CA1054913A - Laminated pneumatic tire and method of making same - Google Patents
Laminated pneumatic tire and method of making sameInfo
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- CA1054913A CA1054913A CA316,437A CA316437A CA1054913A CA 1054913 A CA1054913 A CA 1054913A CA 316437 A CA316437 A CA 316437A CA 1054913 A CA1054913 A CA 1054913A
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Abstract
Abstract of the Disclosure A laminated pneumatic rubber tire is disclosed which may be free of reinforcing fabric and which is made of at least seven alternating layers of high-modulus and low-modulus polymeric material such as synthetic rubber, polyurethane rubber, and various elastoplastic and high-modulus plastic materials including polycarbonate, nylon, epoxide resins, polystyrene and the like. The alternating hard and soft layers provide the tire with a necessary durability and resistance to flex cracking. The tire may contain low-modulus polymeric layers with a Young's flexural modulus not in excess of 3000 pounds per square inch. The high-modulus layers of the tire may have a Young's modulus from 3000 to 50,000 or higher. The high-modulus layers have a 10 percent modulus which is at least twice that of the low-modulus layers.
The polymeric material has a calculated molecular weight of at least 10,000.
The polymeric material has a calculated molecular weight of at least 10,000.
Description
~ e present invention relates to pneumatic tires having portions which are free of reinforcing fabric and more particularly to laminated pneumatic tires containing hard and soft layers arranged to provide a high resistance to flex cracking.
This application is a division of Canadian patent application Serial No. 279,751 filed June 2, 1977~
It has long been recognized in the pneumatic tire industry that fabric reinforced tires have many disadvantages and that it might be desirable to build a fabric-free tire which could be manufactured by less expensive proceduresO Not only is the conventional method of tire fabrication slow and expensive, requiring separate handling and processing of one or more kinds of rubber and/or cord fabric for each tire, calendering and handling of individual plies, and final manual assembly of all of the components, but also, the conventional tire construction is not readily adapted to any kind of automation which would reduce the labor costs and improve the tire quality and uniformityO
An additional cause of excessive manufacturing expense associated with conven-tional tire construction is the large amount of factory space taken up, first, by the many large curing presses required to cure green tires, one at a time, for anywhere from about 12 minutes to more than 20 minutes, and second, by the rubber processing and mixing equipment such as mills, Banburys, extruders, . calenders, and tire building machines.
Other problems in conventional fabric-reinforced tires are the difficulty of uniform placement of the many components of the tire and the difficulty of obtaining uniform expansion from the cylindrical shape on a flat drum to the inal toroidal shapeO The laminated tire of the present invention eliminates some of these problems.
In its search for a tire configuration and construction method which does not require the lamination of cords and rubber compound and the ':
subsequent manual buildup o~ ply layers, the tire industry has attempted to make at least the carcass portion of the tire by molding or casting a liquid polymer, such as a polyurethane, to the desired shape. The tire illustrated in United States Patent No. 2,902,072 issued September 1, 1959 to Mobay Chemical Company comprises a tread, inner and outer sidewalls, and a cellular poly-urethane filling the space between the inner and outer sidewallsO United States Patent 3,20~,500 da~ed September 28, 1965 to U. Knipp et al. discloses the fabrication of the carcass portion of a pneumatic tire by mo~ding a poly-urethane or polyamide into a single, generally homogeneous layerO United States Patent 3,27~,322 issued September 20, 1966 to Chemechanical IncO dis-closes a method of flow-forming a material such asapolyurethane, using a doctor blade, to make a strip of material which can subsequently be formed into a tire carcass. United States Patent 3,386,485 issued June 4, 1968 to The Dunlop Company Ltdo illustrates a method of making a "fabricless" pneumatic tire from any one of a number of suggested polymers and copol~mers by separately molding the annular halves of a tire and subsequently molding the two halves together in a different pressO
U~ted States Patent 3,396,773 issued August 13, 1968 to Sterling Alderfer Company illustrates the application of centrifugal casting techniques for making a tire which is described as being solid rather than pneumaticO
The general concept of centrifugal casting has been applied to pneumatic tires as illustrated in United States Patent 3,555,141 dated January 12, 1971 ~0 H~Wo Beneze which discloses a method in which a heated mold, having its internal surface conforming to the ex~ernal shape of a tire, is rotated while a liquid polyurethane is introduced thereinO The rotation of the mold causes the polyurethane to flow and cover the entire inner surface of the mold and a stationary -~emplate, having the same shape as the inside of the tire, serves to spread the material in the same manner as a doctor bladeO In llnited States ~ .
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.3 Patent No. 3,701,374 dated October 31, 1972 to DoR~ McGillvary there is a disclosure of a fabric-free tire carcass made of a polyurethane elastomer, another elastomer, and methods of making the tire to produce the necessary physical propertiesO
While many of the problems associated with conventional tire con-struction can be reduced or eliminated by fabrication of tires in accordance with the prior art patents discussed above, the cast tire configuration such as the type proposed in these patents has a number of serious problems, and use o such special tires has not been widespread. The major problem in the cast tire, in terms of tire life, is what is known as flex fa~igue failureO
Under the weight of the vehicle the portion of a tire in contact with the ground is deformed with the result that the rubber is continually flexed dur-ing operation of the ~ireO In conventional fabric reinforced tires, the fabric may for example withstand at least 85 percent of the inflation pressure and the rubber less than 15 percentO If the fabric is to be eliminated without changing the general shape of the tire, then it would be necessary to employ a rubber of higher-modulus to enable the tire to maintain its shape. ~owever, the harder rubbers have a relatively short life due to flex fatigue failure.
For example, whenever a small crack or defect occurs due to a microscopic flaw or a cut ~rom a sharp object, there is a tendency for a crack to develop and grow during continual flexing until the tire fails or becomas dangerous.
When using fabric reinforcement it is possible to employ softer rubbers which do not have the serious flex fatigue problem~ However, when making a fabric-free tire using stiffer polymars, which are required to obtain the necessary ; strength, the flex fatigue problem is extremely serious. Experimental data with respect to fabric-free tires seems to indicate that sidewall flex crack-ing is the principle mode of failureO
kcording to one aspect of the invention, a pneumatic tire casing ~ 3 ,~, .
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5~ 3 has a tread portion and flexible sidewall portions which are free of fabric reinforcement~ each sidewall portion comprising a series of layers of flexible polymeric ma~erial with a calculated molecular weight of at least 10,000 and a Shore A durometer hardness of at least 20, a series of said layers compris-ing low-modulus polymeric material with a Young's modulus which is from about 100 to about 5,~00 pounds per square inch, a plurality of said layers being interspersed with the low-modulus layers and comprising a higher-modulus polymeric material with a Young's modulus which is from about 3000 to 100~000 -pounds per square inch, each of which layers has a Young's modulus at least twice that of the next adjacent low-modulus layer.
According to one preferred embodiment, the tread portion and side-wall portions include a carcass in the form of a flexible laminate, there are at least seven layers of said flexible polymeric material having a tensile strength of at least 2000 pounds per square inch, each layer has a Young's :Elexural modulus of at least 1000, and the series of higher Young's modulus layers have a tensile modulus in one direction at 10 percent elongation which is at least twice the tensile modulus of adjacent layers in said one direction at 10 percent elongation, whereby the laminate has a high resistance to flex - cracking.
The plurality of layers of polymeric material having a relatively high tensile modulus preferably have a modulus between 5000 to 50,000 pounds per square inch. The layers are preferably arranged in an alternate pattern in such a manner as to provide the overall tire carcass with the desired strength and stiffness ~hile at the same time providing a much greater resis-tance to flex fatigue failure than could be obtained from a homogeneous construction.
The tires o the present invention are preferably made from fluid ,~ :
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poly~neric materials ~hich haye a viscosity at processing temperatures such that they can flo~ and form the desired layers of the tire in a reasonable period of time. Rotational casting methods may be employed with the fluid polymers as well as other forming processes.
T he process for making a lamina~ed pneumatic tire carcass having improved resistance to flex cracking comprises applying to an annular form a first continuous layer comprising a liquid polymeric material having a vis-cosity less than 100,000 centipoises at 30C then partially curing the liquid thereafterJ applying to the first partially cured layer a continuous layer of a second liquid polymeric material having a viscosity less than 100,000 centipoises at 30C then partially curing the second liquid, and repeating the sequential application and partial cure of polymeric material to form a cur- -able laminate, and heating and curing the laminate while it has a generally toroidal shape, the cured polymeric material of each layer having a Shore A
durometer hardness of at least 20, a first series of said layers comprising a plurality o cured low-modulus polymeric material with a Young9s flexural modulus from about 100 to about 5,000 pounds per square inch, a second series of a plurality of high modulus layers being alternated with the low-modulus layers and having a tensile modulus at 10 percent elongation in any direction which is at least twice that of said low-modulus layers in any direction.
When using fluid polyurethane polymers a preferred method of form-ing the tire is to provide a mold with the desired annular shape of the tire, to apply to the interior surface of the mold a generally uniform layer of the polymeric material, thereafter to cure the layer or allow it to cure at least partially, and thereafter to apply a subsequent generally uniform layer with a different modulus. A large number of layers are applied and cured in this manne~ until the desired thickness is obtainedO A doctor blade may be employ-ed ~o shape the layers o~ to provide a uniform thickness~ and relative ,:
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rotation may be provided between the mold and the blade to achieve this~ Where a liquid polymeric material is applied from a spray no~zle or other applicator, relative movement may be provided between the mold and the applicator during application of the liquid polymer, for example by rotating the mold relative to the applicator or vice versa. If desired the fluid materials may be so compounded and so ~reated that the necessary curing of one layer prior to ~pplication of the next layer takes place during only one or two revolutions of the mold.
The rotational casting method may be employed to form a large number of different layers of polyurethane polymers or other suitable polymers ., in various thicknesses from 0.001 inch to 0Ol inch. The hard and soft layers preferably alternate, but many different arrangements are possible which will provide the desired resistance to flex cracking.
When making a pneumatic tire by the above method from fluid poly-urethane polymers, the tensile modulus and hardness of the different layers can be changed by changing the amount or type of curing agent used and the molecular weight or type of urethane polymer being used.
In the drawings, Figure 1 is a fragmentary perspective view of a pneumatic tire of the type made in accordance with the present invention on a reduced scale;
Figure 2 is a fragmentary cross-sectional view of the laminated tire of Figure 1 showing a portion of the sidewall of the tire;
Figures 3, 4 and 5 are fragmentary views similar to Figure 2 show- :
ing alternate embodiments of the laminated tire of this invention; and Figure 6 is a partially schematic cross-sectional view of one embodiment of an apparatus for making laminated pneumatic tires in accordance with the process of the present inventionO
~eferring more particularly to the drawings, which are for the :.
