CA1168396A - Sealant composition - Google Patents
Sealant compositionInfo
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- CA1168396A CA1168396A CA000358251A CA358251A CA1168396A CA 1168396 A CA1168396 A CA 1168396A CA 000358251 A CA000358251 A CA 000358251A CA 358251 A CA358251 A CA 358251A CA 1168396 A CA1168396 A CA 1168396A
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- butyl rubber
- sealant
- cross
- tire
- composition
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Abstract
SEALANT COMPOSITION
Abstract of the Disclosure A sealant composition particularly suitable for vehicle tires comprising a cured butyl rubber present only in the form of a copolymer having a molecular weight in excess of 100,000 and one or more tackifiers, the tensile strength, elon-gation and cross-link density of the composition being adjusted to produce the necessary properties for tire sealants.
Abstract of the Disclosure A sealant composition particularly suitable for vehicle tires comprising a cured butyl rubber present only in the form of a copolymer having a molecular weight in excess of 100,000 and one or more tackifiers, the tensile strength, elon-gation and cross-link density of the composition being adjusted to produce the necessary properties for tire sealants.
Description
Field of the Invention The sealant com~osi-tion oE this invention was developed as a self-healing tire puncture sealant. As a tire sealan-t, it is adapted for application to the in-ternal surface of a rubber tire and is intended to seal puncture holes in the tread reyion under widely varyiny -temperature condi-tions. Being suitable as a tire sealant, the sealan-t composition of this invention is applicable to other, similar as well as less severe uses.
Background of the Invention To be sui-table for sealing tire punctures, a sealant composition rnust meet a unique and exceptionally demandiny set of physical and chemical criteria. It must be resistant to aging, decor~position and flow at the high temperatures to which tires are heated under summertime driving conditions. In the case where the puncturing object remains in the -tread while the tire continues to be used, the sealant must have sufficient tack and fatigue resistance to remain adhered to the object even as it works back and forth during tire revolution. In the case where the puncturing object is removed from the tread, the sealant must be capable of flowing- into the puncture hole at wintertime temperatures and sealing it. Further properties required of a tire sealant are discussed in greater detail below.
Because butyl rubber has low air permeability, high resistance to aging and an easily con-trolled cross-linked density, the prior art has attempted to utilize bu-tyl rubber as a basic compound of tire sealan-ts. One a;oproach, exemplified by U.S. Patents 2,756,801, 2,765,018 and 2,782,829, has been to util:ize a single grade of butyl rubber to form the sealant network, and to add tackifiers, plasticizers and o-ther more specialized ingredients such as phenols or iron oxide in an a-ttempt to achieve the necessary balance o' physical ~ r :
propertles. Compositions based on such paten-ts, however, have not achieved widespread acceptance, primarily because such sealants have failed to perform satisfac-torily at the temperature extremes (e.g. -20F to 220F) -to which -tires are subjected.
A second approach -to butyl rubber based tire sealants has utilized a combination of hiyh and low molecular weigh-t butyl rubber grades cross-linked toge-ther -to form a single elastomeric network. Such sealants have been found to perform quite well over wide temperature ranges. ~lowever low molecular weight butyl rubber is less readily available commercially than the high weight variety, and sealants based in part on low molecular weight butyl are therefore less attractive.
One of the main difficulties in developing an accept-able tire sealant composition is that a single physical property of such a composition can depend on a great variety of chemical variables. Thus in a sealant composition generally comprising a cured, reinforced butyl rubber and a tackifier, a single property such as -tensile strength will depend on the fraction of butyl rubber present, the molecular weight and mole percent unsaturation of the butyl rubber, the amount of cross-linking agent used, the amount of reinforcing agent used, and to a cer-tain extent on the tackifiers and on the curing and ap;olication techniques employed. Under these circums-tances, it is dif-ficult to specify unique ranges for individual chemical variables, since the overall physical properties of interest depend on the combined effect of many variables. For example it has been found that compositions in which the fraction of butyl rubber present lies within a certain range may be formulated having desirable tensile properties. Yet it may well be possible to reproduce such properties outside such range by adjusting the amount of cross-linking agent used and other variables.
_;~_ ~ .
Summary o~ the_Invention Applicants have discovered tha-t sunerior sealant compositions can be formula-ted by adjusting the composi-tions so that three key properties are controlled. These three proper-ties are tensile strength, elongation and cross-link density. Tensile strength reEers to the maximum stress (force per unit area) tha-t a specimen of sealant material can wi-th stand before rupturlng. Elonyation measures the rela-tive increase in lenyth of a specimen oE ma-terial at the point of rupture. Cross-link density is a molecular property which measures the concentration of cross-links present in that par-t of the sealant which has been cured into a -three dimensional cross-linked network. It is most conveniently measùred by a swell test which determines the amount of solvent that the three dimensional network present in a given specimen of sealan-t will absorb.
These three properties -- tensile s-trength, elongation and cross-link density -- are important because of their relation-ship to the properties that a tire sealant must have in order to perform properly. If the tensile strength of a sealant is too low, the sealant will flow under typical tire operating conditions and will also "blow through" a puncture hole when a puncturing object is removed from -the tire and fail to seal the hole. An acceptable sealant must therefore be formulated with sufficient tensile strength to withstand such a "blow through".
If the elonga-tion of a sealant is too low7, it will have several defects. When an object such as a nail enters a tire whose interior is coated with a sealant composition, the sealant should preferably adhere to the nail and form a tent-like structure surrounding it. ~dhesion of the sealant to -the nail at this time will assist in preserving an air barrier at the puncture and will also result in the sealant being drawn --3~
:
by the nail into -the punc-tuxe hole as the nail is removed. If the sealant has insufficient elongation, it will be unable to stretch enough to form a ten-t. The sealan-t may -then "cap'l the nail, i.e., a sma].l portion of sealan-t surrounding -the tip of the nail will break away from the remainder of the sealant and remain adhered to the nail near its tip. Capping generally results in poor nail-in sealing performance. ~ fur-ther resul.-t of low elongation will be that in the case of a large puncture, not enough sealant will be able -to flow over and into the hole to effect a seal when the punc-turing object is removed.
The cross-link density of a polymeric sealant deter-mines how strongly the sealant will resist permanent deformation.
If the sealant has too high a cross-link density, it will be too resistant to permanent deformation, and the sealant will cap a puncturing object rather than form a tent, with the results described above. If the cross-link density is too low, centrifugal force will cause the sealant to creep or flow at elevated temperatures, resulting in insufficnet sealant under-lying the shoulder portion of the tire. Too low a cross-link density will also result in a low fatigue resistance :Eor the sealant composition. Fatigue resistance is an important re-quirement for an effective tire sealant, most particularly in the situation where an object such as a nail enters a tire, and the tire is then used for a considerable time without the nail being removed. In a typical case, of course, a motorist will not even be aware of the nail's presence. Periodic contact between the punctured portion of the tire and the road will result in the nail flexing back and forth as the tire rotates.
~ssuming that the sealant has formed a -tent over the nail, the sealant forming the tent will be continually stretched and relaxed, a process which over time will break cross-links and make the sealant susceptible to flowing away from the nai]., . thus destroying the air seal.
~ D
Sealants according to -the present inverl-tion comprise cured butyl rubbers present only in the form of a copolymer having a viscosity averaye molecular weight yreater than 100,000, in combination with appropriate tackifiers, in which the -tens:ile strength, elongation and cross-lin]c densi-ty of -the composi-tion have been adjusted to produce the required sealant charac-teristics as described above. In general, -tensile s-trenyth, elongation and cross-link density rnay mos-t readily be controlled by adjusting the fraction of butyl rubber in -the total composition, the amount of cross lin]cing agent used, the amount oE reinforcer used, the molecular weight and degree oE mole unsaturation of the butyl rubber, and to a lesser ex-tent -the tackifiers and processing methods used. It has been found that preferred sealants for vehicle tires are those in which -the tensile s-trength is in excess of 30 psi, the elongation is in excess of 600~o ~ and the swell ratio in -toluene lies between 12 and 40.
Furthermore, sealants having elongations in excess of 300O and swell ratios in the range of 12-35 have been found to be particularly suitable as vehicle -tire sealants and are especially preferred. Such sealants may be formulated by adjus-ting the butyl rubber to comprise about 13-40% by weight of the total composition excluding the cross~linking agents, by using a butyl rubber having a mole percent unsaturation between about 0.5 and 2.5 and a molecular weight of about 100,000 - 450,000, and by using between about 0.5 - 6 phr of a quinoid cross-linking agent and at least about 2 phr of carbon black. Such sealants having 13 - 20P~, butyl rubber, 30 - 60 phr carbon black and 2 - 6 phr of a quinoid cross-linking agent are especially preferred because they are readily formulated having properties in the above ranges and because they possess significant processing advantages as described below. Sealants having tensile strengths, elongations, and swell ratios in the ranges set forth above may also be formulated by adjusting -the butyl rubber -to comprise about 13 - 50Po by weigh-t of the -total :
composition less the cross-linking agents, by using a bu-tyl rubber having a mole % unsa-turation between abou-t 0.5 - 2.5 and a molecular weight of about 100,000 - 450,000, and by using between abou-t 5 - 25 phr of a bromomethylated phenolic resin curing agent and at least 3 phr of zinc oxide.
Brief Desc ption of the D a _ ~
Fig. 1 is a perspec-tive view oE a cross-section of a vehicle -tire illus-trating one embodiment of the invention in which the sealant composition layer is loca-ted on -the innerrnost surface of the tire behind the tread;
Fig. 2 is a perspective view similar to Fig. 1, illus-tra-ting a second embodimen-t of the invention in which the subjec-t sealant layer is located behind the tread portion of the vehicle tire and between an air impervious film conventionally eMployed in a tubeless tire and the carcass portion of the tire.
Detailed Description of the Inventlon The copolymer netwoxk which provides the strength and continuity of the sealant compositions of the present invention is comprised of cured butyl rubber. Butyl rubber is intended to include copolymers of 96 - 99.5 wt.% isobutylene and 4 - 0.5 wt.% isoprene (Butyl IIR) as well as other rubbery copolymers of a major proportion (i.e., over 50% by weight) of an isoolefin having from 4 to 7 carbon a-toms with a minor proportion by weight of an open chain conjugated diolefin having from 4 to 8 carbon atoms. The copolymer may consist of from 70 to 99.5~ by weight of an isomonoolerin such as isobutylene or ethyl methyl ethylene copolymerized with from 0.5 to 30% by weight of an open chain conjugated diolefin such as isoprene; butadiene -1,3; piperylene;
Background of the Invention To be sui-table for sealing tire punctures, a sealant composition rnust meet a unique and exceptionally demandiny set of physical and chemical criteria. It must be resistant to aging, decor~position and flow at the high temperatures to which tires are heated under summertime driving conditions. In the case where the puncturing object remains in the -tread while the tire continues to be used, the sealant must have sufficient tack and fatigue resistance to remain adhered to the object even as it works back and forth during tire revolution. In the case where the puncturing object is removed from the tread, the sealant must be capable of flowing- into the puncture hole at wintertime temperatures and sealing it. Further properties required of a tire sealant are discussed in greater detail below.
Because butyl rubber has low air permeability, high resistance to aging and an easily con-trolled cross-linked density, the prior art has attempted to utilize bu-tyl rubber as a basic compound of tire sealan-ts. One a;oproach, exemplified by U.S. Patents 2,756,801, 2,765,018 and 2,782,829, has been to util:ize a single grade of butyl rubber to form the sealant network, and to add tackifiers, plasticizers and o-ther more specialized ingredients such as phenols or iron oxide in an a-ttempt to achieve the necessary balance o' physical ~ r :
propertles. Compositions based on such paten-ts, however, have not achieved widespread acceptance, primarily because such sealants have failed to perform satisfac-torily at the temperature extremes (e.g. -20F to 220F) -to which -tires are subjected.
A second approach -to butyl rubber based tire sealants has utilized a combination of hiyh and low molecular weigh-t butyl rubber grades cross-linked toge-ther -to form a single elastomeric network. Such sealants have been found to perform quite well over wide temperature ranges. ~lowever low molecular weight butyl rubber is less readily available commercially than the high weight variety, and sealants based in part on low molecular weight butyl are therefore less attractive.
