CA1068460A - Irradiation of rubber in the manufacture of tires - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The inner surface of a green tire provided with an air-sealing liner, is cured or partially cured to produce a steam- and water-resistant surface, and the tire after such treatment is cured in a usual press without an air-bag or bladder.
One or more plies of a tire, usually the outer fabric plies, are partially cured before assembly in the tire, to insure that plies so located are cured, without over-curing inner and outer portions of the tire.
New tires are made by placing a carcass, whether green or partially cured, in a mold and extruding rubber over the outer surface of this carcass to fill the mold, and then giving the final cure to the resulting tire.
Tires are retreaded by applying ribbons of tread stock over the carcass prepared in any conventional manner, and then completing the cure without the use of a mold.
Retreaded tires are cured by placing a carcass prepared in any conventional manner, in a mold, extruding tread stock into the mold around the carcass, and then curing.
A tire, the inner surface of which is provided with a non-cured liner reinforced with a non-wicking fabric is cured without an air-bag or bladder.
Curing or partial curing may be effected by electron irradiation. Progressive irradiation is disclosed by which an object is repeatedly irradiated to attain a desired cure. Other methods of curing may be preferable in some operations.

Description

-` ~068460 THE INVENTION
The invention relates more particularly to the use of electron radiation in the production of new tires and the re-treading of old tires, although other means of radiation may be employed, and for most operations other means of curing may be used, as explained.
Electron radiation has been known for some years and in recent years equipment utili~ing up to a million volts or more has become available for commercial use. The voltage employed determines the depth of penetration of the electron rays. For example, radiation generated by a million volts will penetrate an item having a density of 1 to a depth of 1/8 inch. By varying the voltage, the depth of the penetration may be varied. Thus, tires may be cured to a depth of 1/8 inch or more, depending upon the rubber employed, the compounding formula, and the voltage used. By using higher voltages and radiating both surfaces of a tire, tires of much greater thickness may be cured. When only one surface is irradiated, beyond the depth at which the rubber is cured there is a partial curing which becomes less as the distance from the rubber surface increases.
The amperage will be varied depending upon the area sub-jected to radiation. The new equipment provides for irradiating an area of several square inches, up to for example 12 square inches or more.
By irradiating natural rubber or synthetics such as butadiene-styrene, polybutadiene, polyisoprene, etc., the mole--cular structure is rearranged. Irradiation has no beneficial effect on so-called "butyl" (copolymer of isobutene and either isoprene or butadiene) rubber. The rearranged rubber is partially or completely cured. By that it is meant that rubber which is thermoplastic, when irradiated becomes partially or entirely thermoset (cured) with or without sulfur.

From the foregoing description it is evident that "irrad-iation" as used in this application defines the activation of - 1 - ~

i~68460 a molecular change by exposure to the proper amount of radiation without the necessity of using heat, pressure or chemical cata-lysts. This radiation may be applied by electrons, gamma rays or X-rays, all of which can be used to rearrange the molecular struc-ture of material for tires without the necessity of using heat or sulfur which are required for vulcanizing tires. The surface of radiation-curable rubber subjected to partial or complete curing by irradiation remains tacky and unites to another piece so treated or to another object. Also partial curing by irradiation dimen-sionally stabilizes rubber which can be cured by irradiation.
Radiation may be used to treat a green tire or part of agreen tire, or the tread in retreading, or plies used as a liner for a green tire or a tread produced from ribbons of tread stock in retreading or the extruded tread stock in the manufacture of new tires or in retreading.
The rubber may be cured instantaneously by subjection to irxadiation, and this may be done in a continuous operation in which the source of radiation and the rubber are moved continu-ously relatively to one another. Alternatively, the rubber may be cured by progressive irradiation. Progressive irradiation is accomplished by partially curing a piece of rubber in one exposure to the source or radiation, and then giving it one or more additional exposures each of which partially cures the rubber, until the rubber is cured. For example, by exposing the same rubber a number of times as by rctating a tire continuously and applying a thin layer of the rubber to the tire as it is rotated, and continuing the application of the thin layer throughout several rotations of the tire and as each thin layer is applied to the tire, exposing the rubber to irradiation to partially cure it so that as the tire is rotated a number of times in building up a desired thickness of the carcass or tread and by continuing the rotation a number of times after completing the application of the rubber, the rubber is progressively and completely cured.

