USE OF FLUOROPOLYMER FILM AS RELEASE FILM IN A METHOD FOR SHAPING COMPOSITE MATERIAL

Abstract

The present invention relates to the use of a single layer fluoropolymer film selected from ethylene tetrafluoroethylene film and polytetrafluoroethylene film as release film in a method for shaping a composite material.

Claims

1. Use of a single layer fluoropolymer film selected from ethylene tetrafluoroethylene film and polytetrafluoroethylene film, as release film in a method for shaping a composite material, wherein the method comprises: (a) placing a substantially planar composite material between an upper fluoropolymer film and a lower fluoropolymer film by creating a pocket between the upper fluoropolymer film and the lower fluoropolymer film which houses the composite material, (b) bringing the upper fluoropolymer film and the lower fluoropolymer film into intimate contact with the composite material, thereby forming a layered structure, wherein the composite material is held stationary between the upper fluoropolymer film and the lower fluoropolymer film until heat or force is applied to the layered structure; (c) optionally pre-heating the layered structure in a heating apparatus at a temperature sufficient to either lower the viscosity of the composite material or soften the upper fluoropolymer film and the lower fluoropolymer film; (d) positioning the layered structure in a press tool comprising a male mold and a corresponding female mold separated by a gap, wherein the male mold and the female mold each independently have a non-planar molding surface, (e) compressing the layered structure between the male mold and the female mold by closing the gap between the male mold and the female mold; and (f) maintaining the male mold and the female mold in a closed position until a viscosity of the layered structure reaches a level sufficient to maintain a molded shape.

2. The use of claim 1, wherein the single layer fluoropolymer film has a melt temperature (T.sub.melt) no less than about 240? C., a thickness (t) in a range of about 10 microns to about 200 microns, An Elastic Modulus (E) in a range of about 300 to about 950 MPa, a Tensile Strength (?) in a range of about 30 to about 90 MPa, and elongation at break (?) in a range of about 400 to about 700% in either longitudinal or transverse directions at a rate of about 8 mm/s, under ambient conditions.

3. The use of claim 1, wherein the upper fluoropolymer film and the lower fluoropolymer film are the same film.

4. The use of claim 1, wherein the single layer fluoropolymer film comprises ethylene tetrafluoroethylene film.

5. The use of claim 1, wherein the single layer fluoropolymer film comprises polytetrafluoroethylene film.

6. The use of claim 4, wherein the ethylene tetrafluoroethylene film has a melt temperature (T.sub.melt) no less than about 240? C., a thickness (t) in a range of about 30 microns to about 100 microns an Elastic Modulus (E) in a range of about 500 to about 900 MPa a Tensile Strength (?) in a range of about 45 to about 90 MPa and an elongation at break (?) in a range of about 400 to about 700% in either longitudinal or transverse directions at a rate of about 8 mm/s, under ambient conditions.

7. The use of claim 5, wherein the polytetrafluoroethylene film has a melt temperature (T.sub.melt) no less than about 300? ? C., a thickness (t) in a range of about 30 microns to about 100 microns, an Elastic Modulus (E) in a range of about 300 to about 500 MPa, preferably of about 350 to about 450 MPa, a Tensile Strength (?) in a range of about 30 to about 55 MPa, preferably of about 35 to about 50 MPa, and an elongation at break (?) in a range of about 400 to about 700%, in either longitudinal or transverse directions at a rate of about 8 mm/s, under ambient conditions.

8. The use of claim 1, wherein step (e) comprises partially closing the gap between the male mold and the female mold such that a smaller gap is formed between the molds, which smaller gap is subsequently closed after a specific time or viscosity is reached.

9. The use of claim 1, wherein the male mold and the female mold are maintained at a temperature above ambient temperature.

10. The use of claim 9, wherein the male mold and the female mold are maintained at a temperature above 100? C.

11. The use of claim 1, wherein step (e) comprises closing the gap between the male mold and the female mold at a speed of between about 0.7 mm/s and about 400 mm/s, while maintaining the male mold and the female mold at a temperature above a softening point of the composite material.

12. The use of claim 1, wherein the upper film and the lower film are held together by a structural frame comprising a top frame, a center frame and a bottom frame, wherein: the lower film is held between the bottom frame and the center frame; and the upper film is held between the center frame and the top frame.

