FI68637C - FOERFARANDE FOER BINDANDE AV OVULKANISERADE URETANKOMPOSITIONER VID ETT VULKANISERAT GUMMIUNDERLAG - Google Patents

Description

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Patent mc-ddelat (51) Kv.ik.Vint.ci/ C 08 J 5/12, B 29 D 30/51 * g y | y | | FINLAND (21) Patent application — Patentansökning 79388 / (22) Filing date - Ansökningsdag 12.12.79 (Fl) (23) Starting date - Giltighetsdag 12.12.79 (41) Published public - Blivit offentlig 15-06.80

National Board of Patents and Registration Date of display and publication - 28.06.85

Patent and Registration Office "Ansökan utlagd och utl.skriften publicerad (32) (33) (31) Privilege claimed — Begärd priority 11 *. 1 2.78 USA (US) 969632 (71) Synair Corporation, 2003 Amnicola Highway, Chattanooga, Tennessee 37406 , USA (US) (72) Edward N. Gomberg, Hixon, Tennessee,

Dana W. Somesla, Riverside, California, USA (74) Oy Kolster Ab (54) A method for attaching vulcanized tower urethane compositions to a vulcanized rubber substrate for attaching dan alloys to substrates, and in particular to substrates of rubber or synthetic rubber.

The desire to achieve maximum bond strength between urethane alloys and substrates of vulcanized rubber or synthetic rubber is known in the art. The attachment of urethane alloys to substrates of vulcanized rubber or synthetic rubber has been one of the most difficult problems faced by the rubber industry and also by users of rubber products. Conventional use of commercially available adhesives, primers, binders, etc. has not succeeded in providing a urethane-rubber bond having the same tensile strength as a rubber-rubber bond.

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Laboratory sizing tests using conventional methods of applying primers or adhesives, allowing them to dry, and then applying the urethane mixture as a liquid or stain and allowing it to vulcanize will normally provide a bond strength ranging from 1 to 30 silicon (pounds per person). The desired bond strength would be at least 80 silicon.

U.S. Patent No. 2,873,790 describes a method of attaching a urethane composition to a rubber wheel by applying an isocyanate adhesive dissolved in a volatile solvent to a rubber substrate. The liquid urethane material is applied to a rubber substrate. The liquid urethane material is then applied to the adhesive. However, this publication does not mention that the adhesive should remain liquid when the liquid urethane paint is applied. U.S. Patent 3,462,328 also describes the application of a urethane material to a rubber substrate. The rubber is coated with fixing cement, which is allowed to harden. The liquid polyurethane is then applied to the dry fixing cement. U.S. Patent No. 2,794,788 discusses the gluing of various materials with a cyanoacrylate adhesive, and in particular deals with the gluing of vulcanized rubber layers together.

This invention relates to a process for combining unvulcanized liquid or pasty urethane with a rubber substrate using liquid cyanoacrylate as a binder. It is not known in the art to apply a liquid urethane composition to a liquid cyanoacrylate adhesive, as known methods require one of these materials to be dry or vulcanized. It is not obvious from the prior art to apply a liquid urethane composition to a liquid cyanoacrylate adhesive, since it would be expected that the binder would disperse and diffuse into the liquid urethane composition and displace the liquid cyanoacrylate adhesive from the substrate. In the process of the present invention, no such penetration problems occur, but a strong adhesion of the urethane composition to the substrate is achieved.

It has been found that if unvulcanized liquid or pasty urethane is applied immediately to the surface of a rubber or synthetic rubber moistened with the liquid cyanoacrylate used as a binder before the binder has dried, the bond between the urethane vulcanization and the rubber or synthetic rubber surface which was achieved in previous methods in which the adhesive was allowed to dry before applying urethane to the surface.

The invention of this application has many uses, such as tearing and repairing worn areas in rubber-based articles that are susceptible to significant wear. The method of the present invention could be effectively used, e.g., to repair conveyor belts of rubber or synthetic rubber material, to repair tires that are torn or cracked, and even to retread tires.

