CA1100401A

CA1100401A - Sealant laminates

Info

Publication number: CA1100401A
Application number: CA284,676A
Authority: CA
Inventors: Georg G. A. Bohm; John N. Anderson
Original assignee: Firestone Tire and Rubber Co
Current assignee: Bridgestone Firestone Inc
Priority date: 1976-08-20
Filing date: 1977-08-12
Publication date: 1981-05-05
Also published as: GB1559939A; DE2737368A1; DE2737368C2; FR2362015B1; FR2362015A1

Abstract

ABSTRACT OF THE DISCLOSURE:
This disclosure relates to a sealant laminate to be primarily used in pneumatic tires to seal punctures made by external objects, such as nails. The laminate of the invention comprises a puncture sealing layer and at least one other layer, the puncture sealing layer containing a polymeric material that has been at least partially degraded by exposure to irradiation or to heat in the presence of a peroxide to yield its sealant properties; the degraded polymeric material is selected from the group consisting of polyisobutylene, copolymers containing polyisobutylene and polyethylene oxide. The laminate may be in sheet or strip form with various cross-sectional shapes.
The layers in the laminate comprise rubber compounds, some of which may contain agents which either assist or retard cure by irradiation so that the layers will have different physical characteristics during the manufacture of end products containing the laminate. The laminate may be cured by any known method, either irradiation or thermal, after its assembly into the final product.

Description

This invention relates to a laminate composite sheet or strip of rubber compound which is made up o~ several separa-te layers of specifically designed rubber compound. The laminate may be made by any of the known methocls, such as calendering and the like; however, it is preferred that the laminate be formed by a process known as coextrusion in which two or more rubber compounds passed through the preform die to ~orm separate layers which are joined in the final die. A
recent technique for this is disclosed in U.S. Patents 3,479,425 and 3,557,265. This coextrusion process has been applied to plas-tics and thermal plastic elastomers -to form laminates -thereof.
This inven-tion :is speciEicall,y reLatecl to a laminate t:hat conta:ins a sealant layer, wherein the :La,yer corlta:ins a mater:ia.l. that ifi at least partially deyraded when exposed to irradiation or hea-t in -the presence oE a peroxide. In addition, the sealant layer may also contain a material that is partially cured by these same treatments.
In this invention the term "degrade" is used to characterize a chain scission type reac-tion in the polymer phase. The term "cure" is used to characterize a cross-linkage typc reaction in the pol,ymer phase.

- 2 - ~, .

~o~

The use of layers of sealant material in pneumatic tires to seal punctures is well known in the art' for example, see U.S. Patents 3,048,509; 3,62~,585 and 2,877,819. These teachings disclose a laminate in which the sealant layer is encased in one or more cover layers to retain the flowable, soft, sealant layer in its proper location during the service life of the -tire. Use of a sealant layer without these cover layers is also disclosed. The laminates taught by these references comprise a sealant layer of unvulcanized rubber and cover layers of rubbers that are vulcanized during the tire curing operation. The sealant layer is devoid of materials which would cause vulcaniza-tion.
Additionally, other laminated articles are known in which the separate layers comprise materials which have different properties. Such articles have been utilized in the manufacture of tires wherein a stiff, partia:L:Iy cured rubber compound has beQn sandwiched betweerl tw~ layers of soft, tacky, uncured ru~ber compouncl by caLerldering the soft :Layers onto t~e a:Lr~ady partially cured co~npound. Sl;rips oE this type 'have beon elnpLoyed in the bead area of the tire, where the tire contacts the rim, as an abrasion gum strip, to resist the chafing -that takes place between the tire and the rim.
In all laminates, an uncured rubber compound tends to flow during the curing operation, thereby decreasing its effective gauge or thickness. In the above described type of composite strip the partial precure of the stiff compound enables it to retain its gauge or thickness during the -tire curing operation, but the precure renders the strip inheren-tly dry, causing an ~d~lesion pro'blem between it and the other parts of the -tire during the building and curing operation. The ex-ternal layers of the soft, -tacky, uncured rubber compound in the laminate help to overcome this deficiency and provide the necessary uncured adhesion so that the composi-te strip will not separate from the remaining pieces of the tire prior to its final cure.
However, there is still an adhesion problem because layers (-the external layers) are being adhered to a partially cured layer.
Additionally, all of these prior composite strips have been difficult and expensive to manufacture. The process has been to calender the inr.er, stiff strip, subject it to a curing

-3-';~

4C~

operation in which it is partially cured, and then calender the soft, tacky strips on both sides of the then stiff strip to form the final composite laminate. With the sealant type laminates, the soft, uncured layer is calendered onto the soft cover layersO These operations have ~een e~pensive and time consuming in the past and involve several stepsO Due to the limitations of the calendering operation, it has also necessitated the use of thicker strips for an adequate safety margin than are necessary to perform the functions in t~.e final produc:t.
The product of -this invention has greatly simplified and improved the composite strip -technology thereby enabling the use of multilayer composite strips in pneumatic tires as the air impervious liner which covers the inner periphery of the tire. ~

" /

, .. _ . .. . . . . .. .

_~_ ;~',

4~

In prior sealant laminates where ths material is a fluid or semi-fluid great difficulty has been encountered in ¦ ~he marlu.facturing operation- l'he fluid or semi-fluid nature 1 of ~he material result;s in inherent processing dif~iculties

5 ¦ in trying to obtain thi.s ~aterial i~ a workable form and retain . I it in this forrn until th~ final product is finished. ~e .
present inventiorl eliminates these drawbacks. In the present .
i~vention the material is in a solid, workable form durin~
. ¦ the initial manufacture; that is, the construction of the ¦ lamirlat;~~ In the radi.ati.on cure system the material retains ¦ its soli.d cha~act~r until the i.~radiatiorl ~tep ~/here :it attain~
¦ i~, flu:icl or ';C~ rltl:kl Char~lCt¢X~ `li.S CIOe; not oc~ur urltil .
¦ af~er the lami.~ate ha.s bee~n con~;t;ruct;ecl ancl the~ flui.d laye ¦ is surroundeà by solid m~terial 1;hat remaills solid. In ths 15 ¦ peroxide ~ystem the mate~ial retains i.ts solid condition ~til the final curing operation in the marluflcture of the product, such ~s the pne~atic tlre.
.he techIlolog~ and in~entiorl of thi~ applica-tion. are not limi.ted to thi.s place lrl a p~eumati.c,t.ire. ~he technolo~y m~y be ap~lied to ~ny of ~ver~l end prodllct~, su~h as conveyo~
~elt.~, containers and in~ust~ial product,sO .
~ he product of the inve~tion is paxticularly useful whs-~ e it is necessary to have one material retain a certain thick~ess iu the end product. This has usually been accomplished in the past by using an excess a~oun-t of material -to insure ths mini~ a is present in the final product after it has thinned out in the processing s-teps. Ths prior partial pre-cure method, although a help, stlll nad this defici.ency because only a ~
partial cure could be obtained; a full cure w~uld hav~ rendered ~0 the cure~ _tock unusable due to its poor a~hesi.on~

. r~ - .
I , ''.