~068460 According to one aspect of this invention there ; is provided a process of forming a tire having a plurality ` of tire elements, the process comprising the s~eps of sub-jecting to electron radiation, or other form of radiation having a similar curing effect on exposed rubber, at least a portion of rubber in one or more of the tire elements in which the rubber is curable by such radiation, thereby at least partiall~ curing said portion of rubber in said one or more o~ the tire elements without full~ curing all said rubber in all the tire elements, assembling the tire elements into a tire, and.subsequently final curing the uncured or partially cured rubber in all the tire elements.
According to a further aspect of this invention there is provided a pneumatic tire comprising a rubber carcass tire element and a rubber tread tire element, the surface of one of said tire elements at the interface therebetween being rubber at least partially cured by electron radiation, or other form of radiation having a similar curing effect on exposed rubber.
The production of new tires will be discussed first, and in this connection reference will be made to the following figures:
Figure 1 is a section through a green tire with a liner with the inner surface being irradiated;
Figure 2 is a section of a small portion of a green tire with a liner after the inner surface has been irradiated;
Figure 3 is a section of a small portion of a tire provided with a pre-cured liner;
Figure 4 is a section through a mold containing a tire being cured without an air-bag or bladder;
Figures 5 and 6 are enlarged details of a portion 1~ .
. ~ - 3 -1~68460 of a modification of the tire and mold shown in Figure 4.
` Figure 7 is a section through a conventional mold containing a tire being cured without an air-bag or bladder;
Figure 8 is a section through a conventional mold provided with means for extrusion of tread rubber into the mold; and Figure 9 is a section of a tire before curing, with several outer fabric plies pre-cured.
Then the retreadin~ of tires will be discussed, and reference will be had to the following figures:
Figure 10 is an elevation of a stand with a tire being retreaded on it, with the tread stock being extruded, and means for shaping the tread;
Figure 11 is a section on the line 11-11 of Figure 10 showing a roller that may be used for shaping the - tread in position on a section through a tire being retreaded;
Figure 12 is a section through a modified roller;
and Figure 13 is a section through the liner for the tubeless tire claimed herein.
NEW TIRES
TIRES CURED WITHOUT AN AIR-BAG OR BLADDER.
. . ~
It has long been the wish of the industry to avoid the use 10~84~60 of an air-bag or bladder in curing tires. The bag or bladder separates the inner surface of the green tire in a mold from the steam or hot water used to apply pressure to the bag or bladder to force the tire against the inner surface of the mold and thus remove air rom the green tire and mold and subsequen~ly cure the tire.
The invention relates to a method of curing a tire wlthout an air-bag or bladder, and to methods which employ an air-bag or bladder. Reference is made to Hopkinson U.S. 1,289,767 and 1~289~771 as prior art.
According to one method~ a green tire is formed in the usual manner, with a liner. Then this green tire is sub~ected to electron irradiation to cure the exposed inner surface to a depth of perhaps 1/16 lnch or more, with partial curing at a greater depth;
or only partially curing the exposed inner surface to a depth of perhaps 1116 of an inch or more.
According to another method, a liner (such as is used in the production of tubeless tires) is partially cured or completely cured, and then this liner is used as the inner ply in building up a green tire. Figure 13 is a modification of a liner such as is used commercially in the production of tubeless tires.
Liners to be cured or partially cured by irradiation must have incorporated in them sufficient natural rubber or synthetics which reacts to irradiation, to accomplish the degree of cure desired. If the liner is composed of a layer of butyl rubber or other rubber which is not cured by irradiation, it may be laminated to natural rubber or other rubber which can be so cured. This layer of butyl rubber is preferably on the inner surface of the liner. Any of the layers may incorporate a rein-forcing element, for example, non-wicking fabric. This layer of natural rubber or synthetic may be cured or partially 1Q6~460 cured by electron irradiation before the tire is cured and act~ as a sealing element during the curing of the tire without an air-bag or bladder, to render ehe tire impervious to the curing fluid brought in contact with the liner. The butyl layer i8 cured when the tire i~ cured in any conventional manner. ~ny of the layers may incorporate a reinorcing element.
Whether a portion of the liner i~ cured before or after bein8 built into the tlre, the liner is incorporated in the tire by ~oining it8 two ends, usually by a beveled splice or by butting the two ends together or by overlapping the ends. To assure a good seal it may be advantageous to place a locking strip, such as a strip of uncured or partially cured stock over the ~oint and/or a layer of non-wicking fabric, such as is used in conventional tire-bead con-struction. This fabric may be incorporated in ehe strip as a stabilizer. The locking ~trip may be cured or partially cured as by irradiation or any other process, before the tire i8 placed in a mold and cured. If the splice is made by overlapping the ends of the liner and a portion of the liner has been made impenetrable to the inflating fluid by curing and a locking strip is not used, then in order to obtain a saeisfactory ~oint during the for~ing and curing of the tire, it will be advantageous to have both the inner and outer surfaces of the liner cured les~ than the impenetrable portion, 80 that on curing or forming before curing the seal will not be broken and the overlapped ends will be cured to one another.
Some layer of the liner of a green tire must be cured sufficiently to make the tire impervious to damaging penetration of inflation fluid such a~ steam or hot water u~ed to inflate the tire while being cured without an air^bag, bladder or the like. The liner need not extend to the edge portions of the carcass plies which are used for wrapplng the beads but may do so. It i8 only the 10 6 ~ D

portion of the liner which is contacted by the inflation fluid that need be made impervious to the penetration of the inflating fluid.
This green tire can be cured in a mold without an air-bag or bladder.
The mold may be of usual construction except that there is no provi-sion for an air-bag, and modification for support and/or formation of the beads may be desirable.
F~gure 1 is an illustration of equipment that may be used for cur~ing the liner of a green tire in which an uncured liner has been incorporated on the tire-building drum. The green tire 5, provided with the liner 6, i8 placed over a roller 8 bhe shaft 9 o which will ordinarily be mechanically driven, although it may be operated by hand. The green tire is readily placed over the roller as indicated in Figure 1. Although the inner surface of the tire, and primarily the liner, may be cured by any means, it is preferably cured by electron irradiation. A suitable device 12 for effecting irradiation is moved into the position shown in Figure 1 to effect the irradiation. Normally, a longitudinal section of 12, extending through approx i tely the entire wideh of the tire, will give off rays, and the entire inner surface of the tire will be irradiated by n~
moving that surface under the longitudinal section by rotating the roller 8. Normally the irradiation will not be sufficient to cure any more than the inner surface of the liner to a depth of perhaps 1/16 inch. It may, however, cure the liner. Figure 2 illustrates how, when the irradiation is controlled to cure only the inner surface of the liner 6', there is partial curing beyond the depth that is "firm cured"~ By "f~rm cured" we refer to ~ufficient cure to prevent inflation fluid such a~ steam or water penetrating the tire when sub~ected to curing in a mold. The outer surface of the liner may be partially cured or nvt cured.
In the alternative method, the liner is cured or partially 10~ 460 cured prior to assembly with the fabric plies. If usual methods of curing are utilized, the entire liner will normally be completely cured and it may be desirable to use an adhesive when assembling with the carcass. If the liner is cured by electron irradiation, the cure generally will only be a surface cure of perhap~ 1/16 inch more or less. Figure 3 illustrates a green tire, the liner o which has been partially cured by irradiation before assembly with the carca~s. The inner surface of the liner has been completely cured, the oppo~ite ~ur~ace of the liner 6" is partially cured or may not be cured.
Instead of irradiating the liner, conventional meaDs ma~
be used for curing all of it or only a portion of it. For example, the ~iddle of three layers may be compounded for rapid curing at ambient temperature, as by compounding this layer with a large amount of accelerator; or a powder or solution of an accelerator may be spread on the intermediate surface of one or both rubber plies of a two-layer liner. All or only a widthwise portion such as that part of the liner treated for rapid acceleration, which is to serve as a barrier to the penetration of the inflation fluid,