As can be appreciated by one skilled in the art, there is a great economic need for a method that allows the user to take advantage of the greater wear resistance of vulcanized urethane, and the cold vulcanization properties of many urethane alloys result in significant energy and cost savings. The ability for the user to equip a rubber or synthetic rubber substrate with a cold volumetric system with good adhesion offers a wide range of cost-saving industrial applications.

The present invention provides a method of attaching unvulcanized urethane compositions to a vulcanized rubber substrate, the method comprising the steps of: (a) cleaning the substrate surface, (b) coating the cleaned substrate surface with a binder, (c) coating the binder-moistened substrate surface with a liquid or wet paste. 4,68637, and (d) allowing the urethane mixture to vulcanize.

Unvulcanized urethane is applied in liquid or stain form until the surface has reached the desired shape or thickness. The urethane is then allowed to vulcanize, and when vulcanization is complete, the repaired surface can be sanded or shaped as desired and can then be used with the urethane-containing repaired area to provide better abrasion resistance than the surrounding rubber base material.

By following the procedure outlined above, it is possible to achieve bond strengths of more than 100 lead.

A particular application of the invention, which is believed to be of great commercial importance, is the use of the invention in retreading tires. In conventional tire retreading practice, the tire is ground to remove worn tread and the adhesive is applied to the ground area. When the adhesive is no longer wet, unvulcanized rubber is applied over the adhesive. The ring with its rubbers is then placed in a steel mold where the rubber is vulcanized using heat and in the process the rubber is bonded to the ring. The conventional coating process requires a significant amount of energy to be consumed.

In the practice of the present invention, to coat the rings, the tire is ground and all ground material is removed from the ring. The clean ring is then dipped in a cyanoacrylate binder and before the binder has dried, a layer of unvulcanized urethane liquid or stain is immediately applied to the moistened surface. Before it is possible to vulcanize with urethane, the ring with urethane fluids or stains is placed in a mold and more unvulcanized urethane is pumped into the mold cavity to complete the process of increasing the desired thickness of tread material to the outer surface of the tire. The urethane is then allowed to vulcanize and with rapidly vulcanizable urethane mixtures the ring can be removed from the amber in about 15 minutes. This mold removal time can be varied depending on the rate of vulcanization of the urethane mixture used in each case.

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It is recommended that the exothermic reaction of the vulcanizable urethane be mild, which makes it possible to use a wider range of materials in the manufacture of the mold.

The recommended technique would be to mount the ground and cleaned ring on the spindle so that it can rotate vertically. As the ring rotates, the adhesive is sprayed onto its surface, and as the tire continues to rotate, an unvulcanized liquid or stain-like urethane material is applied to the surface moistened with the tire's adhesive. The time factor is critical to ensure that the urethane is applied to the surface while the adhesive is still wet. Preferably, the time factor would be about five seconds for most uranium alloys considered suitable for practical applications. The time factor can be adjusted either by moving the urethane spray nozzle closer to the point where the glue nozzle sprays the glue onto the tire or simply by rotating the tire harder. These are all techniques that can be practiced by a person skilled in the art insofar as they use the concept of the invention to apply the first unvulcanized urethane ring while the adhesive is still wet. Due to the slightly exothermic reaction caused by the various urethane alloys, the ring with its first urethane layers can be placed in a mold formed of a plastic material and not in the metal molds traditionally used.

It is recommended that the plastic mold be held in an upright position of the ring sleeve and one or more feed holes inside the mold allow additional unvulcanized urethane material to be pumped into the mold cavity until it is completely filled with unvulcanized urethane. The air vent should be located at the top of the mold so that when unvulcanized urethane enters the mold, the air trapped in the mold is forced out inside the mold, the air trapped in the mold is forced out of the air vent at the top of the mold. The air vent could also be used as an indicator to indicate when the mold is full, as the first appearance of urethane material in the air vent would be an indication that the mold is full. In Pe- 6 68637 slope retreading, the mold time varies depending on the size of the tire to be retreaded. As the tire size and tread thickness increase, the mold removal time increases. With urethane-coated tires, the opposite is true. The higher the urethane mass, the faster it reacts. Thus, small and large tires require approximately the same mold removal time.