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purpose of illustrating preferred embodiments of the invention and not for the purpose of limiting the same, Figure 1 shows a pneumatic tire 10 comprising a tread portion 12 and two sidewall portions 140 It will be understood that Figure 1 is partially schematic and that conventional circumferential rein-. forcing belts or other reinforcing means may be provided in the tread portion 12 without providing fabric reinforcement or other reinforcement in the side-wall portions 14. In other words the cross section of the tire may be general-~ ly as shown in United States Patent No. 3,701,37~ or in other patents .
mentioned previouslyO It will also be understood that~ while the tire pre-ferably has a toroidal cross section, the present invention also applies to ~ tires of special cross section as illustrated for example in United States ; Patent No. 3,840,060 issued October 8, 197~ to Industrie Pirelli S~poAo Conventional means may be provided on the tire or on the wheel to reinforce :
; the bead portion of the tire or to help hold it in place on the wheel rimO
e tire 10 of this invention is preferably made with a substantial number of layers of polymeric material, each layer preferably having a general-ly uniform thickness and completely covering the adjacent layer. In the embodiment of Figure 2, the tire carcass and each o the sidewall porti.ons 1~ :
comprises a thirteen-layer laminate made up of alternating high-and low-modulus layers H and L. The low-modulus layer L is provided at both the inner . and outer surfaces of the tir0, and every other layer comprises a high-modulus Iayer H. This particular configuration makes it possible to obtain a tire of the desired strength and stiff.ness by use of high-modulus layers while at the same time minimizing the tendency for flex crackingO It will be under-stood that while thirteen-layers are often desirable, a different number of layers can also provide good resultsO
., Figure 3 illustrates a different embodiment, also with thirteen-layers, wherein a mèdium modulus layer M is provided in addition to the high-... .
modulus layers H and the lo~-modulus layers Lo This arrangement is similar to that o~ Flgure 2 in that the layers H and L alternate regularly with the low-modulus layer L at the inner and outer surface of the tire, but a medium modulus layer M is provided between each layer L and the nearest layer H.
This makes it possible to employ layers H of extremely high-modulus without so abrupt a change in modulus when going from layer H to layer Lo Where the tire has a very large number of layers such as 25 to 50 or more, it may be desir-able to provide more than one layer of intermediate modulus between thc low-modulus layer and the high-modulus layerO
; 10 ~igure 4 illustrates another embodiment of the invention wherein the low- and high-modulus layers alternate like Figure 2 in the central portion of the laminated structure and wherein several of the outer layers are formed of the same low-modulus material. In this Figure the first three layers on both the inside and outside of the carcass portion are the low-modulus layers Lo One reason for using this type of construction is that the inner and outer surface portions of the tire are subjected to greater bending strains which are withstood better by the low-modulus materialO
Figure 5 shows another embodiment of the invention in which the various layers have different thicknessesO In the embodiments of Figures 2, 3 and 4 all of the layers are shown as having the same thickness, but it will be understood that some variation in thickness can be provided and that it is often desirable to provide low-modulus layers with a thickness somewhat greater than the high-modulus layers. In the embodiment of Figure 5 the low- and high-modulus layers alternate regularly like Figure 2 except that two low-modulus layers L are provided at the inner surface of the carcass~
Many different methods may be employed to build tires according to the present invention. The uncured tire can for example be built by forming a cylindrical laminate having ten or more layers and thereafter expanding the .
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laminate from the cyllndrical to the toroidal shape by a method somewhat similar to the conventional flat-band processO The tire may also be formed by applying the layers to the laminate while the laminate has a toroidal shape or other desired cross section as described hereinafter.
Some of the first tires made in accordance with the present inven-tion were fabricated by manually applying to the outer surface of a metal mold a series of layers of liquid polymeric material having a fairly uniform thick-ness. Another possible method of building a tire is to apply successive layers of uncured sheet rubber or the like. However, manual methods are probably impractical due to the excessive cost of manufacture. In order to reduce cost it is preferable to employ a liquid polymeric material and auto-mated proceduresO
The polymeric materials which may be used to make tires according to the present invention are elastomers, elastoplastic materials or high-modulus plastics. ~le softer low-modulus layers of the tire are made from the - elastomeric and/or elastoplastic materials and the harder high-modulus layers are preferably made from the elastoplastic materials or high-modulus plastics.
The elastomers are characterized by major glass transition tempera-tures below about minus 20 degrees Centigrade, Young's moduli in the range of ~0 100 to 6000 pounds per square inch, and the ability to sustain elongations of 100 percent or more without permanent deformation or ruptureO The useful elastomers include polyurethane rubber, natural rubber, poly(butadiene) and various other synthetic rubbers including SBR rubbers.
The elastoplasticpolymeric materials can have Young's moduli in the range of 3000 to 50,000 pounds per square inchO At room temperature these materials usually exhibit yield points below 50 percent elongation and ultimate tensile strengths above 4000 pounds per square inch and ultimate elongations g~eate~ than 100 percent. These materials are usually characterized by being _ 9 _ : . . . . . .
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multiphase in that glassy or crystalline domain structures are usually detect-able. Typical materials in this group are block polymers, such as s~yrene-butadiene-styrene triblock polymers, polyester block polymers, segmented polyurethane polymers and ionomers.
The high-modulus plastic materials are characteri~ed by Young's moduli of 50,000 pounds per square inch or higher and yield points and/or failure points at elongations below about 15 percent. They ~ould have a major glass or melting transition temperature above 100C. Suitable materials in this group include compositions from polyamides, polycarbonates, epoxide resins and polystyrenes.
The elastomeric ma~erials used in the low-modulus layers of the tire of this invention should have the major glass transition temperature below about -20C. and can contain groupings capable of forming covalent cross-links. The molecular weight of the chains between covalent cross-links is preferably about 5,00 to 40,000 and more preferably 8,000 to 20,000.
Generally the polymeric material forming the various layers of the laminated tire of this invention should have a calculated molecular weight of at least 10,000 and a Shore A durometer hardness o~ at least 20 and preferably provide a tensi]e strength of at least lOOO pounds per square inchO The softer low-modulus layers have an elongation which is usually at least 30 percent and preferably at least 50 percent and a Shore A durometer hardness which is at least 30 and preferably no more than 90O The polymeric material of the so~ter low-modulus layers preferably has a tensile strength of at least 2000 pounds per square inchO
There is a general relationship between Shore hardness and Young's modulus as follows:
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Shore Hardness Young's Modulus CBoSo ~ IoRoH~ (psi) 13~0 It should be ~mderstood tha~ the Shore Hardness and Young's modulus values given herein must generally correlate with this relationshipO
The cured low-modulus layers of the tire preferably have Young's moduli in the range of 300 to 5000 pounds per square inch and usually in the ; range of 500 to 3000 pounds per square inch. The preferred hardness depends on the thicknesses of the various layers, their arrangement, the stiffness of the harder layers and other factors.
The cured high-modulus layers have Young's moduli in the range of 3000 to 100,000 pounds per square inch which is usually at least twice that of the adjacent low~modulus layers and is preferably in the range of about 5000 to 50,000 pounds per square inch~ The ratio of the Young's modulus of each hard layer of the laminated ~ire to the Young's modulus of each soft -layer can be up to 300:1 but is more frequently in the range of 3:1 to 20:1 in a passenger car tireO
The preferred modulus for the harder layers dependsJ of course, on many factors and should be selected to provide the composit~ tire with the desired overall modulus and stiffnessO For example, if the laminated carcass portion of the tire consists of 50 percent by weight of high-modulus polymeric ~ .
material and 50 percent by weight of low-modulus material, then the Young's modulus might be 500 to 2000 psi for the soft layers and 4000 to 8000 psi for the hard layers. If, on the other hand, the amount of the high modulus mater-ial is reduced to only 25 percent of the weight3 then the Young's modulus could be increased to 10,000 to 15,000 psi or perhaps 20,000 psi.
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Generally the total ~eight of the low-modulus layers of the laminated tire carcass should be at least equal to the total weight of the high-modulus layers as illustrated in the accompanying drawings, and it is desirable to provide low-modulus layers a~ the inner and outer surfaces of the laminate, particularly at the outer surfaces of the sidewall portionsO
The number of layers can be limitsd to reduce manufacturing costs, but it is preferable to employ at least 7 layers and more preferably at least 9 layers. The number of layers can vary from 5 to 1000 depending on the thickness of each layer which can be from 0,001 inch to 0.1 inch. The number of layers is preferably in the range of 7 to lO0 with thicknesses of layers in the range of 0.005 to 0.05 inch~ The thickness of each layer is preferably uniform or generally uniform, and each layer is preferably circumferentially continuous and imperforate, but this is not essen~ial. The layers may be deformed during manufacture of the tire as, for example, where the tire is shaped after the laminate is formed and before it is fully cured.
By varying the number o layers, their thicknesses, the arrangement of the layer and the hardness of the polymers used, it is possible to make an infinite number of different laminated tires in accordance with this invention~
The simpler arrangements are generally preferred with each low-modulus layers of the same hardness and each high-modulus layer of the same hardnessO To improve adhesion between layers, it is desirable to make all layers of general-ly the same type of polymer (iOeO~ polyurethane)O ~lowever, it will be under-stood that adhesion problems can be solved by use of adhesives or perforations in the layers or in various other waysO
Good results can be obtained where all of the high-modulus layers are formed of the same elastoplastic material having an elongation at yield of about 5 to about 10 percent and a Young's modulus of 5,000 to 20,000 psi and all of the low-modulus layers are formed of the siame elastomeric material - . , . , - . .
~5~ ,3 having an elongation of at least 50 percent and a Young's modulus of 500 to 2000 psiO The tensile strength of the high-modulus layers should be at least 2000 psi and preferably at least 3000 psiO
In a special laminate of the type illustrated in Figure 3, the layers L could have a Young's modulus of 300 to 1000 psi, the layers M could have a Young's modulus of 1000 to 3000 psi and the layers H could have a Young's modulus of 10,000 to 50,000 psi.
The laminated tires of this invention can be built in many dif-ferent ways from curable sheets of rubber or plastic or from flowable poly~
meric materials as by centrifugal casting or extrusion. The preferred method requires a flowable curable polymeric material with a viscosity at processing temperatures which enables the material to flow under its ol~n weight in a reasonable period. The material of the low-modulus layers should be one which cures in a reasonable period of time to provide a tensile strength, preferably `
of at least 1000 pounds per square inch.
The polymeric material preferred for use in the present invention is a fluid polymer, such as a polurethane, which can be cured rapidly and which can be processed easily in automated equipment. The viscosity of the polymeric material can be adjusted by use of solvents or plasticizers, by use of heat~ or by proper selection of curing agents, by changing the curing tem-perature, or in other ways. A large number of different polymers can be employed as are described in more detail hereinafterO
In carrying out the present invention it is preferable to form the laminations of the tire by spraying or otherwise applying curable liquid polymeric material to the inside of a tire moldO This can be done with or without a doctor blade to shape the layersO - ~`
~igure 6 illustrates in partly schematic form one type of mold which may be employed to fabricate a laminated tire. The mold is illustrated ~ '~
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~Q5~3 for purposes of illustration rather than limitation, and it will be understood that many other types of molds may be employed. As herein shown the mold, generally designated as 20, comprises a left mold half 22L and a right mold half 22R. The mold halves are attached ~o flat circular restraining plates 24L and 24R which are attached respectively to bearing blocks 26L and 26R.
This arrangement permits the assembly of the mold halves, plates and bearing blocks to rotate freely about hollow shaft 30 on ball bearings 280 A pair of spray tubes 32 and 34 is positioned within the shaft 30 to deliver liquid polymer to the mold. The polymer is discharged from the spray nozzles at the end of the tubes 32 and 34 to the inside surface of the mold cavity. The ends of the tubes are held firmly in place by an annular support member 36 which is mounted on the shaft 30. Ball bearings 3~ are provided around periphery o~
the member 36 at opposite ends thereof to provide a rotatable support for the mold halves 22L and 22R so that they can rotate freely relative to the shaft.