2~ may be heated, as by infrared light or other means to effect rapid curing. A ~atisfactory procedure of producing a three-layer liner iB to irradiate or otherwi~e cure only the middle layer or only a part of it, at any suitable time, such as before incorporating it in the liner as, for example, by irradiating or heating it, whichever is required, just as it is being introduced between the other two layers. This intermediate layer which is treated for rapid accelerating, may be narrower than the ou~er layers.
Another satisfactory pro~edure i~ to properly accelerate the middle layer so that when it is heated ~ust before being intro-duced between the other layers it will not be cured until after it iO 6 ~9~i0 is between said layers. This may be advantageously accomplishedwhen the three layer~ are formed at the same time and are hot due to the for~ing, as by calendering, eubing, etc., and the middle layer has had additional heat added to it, as by infr~red light or other means. After it has been introduced between the other layers said other layer~ act a~ in~ulators and retain the heat in the ~iddle layer fos a sufficlent time to cure said middle layer suffic-iently to render the liner imperviou~ to penetration by inflation fluid under inflation pres~ure. Another procedure i8 the same as ~u~t described except that no such additional heat has been added but the middle layer has been compounded with sufficient accelerator to cure at the temperature of sald ~iddle layer sufficiently to render the liner iqperviou~ to penetration by inflation fluid under inflation pressure. A~other procedure is to accelerate the middle layer to a greater degree than the outside and inside layers and after the liner has been assembled sub~ect the liner to a heat for a period of time which will not materially cure the outer and inner surfaces of the liner bue will cure the middle portion of the liner sufficiently to render it impervious to penetration by inflation fluid under inflation pressure.
Although the foregoing relates to two-layer and three-layer liners, any number of layers may be treated to produce the same effect.
Thus, according to this invention, portions of the liner which i~ to be impermeable, may be precured, completely or only partially, before incorporation in the tire, or it may be completely or only partially cured after being incorporated in the tire.
A reinforcing element ~uch as a sheet of fabric made of non-wicking material, such as nylon-i,monofilament, or a non-wicking fabric, such a~ is used in conventional tire-bead construction, may ,, .
-8~

~ 06~4 6 0 be incorporated on the inner surface or outer surface of the liner, or in between these surfaces. This liner will ùsually be composed o butyl rubber. A sheet of such fabric may be coated with natural or synthetic rubber in a conventional manner and be assembled with the tire ad~acent to the liner, which may be made of butyl rubber, and preferably on the inner surface of the liner. The outer ~urface of fabric-containing liners i8 of curable rubber so that it will bond to the carcas~ when cured, and the inner surface may be of curable rubber ~o that the ends of the liner will adhere to one another and may be vulcanized to one another. The reinforcing element prevents moisture from getting into the carca~s.
Instead of laminating layers to make the liner, the same ob~ective may be accomplished by making the liner from a ~ingle sheet and doubling this over by folding it down the middle, or by folding both edges of the single sheet in and bringing them into touching contact, usually at or near the middle of the ~heet. By irradiating only a portion of such a sheet or coating only a portion with excessive accelerator, that portion may be at least partially cured and made impervious to penetration by the inflating fluid under inflation pressure at any time before the tire is put in the mold.
A tire with any liner such as described may be built in a conventional manner and may be formed and/or cured in a mold with-out an air-bag. The ~limination of the air-bag lowers the cost of manufacture. When an air-bag is used, due to the ~act that the liners described stab~lize the thickness of the liners during inflation, liners of a thinner gauge may be used thus creating a substantial saving.
Figure 4 illustrates a mold for curing any of these tires, and it will be noted that no air-bag or bladder is utilized. The _g_ " ~ 0 6~3~U60 mold is constructed in any usual manner. It is shown as being formed of an upper part 15 and lower part 16 with two bead rings 17 fitted into the upper and lower parts to contact the beads of the tire 5.
The liner 6 has been pre-treated or prepared in any of the ways previou~ly discu~sed, 80 a~ to render lt lmpervious to steam and hot -9a-~ 0684~0 water. The bead-~ealing ring 18 may be inserted in the ~ame operation that the conventional b~dder or air-bag i8 inserted.
The ring 18 may be a bull ring made of steel or other metal, or lt may be made o$ rubber or other hard elastomeric material.
This ring may be segmented. The rin8 i8 placed between the beads of the tire before the mold i8 closed, and serve~ a8 a ga~ket.
To prevent leakage between the inner surface of the tire and this ring 18 whon liquid pressure i8 generated in the tlre, it may b~ desirable to provide irregularities in that portion of the surface of the ring 18 ~hich 18 contacted b~ the tire at or above the beads, or both. These irregularltie~ may be in the nature of pro~ections 20 a8 shown on an enlarged scale in Figure 5, or grooves 21 sho~n on an enlarged scale in Figure 6. These run longitudinally around the circumference of the ring 18. The steam or hot water i~
led into the mold through the pipe 19 and provides sufficient pressure within the tire to force it against the mold to groove the tread and form any desired identification and indicia marks desired on the tire 3urface. In Figure 7 the ring 28 is for~ed with spring exte~i~
sions 29. Before the mold i8 closed these are in the position shown in dotted lines. As the mold is closed these extensions are pressed inwardly by the tire and shape the bead and form a tight seal. T~is ring 28 may be a ~teel ring or ~t may be of a firm rubber or resinous material. If made of material other than steel, the extensions 29 may be much thicker and the ring may be solid up to the3e extensions 29 and be compres~ible. Various devices may be employed to permit deflection of the outer ~urface of the member 29 from the position shown in dotted lines, to that shown in ull line~.
The ~ire will be cured at usual temperatures, and steam or hot water is used in the usual manner, but without an air-bag or bladder. Air-bags and bladders are short-lived. By eliminat1ng them, not only i~ the original cost eliminated ~ut also the labor and other ~0684t;0 cost of frequent replacement are eliminated.
A new method of applying a tread to a green carcass i8 illustrated in Figure 8. The carcass 20 is built up in a conven^
tional manner, with or without liner ~1, on a tire-building machine and the carca~s 20 is placed in the mold shown in Figure 8, which may be heated in the conventional manner, which comprises a lower part 22 and an upper part 23 with two bead rings 24 fitted into the upper and lower parts to contact the beads of the tire 20. The mold i8 conventlonal except or the orifice 26 through which tread rubber ~5 18 in~ected, being fed from nozzle 27. A conventional air-bag or bladder may be used or the process using neither of these and previously described may~b~ u~ed~ Hot water or steam under pressure i8 used to expand the green carcass against the sides of the mold.
This pressure, before the tread is in~ected into the mold, may be less than conventional curing pressures and only sufficient to pre~s the green carcass into position against the sides of the mold. The tread stock is in~ected at temperatures at which it flows readily under pressure, such as temperatures of approximately 280 F. and higher, through orifice 26 from nozzle 27.
8he tread stock is usually introduced at or near the low point of the empty portion of the mold cavity outside of the carcass.
It ~ay be introduced at several points. As it is introduced, the air is vented through the air vents usually found in the tire ~old, or separate vent means may be provided. When thettread ha~ been inject-ed the pres~ure in the tire is raised to conventional levels and the csrcass i8 completely cured. It is impractical to thus in~ect tread stock which contains the usual quantity of sulfur and accelerator or the like for curing because the temperature required for rendering the rubber sufficiently fluid for in~ection is high enough to cure such stock. An exception is, when cold-feed extruders are used, in ~ 06~4~;0 which case cold stock is fed into the machine and is raised to high temperatures only for a small increment of time before being extruded According to this invention, the curing sgent added to the tread rubber is only sufficient to partially cure the tread 90 that it may be removed from the mold after curing the carcass, without causing damage to the tread, such as blowing. The tire is then removed from the mo~d and the tread is cured by rearrangement of the molecules of the rubber in the tread stock, by irradiation or other means. An advanta~e of this method ~8 the elimination of inventories of uncured tread8 with lnherent savings such as floor space, investment, labor, etc.
~ Alternatlvely, if irradiation which penetrates to a suffi~ient depth is used, the tread ~ay be cured in the mold before the tire is removed.
'-4~f4 f-~'3 When tires are cured by irradiaeion, even though no ~ulfer be employed, reinfor~ing agents, antiox~dants, antiozonants, etc.
may advantageously be added.