One of the main difficulties in developing an accept-able tire sealant composition is that a single physical property of such a composition can depend on a great variety of chemical variables. Thus in a sealant composition generally comprising a cured, reinforced butyl rubber and a tackifier, a single property such as -tensile strength will depend on the fraction of butyl rubber present, the molecular weight and mole percent unsaturation of the butyl rubber, the amount of cross-linking agent used, the amount of reinforcing agent used, and to a cer-tain extent on the tackifiers and on the curing and ap;olication techniques employed. Under these circums-tances, it is dif-ficult to specify unique ranges for individual chemical variables, since the overall physical properties of interest depend on the combined effect of many variables. For example it has been found that compositions in which the fraction of butyl rubber present lies within a certain range may be formulated having desirable tensile properties. Yet it may well be possible to reproduce such properties outside such range by adjusting the amount of cross-linking agent used and other variables.
_;~_ ~ .
Summary o~ the_Invention Applicants have discovered tha-t sunerior sealant compositions can be formula-ted by adjusting the composi-tions so that three key properties are controlled. These three proper-ties are tensile strength, elongation and cross-link density. Tensile strength reEers to the maximum stress (force per unit area) tha-t a specimen of sealant material can wi-th stand before rupturlng. Elonyation measures the rela-tive increase in lenyth of a specimen oE ma-terial at the point of rupture. Cross-link density is a molecular property which measures the concentration of cross-links present in that par-t of the sealant which has been cured into a -three dimensional cross-linked network. It is most conveniently measùred by a swell test which determines the amount of solvent that the three dimensional network present in a given specimen of sealan-t will absorb.
These three properties -- tensile s-trength, elongation and cross-link density -- are important because of their relation-ship to the properties that a tire sealant must have in order to perform properly. If the tensile strength of a sealant is too low, the sealant will flow under typical tire operating conditions and will also "blow through" a puncture hole when a puncturing object is removed from -the tire and fail to seal the hole. An acceptable sealant must therefore be formulated with sufficient tensile strength to withstand such a "blow through".
If the elonga-tion of a sealant is too low7, it will have several defects. When an object such as a nail enters a tire whose interior is coated with a sealant composition, the sealant should preferably adhere to the nail and form a tent-like structure surrounding it. ~dhesion of the sealant to -the nail at this time will assist in preserving an air barrier at the puncture and will also result in the sealant being drawn --3~
:
by the nail into -the punc-tuxe hole as the nail is removed. If the sealant has insufficient elongation, it will be unable to stretch enough to form a ten-t. The sealan-t may -then "cap'l the nail, i.e., a sma].l portion of sealan-t surrounding -the tip of the nail will break away from the remainder of the sealant and remain adhered to the nail near its tip. Capping generally results in poor nail-in sealing performance. ~ fur-ther resul.-t of low elongation will be that in the case of a large puncture, not enough sealant will be able -to flow over and into the hole to effect a seal when the punc-turing object is removed.
The cross-link density of a polymeric sealant deter-mines how strongly the sealant will resist permanent deformation.
If the sealant has too high a cross-link density, it will be too resistant to permanent deformation, and the sealant will cap a puncturing object rather than form a tent, with the results described above. If the cross-link density is too low, centrifugal force will cause the sealant to creep or flow at elevated temperatures, resulting in insufficnet sealant under-lying the shoulder portion of the tire. Too low a cross-link density will also result in a low fatigue resistance :Eor the sealant composition. Fatigue resistance is an important re-quirement for an effective tire sealant, most particularly in the situation where an object such as a nail enters a tire, and the tire is then used for a considerable time without the nail being removed. In a typical case, of course, a motorist will not even be aware of the nail's presence. Periodic contact between the punctured portion of the tire and the road will result in the nail flexing back and forth as the tire rotates.
~ssuming that the sealant has formed a -tent over the nail, the sealant forming the tent will be continually stretched and relaxed, a process which over time will break cross-links and make the sealant susceptible to flowing away from the nai]., . thus destroying the air seal.
~ D
Sealants according to -the present inverl-tion comprise cured butyl rubbers present only in the form of a copolymer having a viscosity averaye molecular weight yreater than 100,000, in combination with appropriate tackifiers, in which the -tens:ile strength, elongation and cross-lin]c densi-ty of -the composi-tion have been adjusted to produce the required sealant charac-teristics as described above. In general, -tensile s-trenyth, elongation and cross-link density rnay mos-t readily be controlled by adjusting the fraction of butyl rubber in -the total composition, the amount of cross lin]cing agent used, the amount oE reinforcer used, the molecular weight and degree oE mole unsaturation of the butyl rubber, and to a lesser ex-tent -the tackifiers and processing methods used. It has been found that preferred sealants for vehicle tires are those in which -the tensile s-trength is in excess of 30 psi, the elongation is in excess of 600~o ~ and the swell ratio in -toluene lies between 12 and 40.
Furthermore, sealants having elongations in excess of 300O and swell ratios in the range of 12-35 have been found to be particularly suitable as vehicle -tire sealants and are especially preferred. Such sealants may be formulated by adjus-ting the butyl rubber to comprise about 13-40% by weight of the total composition excluding the cross~linking agents, by using a butyl rubber having a mole percent unsaturation between about 0.5 and 2.5 and a molecular weight of about 100,000 - 450,000, and by using between about 0.5 - 6 phr of a quinoid cross-linking agent and at least about 2 phr of carbon black. Such sealants having 13 - 20P~, butyl rubber, 30 - 60 phr carbon black and 2 - 6 phr of a quinoid cross-linking agent are especially preferred because they are readily formulated having properties in the above ranges and because they possess significant processing advantages as described below. Sealants having tensile strengths, elongations, and swell ratios in the ranges set forth above may also be formulated by adjusting -the butyl rubber -to comprise about 13 - 50Po by weigh-t of the -total :
composition less the cross-linking agents, by using a bu-tyl rubber having a mole % unsa-turation between abou-t 0.5 - 2.5 and a molecular weight of about 100,000 - 450,000, and by using between abou-t 5 - 25 phr of a bromomethylated phenolic resin curing agent and at least 3 phr of zinc oxide.
Brief Desc ption of the D a _ ~
Fig. 1 is a perspec-tive view oE a cross-section of a vehicle -tire illus-trating one embodiment of the invention in which the sealant composition layer is loca-ted on -the innerrnost surface of the tire behind the tread;
Fig. 2 is a perspective view similar to Fig. 1, illus-tra-ting a second embodimen-t of the invention in which the subjec-t sealant layer is located behind the tread portion of the vehicle tire and between an air impervious film conventionally eMployed in a tubeless tire and the carcass portion of the tire.
Detailed Description of the Inventlon The copolymer netwoxk which provides the strength and continuity of the sealant compositions of the present invention is comprised of cured butyl rubber. Butyl rubber is intended to include copolymers of 96 - 99.5 wt.% isobutylene and 4 - 0.5 wt.% isoprene (Butyl IIR) as well as other rubbery copolymers of a major proportion (i.e., over 50% by weight) of an isoolefin having from 4 to 7 carbon a-toms with a minor proportion by weight of an open chain conjugated diolefin having from 4 to 8 carbon atoms. The copolymer may consist of from 70 to 99.5~ by weight of an isomonoolerin such as isobutylene or ethyl methyl ethylene copolymerized with from 0.5 to 30% by weight of an open chain conjugated diolefin such as isoprene; butadiene -1,3; piperylene;
2,3- dimethyl-butadiene -,3; 1,2- dimethyl-butadiene -1,3 (3-methyl pentadiene -1,3); 1,3 -dimethyl butadiene -1,3;
l-ethyl butadiene -1,3 (hexadiene -1,3); 1,4-dimethyl butadiene -1,3 (hexadiene -2,4); the copolymerization being affected by the usual rnanner of copolymerizing such monomeric materials.
"Butyl rubber" as used herein also includes halogenated butyl rubber, of which chlorobutyl and bromobutyl are the best known varieties. The halogen is generally believed to en-ter the butyl rubber molecule by substitution at the allylic position in the diolefin unit. Y'ypical chlorobu-tyl rubbers have about 1.0 - 1.5 weight percent chlorine. "Bu-tyl rubber" also includes those varieties of butyl rubber in which conjugated diene functionali-ty has been added in -the linear backbone at the diolefin uni-ts. Such conjugated diene butyls are described in U.S. Patent 3,816,371.
The sealant compositions of the present invention may be formulated using any of the standard high molecular weight grades of butyl rubber. Such grades have viscosity average molecular weigh-ts in excess of 100,000, and most commonly in the range 300,000 - 450,000. They are to be distinguished from the low molecular weight butyl grades, which have viscosity average molecular weights on the order of one-tenth of the high weight grades. Sealants of the present invention do not include low molecular weight butyl grades. Representative examples of high weight butyl grades are Butyl 065, Butyl 165, Butyl 268, Butyl 365, Butyl 077, Chlorobutyl 1066 and Chlorobutyl 1068, all available from the Exxon Oil Company, and BUC~R 1000 NS, BUCAR 5000 NS, BUCAR 5000 S and BUCAR 6000 IIS, all available from Cities Service Oil Company. While the use of butyl rubber having a molecular weight in excess of abou-t 450,000 will not detract from the sealing qualities of the sealant, such bu-tyl rubber is comparatively difficult to dissolve and combine with other constltuen-ts, as well as di.-ficult to apply via an airless spraying technique. Thus the preferred weight range ~or the high molecular weight butyl rubber is from 100,000 to about
l-ethyl butadiene -1,3 (hexadiene -1,3); 1,4-dimethyl butadiene -1,3 (hexadiene -2,4); the copolymerization being affected by the usual rnanner of copolymerizing such monomeric materials.
"Butyl rubber" as used herein also includes halogenated butyl rubber, of which chlorobutyl and bromobutyl are the best known varieties. The halogen is generally believed to en-ter the butyl rubber molecule by substitution at the allylic position in the diolefin unit. Y'ypical chlorobu-tyl rubbers have about 1.0 - 1.5 weight percent chlorine. "Bu-tyl rubber" also includes those varieties of butyl rubber in which conjugated diene functionali-ty has been added in -the linear backbone at the diolefin uni-ts. Such conjugated diene butyls are described in U.S. Patent 3,816,371.
The sealant compositions of the present invention may be formulated using any of the standard high molecular weight grades of butyl rubber. Such grades have viscosity average molecular weigh-ts in excess of 100,000, and most commonly in the range 300,000 - 450,000. They are to be distinguished from the low molecular weight butyl grades, which have viscosity average molecular weights on the order of one-tenth of the high weight grades. Sealants of the present invention do not include low molecular weight butyl grades. Representative examples of high weight butyl grades are Butyl 065, Butyl 165, Butyl 268, Butyl 365, Butyl 077, Chlorobutyl 1066 and Chlorobutyl 1068, all available from the Exxon Oil Company, and BUC~R 1000 NS, BUCAR 5000 NS, BUCAR 5000 S and BUCAR 6000 IIS, all available from Cities Service Oil Company. While the use of butyl rubber having a molecular weight in excess of abou-t 450,000 will not detract from the sealing qualities of the sealant, such bu-tyl rubber is comparatively difficult to dissolve and combine with other constltuen-ts, as well as di.-ficult to apply via an airless spraying technique. Thus the preferred weight range ~or the high molecular weight butyl rubber is from 100,000 to about
3~6 450,000. Furthermore, butyl rubber having molecular we;yhts in the range of 300,000 - ~50,~00 have been found par-ticularly useful for formulating sealants having desirable tensile and elongation properties, and are especially preferred.
Cross-linking of the butyl rubber may be effected by any of the well-]cnown curing systerns, including sulfur and sulfur containing systerns, quinoid systems, and phenolic resin systems. For halogenated butyl, additional u.seable curiny agents include primary amines and diamines, secondary diamines, zinc oxide combined with alkyl dithiol cahamates such as tetramethyl thiuram disulfide, and 1,2-1,3 dialkyl thioureas.
For butyl containing conjugated diene functionality, additional useable curing agents include poly-functional dieneophiles, such as ethylene glycol dimethacrylate and trimethylol propane trimethacrylate.
Although butyl rubber may be cured using a vulcanization process (sulfur and accelerators such as mercaptobenzothiazole), such a cure results in a rubber that over time is subject to degradation caused by oxygen or ultraviolet radiation. Such degradation may be partially prevented through the use of antioxidants, such as diphenyl - p - ~henylene-diamine, phenyl ~ beta-naphthylamine and hydroquinone, and antiozonants, such :. as N,N'-di (2-octyl) p- phenylenediamine and N-(1-3-demethyl-; bu-tyl) -N'- phenyl p-phenylenediamine. Nevertheless, the charac-teristics o~ the resulting sealant change sufficlently over time to make quinoid`and phenolic resin curiny systems pre-ferable to vulcanization for the -tire sealing applications, where the sealant must be capable of lasting years in a harsh environment.
