CA1066467A - Laminated pneumatic tire and method of making same - Google Patents
Laminated pneumatic tire and method of making sameInfo
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- CA1066467A CA1066467A CA279,751A CA279751A CA1066467A CA 1066467 A CA1066467 A CA 1066467A CA 279751 A CA279751 A CA 279751A CA 1066467 A CA1066467 A CA 1066467A
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Abstract
ABSTRACT OF THE DISCLOSURE
A process for making a laminated pneumatic tire is disclosed.
The tire may be free of reinforcing fabric and is made of a substantial number of alternating layers of high-modulus and low-modulus polymeric material. The process includes applying to an annular form a first continuous layer having a viscosity less than 100,000 centipoises at 30°C, then partially curing the layer, and thereafter applying to the first layer a continuous layer of a second polymeric material. This process is then repeated to form a laminate. 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 from 100 to about 5000 per square inch. The high-modulus layers of the tire may have a Young's modulus from 3000 to 50,000 or higher.
The laminate is heated and cured while it has a general toroidal shape.
The cured material of each layer has a Shore A durometer hardness of at least 20. The high-modulus layers have a tensile modulus at 10 per cent elongation in any direction which is at least twice that of the low-modulus layers.
A process for making a laminated pneumatic tire is disclosed.
The tire may be free of reinforcing fabric and is made of a substantial number of alternating layers of high-modulus and low-modulus polymeric material. The process includes applying to an annular form a first continuous layer having a viscosity less than 100,000 centipoises at 30°C, then partially curing the layer, and thereafter applying to the first layer a continuous layer of a second polymeric material. This process is then repeated to form a laminate. 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 from 100 to about 5000 per square inch. The high-modulus layers of the tire may have a Young's modulus from 3000 to 50,000 or higher.
The laminate is heated and cured while it has a general toroidal shape.
The cured material of each layer has a Shore A durometer hardness of at least 20. The high-modulus layers have a tensile modulus at 10 per cent elongation in any direction which is at least twice that of the low-modulus layers.
Description
10~;6~67 Description of the Prior Art The present invention relates to a process for making pneumatic tires having portions which are free of reinforcing fabric and, more particularly, laminated pneumatic tires containing hard and soft layers arranged to provide a high resistance to flex cracking.
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 manu-factured by less expensive procedures. 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 uniformity. An additional cause of excessive manufactur-ing expense associated with conventional tire construction is the large a~ount of factory space taken up, first, by the many large cur-ing presses required to cure green tires, one at a time, for any-where 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 t~e difficulty of uniform placement of the many components of the tire and the difficulty of obtaining uniform expansion from the cylindrical shape or a flat dTum to the final toroidal shape.
T~e l~minated tire of the present invention eliminates some of these problems.
In its search for a tire configuration and construction method ~hich does not require the lamination of cords and rubber compound and the subsequent manual buildup of ply layers, the tire industry has attempted to make at least the carcass portion *Trade ~ark ~ 2 1066~
of the tire by molding or casting a liquid polymer, such as a polyurethane, to the desired ~hape. The tire illustrated in U.S.
Patent No. 2,902,072 comprises a tread, inner and outer side-walls, and a cellular polyurethane filling the space between the inner and outer sidewalls. U. S. Patent 3,208,500 discloses the fabrication of the carcass portion of a pneumatic tire by molding a polyurethane or polyamide into a single, generally homogeneous layer. U. S. Patent 3,274,322 discloses a method of flow-forming a material such as a polyurethane, using a doctor blade, to make a strip of material which can subsequently be formed into a tire carcass. U. S. Patent 3,386,485 illustrates a method of making a "fabricless" pneumatic tire from any one of a number of suggested polymers and copolymers by separately molding the annular halves of a tire and subsequently molding the two halves together in a different press.
U. S. Patent 3,396,773 illustrates the application of centrifugal casting techniques for making a tire which is de-scribed as being solid rather than pneumatic. The general con-cept of centrifugal casting has been applied to pneumatic tires as illustrated in U. S. Patent 3,555,141 which dis~loses a method in which a heated mold, having its internal surface conforming to the external shape of a tire, is rotated while a liquid poly-urethane is introduced therein. The rotation of the mold causes the polyurethane to flow and cover the entire inner qurface of the mold and a stationary template, having the same shape as the inside of the tire, serves to spread the material in the same manner as a doctor blade. In U. S. Patent No. 3,701,374 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 properties.
~Oti6~'7 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 of 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 fatigue failure.
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 during operation of the tire. 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 percent. 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. However, 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 from a sharp object, there is a tendency for a crack to develop and grow during continual flexing until the tire fails or becomes 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 polymers, 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 cracking is the principle mode of failure.
According to the invention a process for making a laminated pneumatic tire carcass having improved resistances to flex cracking comprises applying to an annular form a first continuous layer comprising a liquid polymeric material having a viscosity less than 100,000 centipoises at 30C, then partially curing the liquid; thereafter 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 curable laminate, and heating and curing the ~0~6467 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 of cured low Young's flexural modulus layers with a Young's flexural modulus from about 100 to about 5,000 pounds per square inch, a second series of a plurality of high Young's flexural modulus layers being alternated with the low- dulus 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.
The plurality of layers of polymeric material having a relatively high tensile dulus preferably having 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 while at the same time providing a much greater resistance to flex fatigue failure than could be obtained from a ho geneous construction.
The tires are preferably made from fluid polymeric materials which have a viscosity at processing temperatures such that they can flow 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.
When using fluid polyurethane polymers a preferred method of forming the tire is to provide a mold with the desired annular shape of the tire, to apply to the interior surface of the ld 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 manner until the desired thickness is obtained. A doctor blade may be employed to shape the layers or -` ~066~t;7 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 nozzle or other applicator, relative movement may be provided between the mold and the applicator during application of the liquid poly-mer, for example by rotating the mold relative to the applicator or vice versa. If desired the fluid materials may be so com-pounded and so treated that the necessary curing of one layer prior to application 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 0.1 inch. The hard and soft layers preferably alternate, but many different arrangements are possible which will provide the desired resistance to flex cracking.
When ma~ing a pneumatic tire by the above method from fluid polyurethane 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.
Brief Description of the Drawings Figure 1 is a fragmentary perspective view of 8 pneu-matic tire of the type made in accordance with the present in-vention 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 showing 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 invention.
Description of the Preferred Embodiment Referring more particularly to the drawings, which are for the purpose of illustrating preferred embodiments of the in-vention and not for the purpose of limiting the same, Figure 1shows a pneumatic tire 10 comprising a tread portion 12 and two sidewall portions 14. 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 sidewall portions 14. In other words the cross section of the tire may be generally as shown in U. S. Patent No. 3,701,374 or in other patents mentioned pre-viously. It will also be understood that, while the tire pre-ferably has a toroidal cross section, the present invention alsoapplies to tires of special cross section as illustrated for example in U. S. Patent No. 3,840,060. 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 rim.
The tire 10 of this invention is preferably made with a substantial number of layers of polymeric material, each layer preferably having a generally uniform thickness and completely covering the ad~acent layer. In the embodiment of Figure 2, the tire carcass and each of the sidewall portions 14 comprises a ~066~67 thirteen-layer laminate made up of alternating high-and low-modulus layers H and L. The low-modulus layer L i~ prov~ded at both the inner and outer surfaces of the tire, and every other layer comprises a high-modulus layer H. This particular con-figuration makes it possible to obtain a tire of the desired strength and stiffness by use of high-modulus layers while at the same time minimizing the tendency for flex cracking. It will be understood that while thirteen-layers are often desirable, a different number of layers can also provide good results.
Figure 3 illustrates a different embodiment, also with thirteen-layers, wherein a medium modulus layer M is provided in addition to the high-modulus layers H and the low-modulus layers L. This arrangement is similar to that of Figure 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 L. Where the tire has a very large number of layers such a9 25 to 50 or more, it may be desirable to provide more than one layer of intermediate modulus between the low-modulus layer and the high-modulus layer.
Figure 4 illustrates another embodiment of the inven-tion 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 L. One reason for using this type of construction ~s that the inner and outer surface portions of the tire are subjected 1066~67 to greater bending strains which are withstood better by the low-modulus material.