PRE-CURING CERTAIN CARCASS PLIES.
-It is common knowledge in the industry that when very thick tires are cured in`a mold in the ordinary manner~ either (1) outercarcass plies are only partially cured or (2) inner carcass plies are over-cured when the heat for curing is supplied internally b~
steam or hot water through an air-bag ar bladder and additional steam or other means is provided for heating the mold. It i~ pro-posed to overcome this difficulty and shorten the curing time by pre-curing certain of the plies--either completely or preferably only partially. Ordinarily these will be several of the outer fabric plies, because the diff~culty experienced has been encountered in attempting to insure the curing of these outer plies at the inter-face between the fabric plies and the tread, and usually in the outer 10684~0 fabric plies.

OTHER METHODS OF MANUFACTURING NEW TIRES.
Figure 9 shows a cro~s-sec~ion of a tire, with eight fabric plies 30 and tread 31, the carcass of which may be built in the usual manner. The portion of the carcass under the tread 31, prior to the asse~bly of tread 31, ~8 sub~ected to electron irrad~atlon and one or more of the plies msy be part~ally cured or cured~ The building of the tire is then completed in the usual manner. During the during operation in the mold it will take le~s "tlme temperature" to cure 8uch a tire because the plies under the tread have been pre-cured, than in the conventional method. Therefore, the re~ult i8 a more uniformly cured tire. Also a shorter curing time i~ required in the mold which lowers cost. An adhesive ~ay be employed between the carcass 30 and the tread 31.
Difficulty is experienced in uniformly curing the thickest portion of very large tires--that is, tires which comprise many plies, such as fifteen or twenty plies or more. The time required is al90 ob~ectionably great. It is th~ section of the tire through the tread which i~ thickese and therefore most difficult to cure. To cvercome this, it is proposed to pre-cure, partially or completely~ certain of the plies before the assembly of the tire is completed. It i8 not necessary to pre-cure any of the inner plies because they are read~ly cured by heat from the ~team or hot water used to inflate the tire in the mold. Thus, for example, if there are twenty plies in the tire, it i8 not necessary to pre-cure any of the first five plies. T~u~, the first ten plies may be built on the drum in the usual ~anner.
Then the outer surface of this partially built carcass, and prefer-ably the center portion which is to come under the tread, i8 irrad-iated to partially cure the five outer plies. Then several more plies, for example five more, are built up in the usual manner and ~068460 these are similarly cured. The last five are then applied and these are similarly treated, except, as the tire is enlarged, it may be des~rable to fur~her cure the outer plie~ than those which are locs-ted near the inside o the tire. If the tire is very large it may be desirable to vary the amounts of cure in ehe various ~egments as they are applied 80 that those plies which are farthest from the ~urfaces of the completed tire are cured to a greater degree than tho8e nearer the surace. If the ~read is very thin, the plies immediately under it will not be pre-cured to ~he same extent as those farther from the ~urface of the tread.
~ desirable method of pre-curing i8 by progressive irrad-iation. This is accomplished by placing over the building drum a radiation device 12 which covers only the tread portion of the tire, as shown in Figure 1~ During the progressive irradiating operation the number of plies pre-cured in each group may Yary and the number of groups may vary as well as the number of plies that are to be irradiated, depending on the thickness of the plies, compound-ing, voltage used, etc. The number of times the tire is rotated t~
pre-cure the different groups of plies may be ~aried to control the degree of cure in each group. This progresslve curing with irrad-iation assures a more uniformly cured tire and a shorter curing time which will lower the cost.
In building a tire, certain of the plies may be precured before assembly on the drum. Figure 9 shows a cross-section of a tire with eight fabric plies 30 and tread 31. It may be built in by the following method. A conventional tire-building machine i8 used and the first, second, third, fourth and fifth plies, for ex-ample, are assembled in the usual manner and are uncured. Then the sixth, seventh and eighth plies which have been partially or com-pletely pre-cured are assembled into the tire. These cured or par-1068~0 tially cured plies are so thin that they can be shaped as desired.
Then the tread i8 added. If these cured plies are pre-cured by electron irradiation it i8 not necessary that they contain any sul-fur~ but they may be completely cured unless the subsequent curing of the tire is accomplished by irradiation. By only partlally cur-ing certain plies, adhesion between the partially cured and cured plies is improve~. Adhesive msy be e~ployed to insure adhesion.
When a tire is built with many plies in the carcass, such a8 twenty, it may be advantageous to use a combination of methods di8clo8ed in these specifications, The conventional tire-building machine may be used. Also the conventional method o building a tire with the incorporation of irradiating and the use of pre-cured and~or partially pre-cured plies ~ay be used. For exa~ple, the first, second, third, fourth and fifth plies are uncured, and are assembled in the usual manner. The next ten plies which are the sixth through the fifteenth, are partially pre-cured, as by irradi-ation, and assembled in the usual manner. Plies sixteen, seventeen, eighteen, nineteen and twenty are uncured, a~d assembled in the usual manner. Then that portion of these last five plies which will be under the tread after it is assembled is irradiated and partiaLly curedO The tread is then assembled and the tire is cured and fin-ished in the usual ~anner.
This method assures a more uniform cure than the conven-tional method and shortens the oure time which saves cost.