.. Quinoid cures depend on cross-linking through the nitroso groups of aromatic nitroso compounds. In the quinoid curing system, p-quinone dioxime and p,p-di-bénzoylq~linone dioxime are preferred as the curing agen-ts. Other suitable 3~ 1 curing agents include dibenzoyl-p-quinone dioxime, p-dinitrosobenzene and N~~lethyl-N,~-dini-trosoanilene, the latter two being available on a clay base as "Polyac" from E.I. duPon-t de Nemours & Co. and as "Elastopar" from Monsanto Chemical Co., respectively. The cross-linking activators which may be employed in the sealant composi-tion include inorganic peroxides, organic peroxides (including diaroyl peroxides, diacyl peroxides and peroxyesters) and polysulfides. Exemplary are lead peroxide, zinc peroxide, barium peroxide, copper peroxide, po-tassium peroxide, silver peroxide, sodium peroxide, calcium peroxide;
metallic peroxyborates, peroxychromates, peroxycolumbates, peroxydicarbonates, peroxydiphosphates, peroxydisulfates, peroxygermanates, peroxymolybdates, peroxynitrates, magnesium peroxide, sodium pryophospha-te peroxide, and the like; -the organic peroxides such as lauryl peroxidç, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butyl peroxybenzoate, dibenzoyl peroxide, bis (p-monomethoxy-benzoyl) peroxide, p-monomethoxy-benzoyl peroxide, bis (p-nitrobenzoyl) peroxide, and phenacetyl peroxide; the metallic polysulfides such as calcium polysulfide~
sodium polysulfide, potassium polysulfide, barium polysulfide and -the like, some sulfur bearing organic compounds such as disclosed in U.S. patent ~lo. 2,619,~81, and -the organic poly-sulfides, which possess the general formula R-(S)x -R where R
is a hydrocarbon group and x is a nurnber from 2 to ~. The actual cross-linking agent is believed to be the oxidation product of quinone dioxime, p-dinitroso benzene.
The quinoid curing agent/cross-linking activator cornbina-tion which has been found to result in the shortest gel time is the p-quinone dioxime/benzoyl peroxide combination.
The preferred concentration of p-quinone dioxime is 0.5 - 6 phr.
The preferred concentration of benzoyl peroxide is 1.5 - 1~ phr.
Accelera-tors may be employed as appropriate. For example, cobal-t napthenate may be used in combination wi-th t-bu-tyl perxybenzoa-te, and chloranil (2,3,5,G - tetrachloro - 1,~ -benzoquinone) may be used in combination with -t butyl peroxy-benzoate or benzoyl peroxide.
The phenolic resins which may be used as curing agents in this invention include halorne-thylated alkyl phenolic resins, me-thylol phenolformaldehyde resins, and related species.
Bromomethyl alkyl phenolic resins availab:Le from Schenectady Chemi.cals, Inc. wlder the -tradenames CP~J~328 and SP-1056 are suitable. rrhe 2referred concen-tra-tion of phenolic resin is 5-25 phr. Such resins do not require the use of activators.
rrhe compositions of -the presen-t invention include one or more tackifying agents which enable the composition -to adhere to the tire, to a puncturing object, and to self-heal over a puncture hole after the puncturing object has been rernoved. In general, any tackifying agent compatible with a butyl rubber system may be used. Such agents include polybutenes, polypropenes, paraffinic oils, petrolatum, phthalates, and a number of resins including polyterpenes, terpene-phenolics, blocked-phenolics, modified rosin and rosin esters, and hydro-carbon resins. Preferred tackifiers are polyisobutylenes and hydrocarbon resins, and particularly combinations thereoE.
The sealant compositions of the present invention may include one or more reinEorcing agents or fillers. For compo-sitions cured by a quinoid curing system, one of the reinforcing agents ~IUSt be finely divided carbon. Carbon, such as carbon black, provides reacti.on sites for the quinoid curing process, and should cornprise at least 2 parts of the sealant by weight for each 100 parts of butyl rubber. Pre~erred concentrations of carbon black are 30 - 60 phr. The substance comprising the remainder o~ the reinforcing agent may either be carbon black or some other suitable substance selected on the basis of the desired color of khe sealan-t. For compositions cured by a phenolic resin curing agent, one of the reinforcing agen-ts must be a-t least 3 phr of zinc oxide. The preferred concentra--tion of zinc oxide is 5 - 30 phr. Carbon black may also be used with compositions cured by means of phenolic resins, but its presence is no-t required. Other well-known reinforcing agents and fillers for butyl rubbers include aluminum hydrate, lithopone, whiting, clays, hydra-ted silicas, calcium silicates, silicoaluminates, magnesium oxide, and maynesium carbona-te.
To aid in maintaining su~ficient tackiness and -thermal stability at elevated temperatures, the sealant compositions oE the present invention may incl-ude a thermoplastic ancl elasto-meric par-tially-hydrogenated block copolymer up to abou-t 10 wt.
% of the eomposition, the block copolymer having a general config-uration of A-(B-A)l 5 wherein prior to hydrogenation each A is a monovinyl arene polymer block and each B is a conjugated diene polymer block. Typical A monomers are styrene, alpha methyl styrene and ring alkylated styrenes. Typical B monomers are butadiene and isoprene. The A bloc~s make up the end groups and typically comprise about one third of the copolymer by weight, and the B blocks make up the mid groups and the balance of the copolymer. The copclymer is partially hydrogenated so -that the conjugated diene block segments are substantially fully sa-turated.
The mon`ovinyl arene polymer bloek segments are not appreciably saturated. Hydrogenation in this fashion enhances -the utility of the block copolymer as an oxidation and high temperature-degradation resistant constituent of the sealant composition.
The average molecular weight of the copolymer is in the range of about 60,000 -to 400,000. Block copolymers of this type are described in V.S. Patent No. 3,595,942.
The sealant compositions of the present invention are those comprised of the chemical components described above in which the tensile strength, elongation and cross-link density have been controlled so as to provide the optimum properties for tire sealants. Tensile strength is the stress per unit --:1.1--area that a sample of sealant can wi-thstand before rup-turing.
As used herein, tensile streng-th is cleterrnined by firs-t curing a sample of -the sealant in a thin sheet for 24 hours at room tempera-ture, then at 150F for another 24 hours, and -then at 190~F for 4 hours. Dumbell shaped specimens of sealant are then cut using ASTM die "D", and the dlmensions of the dumbell shaped specimen are determined. The speci~len is then placed in a conventional Dillon tensile -testing apparatus having jaws which grip it at i-ts wider end portions, and the specimen is stretched at a cross-head speed of 10 inches per rninute until rupture. The tensile strength is the force at rupture divided by the initial cross sectional area of the narrow portion of the specimen.
Elongation, as used herein, is determined by a pro-cedure iden-tical to that for tensile strength. The elongation, expressed as a percentage, is calculated by subtracting the initial length of the specimen from its length at rupture, multiplying by 100, dividing by the initial length, and then if necessary by multiplying the result by a correction factor which compensates for any material which may have been pulled out of the jaws gripping each end of the specimen. The initial and final rupture lengths are de-termined by measuring the distances between the jaws. Thus the specimen be;ng elonga-ted includes not only the narrow, central portion bu-t also some of the wider end portions of the specimen.
Cross-link density may be measured by performing a swell test on a specimen of the sealant using toluene as a solvent. As is known by those skilled in the art, a swell test provides a reliable and repeatable relative measure of cross-link density. The swell test measures the aMount of solvent absorbed by a given amount of cross~linked rubber, and the test results are expressed as a swell ratio of weight of solvent absorbed to weight o~ cross-linked rubber. The greater the cross-link density of a given specimen of rubber the less the elastomeric network is free to expand by absorblng solvent and the smaller the swell ra-tio will be. The tes-t herein is performed by weighing a specimen o} dry (solventless) sealant, soaking the specimen in toluene for 60-72 hours, removing and weighing the wet specimen, and then dryiny the specimen at 300F for 30 rninutes and reweighing. The weigh-t o F solven-t absorbed is the wet weight less -the final dry weigh-t. Soaking the specimen in -toluene will remove the ingredients which have not been incorporated into the toluene insoluble polymer network, and the specimen after soaking and drying will there-fore essentially include the cross-linked rubber and the carbon black or other fillers if present. In the case where the sealant included a tackifier such as polyisobutylene containing func-tional end groups, a portion of the tackifier will remain - incorporated into the network as side chains as well. The quantity of toluene insolubles present can be calcula-ted from the initial pre-soaking weight of the specimen plus its known cornposition, and these figures can be subtracted from the dry, post-soaking weight to yield the weight of cross-linked rubber.
The above described tests ma~7 readily be carried out by those skilled in the art, and the resul.ts of such tests may : be used to guide the formulation of sealant composition of the : present invention. As previously descri.bed, the tensile strength of the sealant must be sufficiently high so that the sealan-t will not "blow through" a typical plmcture hole in the range of tire inflation pressures normally encountered. A reliable guide has been found to be that no more than 1/2 inch of sealant should extrude through a .203 inch diameter hole at 32 psig. The elongation must be sufficien-tly great so that th~ sealant will be able to adhere to a puncturing object without ca?ping and be able to flow over and into a puncture hole after the puncturing object is removed. The cross-link density must be sufficiently high such tha'~ the sealant will not flow at ele-vated temperatures (e.g. up to 220F) or fatigue when a punc-turing objec-t is left ln the tire during use. The cross-link density must not be so high, however, as to cause capping of the sealant when a puncturing object enters the tire. A reliable guide as to whether the elonga-tion is sufficiently high and the cross-link density is sufficiently low has been found -to be an 80% or higher pass rate in the static puncture test described in Example I
. below.
: It has been found by applicants that preferred tire sealant compositions are those having a -tensile strength of at least about 30 psi, an elonya-tion of greater than about 600%, and swell ratios of between abou-t 12 and ~0. Within these ranges, compositions of the present invention have been found to have good tire sealing properties, both when the puncturing object remains in the tire and when it is removed, over the entire temperature range to which tire sealants are normally - subjected. ~urthermore, sealant compositions of the present invention having elonyations in excess of 800% and swell ratios in the range of 12-35 have been found to be particularly suitable as vehicle tire sealants, and are especially preferred.
Sealants having tensile strengths, elonga-tions and swell ratios within these xanyes may be formulated by including in the compositions of the present invention 13-~% by weight of butyl rubber having a molecular weight greater than about lO0,000 and a mole % unsaturation of between about 0.5 and 2.5, and by employing at :.least 2 phr of carbon black and about 0..5 - 6 phr of a quinoid cross linking agent. The remainder of such compositions are comprised of appropriate tackifying agents, block copolymers, fillers, pigments, and the like.
Compositions havi.ng 13 - 20% butyl rubber have been found to have short gel times and to be readily applicable by spray --1~--335~
technique, and are therefore especially preferred. Sealant compositions having tensile strenyths, elongations and swel:L
ratios as described above may also be formula-ted by employing 13-50% by weight of butyl rubber having a molecular weight greater -than about 100,000 and a mole % unsaturation of be-tween about 0.5 and 2.5, 5-25 phr o, a phenolic resin curing agent, at least 3 phr of zinc oxide, with the remainder of -the composi-tion comprising tac]cifying agents and o-ther modifiers.
The sealan-t compositions of the presen-t inven-tion may be applied by a variety oE means. ~1hey may be formulated as sprayable compositions that cure in situ, e.g., on the inner surface of a tire, or as composi-tions that are first cured in sheet form and -then applied. They may also be extruded or brushed onto a substrate. A solvent may be employed in the preparation of the sealant composition. Sui-table solvents include hexane, -toluene, heptane, naptha r cyclohexanone, trichloroethylene, cyclohexane, methylene chloride, chloro-benzene, e-thylene dichloride, 1,1,1 - trichloroethane, and tetrahydrofuran, as well as combinations thereof.
Each particular sealant application process will -tend to place constraints on the composition of the sealan-t itself.
Thus for exar,lple if -the sea]ant is to be solvated and sprayed directly onto a tire, it is desirable to keep the amount of solvent used to a minimum (e.g. 35% or less), so as to simplify solvent recovery procesures and decrease processing tir.le. At solvent levels of 35% or less, however, it has been found that compositions according to the present invention compris-ing more than about 206 butyl rubber by weight cannot effectively be sprayed by an airless technique by a single fixed nozzle.