Figure 5 shows another embodiment of the invention in which the various layers have different thicknesses. 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 and 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 Fig-ure 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 cylin-drical to the toroidal shape by a method somewhat similar to the conventional flat-band process. 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 invention 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 thickness. Another possible method of building a tire is to apply successive layers of un-cured 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 automated procedures.
_g_ 1066~67 The polymeric materials which may be used to make tires according to the present invention are elastomers, elastoplastic materials or high-modulus plastics. The softer low-modulus layers of the tire are made from the elastomeric and/or elasto-plastic materials and the harder high-modulus layers are pre-ferably made from the elastoplastic materials or high-modulus plastics.
The elastomers are characterized by major glass trans-ition temperatures below about minus 20 degrees Centigrade, Young's moduli in the range of 100 to 6000 pounds per square inch, and the ability to sustain elongations of 100 percent or more without permanent deformation or rupture. The useful elastomers include polyurethane rubber, natural rubber, poly (butadiene) and various other synthetic rubbers including SBR
rubbers.
The elastoplastic polymeric materials can have Young's moduli in the range of 3000 to 50,000 pounds per square inch. At room temperature these materials usually exhibit yield points below 50 percent elongation and ultimate tensile strength~ above ~000 pounds per square inch and ultimate elongations greater than 100 percent. These materials are usually characterized by being multiphase in that glassy or crystalline domain structures are usually detectable. Typical materials in this group are block polymers, such as styrene-butadiene-styrene triblock poly-mers, polyester block polymers, segmented polyurethane polymers and ionomers.
~ The high-modulus plastic materials are characterized 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 would have a major glass or melting transition 1066~6~ - `
temperature above 100C. Suitable materials in this group include compositions from polyamides, polycarbonates, epoxide resins and polystyrenes.
The elastomeric materials 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 5,000 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 of at least 20 and preferably provide a tensile strength of at least 1000 pounds per square inch. 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 90. The polymeric material of the softer low modulus layers preferably has a tensile strength of at least 2000 pounds per square inch.
There is a general relationship between Shore hardness and Young's modulus as follows:
Shore Hardness Young's Modulus (B.S. & I.R.H.) (psi) It should be understood that the Shore hardness and Young's modulus values given herein must generally correlate with this relationship.
6'7 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 tire 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 tire.
The preferred modulu~ for the harder layers depends, of course, on many factors and should be selected to provide the composite tire with the desired overall modulus and stiffness.
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 p8i for the hard layers. If, on the other hand, the amount of the high-modulus material is reduced to only 25 per-cent of the weight, then the Young's modulus could be increased to 10,000 to 15,000 psi or perhaps 20,000 psi.
Generally the total weight 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 ~066~67 layers at the inner and outer surfaces of the laminate, particu-larly at the outer surfaces of the sidewall portions.
The number of layers can be limited to reduce manu-facturing 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 i6 preferably uniform or generally uniform, and each layer i8 preferably circumferentially continuous and imperforate, but this is not essential. 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 of 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 arr~ngements are generally preferred with each low-modulus layers of the same hardness and each high-modulus layer of the same hardness. To improve adhesion between layers, it is desirable to make all layers of generally the same type of polymer (i.e., polyurethane). However, it will be understood that adhesion problems can be solved by use of adhesives or perforations in _he layers or in various other ways.
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-66~6'7 modulus layers are formed of the same elastomeric material having an elongation of at least 50 percent and a Young's modulus of 500 to 2000 p8i. The tensile strength of the high-modulus layers should be at lea~t 2000 psi and preferably at least 3000 psi.
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 different ways from curable sheets of rubber or plastic or from flowable polymeric material~ 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 own 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 polyurethane, which can be cured rapidly and which can be processed easily in automated equipment. The viscosity of the polymeric material can be ad-justed by use of solvents or plasticizers, by use of heat, or by proper selection of curing agents, by changing the curing tempera-ture, or in other ways. A large number of different polymers can be employed as are described in more detail hereinafter.
In carrying out the present invention it is preferable to form the laminations of the tire by spraying or otherwise ap-plying curable liquid polymeric material to the inside of a tire 6~7 mold. This can be done with or without a doctor blade to shape the layers.
Figure 6 illustrates in partly schematic form one type of mold which may be employed to fabricate a laminated tire. The mold i8 illustrated for purposes of illustration rather than li-mitation, 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 ha~vels are attached to 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 28. A pair of spray tubes 32 and 34 is position-ed 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 sup-port member 36 which is mounted on the shaft 30. Ball bearings 38 are provided around periphery of the member 36 at opposite end~ 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 ~tationary or may be mounted to rotate or turn if this is desired.
As herein shown the inner surface of the mold defined by the combination of mold halves 22L and 22R may be such that the pneumatic tire, including both the tread portion and the sidewall portions, may be totally fabricated 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 -~066~67 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 belt~ can be provided under the tread if desired.
In the mold shown in Figure 6 the spray nozzle or noz-zles may be designed to deliver a spray of the liquid polymer to the radially outer (tread) surface and also to the interior side-wall surface of the mold as is illustrated by the broken lines radiating from the end of tube 34 in Figure 6. In other words, the spray nozzles would deliver the liquid polymer in such a manner as to provide a layer of substantially uniform thickness covering the entire 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 ~hown herein two spray tubes 32 and 34 are provided for the two different polymeric materials. If three different polymeric mat-erials were to be employed, then three spray nozzle~ could be provided. It i8 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 off. By alternately supplying the polymers through the different tubes, alternate layers may be formed 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. Sub-quently another layer may be formed in a similar manner during 1066~6'7 one or more rotations by spraying polymeric material from the other spray tube. The centrifugal force from rotation of the mold can help to shape the layers, and it will be understood that various centrifugal casting methods may be employed to assure proper coating of the mold. However, it is desirable to provide curable polymeric material which will cure fast enough so that one layer will maintain its shape while the next layer iB being applied. Also fast-curing material is desirable to assure formation of layers of substantially uniform thickness which can maintain their shape during rotation of 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 supplied. For example, the mold may be rotated 510wly 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 mold. Also the process can be varied to require several rotations of the mold during forma-tion 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 substantial curing before spraying the next layer. If the rate of curing is fast enougil it may be possible to begin spraying the subsequent layer within one-half of a revolution after the previous layer was applied.
As used herein the expression "partially curingN indi-cates that the material has stiffened or set up sufficiently to maintain reasonable dimensionable stability so that a subsequent layer may be applied. Such expression does not necessarily require a true curing of the material.
It will be understood that various fluid polymeric materials may be employed using molds of the general type il-lustrated in Figure 6 and that the viscosity or flowability of the liquid polymers may be controlled by the use of heat, sol-vents, plasticizers or other techniques to allow the movement of the liquid material 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 incIuding monomers, melts, prepolymers and solutions. The fluid polymeric materials must be liquid at the time of proces-sing and have a viscosity at processing temperatures such that they will flow under their own weight in a reasonable period of time.
one of the polymers preferred for use in the practice of the present invention is polyurethane. Such polymer is usual-ly prepared by reacting 0.95 to 1.2 equivalent weights of an or-ganic polyisocyanate having 2 to 3 functional isocyanate groups with one equivalent of an organic compound having a molecular weight of at least 1000 and containing active hydrogen atoms which are reactive with isocyanate (-NCO~ groups. In many in-stances an organic chain-extending agent may be employed contain-ing 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, polyester amides, polyhydric polyalkylene ethers, polyhydric polythioethers, polyacetals and the like.
The organic polyisocyanates used to form the poly-urethane in the process of this invention may be of various types 6'7 including aliphatic, aromatic, alicyclic and heterocylic as difi-closed in said U. S. Patent No. 3,208,500 and preferably contain at least 8 carbon atoms. Excellent results are obtained using aromatic diisocyanates such as toluene diisocyanate (TDI), 4,4'-diphenyl-methane diisocyanate (MDI) or other diphenyl-alkane diisocyanate or the like. For example, the organic diisocyanate may be an 80:20 or 65:35 blend of 2,4- and 2,6-toluene diisocy-anate.
The diisocyanates suitable for use in the practice of the invention preferably have 8 to 20 carbon atoms and include the various toluene diisocyanates, the various naphthalene diisocyanates, the various phenylene diisocyanates, and the various diphenyl alkane diisocyanates as described in U. S.