RETREADING TIRES

Various ~ays are disclosed for retreading ~ires. In each case the carcass will be prepared for retreading in the usual manner by removing unwanted tread and, depending upon the shape of the re-tread which is to be applied, a part of the sidewall stock may be ~06~4~ ~

removed, all of which is customary in the different methods of retreading, u~ing different equipment.
Figuxe 8 shows a mold for extruding tread into position on the undured or cured carcass of a new tlre. The equipment of Figure 8 and the general method there disclosed may be used for applying the tread to a carcass which i8 to be retreaded; thi~ oper-ation taking place after the carcas~ has been prepared in the usual manner. It may be desirable to u~e air at room temperature or cooler, and water at tap temperature or cooler in the tire to create pressure in the tire. It may also be desirable to so de~ign the ~old that the heating cavity is only approximately over the tread which is being applied.
The advantages of this method of retreading tire~ are elimina~nn of tread building facilities and the inventorie~ of pre-pared uncured treads all of which reduce costs. Also the carcass i8 sub~ected to less heat which has a deteriorating effect.
- Instead of extruding the tread into a mold, the tread may be extruded onto a prepared carcass by rotating the carcass and using a suitably shaped nozzle that covers the width of the tread, or a narrower nozzle, the stock being reciprocated back and forth over the surface of the carcass to build up a tread. Suitable apparatus is illustrated in ~igure 10. The extruded rubber will or-dinarily be heated to approximately 280 F. or lower or higher to make it sufficiently plastic to be used as described. It may or may not contain sulfur and/or curing agents and/or accelerators. SQme volatile solvent may be added to the rubb~r which will be evaporated before the curing of the tread is commended, although usually this will be avoided because of the danger of solvent vapor forming pockets in the tread.

The methods illustrated in Figures 10 and 11 are ~ 06~34~i0 particularly designed for the retreading of airplane and truck tires which have a tread which i8 only grooved, but may be used for any tires. Figure 10 shows stand 50 with axle 51 supporting wheel 52 with rim 53 on which the tire carcass 54 i~ mounted. A valve 56 in the rim through which the tire may be inflated gives it some rigidity during the application of the tread. The tire is provided with a ~cuff ring 57, but it i8 to be under~tood that tires of sny shape and design may be retreaded by the method disclosed. As illus-trated in Figure 10, stock 58, sufficient to form the tread, is ex-truded from extruder 60 thro~gh nozzle 61 or it may be applied as àcalendered strip or in any other suitable manner. A forming tool 65 i8 po~itioned on the supporting means 66 to shape the tread as the tread stock is extruded; and if desired, forming tool 65 may exert some pre~sure to force the formed tread against the carcass. There may be additional forming tools, such as 65, at other point~ on the circumerence of the tread for the purpose ~ shapiDg and/or pressure. After the tread is applied the tire may be rotated ~ev-eral times for the purpose of shaping and/or pressure.
The tread may be extruded with the proper tread outiine and tread-forming tool 65 may be positioned on the supporting means 66 to maintain the proper ~hape and/or exert pressure on the tread to press it against the carcas~. There may be other forming tools, such as 65, at other points on the circumference of the tire.
Another method of operating is by extruding, calendering or otherwise shaping the tread stock as a thin ribbon the width of the tread or apply it as a calendered strip, while the tire i8 being rotated, and after quite a few rotations sufficient tread ~ill be applied to build up the desired tread thickness. As the ribbons are being applied to the tire, the tread-forming roller wlll ~hape them to the proper design. A roller 70, such as illustrated iD Figure 12, 10~46~
may be used. The carc ~ s 67 is shown with tread 68 built upon it.
Another method of operating is to extrude a tread stock as a thin, narrow strip while the tire is being rotated. The stri~ i8 oscillated back and forth across the tread portion and after quite a few rotation~ sufficient tread will be applied to build up the de-sired tread thickness. As the ribbon is being applied to the tire ehe tread-forming tool 65 or tools may be used to shape it to the proper design. A tire retreaded in manners ~ust disclosed, is pref-erably cured by electron irradiation which may be accompli8hed by rot8ting tire and wheel 54 and 52, re8pectively, under a radiation device 8uch as device 12 shown in Figure l; and, if desired, may becured in a conventional manner or a combination of both. A grooved tread design may be cut into the tread by any conventional method or a groove may be rolled into the green tread by forming tool as shown in Figure 12, preferably after the tread has been built up or while the last layer is being laid on the tread.
A method which is preferred is illustrated by Figur~ 10.
Stock 58, being a thin ribbon, for example, approximately 1/8 inch thick, and approximately the width of the tread, is extruded as the tire is roeated and the tread is built up to any desired thickness.
For~ing tool 65 shapes the tread and several other forming tools may be u8ed. Radiation device 59, similar to or identical with device 12 in Figure 1, is illustrated in Figure 10. It only par-tially cures the tread stock during each exposure as the stock i8 passed by it. The cure ~ay, for example, be only a one-fourth cure.
The radiation device may be ad~usted to cure to a depth of 1/2 inch, more or less. At the completion of each rotation the surface stock i~ only partially cured and, therefore, the next layer of hot stock adheres to it. The stock is progr~ ~vely cured as the rotation continues and the successive layers are adhered to one another.