In airless spray applications, therefore, compositions com-prising 20% or less butyl rubber are preferred. Compositions having greater than 20% butyl rubber may be sprayed by a nozzle which tracks back and forth across the tire tread.
A second processing constraint on sealants of -the :
~6~33~
presen-t inven-tion involves cure -time. The -time required for a given sealant to cure wlll generally affect throughput re-gardless of the application process used. It has been found that sealants according -to the p~esent invention which are formulated with less than about 2 0 phr of a quinoid cross-linking agent will have yel times which are unacceptably long for many applications. Sealants cured with in excess ofabout 2.0 phr of quinoid cross linking agent: are -therefore preferred.
Such sea~nts mus-t also, of course, have values of -tensile strength, elongation and cross link density as described above.
Since it in general has been found that quinoid cured sealants comprised of more than abou-t 20~ butyl rubber will not have adequate elong~ions unless less than about 2~0 phr of cross-linking agent are used, the practical effec-t is that preferred quinoid cured sealants are those comprised of no more than about 20%
butyl rubber by weigh-t.
Because the sealant compositions described herein have the unique ability to resis-t oxidation and to remain stable and effective over a wide temperature range, they have numerous applications, such as caulking compounds and as roofing sealants, in addition to their utility as tire sealants. Be-cause the environments to which a tire sealant is subjected is the most severe, the following examples relate the sealant composition to -this environment for purposes of illustration.
It will be understood that the ra-tio of -the essential ingre-dients may be varied within the ranges set forth above and that other compounding materials may be replaced by and/or supplemented with such other materials as may be appropriate -to deal wi-th the environment contemplated.
With particular respect to the vehicle tire sealant embodiment and with reference to Fig. 1, a vehicle tire 10 conventionally includes a tread portion 12, a carcass portion 14 and side walls 16. :[n tubeless vehicle tires it is generally desirable to employ a barrier layer or lining 1~ which is 39qE~
iMpermeable to air. The air impermeable lining 18 -typically extends over the entire inner surface of -the -tire 10 from one rim contact portion 20 to the other rim portion 22. In accordance wi-th the embodiment of -the presen-t invention illus-trated in E'ig.
1, a sealant layer 24 is placed on the inside of the tire 10 agains-t -the air barrier layer 18. The sealant layer 24 is arranged to lie principally behind the -tread 12 of -the tire 10 so -that the sealant layer will principally serve -to seal punctures occurrins in the -tread portion of the -tire.
Fig. 2 illustrates another embodimen-t of -the presen-t invention wherein a vehicle tire 10 has parts similar to -those illustrated in Fig. 1, and iden-tified by like numerals.
IIowever, in this particular embodimen-t the sealant layer 24 is located between the carcass por-tion 14 of -the tire 10 and -the air impermeable barrier layer 18. The vehicle tire embodiment illustrated in Fig. 1 normally occurs when the sealan-t layer 24 is applied af-ter the -tire 10 has been formed and cured. The vehicle tire eMbodiment illustrated in FigO 2 occurs when the sealan-t layer 24 is incorporated in-to tire 10 when the tire 10 is i-tself being formed and cured. The sealant layer may be formed and cured at the same time the vehicle tire is being manufactured to realize production economies, since the subject sealant layer can be cured at the temperatures, about 350F, employed in curing the other rubber components of -the tire.
When -this is done, it is possible to locate the sealant layer in either position as depicted by Figs. 1 and 2, whereas if the sealant layer is applied after -the tire is manufactured, it is only possible -to place such a layer inside the air imperMeable barrier as illustrated in Fig. 1. Finally, it should be noted if layer 24 is intended to cover the entire inner surface of the tire, the air barrier layer 18 may be eliminated entirely from the vehicle -tire cons-truction.
The sealan-t compositions utilized in the following examples were prepared by comblniny the ingredients listed ln Table 1 in the proportions indicated, all proportions being given by dry weigh-t.
TABLE I
Inyredient - A _B C _D _h E' G Il Butyl 1651 15 - - 20 ~ 35 - 40 Butyl 365 - 13 20 - 10 Butyl 065 - - ~ ~ ~ ~ 40 Vis-tanex4 10 9.78 8.98 10 10 H-100 - 19.55 17.97 - 20 H-19007 40 ~3 35.05 40 40 32 29 Piccotac~ 5 4.89 a.49 5 5 Zinc Oxide - - - - - 10 10 10 Carbon Black 7 4.89 8.98 10 10 Block Copolymerl0 _ 4.894.49 - 5 Para Qu~one 3.03.0 2.47 3.0 3.0 0.51.0 Dioxime Benzoyl 11 11.09.0 7~.41 9.0 9.0 1.53.0 Peroxide CJR-32gll,12 15 1 A butyl rubber having a viscosity averaye - molecular weiyht of 350,000 and a mole %
unsaturation (isoprone units/100 monomer units) of 1.2, available from Exxon Oil Company under the trademark "Butyl 165".
: 2 A butyl rubber having a viscosity average molecular weiyht of 350,000 and a mole %
unsaturation of 2.0, available from Exxon Oil Company under the trademark "Butyl 365".
3 A butyl rubber having a viscostiy average molecular weight of 350,000 and a mole %
unsaturation of 0.8, available from Exxon Oil Company under the trademark "Butyl 065".
Cross-linking of the butyl rubber may be effected by any of the well-]cnown curing systerns, including sulfur and sulfur containing systerns, quinoid systems, and phenolic resin systems. For halogenated butyl, additional u.seable curiny agents include primary amines and diamines, secondary diamines, zinc oxide combined with alkyl dithiol cahamates such as tetramethyl thiuram disulfide, and 1,2-1,3 dialkyl thioureas.
For butyl containing conjugated diene functionality, additional useable curing agents include poly-functional dieneophiles, such as ethylene glycol dimethacrylate and trimethylol propane trimethacrylate.
Although butyl rubber may be cured using a vulcanization process (sulfur and accelerators such as mercaptobenzothiazole), such a cure results in a rubber that over time is subject to degradation caused by oxygen or ultraviolet radiation. Such degradation may be partially prevented through the use of antioxidants, such as diphenyl - p - ~henylene-diamine, phenyl ~ beta-naphthylamine and hydroquinone, and antiozonants, such :. as N,N'-di (2-octyl) p- phenylenediamine and N-(1-3-demethyl-; bu-tyl) -N'- phenyl p-phenylenediamine. Nevertheless, the charac-teristics o~ the resulting sealant change sufficlently over time to make quinoid`and phenolic resin curiny systems pre-ferable to vulcanization for the -tire sealing applications, where the sealant must be capable of lasting years in a harsh environment.
.. Quinoid cures depend on cross-linking through the nitroso groups of aromatic nitroso compounds. In the quinoid curing system, p-quinone dioxime and p,p-di-bénzoylq~linone dioxime are preferred as the curing agen-ts. Other suitable 3~ 1 curing agents include dibenzoyl-p-quinone dioxime, p-dinitrosobenzene and N~~lethyl-N,~-dini-trosoanilene, the latter two being available on a clay base as "Polyac" from E.I. duPon-t de Nemours & Co. and as "Elastopar" from Monsanto Chemical Co., respectively. The cross-linking activators which may be employed in the sealant composi-tion include inorganic peroxides, organic peroxides (including diaroyl peroxides, diacyl peroxides and peroxyesters) and polysulfides. Exemplary are lead peroxide, zinc peroxide, barium peroxide, copper peroxide, po-tassium peroxide, silver peroxide, sodium peroxide, calcium peroxide;
metallic peroxyborates, peroxychromates, peroxycolumbates, peroxydicarbonates, peroxydiphosphates, peroxydisulfates, peroxygermanates, peroxymolybdates, peroxynitrates, magnesium peroxide, sodium pryophospha-te peroxide, and the like; -the organic peroxides such as lauryl peroxidç, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butyl peroxybenzoate, dibenzoyl peroxide, bis (p-monomethoxy-benzoyl) peroxide, p-monomethoxy-benzoyl peroxide, bis (p-nitrobenzoyl) peroxide, and phenacetyl peroxide; the metallic polysulfides such as calcium polysulfide~
sodium polysulfide, potassium polysulfide, barium polysulfide and -the like, some sulfur bearing organic compounds such as disclosed in U.S. patent ~lo. 2,619,~81, and -the organic poly-sulfides, which possess the general formula R-(S)x -R where R
is a hydrocarbon group and x is a nurnber from 2 to ~. The actual cross-linking agent is believed to be the oxidation product of quinone dioxime, p-dinitroso benzene.
The quinoid curing agent/cross-linking activator cornbina-tion which has been found to result in the shortest gel time is the p-quinone dioxime/benzoyl peroxide combination.
The preferred concentration of p-quinone dioxime is 0.5 - 6 phr.
The preferred concentration of benzoyl peroxide is 1.5 - 1~ phr.
Accelera-tors may be employed as appropriate. For example, cobal-t napthenate may be used in combination wi-th t-bu-tyl perxybenzoa-te, and chloranil (2,3,5,G - tetrachloro - 1,~ -benzoquinone) may be used in combination with -t butyl peroxy-benzoate or benzoyl peroxide.
The phenolic resins which may be used as curing agents in this invention include halorne-thylated alkyl phenolic resins, me-thylol phenolformaldehyde resins, and related species.
Bromomethyl alkyl phenolic resins availab:Le from Schenectady Chemi.cals, Inc. wlder the -tradenames CP~J~328 and SP-1056 are suitable. rrhe 2referred concen-tra-tion of phenolic resin is 5-25 phr. Such resins do not require the use of activators.
rrhe compositions of -the presen-t invention include one or more tackifying agents which enable the composition -to adhere to the tire, to a puncturing object, and to self-heal over a puncture hole after the puncturing object has been rernoved. In general, any tackifying agent compatible with a butyl rubber system may be used. Such agents include polybutenes, polypropenes, paraffinic oils, petrolatum, phthalates, and a number of resins including polyterpenes, terpene-phenolics, blocked-phenolics, modified rosin and rosin esters, and hydro-carbon resins. Preferred tackifiers are polyisobutylenes and hydrocarbon resins, and particularly combinations thereoE.
The sealant compositions of the present invention may include one or more reinEorcing agents or fillers. For compo-sitions cured by a quinoid curing system, one of the reinforcing agents ~IUSt be finely divided carbon. Carbon, such as carbon black, provides reacti.on sites for the quinoid curing process, and should cornprise at least 2 parts of the sealant by weight for each 100 parts of butyl rubber. Pre~erred concentrations of carbon black are 30 - 60 phr. The substance comprising the remainder o~ the reinforcing agent may either be carbon black or some other suitable substance selected on the basis of the desired color of khe sealan-t. For compositions cured by a phenolic resin curing agent, one of the reinforcing agen-ts must be a-t least 3 phr of zinc oxide. The preferred concentra--tion of zinc oxide is 5 - 30 phr. Carbon black may also be used with compositions cured by means of phenolic resins, but its presence is no-t required. Other well-known reinforcing agents and fillers for butyl rubbers include aluminum hydrate, lithopone, whiting, clays, hydra-ted silicas, calcium silicates, silicoaluminates, magnesium oxide, and maynesium carbona-te.
To aid in maintaining su~ficient tackiness and -thermal stability at elevated temperatures, the sealant compositions oE the present invention may incl-ude a thermoplastic ancl elasto-meric par-tially-hydrogenated block copolymer up to abou-t 10 wt.
% of the eomposition, the block copolymer having a general config-uration of A-(B-A)l 5 wherein prior to hydrogenation each A is a monovinyl arene polymer block and each B is a conjugated diene polymer block. Typical A monomers are styrene, alpha methyl styrene and ring alkylated styrenes. Typical B monomers are butadiene and isoprene. The A bloc~s make up the end groups and typically comprise about one third of the copolymer by weight, and the B blocks make up the mid groups and the balance of the copolymer. The copclymer is partially hydrogenated so -that the conjugated diene block segments are substantially fully sa-turated.
The mon`ovinyl arene polymer bloek segments are not appreciably saturated. Hydrogenation in this fashion enhances -the utility of the block copolymer as an oxidation and high temperature-degradation resistant constituent of the sealant composition.
The average molecular weight of the copolymer is in the range of about 60,000 -to 400,000. Block copolymers of this type are described in V.S. Patent No. 3,595,942.