~ :
This invention provides an improved laminate by ~;e~lectively altering some of the layers in the lamir.ate so . ~ .
that thS3 layers will either be uneffec1,ed 1 paxtially cur~d, lully cured, partiall~ d~raded or ful~y de~raded wherl subjected ..
to irxadiation or heat in the presenc e of a peroxl~e D
- This technique eliminates at least one of the steps necessa~- iIl the prior processes, In th~s technique, the cumposil,e strip i.s obtairle(l by calendering or, preferably~
by coes:trv;sionD l~1e rubber co~pou.nds i.n the va:cious layers lO ~ay be ~,electively either se~sitizecl or deseIIsitiz.ecl to react t;o ir~aclia-~;ion in variou.s. cle~:r~e~D Th~ c,ompc)s:it~ ~ltrip is th~ ject~:d 1:;o irrad1.at;io~ rh~Ie~ l;h~: ~.;clns:~.'JiY.~cl :I.a~e~
ox~ e~ 3 I~r~ i.all y c u~ed. c~r fUIly cux~d and. l;h~ d~se~ izcd lrly~r o c layers are uI1crfecte(l. t)n~ of t:hc~ layers also conl;ains a materi.al that ~,ril] dee;rade on exposure to irradiati.on or a ~ .
blelld of a degcadable material a.~d a cross linkable materlal~ The ~egradation and cross~lin~cage may cllso be obtained by heating in the presence Or a peroxide~ This xesull;s in the differ~rlt; . .
].ay~rs in the c or~ osite h~vin~; di.î1`ererlt physical c,llalr~ct:~r;.stlcs which may be uti liY~ed i.n l;h~: u].ti.~nate m~nufact;ur:? . .
Or the ~ld ~)roduct.
. It i~; an ob~eot oî this iIIvent;ion to prc)vi(l.e a 1 a~ ate which can be rr1e~nufactuIed in a relati-vely ch~ap and uncomplicat,ed manner~ . . .
2S ~t is a fu~t;hcr object of this in~ention to provide a l~minclte i.~ ~.hich the thi.clcness of th2 separate~ laye~s is . dictated by the amount of the layer necessary ~o perform its . function and not by the prob]ems inherent in the manufactur~
of the la~inate~
. . , '.
. .' I

It is a further object of this invention to provide a sealant laminate in which one layer contains a material that will at least partially degrade when exposed to irradiation or heat in the presence of a peroxide.
In its broadest aspec-t, the present invention provides a laminate comprising a puncture sealing layer and at least one other layer, the puncture sealing layer containing a polymeric material that has been at least partially degraded by exposure to irradiation or to heat in the presence of a peroxide to yield its sealant properties; the degraded polymeric material is selected from the group consisting of polyisobutylene, copolymers containing polyisobutylene and polyethylene oxide.
The invention relates to the technology of obtaining a composite laminate of several layers of material and the res~ltillg laminate. It is known that rubber compounds may be sensitized to cure or partially cure when subjected to irradiation. Also, it is known certain materials wlll degrade when exposed to irradiation or heat in the presence of a ~peroxide. The inven-tion's utilization of these concepts is novel in that it may yield laminates with layers having sensitizing materials, l B~ ' ' I4~ :`~

layer avin~; desens it izin~; materiAls, ~nd layers hav ~ng de~ra~d~
mate~:ials. This results in ~he laminate ha~tins cure~l laye.rs, relat:ively uneured laycrs and de~;Iaded layers after it has been subject~d to irradiationv Thi.s tech:llique enables the producti3n of composite laminates ir~ which predc'c~rlllined 12.;ers have predetermi.ned physioal charac,t~istics ~hich are clesirable in the manuîactvr~ oî the ul'cima1;e end prod.uctO
For ~xample, the i~lexlinc~r in a pneumatic tir~ muC t b~ ufl ici.~l~.tly iL~pervi.ous to aix l;cJ pre~c~nt the air in t~le inf]aJGion charnber from ~.ntering inko th~ t;.ire. I* the air do~s eJ~ter ix~l;o thc t;i.rc, i.-l; ~!i.ll c~p~md dllo l;o the hea-t ~renerated clu~:i.n~!; op~rnt; i.c~n arld ~ nt;~ l,y c:a~l~3e ~ pa.x~ltioll in t;h~
~ h~ r~ , a:i.x~ r~ vi.~ t~ r ~3xalr,~)~.0, ~ . .
halo~lcnal;~d b~ yl rubbora, do ~o t ~)0~;5eS~ ~oocl builcllI16 tac k 15 1 c~ld aclhesi.on, are soft, ~nd will t;hi.n out in the hi~ll press~lre - .
areas when the tire is expanded &nd v~llcani7..ed in the I Vu ~L c E3~ g ~) I O C, e S S . , , ¦ . It :i~ nec essa~y that the innf?rl.ine~7 be sufîi.c,ient;ly I air iJnpervious and retc~ i ts (limen~;iona]. s I;~bility so that i.t 2C) ¦ wil]. rlol; 1,11i.n olll; in the.se hi~h pI~s~ re ale~.s c)f t~le t:ire y:icl~ ; a~ s~l.r.r;.~.iont l,~Iickne.s.c; to ~îfe~cl;ively ~it;o}? I;h.
nir passa~r~ t~hrol~hout the enti.le inn~l~ pe~iphery OI the tire ~;o that the mi.nimum l;hickness is mail)taiIled. in the high press~xe areas (the tre-ld shoulders) of the tixe. ~his invent:ion may - f 25 . eliminate the necessity for provicling a thick innerliner acro,ss ; the entire periphel~jr o~ the tire by proIile extrusion~ ~hen ~ this echnique is uti~lized, it is possj.ble to exh~ude e ¦
. . , ' ' ' . ,~

. ' ' ~ ' . ,~, : "

. ' . ,J'` ;
. ,. , ~", contoured innerliner in which the thickness is increased in the high pressure areas o-E the tire without an increase in the thickness in t~le low pressure areas. This results in a significant savings of rnaterial as the minimum amount of material necessary may be utilized across the en-tire periphery of the innerliner.
This invention also enables the manufacture of an innerliner in which inner layers of the laminate may be designed to give certain characteristics to t'he overall laminate and the outer layers may be designed to give building adhesion so that separations will not occur prior to -the vulcanization of the tire. This is accomplished by having one of the inner layers comprised of a halogenated butyl compound which will give the necessary air impermeability, another inner layer comprised of a polybutadiene rubber compound which provides the stiffness on exposure to irradiation so that it will maintain its dimensional integrity during the~ vulcanizatio~ operation, and an outer layer on both sides comprised Oe a nat:ura:l rubber cornpound having suEEicient tac'k ko adhexe to t'he contiguous components of the tire and to i~sele in th0 spLice area of thQ
innerliner~ The two inner layers may be sensitized to cross~
link or cure on exposure to irradiation whereas the outer layers are desensitized so tha-t such irradiation treatment does not effect any tacky characteristics. This composite strip can be manufa~ured at much lower gauges than the prior art strips due to this technique, thereby saving a considerable amount of raw materials and costs.
The innerliner laminate also contains a layer of material which will have sealant properties in the end product. The la~er with sealant properties will be in a condition that permits easy processing during the manufacture of the laminate and until it is subjec-ted to the treatment which will degrade one of the materials in the laminate. This degradation results in a softening of the sealant material to a soft or semi-fluid orfluid composition. In this degradaiion process a relatively ' high molecular weight material is degraded (chaln scission) to a lower molecular weight material which is moreE~ . 'rhe degradable material will act as, and process as, a high molecular weight material until the degradation s-tep.
This degradation is obtained either by irradiation or by heat in the presence of a peroxide. One such rnaterial which _g_ ~, ' ' . .

