Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2002-02-11
2004-03-16
Robertson, Jeffrey B. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S447000, C427S386000, C427S387000, C523S425000, C523S440000, C523S442000, C523S443000, C524S413000, C524S428000, C524S493000, C524S518000, C524S588000
Reexamination Certificate
active
06706405
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to coating compositions that impart particle-erosion resistance and articles having such coatings disposed on some portion of their surface. More particularly, it relates to coating compositions comprising an interpenetrating network of polymers and hard particles whereby a resilient matrix with a dispersion of fine particles is formed, where said interpenetrating network of polymers comprise a mixture of a poly(Bisphenol A-co-epichlorohydrin) glycidyl end-capped component, an active hydrogen compound, a linear siloxane, and a silsesquioxane.
2. Description of Prior Art
Many mechanical parts are subjected to the action of moving particles suspended in air or water resulting in erosion. Erosion is the loss of material from a surface due to the mechanical interaction between the surface and particles. For example impellers, airfoil leading edges, propeller blades and similar parts are subjected to operating conditions that may contain large amounts of sand or other particles. The action of the moving particles causes loss of material that may impair the operation of the part, leading to a shortened service life. The shortened service life leads to higher maintenance costs and increased down time.
In an attempt to provide longer service life, coatings have been applied to parts. The prior coatings failed to provide significantly longer service life, used dense materials that increased stresses in rotating machinery, were not adequately resilient to impact and were not sufficiently resistant to abrasion, that is they did not adequately resist wear when they come into moving contact with an abrasive surface.
A common attempt to extending service life was to apply a layer of a high elastic modulus material such as a metal oxide, carbide or nitride using chemical vapor deposition or plasma spray. This method applies a very thin, hard coating to protect the part. This method may be undesirable because it often requires the part to be heated, which can damage the part through thermal degradation and the negation of prior heat treatments. Also high elastic modulus materials disposed on a surface tend to significantly reduce the service life of a part by promoting fatigue cracks that reduce the mechanical strength of the part.
Another approach to extending service life was to apply a urethane coating containing an isocyante-terminated prepolymer comprising a polytetramethylene ether glycol having a molecular weight between 500 and 700. For example, see U.S. Pat. No. 4,110,317. This method applies a thicker, more resilient coating than chemical vapor deposition or plasma spray. The polytetramethylene ether glycol is a linear molecule, but the molecular weight is too small to provide a resilient coating. While this coating provides some erosion resistance, it does not resist erosion well.
Fluorinated polyurethanes, similar to those presented in U.S. Pat. No. 6,001,923, are highly crosslinked, as are straight epoxy-type coatings similar to those presented in U.S. Pat. No. 6,274,650. A high level of crosslinking implies short linear segments, which are linear segments of low molecular weight, which in turn suggests a lack of resilience necessary for resisting erosion. Further, these prior compositions lacked a dispersion of hard particles for improving strength and abrasion resistance.
Prior coatings did not form interpenetrating networks like the present invention. Nor did they attain the essential physical qualities necessary for providing erosion resistance. U.S. Pat. No. 5,904,959 employs an epoxy resin and epoxy-modified polysiloxanes that results in a stratified coating which is silicone rich at the surface, and decreases in silicone content as one moves away from the surface. Because of the quantities of polysiloxane used and the epoxy modification to the siloxane, one would expect a high degree of crosslinking that would limit the quantity and length of the linear siloxane segments. Also, because it is not a uniform coating, as the surface is worn the coating properties can be expected to change.
An epoxy-polysiloxane polymer composition is described in U.S. Pat. No. 5,804,616. This composition combines non-aromatic epoxy resin and polysiloxane ingredients using water to promote hydrolysis. In the cured form, the epoxy polysiloxane composition is a uniformly dispersed arrangement of linear epoxy chain fragments that are crosslinked with a continuous polysiloxane chain, thereby forming a non-interpenetrating network. The polysiloxane specified has a molecular weight of between 400 and 10,000, which is too small to provide adequate resilience. Further, the crosslinking of the polysiloxane with the epoxy chain fragments produces a rigid structure, further reducing resilience. The use of water in this composition prevents the use of some silanes and curing agents that rely upon exposure to atmospheric moisture to enable curing. When water is added directly to the composition before the removal of solvents, an undesirable gel may be formed.
A siliconized epoxy coating is described in U.S. Pat. No. 6,107,370. The coating comprises an epoxy resin, a silanol based poly dimethylsiloxane, an amine functional silicone polymer, and a distilled fatty nitrile. The coating is prepared from silicone emulsions, which introduce water having the undesirable effects mentioned previously. The coating contains less than 5% polydimethylsiloxane, which is insufficient for producing resilience. Further, the polysiloxane is in large measure crosslinked with the epoxy polymer, which creates a rigid structure further reducing resilience.
An interpenetrating polymer network comprising epoxy polymer and polysiloxane is taught in U.S. Pat. No. 4,250,074. This teaches a cross-linked, interpenetrating polymer network comprising epoxy resin and silane groups. The mixture requires a substantially balanced rate of cure for the two components and yields a heavily cross-linked network essentially free from linear siloxane segments. The siloxane component is formed from silanes having three or more hydrolyzable groups per silicon. The hydrolyzable groups react with water in the mixture to form silanols, which subsequently undergo polycondensation. Because the silanes have three or more hydrolyzable groups per silicon, the polycondensation products will be essentially 100 percent cross-linked. Such a network is too stiff to provide the necessary resilience for resisting particle erosion. For good resilience it is essential that long linear siloxane segments be present in sufficient quantity, which can only be achieved with silanes having two hydrolyzable groups per silicon and only under conditions that cannot be achieved by ordinary polycondensation or when substantial quantities of silanes having three more hydrolyzable groups per silicon are present. The mixture also lacks a dispersion of hard particles to provide the necessary strength and resistance to abrasion. Due to the composition of the mixture, the required balanced co-curing of components limits the flexibility of formulation and also limits the conditions for using the mixture.
In U.S. Pat. No. 5,650,453, a coating is taught that combines epoxy functional polysiloxane polymers with vinyl ether monomers and oligomers. This combination results in an ultraviolet (UV) light cured, highly-crosslinked hard coating. Because this coating is hard, it lacks the resiliency that the present invention has. Also, because it is UV cured, hard particles that resist abrasion cannot be added because they block UV light and thus interfere with the curing process.
Prior coatings lacked the required dispersion of hard particles to provide strength and abrasion resistance. They did not contain linear siloxane segments in sufficient quantity or sufficient length to provide resilient matrices. They required co-curing of components that was difficult to balance, thus they restricted the ability to formulate and use the coatings. The prior coatings failed to provide significantly longer service life for parts exposed t
Sanders Bridget Marion
Wiedemann Karl Erik
Analytical Services & Materials, Inc.
Robertson Jeffrey B.
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