~06~46V
If the stock is one-quarter cured on each exposure, at the completion of the fourth rotation the first layer is fully cured, the second layer is three-fourths cured, the third layer is one-half cured, and the fourth layer is only one-fourth cured. This "progres~
ive irradiation" continues until the last layer i~ applied and then the tire is given three additional xotations which cures the last three layers.
A ribbon not the full width o~ the tread may be used and osc~llated back and or~h across the tread surface until the desired tread thickness i8 obtained, the level of radiation being ad~ustad to obtain the proper cure.
Grooves in the tread may be made by the use of a for~ing tool such as the tool 70 shown in Figure 12.
In each of the retreading operations in which the tread stock is cured by irradiation, this stock may include sulfur and other curing ingredients, or it may contain no such curing co~posi-tions because irradiation rearranges the molecular structure of the rubber and thus cures it. A small amount of sulfur may be included in such stock, and the extrusion will take place rapidly before the rubber becomes ob~ectionably cured at the extrusion temperature. The amount of curing ingredient~ that can be incorporated in the stock will depend upon the extruding temperature and the length of time that the stock is maintained at this temperature. It i8 desirable to include a ~mall amount of sulfur and accelerator so that the stock will cure to a slight extent after it has left the extruslon device and been shaped on the carcass. Such ~etting of the retread-ing stock will facilitate handling the retreaded tire before the cure is completed. If a normal amount of sulfur, etc. are included in the rubber, unless the time ~uring which the stock i5 heated is very short, curing will set in and the rubber will become ~re-cured -` 10ti8460 before it is shaped on the carcass. An exception is, when cold-feed extruders are used, in which case cold stock i~ fed into the machine and i8 raised to high temperatures only for a small incre-ment of time before being extruded.
The advantages of these methods of retreading include not heating the carcass in a mold, and, therefore, the life of the tire is increased and the tire may be retreaded a greater number o~ times, the curing time i~ shorter, press equipment i8 eliminated and inventories of green tread stocks are eliminated and thus savings in cost are made.
Apparatus and processes for forming treads and curing them by electron irradiation have been disclosed. These tread stock~ may be of ordinary rubbers (except those which cannot be cured by elec-tron irradiation, such as butyl rubber), and it has been explained that no sulfur i8 required for curing by irradiation. A desirable tread stock is a high molecular weight butadiene-styrene copolymer such as has been found desirable for tread stocks, but which i~ of high viscosity and difficult to handle in ordinary processing equip-ment. Reinforcing agents, antioxidants, antiozonants, etc. may be 20included even though no sulfur is added.

Claims (99)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process of forming a tire having a plurality of tire elements, the process comprising the steps of subjecting to electron radiation, or other form of radiation having a similar curing effect on exposed rubber, at least a portion of rubber in one or more of the tire elements in which the rubber is curable by such radiation, thereby at least partially curing said portion of rubber in said one or more of the tire elements without fully curing all said rubber in all the tire elements, assembling the tire elements into a tire, and sub-sequently final curing the uncured or partially cured rubber in all the tire elements.

2. A process according to claim 1 in which said rubber is in a pneumatic tire liner and at least a part of said rubber is irradiated.

3. A process according to claim 1 in which said rubber is in a tire tread stock and at least a part of said rubber is subjected to said radiation.

4. A process according to claim 1 in which said rubber is in a tire carcass ply and at least a part of said rubber is subjected to said radiation.

5. A process according to claim 1 in which said rubber is in a carcass in a pneumatic tire and at least a part of said rubber is subjected to said radiation.

6. A process according to claim 1 in which at least a portion of a rubber layer in a multi-layer element of a tire is subjected to said radiation.

7. A process according to claim 1 in which movement is effected between the source of the irradiation and the one or more elements.

8. A process according to claim 7 in which the irradiation is continuous.

9. A process according to claim 7 in which a length of rubber-containing element is progressively irradiated as it is wound Up.

10. A process according to claim 1 in which a portion of the tire is built up by successive layers containing rubber, and progressively partially curing at least one of said layers by irradiation as it is placed in contact with another layer which is partially cured by irradiation and eventually completing the cure.

11. A process according to claim 1 in which said rubber which is at least partially cured presents a surface which is contacted with a rubber surface of another of the tire elements.

12. A process according to claim 1 in which one surface of one of the tire elements is irradiated beyond the depth at which the rubber is completely cured, and beyond this depth the rubber is partially cured.

13. A process according to claim 1 in which one surface of a tire sheet element is at least partially cured and is not cured to a depth greater than 1/8 of an inch.

14. A process according to claim 1 in which one surface of a tire sheet element is cured by irradiation to a depth greater than 1/8 of an inch.

15. A process according to claim 1 in which only one surface of a tire sheet element is cured by irradiation to a depth of at least 1/8 of an inch.

16. A process according to claim 1 in which one surface of a tire sheet element is irradiated using such voltage that said surface is cured to a greater extent than the opposite surface.

17. A process according to claim 1 in which two rubber elements are bonded together, at least one of said elements being composed of rubber which is curable by said irradiation, and the process comprising irradiating the surface of said one element and bonding it to the other element by pressing the two surfaces together.

