Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2001-05-10
2004-08-31
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S413000, C428S424800, C428S447000
Reexamination Certificate
active
06783865
ABSTRACT:
BACKGROUND OF THE INVENTION
Polyethylene (“PE”) has many desirable mechanical properties and it is readily synthesized, and manufactured in any desired shape and size. In particular, there are many uses for PE, in its several grades, and particularly for high density polyethylene (“HDPE”) in the form of tubing, pipes, conduits, and the like. For ease of reference, the use of the term, “pipe” or “piping” in the singular or plural herein, should be understood to also encompass any other configuration of tubing or conduit, and the joiner and/or connector components, such as straight joints, elbow joints, end-caps and the like, unless otherwise specified.
It is also known to the art that many potential uses for pipe comprising PE, in whole or in part, have previously been impractical due to the inherent limitations of this polymer material. This is of particular concern in the manufacture of extruded, pre-insulated pipes for general industry, the building trades, ocean platforms, e.g., offshore oil and gas platforms, and ship building. In all of those environments, there is a demand for insulated pipes. Generally, pipes that are pre-insulated during the manufacturing process are more economical to produce and install. One preferred type of pre-insulated pipe has an inner carrier pipe, manufactured from any art-known material such as, for example, mild steel, stainless steel, PE formulated with any art-known copolymer (“PEX”) and/or HDPE, and the like. This inner carrier pipe is jacketed with a foam insulating layer, e.g., a hard polyurethane foam, that is, in turn, jacketed by a protective outer shell, preferably of HDPE, although steel is used for some applications. Optionally, one or more additional layers of foam, or other insulating materials, e.g., mineral wool or fiberglass or similar material, can also be incorporated into the structure of such insulated pipe. This type of pipe, with an HDPE outer shell, is typically manufactured as a single unit by an extrusion process.
HDPE pipes, including insulated pipes with an HDPE outer shell, are economical to manufacture and install, light, strong, and corrosion resistant. Of particular importance for the ship-building industry, pre-insulated extruded HDPE pipe is more resistant to penetration of moisture into the insulating layer than are conventional insulated pipes. However, there are obstacles to wider use of this type of pre-insulated pipe manufactured solely from polymer materials. The most important obstacle is that pipe manufactured from conventional PE-based polymers, including HDPE, is generally unsuitable for use in areas where flame retardancy is required. For example, the melting point for HDPE is about 120° C. When exposed to sufficient heat for even a brief period of time, HDPE readily melts and forms burning drops which can spread fire and/or cause severe burns on contact with human skin and clothing. Once ignited, HDPE bums intensely, producing noxious gas and smoke.
Other shortcomings of conventional HDPE pipes, whether insulated or single wall, relate to difficulties in adhering coatings to HDPE. PE-based polymers such as HDPE are among the most difficult polyolefins to successfully coat with a paint or glue, and there is a long-standing need in the art for a solution to this problem.
Paintability and/or gluing onto a surface is considered to require a minimum surface energy of at least 38 dynes/cm
2
. In fact, it is considered that successful adhesion with most standard paints generally requires a surface energy over 50 dynes/cm
2
, but HDPE is reported to have a surface energy of only about 31 dynes/cm
2
. A surface energy of 80 dynes/cm
2
, or higher, is considered to be best for optimum post-manufacture painting, marking or adhesion, particularly when the paint or adhesive must remain on the surface for many years, while withstanding extreme environmental conditions.
The requirement for painting relates to the practical and economic importance of color coding for identification of specific components in the construction and maintenance of tubing, pipes and/or conduits in a complex installation. The requirement for gluing and adhesion relates, for example, to the practical need to attach other construction materials, as well as markings and/or indicia of various kinds, to the pipe after installation.
Previous efforts to address some of these shortcomings in HDPE pre-insulated pipes have required the use of a metal-jacketed pre-insulated pipe for the outer shell to provide flame retardancy and paintability. However, the use of a metal jacket, e.g., steel, as the outer shell adds weight and cost to manufacture and installation, among other limitations.
Another way in which the surface properties of materials formed of PE-based polymers have previously been enhanced is by blending other polymers with the stock polyethylene, before extrusion, to impart flame retardant properties and/or paintability. For example, various products are commercially available in the form of granules, which, when blended with HDPE during manufacture, impart some protection against heat and flame. However, they all have the disadvantage that they change the mechanical properties for polyethylene. In addition, the processing requirements of blending other polymers into the HDPE adds to the costs of materials, and requires custom manufacture, which makes it difficult to economically supply pipe as required by the end user in the various industries.
Yet another problem with conventional PE compositions is its sensitivity to degradation by ultraviolet radiation in outdoor applications. The normal color of polyethylene is a milk-white. One way that PE has previously been protected from ultraviolet radiation in outdoor applications is by the addition of carbon black to the composition. Of course, this does not help any of the other shortcomings of PE, and for outdoor applications, a black PE composition can experience excessive heating from the infrared portion of sunlight, particularly with outdoor use in regions with a high solar flux, such as the tropics.
Another possible method for enhancing surface properties of polymeric materials is by grafting or bonding coatings onto the surfaces in need of such treatment. Polymers have been grafted onto non-metallic substrate surfaces, such as cellophane, and polyolefins. For example, U.S. Pat. No. 5,753,557 describes grafting of a polymer onto cellophane using ultrasound to cure the grafted layer. U.S. Pat. Nos. 5,342,659 and 5,232,748, describe grafting of a polymer onto cellophane using radiation energy, e.g., microwave, laser or ultrasonic energy to cure the grafted layer.
U.S. Pat. No. 3,880,580 describes methods of activating polymer substrates such as polyolefins, polypropylene, polyester and polyvinylchloride materials to accept sulfonation in the presence of a chlorinating hydrocarbon solvent, so that the grafted substrate can be dyed.
U.S. Pat. No. 5,407,728 describes a solution for grafting a polymer onto fabrics, such as polyamides, polyaramids or polyesters, to enhance flame retardant properties and resistance to fraying, for use in the manufacture of fabrics, including fabrics for airbags. As described by U.S. Pat. No. 5,741,548, polymers can be grafted onto fabrics, including polyethylene fabrics, to enhance the printability of satin and reemay acetate fabrics.
The descriptions of the patents mentioned above provide grafting solutions for very specific purposes, which cannot be readily generalized to other materials. Nowhere do any of these patents teach or suggest grafting onto solid PE or PE-based polymers, to provide for enhanced flame retardant properties and other improved surface properties in pipes, beams and other similar articles of manufacture. For instance, U.S. Pat. No. 5,407,728 teaches the need to avoid excessive crosslinking in the graft coating to prevent undesirable stiffness, whereas in the graft coating of a solid substrate a high level of crosslinking is typically desired in order to enhance such properties as, e.g., flame retardancy and scratch resistance.
Thus,
Horowitz Carl
Mishiyev Robert
Sanduja Mohan L.
Thottathil Paul
Bissett Melanie
Logstor Ror A/S
Seidleck James J.
Steinberg & Raskin, P.C.
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