Patent No. 3,701,374, the entire disclosure of which is in-corporated herein by reference. Suitable diisocyanates include 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diiso-cyanate and the like. Mixtures of the various diisocyanates men-tioned ~bove may also be used.
Polyurethanes of the desired molecular weight suitable for use in the present invention may be made in various ways and many different types are suitable, but it is preferable to em-ploy 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 with a molecular weight of 800 to 20,000 having essentially either all hydroxyl end groups or all isocyanate end groups, and thereafter the prepoly-mer can be cured by means of diamines, diols or diisocyanates, 10664~;7 depending upon the terminal or end group in the prepolymers.
The preferred polyurethanes are those formed by capping the hydroxyl groups of polyalkylene glycsls 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 polycar-boxylic acid and a polyhydric alcohol as described in said U.S.
Patent No. 3,208,500. The alcohol may, for example, be ethylene glycol or propylene glycol.
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 No.
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, pro-pylene glycol, butylene glycol or the like. Any suitable alkylene oxide condensate may also be used such as, for example, con-densates of ethylene oxide, propylene oxide, butylene oxide,amylene oxide, styrene oxide and mixtures thereof.
In forming liquid prepolymers for use in tha process of this invention, it is preferable to react the organic diiso-cyanate (preferably MDI or TDI) with polyalkylene glycols having molecular weights in the range of 800 to 20,000, particularly poly(alkylene glycols) having alkylene groups of from 2 ~o 10 carbon atoms, such as poly(ethylene glycol), poly(propylene glycol), poly(trimethylene glycol), poly(tetramethylene glycol), poly(hexamethylene glycol), high molecular weight copolymers of such glycols, and mixtures of the above poly(alkylena glycols).
~646~ - `
The preferred prepolymers have terminal isocyanate groups, and may be cured with various diamines. The diamines preferably contain an organic central radical of 2 to 20 carbon atoms linked to two amino groups such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, p-phenyl-enediamine, methylene-bis-2-chloroaniline ("MOCA"*), 4,4'-methylenebis-aniline, 3,3'-dichloro-4,4'-diaminodiphenylmethane, benzidine, 3,3'-dimenthylbenzidine, 3,3'-dimethoxybenzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylmethane, and cumene diamine.
In these polyurethane rubbers, the chains of the cured polymer contain the repeating linkage ~ P-0-C0-NH-Rl-NH-C0-NH-R2-NH-C0-NH-Rl-NH-C0-0 wherein P represents the high molecular weight poly (alk~-lene ether) chain, Rl is the organic radical of the diisocyanate, and R2 is the organic central radical of the diamine. 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- ~nd low-modulus layers of the tire laminate.
The hardness and modulus of these polyurethane polymers may, for example, be increased by increasing the isocyanate and glycol or diamine content of the system.
The type of polyurethane selected for use in making tires accord-ing to this invention will depend on the type of manufacturing processemployed. The polyurethane best suited for spraying may not be best for film extrusion or some other method.
Liquid polyurethane rubbers are now available commercially which can be used in the practice of the present invention. Good results can be obtained, for example, with Adiprene* L-100 prepolymers (4.1% NC0), Adiprene* L-167 prepolymers * Trade Marks (~ 3~ NCO), and Adipren- L-315 prepolymers ~9 5~ NCO), made by I ~u Pont de Nemours ~ Co Th -e liquld prepoly~ers can be our d ~lth oonv ntlonal di~aine~, ~uch a~ ~OCA, Caytur*7 or CaytUr*
21 (~ thyl-n--bl--anllln-~ u-lng an eyuival-nt ~ ight ratio of d~ _ ln- to propolya r of about 0 95 to about 1 10 Caytur*7 a ut ctlc Dixtur- of -phenylene and ¢umene diamine Polyur-thane prepolymers, uch as Adiprene-L prepolymers, ay, for xample, be ~do from TDI and a polyal~ylen- glycol or polyol, Juch as poly(tetramethylene ether diol), and ~imilar pr-poly~ers ¢an be mad- u~ing ~DI in-tead of TDI or using a some what diffor-nt polyol V~rious poly(alkylene glycol-) and poly (alkylene ether) polyols can be u-od, both diol~ and triol~, and th pr polym~rs can have eith-r terminal -O~ groups or terminal -NCO group~ (preferably th latter) Th poly~eric mat-rlal u-ed in the tir- of the present inv ntion ~ay ~l-o b a polyamia pla-tic, ~uch a- nylon 66, nylon C10 or nylon 6 V riou- lonq-chain ynthetlc poly~ rlc umides ha~ing r~curring _l~b group- a- n int gral part of the main polymor ohaln o n b u~ d, uch a- tho e prap~red ky the conden-atlon of dlamin-- nd dlba-lc acid-, tho-- obtain-d by the c~n-d n-ation of polycarboxyllc acid- wlth polyamine-, or those ob-taln-d by th polycond n-ation of caprolact~m Variou~ triamin-- ~ay be u--d, ~uch a- diethylenetri-~ine and the li~e, but it 1- preferable to employ di~ines Suitable diamine- lnclude thylenedlamine, diethylenedia~ine, p nt~methylenedl~mine, hexamethylenediamine, ph-nylen-diamine, and the like or mixture~ ther of Variou~ polyba-ic acid~ may be used to makQ the poly-amid- ranging from uccinic acid to Je~acic acid nd including, *Trade Mark .
1CH66 ~ 7 for xa~ple, ~uooinlc ~cid, conic wid, ~alpic acid, malic acid lt~eonie acid, fumar$c acid na th lik~
The polyamid - ~uitabl~ for u-e in Nbber tire~ which ¢~n b u--d in tbe practia~ of th- pr --nt lnv ntion are d~scribed ln U ~ Pat nt No 3,208,S00 The pre~err-d polyamide- ro tho~e mad from diamin~
and dibasic acids, ~uch as the reaction products of hexamethy-l-nediamine or similar diamine with a dibasic acid, such as adipic acid or ~ebacic acid While there re ~ ny differ nt type~ of polymRrs which can b ~ploy-d in the pr~ctice of thi~ inv ntion, th- most pro~i-ing polyD~r- ~pp- r to b- polyur~th~n - nd polyamide~ or nylon~ ~- di-eu--ed g~n~r~lly ln ~id U S ~tent No 3,208,500 At pr -~nt th~ ~t pr ctlcal poly~ r- -mJ to be polyurethanes p~rtloul rly poly~th~r ur~th~n~- ~nd poly~t-r ur-thnnc~ ~
Ono d~ntng- of th polyur th~n-- i- th~t th-y c-n be o~k~ln d ln ll~ula for~ ~lth ~i-co-l~i-- uit bl- for praying or ~or pr ~ding al-o th y o n ~ u d in both the high- and lo~-~oaulu- lay~r-, th r by r ducing th ~dh--ion proble~ It is ~l-o po--lbl- to bl-nd polyur-th neJ of different ~ol-cular ~elght~ to gct tho d--ir d properti--For ~xample, the laolnated tire of thi- invention can b ~ade u-ing Adiprene*L-~2 t~ol-cul~r w-ight bout 3000) for th- low-modulus lay r- ~nd Adiprone*L-167 (molccular weight about 1330) for the hlgh~odulu- l~y r- Al-o th high-modulus l~y r could b mado u-lng a bl-nd of 60 part- by weight of Ad 4 r n L-167 ~nd ~0 part- by w-lght of Ad$pren- L-315 t~olecu-lar ~eight about 900) ~h~ curing a~ nt could b~ MOCA, Caytur*
21 or oth r uitabl~ dia~in~, and th pla-ticiz-r, if ny, could *Trade Marks _ , . -- .. . .
