Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-04-20
2001-04-03
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S077000, C522S081000, C522S082000, C522S079000, C522S027000, C522S053000, C522S035000, C522S100000, C522S102000, C522S109000, C522S110000, C522S111000, C522S121000
Reexamination Certificate
active
06211262
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to corrosion resistant coatings for metal surfaces cured by the means of actinic radiation. These coatings are intended to protect metal surfaces in a variety of corrosive environments, and particularly, in a salt water environment.
Corrosion is an electrochemical process which leads to the deterioration and eventual destruction of exposed metal surfaces. The presence of conducting electrolyte, moisture and oxygen to successfully complete the electric circuit on the thermodynamically unstable metal surface are the main factors of a corrosion process. The mechanism of steel corrosion can be illustrated by a series of electrochemical reactions which involve iron (Fe), according to the mechanism outlined in “Corrosion Basics: An Introduction” published by NACE International, Houston 1984. Metal dissolution takes place at the anode in the course of the oxidation reaction:
Fe→Fe
2+
+2
e
−
[1]
Released electrons can migrate to a cathodic site either through steel or via electrolyte. There they react with available water and oxygen. In neutral or basic conditions hydroxyl ions are produced:
2H
2
O+O
2
+4
e
−
→4OH
−
[2]
Hydroxyl ions then recombine with ferrous ions producing corrosion products (red rust upon further oxidation):
Fe
++
+2OH
−
→Fe(OH)
2
[3]
One of the most efficient ways to thwart corrosion is to shield metal surfaces from the environment with protective coatings. These coatings are of great importance for numerous civilian and military uses. The range of applications is extremely broad: ship hulls and topside exterior surfaces; bridges and supports; various fuel, potable water, chemical and sewage tanks; numerous structural and building uses, etc.
The type and level of coating protection needed is determined by many factors including the environmental exposure conditions (salt water, UV, temperature, chemicals, oil and greases), use and handling of the part (toughness, scratch resistance, impact), service life, etc.
Over the years coatings based on alkyd, urethane, epoxy and other technologies have been developed. However, many of these coatings use organic solvents (VOC's, Volatile Organic Compounds) which present environmental, energy and safety concerns. For example, epoxy/amido-amine modified polyamide cured paints are discussed by Hare, “Protective Coatings” Technology Publishing Co. Pittsburgh, Pa. 1994. These paints reportedly give 6 years of service in marine immersion with slightly reduced service life in ballast tank areas. Water and corrosion resistance of these paints is attributed to a high degree of crosslinking and excellent adhesion to steel which prevents or significantly delays the corrosion process from starting. In addition, efficient corrosion protection can be attributed to good substrate wetting by the amide linkages and high peel strength. Epoxy/polyamide systems are easily recoatable and can be repeatedly cleaned without deterioration. However, these paints are solvents based, take long time to cure, require accurate two-part mixing, have a limited pot life, and their cure is temperature dependent. Consequently, new approaches in the coating industry to reduce VOC's are often driven by regulatory, environmental, productivity and related issues.
Recent and current efforts center around water based, powder, high solids, radiation cure and other coating technologies. Some of them have resulted in environmentally friendly coatings that meet many of the desired requirements.
SUMMARY OF THE INVENTION
This invention is directed to a novel approach of corrosion prevention based on corrosion resistant paints cured with actinic radiation (visible or UV light, etc.). Radiation cure is generally regarded as environmentally friendly, 100% solids essentially zero VOC technology. The coatings are applied as a premixed one-part system having very long pot life. Light sources are selected on the basis of the desired type of the actinic radiation and achieve very short cure times which allow for high productivity.
Developed formulations may or may not incorporate anti-corrosion fillers and may be acrylate or epoxy based. In the most common example of this invention the formulations are acrylate based. These coatings consist of oligomeric acrylate resins, monomeric diluents, various fillers and other additives which provide a balance of critical properties. Depending on the type of actinic radiation (UV or visible light) certain photoinitiators required for cure are selected. A blend of photoinitiators including Spectra Group Limited's H-NU 470 achieves tack-free cure using pulsed or continuous visible light sources.
Corrosion protection in salt water environment is achieved through improvement in adhesion and/or use of anti-corrosion fillers. Optimized paints exhibit good adhesion to metal, hydrophobicity, toughness, scratch resistance and other properties, and perform well under long term salt water immersion (SWIM) and salt fog (SF) testing.
In accordance with one embodiment of the invention, radiation curable, corrosion resistant compositions are provided which contain a silane adhesion promoter (e.g., see Examples 1 and 10), a metal surface passivator (e.g., see Example 2, 3 and 4), overbased calcium sulfonate complex (e.g., see Example 8) or a barrier pigment (e.g., see Example 7) or a combination of two or more of these agents. In accordance with a preferred embodiment of the invention, to further enhance the adhesion and anti-corrosion protection of the coatings, the compositions are formulated to minimize the stress which accompanies polymerization by incorporating a plasticizer or controlling the rate of polymerization or the extent of crosslinking to minimize shrinkage (e.g., see Examples 5 and 6).
In accordance with another embodiment of this invention, the radiation curable, corrosion resistant compositions can be utilized in conjunction with other conventional coatings (for example, as primers for paints).
DETAILED DESCRIPTION OF THE INVENTION
The filled protective coating consists of three major components: the polymeric matrix binder, the anti-corrosion fillers and the additives (“Protective Coatings” by C. H. Hare). The polymeric resin blend should exhibit excellent adhesion to metal, good mechanical properties and low shrinkage. Related, low induced stress in the cured film or the ability to dissipate stress is important. This issue is addressed in detail below. Minimal water permeability is favored as is hydrolytic stability of the polymer. The fillers provide the primary corrosion protection and are selected from among the materials which operate by one or several corrosion protection mechanisms. Compatibility between the resin blend and the fillers, acceptable filler wetting by the resin blend and hydrolytic stability of the polymer/filler interface is necessary to maintain coating integrity.
The unfilled protective coatings of the invention consist of two major components: the polymeric matrix binder and the additives, namely adhesion promoters. In this case, the adhesion promoters, and particularly, silane adhesion promoters, improve corrosion protection over the same resin binder without the adhesion promoters. Since it does not contain the fillers, these corrosion protective coatings are clear offering transparency when needed.
In most cases radiation curable coatings are produced either by a free-radical mechanism in an acrylate based matrix or by a cationic mechanism in an epoxy based matrix. Both systems have their advantages and disadvantages as discussed below.
A very wide selection of acrylate resins is available which allows for broad property and performance design. When optimized, acrylate cure is very fast, not temperature sensitive and, with proper photoinitiator selection under certain cure conditions, permits relatively thick cure of pigmented materials. The free-radical cure of acrylates is, however, inhibited by o
Lungu Violeta
Marino Thomas
Martin Dustin
Mejiritski Alexandre
Neckers Douglas
McClendon Sanza L.
Seidleck James J.
Spectra Group Limited, Inc.
Thompson Hine & Flory LLP
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