Coating processes – With pretreatment of the base – Heating or drying pretreatment
Reexamination Certificate
2003-06-11
2004-08-24
Dixon, Merrick (Department: 1774)
Coating processes
With pretreatment of the base
Heating or drying pretreatment
C427S293000, C427S301000, C427S324000, C427S372200, C427S442000, C428S361000, C428S375000, C428S401000, C428S359000, C428S378000
Reexamination Certificate
active
06780468
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
The invention relates to a string binder for use in reinforced composite molding applications, and composite articles formed therefrom. Specifically, the novel string binder of the present invention comprises solid strands of a resin composition comprising one or more modified binder resins of low acid value, and, optionally, a fibrous carrier substrate material. The string binder preferably comprises at least one thermoformable resin as the binder resin component, and an effective amount of a catalyst having a high activation temperature. The string binder strands may be combined with one or more fibrous reinforcing materials to form a multi-end roving product, which may be used either in chopped or continuous form as a reinforcement material having improved impact strength. Such reinforcement materials are useful in numerous reinforced composite applications, including the molding of preforms typically used in liquid resin molding of fiber-reinforced articles. The invention further comprises a method of making the novel string binders of the invention.
BACKGROUND OF THE INVENTION
Reinforcing fibers comprising glass, polymer, other reinforcing fibers, or blends thereof are commonly used as reinforcement materials in molded plastic composite articles. These reinforcing materials, when incorporated into the matrix resin of the composites, provide the finished product with a higher level of tensile strength and durability than could possibly be achieved if either the fibers or the resins were used separately. Reinforcing fibers may be incorporated into a composite resin matrix either in continuous form, as is done in the manufacture of filament-wound composites, or the fibers may be introduced into the matrix as chopped segments that may be dispersed throughout the matrix in linear or random fashion, depending on the characteristics that are desired in the final product.
Generally, in the manufacture of reinforcing articles for use in liquid resin molding processes, chopped segments of a fibrous substrate, typically glass strands, may be combined with a binder resin and the resulting composition is laid down over a form and solidified to form a matted structure such as a preform, which can then be cured and/or subjected to further molding processes to form the composite end product.
Several means of combining the binder resin with a glass carrier substrate strand to make preforms are known in the art. For example, an emulsion comprising a heat-curable binder resin may be blended with the glass carrier strand; or the resin and the carrier strand may be combined to form a slurry. The emulsion or the slurry may then be poured onto a form or mold and suction or a vacuum applied to remove the diluent or solvent component, thereby solidifying the preform. The obvious drawbacks associated with using an emulsion binder include the requirement for extensive clean-up of the forming screens; the environmental hazards relating to the discharge of solvent or diluent vapors containing volatile organic chemicals (VOCs); risks to the safety of personnel from exposure to such chemicals; and added costs arising from a lengthy drying period or the need for additional equipment to prepare the preform.
Dry compositions using, for example, a powdered binder in combination with the fibrous carrier material are also known. The powdered binder is heated sufficiently to melt and cure the binder after it is combined with the carrier material. One disadvantage of using the powdered binder is that it may be difficult to control the amount of binder powder required to create an acceptable preform, and the addition of excess resin may foul equipment and require extensive cleanup operations.
To make a preform using molten binder, typically, a glass fibrous carrier substrate is chopped into segments, which are combined with the binder resin and placed over a porous structural form such as a mesh screen. Alternatively, the glass carrier substrate material may be formed into strands that are then chopped into segments and sprayed over the form in combination with a binder. The method of adding the binder may be via a flame-spray process, in which solid, powdered binder resin is sprayed through a flame immediately before it contacts the fibrous carrier material. In this fashion, the binder is melted before it mixes with the fibrous carrier. A process involving the steps of heating, curing and cooling of the material is then applied to form, shape and consolidate the material, as well as to remove any solvents or diluents that may be present, thereby solidifying the product into a preform ready for molding or further processing. The resulting preform may then be removed and used in a subsequent molding operation, such as injection molding, in which a resin is injected around the preform and cured to form a structurally molded composite.
Because these techniques of making the preform typically require applying an excess of binder resin, a commonly observed drawback is the build-up of excess molten binder resin on the equipment, the removal of which is both costly and time-consuming. Moreover, the process includes the inherent difficulties of dealing with the molten binder. The process of adding the binder is difficult to control, and the handling of the molten resin poses an additional safety concern.
Continuous glass fibers that have been pre-impregnated with a binder resin may also be used to form fiber segments for preform manufacture. The impregnated strands, known as string binders, may be formed by applying one or more layers of a binder resin onto the surface of a continuous glass fiber strand after it is formed, then allowing the binder to set on the surface of the strand. After the coating is solidified, the strand is then chopped into coated segments that may be used in the spray-up process to make preforms.
The binders used in preform manufacture are usually either thermoplastic polymers in molten or powdered form, or high acid value thermoset emulsion polymers such as crystalline polyesters. The term “crystalline” relates to the inherent ability of the thermosetting resin to form crystallites or regions of order dispersed among regions of disorder within the solidified polymer. The ability of a polymer to display crystalline properties is determined principally by its composition. For example, thermoplastic polyesters are macromolecules that contain no chemical groups to effect inter-linking. Such materials are typically heated to the softening point, forced into the shape of the desired article, then cooled below the softening point to yield the finished reinforcing article. Like thermosetting polyesters, they may display many levels of crystallinity, again depending on composition. Crystalline polyesters find use in organic fiber manufacture. Perhaps the best known crystalline polyester is polyethylene terephthalate, PET, which is commonly known as DACRON polyester, available from DuPont Inc.
The term “high acid value”, as used herein, is intended to represent the acidity of the polymer in terms of the amount of potassium hydroxide (KOH) required to neutralize the acidic functional groups in one gram of the polymer. A high acid polymer is one that contains acidic functional groups such that the measured acid value of the polymer is greater than 30 mg KOH/g of polymer. The known drawbacks of using the above high acid polymers include a high level of incompatibility between the binder resin molecules and the composite matrix resin because of the large degree of difference in polarity between the binder polymer molecules and the matrix resin molecules and/or the absence or unavailability of reactive functional groups that can cross-link with the composite matrix resin. This incompatibility can result in a lesser degree of wet-out of the reinforcing fibers in the composite matrix resin, and associated product defects such as blistering during the composite molding phase, and bleeding or blistering during post-bake of the composite product.
Blee
Beckman Jay Joseph
Hager William Gerard
Hulett Diane Marie
Dixon Merrick
Eckert Inger H.
Gasaway Maria C.
Owens Corning Fiberglas Technology Inc.
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