;6/~6~
b- dioctylphthalate or the llke The CuriAg agent could provide rolative faot curing to minimise the time delay a~ter each layer i- ap~li-d before t~e next layer is applied The polyurethane prepolymer~ can also be modified in various ways to produce the ~esired propertie~ For example, Adlpron~ ~-167 (a prepolymer with a ~roo~field viscosity of about 5000 to about 7000 centipoise~ at 30C nd about 250 to about 350 c-ntipoises at lOO C ) can be cure with l,~-butane-diol and trimathylolpropane in uitabl- proportions to provide a rubb r lay r of the d-~ired typ- A ourable polyur~thane com-po-ition oould, for xa~pl~, b aade by mixing 160 parts by ight of Adipr ne L-167 ~lth about ~ p rt- of 1,4-butanediol, about 1 6 p rt~ of tri athylolprop ne and a mall amount of dioctylphthalat The laminatod tire of thl- lnventlon i~ pr-ferably oon-truct-d o that th t-ar trength of ~he laminato (~plit ~mpl- thod) 1- 50 to ~00 or more pound~ per lineal inch and o that the low-modulu~ layer- have a tenslle strength of at l-a~t 1000 pounds per square inch, a Shore A durometer hardness in the range of about 30 to 90, and an elongat~on of at least 50 percent (more preferably at least 100 p rcentl The curable polymer~ u~ed in the practic- of this inv ntion n ed not be liquid, but liquid poly~ors are preferred to facilitate m nufactur Th- viJco-ity of the liquid polymers nay, for exa~pl-, bo 1000 to 50,000 o ntipoi--- and hould be 1 -- th n 100,000 oontipoi--- at 30 C Th vl~co~lty ~ay be a~u-t d by dding ub-t ntial _ ount-, ~o~ times up to 10 or 20 p rt-, of a pl~-t~ci~-r, uch ~J dioctylphthalate, p~r 100 parts by ~oight o~ tha polya-r *Trade Mark . .
106646'7 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 system. Various solvents which may be used include ethyl acetate, acetone, toluene, methy~ ethyl ketone, xylene, beta-ethoxyethyl acetate and the like. These are preferably relatively pure and free of moisture.
While the laminates of the pneumatic tires above employ substantially different polymer formulations in the low- 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, etc.) is substantially different in adja-cent layers. In accordance with the invention a difference in tensile modulus can be provided between adjacent layers H and L
(Figure 2, for example) when using the same polymer in both lay-ers as a result of a different molecular orientation in the adja-cent layers.
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 constructed according to the pre-sent invention (as in Figure 2, for example) each layer prefer-ably 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 s~ecies of Figures 2 through 5 may be achieved by molecular orientation or by use of different polymers in different layers, or both.
1066~6~
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 parts by weight and the term "polymer" includes homopolymers or copolymers un-less the context shows otherwise.
The term "fluid" as applied to a polymeric material indicates that the material has viscosity such that it can flow during processing. The viscosity may, for example, be from 100 to 10,000 centipoises at 30C. and should not exceed 100,000 centipoises at that temperature.
The following example is provided for purposes of il-lustrating the nature of the invention, and is not for the pur-pose of limiting the invention.
Example This example is included to illustrate the greatly improved ability of a tire made in accordance with the present invention to resist the propagation of a cut flaw or to form a crack. In order to illustrate this ability, laminated and homo-.
geneous samples were sub~ected 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 proportions. Each of the samples was one inoh wide, one-quarter of an inch thick and 8iX inches long. They were press cured for two hours at 250F. (121C.) followed by post curing in an oven for another two hours at 176F. (80C.).
Each sample then has an artificial flaw of .1 inch (.254 cm.) imposed across the quarter inch wide surface, perpendicular to the one inch wide surface. The fatigue test was performed on a 1066~67 De Mattia flex machine which ~lexes the sample (at 333 cycles per minute and at room temperature) c~using the ~mposod ~law to propagate laterally acros~ the width o~ the ~mple.
For thi~ experiment, two different material fonmulations wer- used which will be referred to as 100" and 167" as follows ~parts" refer~ to parts by weight):
Ingredient Parts 100~ ~167 **Adiprene L-100 (1)* 100 **Adipr-ne L-167 (2)~ - 100 **DC - 203 (3)* 0.1 0.1 **Dioctylphthalate pla-ticizer 10.0 **Caytur 21 (~)~ 20.3 31.1 130.4 131.2 $umple~ were made from each of these formulations alone and th- Do Mattia te-t wa~ used to determine the number of cycles neces~ary for the .1 inch (.254 cm.) flaw to become .5 inch (1.27 cm.). The number in parenthe~es under each psi. reading r-pre-ent~ 10 pa~cals. In addition other propertie~ were mea~ured a8 follow~s _ _ _ ~Notes (1) and (2) are liquid prepolymer~ a~ previou-ly de-~cribed; (3) iJ a liquid ilicone mold relea~e ~nd mul~ifying ag-nt Dow Corning~ and (~ a 50~ dispersion of methylen- di-~niline/ ~odium chloride c plex in dioctyle phthalate du Pont.
**Trade Marks ~0~6~
Table Property"100" "167"
10% Modulus 160 psi. 370 psi.
(1.1030) (2.5507) 100% Modulus 405 psi. 690 psi.
(2.7920) (4.7568) 200% Modulus 510 psi. 860 psi.
(3.5159) (5.9288) ~ensile (rupture) 2055 psi. 2290 psi.
(14.167) (15.787) Elongation (rupture) 750% 575%
Lardne3s Shore A 83 91 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 H167~, with both outer layers being the "100".
-" 1066~67 Lq ~ 10 _~ p~ O
o~ ,` 1 I~ _I O ~ D ~ O
~r o . o .o~ u~ oOD ~ O
.. 10 ~1~ ~)~1 ~1 N ~r Ir~ N--~r--~-- 1 a) ~q 0,bq ~rQ ~
~o o O~ O dP O
~I o o o ~ I o O ~1 ~ ~
U~ ~ o . ~P ~ ~ o u~ o oo ~ u~
.. ~ _I ~ ~ ~ ~ U~
N-- ~--~1--rl ~ ~1 _ 0 _ u~
Q~
000 ~D dP O
~1 U~ O _I O I I O
O ~1~ t'~ ~ O
rl _ rl ~ ~q ~
O D O d~ ~` ~ o U~ O ~ CO ~ O
- a~ ~1 ~ o .~0 Il`) r~
U~ O
~1 U~ O U~ I I O
rJ la~ ~1~ N cn ~D ~ O
.,i .~1 _ rl _ 07--U~ O ~~O ~ O
~1 U) ~ O ~ O OCO ~ O
N N ~
~i~i ~D~ _ ~u a~
U~Q~ O U~
U~ ~ O dP O
~1 1~ Ir~ ~ N O I I O
.
a) _ ~ 1 ~
~ tn ~ S
D~ :~ _I h C
~0~ ~ ~
P~ ~ O Q) O O ~
S S ~ ~0 dP O ~ O
O O
.
10~6~6'7 Referring to Table II, the second column has the heading "3-layer" de~ignating 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 proportions. 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 column.
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 ade-quate 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 round in end use and does detract from the fact that a marked improvement i8 observed in fatigue life. The somewhat erratic behavior in tensile strength and rupture elongations in these spocimens is related to flaws in the specimen that influence these properties but not the flexing behavior.
It will be understood that, in accordance with the pro-visions of the patent statutes, variations and modification~ of the specific methods and articles disclosed herein may be made without departing from the spirit of the invention.
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 manu-factured by less expensive procedures. 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 uniformity. An additional cause of excessive manufactur-ing expense associated with conventional tire construction is the large a~ount of factory space taken up, first, by the many large cur-ing presses required to cure green tires, one at a time, for any-where 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 t~e difficulty of uniform placement of the many components of the tire and the difficulty of obtaining uniform expansion from the cylindrical shape or a flat dTum to the final toroidal shape.
T~e l~minated tire of the present invention eliminates some of these problems.
In its search for a tire configuration and construction method ~hich does not require the lamination of cords and rubber compound and the subsequent manual buildup of ply layers, the tire industry has attempted to make at least the carcass portion *Trade ~ark ~ 2 1066~
of the tire by molding or casting a liquid polymer, such as a polyurethane, to the desired ~hape. The tire illustrated in U.S.
Patent No. 2,902,072 comprises a tread, inner and outer side-walls, and a cellular polyurethane filling the space between the inner and outer sidewalls. U. S. Patent 3,208,500 discloses the fabrication of the carcass portion of a pneumatic tire by molding a polyurethane or polyamide into a single, generally homogeneous layer. U. S. Patent 3,274,322 discloses a method of flow-forming a material such as a polyurethane, using a doctor blade, to make a strip of material which can subsequently be formed into a tire carcass. U. S. Patent 3,386,485 illustrates a method of making a "fabricless" pneumatic tire from any one of a number of suggested polymers and copolymers by separately molding the annular halves of a tire and subsequently molding the two halves together in a different press.