The shaft 30 and the support member 36 may be stationary or may be mounted to rotate or turn if this is desired.
As herein shown the inner surface o~ the mold defined by the com-bination of mold halves 22L and 22R may be such that the pneumatic tire, in-cluding both the tread portion and the sidewall portions, may be totally ~abricated within the mold 20. It will be understood, however, that the mold - may be shaped and employed to form a laminated carcass portion to which the tread portion is applied subsequent to removal of the carcass from the mold In such case, various techniques may be employed to apply the tread portion, and it will be understood that reinforcing belts can be provided under the tread if desired.
In the mold shoun in Figure 6 the spray nozzle or nozzles may be designed to deliver a spray of the liquid polymer to the radially outer (tread) surface and also to the interior sideuall surface of the mold as is illustrated by the broken lines radiating from the end of tube 3~ in Figure 6. In other words, the spray nozzles would deliver the liquid polymer in such a manner as to provide a layer of substan~ially uni~orm thickness covering the en~ire inner surface of the mold.
In forming a tire according to the present invention, it is usually preferable to provide alternating layers of low~modulus and high-~- modulus polymeric materials. In the mold 20 shown herein two spray tubes 32 and 34 are provided for the two different polymeric materialsO If three different polymeric materials were to be employed, then three spray noz21es could be pro~ided. It is contemplated that a high-modulus polymer would be supplied through the spray tube 34 while the flow through tube 32 is shut off and that a low-modulus polymer would be provided through the spray tube 32 while the flow through tube 34 is shut offO By alternately supplying the polymers through the different tubes, alternate layers may be ~ormed on the tire.
Assuming that the mold 20 is rotated continuously rather than being stopped periodically, one layer of polymeric material may be formed on the interior surface of the mold by spraying from one of the spray tubes 32 or 34 throughout one or more rotations of the mold relative to the spray nozzle. Subsequen~ly another layer may be formed in a s~milar manner during one or more rotations by spraying polymeric material from the other spray tube. The centriugal force from rotation of the mold can help to shape the layers, and it will be understoGd that various centrifugal casting methods ; may be employed to assure proper coating of the mold. However, it is desir-able to provide curable polymeric material which will cure fast enough so that one layer will maintain its shape while the next layer is being appliedO Also fast-curing material is desirable to assure formation of layers of substan-tially uniform thickness which can maintain their shape during rotation of , . , : - . . ,. , . .-~ ....... . . .; . ......... ... . . .
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the mold.
The sequence of operations depends to some extent on the rate of ~' curing and the rate at which the liquid polymeric material can be suppliedO
For example, the mold may be rotated slowly and the polymeric material may be supplied from one spray tube at such a rate that the desired circumferential ~ layer is formed in one revolution of the moldO Also the process can be varied ; to require several rotations of the mold during formation of one layer. In some cases it may be necessary, after forming a circumferential layer, to continue to rotate the mold through one or more revolutions to allow substan-tial curing before spraying the next layer. If the rate of curing is fast enough it may be possible to begin spraying the subsequent layer within one-half of a revolution after the previous layer was appliedO
As used herein the expression "partially curing" indicates that the material has stiffened or set up sufficiently to maintain reasonable dimensionable stability so that a subsequent layer may be applied. Such ex-pression does not necessarily require a true curing o the materialO
~t will be understood that various fluid polymeric materials may be employed using molds of the general type illustrated in Figure 6 and that the viscosity or flowability of the liquid polymers may be controlled by the use of heat, solvents, plasticizers or other techniques to allow the movement of the liquid mate~ial to the mold surface at the proper rate.
In carrying out the method of the present invention it will be understood that various fluid polymers may be employed including monomers, melts, prepolymers and solutionsO The fluid polymeric materials must be liquid at the time of processing and have a viscosity at processing tempera-tures such that they will flow under their own weight in a reasonable period ; of timeO
One o~ the polymers preferred for use in the practice of the present `' ' ' ,,, , ",~ , "," ~ ~ - ., :, "
. . , . ", invention is polyure~hane. Such polymer is usually prepared by reacting 0O95 to 1O2 equivalent ~eights o~ an organic polyisocyanate having 2 to 3 functional isocyanate groups with one equivalent of an organic compound havin~ a molecular weight of at least 1000 and containing active hydrogen atoms which are reactive with isocyana~e (-NCO) groups. In many instances an organic chain-extending agent may be employed containing hydroxyl groups, amino groups, carboxyl groups or other groups with active hydrogen atoms reactive with isocyanate groups.
The organic compounds with active hydrogen atoms which are reactive with -NCO groups may, for example, be hydroxyl-terminated polyesters, poly-ester amides, polyhydric polyalkylene ethers, polyhydric polythioethers, poly-acetals and the like.
The organic polyisocyanates used to form the polyurethane in the process of this invention may be of various types including aliphatic, aromatic, alicyclic and heterocyclic as disclosed in said United States Patent NoO 3,208,500 and preferably contain at least 8 carbon atoms. Excellent results are obtained using aromatic diisocyanates such as ~oluene diisocyanate (TDI), 4,4'-diphenyl-methane diisocyanate (MDI) or other diphenyl-alkane diisocyanate or the like. For example, the organic diisocyanate may be an ~0:20 or 65:35 2Q blend o~ 2,4- and 296~toluene diisocyanate The diisocyanates suitable for use in the practice of the invention preferably have ~ to 20 carbon atoms and include the various toluene diiso-cyanates, the various naphthalene diisocyanates, the various phenylene diisocyanates, and the various diphenyl alkane diisocyanates as described in the a~orementioned United States Patent NoO 3,701,3740 Suitable diisocyanates include 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3l-dimethyl-4,4'- -~
-biphenyl diisocyanate, 3,3'-dimethoxy-4,4' biphenyl diisocyanate and the likeO
Mixtures o~ the various diisocyanates mentioned above may also be usedO
,'. ~ . ' ' ' ` '~ ', ' , ' : ' , ,. , ' ~ -'. , ' ' . ' . ' ' ' ' . " . ' ' . ' : ' ' ' Polyurethanes of the desired molecular ~eight suitable for use in the present invention may be made in various ~ays and many different types are suitable, but it is preferable to employ bifunctional reactants which will produce flexible linear polymers. For example, a polyhydric alcohol or a ; hydroxyl-terminated polyether or polyester may be reacted with an organic diisocyanate to form a liquid prepolymer ~ith a molecular weight of 800 to 20,000 having essentially either all hydroxyl end groups or all isocyanate end groups, and thereafter the prepolymer can be cured by means of diamines, diols or diisocyanates, depending upon the terminal or end group in the pre-polymersO The preferred polyurethanes are those formed by capping the hydroxyl groups of polyalkylene glycols with a molecular weight from 800 to 20,000 with ` diisocyanates to form prepolymers, and then chain-extending and curing the prepolymers by means of diamine or diol curing agents, such as MOCA or an alkylene glycol.
The hydroxyl-terminated polyesters which can be used to form the polyurethane may be reaction products of a polycarboxylic acid and a poly-hydric alcohol as described in said United States Patent No. 3,208,500. The alcohol may, for example, be ethylene glycol or propylene glycolO
The organic compound containing active hydrogens for reaction with the isocyanate groups may also be a polyhydric polythioether or polyester amide as defined in said Patent NoO 3,208,500 but is more preferably a polyhydric polyalkylene ether~ The ether may, for example, be the condensation product of an alkylene oxide with a glycol, such as ethylene glycol, propylene glycol, butylene glycol or the like. Any suitable alkylene oxide condensate may also be used such as, for example, condensates of ethylene oxide, propylene oxideg butylene oxide, amylene oxide, styrene oxide and mixtures thereofO
In forming liquid prepolymers for use in the process of this invention, it is preferable to react the organic diisocyanate (preferably MDI
or TDI) with polyalkylene glycols having molecular ~eights in the range of 800 to 20,000, particularly polyCalkylene glycols) having alkylene groups of from ~ to 10 carbon atoms, such as poly(ethylene glycol), poly(propylene glycol~, poly(trime~hylene glycol), poly(tetramethylene glycol), poly~hexa-methylene glycol), high molecular weight copolymers of such glycols, and mix-tures of the above poly(alkylene glycols).
The preferred prepolymers have terminal isocyanate groups, and may be cured with various diamines. The diamines preferably contain an organic central radical of 2 ~o ~0 carbon atoms linked to two amino groups such as ethylenediamine, tetramethylenediamine, hexame~hylenediamine, p-phenylenedi-amine, methylene-bis-2-chloroaniline ("MO~A*"), 4,4'-methylene-bis-aniline, 3,3'-dichloro-4,4'-diaminodiphenylmethane, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine3 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylmethane, d cumene diamine.
In these polyurethane rubbers, the chains of the cured polymer con-tain ~he repeating linkage ~ P-O~CO-NH-Rl-NH-CO-MH-R2-NH-CO-NH-Rl-N~I-CO-O
` wherein P represen~s the high molecular weight poly (alkylene ether) chain, Rl is the organic radical of the diisocyanate, and R2 is the organic central radical of the diamineO This type of polymer with the proper molecular weight can provide excellent results in the practice of the present invention when used to provide the high- and low-modulus lay~rs of the tire laminateO The hardness and modulus of these polyurethane polymers may, for example, be in-creased by increasing the isocyanate and glycol or diamine content of the systemO
The type of polyurethane selected for use in making tires according to this inventicn will depend on the type of manufacturing process employedO
The polyurethane best suited for spraying may not be hest for film extrusion or some otheT method.
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Liquid polyurethane rubbers are now available commercially which can be used in the practice of the present invention. Good results can be `~ obtainedJ for example, with Adiprene* L-100 prepolymers (~o1% NCO), Adiprene*
L-167 prepolymers (6.3% NCO), and Adiprene* L-315 prepolymers (905% NCO), made by E. I. duPont de Nemours ~ CoO These liquid prepolymers can be cured with conventional diamines, such as MOCA*, Caytur 7 or Caytur 21 (~,4'-` methylene-bis-aniline) using an equivalent weight ratio of diamine to pre-polymer of about 0.95 to about 1.10. Caytur 7 is a eutectic mixture of m-phenylene and cumene diamine.
Polyurethane prepolymers, such as Adiprene-L prepolymers, may, for example, be made from TDI and a polyalkylene glycol or polyol, such as poly (tetramethylene ether diol), and similar prepolymers can be made using MDI
lnstead of TDI or using a somewhat different polyolO Various poly(alkylene glycols) and poly~alkylene ether) polyols can be used, both diols and tr]ols, and the prepolymers can have either terminal -OH groups or terminal ~CO groups (preferably the latter)O
The polymeric material used in the tire of the present invention may also be a polyamide plastic, such as nylon 66, nylon 610 or nylon 6~
Various long-chain synthetic polymeric amides having recurring amide groups as an integral par~ of the main polymer chain can be used, such as those pre-pared by the condensation of diamines and dibasic acids, those obtained by the condensation of polycarboxylic acids with polyamines, or those obtained by ; the polycondensation of caprolactam~
Various triamines may be used, such as diethylenetriamine and the like, but it is preferable to employ diaminesO Suitable diamines include ethylenediamine, diethylenediamine, pentamethylenediamine, hexamethylenedi-amine, phenylenediamine, and the like or mixtures thereofO
Various polybasic acids may be used to make the polyamide ranging *Trade mark - 20 -` ~35~L3 from succinic acid to sebacic acid and including, for example, succinic acid, aconic acid~ adipic acid, malic acid, itaconic acid, fumaric acid and the likeO
The polyamides suitable for use in rubber tires which can be used in the practice o the present invention are described in said United States Patent NoO 3,208,5000 The preferred polyamides are those made from diamines -and dibasic acids, such as the reaction products of hexamethylenediamine or similar diamine with a dibasic acid, such as adipic acid or sebacic acid.
