Production of improved preimpregnated material comprising a particulate thermosetting resin suitable for use in the formation of a substantially void-free fiber-reinforced composite article

A method for the production of an improved fibrous material suitable for the formation of a substantially void-free composite article comprising a plurality of adjoining substantially parallel reinforcing filaments in association with a matrix-forming thermosetting resin comprising:

• (a) preparing a dispersion of solid particles of a thermosetting resin in an aqueous medium which contains an effective amount of dissolved polyacrylic acid binding agent possessing a cross-linked molecular structure,
• (b) raising the pH of said aqueous medium to form an improved impregnation bath wherein the viscosity of the resulting bath is substantially increased to at least 50,000 cps. through stiffening of the molecules of said binding agent and said impregnation bath has a plastic flow characteristic with shear-thinning behavior which is sufficient to substantially uniformly suspend said particulate thermosetting resin within said bath,
• (c) impregnating said adjoining substantially parallel reinforcing filaments with said bath under conditions wherein said bath is caused to flow between said adjoining filaments by the application of work wherein said flow inherently results in a reduction of the viscosity of said bath which aids in the incorporation of said particulate thermosetting resin between adjoining filaments, and
• (d) controlling the content of said aqueous medium in the resulting fibrous material to provide a product having said particles of matrix-forming thermosetting resin substantially uniformly dispersed between adjoining filaments in the absence of fusion bonding which inherently (1) is drapable and tacky at ambient conditions, (2) is handleable without segregation of said particles within the fibrous material, and (3) which upon the application of heat and pressure can be transformed into a substantially void-free fiber-reinforced composite article of a predetermined configuration wherein said thermosetting resin becomes substantially completely cured and forms the matrix phase.

A method for the production of an improved fibrous material suitable for the formation of a substantially void-free composite article comprising a plurality of adjoining substantially parallel reinforcing filaments in association with a matrix-forming thermosetting resin comprising:

• (a) providing a plurality of reinforcing fibrous tows each comprising a plurality of adjoining substantially parallel filaments,
• (b) preparing a dispersion of solid particles of thermosetting resin in an aqueous medium which contains an effective amount of dissolved polyacrylic acid binding agent possessing a cross-linked molecular structure,
• (c) raising the pH of said aqueous medium to form an improved impregnation bath wherein the viscosity of the resulting bath is substantially increased to at least 50,000 cps. through the stiffening of the molecules of said binding agent and said impregnation bath has a plastic flow characteristic with shear-thinning behavior which is sufficient to substantially uniformly suspend said particulate thermosetting resin within said bath,
• (d) situating said resulting bath within an impregnation apparatus,
• (e) aligning said reinforcing fibrous tows in a side-by-side relationship to form a substantially uniform sheet-like tape,
• (f) feeding said sheet-like tape to said impregnation apparatus,
• (g) impregnating said substantially uniform sheet-like tape with said bath while present in said impregnation apparatus under conditions wherein said bath is caused to flow between said adjoining filaments of said sheet-like tape by the application of work wherein said flow inherently results in a reduction of the viscosity of said bath which aids in the incorporation of said particulate thermosetting resin between adjoining filaments, and
• (h) controlling the content of said aqueous medium in the resulting sheet-like tape to provide a product having said particles of said matrix-forming thermosetting resin substantially uniformly dispersed between adjoining filaments in the absence of fusion bonding which inherently (1) is drapable and tacky at ambient conditions, (2) is handleable without segregation of said particles, and (3) which upon the application of heat and pressure can be transformed into a substantially void-free fiber-reinforced composite article of a predetermined configuration wherein said thermosetting resin becomes substantially completely cured and forms the matrix phase.