U. S. Patent 3,396,773 illustrates the application of centrifugal casting techniques for making a tire which is de-scribed as being solid rather than pneumatic. The general con-cept of centrifugal casting has been applied to pneumatic tires as illustrated in U. S. Patent 3,555,141 which dis~loses a method in which a heated mold, having its internal surface conforming to the external shape of a tire, is rotated while a liquid poly-urethane is introduced therein. The rotation of the mold causes the polyurethane to flow and cover the entire inner qurface of the mold and a stationary template, having the same shape as the inside of the tire, serves to spread the material in the same manner as a doctor blade. In U. S. Patent No. 3,701,374 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 properties.
~Oti6~'7 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 of 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 fatigue failure.
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 during operation of the tire. 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 percent. 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. However, 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 from a sharp object, there is a tendency for a crack to develop and grow during continual flexing until the tire fails or becomes 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 polymers, 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 cracking is the principle mode of failure.
According to the invention a process for making a laminated pneumatic tire carcass having improved resistances to flex cracking comprises applying to an annular form a first continuous layer comprising a liquid polymeric material having a viscosity less than 100,000 centipoises at 30C, then partially curing the liquid; thereafter 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 curable laminate, and heating and curing the ~0~6467 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 of cured low Young's flexural modulus layers with a Young's flexural modulus from about 100 to about 5,000 pounds per square inch, a second series of a plurality of high Young's flexural modulus layers being alternated with the low- dulus 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.
The plurality of layers of polymeric material having a relatively high tensile dulus preferably having 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 while at the same time providing a much greater resistance to flex fatigue failure than could be obtained from a ho geneous construction.
The tires are preferably made from fluid polymeric materials which have a viscosity at processing temperatures such that they can flow 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.
When using fluid polyurethane polymers a preferred method of forming the tire is to provide a mold with the desired annular shape of the tire, to apply to the interior surface of the ld 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 manner until the desired thickness is obtained. A doctor blade may be employed to shape the layers or -` ~066~t;7 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 nozzle or other applicator, relative movement may be provided between the mold and the applicator during application of the liquid poly-mer, for example by rotating the mold relative to the applicator or vice versa. If desired the fluid materials may be so com-pounded and so treated that the necessary curing of one layer prior to application 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 0.1 inch. The hard and soft layers preferably alternate, but many different arrangements are possible which will provide the desired resistance to flex cracking.
When ma~ing a pneumatic tire by the above method from fluid polyurethane 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.
Brief Description of the Drawings Figure 1 is a fragmentary perspective view of 8 pneu-matic tire of the type made in accordance with the present in-vention 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 showing 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 invention.
Description of the Preferred Embodiment Referring more particularly to the drawings, which are for the purpose of illustrating preferred embodiments of the in-vention and not for the purpose of limiting the same, Figure 1shows a pneumatic tire 10 comprising a tread portion 12 and two sidewall portions 14. 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 sidewall portions 14. In other words the cross section of the tire may be generally as shown in U. S. Patent No. 3,701,374 or in other patents mentioned pre-viously. It will also be understood that, while the tire pre-ferably has a toroidal cross section, the present invention alsoapplies to tires of special cross section as illustrated for example in U. S. Patent No. 3,840,060. 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 rim.
The tire 10 of this invention is preferably made with a substantial number of layers of polymeric material, each layer preferably having a generally uniform thickness and completely covering the ad~acent layer. In the embodiment of Figure 2, the tire carcass and each of the sidewall portions 14 comprises a ~066~67 thirteen-layer laminate made up of alternating high-and low-modulus layers H and L. The low-modulus layer L i~ prov~ded at both the inner and outer surfaces of the tire, and every other layer comprises a high-modulus layer H. This particular con-figuration makes it possible to obtain a tire of the desired strength and stiffness by use of high-modulus layers while at the same time minimizing the tendency for flex cracking. It will be understood that while thirteen-layers are often desirable, a different number of layers can also provide good results.
Figure 3 illustrates a different embodiment, also with thirteen-layers, wherein a medium modulus layer M is provided in addition to the high-modulus layers H and the low-modulus layers L. This arrangement is similar to that of Figure 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 L. Where the tire has a very large number of layers such a9 25 to 50 or more, it may be desirable to provide more than one layer of intermediate modulus between the low-modulus layer and the high-modulus layer.
Figure 4 illustrates another embodiment of the inven-tion 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 L. One reason for using this type of construction ~s that the inner and outer surface portions of the tire are subjected 1066~67 to greater bending strains which are withstood better by the low-modulus material.
Figure 5 shows another embodiment of the invention in which the various layers have different thicknesses. 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 and 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 Fig-ure 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 cylin-drical to the toroidal shape by a method somewhat similar to the conventional flat-band process. 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 invention 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 thickness. Another possible method of building a tire is to apply successive layers of un-cured 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 automated procedures.
_g_ 1066~67 The polymeric materials which may be used to make tires according to the present invention are elastomers, elastoplastic materials or high-modulus plastics. The softer low-modulus layers of the tire are made from the elastomeric and/or elasto-plastic materials and the harder high-modulus layers are pre-ferably made from the elastoplastic materials or high-modulus plastics.
The elastomers are characterized by major glass trans-ition temperatures below about minus 20 degrees Centigrade, Young's moduli in the range of 100 to 6000 pounds per square inch, and the ability to sustain elongations of 100 percent or more without permanent deformation or rupture. The useful elastomers include polyurethane rubber, natural rubber, poly (butadiene) and various other synthetic rubbers including SBR
rubbers.
The elastoplastic polymeric materials can have Young's moduli in the range of 3000 to 50,000 pounds per square inch. At room temperature these materials usually exhibit yield points below 50 percent elongation and ultimate tensile strength~ above ~000 pounds per square inch and ultimate elongations greater than 100 percent. These materials are usually characterized by being multiphase in that glassy or crystalline domain structures are usually detectable. Typical materials in this group are block polymers, such as styrene-butadiene-styrene triblock poly-mers, polyester block polymers, segmented polyurethane polymers and ionomers.
~ The high-modulus plastic materials are characterized 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 would have a major glass or melting transition 1066~6~ - `
temperature above 100C. Suitable materials in this group include compositions from polyamides, polycarbonates, epoxide resins and polystyrenes.
The elastomeric materials 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 5,000 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 of at least 20 and preferably provide a tensile strength of at least 1000 pounds per square inch. 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 90. The polymeric material of the softer low modulus layers preferably has a tensile strength of at least 2000 pounds per square inch.
There is a general relationship between Shore hardness and Young's modulus as follows:
Shore Hardness Young's Modulus (B.S. & I.R.H.) (psi) It should be understood that the Shore hardness and Young's modulus values given herein must generally correlate with this relationship.
6'7 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 tire 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 tire.
The preferred modulu~ for the harder layers depends, of course, on many factors and should be selected to provide the composite tire with the desired overall modulus and stiffness.
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 p8i for the hard layers. If, on the other hand, the amount of the high-modulus material is reduced to only 25 per-cent of the weight, then the Young's modulus could be increased to 10,000 to 15,000 psi or perhaps 20,000 psi.
Generally the total weight 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 ~066~67 layers at the inner and outer surfaces of the laminate, particu-larly at the outer surfaces of the sidewall portions.
The number of layers can be limited to reduce manu-facturing 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 i6 preferably uniform or generally uniform, and each layer i8 preferably circumferentially continuous and imperforate, but this is not essential. 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 of 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 arr~ngements are generally preferred with each low-modulus layers of the same hardness and each high-modulus layer of the same hardness. To improve adhesion between layers, it is desirable to make all layers of generally the same type of polymer (i.e., polyurethane). However, it will be understood that adhesion problems can be solved by use of adhesives or perforations in _he layers or in various other ways.
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-66~6'7 modulus layers are formed of the same elastomeric material having an elongation of at least 50 percent and a Young's modulus of 500 to 2000 p8i. The tensile strength of the high-modulus layers should be at lea~t 2000 psi and preferably at least 3000 psi.