; While there are many different types of polymers which can be employed in the practice of this invention, the most promising polymers appear to be polyurethanes and polyamides or nylons as discussed generally in said United States Patent No. 3,208,5000 A~ present the most practical polymers seems to be polyurethanes, particularly polyether urethanes and polyester urethanes.
One advantage of the polyurethanes is that they can be obtained in liquid form with viscosities suitable for spraying or for spreading. Also they can be used in both the high- and low-modulus layers, thereby reducing the adhesion problemO It is also possible to blend polyurethanes of different molecular weights to get the desired properties.
For example, the laminated tire of thls invention can be made using Adiprene L-42 (molecular weight about 3000) for the low-modulus layers and Adiprane L-167 (molecular weight about 1330) for the high-modulus layers~ Also the high-modulus layer could be made using a blend of 60 parts by weight of Adiprene L-167 and 40 parts by weight of Adiprene L-315 ~molecular weight ; about 900). The curing agent could be MOCA, Caytur 21 or other suitable diamine, and the plasticizer~ i any, could be dioctylphthalate or the like.
The curing agent could provide relative fast curing to minimize the time delay after each layer is applied before the next layer is applied The polyurethane prepolymers can also be modi~ied in various ways ,, : :
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~1~5~ ~3 to produce the desired properties. For exampleJ Adiprene L-167 (a prepolymer with a Brookfield viscosity of about 5000 to about 7000 centipoises at 30Co and about 250 to about 350 centipoises at 100Co) can be cured with 1,~-- butane-diol and trimethylolpropane in suitable proportions to provide a rubber layer of the desired type. A curable polyurethane composition could, for example, be made by mixing 160 parts by weight of Adiprene L-167 with about 9 parts of 1,4-butanediol, about 1.6 parts of trimethylolpropane and a small amount of dioctylphthalate.
; The laminated tire of this invention is preferably constructed so that the tear strength of the laminate ~split sample method) is 50 to 400 or more pounds per lineal inch and so that the low-modulus layers have a tensile strength of at least 1000 pounds per square inch, a Shore A durometer hardness in the range of about 30 to 90, and an elongation of at least 50 percent (more preferably at least 100 percent)O
The curable polymers used in the practice of this invention need not be liquid, but liquid polymers are preferred to facilitate manufactureO
The viscosity of the liquid polymers may~ for example, be 1000 to 50,000 centi-poises and should be less than 100,000 centipoises at 30C. The viscosity may be adjusted by adding substantial amounts, sometimes up to 10 or 20 parts of a plasticizer, such as dioctylphthalate, per 100 parts by weight of the polymer.
In some cases solvents may be used with the polymers to provide the desired flowability. The choice of solvent depends on the type of polymer and the type of curing systemO Various solvents which may be used include ethyl acetate, acetone, toluene, methyl ethyl ketone, xylene, beta-ethoxyethyl acetate and the likeO These are preferably relatively pure and free of moisture.
While the laminates of the pneumatic tires above employ substan- ;
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.3 tially different polymer formulations in the lo~- and high-modulus layers, it will be understood that the invention also contemplates improved laminates with improved flex crack resistance wherein similar formulations are used in all of the layers and the tensile moduli in any given direction (such as cir-cumferential or radial, etcO) is substantially different in adjacent layers~
In accordance with the invention a difference in tensile modulus can be pro-vided between adjacent layers H and L (Figure 2, for example) when using the same polymer in both layers as a result of a different molecular orientation in the adjacent layersO
- 10 The term "tensile modulus" as used herein refers to the stress in - psi which must be exerted on a sample to stretch it to a stated elongation such as 10 percent, 100 percent or 200 percent.
In a laminated tire constructèd according to the present invention ~as in Figure 2, for example) each layer preferably has a 10 percent modulus in one direction which is at least about twice the 10 percent modulus of the next adjacent layer in that direction. For example, the desired difference in tensile modulus between layers H and layers L in the various species of Fig-ures 2 through 5 may be achieved by molecular orientation or by use of differ-ent polymèrs in different layers, or bothO
One advantage of using the same or similar polymers in adjacent layers is the ease of achieving good adhesion.
As used herein the term "parts" means par~s by weight and the term "polymer" includes homopolymers or copolymers unless the context shows other-wise.
The term "fluid" as applied to a polymeric material indicates that the material has viscosity such that it can flow during processingO The viscosity may, for example, be from 100 to 10,000 centipoises at 30C. and should not exceed 100,000 centipoises at that temperatureO
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, ~15~3 The followin~ example is provided for purposes of illustrating the nature of the invention, and is not for the purpose of limiting the inventionO
Example This example is included to illustrate the greatly improved ability of a tire made in accordance with the present invention to resist the pro-pagation of a cut flaw or to form a crack. In order to illustrate this ability, laminated and homogeneous samples were subjected to a De Mattia flex test, with a comparison being made between each laminated sample and a homo-geneous sample made from a blend of the materials in the particular laminate, and in the same proportionsO Each of the samples was one inch wide, one-quarter of an inch thick and six inches long. They were press cured for two hours at 250F. (121C.) followed by post curing in an oven for another two ; hours at 176Fo ~80C~)o Each sample then has an artificial flaw of ol inch (.254 cm.) imposed across the quarter inch wide surface, per~endicular to the one inch wide surface. The fatigue test was performed on a De Mattia flex machine which flexes the sample ~at 333 cycles per minute and at room tempera-ture) causing the imposed flaw to propagate laterally across the width of the sampleO
For ~his experiment, two different mat0rial formulations were used which will be referred to as "100" and "167" as follows ~"parts" refers to parts by weight): ~ i , .
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In~redient Parts "100" "167"
-Adiprene L-100 (1)* 100 Adiprene L-167 (2)* - 100 DC - 203 (3)* 0.1 0.1 Dioctylphthalate - plasticizer lOoO
Caytur 21 (4)* 20.3 31O1 Samples were made from each of these formulations alone and the De Mattia test was used to determine the number of cycles necessary for the ol inch (D254 cmO) flaw to become D5 inch ~1.27 cmO). The number in parentheses under each p5io reading represents 106 pascals. In addition, other properties were measured as follows:
*Note: ~1) and ~2) are liquid prepolymers as previously described; ~3) is a i liquid silicone mold release and emulsifying agent, Dow Corning; and ' ~4) is a 50% dispersion of methylene dianiline/sodium chloride complex in dio~tyl phthalate, du Pont.
Table I
Property "100" "167'l 10% Modulus 160 psi. 370 psi.
(lo 1030) ~2.5507) 20100% Modulus 405 psi. 690 psi.
~2O7920) (4O7568) 200% Modulus 510 psi. 860 psi.
(3,5159) (509288) . Tensile (rupture) 2055 psi, 2290 psi.
(14O167) ~15.787) Elongation (rupture) 750% 575%
Hardness Shore A 83 91 Table I ~continued) Property "100" "167"
Shore D 29 42 : De Mattia (cycles to .5 inch crack) 500 1000 Formulations "100" and "167" were next used to make the samples containing both materials. In the case of the blends, the ratio stated in ~ Table II is the ratio of "100" to "167" and for the laminates reported in : Table II, there is one more layer of "100" than of "167", with both outer layers being the "100".
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and a central layer of "167". The next column "2:1" designates a homogenous sample made from a blend of 2 parts by weight of "100" and 1 part by weight of "167". The subsequent columns designate laminated and homogenous samples with different proportionsO The 9-layers laminated sample, for example, can be compared with the homogenous sample made from the 5:4 blend as indicated in the last columnO
; The above data demonstrates that a marked increase in fatigue life, such as 400 to 500 percent, can be achieved in a laminated sample while still retaining physical properties adequate for conditions to be expected in a pneumatic tire. While the data for tensile strength and elongation are somewhat erratic, this behavior occurs at strains far above those that would be found in end use and does not detract from the fact that a marked improve-ment is observed in fatigue life. The somewhat erratic behavior in tensile ~; strength and rupture elongations in these specimens is related to flaws in the specimen that influence these properties but not the flexing behavior.
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This application is a division of Canadian patent application Serial No. 279,751 filed June 2, 1977~
It has long been recognized in the pneumatic tire industry that fabric reinforced tires have many disadvantages and that it might be desirable to build a fabric-free tire which could be manufactured by less expensive proceduresO Not only is the conventional method of tire fabrication slow and expensive, requiring separate handling and processing of one or more kinds of rubber and/or cord fabric for each tire, calendering and handling of individual plies, and final manual assembly of all of the components, but also, the conventional tire construction is not readily adapted to any kind of automation which would reduce the labor costs and improve the tire quality and uniformityO
An additional cause of excessive manufacturing expense associated with conven-tional tire construction is the large amount of factory space taken up, first, by the many large curing presses required to cure green tires, one at a time, for anywhere from about 12 minutes to more than 20 minutes, and second, by the rubber processing and mixing equipment such as mills, Banburys, extruders, . calenders, and tire building machines.
Other problems in conventional fabric-reinforced tires are the difficulty of uniform placement of the many components of the tire and the difficulty of obtaining uniform expansion from the cylindrical shape on a flat drum to the inal toroidal shapeO The laminated tire of the present invention eliminates some of these problems.
In its search for a tire configuration and construction method which does not require the lamination of cords and rubber compound and the ':
subsequent manual buildup o~ ply layers, the tire industry has attempted to make at least the carcass portion of the tire by molding or casting a liquid polymer, such as a polyurethane, to the desired shape. The tire illustrated in United States Patent No. 2,902,072 issued September 1, 1959 to Mobay Chemical Company comprises a tread, inner and outer sidewalls, and a cellular poly-urethane filling the space between the inner and outer sidewallsO United States Patent 3,20~,500 da~ed September 28, 1965 to U. Knipp et al. discloses the fabrication of the carcass portion of a pneumatic tire by mo~ding a poly-urethane or polyamide into a single, generally homogeneous layerO United States Patent 3,27~,322 issued September 20, 1966 to Chemechanical IncO dis-closes a method of flow-forming a material such asapolyurethane, using a doctor blade, to make a strip of material which can subsequently be formed into a tire carcass. United States Patent 3,386,485 issued June 4, 1968 to The Dunlop Company Ltdo illustrates a method of making a "fabricless" pneumatic tire from any one of a number of suggested polymers and copol~mers by separately molding the annular halves of a tire and subsequently molding the two halves together in a different pressO
U~ted States Patent 3,396,773 issued August 13, 1968 to Sterling Alderfer Company illustrates the application of centrifugal casting techniques for making a tire which is described as being solid rather than pneumaticO
The general concept of centrifugal casting has been applied to pneumatic tires as illustrated in United States Patent 3,555,141 dated January 12, 1971 ~0 H~Wo Beneze which discloses a method in which a heated mold, having its internal surface conforming to the ex~ernal shape of a tire, is rotated while a liquid polyurethane is introduced thereinO The rotation of the mold causes the polyurethane to flow and cover the entire inner surface of the mold and a stationary -~emplate, having the same shape as the inside of the tire, serves to spread the material in the same manner as a doctor bladeO In llnited States ~ .
