It is extremely difficult to make an effective inside repair. One of the principal reasons for this is that the vulcanized inner surface of a tubeless tire is a difficult surface to which to make a bond. This is due not only to the ribs on the surface, its imperviousness, and the completely cross-linked nature of the rubber material, but also to the presence of talc or other contaminants on the surface, as well as to a microscopic and extremely difficult to remove penetration into the rubber of the mold release employed in the manufacture of the tire. It is, of course, possible to abrade the tire's inner surface and remove the contaminated layer with an abrasive in order to provide "clean rubber" and an anchoring surface for an adhesive, but such a procedure is undesirable as it weakens the tire and promotes delamination of the plies besides being time consuming. In addition, even with a roughened surface a true, chemical bond still cannot be made to rubber. The crevices in a roughened surface provide a form of mechanical linkage or interlocking which gives an appearance of a good bond, but the bond is not, in fact, really a strong chemical bond at any specific microscopic point on the surface.
As a a result, making inside repairs of tubeless tires has never, to date, been entirely satisfactory. In one method, the puncture hole is reamed out and an adhesively coated rubber plug is inserted under pressure into the hole with the adhesive serving both to hold the plug in the hole and to seal the gap between the plug and the tire. Besides causing damage to the tire from the reaming, especially for steel belted radials, such plug repairs tend to cause growth of cracks adjacent to the puncture hole. When rubber is pierced, the incision is never clean, but instead forms a star-like cluster of cracks which are accentuated by the reaming. These cracks will develop into tears if stretched and since the rubber plug will not provide a good seal unless it is confined under high pressure in the puncture hole, such plugs tend to elongate the cracks. Also if the pucture takes the form of an elongated cut, as is often the case, plugs are not suitable for repairing same. As a result, the plug-type repair is not universally applicable and is not highly regarded.
Another way to make an inside repair is by placing an impervious patch over the puncture hole on the inside of the tire and attempting to adhere it to the tire. To date an effective adhesive for this purpose (as far as the inventor hereof is aware) has not been developed. A good bond cannot be made without pressure, but pressure tends to squeeze out the adhesive so much that the bond is lost. Attempting to do it with a vulcanized adhesive has met with only limited success. Even if high heat and pressure are used (which incidentally are necessary for vulcanization), so much of the adhesive squeezes out through the puncture hole and laterally of the patch that the bond is lost. Serrating the surface helps retain some of the adhesive and a fairly good bond can be made, but as we have noted above, even the serrations do not provide anything more than a mechanical interlinkage, not a true chemical bond. As a result the patch-type seal is prone to failure.
One attempt to solve these problems is described in U.S. Pat. No. 4,109,697 in which a layer of vulcanizable "rubbery material" was applied over the puncture hole on the inside of the tire. Next an "O" ring was placed around the puncture hole over the "rubbery material," and a patch was placed on top of the "O" ring. Thereafter hot steam, or steam and air under pressure, were applied to the repair while means on the outside of the puncture were employed to keep the adhesive from flowing out of the puncture hole. How the pressurized steam was to be applied to the surface is not stated in the patent. The outward flow of material out of the puncture hole is described as being prevented by a seal, but how the seal was to be adhered to the tire is not described. The "O" ring is described as preventing the lateral flow of the rubbery material on the inside surface of the tire. It is not known, however, whether the repair of U.S. Pat. No. 4,109,697 was practical. At least one can state with assurance that applying hot pressurized steam to an inside puncture would be both difficult and expensive. Also, effectively to seal the outside of the puncture hole is not only very hard to do, but would be time consuming and expensive. Further, whether or not an "O" ring can actually prevent the lateral flow of the rubbery material under the pressures involved is questioned. For example, in U.S. Pat. No. 4,109,697, vulcanizing temperatures of 200.degree. F. and 250.degree. F. are mentioned. Actually, 200.degree. F. is essentially too low for vulcanizing, and even 250.degree. F. is marginal, but yet, to maintain steam at 250.degree. F., a pressure of 15 psi above atmosphere is needed. At such a pressure all of the adhesive would be squeezed out. On the other hand, U.S. Pat. No. 4,109,697, even if of questionable practicality, at least demonstrates a recognition of (a) the need to form the bond under high heat and pressure, (b) the need to prevent the adhesive from being squeezed out of the adhesion area, laterally and axially of the puncture, and (c) the desireability of providing a repair which avoids reaming out the hole or serrating the surface and which can be employed with puncture of different sizes and shapes.
Another factor, however, is involved, of which the prior art appears to have been unaware, relating to the condition of strain between the sealing material and the tire while the tire is in use. In all prior art repairs (known to the inventor hereof), the repair is cured in one condition of strain and used in another. This is a distinct disadvantages because at best, the adhesive bond is weak, and any residual strain in the repair tends to loosen the bond between the repair and the tire under the rigorous conditions of flexing during use. This disadvantage, however, exists in all prior art repairs of which the inventor hereof is aware. For example, in the plug-type repair the plug remains under high compression in the puncture with the attendant disadvantages mentioned above. In the patch-type repair the vulcanization takes place under vertical stress with the tire deflated. Thereafter when the tire is inflated, the tire stretches both longitudinally and laterally introducing strain in the patch which tends to pull it away from the inner surface of the tire. In the repair of U.S. Pat. No. 4,109,697, the adhesive likewise cures while the tire is deflated, and the cracks surrounding the puncture are held tightly closed due to the surrounding rubber, in which condition, penetration of the "rubbery" material into the cracks even under pressure is virtually impossible. Thereafter when the tire is inflated, the stretching of the tire opens up the cracks surrounding the puncture hole, and pulls the rubber of the tire away from the "rubbery" material of the repair at the critical point. In all such prior art repairs, the vulcanized bonding material is permanently cross-linked in a condition of strain which changes when the tire is inflated. As a result, the repair is constantly under a strained condition in use, which condition promotes pulling away of the seal from the rubber of the tire. In addition, if the repair is made to an unsuitably large cut, in the prior art repairs nothing warns the user of it. Such a tire will tend to hold its shape and will appear normal until it is used, and the user is left to find out the hard way, i.e., by a blow-out on the road, that the repair is ineffective.
Accordingly, among the objects of the present invention are to provide an inside repair in which a permanent bond of an impervious material is made in a puncture hole of random shape under conditions designed to promote as near to a chemical bond to the rubber of the tire as possible without squeezing the bonding material out of the critical bonding area. Another object is to provide a seal for an inside repair in which the bonding material of the seal is cured in such a way as to reduce to a minimum all residual strain in the bonding material during use. A further object is to provide an inside repair which fully seals the cracks surrounding a randomly shaped hole as they exist in the stretched state of tire inflation. Still another object is to provide such a repair which can be made to a tire inexpensively and without either reaming out the hole or roughening the inner surface of the tire. An even further object is to provide an inside repair for randomly sized and shaped cuts which provides a visible indication, prior to road testing, of whether the reinforcing of the tire has been damaged too much or the cut is too large to be safely repaired by the method of the invention.