Since urethane has significantly better abrasion resistance than rubber, it would be possible to coat the sleeve with a thinner layer of urethane and still obtain the same length of service as would be obtained with a retreaded tire with a much thicker layer of rubber material. It is estimated that with an embodiment of the invention as described applied to car tires coated with urethane material, it would be possible to achieve a service life of 80,000 to 100,000 miles compared to 25,000 to 40,000 miles with rubber tires.

Mixtures of urethane materials that could be used in the practice of this invention can be readily prepared by those skilled in the art using known chemical methods used in the preparation of urethanes. RUBBER TECHNOLOGY 17, edited by Maurice Morton and published by Von Nostrand Reinhold Company, provides information on the compositions of urethane mixtures and commercially available urethanes that can be used in the practice of this invention. As is known in the art, anhydrous fillers can be added to the urethane material to provide properties such as hardness, abrasion resistance, tear strength and color. Such anhydrous fillers include, for example, various talc, hydrated aluminas, calcium carbonate, diatomaceous earth, silica fume, carbon black, glass fiber, titanium dioxide, zinc dioxide, bentonite, and other fillers commonly used in urethane technology. The fillers are used in amounts that provide the characteristics of the desired properties to the urethane material.

A preferred cyanoacrylic tile adhesive for the practice of this invention would be a blend of alkyl esters of cyanoacrylic acid, as disclosed in U.S. Patent No. 2,794,788. Such adhesives may have different viscosities. We have found that an average viscosity between 100 and 120 cP on a Brookfield scale at 78 ° F is recommended to prevent excessive adhesion of the adhesive to the rubber substrate and to provide sufficient "working time" to apply the polyurethane layer while the adhesive is still wet.

For more information regarding cyanoacrylate adhesives, attention is drawn to the article entitled "Cyanoacrylate Adhesives", pages 569-580 of the second edition of the "Handbook of Adhesives", published by Von Nostrand Reinhold Company.

In the foregoing description and claims, the use of the terms "rubber" and "synthetic rubber" is not intended to encompass silicone rubber.

Claims (6)

8,68637 A method of attaching unvulcanized urethane compositions to a vulcanized rubber substrate by (a) cleaning the substrate surface, (b) coating the cleaned substrate surface with a binder, (c) applying a liquid or pasty urethane composition to the binder-moistened substrate surface, and (d) applying a groove; characterized in that a liquid cyanoacrylate binder is used. A method according to claim 1, characterized in that the urethane composition is applied to the surface of the substrate moistened with a cyanoacrylate binder as a first layer and further urethane is applied before the first layer of urethane is vulcanized until the desired volume of urethane is reached. A method according to claim 2, characterized in that said volume of urethane is cast into a final shape. A method according to claim 2, characterized in that said volume of urethane is ground to a final shape. A method of recoating a rubber ring with a urethane composition according to claim 1, characterized in that it comprises the steps of: (a) grinding off the surface of the ring sleeve to remove the old tread and clean the surface of foreign materials; (b) coating the surface of the ground ring sleeve with a liquid cyanoacrylate binder to dip the surface with the binder; (c) applying a first liquid or pasty layer of unvulcanized urethane composition to said surface while the surface is still wet with the cyanoacrylate binder; (d) placing the ring in a mold having an inner pattern of the desired shape of the coated portion of the ring; adding a liquid or moist paste-like urethane composition to the mold before the first urethane layer is vulcanized and filling the mold cavity, (f) removing the recoated ring from the mold as soon as the urethane composition has hardened, and (g) allowing the urethane composition to vulcanize. Process according to any one of claims 1 to 5, characterized in that the urethane composition contains at least one anhydrous filler. 10 68637