18. A process according to claim 17 in which one surface of both elements is irradiated and the surfaces are pressed into contact with one another.

19. A process according to claim 1 which comprises partially curing rubber by irradiation, placing said partially cured rubber in contact with other curable rubber, and sub-sequently curing both rubbers.

20. A process according to claim 19 in which the sub-sequent curing of both rubbers is effected by said irradiation.

21. A process according to claim 1 in which the rubber has a butyl rubber incorporated in it but comprises sufficient rubber curable by said irradiation to accomplish the degree of cure desired and irradiating to obtain the desired cure.

22. A pneumatic tire comprising a rubber carcass tire element and a rubber tread tire element, the surface of one of said tire elements at the interface therebetween being rubber at least partially cured by electron radiation, or other form of radiation having a similar curing effect on exposed rubber.

23. A process according to claim 1 in which the final curing is performed in a mold without an air bag or bladder.

24. A process according to claim 2 in which the liner is provided at the surface of a tire carcass which is adapted to contact inflation fluid.

25. A process according to claim 24 in which the rubber is natural and/or synthetic rubber.

26. A process according to claim 24 in which the liner is composed of a plurality of layers at least a portion of one of which is curable by irradiation, which process comprises subjecting said layer to irradiation and thereby at least partially curing a portion of said layer and laminating another layer to said layer.

27. A process according to claim 26 in which the lamination is accomplished after the irradiation.

28. A process according to claim 24 in which the liner has an inner surface and an outer surface, said inner surface being completely cured and said outer surface being no more than partially cured.

29. A process according to claim 24 in which the irradiation is effected to at least partially cure an outer surface of the liner.

30. A process according to claim 24 in which the irradiation is effected to at least partially cure an inner surface of the liner.

31. A process according to claim 26 in which one layer of the liner is composed of a rubber curable by irradiation and another layer is composed of rubber which is not so curable, and the liner is subject to irradiation.

32. A process according to claim 26 which comprises irradiating only an outer layer of the liner.

33. A process according to claim 24 in which the irradiation is progressive and continuous.

34. A process according to claim 26 which comprises at least partially curing by irradiation at least a portion of said layer and said other layer and then laminating these two layers.

35. A process according to claim 34 in which the inner layer is composed of a butyl rubber.

36. A process according to claim 34 in which the layer is coextensive with the liner.

37. A process according to claim 26 in which at least one layer other than an inner layer of the liner is composed of rubber which is curable by said irradiation, which process comprises curing at least one of said other layers by said irradiation without curing the inner layer.

38. A process according to claim 26 in which an inner layer of the liner is composed of a butyl rubber and at least one other layer comprises rubber which is curable by said irrad-iation, which process comprises at least partially curing by said irradiation at least one of said other layers which is coextensive with the liner.

39. A process according to claim 26 which comprises at least partially curing the surface and the underlying stratum of one layer of the liner by irradiation without curing an inner layer of the liner which layer is a butyl rubber and which is adapted to face toward subsequent tire-inflating fluid, and without completely curing the surface of the liner which is adapted to contact the tire carcass, and laminating the layers, the uncured inner layer and the surface which is adapted to contact the tire carcass being suitable to be joined by a good seal when the ends of the liner are united.

40. A process according to claim 2 in which at least a por-tion of said rubber is at least partially cured before incor-poration in the tire.

41. A process according to claim 26 wherein the liner has inner and outer surfaces, the process comprising at least partially curing by irradiation one layer which incorporates rubber, which layer is substantially coextensive with the liner, and forming the inner surface of the liner by laminating to said layer another layer which includes rubber, without completely curing the outer surface of the liner.

42. A process according to claim 5 in which at least a por-tion of an outer surface of the carcass of the tire is sub-jected to said radiation before tread stock is applied thereto.

43. A process according to claim 42 in which the central portion of an outer carcass ply is irradiated to a greater degree than edge portions thereof.

44. A process according to claim 5 in which a ply of a multi-ply carcass other than an inner ply thereof is at least partially cured by exposure to said radiation.

45. A process according to claim 19 in which the subsequent curing of both rubbers is effected by sulfur.

46. A process according to claim 5 in which prior to assembly of the carcass at least a portion of only that portion of an outer carcass ply which is to come under tread is irradiated to a greater degree than edge portions thereof.

47. A process according to claim 5 in which the portion of the carcass which is located under tread in the finished tire is irradiated prior to assembly with the tread to insure its being satisfactorily cured after the final cure of the tire.

48. A process according to claim 5 in which that portion of an outer ply which will be under tread is at least partially cured by irradiation before assembly of the carcass with the tread, and thereafter the tread is assembled with the carcass.

49. A process according to claim 5 in which, before assembly in a carcass, that portion of a plurality of carcass plies which will be located under tire tread are irradiated to a greater degree than portions of those plies which will not be located under the tread.

50. A process according to claim 5 in which the central portion of the carcass which is the portion which will come under tread is irradiated to a greater degree than adjacent outer portions.

51. A process according to claim 5 in which that portion of one or more carcass plies which will come under tread is so irradiated prior to assembly with the tread that after such assembly the outer portion of the carcass under the tread is cured more uniformly than if no such irradiation were carried out.

52. A process according to claim 5 in which that portion of one or more carcass plies which will come under tread is so irradiated prior to assembly with the tread, as to permit shortening of the cure of the completed tire.

53. A process according to claim 5 in which the carcass is built up from a plurality of plies at least one of which includes radiation-curable rubber and at least a portion of the ply is at least partially cured by irradiation before assembly in the carcass.

54. A process according to claim 5 in which the rubber in only one portion of a carcass ply is subjected to irradiation.

55. A process according to claim 5 in which one ply of a multi-ply carcass is at least partially cured without curing an inner ply thereof.

56. A process according to claim 5 in which plies of the carcass which are to be farther from tire tread and irra-diated to a greater degree than plies that are nearer the tread.

57. A process according to claim 5 in which plies of the carcass which are to be nearer tire tread are irradiated to a greater degree than plies that are further from the tread.