~ ;aQ~

will degrade upon exposure to irradiation or upon ~he application of heat in the presence o a peroxide is poly-isobutylene tPIB) and its copolymers. Another such material is a polyethylene oxide. These materials are mixed with -carbon black and oil to achieve desired end properties~ Such a rubber compound will be degraded upon exposure to irradiation. ' Alternatively, a peroxide may be added to this compound so that the compound will degrade-on exposure to heat and the irradiation step eliminated.
The sealant layer may contain a blend of one of the degradable materials mentioned above and a cross-linkable material along with carbon blaclc and oil. The cross-linkable rnaterial may be any Oe the dioleE:Lrl elastomeric types, either copolymers or homopol~ners. The ratio o the degradable material to the cross-:lin]cable material in -the b:lend is within the range of 25% degradable-75% crosa linkable to 75% degradable-25% cross-linkable. Such blends may be heterogeneous or non-miscible having a continuous phaGe and a discontinuous phaseO ~he blend may also be a co-continuous mixture of the degradable and cross-linkable materials when appropriate mixing techniques are used.
If a heterogeneous blend i9 Eormed, the degradable material is contained in the discontinuous phase, as the dispersed phase, and the cross-lin]cable material for the continuous phase, as the matrix phase. It has also been found that the levels of carbon black and oil are important to processability.
rrhe physical character of the sealant layer may range from a fluid to a semi~fluid or a solid type consistencyO rrhis fluid nature is directly proportional to the amount of degradable material (low molecular weight material) present ~ 1~?~

in the layer; that is, as the amoun-t of low molecular weight material increases, the sealant layer becomes more fluid or more soft. When the sealant layer contains no high molecular weight material, i-ts final consistency, after irradiation or heat in the presence of a peroxide is -fluid or very soft in nature. When higher levels of the cross-linkable material (high molecular weight) are present, the final consistency of the sealant layer is solid in nature.
In the ratios disclosed above adhesion problems may occur between the sealant layer and o-ther layers. This type of problem is more predominant when the sealant l~yer contains higher levels oE the degradable material.
rrhe invention is not limite~ to a spccific cnd use but may be ~mployc~ in other ~nd products, such as, l:in~rs for tanks and containers Oe all types, hoses and fabric reinforce-ment for the manufacture of tanks. It is envisioned that composite laminates may be manufactured with layers of different materials dependiny upon the properties desired and the end use.
~ny of the standard, rubber curing peroxides may be utiliz~d in the peroxide system used to obtain the degradable material~ ~xamples of such peroxides are dicumyl peroxide and Varox powder which is a blend of inert filler with 50%
of 2, 5-bis (t-bu-tylperoxy) 2,5 dimethylhexane.
Several chemicals have been found usefal to accelerate, in varyin~ degrees, the cure of rubbercompounds by irradiation and several chemicals have been found useful to inhibit the cure of rubber compounds by irradiation. These promoters and retarders are classified as sensitiæing or desensitizing agents.
The type of rubber utilized in the compound is critical and dictates the type of promoter or retarder that will function.

4~

The type of promoter or retarder will vary when different type~
of rubbers are used in the compound and the amount of the~e chemicals may vary depending upon the type of rubber used or the dosage (amount) of irradiation which the rlubber compound receives~
Specifically, it has been determined that paradichloro-benzene ~PDCB) is an effective for irradiation cure in rubber compounds. It has also been determined that certain of the thiotherpolythiols are effective promoters. The specific polythiols which have been evaluated and found useful are set out in Table I. Compound 2 identified in this table was utilized in the examples which follow and is designed "TEPT"
therein.
TABLE I
POLYTHIOETHER POLYT~IIOLS DERIVED FRO~
.. , .. ..., . .. ~
TRIEN~ DITHIOL OR TRIENE-H2S POLY_ADDITIONS

COMPOUND THIOL FUNCT. IDEALIZED CHEMICAL
SH. E~UIV.~GM STRUCTURE_AND DER VATION
0050 ,r--rl-r~S ~CH2 ) 3S~ from cyclodocetriene and 1,3 propane dithiol.
2 .0082 , S~CH2CH2 r I
~ ~(C~l2cH2s}i)272 from trivinyl cyclohe~ane and H2S.
3 .0045 S/CH2CH2 ( CH2 C~2 S ( C~2 ) ' SH)~/2 from trivinyl cyclohexane and ethanol dithiol.
4 .00~ r-/CH2CH2~S(CH2)~Sl~3f rom trivinyl cyclohexane and 1,4 butane dithiol.

, COMPOUMD THIOL FUNCT. IDEALIZED CHEMICAL
SH. EQUIV./~M STRUCrURE AND DERIVATION
_ S ~ H2)2 ~ ((CH232 (CH2) 3SH 272from trivinyl cyclohexane and 1,3 propane dithiol.
It has also been determined that effective retarders of irradiation curing or cross~linking include aromatic oils, sulfur, sulfur cure accelerators and some rubber antioxidants and/or antiozonants of the substituted diphenylamine type, such as N (1, 3-dimethylbutyl)N'-phenyl-p-phenylene diamine,~
Table II lists some commercial antioxidants/antiozonants which h~ve been found useful as retarders o~ irradiation cure~
A higher swelling ratlo indicates more retarding ~ffect. ~he swelling ra-tio were ob-tained by compounding one part of the particular antioxidant into 100 parts of polybutadiene rubber, subjecting the compound to S Megarads of irradiation, immersing the sample in toluene for 48 hours at room temperature and measuring the weight of the swollen rubber against the weight ~ of the dry rubber.
T~BLE II

TEST ANTIOXIDANT CHEMICAL COMPOSITION _ SWELLING
RATIO :
1 None --- 11.5 .
2 DBPC 2,6-di-t-butyl-para cresol 15.1 3 Santowhite* 4,4'thiobist6-T-butyl-m-Crystals cresol) 13.6 4 PBNA phenyl beta-naphtylamine 14.7 Agerite White* syn-di-betanaphthyl-p- 1:1.9 phenylene diamine - :

*trademark . .
:

- 1~0~4~

TEST ANTIOXIDANT CHEMICAL CO~lIPOSITION SWELLING
RATIO

6 Santoflex* 13 N-(1,3 dimethylbutyl)-N' 27.4 phenyl-p-phenylene diarnine The dosage of irradiaticn which is utilized to accompiish this invention and the conditions under wh;ch the dosage is applied are dependent upon ~everal variables, the type of rubber in the rubber compound, the promoter or retarder -utilized in the rubber compound, the level of the promoter or retarder utilized in the rubber compound, the thickness of the layer of material, the thickness of adjacent layers of materials, the sequence of the layers of material, the number oE the layers oE material and whether the irradiation is app:Lied to one or both sicles of the colTIpo~ite str:ip. The proper combination is obtained to yield the desired physical properties in the laminate.
The dosage also may be controlled by conditions under which the dosage is applied, such as the amount of energy of the electron beam employed. This may be controlled so that the electrons do not completely penetrate the entire strip. This results in the irradiation of part of the strip, but not the entire stri~. . .
DET~II,ED DESCRIPTION OF TIIE INVE:NTION
Figures 1 and 2 are partial cross-section views of this invention as embodied in a sealant containing innerliner for tires.
Figure 3 is a partial cross-section view of this inven~ion as embodied in a contoured, sealant containing innerliner for tires.

