Surfacing materials for composite structures

An integrated electrically conductive surfacing material comprising:

• (a) a stiffening layer;
• (b) a curable resin layer comprising one or more thermoset resins and a curing agent;
• (c) a conductive layer between the stiffening layer and the curable resin layer;
• and
• (d) a nonwoven layer laminated to the curable resin layer,
• wherein the stiffening layer (a) and the nonwoven layer (d) are outermost layers and the exposed surfaces of the outermost layers are substantially tack-free at room temperature of 20° C. to 25° C., and
• wherein the stiffening layer is a nonporous thermoplastic layer having the following properties:
• a tensile modulus of from about 640 MPa (or 93 ksi) to about 2.1 GPa (or 305 ksi), as measured by ASTM D-882;
• a tensile strength at yield of from about 27 MPa (or 4 ksi) to about 76 MPa (or 11 ksi), as measured by ASTM D-882, a tensile strength at break of from about 41 MPa (or 5.9 ksi) to about 110 MPa (or 16 ksi), as measured by ASTM D-882;
• and an elongation at yield or break of from about 4% to about 10%, as measured by ASTM D-882, all properties being determined at about 23° C.

A composite structure comprising:

• a composite substrate comprising reinforcement fibers impregnated with a curable matrix resin;
• and
• an integrated electrically conductive surfacing material comprising:
• (a) a nonporous thermoplastic layer that functions as a stiffening layer;
• (b) a curable resin layer comprising one or more thermoset resins and a curing agent;
• (c) a conductive layer between the nonporous thermoplastic layer and the curable resin layer;
• and
• (d) a nonwoven layer laminated to the curable resin layer,
• wherein the nonporous thermoplastic layer (a) and the nonwoven layer (d) are outermost layers, and the exposed surfaces of the outermost layers are substantially tack-free at a temperature in the range of 20° C. to 25° C., and
• wherein the electrically conductive surfacing material is laminated to a surface of the composite substrate such that the nonporous thermoplastic layer (a) is in contact with the composite substrate.