Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With coating
Reexamination Certificate
1997-05-23
2001-02-13
Silverman, Stanley S. (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With coating
C065S430000, C065S432000, C065S443000, C065S450000, C065S451000, C427S372200, C427S379000, C427S389000, C427S389700
Reexamination Certificate
active
06185962
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention relates to a method for forming coated fibers suitable for reinforcing composite products, and more particularly to a method of forming coated fibers in which fiber strands are coated with a chemical treatment containing a curable thermoset resin which is uncured or only partially cured during the manufacture of the strand, but is fully cured during off-line processing of the coated fiber strand into a composite article or product.
BACKGROUND OF THE INVENTION
Fiber reinforced composite products or articles have been made using a variety of processes and materials. One common type of composite article includes a polymeric matrix reinforced with a plurality of ceramic reinforcing fibers (e.g., glass fibers). Glass and other ceramic reinforcing fibers are commonly manufactured by supplying the molten ceramic material to a bushing, drawing fibers from the bushing, applying a chemical treatment, such as an aqueous-based system, so as to size the drawn fibers, and then gathering the sized fibers into a tow or strand.
In fabricating a composite part, the fibers in each of a plurality of fiber strands are often further chemically treated in an off-line impregnation process with either a thermoset resin, one or two part, or a thermoplastic resin. For example, in one such process a bundle or strand of glass fibers is impregnated with a heat curable thermosetting resin and then pulled through a heated pultrusion die, simultaneously curing the resin and making a composite part such as, for example, a ladder rail. Composite products have also been fabricated in a filament winding process by feeding the fiber strands through a bath of a heat curable thermosetting resin, winding the impregnated strand around a mandrel and curing the thermoset resin to form a filament wound part such as a pipe.
Composite articles made with a thermosetting polymer matrix can exhibit superior mechanical properties compared to composite articles made with a thermoplastic polymer matrix. This is particularly true when the composite article is exposed to high temperatures.
However, once the thermosetting resin is cured, the impregnated strand cannot be molded or reshaped in subsequent processing. This characteristic of a thermoset impregnated fiber strand has caused such strands to be formed into the desired composite article soon after the strand is impregnated. Typically, when a thermoset resin is used, the composite article has had to be formed in-line with the process of impregnating the fiber strand. In contrast, the ability of thermoplastic polymers to be remelted enables thermoplastic impregnated strands to be subsequently heated and molded or otherwise shaped into various articles or products in off-line processes. Thus, thermoplastic impregnated strands are typically easier to work with and more versatile.
Accordingly, there is a need in the art for a method for forming a fiber strand which exhibits the mechanical properties of a fiber strand coated with a thermosetting resin while also being easier to work with and more versatile than previous thermoset impregnated fiber strands. In particular, there is a need for a method of forming a thermoset coated fiber strand which can be formed into a composite article in a subsequent off-line forming operation and then fully cured.
SUMMARY OF THE INVENTION
The present invention meets this need by providing a method for coating fibers by applying an aqueous or non-aqueous chemical treatment or composition to the fibers. The chemical treatment comprises a thermoset resin system which undergoes little or no curing during in-line processing, but which can be completely cured or crosslinked during a subsequent off-line composite forming operation. The thermoset resin system includes a curable resin and may or may not include a curing agent, a catalyst or an accelerant. The chemical treatment may be applied with sufficient amounts of the thermosetting resin to form all of the matrix of the final composite article. Alternatively, additional resin material, which may be the same or different than the type of resin material used in the chemical treatment, may be added with the coated fibers during the final composite product forming process to form the balance of the matrix.
In accordance with one aspect of the present invention, a method of forming coated fibers suitable for making a composite article is provided comprising the steps of providing a plurality of fibers and then applying a chemical treatment containing a curable thermosetting resin with or without other chemical treatment constituents (e.g., a curing agent, catalyst, accelerant, silane coupling agent, citric acid, etc.) to the fibers. The thermosetting resin is in a partially cured or uncured state. For purposes of the present invention, a “curing agent” is defined as a chemical compound which increases the rate of cure of a resin and adds to the molecular weight or stoichiometry of the final cured resin. An “accelerant” is defined as a chemical compound which increases the rate of cure of a resin without adding to the molecular weight or stoichiometry of the final cured resin.
In one embodiment, the chemical treatment is aqueous-based, with a concentration of about 20-70% by weight of the curable thermoset resin and, if present, other chemical treatment constituents, with the remaining balance being water. In an alternative embodiment, the chemical treatment may be non-aqueous, with a concentration of about 98-100% by weight of the curable thermoset resin and, if present, other chemical treatment constituents, with the remaining balance being water.
In one embodiment, the chemical treatment of the present invention is coated on a plurality of fibers. It is desirable for the chemical treatment to preimpregnate or impregnate the plurality of fibers. Pre-impregnating or impregnating involves applying a sufficient amount of the chemical treatment to a plurality of fibers such that the spaces between the fibers are substantially filled when the fibers are formed into a bundle or strand. Sizing on the other hand, involves applying a relatively thin protective coating of chemical treatment to the surface of each glass fiber. Glass reinforcing fibers are generally considered sized when they contain chemical treatment constituents on the order of about 0.5% by weight, as determined by a conventional loss on ignition (LOI) test. A conventional loss on ignition (LOI) method can be used to determine the amount of the organic compounds loaded onto the ceramic fibers (e.g., glass fibers). Coating includes sizing, preimpregnating, impregnating, or any other application of chemical treatment on a plurality of fibers.
When an aqueous based chemical treatment is applied, it is desirable for the chemically treated fibers to be heated to drive off a substantial amount of the water in the chemical treatment to dry the fibers. This heat can be provided, for example, by bringing the coated fibers into contact with a heating device, (e.g., a hot plate) which heats the coated fibers without effecting full curing of the resin. It is desirable for the resin not to be cured at all. Where the chemical treatment is aqueous-based, the heating step functions to drive off water, effecting drying of the fibers. Where the chemical treatment is non-aqueous, the heating step may effect partial curing, and thereby, thickening of the chemical treatment.
The resin applied to the fibers can be a heat curable type. For example, the curable thermoset resin can be a heat curable epoxy resin. An epoxy resin chemical treatment may include a curing agent such as, for example, an amine or amide. An accelerant may also be included in the resin system. Where the chemical treatment includes a curing agent and/or an accelerant, the curing time of the thermosetting resin may be tailored such that little or no curing, or only partial curing takes place when the fibers are brought into contact with the heating device.
In one embodiment of the invention, the fibers are glass f
Hartman David R.
Muellerleile Joan T.
Shipp David L.
Woodside Andrew B.
Colaianni Michael P.
Eckert Inger H.
Owens Corning Fiberglas Technology Inc.
Silverman Stanley S.
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