Figure 4 is a partial cross-sectional view of another embodiment of this inven-tion which is used for a self-sealing innerliner for tiresO

*trademark ~ ` :

4~

Figure 5 is a cross-sectional view of a tire embodying this invention as an innerlinerO
Figure 6 is a cross-sectional view of a tire embodying this invention wherein the sealant layer is only located in the crown of the tire.
In Figure 1 the laminate is shown generically as 10 havin~ internal layer, 12, and two external layers, 11. The internal layer contains a material which will de~rade when subjec-ted to irradiation or heat in the presence oE a peroxide, or a blend of the degradable material and one that cross-links when subjected to irradiation or heat in -the presence of a peroxide. The outer layers, 11, are designed to be relatively uneEEected by irradiation~ ~ley may comprise a rubber compound ~es:Lgned to hav~ air L~lpermeability properties or a rubber compound designed to have good building tac]~. An exa~ple of the latter t~pe is a rubber cornpound comprising 100 parts of natural rubber, 4S parts of carbon black and other compounding ingredients, including the following which retard irradiation cross-links, Santoflex 13, Aromatic Oil, Sulfur and Sulfur Cure Accelerators.
When the irradiation s~stem is used, the laminate, 10, after its construction, is subjected to an irradiation treatment which will degrade the degradable material in layer 12, whether this material be blended with one that cross-links or not, will cross-link the cross-linkable material in layer 12, if any is present; and will have little effect on layers 11. The laminate is then placed in the final product and the subsequent processing steps accomplished to yield the final produc-t, including the vulcanization thereof which cures layers 11 and does not degrade layer 12.

When the peroxide s~stem is used, a peroxide compound is mixed into the internal layer. After the laminate is constructed it is placed in the final product and the product is cured.
This curin~ process wîll degrade the degradable material in layer 12 whether -this material be blended with one that cross-links or not; will cross-link the cross-linkable material in layer 12, if any is present; and will cure layers 11.
In the application of this invention, the laminate, 10, may be obtained by calendering or coextrusion. The coextrusion method is preferred as it provides better control of the -thickness of the layers at lower gauges, gives better adhesion between the layers and permits the formation of laminates having contours at preselected positions, such as those sh~wn in Figure 3.
~ lalninate of the construct:ion shown in I'igure 1 was as~mbl~d wherein the degradable, sealant layer, 12, comprised a compound having the following :ingredients:
Parts per 100 Polymer Solution styrene/butadiene polymer 25 Polyisobutylene 75 Carbon black 60 oil I'his compound was calendered into a sheet 8 inches wide and .082 inches thick. A standard, halogenat~d butyl rubber containing innerliner compound was used for layers 11. Strips of this compound were calendered and faced on each side of the sealant layer. These external layers were .014 inches thick, making the total laminate .110 inches thick This laminate was irradiated by two passes with a single side surface dose of 8.5 Megarads(MRADS). This resulted in a radiation dose of 10.8 MRADS on the back side of the laminate. A portion of this laminate was cured in a laboratory press and subjected to the laboratory puncture sealank tes-t described below. This laminate yielded good air reten-tion results on this tes-t:.

This cured laminate was placed in a laboratory apparatus to determine its sealing properties. The laminate was first covered with a backing layer of fabric coated with cured skim stock to provide support for the laminate during the test.
In this apparatus a strip of the laminate covers a chamber ;-which is supplied with an internal pressure by an air cylinder.
The chamber is equipped with a gauge to measure the pressure in the chamber. The pressure is regulated by a valve between the cylinder and the chamber. The apparatus is so constructed that a nail may be driven into the laminate and then removed~
Upon removal of the nail from the laminate, the pressure retained in the chamber is determined. The coverage of -the nail with the s~alan~ mat~ria:l is also evaluated.
In thls test on the cur~d laminate descrlbed a~ove, a 16 penny nail was repeatedly driven into and then pulled out of the laminate. The nail had a uniform coating of the sealant material after it had been pulled out. ~o significant air loss occurred in the chamber even after repeated nail punctures.
Tires have been manufactured and tested containing the laminate described above. Production tires were built containing this laminate by the following techni~ue. During the production o~ a standard E78-l~ size tire having two polyester cord body plies and two glass cord belt plies the sealant laminate was applied to thé building drum. The splice in this strip was covered with a layer of the body ply compound.
The remainder of the tire was built and vulcanized using standard methods and e~uipment~ This resulted in a tire in which the crown area had an 8 inch wide s-trip of the sealant laminate, similar to the construction shown in Figure 6.

This tire was tested according to a test specified by the General Motors Corpora-tion for tires with puncture sealan-t .""~
, .. ..

capabilities. Under this test procedure the tire is mounted and inflated on its recommended rim. The tire is then run 2 hours at 50 miles an hour using its rated load and inflation on a laboratory tire testing wheel After this break-in period, one of the center grooves of the tire is punctured `
with a 20 penny nail. The nail is removed, the tire air pLessure is checked, and the hole is checked ~or air leakage by the application of a soap solution with any bubbles in the solution indicating air leakage. In the test on this tire no leakage was detected. Tbe tire is then run for 1,000 miles on the test wheel, again at 50 miles an hour and rated load.
At the end of this 1,000 miles, the tire is again checked for leakage with the soap solution and the inElation pressure is again checked. In this test no leakage was detected and th0 in~lation pressure was the same as the initial inflation pressure.
At this time, a shoulder groove is punctured with the 20 penny nail and the nail is removed. The leakage and pressure checks are repeated and the tire is run a second 1,000 miles.
At the end of the second 1,000 miles the leakage check procedure is repeated and the inElation is checked. Again, with this tire no lea]cage was dictated and no loss of inflation pressure was indic&~ed.
At this time, a third puncture is made in~the tire with the 20 penny nail in a groove intermediate between the center groove and the shoulder groove~ The leakage and pressure tests are again performed on this third hole and the tirc is then run another 1,000 miles. After this third 1,000 miles the -tire is removed and the test is completed.
In the test performed on this tire, the tire was run 965 miles making a total mileage of 2,965. No leakage was found at any o~ the puncture holes a-t the end of the test and ;:'~. ' .