.. . . .. ..
.3 Patent No. 3,701,374 dated October 31, 1972 to DoR~ McGillvary there is a disclosure of a fabric-free tire carcass made of a polyurethane elastomer, another elastomer, and methods of making the tire to produce the necessary physical propertiesO
While many of the problems associated with conventional tire con-struction can be reduced or eliminated by fabrication of tires in accordance with the prior art patents discussed above, the cast tire configuration such as the type proposed in these patents has a number of serious problems, and use o such special tires has not been widespread. The major problem in the cast tire, in terms of tire life, is what is known as flex fa~igue failureO
Under the weight of the vehicle the portion of a tire in contact with the ground is deformed with the result that the rubber is continually flexed dur-ing operation of the ~ireO In conventional fabric reinforced tires, the fabric may for example withstand at least 85 percent of the inflation pressure and the rubber less than 15 percentO If the fabric is to be eliminated without changing the general shape of the tire, then it would be necessary to employ a rubber of higher-modulus to enable the tire to maintain its shape. ~owever, the harder rubbers have a relatively short life due to flex fatigue failure.
For example, whenever a small crack or defect occurs due to a microscopic flaw or a cut ~rom a sharp object, there is a tendency for a crack to develop and grow during continual flexing until the tire fails or becomas dangerous.
When using fabric reinforcement it is possible to employ softer rubbers which do not have the serious flex fatigue problem~ However, when making a fabric-free tire using stiffer polymars, which are required to obtain the necessary ; strength, the flex fatigue problem is extremely serious. Experimental data with respect to fabric-free tires seems to indicate that sidewall flex crack-ing is the principle mode of failureO
kcording to one aspect of the invention, a pneumatic tire casing ~ 3 ,~, .
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5~ 3 has a tread portion and flexible sidewall portions which are free of fabric reinforcement~ each sidewall portion comprising a series of layers of flexible polymeric ma~erial with a calculated molecular weight of at least 10,000 and a Shore A durometer hardness of at least 20, a series of said layers compris-ing low-modulus polymeric material with a Young's modulus which is from about 100 to about 5,~00 pounds per square inch, a plurality of said layers being interspersed with the low-modulus layers and comprising a higher-modulus polymeric material with a Young's modulus which is from about 3000 to 100~000 -pounds per square inch, each of which layers has a Young's modulus at least twice that of the next adjacent low-modulus layer.
According to one preferred embodiment, the tread portion and side-wall portions include a carcass in the form of a flexible laminate, there are at least seven layers of said flexible polymeric material having a tensile strength of at least 2000 pounds per square inch, each layer has a Young's :Elexural modulus of at least 1000, and the series of higher Young's modulus layers have a tensile modulus in one direction at 10 percent elongation which is at least twice the tensile modulus of adjacent layers in said one direction at 10 percent elongation, whereby the laminate has a high resistance to flex - cracking.
The plurality of layers of polymeric material having a relatively high tensile modulus preferably have a modulus between 5000 to 50,000 pounds per square inch. The layers are preferably arranged in an alternate pattern in such a manner as to provide the overall tire carcass with the desired strength and stiffness ~hile at the same time providing a much greater resis-tance to flex fatigue failure than could be obtained from a homogeneous construction.
The tires o the present invention are preferably made from fluid ,~ :
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poly~neric materials ~hich haye a viscosity at processing temperatures such that they can flo~ and form the desired layers of the tire in a reasonable period of time. Rotational casting methods may be employed with the fluid polymers as well as other forming processes.
T he process for making a lamina~ed pneumatic tire carcass having improved resistance to flex cracking comprises applying to an annular form a first continuous layer comprising a liquid polymeric material having a vis-cosity less than 100,000 centipoises at 30C then partially curing the liquid thereafterJ applying to the first partially cured layer a continuous layer of a second liquid polymeric material having a viscosity less than 100,000 centipoises at 30C then partially curing the second liquid, and repeating the sequential application and partial cure of polymeric material to form a cur- -able laminate, and heating and curing the laminate while it has a generally toroidal shape, the cured polymeric material of each layer having a Shore A
durometer hardness of at least 20, a first series of said layers comprising a plurality o cured low-modulus polymeric material with a Young9s flexural modulus from about 100 to about 5,000 pounds per square inch, a second series of a plurality of high modulus layers being alternated with the low-modulus layers and having a tensile modulus at 10 percent elongation in any direction which is at least twice that of said low-modulus layers in any direction.
When using fluid polyurethane polymers a preferred method of form-ing the tire is to provide a mold with the desired annular shape of the tire, to apply to the interior surface of the mold a generally uniform layer of the polymeric material, thereafter to cure the layer or allow it to cure at least partially, and thereafter to apply a subsequent generally uniform layer with a different modulus. A large number of layers are applied and cured in this manne~ until the desired thickness is obtainedO A doctor blade may be employ-ed ~o shape the layers o~ to provide a uniform thickness~ and relative ,:
. .
rotation may be provided between the mold and the blade to achieve this~ Where a liquid polymeric material is applied from a spray no~zle or other applicator, relative movement may be provided between the mold and the applicator during application of the liquid polymer, for example by rotating the mold relative to the applicator or vice versa. If desired the fluid materials may be so compounded and so ~reated that the necessary curing of one layer prior to ~pplication of the next layer takes place during only one or two revolutions of the mold.
The rotational casting method may be employed to form a large number of different layers of polyurethane polymers or other suitable polymers ., in various thicknesses from 0.001 inch to 0Ol inch. The hard and soft layers preferably alternate, but many different arrangements are possible which will provide the desired resistance to flex cracking.
When making a pneumatic tire by the above method from fluid poly-urethane polymers, the tensile modulus and hardness of the different layers can be changed by changing the amount or type of curing agent used and the molecular weight or type of urethane polymer being used.
In the drawings, Figure 1 is a fragmentary perspective view of a pneumatic tire of the type made in accordance with the present invention on a reduced scale;
Figure 2 is a fragmentary cross-sectional view of the laminated tire of Figure 1 showing a portion of the sidewall of the tire;
Figures 3, 4 and 5 are fragmentary views similar to Figure 2 show- :
ing alternate embodiments of the laminated tire of this invention; and Figure 6 is a partially schematic cross-sectional view of one embodiment of an apparatus for making laminated pneumatic tires in accordance with the process of the present inventionO
~eferring more particularly to the drawings, which are for the :.
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purpose of illustrating preferred embodiments of the invention and not for the purpose of limiting the same, Figure 1 shows a pneumatic tire 10 comprising a tread portion 12 and two sidewall portions 140 It will be understood that Figure 1 is partially schematic and that conventional circumferential rein-. forcing belts or other reinforcing means may be provided in the tread portion 12 without providing fabric reinforcement or other reinforcement in the side-wall portions 14. In other words the cross section of the tire may be general-~ ly as shown in United States Patent No. 3,701,37~ or in other patents .
mentioned previouslyO It will also be understood that~ while the tire pre-ferably has a toroidal cross section, the present invention also applies to ~ tires of special cross section as illustrated for example in United States ; Patent No. 3,840,060 issued October 8, 197~ to Industrie Pirelli S~poAo Conventional means may be provided on the tire or on the wheel to reinforce :
; the bead portion of the tire or to help hold it in place on the wheel rimO
e tire 10 of this invention is preferably made with a substantial number of layers of polymeric material, each layer preferably having a general-ly uniform thickness and completely covering the adjacent layer. In the embodiment of Figure 2, the tire carcass and each o the sidewall porti.ons 1~ :
comprises a thirteen-layer laminate made up of alternating high-and low-modulus layers H and L. The low-modulus layer L is provided at both the inner . and outer surfaces of the tir0, and every other layer comprises a high-modulus Iayer H. This particular configuration makes it possible to obtain a tire of the desired strength and stiff.ness by use of high-modulus layers while at the same time minimizing the tendency for flex crackingO It will be under-stood that while thirteen-layers are often desirable, a different number of layers can also provide good resultsO
., Figure 3 illustrates a different embodiment, also with thirteen-layers, wherein a mèdium modulus layer M is provided in addition to the high-... .
modulus layers H and the lo~-modulus layers Lo This arrangement is similar to that o~ Flgure 2 in that the layers H and L alternate regularly with the low-modulus layer L at the inner and outer surface of the tire, but a medium modulus layer M is provided between each layer L and the nearest layer H.
This makes it possible to employ layers H of extremely high-modulus without so abrupt a change in modulus when going from layer H to layer Lo Where the tire has a very large number of layers such as 25 to 50 or more, it may be desir-able to provide more than one layer of intermediate modulus between thc low-modulus layer and the high-modulus layerO
; 10 ~igure 4 illustrates another embodiment of the invention wherein the low- and high-modulus layers alternate like Figure 2 in the central portion of the laminated structure and wherein several of the outer layers are formed of the same low-modulus material. In this Figure the first three layers on both the inside and outside of the carcass portion are the low-modulus layers Lo One reason for using this type of construction is that the inner and outer surface portions of the tire are subjected to greater bending strains which are withstood better by the low-modulus materialO
Figure 5 shows another embodiment of the invention in which the various layers have different thicknessesO In the embodiments of Figures 2, 3 and 4 all of the layers are shown as having the same thickness, but it will be understood that some variation in thickness can be provided and that it is often desirable to provide low-modulus layers with a thickness somewhat greater than the high-modulus layers. In the embodiment of Figure 5 the low- and high-modulus layers alternate regularly like Figure 2 except that two low-modulus layers L are provided at the inner surface of the carcass~
Many different methods may be employed to build tires according to the present invention. The uncured tire can for example be built by forming a cylindrical laminate having ten or more layers and thereafter expanding the .
- . .. ~ .: : .. . .
laminate from the cyllndrical to the toroidal shape by a method somewhat similar to the conventional flat-band processO The tire may also be formed by applying the layers to the laminate while the laminate has a toroidal shape or other desired cross section as described hereinafter.
Some of the first tires made in accordance with the present inven-tion were fabricated by manually applying to the outer surface of a metal mold a series of layers of liquid polymeric material having a fairly uniform thick-ness. Another possible method of building a tire is to apply successive layers of uncured sheet rubber or the like. However, manual methods are probably impractical due to the excessive cost of manufacture. In order to reduce cost it is preferable to employ a liquid polymeric material and auto-mated proceduresO
The polymeric materials which may be used to make tires according to the present invention are elastomers, elastoplastic materials or high-modulus plastics. ~le softer low-modulus layers of the tire are made from the - elastomeric and/or elastoplastic materials and the harder high-modulus layers are preferably made from the elastoplastic materials or high-modulus plastics.
The elastomers are characterized by major glass transition tempera-tures below about minus 20 degrees Centigrade, Young's moduli in the range of ~0 100 to 6000 pounds per square inch, and the ability to sustain elongations of 100 percent or more without permanent deformation or ruptureO The useful elastomers include polyurethane rubber, natural rubber, poly(butadiene) and various other synthetic rubbers including SBR rubbers.