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 different ways from curable sheets of rubber or plastic or from flowable polymeric material~ 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 own 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 polyurethane, which can be cured rapidly and which can be processed easily in automated equipment. The viscosity of the polymeric material can be ad-justed by use of solvents or plasticizers, by use of heat, or by proper selection of curing agents, by changing the curing tempera-ture, or in other ways. A large number of different polymers can be employed as are described in more detail hereinafter.
In carrying out the present invention it is preferable to form the laminations of the tire by spraying or otherwise ap-plying curable liquid polymeric material to the inside of a tire 6~7 mold. This can be done with or without a doctor blade to shape the layers.
Figure 6 illustrates in partly schematic form one type of mold which may be employed to fabricate a laminated tire. The mold i8 illustrated for purposes of illustration rather than li-mitation, 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 ha~vels are attached to 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 28. A pair of spray tubes 32 and 34 is position-ed 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 sup-port member 36 which is mounted on the shaft 30. Ball bearings 38 are provided around periphery of the member 36 at opposite end~ 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 ~tationary or may be mounted to rotate or turn if this is desired.
As herein shown the inner surface of the mold defined by the combination of mold halves 22L and 22R may be such that the pneumatic tire, including both the tread portion and the sidewall portions, may be totally fabricated 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 -~066~67 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 belt~ can be provided under the tread if desired.
In the mold shown in Figure 6 the spray nozzle or noz-zles may be designed to deliver a spray of the liquid polymer to the radially outer (tread) surface and also to the interior side-wall surface of the mold as is illustrated by the broken lines radiating from the end of tube 34 in Figure 6. In other words, the spray nozzles would deliver the liquid polymer in such a manner as to provide a layer of substantially uniform thickness covering the entire 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 ~hown herein two spray tubes 32 and 34 are provided for the two different polymeric materials. If three different polymeric mat-erials were to be employed, then three spray nozzle~ could be provided. It i8 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 off. By alternately supplying the polymers through the different tubes, alternate layers may be formed 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. Sub-quently another layer may be formed in a similar manner during 1066~6'7 one or more rotations by spraying polymeric material from the other spray tube. The centrifugal force from rotation of the mold can help to shape the layers, and it will be understood that various centrifugal casting methods may be employed to assure proper coating of the mold. However, it is desirable to provide curable polymeric material which will cure fast enough so that one layer will maintain its shape while the next layer iB being applied. Also fast-curing material is desirable to assure formation of layers of substantially uniform thickness which can maintain their shape during rotation of 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 supplied. For example, the mold may be rotated 510wly 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 mold. Also the process can be varied to require several rotations of the mold during forma-tion 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 substantial curing before spraying the next layer. If the rate of curing is fast enougil it may be possible to begin spraying the subsequent layer within one-half of a revolution after the previous layer was applied.
As used herein the expression "partially curingN indi-cates that the material has stiffened or set up sufficiently to maintain reasonable dimensionable stability so that a subsequent layer may be applied. Such expression does not necessarily require a true curing of the material.
It will be understood that various fluid polymeric materials may be employed using molds of the general type il-lustrated in Figure 6 and that the viscosity or flowability of the liquid polymers may be controlled by the use of heat, sol-vents, plasticizers or other techniques to allow the movement of the liquid material 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 incIuding monomers, melts, prepolymers and solutions. The fluid polymeric materials must be liquid at the time of proces-sing and have a viscosity at processing temperatures such that they will flow under their own weight in a reasonable period of time.
one of the polymers preferred for use in the practice of the present invention is polyurethane. Such polymer is usual-ly prepared by reacting 0.95 to 1.2 equivalent weights of an or-ganic polyisocyanate having 2 to 3 functional isocyanate groups with one equivalent of an organic compound having a molecular weight of at least 1000 and containing active hydrogen atoms which are reactive with isocyanate (-NCO~ groups. In many in-stances an organic chain-extending agent may be employed contain-ing 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, polyester amides, polyhydric polyalkylene ethers, polyhydric polythioethers, polyacetals and the like.
The organic polyisocyanates used to form the poly-urethane in the process of this invention may be of various types 6'7 including aliphatic, aromatic, alicyclic and heterocylic as difi-closed in said U. S. Patent No. 3,208,500 and preferably contain at least 8 carbon atoms. Excellent results are obtained using aromatic diisocyanates such as toluene diisocyanate (TDI), 4,4'-diphenyl-methane diisocyanate (MDI) or other diphenyl-alkane diisocyanate or the like. For example, the organic diisocyanate may be an 80:20 or 65:35 blend of 2,4- and 2,6-toluene diisocy-anate.
The diisocyanates suitable for use in the practice of the invention preferably have 8 to 20 carbon atoms and include the various toluene diisocyanates, the various naphthalene diisocyanates, the various phenylene diisocyanates, and the various diphenyl alkane diisocyanates as described in U. S.
Patent No. 3,701,374, the entire disclosure of which is in-corporated herein by reference. Suitable diisocyanates include 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diiso-cyanate and the like. Mixtures of the various diisocyanates men-tioned ~bove may also be used.
Polyurethanes of the desired molecular weight suitable for use in the present invention may be made in various ways and many different types are suitable, but it is preferable to em-ploy 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 with a molecular weight of 800 to 20,000 having essentially either all hydroxyl end groups or all isocyanate end groups, and thereafter the prepoly-mer can be cured by means of diamines, diols or diisocyanates, 10664~;7 depending upon the terminal or end group in the prepolymers.
The preferred polyurethanes are those formed by capping the hydroxyl groups of polyalkylene glycsls 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 polycar-boxylic acid and a polyhydric alcohol as described in said U.S.
Patent No. 3,208,500. The alcohol may, for example, be ethylene glycol or propylene glycol.
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 No.
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, pro-pylene glycol, butylene glycol or the like. Any suitable alkylene oxide condensate may also be used such as, for example, con-densates of ethylene oxide, propylene oxide, butylene oxide,amylene oxide, styrene oxide and mixtures thereof.
In forming liquid prepolymers for use in tha process of this invention, it is preferable to react the organic diiso-cyanate (preferably MDI or TDI) with polyalkylene glycols having molecular weights in the range of 800 to 20,000, particularly poly(alkylene glycols) having alkylene groups of from 2 ~o 10 carbon atoms, such as poly(ethylene glycol), poly(propylene glycol), poly(trimethylene glycol), poly(tetramethylene glycol), poly(hexamethylene glycol), high molecular weight copolymers of such glycols, and mixtures of the above poly(alkylena glycols).
~646~ - `
The preferred prepolymers have terminal isocyanate groups, and may be cured with various diamines. The diamines preferably contain an organic central radical of 2 to 20 carbon atoms linked to two amino groups such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, p-phenyl-enediamine, methylene-bis-2-chloroaniline ("MOCA"*), 4,4'-methylenebis-aniline, 3,3'-dichloro-4,4'-diaminodiphenylmethane, benzidine, 3,3'-dimenthylbenzidine, 3,3'-dimethoxybenzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenylmethane, and cumene diamine.
In these polyurethane rubbers, the chains of the cured polymer contain the repeating linkage ~ P-0-C0-NH-Rl-NH-C0-NH-R2-NH-C0-NH-Rl-NH-C0-0 wherein P represents the high molecular weight poly (alk~-lene ether) chain, Rl is the organic radical of the diisocyanate, and R2 is the organic central radical of the diamine. 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- ~nd low-modulus layers of the tire laminate.
The hardness and modulus of these polyurethane polymers may, for example, be increased by increasing the isocyanate and glycol or diamine content of the system.
The type of polyurethane selected for use in making tires accord-ing to this invention will depend on the type of manufacturing processemployed. The polyurethane best suited for spraying may not be best for film extrusion or some other method.
