Method for applying chemical coatings

Abstract

A method of anti-fouling a metal structure disposed in water, the method comprising providing a clean surface on the metal structure, applying a tie coat to the surface, and applying a thermoplastic top coat to the tie coat.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] U.S. patent application entitled “Apparatus for Applying Chemical Coatings” filed concurrently herewith (Atty Docket No. 2440-00200), hereby incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates to chemical coating technology and more particularly to methods for applying thermoplastic coatings and still more particularly to a method for coating surfaces exposed to sea wash with an anti-fouling coating. BACKGROUND OF THE INVENTION [0003] Coatings are applied to various surfaces to protect the surface. For example, coatings are used to waterproof and insulate and to prevent corrosion, rust, rot, water damage, fouling, burning, as well as other types of deterioration and damage to a surface. The surfaces may include, but are not limited to, metal, wood, concrete or a synthetic, such as composites, tile, foam, fiberglass, PVC, plastic or the like, as for example. The surface may be the surface of a veh...

AI Technical Summary

Benefits of technology

[0014] Preferably the process for coating a surface of the present invention includes the steps of cleaning the surface, applying an undercoat or tie coat to the cleaned surface, and finally applying a top coat or outer coat that contains the anti-fouling compounds. Suitable surfaces include, but are not limited to metal, wood, foam, fiberglass, plastic and combinations thereof. The preferred tie coat comprises a two-part epoxy including a curing agent and a resin. Application of the tie coat is carried out at ambient conditions directly onto the clean metal using a spray technique. The tie coat bonds to the surface and preferably is applied so as to achieve a total dry layer thickness of about 3-4 mils on the surface. Before complete curing of the tie coat, the outer coat or top coat is applied. Depositing the outer coat onto the tie coat prior to full cure of the tie coat allows the two coatings to interact and / or react at their interface to create a strong bond to the surface as compared to applying the anti-fouling coating directing to the surface.

[0017] The coating process of the present invention has many advantages. The tie coat creates a stronger bond with the metal surface and top coat resulting in more adherent coatings. Using the tie coat also allows for faster drying times and less time needed between applications of multiple coats. Thus, down time or time in dry dock is significantly reduced because the process takes a matter of hours or days as opposed to weeks or months, which reduces cost and increases the time the vessel is in commission. The low time requirements associated with the process allow for easier handling and greater flexibility in the equipment used. The tie coat also waterproofs the hull, preventing corrosion and other damage.

[0020] The method disclosed herein comprising an apparatus in accordance with the present invention has several advantages. The unique design combines thermoplastic technology with finishing technology, preventing the metal anti-fouling agents from precipitating out of the top coat and allowing the top coat to be applied like a finishing paint. In other words, the top coat can be applied uniformly and consistently with respect to both the physical thickness of the deposited coating and the chemical distribution throughout the coating (i.e., more homogenous coatings). The relatively small size of the equipment needed allows for a more mobile process.

Problems solved by technology

In one application of coatings, surfaces exposed to sea wash or water containing marine organisms are susceptible to fouling.

However, with time (often relatively quickly), the hulls of ships or other exposed surfaces become fouled by all types of organic and inorganic material, i.e., the attachment of organisms to the exposed surfaces.

Other structures exposed to water may also become fouled.

Fouling causes the once smooth hull to become extremely rough, promoting corrosion, weakening the hull, eventually decreasing the ships maneuverability and increasing drag.

The domino effect is obvious—fuel consumption is increased (in some cases by as much as 30%), which causes both economic (e.g., increased fuel costs) and environmental consequences (e.g., increased greenhouse gases).

However, this cumbersome process is time consuming and costly.

In addition, frequent scraping of the hull can result in weakening the hull.

Common anti-fouling coatings contain amounts of metals, e.g., copper, aluminum or tin, which the organisms find distasteful, even toxic.

Although such anti-fouling compositions are an improvement, they do not represent a perfect solution.

Several problems exist today, e.g., applying the coating evenly, difficulty in handling the material, the need for an efficient, consistent and durable apparatus for applying the materials, and the fact that the coatings are notorious for their inability to adhere to the surfaces.

In fact, the composition developed in U.S. Pat. No. 2,602,752 achieved minimal success because of the difficulty of the coating adhering to the metal ship hulls and because of the difficulty in achieving an even, smooth, homogenous coating.

These high temperatures create difficult equipment and handling requirements.

New problems have also emerged.

The high leaching of toxic metal compounds over short periods of time unnecessarily contaminates the water.

In addition, high leaching results in a shorter lifetime of the coating, i.e., once the toxic chemicals have been leached away, the coating will no longer be a deterrent to fouling organisms.

Further, the lifetime of coatings on the market today is relatively short in that ships have to be dry docked for cleaning at a frequency of about every 18 months.

Every day represents a significant loss for the ship owner in that they are paying to be in dry dock and losing money due to the ship being out of commission.

In addition, the organic compounds present in the prior art anti-fouling coatings pose a pollution problem and they require volatile organic compounds (VOC) to assist in application and drying.

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