The elastoplasticpolymeric materials can have Young's moduli in the range of 3000 to 50,000 pounds per square inchO At room temperature these materials usually exhibit yield points below 50 percent elongation and ultimate tensile strengths above 4000 pounds per square inch and ultimate elongations g~eate~ than 100 percent. These materials are usually characterized by being _ 9 _ : . . . . . .
, . . . . . . .
.
multiphase in that glassy or crystalline domain structures are usually detect-able. Typical materials in this group are block polymers, such as s~yrene-butadiene-styrene triblock polymers, polyester block polymers, segmented polyurethane polymers and ionomers.
The high-modulus plastic materials are characteri~ed by Young's moduli of 50,000 pounds per square inch or higher and yield points and/or failure points at elongations below about 15 percent. They ~ould have a major glass or melting transition temperature above 100C. Suitable materials in this group include compositions from polyamides, polycarbonates, epoxide resins and polystyrenes.
The elastomeric ma~erials used in the low-modulus layers of the tire of this invention should have the major glass transition temperature below about -20C. and can contain groupings capable of forming covalent cross-links. The molecular weight of the chains between covalent cross-links is preferably about 5,00 to 40,000 and more preferably 8,000 to 20,000.
Generally the polymeric material forming the various layers of the laminated tire of this invention should have a calculated molecular weight of at least 10,000 and a Shore A durometer hardness o~ at least 20 and preferably provide a tensi]e strength of at least lOOO pounds per square inchO The softer low-modulus layers have an elongation which is usually at least 30 percent and preferably at least 50 percent and a Shore A durometer hardness which is at least 30 and preferably no more than 90O The polymeric material of the so~ter low-modulus layers preferably has a tensile strength of at least 2000 pounds per square inchO
There is a general relationship between Shore hardness and Young's modulus as follows:
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Shore Hardness Young's Modulus CBoSo ~ IoRoH~ (psi) 13~0 It should be ~mderstood tha~ the Shore Hardness and Young's modulus values given herein must generally correlate with this relationshipO
The cured low-modulus layers of the tire preferably have Young's moduli in the range of 300 to 5000 pounds per square inch and usually in the ; range of 500 to 3000 pounds per square inch. The preferred hardness depends on the thicknesses of the various layers, their arrangement, the stiffness of the harder layers and other factors.
The cured high-modulus layers have Young's moduli in the range of 3000 to 100,000 pounds per square inch which is usually at least twice that of the adjacent low~modulus layers and is preferably in the range of about 5000 to 50,000 pounds per square inch~ The ratio of the Young's modulus of each hard layer of the laminated ~ire to the Young's modulus of each soft -layer can be up to 300:1 but is more frequently in the range of 3:1 to 20:1 in a passenger car tireO
The preferred modulus for the harder layers dependsJ of course, on many factors and should be selected to provide the composit~ tire with the desired overall modulus and stiffnessO For example, if the laminated carcass portion of the tire consists of 50 percent by weight of high-modulus polymeric ~ .
material and 50 percent by weight of low-modulus material, then the Young's modulus might be 500 to 2000 psi for the soft layers and 4000 to 8000 psi for the hard layers. If, on the other hand, the amount of the high modulus mater-ial is reduced to only 25 percent of the weight3 then the Young's modulus could be increased to 10,000 to 15,000 psi or perhaps 20,000 psi.
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Generally the total ~eight of the low-modulus layers of the laminated tire carcass should be at least equal to the total weight of the high-modulus layers as illustrated in the accompanying drawings, and it is desirable to provide low-modulus layers a~ the inner and outer surfaces of the laminate, particularly at the outer surfaces of the sidewall portionsO
The number of layers can be limitsd to reduce manufacturing costs, but it is preferable to employ at least 7 layers and more preferably at least 9 layers. The number of layers can vary from 5 to 1000 depending on the thickness of each layer which can be from 0,001 inch to 0.1 inch. The number of layers is preferably in the range of 7 to lO0 with thicknesses of layers in the range of 0.005 to 0.05 inch~ The thickness of each layer is preferably uniform or generally uniform, and each layer is preferably circumferentially continuous and imperforate, but this is not essen~ial. The layers may be deformed during manufacture of the tire as, for example, where the tire is shaped after the laminate is formed and before it is fully cured.
By varying the number o layers, their thicknesses, the arrangement of the layer and the hardness of the polymers used, it is possible to make an infinite number of different laminated tires in accordance with this invention~
The simpler arrangements are generally preferred with each low-modulus layers of the same hardness and each high-modulus layer of the same hardnessO To improve adhesion between layers, it is desirable to make all layers of general-ly the same type of polymer (iOeO~ polyurethane)O ~lowever, it will be under-stood that adhesion problems can be solved by use of adhesives or perforations in the layers or in various other waysO
Good results can be obtained where all of the high-modulus layers are formed of the same elastoplastic material having an elongation at yield of about 5 to about 10 percent and a Young's modulus of 5,000 to 20,000 psi and all of the low-modulus layers are formed of the siame elastomeric material - . , . , - . .
~5~ ,3 having an elongation of at least 50 percent and a Young's modulus of 500 to 2000 psiO The tensile strength of the high-modulus layers should be at least 2000 psi and preferably at least 3000 psiO
In a special laminate of the type illustrated in Figure 3, the layers L could have a Young's modulus of 300 to 1000 psi, the layers M could have a Young's modulus of 1000 to 3000 psi and the layers H could have a Young's modulus of 10,000 to 50,000 psi.
The laminated tires of this invention can be built in many dif-ferent ways from curable sheets of rubber or plastic or from flowable poly~
meric materials as by centrifugal casting or extrusion. The preferred method requires a flowable curable polymeric material with a viscosity at processing temperatures which enables the material to flow under its ol~n weight in a reasonable period. The material of the low-modulus layers should be one which cures in a reasonable period of time to provide a tensile strength, preferably `
of at least 1000 pounds per square inch.
The polymeric material preferred for use in the present invention is a fluid polymer, such as a polurethane, which can be cured rapidly and which can be processed easily in automated equipment. The viscosity of the polymeric material can be adjusted by use of solvents or plasticizers, by use of heat~ or by proper selection of curing agents, by changing the curing tem-perature, or in other ways. A large number of different polymers can be employed as are described in more detail hereinafterO
In carrying out the present invention it is preferable to form the laminations of the tire by spraying or otherwise applying curable liquid polymeric material to the inside of a tire moldO This can be done with or without a doctor blade to shape the layersO - ~`
~igure 6 illustrates in partly schematic form one type of mold which may be employed to fabricate a laminated tire. The mold is illustrated ~ '~
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~Q5~3 for purposes of illustration rather than limitation, and it will be understood that many other types of molds may be employed. As herein shown the mold, generally designated as 20, comprises a left mold half 22L and a right mold half 22R. The mold halves are attached ~o flat circular restraining plates 24L and 24R which are attached respectively to bearing blocks 26L and 26R.
This arrangement permits the assembly of the mold halves, plates and bearing blocks to rotate freely about hollow shaft 30 on ball bearings 280 A pair of spray tubes 32 and 34 is positioned within the shaft 30 to deliver liquid polymer to the mold. The polymer is discharged from the spray nozzles at the end of the tubes 32 and 34 to the inside surface of the mold cavity. The ends of the tubes are held firmly in place by an annular support member 36 which is mounted on the shaft 30. Ball bearings 3~ are provided around periphery o~
the member 36 at opposite ends thereof to provide a rotatable support for the mold halves 22L and 22R so that they can rotate freely relative to the shaft.
The shaft 30 and the support member 36 may be stationary or may be mounted to rotate or turn if this is desired.
As herein shown the inner surface o~ the mold defined by the com-bination of mold halves 22L and 22R may be such that the pneumatic tire, in-cluding both the tread portion and the sidewall portions, may be totally ~abricated within the mold 20. It will be understood, however, that the mold - may be shaped and employed to form a laminated carcass portion to which the tread portion is applied subsequent to removal of the carcass from the mold In such case, various techniques may be employed to apply the tread portion, and it will be understood that reinforcing belts can be provided under the tread if desired.
In the mold shoun in Figure 6 the spray nozzle or nozzles may be designed to deliver a spray of the liquid polymer to the radially outer (tread) surface and also to the interior sideuall surface of the mold as is illustrated by the broken lines radiating from the end of tube 3~ in Figure 6. In other words, the spray nozzles would deliver the liquid polymer in such a manner as to provide a layer of substan~ially uni~orm thickness covering the en~ire inner surface of the mold.
In forming a tire according to the present invention, it is usually preferable to provide alternating layers of low~modulus and high-~- modulus polymeric materials. In the mold 20 shown herein two spray tubes 32 and 34 are provided for the two different polymeric materialsO If three different polymeric materials were to be employed, then three spray noz21es could be pro~ided. It is contemplated that a high-modulus polymer would be supplied through the spray tube 34 while the flow through tube 32 is shut off and that a low-modulus polymer would be provided through the spray tube 32 while the flow through tube 34 is shut offO By alternately supplying the polymers through the different tubes, alternate layers may be ~ormed on the tire.
Assuming that the mold 20 is rotated continuously rather than being stopped periodically, one layer of polymeric material may be formed on the interior surface of the mold by spraying from one of the spray tubes 32 or 34 throughout one or more rotations of the mold relative to the spray nozzle. Subsequen~ly another layer may be formed in a s~milar manner during one or more rotations by spraying polymeric material from the other spray tube. The centriugal force from rotation of the mold can help to shape the layers, and it will be understoGd that various centrifugal casting methods ; may be employed to assure proper coating of the mold. However, it is desir-able to provide curable polymeric material which will cure fast enough so that one layer will maintain its shape while the next layer is being appliedO Also fast-curing material is desirable to assure formation of layers of substan-tially uniform thickness which can maintain their shape during rotation of , . , : - . . ,. , . .-~ ....... . . .; . ......... ... . . .
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the mold.
The sequence of operations depends to some extent on the rate of ~' curing and the rate at which the liquid polymeric material can be suppliedO
For example, the mold may be rotated slowly and the polymeric material may be supplied from one spray tube at such a rate that the desired circumferential ~ layer is formed in one revolution of the moldO Also the process can be varied ; to require several rotations of the mold during formation of one layer. In some cases it may be necessary, after forming a circumferential layer, to continue to rotate the mold through one or more revolutions to allow substan-tial curing before spraying the next layer. If the rate of curing is fast enough it may be possible to begin spraying the subsequent layer within one-half of a revolution after the previous layer was appliedO
As used herein the expression "partially curing" indicates that the material has stiffened or set up sufficiently to maintain reasonable dimensionable stability so that a subsequent layer may be applied. Such ex-pression does not necessarily require a true curing o the materialO
~t will be understood that various fluid polymeric materials may be employed using molds of the general type illustrated in Figure 6 and that the viscosity or flowability of the liquid polymers may be controlled by the use of heat, solvents, plasticizers or other techniques to allow the movement of the liquid mate~ial to the mold surface at the proper rate.