4~
the inflation pressure was .5 psi less than the initial inflation pressure. It is believed that this pressure loss was due to the technique of measuring the pressure and not to any air loss through any of -the punctures.
To demonstrate the feasibility of the feature of the differential properties in the laminate layers in this invention, laminated were manufac-tured having a layer of soft, natural rubber compound comprising 100 parts of natural rubber, 45 parts of carbon black and other compounding ingredients, such as Santoflex 13, aromatic oil, sulfur and sulfur cure accelerators, all of which have a desensitizing effect on irradiation cure, and a layer of a hard, rubber compound comprising 100 parts of a soLution styrene/butadiene copoLymcr, ~0 parts o~ reitl~orcing c~rbon black and ~our parts of PDC~, a sensitl~ing ,Igent. In thi3 laminate the ~oft, natural rubber cornpound had a thickness of ~045 inches (.1143 cm) and the hard, solu-tion styrene/
butadiene compound had a thickness of .035 inches (.0889 cm).
These layers were separated by two Layers of Mylar and a blue cellophane dosimetry layer to measure the irradiation dosage used. Two identical pairs o-f laminate samples were initially subjected to irrad:iation on one side and were turned over and subjected to irradiation on the other side; a double side irradiation. ~fter this irradiation step the laminates were disassembled. The layers of one of each pairs of such strips were ch~cked for physical properties (stress-strain data).
These results are set out in Table III under the column "Radiation Cure". The separated layers of the remaining irradiated strips were~ given an additional thermal cure for 10 minutes at 328 degrees F. in a .040 gauge mold and their physical properties were then ob~ained. These resul-ts are reported in Table III under the column "Radiation and Thermal Cure". Three separate -tests were run in this manner, each a-t a di~erent dosage as shown in Table III.

; ' . .

4~
TABLE III
TEST RADIATION CURE RADIATION AND
THERMAL CURE
Rubber Desensitized Sensitized Desensitized Sensi-Compou~d Natural Rubber Stereon Naturaltized Rubber _Stereon TE~T 1 Ave. Dosage 8.6 Megarads Tensile Strength (psi) 590 228S 2860 2490 Modulus (psi) at 100% elongatiorl ~5 570 285 670 200% elongat:ion 75 :L290 800 1815 300% elongation 150 2240 1590 Elongation at Break (%) 560 300 445 260 Tl~:ST 2 ':
Ave. Dosage 11 Meqarads Ten~ile Strength (pBi ) 840 2620 28951695 Modulus ~psi) at 100% elongation 50 605 260 530 :
200% elongation 90 1495 700 1200 300% elonga-tion 190 2515 1435 Elongation at Brcak (%) 630 315 ~60 260 Ave. Dosage :~.
12.3 Megarads Tensile Streng-th (psi3 855 2440 25~5 2050 : :~

Rubber Desensitized Sensitized Desensitized Sensi Compound Natural Rubber StereonNatural tized Rubber _ Stereon Modulus (psi) at 100% elongation 55 705 220 610 200% elongation 100 1745 690 1425 300% elongation 205 - 1295 Elongation a-t Break ~%) 595 265 455 265 This data clearly demonstrates the feasibility of this invention showing khat the sensitized layer is cure~ by the irradiation step, the desensit:Lzed :layer is not, the desensitized l~yer i~ cured by the ~ub~equ~nt vulcanizatlon step and the sensitized layer is not adversely a~fected by the subsequent vulcanization step.
In Figure 2 the sealant laminate is shown generally as 20 havin~ two layers, 21 and 22O Layer 21 is the layer containing the degradable sealant type ma-terial. Layer 22 is the external layer which is used to cover the sealant material so that it wi~l remain in its proper position in the end product. Layer 22 may be the standard tire innerliner compound or it may be a standard tire skim stock as previously described in this specification. Figure 5, which will be discussed later, demonstrates the utilization of the laminate of Figure 2 as a sealant layer in a pneumatic tire.
If a sealant material which will be de~raded upon exposure to irradiation is used, the procedure for Figure 1 will be 3U followed. Alternatively, the peroxide system described in relation to Figure 1 may be used. As explained in relation to Figure 1, in this sys-tem the irradiation step is not ut.ilized.

~, .

Upon the application of heat, such as in the tîre vulcanization s-tep, the peroxide degrades the degradable material and cross-links the cross-linkable material.
qhis peroxide system may be utili~:ed with a rubber compound containing 100% of degradable material (PIB) or blends of the degradable material with a cross-linkable diolefin. When blends are utilized, the split masterbatch technique of mixing is preferred to insure that the peroxide does not prei~erentially cross-link the cross-linkable material wi-th a small amount of degradation in the degradable material.
In the split masterbatch technique, separate masterbatches - `
are made containing l()0 parts o~ the degradable or cross-lin}cahle rnateri~l with 60 parts carbon b:Lack and 40 parts oil. These sepaxat~ mast~rbatches ma~ t,hen be bLended in any desired proportions to obtain any ratio Oe degradable materLa:L to cross-Linkable material thak may be desired. The peroxide is added during this blending operation. By this technique the Applicants have made sealant layers with varying levels of the degradable material and have subjected these layers to the laboratory puncture sealant tes-t described above. r~le results Oe these determinations are disc Losed. Table IV along with a compound containing 100% Oe the degradable mat~rial.
TABLE IV
PIB (Degradable) 100 75 50 25 75 50 25 Solution SBR
(cross-linkable) - 25 50 75 25 50 75 Carbon black 60 60 60 60 60 60 60 oi 1 ~o ~o a~o ~o ~o ~o ~o Peroxide 2 2 2 2 Seal good good good bad good good bad This data demonstrates the feasibility Oe -the peroxide system to obtain a ma-terial with puncture sealant properties.

.. ~ .

Li4~

It is understood that the levels of oil, carbon black ~nd peroxide, as we~l as the ratio of the degradable material to the cross-linkable material, are within the discretion of the persons skilled in the art and depend upon the speci~ic nature of each ingredient used and the overall manufacturing system to which the compound is subjected. ' Figure 3 represents another embodiment of the innerliner laminate o~ this invention. This figure demons-trates the contoured embodil~ent . In Figure 3 ext~rnal layers, 3:L, are comprised of a soft rubber compound designed to have good building tack and, when the irradiation system is used, these layers may be desensitized against curing by, Eor examp:le, t'he inclusion of an antiox:Ldant such as Santoflex ~3. Inte:rnal .~ay~rs 3~ and 33 are showrl as 'being thic]cer irl certain p~edetermined areas. 'I~lis excessive thickness rnay be pre'located in an area of the end product (in this case a pneumatic tire) where the laminate is subjected to the highest pressure in its shaping and curing operation. This extra thickness provides additional material in the high pressure areas which yields an end product with an adequate thickness of the mater.ial in the high pressure areas without having the ex-tra thickness in lower p.ressure areasO 'I'his erabo~irnent resu:lts in a savincJs of material.
In a pneuraatic tire innerliner application of -the contoured shape, the thicker areas of the lamin~te are located in the area of the tire that is subjected to the highest pressure in the shaping and curing operations or the greatest expansion in these opera-tions. The extra thickness in high expansion areas prevents innerliner thinning out and cord shadowing (body cords actually striking through the thinned-out innerliner) that may occur in this area of the tire. By this Application, the con-toured strip provides the necessary thickness in the trouble-~LQC~4~