The sealant compositions of the present invention are those comprised of the chemical components described above in which the tensile strength, elongation and cross-link density have been controlled so as to provide the optimum properties for tire sealants. Tensile strength is the stress per unit --:1.1--area that a sample of sealant can wi-thstand before rup-turing.
As used herein, tensile streng-th is cleterrnined by firs-t curing a sample of -the sealant in a thin sheet for 24 hours at room tempera-ture, then at 150F for another 24 hours, and -then at 190~F for 4 hours. Dumbell shaped specimens of sealant are then cut using ASTM die "D", and the dlmensions of the dumbell shaped specimen are determined. The speci~len is then placed in a conventional Dillon tensile -testing apparatus having jaws which grip it at i-ts wider end portions, and the specimen is stretched at a cross-head speed of 10 inches per rninute until rupture. The tensile strength is the force at rupture divided by the initial cross sectional area of the narrow portion of the specimen.
Elongation, as used herein, is determined by a pro-cedure iden-tical to that for tensile strength. The elongation, expressed as a percentage, is calculated by subtracting the initial length of the specimen from its length at rupture, multiplying by 100, dividing by the initial length, and then if necessary by multiplying the result by a correction factor which compensates for any material which may have been pulled out of the jaws gripping each end of the specimen. The initial and final rupture lengths are de-termined by measuring the distances between the jaws. Thus the specimen be;ng elonga-ted includes not only the narrow, central portion bu-t also some of the wider end portions of the specimen.
Cross-link density may be measured by performing a swell test on a specimen of the sealant using toluene as a solvent. As is known by those skilled in the art, a swell test provides a reliable and repeatable relative measure of cross-link density. The swell test measures the aMount of solvent absorbed by a given amount of cross~linked rubber, and the test results are expressed as a swell ratio of weight of solvent absorbed to weight o~ cross-linked rubber. The greater the cross-link density of a given specimen of rubber the less the elastomeric network is free to expand by absorblng solvent and the smaller the swell ra-tio will be. The tes-t herein is performed by weighing a specimen o} dry (solventless) sealant, soaking the specimen in toluene for 60-72 hours, removing and weighing the wet specimen, and then dryiny the specimen at 300F for 30 rninutes and reweighing. The weigh-t o F solven-t absorbed is the wet weight less -the final dry weigh-t. Soaking the specimen in -toluene will remove the ingredients which have not been incorporated into the toluene insoluble polymer network, and the specimen after soaking and drying will there-fore essentially include the cross-linked rubber and the carbon black or other fillers if present. In the case where the sealant included a tackifier such as polyisobutylene containing func-tional end groups, a portion of the tackifier will remain - incorporated into the network as side chains as well. The quantity of toluene insolubles present can be calcula-ted from the initial pre-soaking weight of the specimen plus its known cornposition, and these figures can be subtracted from the dry, post-soaking weight to yield the weight of cross-linked rubber.
The above described tests ma~7 readily be carried out by those skilled in the art, and the resul.ts of such tests may : be used to guide the formulation of sealant composition of the : present invention. As previously descri.bed, the tensile strength of the sealant must be sufficiently high so that the sealan-t will not "blow through" a typical plmcture hole in the range of tire inflation pressures normally encountered. A reliable guide has been found to be that no more than 1/2 inch of sealant should extrude through a .203 inch diameter hole at 32 psig. The elongation must be sufficien-tly great so that th~ sealant will be able to adhere to a puncturing object without ca?ping and be able to flow over and into a puncture hole after the puncturing object is removed. The cross-link density must be sufficiently high such tha'~ the sealant will not flow at ele-vated temperatures (e.g. up to 220F) or fatigue when a punc-turing objec-t is left ln the tire during use. The cross-link density must not be so high, however, as to cause capping of the sealant when a puncturing object enters the tire. A reliable guide as to whether the elonga-tion is sufficiently high and the cross-link density is sufficiently low has been found -to be an 80% or higher pass rate in the static puncture test described in Example I
. below.
: It has been found by applicants that preferred tire sealant compositions are those having a -tensile strength of at least about 30 psi, an elonya-tion of greater than about 600%, and swell ratios of between abou-t 12 and ~0. Within these ranges, compositions of the present invention have been found to have good tire sealing properties, both when the puncturing object remains in the tire and when it is removed, over the entire temperature range to which tire sealants are normally - subjected. ~urthermore, sealant compositions of the present invention having elonyations in excess of 800% and swell ratios in the range of 12-35 have been found to be particularly suitable as vehicle tire sealants, and are especially preferred.
Sealants having tensile strengths, elonga-tions and swell ratios within these xanyes may be formulated by including in the compositions of the present invention 13-~% by weight of butyl rubber having a molecular weight greater than about lO0,000 and a mole % unsaturation of between about 0.5 and 2.5, and by employing at :.least 2 phr of carbon black and about 0..5 - 6 phr of a quinoid cross linking agent. The remainder of such compositions are comprised of appropriate tackifying agents, block copolymers, fillers, pigments, and the like.
Compositions havi.ng 13 - 20% butyl rubber have been found to have short gel times and to be readily applicable by spray --1~--335~
technique, and are therefore especially preferred. Sealant compositions having tensile strenyths, elongations and swel:L
ratios as described above may also be formula-ted by employing 13-50% by weight of butyl rubber having a molecular weight greater -than about 100,000 and a mole % unsaturation of be-tween about 0.5 and 2.5, 5-25 phr o, a phenolic resin curing agent, at least 3 phr of zinc oxide, with the remainder of -the composi-tion comprising tac]cifying agents and o-ther modifiers.
The sealan-t compositions of the presen-t inven-tion may be applied by a variety oE means. ~1hey may be formulated as sprayable compositions that cure in situ, e.g., on the inner surface of a tire, or as composi-tions that are first cured in sheet form and -then applied. They may also be extruded or brushed onto a substrate. A solvent may be employed in the preparation of the sealant composition. Sui-table solvents include hexane, -toluene, heptane, naptha r cyclohexanone, trichloroethylene, cyclohexane, methylene chloride, chloro-benzene, e-thylene dichloride, 1,1,1 - trichloroethane, and tetrahydrofuran, as well as combinations thereof.
Each particular sealant application process will -tend to place constraints on the composition of the sealan-t itself.
Thus for exar,lple if -the sea]ant is to be solvated and sprayed directly onto a tire, it is desirable to keep the amount of solvent used to a minimum (e.g. 35% or less), so as to simplify solvent recovery procesures and decrease processing tir.le. At solvent levels of 35% or less, however, it has been found that compositions according to the present invention compris-ing more than about 206 butyl rubber by weight cannot effectively be sprayed by an airless technique by a single fixed nozzle.
In airless spray applications, therefore, compositions com-prising 20% or less butyl rubber are preferred. Compositions having greater than 20% butyl rubber may be sprayed by a nozzle which tracks back and forth across the tire tread.
A second processing constraint on sealants of -the :
~6~33~
presen-t inven-tion involves cure -time. The -time required for a given sealant to cure wlll generally affect throughput re-gardless of the application process used. It has been found that sealants according -to the p~esent invention which are formulated with less than about 2 0 phr of a quinoid cross-linking agent will have yel times which are unacceptably long for many applications. Sealants cured with in excess ofabout 2.0 phr of quinoid cross linking agent: are -therefore preferred.
Such sea~nts mus-t also, of course, have values of -tensile strength, elongation and cross link density as described above.
Since it in general has been found that quinoid cured sealants comprised of more than abou-t 20~ butyl rubber will not have adequate elong~ions unless less than about 2~0 phr of cross-linking agent are used, the practical effec-t is that preferred quinoid cured sealants are those comprised of no more than about 20%
butyl rubber by weigh-t.
Because the sealant compositions described herein have the unique ability to resis-t oxidation and to remain stable and effective over a wide temperature range, they have numerous applications, such as caulking compounds and as roofing sealants, in addition to their utility as tire sealants. Be-cause the environments to which a tire sealant is subjected is the most severe, the following examples relate the sealant composition to -this environment for purposes of illustration.
It will be understood that the ra-tio of -the essential ingre-dients may be varied within the ranges set forth above and that other compounding materials may be replaced by and/or supplemented with such other materials as may be appropriate -to deal wi-th the environment contemplated.
With particular respect to the vehicle tire sealant embodiment and with reference to Fig. 1, a vehicle tire 10 conventionally includes a tread portion 12, a carcass portion 14 and side walls 16. :[n tubeless vehicle tires it is generally desirable to employ a barrier layer or lining 1~ which is 39qE~
iMpermeable to air. The air impermeable lining 18 -typically extends over the entire inner surface of -the -tire 10 from one rim contact portion 20 to the other rim portion 22. In accordance wi-th the embodiment of -the presen-t invention illus-trated in E'ig.
1, a sealant layer 24 is placed on the inside of the tire 10 agains-t -the air barrier layer 18. The sealant layer 24 is arranged to lie principally behind the -tread 12 of -the tire 10 so -that the sealant layer will principally serve -to seal punctures occurrins in the -tread portion of the -tire.
Fig. 2 illustrates another embodimen-t of -the presen-t invention wherein a vehicle tire 10 has parts similar to -those illustrated in Fig. 1, and iden-tified by like numerals.
IIowever, in this particular embodimen-t the sealant layer 24 is located between the carcass por-tion 14 of -the tire 10 and -the air impermeable barrier layer 18. The vehicle tire embodiment illustrated in Fig. 1 normally occurs when the sealan-t layer 24 is applied af-ter the -tire 10 has been formed and cured. The vehicle tire eMbodiment illustrated in FigO 2 occurs when the sealan-t layer 24 is incorporated in-to tire 10 when the tire 10 is i-tself being formed and cured. The sealant layer may be formed and cured at the same time the vehicle tire is being manufactured to realize production economies, since the subject sealant layer can be cured at the temperatures, about 350F, employed in curing the other rubber components of -the tire.
When -this is done, it is possible to locate the sealant layer in either position as depicted by Figs. 1 and 2, whereas if the sealant layer is applied after -the tire is manufactured, it is only possible -to place such a layer inside the air imperMeable barrier as illustrated in Fig. 1. Finally, it should be noted if layer 24 is intended to cover the entire inner surface of the tire, the air barrier layer 18 may be eliminated entirely from the vehicle -tire cons-truction.
The sealan-t compositions utilized in the following examples were prepared by comblniny the ingredients listed ln Table 1 in the proportions indicated, all proportions being given by dry weigh-t.
TABLE I
Inyredient - A _B C _D _h E' G Il Butyl 1651 15 - - 20 ~ 35 - 40 Butyl 365 - 13 20 - 10 Butyl 065 - - ~ ~ ~ ~ 40 Vis-tanex4 10 9.78 8.98 10 10 H-100 - 19.55 17.97 - 20 H-19007 40 ~3 35.05 40 40 32 29 Piccotac~ 5 4.89 a.49 5 5 Zinc Oxide - - - - - 10 10 10 Carbon Black 7 4.89 8.98 10 10 Block Copolymerl0 _ 4.894.49 - 5 Para Qu~one 3.03.0 2.47 3.0 3.0 0.51.0 Dioxime Benzoyl 11 11.09.0 7~.41 9.0 9.0 1.53.0 Peroxide CJR-32gll,12 15 1 A butyl rubber having a viscosity averaye - molecular weiyht of 350,000 and a mole %
unsaturation (isoprone units/100 monomer units) of 1.2, available from Exxon Oil Company under the trademark "Butyl 165".
: 2 A butyl rubber having a viscosity average molecular weiyht of 350,000 and a mole %
unsaturation of 2.0, available from Exxon Oil Company under the trademark "Butyl 365".
3 A butyl rubber having a viscostiy average molecular weight of 350,000 and a mole %
unsaturation of 0.8, available from Exxon Oil Company under the trademark "Butyl 065".
4 A polyisobutylene having a viscosity average molecular weight of 55,000, available from : Exxon Oil Company under the trademark "Vistanex L~1-MS".
33~
A polybutene having an average m~lecular weight o:E 920 avai.lable from AIIOCO under the -trademark "H-100".
~ 6 A polybutene having an average molecular .~ wei~ht of 1290 available from~lOCO under -the trademark "H-300".
7 A polybutene having an average molecular weight of 2300 available from A~OCO under the trade-mark "II-1900".
8 A hydrocarbon resin having a softening point of 97C available from ~lercules, Inc. wnder the trademark "Piccotac B".
9 A2furnace black having a surface area of 235 m /gm, arithmetic mean:particle diame-ter of 17 millimicrons and a p~l of 6.0 - 9.0 avail-: able from Cities Servlce Oil Company under the trademark "Raven-2000".