In carrying out the method of the present invention it will be understood that various fluid polymers may be employed including monomers, melts, prepolymers and solutionsO The fluid polymeric materials must be liquid at the time of processing and have a viscosity at processing tempera-tures such that they will flow under their own weight in a reasonable period ; of timeO
One o~ the polymers preferred for use in the practice of the present `' ' ' ,,, , ",~ , "," ~ ~ - ., :, "
. . , . ", invention is polyure~hane. Such polymer is usually prepared by reacting 0O95 to 1O2 equivalent ~eights o~ an organic polyisocyanate having 2 to 3 functional isocyanate groups with one equivalent of an organic compound havin~ a molecular weight of at least 1000 and containing active hydrogen atoms which are reactive with isocyana~e (-NCO) groups. In many instances an organic chain-extending agent may be employed containing hydroxyl groups, amino groups, carboxyl groups or other groups with active hydrogen atoms reactive with isocyanate groups.
The organic compounds with active hydrogen atoms which are reactive with -NCO groups may, for example, be hydroxyl-terminated polyesters, poly-ester amides, polyhydric polyalkylene ethers, polyhydric polythioethers, poly-acetals and the like.
The organic polyisocyanates used to form the polyurethane in the process of this invention may be of various types including aliphatic, aromatic, alicyclic and heterocyclic as disclosed in said United States Patent NoO 3,208,500 and preferably contain at least 8 carbon atoms. Excellent results are obtained using aromatic diisocyanates such as ~oluene diisocyanate (TDI), 4,4'-diphenyl-methane diisocyanate (MDI) or other diphenyl-alkane diisocyanate or the like. For example, the organic diisocyanate may be an ~0:20 or 65:35 2Q blend o~ 2,4- and 296~toluene diisocyanate The diisocyanates suitable for use in the practice of the invention preferably have ~ to 20 carbon atoms and include the various toluene diiso-cyanates, the various naphthalene diisocyanates, the various phenylene diisocyanates, and the various diphenyl alkane diisocyanates as described in the a~orementioned United States Patent NoO 3,701,3740 Suitable diisocyanates include 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3l-dimethyl-4,4'- -~
-biphenyl diisocyanate, 3,3'-dimethoxy-4,4' biphenyl diisocyanate and the likeO
Mixtures o~ the various diisocyanates mentioned above may also be usedO
,'. ~ . ' ' ' ` '~ ', ' , ' : ' , ,. , ' ~ -'. , ' ' . ' . ' ' ' ' . " . ' ' . ' : ' ' ' Polyurethanes of the desired molecular ~eight suitable for use in the present invention may be made in various ~ays and many different types are suitable, but it is preferable to employ bifunctional reactants which will produce flexible linear polymers. For example, a polyhydric alcohol or a ; hydroxyl-terminated polyether or polyester may be reacted with an organic diisocyanate to form a liquid prepolymer ~ith a molecular weight of 800 to 20,000 having essentially either all hydroxyl end groups or all isocyanate end groups, and thereafter the prepolymer can be cured by means of diamines, diols or diisocyanates, depending upon the terminal or end group in the pre-polymersO The preferred polyurethanes are those formed by capping the hydroxyl groups of polyalkylene glycols with a molecular weight from 800 to 20,000 with ` diisocyanates to form prepolymers, and then chain-extending and curing the prepolymers by means of diamine or diol curing agents, such as MOCA or an alkylene glycol.
The hydroxyl-terminated polyesters which can be used to form the polyurethane may be reaction products of a polycarboxylic acid and a poly-hydric alcohol as described in said United States Patent No. 3,208,500. The alcohol may, for example, be ethylene glycol or propylene glycolO
The organic compound containing active hydrogens for reaction with the isocyanate groups may also be a polyhydric polythioether or polyester amide as defined in said Patent NoO 3,208,500 but is more preferably a polyhydric polyalkylene ether~ The ether may, for example, be the condensation product of an alkylene oxide with a glycol, such as ethylene glycol, propylene glycol, butylene glycol or the like. Any suitable alkylene oxide condensate may also be used such as, for example, condensates of ethylene oxide, propylene oxideg butylene oxide, amylene oxide, styrene oxide and mixtures thereofO
In forming liquid prepolymers for use in the process of this invention, it is preferable to react the organic diisocyanate (preferably MDI
or TDI) with polyalkylene glycols having molecular ~eights in the range of 800 to 20,000, particularly polyCalkylene glycols) having alkylene groups of from ~ to 10 carbon atoms, such as poly(ethylene glycol), poly(propylene glycol~, poly(trime~hylene glycol), poly(tetramethylene glycol), poly~hexa-methylene glycol), high molecular weight copolymers of such glycols, and mix-tures of the above poly(alkylene glycols).
The preferred prepolymers have terminal isocyanate groups, and may be cured with various diamines. The diamines preferably contain an organic central radical of 2 ~o ~0 carbon atoms linked to two amino groups such as ethylenediamine, tetramethylenediamine, hexame~hylenediamine, p-phenylenedi-amine, methylene-bis-2-chloroaniline ("MO~A*"), 4,4'-methylene-bis-aniline, 3,3'-dichloro-4,4'-diaminodiphenylmethane, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine3 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylmethane, d cumene diamine.
In these polyurethane rubbers, the chains of the cured polymer con-tain ~he repeating linkage ~ P-O~CO-NH-Rl-NH-CO-MH-R2-NH-CO-NH-Rl-N~I-CO-O
` wherein P represen~s the high molecular weight poly (alkylene ether) chain, Rl is the organic radical of the diisocyanate, and R2 is the organic central radical of the diamineO This type of polymer with the proper molecular weight can provide excellent results in the practice of the present invention when used to provide the high- and low-modulus lay~rs of the tire laminateO The hardness and modulus of these polyurethane polymers may, for example, be in-creased by increasing the isocyanate and glycol or diamine content of the systemO
The type of polyurethane selected for use in making tires according to this inventicn will depend on the type of manufacturing process employedO
The polyurethane best suited for spraying may not be hest for film extrusion or some otheT method.
*Trade mark - 19 -' ,, " '': ,' ' ':" ." ' :~' ,.. '` ': . : . ' ,': ,' ~." .. ' .: ' ' .: . ' ' ' ' "' ' ' ' ~ , ' "' '',' ' '' ~, `'.' ' :, '' ' ,, , ' . ' ' ' '':' " "'' ' , . . '.,, .,, "' '~ ' . ' ' '' " " ' ' '~' - ~s~
Liquid polyurethane rubbers are now available commercially which can be used in the practice of the present invention. Good results can be `~ obtainedJ for example, with Adiprene* L-100 prepolymers (~o1% NCO), Adiprene*
L-167 prepolymers (6.3% NCO), and Adiprene* L-315 prepolymers (905% NCO), made by E. I. duPont de Nemours ~ CoO These liquid prepolymers can be cured with conventional diamines, such as MOCA*, Caytur 7 or Caytur 21 (~,4'-` methylene-bis-aniline) using an equivalent weight ratio of diamine to pre-polymer of about 0.95 to about 1.10. Caytur 7 is a eutectic mixture of m-phenylene and cumene diamine.
Polyurethane prepolymers, such as Adiprene-L prepolymers, may, for example, be made from TDI and a polyalkylene glycol or polyol, such as poly (tetramethylene ether diol), and similar prepolymers can be made using MDI
lnstead of TDI or using a somewhat different polyolO Various poly(alkylene glycols) and poly~alkylene ether) polyols can be used, both diols and tr]ols, and the prepolymers can have either terminal -OH groups or terminal ~CO groups (preferably the latter)O
The polymeric material used in the tire of the present invention may also be a polyamide plastic, such as nylon 66, nylon 610 or nylon 6~
Various long-chain synthetic polymeric amides having recurring amide groups as an integral par~ of the main polymer chain can be used, such as those pre-pared by the condensation of diamines and dibasic acids, those obtained by the condensation of polycarboxylic acids with polyamines, or those obtained by ; the polycondensation of caprolactam~
Various triamines may be used, such as diethylenetriamine and the like, but it is preferable to employ diaminesO Suitable diamines include ethylenediamine, diethylenediamine, pentamethylenediamine, hexamethylenedi-amine, phenylenediamine, and the like or mixtures thereofO
Various polybasic acids may be used to make the polyamide ranging *Trade mark - 20 -` ~35~L3 from succinic acid to sebacic acid and including, for example, succinic acid, aconic acid~ adipic acid, malic acid, itaconic acid, fumaric acid and the likeO
The polyamides suitable for use in rubber tires which can be used in the practice o the present invention are described in said United States Patent NoO 3,208,5000 The preferred polyamides are those made from diamines -and dibasic acids, such as the reaction products of hexamethylenediamine or similar diamine with a dibasic acid, such as adipic acid or sebacic acid.
; While there are many different types of polymers which can be employed in the practice of this invention, the most promising polymers appear to be polyurethanes and polyamides or nylons as discussed generally in said United States Patent No. 3,208,5000 A~ present the most practical polymers seems to be polyurethanes, particularly polyether urethanes and polyester urethanes.
One advantage of the polyurethanes is that they can be obtained in liquid form with viscosities suitable for spraying or for spreading. Also they can be used in both the high- and low-modulus layers, thereby reducing the adhesion problemO It is also possible to blend polyurethanes of different molecular weights to get the desired properties.
For example, the laminated tire of thls invention can be made using Adiprene L-42 (molecular weight about 3000) for the low-modulus layers and Adiprane L-167 (molecular weight about 1330) for the high-modulus layers~ Also the high-modulus layer could be made using a blend of 60 parts by weight of Adiprene L-167 and 40 parts by weight of Adiprene L-315 ~molecular weight ; about 900). The curing agent could be MOCA, Caytur 21 or other suitable diamine, and the plasticizer~ i any, could be dioctylphthalate or the like.
The curing agent could provide relative fast curing to minimize the time delay after each layer is applied before the next layer is applied The polyurethane prepolymers can also be modi~ied in various ways ,, : :
.. .. . ..
~1~5~ ~3 to produce the desired properties. For exampleJ Adiprene L-167 (a prepolymer with a Brookfield viscosity of about 5000 to about 7000 centipoises at 30Co and about 250 to about 350 centipoises at 100Co) can be cured with 1,~-- butane-diol and trimethylolpropane in suitable proportions to provide a rubber layer of the desired type. A curable polyurethane composition could, for example, be made by mixing 160 parts by weight of Adiprene L-167 with about 9 parts of 1,4-butanediol, about 1.6 parts of trimethylolpropane and a small amount of dioctylphthalate.
; The laminated tire of this invention is preferably constructed so that the tear strength of the laminate ~split sample method) is 50 to 400 or more pounds per lineal inch and so that the low-modulus layers have a tensile strength of at least 1000 pounds per square inch, a Shore A durometer hardness in the range of about 30 to 90, and an elongation of at least 50 percent (more preferably at least 100 percent)O
The curable polymers used in the practice of this invention need not be liquid, but liquid polymers are preferred to facilitate manufactureO
The viscosity of the liquid polymers may~ for example, be 1000 to 50,000 centi-poises and should be less than 100,000 centipoises at 30C. The viscosity may be adjusted by adding substantial amounts, sometimes up to 10 or 20 parts of a plasticizer, such as dioctylphthalate, per 100 parts by weight of the polymer.
In some cases solvents may be used with the polymers to provide the desired flowability. The choice of solvent depends on the type of polymer and the type of curing systemO Various solvents which may be used include ethyl acetate, acetone, toluene, methyl ethyl ketone, xylene, beta-ethoxyethyl acetate and the likeO These are preferably relatively pure and free of moisture.