some areas without having to retain that thickness across the complete width oE the strip as in prior laminates~
In Figure 3 layer 32 may be a hard rubber layer which is sensitized to cure when subjected to irradiation. This layer may be comprised of a solution polybutadiene rubber and reinforcing carbon black. As such, this layer is utilized to retain the thickness of the laminate during the subsequent shaping and curing operations. Alternatively, this layer may be a hard rubber layer comprised of a halog~nated bu-tyl rubber and reinforcing carbon black. As such, this layer is the barrier layer w~lich resists the passage o~ air from the internal air chamber of the tire into the tire.
The layer, 33, in Figure 3 ls the puncture sealant layer.
tk ma~ be compr:ised o~ any o~ th~ sca:Lant mater:lals that are disclosed in thi~ sp~ciE~cation. ~t rnay conl;ain a peroxide for the peroxide degradation system previously described or it may not and be used in the irradiation system previously described.
~ t is understood that additional layers may be included in any of the lamina'es disclosed in this specification or that any combination of the layers disclosed in this specification may be contained in one laminate. For example, a laminate may contain two external layers o~ soEt rubber compound designed to have good building tack, and an internal sealant layer designed to seal when punctured and containing a ma1erial that is degraded upon exposure to irradiation or upon exposure to heat in the presen~e of a peroxide, another internal layer containing a halogenated butyl compound designed to provide a barrier against the passage of air and yet another in-ternal layer of a hard rubber compound designed to cross-link when exposed to irradiation to provide a layer which will maintain the integrity of -the laminate during subse~uent processing steps.

Fi~ure ~ represents another embodiment of an innerliner -2~-laminate. In Figure 4 the laminate is designated generically as 40. It contains two ou-ter layers, 41, comprising a soft rubber compound which is designed to have good building tack and is desensitized against irradiation curing by, ~or exampler the inclusion of an antioxidant such as Santoflex 13. Two intermediate layers, 42 and 43, are located inside OI layers 41. These layers comprise a hard rubber compound ~ontaining halogenated butyl rubber and reinforcing carbon black which have been sensitized to cure on exposure to irradiation, ror exarnple, by the inclusion o~ TEPT. Between layers 42 and 43 is a layer of polyisobutylene, 44, without any sensitizing or desensitizing agen~s~ This material may or may not contain solne r~inforcing material, such as carbon black~ Bridges 45 and ~6 o~ the salne material uti:Lized :in layers ~ and 43 conneck layers 42 and 43 to one another. These bridges form pockets which contain the layer 44.
When the laminate of Figure 4 is subjected to irradiation, the layers 41 will be unaffected and will remain soft and tacky to provide adhesion during the subsequent processing steps for the end product. The layers 42 and 43 wilL partially or fully cure t~e~eby providing a stiff, hard foundation for the composite lamin,3te. r~he material in layer ~4 wilL be degraded by chain scission and will form a liquid, pasty material. This laminate can -then be applied as the innerliner of a tire and subjected to the later vulcanization step. The resulting tire will have an innerliner wllich contains pocKets of the liquid polyisobutylene ma-terial. '~liS material will ac-t as a sealant to any punctures which may occur in the tire thercby giving the tire a self-sealing capability. The bridges 45 and 46 are necessary to maintain the integrity of the colnposite laminate arter the irradia-tion step due to the fact that the layer 44 is liquified by the irradia-tion step.

~10~

The laminate of Figure 4 is feasi~le because irradiation causes chain scission in the polyisobutylene while the cross-linking which occurs will not balance the degradation due to this chain scission reaction in this material. Standard butyl rubber, a copolymer of polyisobutylene and isoprene, is degraded to a certain degree by irradiation but this degradation is partially compensated by a concurrent cross-linking reaction.
The same two compensating reactions occur in halogenated butyl rubbers except the cross-linking reaction is more predominant in the halogenated butyl than it is in the standard butyl. This performance of the butyl rubbers demonstrates the critical nature of the irradia-tion treatment and the criticali-ty of selecting the propor sonsitizing or desensitizing acJents for ~ach specific rubber.
It ls envisioned that this chain-scission versus cross-linking situations may also be employed in a three layer laminate in which the two outer layers are soft, tacky rubber compounds desensitized to resist irradiation cure and the inner layer contains a blend of polymers, such as polyisobutylene and halogenated butyl rubber. Upon irradiation the poly:isobutylene will degrade and form a liquid which will be trapped in the cross-linked halogenated butyl rubber. Th:is composite would have self-sealing ~haracteristics.
Figure 5 represents a tire containing this invention. The tire is shown generically as 50 having tread 51, sidewalls, 52, and beads, 53. The placement of the innerliner of this invention on the inner periphery of the tire is shown as strip 54. ~he other featureof -the tire may be any of the known constructions (radial, bias, belted-bias) for passenger, truck, airplane off-the-road, tractor or industrial tires.
Figure 6 represents a tire containing a sealant layer as described in Figure 2. The basic components of the tire in .~

.

~0~4~

Figure 6 are identical to the components in Figure 5.
Additionally, Figure 6 depicts the laminate, 20, of Figure 2, with sealant layer 21 and cover layer, 22, in the crown area o-F the tire. This is the area where nail punctures predominantly occur, It is understood that layer, 22, of laminate, 20, may contain air-resistant properties such as those provided by halogenated butyl innerliner compounds.
Table V demonstrates the sensitizing and desensitizing characteristics of severa:l. chemicals on a rubber compound of the followin~ basic formula:
Solution styrene/butadiene copolymer (SBR) - 100 parts Reinforcing furnace black ~CB) - 50 parts Each comparison is llsted under a test number, the first c~lumn d~f in~s tl~ g~di~nts .in th~ above basic :Eormula, the second colurnn the modulus at different elongations and the last the average irradiation dosage to which each compound was exposed. In the tests the two compounds were laminated together and irradiated, the compounds were then separated and the physical properties of each determined.

