other mineral fillers, as well as mixtures of fillers, may be included in the rubber composition.
• Other additives such as process oils, tackifiers, waxes, antioxidants, antiozonants, pigments, resins, plasticizers, process aids, factice, compounding agents and activators such as stearic acid and zinc oxide may be included in conventional, known amounts.
• process oils such as process oils, tackifiers, waxes, antioxidants, antiozonants, pigments, resins, plasticizers, process aids, factice, compounding agents and activators such as stearic acid and zinc oxide may be included in conventional, known amounts.
• scorch retarders such as phthalic anhydride, pyromellitic anhydride, benzene hexacarboxylic trianhydride, 4-methyl phthalic anhydride, trimellitic anhydride, 4-chlorophthalic anhydride, N-cyclohexyl-thiophthalimide, salicylic acid, benzoic acid, maleic anhydride and N-nitrosodi phenyl ami ne may also be included in the rubber composition in conventional, known amounts.
• steel-cord adhesion promoters such as cobalt salts and dithiosul fates in conventional, known quantities.
• the present invention also relates to a vulcanization process which comprises the step of vulcanizing at least one natural or synthetic rubber in the presence of 0.1 to 25 parts by weight of sulfur or a sulfur donor per 100 parts by weight of rubber, characterized in that said process is carried out in the presence of an effective amount of an anti -reversion coagent and an effective amount of an additive component to improve the effect of the anti-reversion coagent.
• the process is carried out at a temperature of 110-220°C over a period of up to 24 hours. More preferably, the process is carried out at a temperature of 120-190°C over a period of up to 8 hours in the pre sence of 0.1 to 5 parts by weight of anti-reversion coagent and 0.1 to 8 parts by weight of additive component. Even more preferable is the use of 0.2-3 parts by weight of anti-reversion coagent with 0.2-2 parts by weight of additive component. All of the additives mentioned above with respect to the rubber composition may also be present during the vulcanization process of the invention.
• the vulcanization is carried out at a temperature of 120-190°C over a period of up to 8 hours and in the presence of 0.1 to 8 parts by weight, based on 100 parts by weight of rubber, of at least one vulcanization accelerator.
• the anti-reversion coagent is selected from a compound of the formula A.
• the present invention also comprises the use of an anti-reversion coagent in combination with an additive component in a process for the sulfur-vulcanization of rubber.
• the present invention also includes articles of manufacture, such as tires, belts or inner tubes which comprise sulfur-vulcanized rubber which is vulcanized in the presence of the anti -reversion coagents and additive components of the present invention.
• the compositions of the present invention can be used in tire treads for truck tires and off-the-road tires, in particular, for sidewalls, for tire carcasses and for steel-cord skim stocks.
• the rubber compositions of the present invention are particularly useful for conveyor belts and V-belts which are subjected to high loading and abrasion in service.
• the invention is further illustrated by the following examples which are not to be construed as limiting the invention in any way. The scope of the invention is to be determined from the claims appended hereto.
• Base compounds were mixed in a Farrel Bridge BR 1.6 liter Banbury type internal mixer (preheating at 50°C, rotor speed 77 rpm, mixing time 6 min with full cooling).
• Vulcanization ingredients and coagents were addded to the compounds on a Schwabenthan Polymix 150L two-roll mill (friction 1:1.22, temperature 70°C, 3 min).
• delta torque or extent of crosslinking is the maximum torque (MH, also denoted as initial torque maximum, T i ) minus the minimum torque (ML).
• Scorch safety (t s 2) is the time to 2% of delta torque above minimum torque (ML), optimum cure time (tg ⁇ ) is the time to 90% of delta torque above minimum.
• Sheets and test specimens were vulcanized by compression molding in a Fontyne TP-400 press. Tensile measurements were carried out using a Zwick 1445 tensile tester (ISO-3712 dumbbells, tensile properties according to ASTM D 412-87, tear strength according to ASTM D 624-86).
• Hardness was determined according to DIN 53505, and ISO 48 (IRHD).
• Compression set was determined after 72 h at 23°C according to ASTM D 395-89 (ISO R 815) .
• Ageing of test specimens was carried out in a ventilated oven in the presence of air or nitrogen at 100°C for 3 days or at 70°C for 14 days (ISO 188).
• Abrasion was determined using a Zwick abrasion tester as volume loss per 40 m path travelled (DIN 53516).
• Natural rubber was vulcanized using formulations listed in Table 1. Comparative Example A was a control example with no coagent or additive component.
