Method of applying protective covering to a substrate

Details Method of applying protective covering to a substrate Method of applying protective covering to a substrate

1998-01-28

2001-05-01

Gallagher, John J. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S086000, C428S420000, C523S457000

Reexamination Certificate

active

06224710

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a curable polymeric composition and the use of the composition in protecting a substrate, in particular a metallic pipe.
INTRODUCTION TO THE INVENTION
To protect substrates such as metallic pipes, pipe joints, and pipelines from corrosion, mechanical damage resulting from abrasion, or degradation due to exposure to sun, soil, moisture, or other elements, a protective coating may be applied to the exterior of the pipe. The protective layer is often polymeric and may be in the form of a polymer tape which is coated with a mastic layer and is then applied to the pipe, a polymer layer which is sprayed or painted onto the pipe, or a fusion bonded epoxy coating which has been applied in the factory. Alternatively, the protective layer may be in form of a heat-recoverable article, i.e. a heat-shrinkable polymeric article such as a sleeve, sheet, or tape, which is recovered onto a pipe or substrate. Such heat-recoverable articles are particularly useful in providing protection to pipe wells or joints which are created when pipe is repaired or retrofitted, e.g. when two pieces of pipe are attached to one another. Using a heat-recoverable article allows protection to be applied in the field without the need for difficult, time-consuming, and craft-sensitive procedures.
In order to enhance the adhesion between the pipe and the heat-recoverable article, it is common to use a heat-activatable sealant or a mastic which can bond to both the pipe and the heat-recoverable article. The sealant or mastic is often in the form of a layer which is applied to the surface of the article which is in contact with the substrate. When heat is applied to the article, generally by means of a torch or other heat source, the heat-activatable sealant is activated and the article recovers. A strong bond is thus formed between the polymeric article and the substrate. Alternately or in addition to the heat-activatable sealant, a primer layer, often in the form of a curable polymeric composition such as an epoxy, may be applied to the substrate to improve the adhesion of the heat-recoverable layer to the substrate.
Curable epoxy primers for pipe coating are known. U.S. Pat. No. 3,876,606 (Kehr), the disclosure of which is incorporated herein by reference, discloses a thermosetting epoxy resin which comprises a polyglycidyl ether of polyhydric phenol, a dihydrazide, and a filler such as barium sulfate, calcium carbonate, or mica. The coating has good adhesion to the substrate when subjected to boiling water and also exhibits good cathodic disbonding performance at room temperature and at 60° C. However, the coating is in the form of a powder which is applied to a preheated substrate. Uniform application of such a powder onto a pipe or a pipe joint in the field is difficult, requiring complex equipment and relatively high temperatures.
U.S. Pat. Nos. 4,732,632 and 4,997,685 (Pieslak et al), the disclosures of which are incorporated herein by reference, disclose a method of applying a protective coating onto a substrate. The method comprises applying to the substrate a curable polymeric composition which is a liquid at about 20° C., comprises a resin component and a curing agent, and cures to a substantial extent within 24 hours at a temperature of not more than about 80° C. A polymeric covering layer having an innermost layer of a heat-activatable sealant is applied over the curable composition and the curable composition is then cured while in intimate contact with the innermost layer. The resulting covering has good adhesion to both the substrate and the heat-recoverable article and exhibits good cathodic disbonding performance. It is necessary, however, that the curable composition be selected to meet the specific requirements for each application; a single composition cannot be used for a wide variety of temperature applications.
SUMMARY OF THE INVENTION
We have not discovered a composition that is suitable for use as a primer on a substrate under a variety of temperature conditions which can be prepared by incorporating a particular mixture of amines in the curing agent. Furthermore, unlike some conventional compositions, the composition of the invention contains a relatively nonvolatile curing agent and thus is not subject to evaporation during curing. This means that special precautions need not be taken during shipping, handling, and use. In a first aspect, this invention discloses a curable polymeric composition which is a liquid at 20° C. and which comprises
(1) 25 to 60% by weight of a resin component which comprises an epoxy;
(2) 5 to 25% by weight of a curing agent which comprises
(a) a first component which is a cycloaliphatic amine or an aromatic amine, and
(b) a second component which is a polyamide amine; and
(3) 20 to 65% by weight of an inert inorganic filer.
Compositions of the invention are particularly useful when used in conjunction with a polymeric covering to provide environmental protection to a substrate such as a pipe. The composition serves to provide excellent adhesion between the substrate and the protective covering which is applied to the curable composition while it is substantially uncured. The innermost layer of the protective covering, generally an adhesive, is held in intimate contact with the curable composition while the curable composition is cured. As a result of the intimate contact, the curable composition of the invention and the adhesive layer are able to interact. Thus the second aspect of the invention provides a method of applying a protective covering to a substrate, said method comprising
(A) applying to the substrate a curable polymeric composition according to the first aspect of the invention;
(B) applying a multiple-layer polymeric covering having an innermost layer and an outermost layer over the curable composition in a manner such that said innermost layer is in intimate contact with said composition, the innermost layer comprising uncured polymeric heat activatable sealant capable of interacting with said curable composition; and
(C) allowing the curable composition to cure while maintaining intimate contact between said innermost layer and said composition.
In a third aspect, this invention provides an assembly for protecting a substrate, the assembly comprising
(A) a substrate;
(B) a first layer in contact with the substrate which comprises a cured composition of the first aspect of the invention;
(C) a second layer which contacts the first layer and interacts with it and which comprises a hot melt adhesive; and
(D) a third layer which contacts the second layer and which is a polymeric covering.


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