Silane Compositions and Methods for Bonding Rubber to Metals

Abstract

Compositions and methods for treating metal substrates and / or bonding metal substrates to polymeric materials, such as rubber, are provided. The compositions include at least one substantially hydrolyzed amino silane and at least one substantially hydrolyzed sulfur-containing silane. Optionally, the compositions include a nano-size particulate material. The compositions provide coatings on metal substrates for protecting the metal from corrosion and for adhering rubber-like polymeric compositions to the metal with polymer-to-metal vulcanization conditions less dependent on the coating thickness, and with use of less coating materials.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. application Ser. No. 10 / 681,422, filed Oct. 8, 2003 (pending), the disclosure of which is hereby incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]I. Field of the Invention[0003]The present invention relates to silane coatings for treating metals. More particularly, the present invention provides organofunctional silane coatings which improve the adhesion of rubber and other polymeric materials to a metal substrate.[0004]II. Description of the Prior Art[0005]Rubber to metal bonded components find two major areas of application which may be classified as tire and non-tire applications. In tires, traditionally brass is used as a thin coating over a steel cord for imparting adhesion to natural rubber compounds. Non-tire applications include components, such as vibration dampers on motor and engine mounts, and applications in the medical, appliance, and other industries, where basic f...

AI Technical Summary

Benefits of technology

[0012]The present invention provides improved silane compositions and methods for coating metal substrates and bonding polymeric materials, such as rubber, to metal substrates while using less silane materials, thinner silane coatings, and providing strong rubber-to-metal bonds with vulcanization conditions less dependent on the thickness of the silane coating than previously believed necessary with traditional silane compositions and methods. The silane compositions and methods are useful in a variety of applications including coatings for protecting metal substrates from damage, such as corrosion, and adhesives to efficiently and economically adhere polymeric compositions to coated metal surfaces with minimal waste of the silane composition. The invention is also amenable for industrial scale of the applications.

[0013]The silane compositions comprise at least one substantially hydrolyzed amino-silane and at least one substantially hydrolyzed sulfur-containing silane. Silanes can generally be hydrolyzed in water or mixtures of organic solvents. The silanes are hydrolyzed substantially, i.e., a majority of their silyl-alkoxide groups (Is-OR) are hydrolyzed to the corresponding silanol (Is-OH). Such silanes reduce the hydrophobicity of the coating without a reduction in bond strength. It is thought that the available silanol groups of hydrolyzed silanes readily bond to metal substrates and polymeric materials in the form of siloxanes to enhance bond strength.

[0016]The silane compositions may further include nano-sized particulate material. The nano-sized particulate material provides improved rubber-to-metal bonding while reducing the need for inclusion of adhesion promoters in the rubber composition. The nano-size particulate material may be, for example, silica, zinc oxide, or a combination thereof and may be used in a concentration ranging from at least about 1 ppm to about 10% by weight of the composition applied to the metal substrate. In one embodiment of the invention, the nano-sized particulate material is silica and in a concentration range from about 50 ppm to about 1000 ppm of the solution. In another embodiment, the nano-sized particulate material is silica and in a concentration range from about 80 ppm to about 200 ppm of the solution.

[0019]The silane coatings provide many advantages including protection of the metal from environmental factors that generally cause the metal to corrode. Other advantages of the silane coatings are realized in their application to metal substrates and bonding of same to polymeric materials. Coatings having a thickness of about 1 μm or less provide good bond strength and bonding characteristics when the coated metal is bonded to a polymeric material while minimizing waste of valuable silane materials. The silane compositions of the prior art generally required a coating thickness of greater than 1 μm to provide good bonding characteristics. Thinner coatings also allow for added control in application generally leading to a more uniform coating, which enhances bond strength and bonding properties. Moreover, it has been found that thinner coatings reduce or eliminate the dependency of the vulcanization conditions, and the vulcanization pressure in particular, on the coating thickness.

Problems solved by technology

For example, while certain silanes may provide improved adhesion between the metal substrate and a peroxide-cured rubber, these same silanes will often not provide the same results for sulfur-cured rubber.

However, formulations of such silane solutions require flammable organic solvents for dissolution, leading to more viscous solutions and thicker final coatings.

Such coatings are difficult to apply, cure, and control, particularly for coating uniformity, and need to be dried, prior to bonding to the rubber, at elevated temperatures, such as about 160° C. which pose additional hazards from flammable solvents.

Such coatings are not very amenable to industrial applications, and tire-cord applications in particular, where efficiency in time and cost is important to the success of the products.

Further, it has been difficult to bond rubbers to metal substrates utilizing various silanes and combinations thereof, and especially in those instances in which the adhesively-bound surfaces are subjected to fuels, oils, and / or other organic solvents, as the silanes may react therewith and / or dissolve therein to weaken or degrade the adhesive bond.

However, solvent-based adhesives are flammable, and hence hazardous, generate high levels of volatile organic compounds and vapors, and pose environmental disposal problems.

These disadvantages render these systems less useful in industrial applications.

Although the performance of the rubber-to-metal bond is adequate for most applications, inclusion of such promoters presents drawbacks.

For example, cobalt salts are expensive and pose availability problems.

Further, cobalt has been found to affect the rubber properties upon aging, and in particular, cobalt causes accelerated degradation of the rubber.

Rubber to metal bonded applications in tires have further drawbacks.

Additionally, brass is prone to galvanic erosion in conjunction with the underlying steel, and furthermore, the brass composition typically requires a copper content of about 63-68% which imposes restrictions on the rubber composition.

These limitations further require consideration when selecting an appropriate adhesive and / or bonding method for bonding rubber, or other tire materials, to the metal tire cord.

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