Liquid polyurethane rubbers are now available commercially which can be used in the practice of the present invention. Good results can be obtained, for example, with Adiprene* L-100 prepolymers (4.1% NC0), Adiprene* L-167 prepolymers * Trade Marks (~ 3~ NCO), and Adipren- L-315 prepolymers ~9 5~ NCO), made by I ~u Pont de Nemours ~ Co Th -e liquld prepoly~ers can be our d ~lth oonv ntlonal di~aine~, ~uch a~ ~OCA, Caytur*7 or CaytUr*
21 (~ thyl-n--bl--anllln-~ u-lng an eyuival-nt ~ ight ratio of d~ _ ln- to propolya r of about 0 95 to about 1 10 Caytur*7 a ut ctlc Dixtur- of -phenylene and ¢umene diamine Polyur-thane prepolymers, uch as Adiprene-L prepolymers, ay, for xample, be ~do from TDI and a polyal~ylen- glycol or polyol, Juch as poly(tetramethylene ether diol), and ~imilar pr-poly~ers ¢an be mad- u~ing ~DI in-tead of TDI or using a some what diffor-nt polyol V~rious poly(alkylene glycol-) and poly (alkylene ether) polyols can be u-od, both diol~ and triol~, and th pr polym~rs can have eith-r terminal -O~ groups or terminal -NCO group~ (preferably th latter) Th poly~eric mat-rlal u-ed in the tir- of the present inv ntion ~ay ~l-o b a polyamia pla-tic, ~uch a- nylon 66, nylon C10 or nylon 6 V riou- lonq-chain ynthetlc poly~ rlc umides ha~ing r~curring _l~b group- a- n int gral part of the main polymor ohaln o n b u~ d, uch a- tho e prap~red ky the conden-atlon of dlamin-- nd dlba-lc acid-, tho-- obtain-d by the c~n-d n-ation of polycarboxyllc acid- wlth polyamine-, or those ob-taln-d by th polycond n-ation of caprolact~m Variou~ triamin-- ~ay be u--d, ~uch a- diethylenetri-~ine and the li~e, but it 1- preferable to employ di~ines Suitable diamine- lnclude thylenedlamine, diethylenedia~ine, p nt~methylenedl~mine, hexamethylenediamine, ph-nylen-diamine, and the like or mixture~ ther of Variou~ polyba-ic acid~ may be used to makQ the poly-amid- ranging from uccinic acid to Je~acic acid nd including, *Trade Mark .
1CH66 ~ 7 for xa~ple, ~uooinlc ~cid, conic wid, ~alpic acid, malic acid lt~eonie acid, fumar$c acid na th lik~
The polyamid - ~uitabl~ for u-e in Nbber tire~ which ¢~n b u--d in tbe practia~ of th- pr --nt lnv ntion are d~scribed ln U ~ Pat nt No 3,208,S00 The pre~err-d polyamide- ro tho~e mad from diamin~
and dibasic acids, ~uch as the reaction products of hexamethy-l-nediamine or similar diamine with a dibasic acid, such as adipic acid or ~ebacic acid While there re ~ ny differ nt type~ of polymRrs which can b ~ploy-d in the pr~ctice of thi~ inv ntion, th- most pro~i-ing polyD~r- ~pp- r to b- polyur~th~n - nd polyamide~ or nylon~ ~- di-eu--ed g~n~r~lly ln ~id U S ~tent No 3,208,500 At pr -~nt th~ ~t pr ctlcal poly~ r- -mJ to be polyurethanes p~rtloul rly poly~th~r ur~th~n~- ~nd poly~t-r ur-thnnc~ ~
Ono d~ntng- of th polyur th~n-- i- th~t th-y c-n be o~k~ln d ln ll~ula for~ ~lth ~i-co-l~i-- uit bl- for praying or ~or pr ~ding al-o th y o n ~ u d in both the high- and lo~-~oaulu- lay~r-, th r by r ducing th ~dh--ion proble~ It is ~l-o po--lbl- to bl-nd polyur-th neJ of different ~ol-cular ~elght~ to gct tho d--ir d properti--For ~xample, the laolnated tire of thi- invention can b ~ade u-ing Adiprene*L-~2 t~ol-cul~r w-ight bout 3000) for th- low-modulus lay r- ~nd Adiprone*L-167 (molccular weight about 1330) for the hlgh~odulu- l~y r- Al-o th high-modulus l~y r could b mado u-lng a bl-nd of 60 part- by weight of Ad 4 r n L-167 ~nd ~0 part- by w-lght of Ad$pren- L-315 t~olecu-lar ~eight about 900) ~h~ curing a~ nt could b~ MOCA, Caytur*
21 or oth r uitabl~ dia~in~, and th pla-ticiz-r, if ny, could *Trade Marks _ , . -- .. . .
;6/~6~
b- dioctylphthalate or the llke The CuriAg agent could provide rolative faot curing to minimise the time delay a~ter each layer i- ap~li-d before t~e next layer is applied The polyurethane prepolymer~ can also be modified in various ways to produce the ~esired propertie~ For example, Adlpron~ ~-167 (a prepolymer with a ~roo~field viscosity of about 5000 to about 7000 centipoise~ at 30C nd about 250 to about 350 c-ntipoises at lOO C ) can be cure with l,~-butane-diol and trimathylolpropane in uitabl- proportions to provide a rubb r lay r of the d-~ired typ- A ourable polyur~thane com-po-ition oould, for xa~pl~, b aade by mixing 160 parts by ight of Adipr ne L-167 ~lth about ~ p rt- of 1,4-butanediol, about 1 6 p rt~ of tri athylolprop ne and a mall amount of dioctylphthalat The laminatod tire of thl- lnventlon i~ pr-ferably oon-truct-d o that th t-ar trength of ~he laminato (~plit ~mpl- thod) 1- 50 to ~00 or more pound~ per lineal inch and o that the low-modulu~ layer- have a tenslle strength of at l-a~t 1000 pounds per square inch, a Shore A durometer hardness in the range of about 30 to 90, and an elongat~on of at least 50 percent (more preferably at least 100 p rcentl The curable polymer~ u~ed in the practic- of this inv ntion n ed not be liquid, but liquid poly~ors are preferred to facilitate m nufactur Th- viJco-ity of the liquid polymers nay, for exa~pl-, bo 1000 to 50,000 o ntipoi--- and hould be 1 -- th n 100,000 oontipoi--- at 30 C Th vl~co~lty ~ay be a~u-t d by dding ub-t ntial _ ount-, ~o~ times up to 10 or 20 p rt-, of a pl~-t~ci~-r, uch ~J dioctylphthalate, p~r 100 parts by ~oight o~ tha polya-r *Trade Mark . .
106646'7 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 system. Various solvents which may be used include ethyl acetate, acetone, toluene, methy~ ethyl ketone, xylene, beta-ethoxyethyl acetate and the like. These are preferably relatively pure and free of moisture.
While the laminates of the pneumatic tires above employ substantially different polymer formulations in the low- 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, etc.) is substantially different in adja-cent layers. In accordance with the invention a difference in tensile modulus can be provided between adjacent layers H and L
(Figure 2, for example) when using the same polymer in both lay-ers as a result of a different molecular orientation in the adja-cent layers.
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 constructed according to the pre-sent invention (as in Figure 2, for example) each layer prefer-ably 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 s~ecies of Figures 2 through 5 may be achieved by molecular orientation or by use of different polymers in different layers, or both.
1066~6~
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 parts by weight and the term "polymer" includes homopolymers or copolymers un-less the context shows otherwise.
The term "fluid" as applied to a polymeric material indicates that the material has viscosity such that it can flow during processing. The viscosity may, for example, be from 100 to 10,000 centipoises at 30C. and should not exceed 100,000 centipoises at that temperature.
The following example is provided for purposes of il-lustrating the nature of the invention, and is not for the pur-pose of limiting the invention.
Example This example is included to illustrate the greatly improved ability of a tire made in accordance with the present invention to resist the propagation of a cut flaw or to form a crack. In order to illustrate this ability, laminated and homo-.
geneous samples were sub~ected 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 proportions. Each of the samples was one inoh wide, one-quarter of an inch thick and 8iX inches long. They were press cured for two hours at 250F. (121C.) followed by post curing in an oven for another two hours at 176F. (80C.).
Each sample then has an artificial flaw of .1 inch (.254 cm.) imposed across the quarter inch wide surface, perpendicular to the one inch wide surface. The fatigue test was performed on a 1066~67 De Mattia flex machine which ~lexes the sample (at 333 cycles per minute and at room temperature) c~using the ~mposod ~law to propagate laterally acros~ the width o~ the ~mple.
