Methods and compositions for coating pipe

Abstract

Compositions and methods for producing multi-layered plastic pipes are described. Some embodiments of the compositions comprise a cross-linkable polymer system (for example, based on either acrylate or epoxy chemistry), a photoinitiator, and one or more additives such as a pigment, an antioxidant, a light stabilizer, or other additive. In an exemplary method of producing a multi-layered plastic pipe, a base pipe, for example comprising cross-linked polyethylene, is conveyed through an oxidizing step in which at least the outer surface of the base pipe is oxidized, through a coating step in which a pre-polymer system is applied to the outer surface of the base pipe and through a curing step in which the pre-polymer is cured to form a layer of the pipe.

1 . A flexible tubular member comprising:
 a flexible tubular polymeric substrate, the substrate having an outer diameter of at least 5/16 inch and a burst strength of at least 475 psi at 23° C. and;   a coating disposed on an outer surface of the tubular substrate, the coating comprising at least one radiation cured crosslinked polymeric layer having a thickness of less than 100 microns thick.   
   
   
       2 . The flexible tubular member of  claim 1  wherein the polymeric substrate comprises a polyolefin. 
   
   
       3 . The flexible tubular member of  claim 2  wherein the polyolefin is polyethylene. 
   
   
       4 . The flexible tubular member of  claim 2  wherein the polyolefin is a cross-linked polyethylene. 
   
   
       5 . The flexible tubular member of  claim 1  wherein the layer is less than 60 microns thick. 
   
   
       6 . The flexible tubular member of  claim 1  wherein the coating comprises at least 2 layers, and each of the layers is individually less than 60 microns thick. 
   
   
       7 . The flexible tubular member of  claim 1  wherein the coating comprises an oxygen barrier or a colorant, or combinations thereof. 
   
   
       8 . The flexible tubular member of  claim 1  wherein the coating comprises a photoinitiator. 
   
   
       9 . The flexible tubular member of  claim 1  wherein the at least one crosslinked layer comprises an acrylate. 
   
   
       10 . The flexible tubular member of  claim 1  wherein the at least one crosslinked layer comprises a carboxyethyl acrylate. 
   
   
       11 . The flexible tubular member of  claim 1  wherein the peel strength between the tubular substrate and the crosslinked polymeric layer is at least 300 psi. 
   
   
       12 . A flexible tubular member comprising:
 a flexible tubular substrate comprising a cross-linked polyethylene;   a coating disposed on an outer surface of the tubular substrate, the coating comprising a radiation cured cross-linked acrylate base polymer layer disposed on an outer surface of the tubular substrate and a radiation cured cross-linked polymer topcoat layer disposed over the base layer wherein the base and topcoat layers each have a thickness of less than 60 microns thick and a total thickness of less than 100 microns wherein the peel strength between the tubular substrate and the crosslinked polymer layers is at least 300 psi.   
   
   
       13 . The flexible tubular member of  claim 12  wherein the coating layer comprises an oxygen barrier material or a colorant, or combinations thereof. 
   
   
       14 . The flexible tubular member of  claim 12  wherein the coating layer comprises a photoinitiator. 
   
   
       15 . The flexible tubular member of  claim 12  wherein at least one of the base or topcoat layers comprises crosslinked carboxyethyl acrylate. 
   
   
       16 . A flexible tubular member comprising:
 a polymeric flexible tubular substrate;   a metallic layer disposed over an outer surface of the flexible tubular substrate;   a coating disposed on an outer surface of the metallic layer, the coating comprising at least one radiation cured crosslinked polymeric layer having a thickness of less than 100 microns.   
   
   
       17 . The flexible tubular member of  claim 16  wherein the metallic layer comprises aluminum. 
   
   
       18 . A process for producing a flexible tubular member having a cross-linked coating including:
 oxidizing an outer surface of a flexible tubular substrate, the substrate comprising a cross-linked polyethylene;   disposing a first layer of a radiation curable pre-polymer formulation on the oxidized outer surface; and   exposing the first layer to radiation to produce a first crosslinked coating layer, having a thickness of less than 60 microns thick.   
   
   
       19 . The process of  claim 18  wherein the oxidizing step comprises heat oxidation. 
   
   
       20 . The process of  claim 18  further comprising disposing a second curable pre-polymer formulation on the first coating layer and curing the second formulation with radiation energy to form a second coating layer. 
   
   
       21 . The process of  claim 20  wherein the first formulation is partially cured prior to disposing the second formulation on the first coating layer. 
   
   
       22 . The process of  claim 18  wherein the exposing step comprises exposing with UV radiation. 
   
   
       23 . The process of  claim 18  wherein in the process is continuous process further including the steps of:
 prior to the oxidizing step, dispensing the flexible tubular substrate from a first roller; and   after the curing step, receiving the flexible tubular member onto a second roll.