While the laminates of the pneumatic tires above employ substan- ;
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.3 tially different polymer formulations in the lo~- and high-modulus layers, it will be understood that the invention also contemplates improved laminates with improved flex crack resistance wherein similar formulations are used in all of the layers and the tensile moduli in any given direction (such as cir-cumferential or radial, etcO) is substantially different in adjacent layers~
In accordance with the invention a difference in tensile modulus can be pro-vided between adjacent layers H and L (Figure 2, for example) when using the same polymer in both layers as a result of a different molecular orientation in the adjacent layersO
- 10 The term "tensile modulus" as used herein refers to the stress in - psi which must be exerted on a sample to stretch it to a stated elongation such as 10 percent, 100 percent or 200 percent.
In a laminated tire constructèd according to the present invention ~as in Figure 2, for example) each layer preferably has a 10 percent modulus in one direction which is at least about twice the 10 percent modulus of the next adjacent layer in that direction. For example, the desired difference in tensile modulus between layers H and layers L in the various species of Fig-ures 2 through 5 may be achieved by molecular orientation or by use of differ-ent polymèrs in different layers, or bothO
One advantage of using the same or similar polymers in adjacent layers is the ease of achieving good adhesion.
As used herein the term "parts" means par~s by weight and the term "polymer" includes homopolymers or copolymers unless the context shows other-wise.
The term "fluid" as applied to a polymeric material indicates that the material has viscosity such that it can flow during processingO The viscosity may, for example, be from 100 to 10,000 centipoises at 30C. and should not exceed 100,000 centipoises at that temperatureO
.
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, ~15~3 The followin~ example is provided for purposes of illustrating the nature of the invention, and is not for the purpose of limiting the inventionO
Example This example is included to illustrate the greatly improved ability of a tire made in accordance with the present invention to resist the pro-pagation of a cut flaw or to form a crack. In order to illustrate this ability, laminated and homogeneous samples were subjected to a De Mattia flex test, with a comparison being made between each laminated sample and a homo-geneous sample made from a blend of the materials in the particular laminate, and in the same proportionsO Each of the samples was one inch wide, one-quarter of an inch thick and six inches long. They were press cured for two hours at 250F. (121C.) followed by post curing in an oven for another two ; hours at 176Fo ~80C~)o Each sample then has an artificial flaw of ol inch (.254 cm.) imposed across the quarter inch wide surface, per~endicular to the one inch wide surface. The fatigue test was performed on a De Mattia flex machine which flexes the sample ~at 333 cycles per minute and at room tempera-ture) causing the imposed flaw to propagate laterally across the width of the sampleO
For ~his experiment, two different mat0rial formulations were used which will be referred to as "100" and "167" as follows ~"parts" refers to parts by weight): ~ i , .
. ' , ~
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In~redient Parts "100" "167"
-Adiprene L-100 (1)* 100 Adiprene L-167 (2)* - 100 DC - 203 (3)* 0.1 0.1 Dioctylphthalate - plasticizer lOoO
Caytur 21 (4)* 20.3 31O1 Samples were made from each of these formulations alone and the De Mattia test was used to determine the number of cycles necessary for the ol inch (D254 cmO) flaw to become D5 inch ~1.27 cmO). The number in parentheses under each p5io reading represents 106 pascals. In addition, other properties were measured as follows:
*Note: ~1) and ~2) are liquid prepolymers as previously described; ~3) is a i liquid silicone mold release and emulsifying agent, Dow Corning; and ' ~4) is a 50% dispersion of methylene dianiline/sodium chloride complex in dio~tyl phthalate, du Pont.
Table I
Property "100" "167'l 10% Modulus 160 psi. 370 psi.
(lo 1030) ~2.5507) 20100% Modulus 405 psi. 690 psi.
~2O7920) (4O7568) 200% Modulus 510 psi. 860 psi.
(3,5159) (509288) . Tensile (rupture) 2055 psi, 2290 psi.
(14O167) ~15.787) Elongation (rupture) 750% 575%
Hardness Shore A 83 91 Table I ~continued) Property "100" "167"
Shore D 29 42 : De Mattia (cycles to .5 inch crack) 500 1000 Formulations "100" and "167" were next used to make the samples containing both materials. In the case of the blends, the ratio stated in ~ Table II is the ratio of "100" to "167" and for the laminates reported in : Table II, there is one more layer of "100" than of "167", with both outer layers being the "100".
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r~ n ._ tn tp~`D Pt~o \
--1 In .o ~n ~o~ ~0 O ~0 ~ O
N --'m ~~ N ~ I~
.j h .,.~
:~ ~41n P~ O ~ o~ ~ ~ o : ~ u) n ~ N O O
~, ~:
3 u~
h ~ h o ~ a .$
., h ~ n ~ ~ rl u~
~ ~ h O ~
o\ ~n ~ O
0~oo ~: O
a :, ' .
: .
~S~3 ~ efer~ing to Table II, the second column has the heading "3-layer" designating a laminated sample comprising two outer layers of "100"
and a central layer of "167". The next column "2:1" designates a homogenous sample made from a blend of 2 parts by weight of "100" and 1 part by weight of "167". The subsequent columns designate laminated and homogenous samples with different proportionsO The 9-layers laminated sample, for example, can be compared with the homogenous sample made from the 5:4 blend as indicated in the last columnO
; The above data demonstrates that a marked increase in fatigue life, such as 400 to 500 percent, can be achieved in a laminated sample while still retaining physical properties adequate for conditions to be expected in a pneumatic tire. While the data for tensile strength and elongation are somewhat erratic, this behavior occurs at strains far above those that would be found in end use and does not detract from the fact that a marked improve-ment is observed in fatigue life. The somewhat erratic behavior in tensile ~; strength and rupture elongations in these specimens is related to flaws in the specimen that influence these properties but not the flexing behavior.
., .
,' .
~.~
:~ , :: .
.
.~ . .
` - 28 -,, :. .
"", . "
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a pneumatic tire casing having a tread portion and flexible sidewall portions which are free of fabric reinforcement, the improvement wherein each of said sidewall portions comprises: a series of layers of flexible polymeric material with a calculated molecular weight of at least 10,000 and a Shore A durometer hardness of at least 20, a series of said layers comprising low-modulus polymeric material with a Young's modulus which is from about 100 to about 5,000 pounds per square inch, a plurality of said layers being interspersed with the low-modulus layers and comprising a higher-modulus polymeric material with a Young's modulus which is from about 3000 to 100,000 pounds per square inch, each of which layers has a Young's modulus at least twice that of the next adjacent low-modulus layer.
2. The tire casing of claim 1 wherein each of said sidewall portions contains high-modulus layers with a Young's modulus of about 5000 to about 50,000 pounds per square inch.
3. The tire casing of claim 1 wherein each of said sidewall portions contains low-modulus layers with a Young's modulus of about 500 to about 3000 pounds per square inch.
4. The tire casing of claim 1 wherein each sidewall portion comprises nine to 100 layers of polymeric material with a thickness from about 0.001 to about 0.1 inch.
5. The tire casing of claim 1 wherein the high-modulus layers have a Young's modulus which is three to 20 times that of the low-modulus layers.
6. The tire casing of claim 1 wherein the low-modulus layers are formed of a polymeric material with an elongation of at least 30 percent and a Shore A durometer hardness from about 30 to 90.
7. The tire casing of claim 1 wherein the low-modulus layers are formed of an elastomeric polymeric material with an elongation of at least 50 percent.
8. The improvement of claim 1 wherein the high-modulus layers are formed of an elastoplastic material with an elongation of about 5 to about 10 percent.
9. The improvement of claim 1 wherein the higher modulus layers are formed of nylon.
10. The improvement of claim 1 wherein the layers of the laminated tire are formed of polyester or polyether urethane.
11. The tire casing of claim 1 including a carcass, wherein each layer is parallel to the outer surface of the sidewall portion in which the layer is incorporated, at least seven of said layers form each sidewall portion, the Young's flexural modulus of the low-modulus material is not in excess of 3000 pounds per square inch, and the higher-modulus layers have a 10 percent modulus which is at least twice that of the low-modulus layers.
12. A tire casing according to claim 11 wherein said laminate has a tear strength of at least 50 pounds per lineal inch and contains at least nine layers, each layer having a tensile strength of at least 3000 pounds per square inch.
13. A tire casing according to claim 11 wherein each layer of said laminate is formed of a vulcanized polyurethane polymer and has a tensile strength of at least 3000 pounds per square inch, and wherein the polymer of each layer is made from a prepolymer prepared by reacting (A) one equivalent weight of a polyester or a polyether having a molecular weight of at least 2000 and terminal hydroxyl groups and having ester linkages or ether oxygen atoms between chains of carbon atoms with (B) 0.95 to 1.2 equivalent weights of an organic diisocyanate having 8 to 20 carbon atoms, said prepolymer being thereafter reacted with an organic polyamine or polyol having two or three amino or hydroxyl groups.
14. A tire casing according to claim 13 wherein said prepolymer is made by reacting a poly(alkylene ether) glycol with said diisocyanate, and said prepolymer is thereafter reacted with about 0.95 to about 1.1 equivalents of a diamine curing agent per equivalent of isocyanate groups in the pre-polymer.
15. A tire casing according to claim 11 wherein the low-modulus layers are formed from a liquid polyester or polyether urethane prepolymer with a molecular weight from about 2000 to about 20,000 and wherein the high-modulus layers are formed from a liquid polyester or polyether urethane prepolymer with a molecular weight from about 800 to about 2000, said pre-polymers being subsequently cured with a diamine or diol.
16. The tire casing of claim 1 wherein said tread portion and sidewall portions include a carcass in the form of a flexible laminate, there are at least seven layers of said flexible polymeric material having a tensile strength of at least 2000 pounds per square inch, each layer has a Young's flexural modulus of at least 1000, and the series of higher Young's modulus layers have a tensile modulus in one direction at 10 percent elongation which is at least twice the tensile modulus of adjacent layers in said one direction at 10 percent elongation, whereby the laminate has a high resistance to flex cracking.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA279,751A CA1066467A (en) | 1977-06-02 | 1977-06-02 | Laminated pneumatic tire and method of making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054913A true CA1054913A (en) | 1979-05-22 |
Family
ID=4108799
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA279,751A Expired CA1066467A (en) | 1977-06-02 | 1977-06-02 | Laminated pneumatic tire and method of making same |
| CA316,437A Expired CA1054913A (en) | 1977-06-02 | 1978-11-17 | Laminated pneumatic tire and method of making same |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA279,751A Expired CA1066467A (en) | 1977-06-02 | 1977-06-02 | Laminated pneumatic tire and method of making same |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1066467A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4004518B2 (en) * | 2005-10-04 | 2007-11-07 | 横浜ゴム株式会社 | Pneumatic tire using rubber laminate |
| JP6701620B2 (en) * | 2015-03-20 | 2020-05-27 | 横浜ゴム株式会社 | Tire laminate, tire inner liner material and pneumatic tire |
-
1977
- 1977-06-02 CA CA279,751A patent/CA1066467A/en not_active Expired
-
1978
- 1978-11-17 CA CA316,437A patent/CA1054913A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1066467A (en) | 1979-11-20 |
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