For thi~ experiment, two different material fonmulations wer- used which will be referred to as 100" and 167" as follows ~parts" refer~ to parts by weight):
Ingredient Parts 100~ ~167 **Adiprene L-100 (1)* 100 **Adipr-ne L-167 (2)~ - 100 **DC - 203 (3)* 0.1 0.1 **Dioctylphthalate pla-ticizer 10.0 **Caytur 21 (~)~ 20.3 31.1 130.4 131.2 $umple~ were made from each of these formulations alone and th- Do Mattia te-t wa~ used to determine the number of cycles neces~ary for the .1 inch (.254 cm.) flaw to become .5 inch (1.27 cm.). The number in parenthe~es under each psi. reading r-pre-ent~ 10 pa~cals. In addition other propertie~ were mea~ured a8 follow~s _ _ _ ~Notes (1) and (2) are liquid prepolymer~ a~ previou-ly de-~cribed; (3) iJ a liquid ilicone mold relea~e ~nd mul~ifying ag-nt Dow Corning~ and (~ a 50~ dispersion of methylen- di-~niline/ ~odium chloride c plex in dioctyle phthalate du Pont.
**Trade Marks ~0~6~
Table Property"100" "167"
10% Modulus 160 psi. 370 psi.
(1.1030) (2.5507) 100% Modulus 405 psi. 690 psi.
(2.7920) (4.7568) 200% Modulus 510 psi. 860 psi.
(3.5159) (5.9288) ~ensile (rupture) 2055 psi. 2290 psi.
(14.167) (15.787) Elongation (rupture) 750% 575%
Lardne3s Shore A 83 91 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 H167~, with both outer layers being the "100".
-" 1066~67 Lq ~ 10 _~ p~ O
o~ ,` 1 I~ _I O ~ D ~ O
~r o . o .o~ u~ oOD ~ O
.. 10 ~1~ ~)~1 ~1 N ~r Ir~ N--~r--~-- 1 a) ~q 0,bq ~rQ ~
~o o O~ O dP O
~I o o o ~ I o O ~1 ~ ~
U~ ~ o . ~P ~ ~ o u~ o oo ~ u~
.. ~ _I ~ ~ ~ ~ U~
N-- ~--~1--rl ~ ~1 _ 0 _ u~
Q~
000 ~D dP O
~1 U~ O _I O I I O
O ~1~ t'~ ~ O
rl _ rl ~ ~q ~
O D O d~ ~` ~ o U~ O ~ CO ~ O
- a~ ~1 ~ o .~0 Il`) r~
U~ O
~1 U~ O U~ I I O
rJ la~ ~1~ N cn ~D ~ O
.,i .~1 _ rl _ 07--U~ O ~~O ~ O
~1 U) ~ O ~ O OCO ~ O
N N ~
~i~i ~D~ _ ~u a~
U~Q~ O U~
U~ ~ O dP O
~1 1~ Ir~ ~ N O I I O
.
a) _ ~ 1 ~
~ tn ~ S
D~ :~ _I h C
~0~ ~ ~
P~ ~ O Q) O O ~
S S ~ ~0 dP O ~ O
O O
.
10~6~6'7 Referring to Table II, the second column has the heading "3-layer" de~ignating 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 proportions. 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 column.
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 ade-quate 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 round in end use and does detract from the fact that a marked improvement i8 observed in fatigue life. The somewhat erratic behavior in tensile strength and rupture elongations in these spocimens is related to flaws in the specimen that influence these properties but not the flexing behavior.
It will be understood that, in accordance with the pro-visions of the patent statutes, variations and modification~ of the specific methods and articles disclosed herein may be made without departing from the spirit of the invention.
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for making a laminated pneumatic tire carcass having improved resistance to flex cracking comprising applying to an annular form a first continuous layer comprising a liquid polymeric material having a viscosity less than 100,000 centipoises at 30°C, then partially curing the liquid; thereafter 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 30°C, then partially curing the second liquid, and repeating the sequential application and partial cure of polymeric material to form a curable 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 of cured low Young's flexural modulus layers with a Young's flexural modulus from about 100 to about 5,000 pounds per square inch, a second series of a plurality of high Young's flexural 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.
2. A process according to claim 1 wherein said second series of layers comprises a high Young's flexural modulus polymeric material with a Young's flexural modulus from about 3,000 to 100,000 pounds per square inch.
3. A process according to claim 1, wherein one of said series of layers is formed by applying a fluid polymeric material which is partially cured after being applied in each layer before the next layer is applied.
4. A process according to claim 3 wherein the fluid polymeric mat-erial is applied by spraying.
5. A process according to claim 4 wherein the fluid polymeric material is a polyester or polyether urethane prepolymer with a molecular weight from about 500 to about 20,000.
6. A process according to claim 1 wherein said annular form has a generally toroidal shape and is rotated during application of the layers.
7. A process according to claim 6 wherein the polymeric material is applied in liquid form to provide layers of generally uniform thickness.
8. A process according to claim 1 wherein said first layer is applied to the internal surface of said annular form and each succeeding layer is applied to the inner surface of the previous layer.
9. A process according to claim 8 wherein an applicator is employed to apply the polymeric material and relative rotation is provided between said applicator and said annular form.
10. A process according to claim 9 wherein a fluid polymeric material is applied by said applicator.
11. A process according to claim 9 wherein said annular form com-prises a tire mold and is rotated during formation of each layer of the laminate.
12. A process according to claim 11 wherein each layer is formed of a curable fluid polymeric composition comprising a high molecular weight polymer and a curing agent and said composition is partially cured long enough to support the application of the next succeeding layer before the latter layer is applied.
13. A process according to claim 12 wherein each layer is heated and partially cured during 1 to 5 revolutions of the tire mold sufficiently to support the next layer and wherein application of the next layer is initiated before the sixth revolution of said mold.
14. A process according to claim 12 wherein each layer is formed by spraying a curable low-viscosity liquid polymeric composition comprising a liquid curing agent and a liquid polyurethane prepolymer formed by reacting substantially equimolecular proportions of an organic diisocyanate and a poly(alkylene ether) glycol.
15. A process according to claim 14 wherein the layers are cured to provide the high Young's flexural modulus layers with a Young's flexural modulus at least ten times that of the low-modulus layers.
16. A process for making a laminated pneumatic tire as set forth in claim 1 wherein the layers are free of fiber reinforcement.
Priority Applications (2)
| 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 |
| CA316,437A CA1054913A (en) | 1977-06-02 | 1978-11-17 | Laminated pneumatic tire and method of making same |
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 |
|---|---|
| CA1066467A true CA1066467A (en) | 1979-11-20 |
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 After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA316,437A Expired CA1054913A (en) | 1977-06-02 | 1978-11-17 | Laminated pneumatic tire and method of making same |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1066467A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007043489A1 (en) | 2005-10-04 | 2007-04-19 | The Yokohama Rubber Co., Ltd. | Layered product comprising thermoplastic resin and rubber and pneumatic tire comprising the same |
| JP2016176028A (en) * | 2015-03-20 | 2016-10-06 | 横浜ゴム株式会社 | Laminated body for tire, inner liner material for tire, 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
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007043489A1 (en) | 2005-10-04 | 2007-04-19 | The Yokohama Rubber Co., Ltd. | Layered product comprising thermoplastic resin and rubber and pneumatic tire comprising the same |
| EP1932686A1 (en) * | 2005-10-04 | 2008-06-18 | The Yokohama Rubber Co., Ltd. | Layered product comprising thermoplastic resin and rubber and pneumatic tire comprising the same |
| EP1932686A4 (en) * | 2005-10-04 | 2009-03-04 | Yokohama Rubber Co Ltd | Layered product comprising thermoplastic resin and rubber and pneumatic tire comprising the same |
| US7798188B2 (en) | 2005-10-04 | 2010-09-21 | The Yokohama Rubber Co., Ltd. | Laminate of thermoplastic resin and rubber and pneumatic tire using the same |
| JP2016176028A (en) * | 2015-03-20 | 2016-10-06 | 横浜ゴム株式会社 | Laminated body for tire, inner liner material for tire, and pneumatic tire |
Also Published As
| Publication number | Publication date |
|---|---|
| CA1054913A (en) | 1979-05-22 |
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