A block copolymer having a configuration A-(B-A)1_5, A representing a polystyrene block a~d B representing a hydrogenated polyisoprene block, the isoprene making up about two thirds of the compound by weight, and the average molecular weight being between 70,000 and 150,000. The compound is available from the Shell Oil Company under the trade-mark 17 Kraton G-6500".
11 In parts ~er 100 parts of butyl rubber.
12 A dibrome-thyl octyl phenol having a number average molecular weight of 500 and a bromine content of 2~ - 31~, available from Schenec-tady Chemicals, Inc. under the trademark "CJR-32~".
EX~lPLE I
A -tire sealant was prepared according to the formula of composition A above. The butyl rubber, Vistanex, and Piccotac were solvated and blended in hexane so that the mixture contained about 50~ solids by weight. The carhon black and the:pol.ybutenes were:then;~added to the.pre.vious1y:solvated mixturei The - p-quinone.. dioxime-w.as then.blended in.~cyclohexanone to a:.::.. m diLution:o.f;.about 4.0~ solidsl~by.~Jeigh-t~, added to -the mixtùre,:...~;
and;dis~persed therein to ~orm a~:first component co~prising- - ;
abou.t.~73~ so.lids ~y.wei.g.ht. lThis-c~mponent has been found to have a~s:helf life o.f greater.tha~:six:.mon:ths.
. For a laboratory analysis, a second cornponent was formed by dissolving the benzoyl peroxide in -toluene to a dilution of abou-t 3% solids. First and second components were then cornbined, poured into molds, and then cured for 24 hours at ambien-t temperature, followed by 24 hours at 150F
and 4 hours at 190F. Specimens of -the sealant were then tested to determine tensile strength, elongation and swell ratio.
Tensile strengths for this sealant were found to lie in the range of 35 - 45 psi, elongations were in -t:he range of 967 - 998%, and swell ratios were in the range 17.9 - 18.5.
New JR-78-lS s-teel bel-ted radial tires were utilized for evaluating the sealant composition on a tire.
The tires were first cleaned by scrubbing their interior sur-faces wi-th a wire brush and soap solution. The surfaces were then rinsed and dried. A first component as described above was prepared and a second component was prepared by dissolving the benzoyl peroxide in methylene chlori~e such that the resultant solution was about 16~ solids. The first component was then pre-heated to 260F, combined with the second component to yield a mixture having about 6~% solids, and sprayed at about 500 psig onto the interior surface of a rotating tire. The temperature of the first and second components after mixing was about 210F.
1200 grams of sealant on a solvent free basis were sprayed onto each tire, the resulting sealant layer being between 0 2 and 0.25 inches thick under the central portion of the tread and 0.15 inches thick at the tire shoulder. After spraying, the tires were continually rotated for about ten minutes until the sealant had cured sufficiently to resis-t flow. The -tires were -then unloaded from the applicator apparatus and placed in an oven at 140F - 150F for 30 minutes.
The coated tires were subjected to a series of tests to evaluate the "on the-tire" effectiveness of the sealan-t.
These tests included a blow through -test, a s-tatic puncture test, and a dynamometer -test. The blow through test was con-duc-ted by drilling six holes in the tire (2 at .14 inch diameter, 2 a-t .187 inch diameter, and 2 a-t .203 inch diame-ter) and plugging the holes with modeling clay prior to sealan-t application. Af-ter application the pluys were remo~ed from -the outside, and the tire was inflated to 32 psig at ambient, 42 psig at 180F, and 46 psig at 220F. The sealan-t was considered acceptable if less than about 1/2 inch of sealant extruded through any hole, and if no loss of air from the tire was detected.
The s-tatic puncture -test was run at three different tempera-tures: -20F; 70F; and 180F. At each temperature, an 8 penny nail (.115 inch diameter) and a 20 penny nail (.180 inch diameter) were inserted in-the tire tread in each outside groove and ~ of-the center tread grooves. Each nail was deflec-ted 45 in-t~o opposite directions for 1 minute, the nails were remDved, and the -tire was inflated to 32 psig and tested for leakage. The same procedures were then followed except that the tire was inflated prior to puncturing. Air leaks occuring at any time during this tes-t procedure were recorded.
The dynamometer -test is perhaps -the most comprehensive -test of tire sealant performance, because it simulates actual driving conditions. The test was carried out on a dynamometer comprising a pivot arm having means for rotatably mounting a tire, movable contact means underlying the tire for contacting the tire tread and causing the tire to rotate, and loading means for forcing the pivot arms downward such that -the tire is loaded at a predetermined amount against the contact means.
The tests were conducted at loads equivalent to 100% of the tires' rated loads.
After being coated with sealan-t as described above and mounted in the dynamometer, -the tires were inflated to 24 psi and broken in for two hours at a rotation rate equivalent to 55 mph. The pressure was then adjusted to 30 psi, and eight nails were ~21-inserted as in the stati~c punc-ture test except using 16 penny (.1~5 inch diameter) rather than 20 penny nails. The tire was then run ayain a-t 55 mph for ten -thousand miles or until the pressure dropped below 20 psi, at which point the responsible nail was determined, ~he nail~pulled and patched if necessary, and the tes-t resumed after adjusting -the pressure back to 30 psi.
In the blow through -test an insignificant amount of sealant was extruded at the holes at ambient -temperatures, an average of 1/8 inch extruded a-t 18()F, and an average of 1/~
inch extruded at 220F. In no cases did -the tire lose a measurable amount of air. These test results were good and indicate that the sealant of composition A possesses adequate tensile strength to function as a vehicle -tire sealan-t.
In the static puncture -test the composition sealed an average of 89% of the puncture holes without significant air leakage. Table II gives a detailed breakdown:
TABLE II
Temperature .115 inches 93% 97% 93%
Nail Diameter 180 inches 83% 90% 77~
These results show good puncture sealing performance, and demonstrate that the sealant posesses sufficient elongation and sufficiently low cross-link density to enable it to adhere to a puncturiny object even when the object is flexed back and forth through an arc of 90.
In the dynamometer test, -the average distance logged by a 16 penny nail before leakage occurred was ~100 miles, and the average distance for an 8 penny nail was 8500 miles. These dis-tances are a significant fraction of the lifetime of an average tire. Furthermore, the dynamome-ter test as conducted herein represents conditions which are harsher than those encountered in average driving, since the test is run at 100%
:
of a -tire's rated load. These average mileayes, -therefore, represen-t excellent all-around sealant performance.
EXA~IPLE I :r Laboratory specimens of composition A were formula-ted as in Example I except that 4.5 phr of p-quinone dioxime and 16.5 phr of benzoyl peroxide were used. The resulting sealant has a tensile strength of 37 psi, an elongation of 804~, and a swell ratio of 16.2. Increasing the amount of cross-lin]cing agent as expected increased the cross-link density (decreased the swell ratio) but also decreased the elongation to -the lower edge of the most preferred range..
EXA~lPLE III
Tire sealants were prepared as in Example I for both labora-tory and on-the-tire testing according to the formula of composi-tion B above. Toluene was substituted for hexane to facilitate solvation of the block copolymer. The tensile strength, elongation and swell ratios were found to be 34 psi, 987~ and 17.83 respectively. In the blow through test, 1/2 inch extruded at 180F, whereas at 220F a leak occurred. These results indicate that the tensile strength of the sealant is near its lower preferred value. In the static puncture test, an average of 98~ of all punc-tures were successfully sealed, . indicating tha-t the sealant- had good elongation and a cross-link density that was not too hiyh. On the dynamometer, the average mileage for 16 and 8 penny nails was 3200 and 6000 miles respectively.
EXA~SPLE IV
Laboratory specimens of composition B were formulated as in Example III except that 5.0 phr of p-quinone dioxime and 15.0 phr of benzoyl peroxide were used. The tensile strength, elongation and swell ratio were found to be 27 psi, 627~ and 13.89 respectively. As in Example II, increasi.ng the amount of cross-linking agent increased the cross-link density, bu-t the tensile s-trength and elongation were simultaneously moved out of their preferred ranges. The low -tenslle s-trength of cornposition B is in general due to the compara-tively low amount of butyl ruhber present (13%). Examples III and IV indicate below this level of bu-tyl rubber, it will be difficul-t to compensa-te for the low rubber conten-t by increas~
- ing the cross-lin]c density while a-t -the same -time retainlng the tensile s-treng-th and elonga-tion in -the preferred ranges.
E,~AMPI,I, V
A -tire sealan-t for laboratory analysis was prepared as in Example III according to the formula of composition C
above. The -tensile strength, elongation and swell ra-tio were 71 psi, 538% and 12.71 respectively. These resul-ts indicate that -the sealant is too inflexible to provide op-timum vehicle tire performance, although it would perform sa-tisfactorily in other, less severe environments. Xesults also indica-te -that at the level of 20% butyl rubber using a quinoid curing system, an appreciable amount of adjusting of other fac-tors will be required to bring- the sealan-t proper-ties within their preferred ranges.
EX~PLE VI
; Tire sealants were prepared as in Example I for both laboratory and on--the-tire testing according to the formula of composi-tion D above. The tensile strength, elongation and swell ratio were found to be G7 psi, 670% and 11.36 respectively.
The elongation has improved as compared to ~xample V, bu-t -the elongation is s-till outside the mos-t preferred range. ~ s-ta-tic puncture tes-t was performed on this composition, and results are indicated in Table III with an average of 6~% of the punctures being sealed successfully.
~2~-T~LE III
Temperature 115_inches 53% 60% ~7 Nail Diameter 1~0 incnes 60% ~0% 87%
As expected based on the elongation test, the composi-tion had the least difficulty sealing punctures at elevated temperatures.
EX~IPLE VII
Laboratory specimens o:E composition D were formula-ted as in Exarnple VI except tha-t 2.0 phr of p-quinone dioxime and 6.0 phr of benzoyl peroxide were used. The resulting sealant had a tensile strength of 68 psi, an elongation of 824%
and a swell ratio of 13.29. Decreasing the amount of cross linking agent has as expected increased the swell ratio and has also increased the elongation to within the most p~e.ferred range. This example illustrates that in general for quinoid cured compositions having a comparatively larger amo.unt of butyl rubber a preferred sealant may in rnany cases be achieved by reducing the cross-link density until adequate elongations are produced.
EXA~IPLE VIII
A tire sealant for laboratory analysis was prepared as in Example III according to the formula of composition E
above. The tensile strength, elongation and swell ratio were found to be 14 psi, 754% and 17.69 respectively. The low tensile strength is principally due to the low amount of bu-t~l rubber (10%~ present.
EXA~lPLE IX
Laboratory specimens of composition E were formulated as in Example VIII except that 5.0 phr of p-quinone dioxime and 15.0 phr of benzoyl peroxide were used. The resulting sealant had a tensile strength of 16 psi, an elongation of 500% and a swell ra-tio of 12.~. Increasing the amoun-t of cross-linking agent has red-uced the swell ratio but has failed by a large margin to increase the tensile strength to within the preferred range. Further the elongation has been decreased.
This exarnple illustra-tes tha-t i-t will be difficult to Eormulate a preferred vehlcle tire sealan-t using only 10% butyl rubber.
However such sealants may well have uses in other applications, Eor example as bicycle tire sealan-ts, caulking compounds and the like.
- EX~PLE X
Tire sealants for both laboratory and on-the-tire analysis were prepared using the formula of composition F above.
The tensile strength, elongation and swell ra-tio of the labora-tory sample were found to be 51 psi, 1850% and 38.05 respectively.
Results of the dynamometer test were average mileage o~ 3800 miles. However inspection of the tire interiors during the test indicated tha-t flow of sealant had taken place. Such flow is attributable to the comparatively low cross-link density of this sealant. The most preferred sealants are those having swell ratios from 12-35.
EX~lPLE XI
Tire sealants were prepared as in ~xample X except that 1.2 phr of p-quinone dioxime and 3.6 phr of benzoyl perox-ide were used. The tensile strength, elonga-tion and swell ratio of the sealant were 91 psi, 986% and 16.68 respectively.