TABLE V
'rest 1 Modulus at Elongation Dosage 100% 200% 300% Ave. Meqarads SBR/CB 187 - - 7.3 SBR~CB + 3.5 TEPT* 1004 - - 7.2 Test 2 SBR/CB ~ 3.5 TEPT 889 - - 7.6 :
SBR/CB ~ 3.5 Santo-flex 13 127 - - 7.2 Test 3 , - . ~ .
SBR/CB 219 325 _ 6.9 SBR/CB ~ 1.5 TEPT, 2 PDCB** 632 1824 - 7.1 :
-27~

., , . - - . . -~o~
Test 4 Modulus at Elongation Dosage 100% 200% 300% _ Ave. Meqarads SBR/CB + 3.5 Santo-flex 13 178 213 - 6.9 SBR/CB + 1.5 TEPT, 2 PDCB 623 1706 - 6.9 Test 5 -SBR/CB + 1.5 TEPT, 2 PDCB, 30 naphthenic oil*** 235 683 1447 8.3 SBR/CB + 3.5 Santo-flex 13, 30 aromatic o:il**** 48 57 6~ 8.0 ~r~ 6 SBR/CB + l.S TEPT, 2 PDCB, 20 naphthenic oil 315 1090 - 10.1 SBR/CB + 3.5 Santo-flex 13, 20 aromatic oil 68 85 _ 10.1 Te t 7 SBR/CB -~ 1.5 TEPT, ...
2 PDCB, 10 naphthenic oil4051165 2267 7.8 ' SBR/CB + 3.5 Santo-flex 13 10 aromatic oil 88 110 145 7.6 'l'~st 8 SBR/CB + 1.5 TEPT, 2 PDCB, 20 naphthenic oil 325 1033 - 9.6 ~A
3L~ILQ(~4~1 Modulus at Elongation Dosage 100% 200%300O/oAve. Meqarads SBR/CB ~ 3.5 Santo-flex 13 -20 aromatic oil 55 55 - 3O5 Test 9 SBR/CB + 20 Naphthenic oil 141 302 702 9.9 SBRfCB + 20 Aromatic oil 75 10~ 143 10.0 Test 10 SBR/CB + 3.5 TEPT293 963 1793 8.3 SBR/CB + 3.5 ,Santoflex 13, 20 Aromatic oil 57 72 92 ~.2 *TEPT= Thioetherpolythiol (compound 2 in Table I) **PDCB= p-dichlorobenzene ***naphthenic oil= Sunthene 4240 ****aromatic o11= Dutrex 72~

This data demonstrates the selective cure of the rubber compound in a laminate when the rubber compounds have been s~nsit.ized or desensitized to react to the irrad.iation treatment. A11 of the tests were subje~cted -to the double side irradiation treatment except Test 6 which was irradiated on only one side, the side having -the higher dosage.
Table VI demonstrates the application of this invention in -a composi-te strip wherein the inner layer is cured by irradiation arld thc two outcr layers aro uncffcct(?~. T}leso laminates werc prepared with three layers each containing a solution styrene/

bu-tadiene copolymer, as indicated in Table V. Mylar film was placed between each layer to facilitate later separation. The laminates were subjec-ted to d double side irradia-tion trea-tment;

:!

, ~ .
the layers were then separated dnd tne physical properties determined for each layer.
Table VI
Laminate A Gauge Dosage Modulus at Tensile Elonga-(inches3 ~Megarads) 300% Elong- Strength tion(%) ation ~psi) (pSi) A. 100 SBR/70CB
40 aromatic oil/2 San-to-flex 13.021 3.8 41 51 800 B. 100 SBR/50CB/
2 PDCB .030 3.5 258 822 733 C. 100 SBR/50CBj 2 Santoflex .33 3.75 :L~3 303 992 ~3 Lamina-te B `
-A. 100 SBR/70CB/
2 Santoflex 13, 40 aro-matic oil .023 5.7 67 107 840 B. 100 SBR/50CB/
2 PDCB .034 5.4 383 1.391 713 C. 10~ SBI~/50CB/
2 Santoflex 13 .035 6 196 628 860 This data demonstrates the irradiation cure of the . .
sensitized inner layer of a three layer lamina-te while the desensitized outer layers are une~fecte~d by the~ irradiation treatment. The outer layers re-tain their building tack while the inner layer is hardened and will retain its dimensionO
The dosage received by the layers in the above examples was measured by the use o~ strips of blue cellophane containing methylene blue dye. These strips were applied to the top and bottom of the laminates to be irradiated. Op-tical density measurements were taken on the strips before and after irradiation. The irradiation reduce~ the dye to a colorless state with the amount of bleaching being proportional to the irradiation dose received by the strip.
The dose on the strip is determined from a plot of the change in op-tical density (before and after irradiation) as a function of dose size. The average dosage on a layer is calculated from the surface dose and a previously determined depth-dose distribution curve for the particular electron accelerator being used. ~ uniform dosage throughout each layer is obtained by a proper se:lectlorl oE the amount oE
~lectrorl energy an~ the double~ si~e dosage tec~hnique.
This invention takes max:imum advantage of the lamlnate theory that the greater the number of interfaces, the greater the resistance to flow of the laminate. This invention makes possible lamina-tes containing more layers and thinner layers -than previously obtained. The in-terfaces more evenly dis-tribute the expansion stresses ~nd give the laminate more d:imensional ~tabil:ity.

,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A laminate comprising a puncture sealing layer and at least one other layer, said puncture sealing layer containing a polymeric material that has been at least partially degraded by exposure to irradiation or to heat in the presence of a peroxide to yield its sealant properties, said degraded polymeric material being selected from the group consisting of polyisobutylene, copolymers containing polyisobutylene and polyethylene oxide.

2. The laminate of claim 1, wherein said degraded polymeric material is polyisobutylene.

3. The laminate of claim 1, wherein said degraded material has been degraded by exposure to irradiation.

4. The laminate of claim 1, wherein said polymeric material has been degraded by a heat treatment in the presence of a peroxide.

5. The laminate of claim 4, wherein said peroxide is 2,5-bis (t-butylperoxy) 2,5 dimethylhexane.

6. The laminate of claim 1, wherein said puncture sealing layer also contains a polymeric material that has cross-linked on exposure to the degradation treatment.

7. The laminate of claim 6, wherein said cross-linked polymeric material is selected from the group consisting of natural rubber, copolymers of butadiene and styrene, and halogenated butyl rubber.

8. A laminate comprising at least three layers having two outer layers and a puncture sealing layer forming an inner layer, said inner, sealant layer containing a polymeric material that has been degraded by exposure to irradiation to yield its sealant properties, with said two outer layers relatively unaffected by said irradiation, said degraded polymeric material being selected from the group consisting of polyiso-butylene, copolymers containing polyisobutylene and polyethylene oxide.

9. The laminate of claim 8, wherein said degraded polymeric material is polyisobutylene.

10. The laminate of claim 8, wherein the outer layers contain sulfur and sulfur cure accelerators so that said outer layers will vulcanize when exposed to a subsequent heat treatment.

11. The laminate of claim 8, wherein at least one of said layers varies in thickness across its cross-section so that said laminate is contoured to provide more of said variable layer in certain, predefined areas along its width.

12. The laminate of claim 8, wherein said inner, sealant layer also contains a polymeric material that has cross-linked on exposure to irradiation so that said inner layer has a degraded polymeric material trapped within a cross-linked polymeric material.

13. The laminate of claim 12, wherein said cross-linked polymeric material is selected from the group consisting of natural rubber, copolymers of butadiene and styrene, and halogenated butyl rubber.