58. A process according to claim 3 in which said rubber, before incorporation in the tire, is at least partially cured by said radiation.

59. A process according to claim 57 in which tire tread stock is shaped, and before incorporation in the tire, is at least partially cured by said radiation.

60. A process according to claim 58 in which the tire tread stock is shaped, said shaping being effected by extrusion.

61. A process according to claim 3 in which a surface of extruded tread stock is irradiated and the irradiated surface and a carcass surface are thereafter brought into contact.

62. A process according to claim 3 in which at least a por-tion of the tire tread stock which contains sulfur-containing rubber is at least partially cured both by heating and by electron irradiation, or other form of radiation having a similar curing effect on rubber, the curing by irradiation being effected before the final curing of the tire.

63. A process according to claim 3 in which one rubber-containing layer of multi-layer tire tread stock is irradiated and said layer is then placed in contact with another layer thereof.

64. A process according to claim 3 in which one rubber-containing layer of multi-layer tire tread stock is irradiated and thereafter the resulting tread stock is united to a tire carcass.

65. A process according to claim 3 in which the tire tread stock is bonded to a tire carcass, the tire tread stock being irradiated.

66. A process according to claim 3 which includes only partially curing the rubber of at least a portion of the tread stock by irradiation before the tire is completed.

67. A process according to claim 3 which comprises at least partially irradiating only one layer of multi-layer tread stock and thereafter uniting the tread stock to a tire carcass.

68. A process according to claim 3 in which a first surface of the tire tread stock is at least partially cured by irradiation using such voltage that said surface is cured to a greater extent than the opposite surface.

69. A process according to claim 3 in which sulfur-curable tread stock containing irradiation-curable rubber is partially cured by irradiation and this tread stock is there-after cured by heating in a mold.

70. A process according to claim 3 in which an inner side of the tread stock is at least partially cured by irradia-tion prior to curing an outer surface thereof.

71. A process according to claim 1 in which two elements of a rubber tire are bonded together, the surface of one element being composed of rubber, which process comprises irradiating at least a portion of said surface by irradiation and thereafter bringing said portion and the other element into pressure contact and thereby bonding the elements together.

72. A process according to claim 71 in which at least a portion of the surface of each element is composed of rubber, and said surfaces are irradiated and then brought into pressure contact, thereby bonding the two elements together.

73. A process according to claim 71 in which the two elements are tire sheet elements and they are bonded together by pressing irradiated surfaces of the two sheets together.

74. A process according to claim 73 in which the surfaces are irradiated by electrons.

75. A process according to claim 71 in which at least one of the rubber surfaces is compounded with sulfur and the bonding by irradiation is supplemented by heating the sulfur-containing surface to cause sulfur vulcanization.

76. A process according to claim 3 which comprises at least partially curing by irradiation at least a portion of an outer portion of the tread stock.

77. A process according to claim 3 which comprises at least partially curing by irradiation at least a portion of an inner portion of the tread stock.

78. A process according to claim 77 in which thereafter at least a portion of an outer portion of the tread stock is cured.

79. A process according to claim 3 in which the tread stock has inner and outer surfaces from which the tread stock is irradiated.

80. A process according to claim 4, in which at least a part of said rubber is at least partially cured by said radiation before assembly in the tire.

81. A process according to claim 4 in which the ply is one of a plurality thereof in a multi-ply carcass, said one of the plies being treated without curing an inner ply of the carcass, and at least a portion of said first-mentioned ply being at least partially cured by irradiation before assembly in the tire.

82. A process according to claim 4 in which, before assembly in the tire, one portion of said ply is at least partially cured to a greater degree than another portion thereof.

83. A process according to claim 4 in which, before assembly in the tire, at least a portion of only that portion of said ply which is to come under tire tread is irradiated and at least partially cured.

84. A process according to claim 4 in which, before assembly in the tire, one portion of said ply is at least partially cured by irradiation without so curing another portion of said ply.

85. A process according to claim 4 in which, before assembly in the tire, at least a portion of that portion of said ply which will be in the thickest section of the tire, is cured or partially cured by irradiation.

86. A process according to claim 4 in which, prior to assembly of the tire carcass ply in the tire, only a portion of the ply is at least partially cured by irradiation.

87. A process according to claim 4 in which a surface of said ply immediately under tire tread is precured to a lesser degree than a ply farther from the surface of the tread.

88. A process of claim 87 in which the precuring is effected by electron irradiation.

89. A process according to claim 5 in which at least a portion of a ply of said carcass immediately under tire tread is precured to a lesser degree than a ply farther from the surface of the tread.

90. A process according to claim 5 in which the carcass is a multi-ply carcass, only a portion of one ply of which is at least partially cured by irradiation and another ply of which is not so cured.

91. A process according to claim 3 in which the tread stock includes no substantial amount of sulfur and incorporates rubber of such high molecular weight that it is difficult to handle in ordinary processing equipment, which process comprises curing said tread stock by irradiation.

92. A process according to claim 3 in which the tread stock contains no sulfur, which process comprises curing or partially curing said tread stock by irradiation.

93. A process according to claim 3 in which at least a portion of the tread stock is irradiated which comprises curing or partially curing by irradiation at least a portion of said tread stock before curing in a conventional manner.

94. A process according to claim 3 in which at least a portion of the tread stock is irradiated which comprises curing or partially curing by irradiation at least a portion of said tread stock before being subject to further curing.

95. A process according to claim 3 in which at least a portion of the tread stock is irradiated which comprises irradiating at least a portion of said tread stock from an outer surface thereof.

96. A process according to claim 3 in which the tread stock is irradiated from one surface which comprises irradiating from said surface at least a portion of said surface and curing a portion of the tread stock below said surface to a lesser degree than said surface.

97. A process according to claim 3 in which a ply of multi-ply tire stock is at least partially cured by irradiation, and thereafter it is placed in contact with another ply of said tread stock.

98. A process according to claim 1, wherein said radiation is electron radiation.

99. A pneumatic tire according to claim 22, wherein said radiation is electron radiation.