Increasing the amount of cross-linking agent has increased the tensile strength considerably and has reduced the swell ratio to within the preferred range. Dynamometer tests indicated no flow of this sealant. In general, cross-link density (e.g. swell ratio) will be more sensitive to the amount of cross-linker present in compositions such as composition F
which include only small amounts of carbon black. Examples X and XI illustrate that a preferred tire sealan-t can be -2~-r~
formed by using 35~ butyl rubber and a quinoid curing sys-tem if the amoun-t of cross-linkiny agent and carbon black are sharply reduced. At paraquinone dioxime levels of less than abou-t 2.0 phr, however, the gel time of the sealant becomes quite long. This can be a critical factor in large scale spray application processes, in which the sprayed -tires must be kept in the application apparatus and rota-ting until the sealant has gelled sufficiently to permit handling wi-thout flow. It has been found that a gel time of abou-t 10 minutes at 150F will permit a reasonable sealan-t application rate The gel time of the sealants of Examples X and XI were 22 minutes and 12 minutes respectively a-t 150F. These -times could be reduced by increasing the amount of p-quinone dioxime used, but as indicated by these examples the result migh-t well be to reduce the elongation outside the preferred range.
EX~PI,E XII
Tire sealants for both laboratory and on-the-tire analyses were prepared as in Example I using the formula of composition G above. The tensile strength, elongation and swell ratio of the laboratory samples were found -to be 80 psi, 1197% and 17.54 respectively. The dynamometer -tests indicated an average mileage of 3100 miles and no perceptible sealant flow. This example, -together wi-th Example XI, illustrates that reducing the mole percent unsaturation of the bu-tyl rubber produces an effect which is opposite to and may partially cancel an increase in the amount of butyl rubber present.
EX~IPI,E XIII
Tire sealants for laboratory analysis were prepared in a manner similar to that of Example I using -the formula of composition II above. The first component is prepared without the p-quinone dioxime ancl 6 parts by weight of -the CRJ-328 are dispersed in 1 part of toluene to form the second , ~
componen-t. The tensile strength, elonga-tion and s~lell ratio of the lahoratory samples were found to be 56 psi, 1790% and 31.14 respectively. This example illustra-tes tha-t preferred tire sealants can readily be prepared usiny phenolic resin curing systems.
EXAMPLE X:[V
Laboratory specimens oE composition H were prepared as in Example XIII, excep-t that 20 phr of the C~J-328 curing agent were used. The tensile strength, elongation and swell ratio were 44 psi, 1191% and 18.07 respectively. As expected, increasing the amount of curing agen-t has decreased the elonga-tion and the swell ratio, but their values are still wi-thin the preferred ranges.
EX~PLE XV
Labora-tory specimens of composition I-I were prepared as in Example XIV, except that 10 phr of the CRJ-323 curing agent were used. The tensile strength, elongation and swell ratio were 44 psi, 2875% and 35.71 respectively. Decreasing the amount of curing agent used has increased the elongation and swell ratio to such an extent that the ]atter is no longer within its most preferred range of 12-35. The swell ratio is less than 40, however, and this composition will perform acceptably as a vehicle tire sealant.
It will be understood that the invention may be embodied in other specific forms without departing from the spirit oE central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not res-trictive, and the invention is not to be lirnited to the details thereof bu-t may be modified within the scope of the appended claims.
-2~-
33~
A polybutene having an average m~lecular weight o:E 920 avai.lable from AIIOCO under the -trademark "H-100".
~ 6 A polybutene having an average molecular .~ wei~ht of 1290 available from~lOCO under -the trademark "H-300".
7 A polybutene having an average molecular weight of 2300 available from A~OCO under the trade-mark "II-1900".
8 A hydrocarbon resin having a softening point of 97C available from ~lercules, Inc. wnder the trademark "Piccotac B".
9 A2furnace black having a surface area of 235 m /gm, arithmetic mean:particle diame-ter of 17 millimicrons and a p~l of 6.0 - 9.0 avail-: able from Cities Servlce Oil Company under the trademark "Raven-2000".
A block copolymer having a configuration A-(B-A)1_5, A representing a polystyrene block a~d B representing a hydrogenated polyisoprene block, the isoprene making up about two thirds of the compound by weight, and the average molecular weight being between 70,000 and 150,000. The compound is available from the Shell Oil Company under the trade-mark 17 Kraton G-6500".
11 In parts ~er 100 parts of butyl rubber.
12 A dibrome-thyl octyl phenol having a number average molecular weight of 500 and a bromine content of 2~ - 31~, available from Schenec-tady Chemicals, Inc. under the trademark "CJR-32~".
EX~lPLE I
A -tire sealant was prepared according to the formula of composition A above. The butyl rubber, Vistanex, and Piccotac were solvated and blended in hexane so that the mixture contained about 50~ solids by weight. The carhon black and the:pol.ybutenes were:then;~added to the.pre.vious1y:solvated mixturei The - p-quinone.. dioxime-w.as then.blended in.~cyclohexanone to a:.::.. m diLution:o.f;.about 4.0~ solidsl~by.~Jeigh-t~, added to -the mixtùre,:...~;
and;dis~persed therein to ~orm a~:first component co~prising- - ;
abou.t.~73~ so.lids ~y.wei.g.ht. lThis-c~mponent has been found to have a~s:helf life o.f greater.tha~:six:.mon:ths.
. For a laboratory analysis, a second cornponent was formed by dissolving the benzoyl peroxide in -toluene to a dilution of abou-t 3% solids. First and second components were then cornbined, poured into molds, and then cured for 24 hours at ambien-t temperature, followed by 24 hours at 150F
and 4 hours at 190F. Specimens of -the sealant were then tested to determine tensile strength, elongation and swell ratio.
Tensile strengths for this sealant were found to lie in the range of 35 - 45 psi, elongations were in -t:he range of 967 - 998%, and swell ratios were in the range 17.9 - 18.5.
New JR-78-lS s-teel bel-ted radial tires were utilized for evaluating the sealant composition on a tire.
The tires were first cleaned by scrubbing their interior sur-faces wi-th a wire brush and soap solution. The surfaces were then rinsed and dried. A first component as described above was prepared and a second component was prepared by dissolving the benzoyl peroxide in methylene chlori~e such that the resultant solution was about 16~ solids. The first component was then pre-heated to 260F, combined with the second component to yield a mixture having about 6~% solids, and sprayed at about 500 psig onto the interior surface of a rotating tire. The temperature of the first and second components after mixing was about 210F.
1200 grams of sealant on a solvent free basis were sprayed onto each tire, the resulting sealant layer being between 0 2 and 0.25 inches thick under the central portion of the tread and 0.15 inches thick at the tire shoulder. After spraying, the tires were continually rotated for about ten minutes until the sealant had cured sufficiently to resis-t flow. The -tires were -then unloaded from the applicator apparatus and placed in an oven at 140F - 150F for 30 minutes.
The coated tires were subjected to a series of tests to evaluate the "on the-tire" effectiveness of the sealan-t.
These tests included a blow through -test, a s-tatic puncture test, and a dynamometer -test. The blow through test was con-duc-ted by drilling six holes in the tire (2 at .14 inch diameter, 2 a-t .187 inch diameter, and 2 a-t .203 inch diame-ter) and plugging the holes with modeling clay prior to sealan-t application. Af-ter application the pluys were remo~ed from -the outside, and the tire was inflated to 32 psig at ambient, 42 psig at 180F, and 46 psig at 220F. The sealan-t was considered acceptable if less than about 1/2 inch of sealant extruded through any hole, and if no loss of air from the tire was detected.
The s-tatic puncture -test was run at three different tempera-tures: -20F; 70F; and 180F. At each temperature, an 8 penny nail (.115 inch diameter) and a 20 penny nail (.180 inch diameter) were inserted in-the tire tread in each outside groove and ~ of-the center tread grooves. Each nail was deflec-ted 45 in-t~o opposite directions for 1 minute, the nails were remDved, and the -tire was inflated to 32 psig and tested for leakage. The same procedures were then followed except that the tire was inflated prior to puncturing. Air leaks occuring at any time during this tes-t procedure were recorded.
The dynamometer -test is perhaps -the most comprehensive -test of tire sealant performance, because it simulates actual driving conditions. The test was carried out on a dynamometer comprising a pivot arm having means for rotatably mounting a tire, movable contact means underlying the tire for contacting the tire tread and causing the tire to rotate, and loading means for forcing the pivot arms downward such that -the tire is loaded at a predetermined amount against the contact means.
The tests were conducted at loads equivalent to 100% of the tires' rated loads.
After being coated with sealan-t as described above and mounted in the dynamometer, -the tires were inflated to 24 psi and broken in for two hours at a rotation rate equivalent to 55 mph. The pressure was then adjusted to 30 psi, and eight nails were ~21-inserted as in the stati~c punc-ture test except using 16 penny (.1~5 inch diameter) rather than 20 penny nails. The tire was then run ayain a-t 55 mph for ten -thousand miles or until the pressure dropped below 20 psi, at which point the responsible nail was determined, ~he nail~pulled and patched if necessary, and the tes-t resumed after adjusting -the pressure back to 30 psi.
In the blow through -test an insignificant amount of sealant was extruded at the holes at ambient -temperatures, an average of 1/8 inch extruded a-t 18()F, and an average of 1/~
inch extruded at 220F. In no cases did -the tire lose a measurable amount of air. These test results were good and indicate that the sealant of composition A possesses adequate tensile strength to function as a vehicle -tire sealan-t.
In the static puncture -test the composition sealed an average of 89% of the puncture holes without significant air leakage. Table II gives a detailed breakdown:
TABLE II
Temperature .115 inches 93% 97% 93%
Nail Diameter 180 inches 83% 90% 77~
These results show good puncture sealing performance, and demonstrate that the sealant posesses sufficient elongation and sufficiently low cross-link density to enable it to adhere to a puncturiny object even when the object is flexed back and forth through an arc of 90.
In the dynamometer test, -the average distance logged by a 16 penny nail before leakage occurred was ~100 miles, and the average distance for an 8 penny nail was 8500 miles. These dis-tances are a significant fraction of the lifetime of an average tire. Furthermore, the dynamome-ter test as conducted herein represents conditions which are harsher than those encountered in average driving, since the test is run at 100%
:
of a -tire's rated load. These average mileayes, -therefore, represen-t excellent all-around sealant performance.
EXA~IPLE I :r Laboratory specimens of composition A were formula-ted as in Example I except that 4.5 phr of p-quinone dioxime and 16.5 phr of benzoyl peroxide were used. The resulting sealant has a tensile strength of 37 psi, an elongation of 804~, and a swell ratio of 16.2. Increasing the amount of cross-lin]cing agent as expected increased the cross-link density (decreased the swell ratio) but also decreased the elongation to -the lower edge of the most preferred range..
EXA~lPLE III
Tire sealants were prepared as in Example I for both labora-tory and on-the-tire testing according to the formula of composi-tion B above. Toluene was substituted for hexane to facilitate solvation of the block copolymer. The tensile strength, elongation and swell ratios were found to be 34 psi, 987~ and 17.83 respectively. In the blow through test, 1/2 inch extruded at 180F, whereas at 220F a leak occurred. These results indicate that the tensile strength of the sealant is near its lower preferred value. In the static puncture test, an average of 98~ of all punc-tures were successfully sealed, . indicating tha-t the sealant- had good elongation and a cross-link density that was not too hiyh. On the dynamometer, the average mileage for 16 and 8 penny nails was 3200 and 6000 miles respectively.
EXA~SPLE IV
Laboratory specimens of composition B were formulated as in Example III except that 5.0 phr of p-quinone dioxime and 15.0 phr of benzoyl peroxide were used. The tensile strength, elongation and swell ratio were found to be 27 psi, 627~ and 13.89 respectively. As in Example II, increasi.ng the amount of cross-linking agent increased the cross-link density, bu-t the tensile s-trength and elongation were simultaneously moved out of their preferred ranges. The low -tenslle s-trength of cornposition B is in general due to the compara-tively low amount of butyl ruhber present (13%). Examples III and IV indicate below this level of bu-tyl rubber, it will be difficul-t to compensa-te for the low rubber conten-t by increas~
- ing the cross-lin]c density while a-t -the same -time retainlng the tensile s-treng-th and elonga-tion in -the preferred ranges.
E,~AMPI,I, V
A -tire sealan-t for laboratory analysis was prepared as in Example III according to the formula of composition C
above. The -tensile strength, elongation and swell ra-tio were 71 psi, 538% and 12.71 respectively. These resul-ts indicate that -the sealant is too inflexible to provide op-timum vehicle tire performance, although it would perform sa-tisfactorily in other, less severe environments. Xesults also indica-te -that at the level of 20% butyl rubber using a quinoid curing system, an appreciable amount of adjusting of other fac-tors will be required to bring- the sealan-t proper-ties within their preferred ranges.