14. In the method of manufacturing a laminate comprising a puncture sealing layer and at least one other layer, the steps comprising providing a layer with a polymeric material which at least partially degrades on exposure to irradiation or to heat to form a material having sealant properties, the degradable layer containing a peroxide when the degradation is to be effected by the application of heat, said degradable polymeric material being selected from the group consisting of polyisobutylene, copolymers containing polyiso-butylene and polyethylene oxide, assembling said degradable layer with said at least one other layer to form said laminate and exposing said laminate to irradiation or to heat whereby said degradable polymeric material degrades to form said puncture sealing layer.

15. The method of claim 14, wherein said degradable layer contains a peroxide and said degradation is effected by the application of heat.

16. The method of claim 14, wherein said degradation is effected by the application of irradiation.

17. The method of claim 16, wherein said at least one other layer contains a sensitizing agent which promotes cross-linkage therein when said irradiation is applied.

18. The method of claim 14, wherein said laminate contains three layers with said degradable layer forming the middle layer, the outer two layers at least partially cross-linking when exposed to the degradation treatment.

19. The method of claim 14, wherein said degradable layer also contains a polymeric material that will cross-link on exposure to the degradation treatment.

20. In the method of manufacturing a laminate containing at least five layers in which one of said layers contains a puncture sealant material, the steps comprising providing at least two outer layers with a desensitizing agent which retards cross-linkage when subjected to irradiation, providing two inner layers with a sensitizing agent which promotes cross-linkage when subjected to irradiation, providing a middle layer located between said sensitized layers with a polymeric material which degrades on exposure to irradiation to form said puncture sealant material, said degradable poly-meric material being selected from the group consisting of polyisobutylene, copolymers containing isobutylene and poly-ethylene oxide, assembling said laminate with said middle layer located between the two sensitized layers and one of said desensitized layers located outside of each of said sensitized layers, and subjecting said laminate to irradiation so that said layers are differentially cross-linked with said sensitized layers being cross-linked to a greater degree than said desensitized layer and said middle layer being degraded to yield a puncture sealing layer.

21. The method of claim 20, wherein said sensitizing agent is selected from the group consisting of paradichloro-benzene and the thioetherpolythiols.

22. The method of claim 20, wherein said desensitizing agent is selected from the group consisting of 2,6-di-t-butyl-p-cresol; phenyl beta-naphthylamine;
4,4' thiobis (6-t-butyl-m-cresol); N-(1,3-dimethylbutyl)-N' phenyl-p-phenylene diamine; syn-di-betanaphthyl-p-phenylene diamine; aromatic oils, sulfur and sulfur cure accelerators.

23. A vulcanizable pneumatic tire comprising as one of its rubber components a laminate comprising a puncture sealing layer and at least one other layer, said puncture sealing layer containing a polymeric material that has been at least partially degraded by exposure to irradiation or to heat in the presence of a peroxide to yield its sealant properties, said degraded polymeric material being selected from the group consisting of polyisobutylene, copolymers containing poly-isobutylene and polyethylene oxide.

24. A vulcanizable pneumatic tire comprising as one of its rubber components a laminate comprising at least three layers having two outer layers and a puncture sealing layer forming an inner layer, the outer layers having a higher degree of cross-linkage than the inner, sealant layer, said sealant layer comprising a blend of an irradiation degraded polymeric material with puncture sealing properties and an irradiation cross-linked polymeric material, said degraded polymeric material being selected from the group consisting of polyisobutylene, copolymers containing polyisobutylene and polyethylene oxide.

25. A vulcanizable pneumatic tire having an innerliner comprising a laminate of a puncture sealing layer and at least one other layer, said puncture sealing layer comprising a blend of an irradiation degraded polymeric material with puncture sealing properties and an irradiation cross-linked polymeric material, said degraded polymeric material selected from the group consisting of polyisobutylene, copolymers containing polyisobutylene, and polyethylene oxide, and said cross-linked polymeric material selected from the group consisting of natural rubber, copolymers of butadiene and styrene, and halogenated butyl rubber, said polymeric materials being present in a ratio between 75% degraded-25% cross-linked to 25% degraded-75% cross-linked.

26. A vulcanizable pneumatic tire having an innerliner comprising a laminate of at least two layers in which an outer layer has a higher degree of cross-linkage than an inner, sealant layer, said sealant layer comprising a blend of an irradiation degraded polymeric material with puncture sealing properties and an irradiation cross-linked polymeric material, said degraded polymeric material selected from the group consisting of polyisobutylene, copolymers containing poly-isobutylene, and polyethylene oxide, and said cross-linked polymeric material selected from the group consisting of natural rubber, copolymers of butadiene and styrene, and halogenated butyl rubber, said polymeric materials being present in a ratio between 75% degraded-25% cross-linked to 25% degraded-75% cross-linked.

27. A pneumatic tire comprising as one of its rubber components a laminate comprising at least five layers in which one of said layers contains a puncture sealant material, said tire manufactured by the steps comprising providing at least two outer layers with a desensitizing agent which retards cross-linkage when subjected to irradiation, providing two inner layers with a sensitizing agent which promotes cross-linkage when-subjected to irradiation, providing a middle layer located between said sensitized layers with a polymeric material which degrades when exposed to irradiation to form said puncture sealant material, said degradable polymeric material being selected from the group consisting of poly-isobutylene, copolymers containing isobutylene and polyethylene oxide, assembling said laminate with said middle layer located between the two sensitized layers and one of said desensitized layers located outside of each of said sensitized layers, subjecting said laminate to irradiation so that said layers are differentially cross-linked with said sensitized layers being cross-linked to a greater degree than said desensitized layers and said middle layer being degraded to yield a puncture sealing layer, assembling said laminate into said tire and vulcanizing said tire.

28. A pneumatic tire comprising an annular, road-engaging tread surface, two sidewalls each connecting a side of said tread surface to an annular bead, reinforcing body plies extending from one bead to the other through the sidewalls and tread and a laminated innerliner member located radially inwar-dly of said reinforcing body plies, said laminated innerliner comprising at least two layers in which one of said layers contains a puncture sealant material, said tire manufactured by the steps comprising providing a first layer of said lamina-ted innerliner with a polymeric material that cross-links on exposure to irradiation, providing a second layer of said laminated innerliner with a polymeric material that at least partially degrades on exposure to irradiation to form said punc-ture sealant material, said degradable polymeric material being selected from the group consisting of polyisobutylene, copolymers containing isobutylene and polyethylene oxide, assembling said layers into said laminate, subjecting said laminate to irradiation whereby said second layer degrades to yield a puncture sealant layer, assembling said laminate into said tire with said sealant layer located between said first layer and said reinforcing body plies, and vulcanizing said tire.

29, The tire of claim 28, wherein said degraded polymeric material is polyisobutylene.

30, The tire of claim 28, wherein said sealant layer comprises a blend of said irradiation degraded polymeric material and another irradiation cross-linked polymeric material.

31. The tire of claim 30, wherein said cross-linked polymeric material is selected from the group consisting of natural rubber, copolymers of butadiene and styrene and halogenated butyl rubber.

32. The tire of claim 31, wherein said degraded and cross-linked polymeric materials are present in a ratio between 75% degraded - 25% cross-linked to 25 degraded-75%
cross-linked.