• Table 2 lists the cure characteristics of the compositions A-C, 1, and 2 obtained at 150°C and 170°C. Values in parentheses designate the values obtained for the vulcanizates cured at 170°C. TABLE 2
• Table 3 lists the properties of the vulcanizates cured at 150 °C for t 90 and for 60 min, all properties measured at room temperature. Values in parentheses designate the values obtained for the vulcanizates cured at 150 °C for 60 min.
• Table 4 lists the properties of the vulcanizates cured at 170°C for t 90 and for 30 min, all properties measured at room temperature. Values in parentheses designate the values obtained for the vulcanizates cured at 170 °C for 30 min. TABLE 5
• Table 5 lists the properties of the vulcanizates cured at 170°C for t 90 and for 30 min, all properties measured at 100°C. Values in parentheses designate the values obtained for the vulcanizates cured at 170°C for 30 min.
• Table 6 lists the heat build up and permanent set properties of samples cured at 150°C for t 90 and for 60 min and then aged for 3 days at 100°C. Values in parentheses designate the values obtained for the aged vulcanizates cured at 150°C for 60 min.
• Table 7 lists the heat build up and permanent set properties of samples cured at 170°C for t 90 and for 30 min and then aged for 3 days at 100°C. Values in parentheses designate the values obtained for the aged vulcanizates cured at 170°C for 30 min.
• compositions according to the invention show no marching effect and have constant or even improved basic properties in the ultimate vulcanizates. More particularly compositions A and C show a decrease in modulus during overcure signifying reversion. Composition B has a marching modulus, i.e. an increase in modulus during overcure. However, compositions 1 and 2 show a retention of the modulus during overcure and improvement of the ultimate vulcanizates, as is seen for example in the reduction of the heat building up and permanent set, resulting in an improved heat resistance.
• Increased loss modulus leads to an improvement of tire properties such as wet grip or skid resistance (K.A. Grosch, Nature, 197, 858, 1963).
• Tables 8-11 show the results of the dynamic mechanical analyses of the compositions of the present invention 1 and 2 compared to the comparative compositions A and B.
• Examples 3-6 and Comparative Examples D-E are formulations for truck tire treads.
• the components of each formulation are given in Table 12, the cure characteristics of these formulations are listed in Tables 13-14, the physical and mechanical properties for different curing conditions are given in Tables 15-16, and the dynamic-mechanical data are listed in Tables 17-18.
• the rubber compounding took place in the following order. Natural rubber (NR) and butadiene rubber (BR) were separately mixed with vulcanization ingredients on a W&P GK 5E (volume 5.0 1: 70% load factor; preheating at 50°C, rotor speed 30 rpm, mixing time 6 min. for NR and 8 min. for BR).
• NR Natural rubber
• BR butadiene rubber
• NR and BR were mixed together in a W&P GK 5E (volume 5.0 1: 71.2% load factor; preheating 50°C, rotor speed 30 rpm, mixing time 3 min.). Finally, coagents and additive components were mixed in on a Schwabenthan Polymix 150L two-roll mill (friction 1:1.22, temperature 50-70°C, 10 minutes).
• Table 13 lists the cure characteristics of the compositions D-E and 3-6 obtained at 150° and 170°C. Values in parentheses designate the values obtained for the vulcanizates cured at 170°C.
• Table 14 lists the torque values of the compositions D-E and 3-6 measured at tmax, 12, 36, and 60 minutes cured at 170°C.
• composition D suffers from an initial fall in torque and continues to reverse.
• Composition E shows the beginning of a marching cure.
• the compositions of the present invention show a clear retention of the torque, thus no initial fall in torque and no marching.
• HBU Heat build up
• Permanent set of vulcanizates cured at 170°C for t 90 and for 30 min Values in parentheses designate the properties of the vulcanizates cured at 170°C for 30 min.
• Tables 19-22 show the results of the dynamic mechanical analyses of the compositions of the present invention 3-6 compared to the comparative compositions D and E.
• Example 7 and Comparative Examples F-G are formulations for off-the- road tire treads.
• the components of each formulation are given in Table 23, the cure characteristics of the formulations are listed in Table 24 and the physical and mechanical properties for different curing conditions are given in Tables 25-26.
• Table 24 lists the cure characteristics of the compositions F-G and 7 obtained at 150° and 170°C. Values in parantheses designate the values obtained for the vulcanizates cured at 170°C.

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