13. The use of claim 12, wherein the center frame supplies a source of vacuum to the assembly.

14. The use of claim 1, wherein the upper film and the lower film are held together by a structural frame comprising a top frame and a bottom frame, wherein both the lower film and the upper film are held between the bottom frame and the top frame.

15. The use of claim 1, wherein the layered structure is positioned in the press tool and in the optional heating apparatus by automated means.

16. The use of claim 1, wherein the substantially planar composite material comprises structural fibers of a material selected from aramid, high-modulus polyethylene (PE), polyester, poly-p-phenylene-benzobisoxazole (PBO), carbon, glass, quartz, alumina, zirconia, silicon carbide, basalt, natural fibers and combinations thereof.

17. The use of claim 1, wherein the composite material comprises a binder or matrix material selected from thermoplastic polymers, thermoset resins, and combinations thereof.

Description

EXAMPLE

[0085] The following example is for illustration purposes only, and is not to be construed as limiting the scope of the appended claims.

Example 1: Double Diaphragm Mechanical Thermoforming, Framed, Using a High Temperature ETFE Film and Rapid Cure Automotive Epoxy Prepreg

[0086] A lower flexible diaphragm made of a 52 micron ETFE film was positioned onto a bed holding a bottom frame. This film exhibits characteristics reported in table 1.

TABLE-US-00001 TABLE 1 Measures of mechanical properties in machine direction (MD) and transverse direction (TD) Temperature resistance (? C.) 240-250 Melting point (? C.) 267 Elastic Modulus (E) (MPa) 765 (MD) 783 (TD) Tensile Strength (?) (MPa) 59.8 (MD) 56.5 (TD) elongation at break (?) (%) 466 (MD) 526 (TD) thickness (t) (?m) 52

[0087] A composite material blank comprising of a carbon-fiber reinforced epoxy (Solvay, formerly Cytec Industries, MTM58B) and surfacing film (Solvay, formerly Cytec Industries, VTF266) was laid on top of the lower flexible diaphragm, followed by a center frame having a vacuum inlet. An upper flexible diaphragm made of the same film as the lower flexible diaphragm was then placed such that it covered the center frame and composite material blank. The top, center and bottom frames were clamped together, thereby creating a vacuum tight seal and a sealed pocket bounded by the lower flexible diaphragm, the upper flexible diaphragm and the center frame. A vacuum was then applied to remove air from between the upper flexible diaphragm and the lower flexible diaphragm, until the vacuum pressure reached minimum of 670 mbar. At that point, the composite material blank was firmly supported by both diaphragms, creating a stationary layered structure.

[0088] The layered structure was then shuttled into ceramic non-contact heating apparatus, where it was heated to 140? C. Once the external film temperature reached a minimum of 120? C., it was shuttled into a press tool comprising a matched male mold and female mold, configured in the shape of a structural automotive Class-A demonstrator component. The female mold was then driven toward the male mold at a rate of approximately 4 mm/s (250 mm/s). The male mold remained stationary, and both molds were held at 150? ? C. until cross linking had begun. The shaped structure was removed from the press tool while still hot and allowed to cool after removal. The process for shaping the composite material blank was 15 minutes from start to finish (i.e., first placement of the lower flexible diaphragm to establishment of final shape).

[0089] Following demoulding and cooling, the part manufactured using a 52 micron ETFE top film was visually inspected and scanned using short and long wave scanning techniques (Visuol) to identify the level of orange peel (fine) and fabric print through (coarse) respectively. From the results, it is apparent that the increased thermal performance and film stiffness of the ETFE top film enabled an important reduction in the measured print through and orange peel.

[0090] The thermal properties of the film were determined using a Differential Scanning calorimetry (DSC) using a TA Q2000 DSC machine) with respect to ASTM 3418. A heat/cool/heat procedure was applied screening a temperature range from ?30? C. to 300? C. with a cooling and heating rate of 10? C./min.

[0091] The mechanical properties of the film were determined in accordance with ASTM D882-09 using a Zwick Z250 test machine. The film was tested in both machine and transverse directions at a test speed of about 8 mm/s (500 mm/min) under ambient conditions of 23? C. and 50% relative humidity.