EX~PLE VI
; Tire sealants were prepared as in Example I for both laboratory and on--the-tire testing according to the formula of composi-tion D above. The tensile strength, elongation and swell ratio were found to be G7 psi, 670% and 11.36 respectively.
The elongation has improved as compared to ~xample V, bu-t -the elongation is s-till outside the mos-t preferred range. ~ s-ta-tic puncture tes-t was performed on this composition, and results are indicated in Table III with an average of 6~% of the punctures being sealed successfully.
~2~-T~LE III
Temperature 115_inches 53% 60% ~7 Nail Diameter 1~0 incnes 60% ~0% 87%
As expected based on the elongation test, the composi-tion had the least difficulty sealing punctures at elevated temperatures.
EX~IPLE VII
Laboratory specimens o:E composition D were formula-ted as in Exarnple VI except tha-t 2.0 phr of p-quinone dioxime and 6.0 phr of benzoyl peroxide were used. The resulting sealant had a tensile strength of 68 psi, an elongation of 824%
and a swell ratio of 13.29. Decreasing the amount of cross linking agent has as expected increased the swell ratio and has also increased the elongation to within the most p~e.ferred range. This example illustrates that in general for quinoid cured compositions having a comparatively larger amo.unt of butyl rubber a preferred sealant may in rnany cases be achieved by reducing the cross-link density until adequate elongations are produced.
EXA~IPLE VIII
A tire sealant for laboratory analysis was prepared as in Example III according to the formula of composition E
above. The tensile strength, elongation and swell ratio were found to be 14 psi, 754% and 17.69 respectively. The low tensile strength is principally due to the low amount of bu-t~l rubber (10%~ present.
EXA~lPLE IX
Laboratory specimens of composition E were formulated as in Example VIII except that 5.0 phr of p-quinone dioxime and 15.0 phr of benzoyl peroxide were used. The resulting sealant had a tensile strength of 16 psi, an elongation of 500% and a swell ra-tio of 12.~. Increasing the amoun-t of cross-linking agent has red-uced the swell ratio but has failed by a large margin to increase the tensile strength to within the preferred range. Further the elongation has been decreased.
This exarnple illustra-tes tha-t i-t will be difficult to Eormulate a preferred vehlcle tire sealan-t using only 10% butyl rubber.
However such sealants may well have uses in other applications, Eor example as bicycle tire sealan-ts, caulking compounds and the like.
- EX~PLE X
Tire sealants for both laboratory and on-the-tire analysis were prepared using the formula of composition F above.
The tensile strength, elongation and swell ra-tio of the labora-tory sample were found to be 51 psi, 1850% and 38.05 respectively.
Results of the dynamometer test were average mileage o~ 3800 miles. However inspection of the tire interiors during the test indicated tha-t flow of sealant had taken place. Such flow is attributable to the comparatively low cross-link density of this sealant. The most preferred sealants are those having swell ratios from 12-35.
EX~lPLE XI
Tire sealants were prepared as in ~xample X except that 1.2 phr of p-quinone dioxime and 3.6 phr of benzoyl perox-ide were used. The tensile strength, elonga-tion and swell ratio of the sealant were 91 psi, 986% and 16.68 respectively.
Increasing the amount of cross-linking agent has increased the tensile strength considerably and has reduced the swell ratio to within the preferred range. Dynamometer tests indicated no flow of this sealant. In general, cross-link density (e.g. swell ratio) will be more sensitive to the amount of cross-linker present in compositions such as composition F
which include only small amounts of carbon black. Examples X and XI illustrate that a preferred tire sealan-t can be -2~-r~
formed by using 35~ butyl rubber and a quinoid curing sys-tem if the amoun-t of cross-linkiny agent and carbon black are sharply reduced. At paraquinone dioxime levels of less than abou-t 2.0 phr, however, the gel time of the sealant becomes quite long. This can be a critical factor in large scale spray application processes, in which the sprayed -tires must be kept in the application apparatus and rota-ting until the sealant has gelled sufficiently to permit handling wi-thout flow. It has been found that a gel time of abou-t 10 minutes at 150F will permit a reasonable sealan-t application rate The gel time of the sealants of Examples X and XI were 22 minutes and 12 minutes respectively a-t 150F. These -times could be reduced by increasing the amount of p-quinone dioxime used, but as indicated by these examples the result migh-t well be to reduce the elongation outside the preferred range.
EX~PI,E XII
Tire sealants for both laboratory and on-the-tire analyses were prepared as in Example I using the formula of composition G above. The tensile strength, elongation and swell ratio of the laboratory samples were found -to be 80 psi, 1197% and 17.54 respectively. The dynamometer -tests indicated an average mileage of 3100 miles and no perceptible sealant flow. This example, -together wi-th Example XI, illustrates that reducing the mole percent unsaturation of the bu-tyl rubber produces an effect which is opposite to and may partially cancel an increase in the amount of butyl rubber present.
EX~IPI,E XIII
Tire sealants for laboratory analysis were prepared in a manner similar to that of Example I using -the formula of composition II above. The first component is prepared without the p-quinone dioxime ancl 6 parts by weight of -the CRJ-328 are dispersed in 1 part of toluene to form the second , ~
componen-t. The tensile strength, elonga-tion and s~lell ratio of the lahoratory samples were found to be 56 psi, 1790% and 31.14 respectively. This example illustra-tes tha-t preferred tire sealants can readily be prepared usiny phenolic resin curing systems.
EXAMPLE X:[V
Laboratory specimens oE composition H were prepared as in Example XIII, excep-t that 20 phr of the C~J-328 curing agent were used. The tensile strength, elongation and swell ratio were 44 psi, 1191% and 18.07 respectively. As expected, increasing the amount of curing agen-t has decreased the elonga-tion and the swell ratio, but their values are still wi-thin the preferred ranges.
EX~PLE XV
Labora-tory specimens of composition I-I were prepared as in Example XIV, except that 10 phr of the CRJ-323 curing agent were used. The tensile strength, elongation and swell ratio were 44 psi, 2875% and 35.71 respectively. Decreasing the amount of curing agent used has increased the elongation and swell ratio to such an extent that the ]atter is no longer within its most preferred range of 12-35. The swell ratio is less than 40, however, and this composition will perform acceptably as a vehicle tire sealant.
It will be understood that the invention may be embodied in other specific forms without departing from the spirit oE central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not res-trictive, and the invention is not to be lirnited to the details thereof bu-t may be modified within the scope of the appended claims.
-2~-
Claims (17)
1. A butyl rubber based sealant composition, the butyl rubber constituent of which is present only in the form of a copolymer having a viscosity aveerage molecular weight in excess of 100,000, comprising the reaction product of said butyl rubber, a curing system including a cross-linking agent selected from the group consisting of at least 2 parts by weight of a quinoid cross-linking agent per hundred parts butyl rubber, and at least one tackifier compatible with butyl rubber, and a filler material, the composition being compounded such that it has a tensile strength of at least 30 psi, an elongation of at least 600% and a cross-link density such that its swell ratio in toluene is between 12 and 40.
2. The sealant composition of claim 1 wherein the curing agent comprises a quinoid cross-linking agent and wherein the butyl rubber comprises about 13-40% by weight of the composition excluding cross-linking agent and activator and wherein said filler material includes at least 2 parts carbon black per hundred parts butyl rubber.
3. The sealant composition of claim 2 wherein the quinoid curing agent is p-quinone dioxime and wherein the curing system further includes at least parts by weight benzoyl peroxide per hundred parts butyl rubber.
4. The sealant composition of claim 1 wherein the butyl rubber comprises 13-50% of the composition exclusive of the curing system, wherein the curing system comprises a phenolic resin cross-linking agent and wherein said filler material composition includes at least 3 parts zinc oxide per hundred parts butyl rubber.
5. The sealant composition of claim 1 further comprising a filler material composed of at least one of the group consisting of carbon black, zinc oxide, aluminum hydrate, lithapone, whiting, clays, hydrated silicas, calcium silicate, silicoaluminates, magnesium oxide and magnesium carbonate.
6. The sealant composition of claim 1, said consti-tuents being chosen such that the elongation is sufficiently high and the cross-link density is sufficiently low that, when the sealant is applied to the interior of a tire, the tire is punctured by a plurality of nails which are repeatedly deflect-ed for a period of one minute and then withdrawn, and the tire is inflated to 32 psig, the sealant seals at least 80% of the punctures.
7. A butyl rubber based sealant composition, the butyl rubber constituent of which is present in the form of a copolymer having a viscosity in the form of a copolymer having a viscosity average molecular weight in excess of 100,000, comprising the reaction product of said butyl rubber, a curing system for said butyl rubber, a tackifier compatible with said butyl rubber and filler material composed of at least one of the group consisting of carbon black, zinc oxide, aluminum hydrate, lithopone, whiting, clays; hydrated slicas, calcium silicate, silicoaluminates, magnesium oxide and magnesium carbonate, the composition being compounded suc that it has a tensile strength of at least 30 psi, an elongation of at least 600% and a cross-linking density such that its swell ratio in toluene is between 12 and 40.
8. The sealant composition of claim 7 wherein said sealant composition is compounded such that it has an elonga-tion of at least 800% and a cross-link density such that its swell ratio in toluene is between 12 and 35.
9. The sealant of claim 8 wherein the composition is compounded such that when the tire is punctured by a plur-ality of nails which are repeatedly deflected for a period of one minute and then witdrawn and the tire is inflated to 32 psig, the sealant seals at least 80% of the punctures.
10. The sealant of claim 9 wherein the curing system comprises at least two parts of a quinoid cross-linking agent per hundred parts butyl rubber and an activator for said cross-linking agent, and wherein said filler material includes at least two parts carbon black per hundred parts of butyl rubber.
11. The sealant composition of claim 10 wherein the butyl rubber comprises 13-40% of the composition exclusive of the curing system.
12. The sealant composition of claim 9 wherein the curing system comprises at least 5 phr of a phenolic resin cross-linking agent per hundred parts butyl rubber and wherein said filler material includes at least 3 parts zinc oxide per hundred parts butyl rubber.
13. The sealant composition of claim 10 wherein the butyl rubber comprises 13-50% of the composition exclusive of the curing system.
14. A butyl rubber based sealant composition the butyl rubber constituent of which is present only in the form of a copolymer having a viscosity average molecular weight in excess of 100,000 comprising the reaction product of said butyl rubber, a quinoid cross-linking agent for the butyl rubber, a cross-linking activator at least one tackifier compatible with butyl rubber and a filler material, said filler material in-cluding at least 2 parts by weight of carbon black per hundred parts butyl rubber, the composition being compounded such that it has a tensile strength of at least 30 psi, an elongation of at least 600% and a cross-link density such that its swell ratio in toluene is between 12 and 40 and such that the elonga-tion is sufficiently high and the cross-link density suffi-ciently low that, when the sealant is applied to the interior of a tire, the tire is punctured by a plurality of nails which are repeatedly deflected for a period of one minute and then withdrawn, and the tire is inflated to 32 psig, the sealant seals at least 80% of the punctures.
15. The sealant composition of claim 14 wherein said quinoid cross-linking agent is present in an amount not less than 2 parts by weight per hundred parts butyl rubber, and wherein said butyl rubber comprises 13-40% by weight of the sealant composition exclusive of the cross-linking agent and activator.
16. The sealant composition of claim 15 wherein said filler material is composed of at least one of the group con-sisting of carbon black, zinc oxide, aluminum hydrate, litho-pane, whiting, clays, hydrated silicas, calcium silicate, silicaaluminates magnesium oxide and magnesium carbonate.
17. The sealant composition of claim 1 or 16 wherein said sealant composition is compounded such that it has an elongation of at least 800% and a cross-link density such that its swell ratio in toluene is between 12 and 35.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000358251A CA1168396A (en) | 1980-08-14 | 1980-08-14 | Sealant composition |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000358251A CA1168396A (en) | 1980-08-14 | 1980-08-14 | Sealant composition |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168396A true CA1168396A (en) | 1984-05-29 |
Family
ID=4117651
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000358251A Expired CA1168396A (en) | 1980-08-14 | 1980-08-14 | Sealant composition |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1168396A (en) |
-
1980
- 1980-08-14 CA CA000358251A patent/CA1168396A/en not_active Expired
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