Decorative iridescent film

A method of producing a multilayer co-extruded iridescent film of sufficient strength to be slit into microfilaments includes orientating a multilayer co-extruded iridescent film of at least 10 generally parallel very thin layers of substantially uniform thickness, the contiguous adjacent layers being of different thermoplastic resinous materials whose refractive index differ by at least about 0.03 until the thickness of the film is about 20% and 50% of the film before orientation.

EXAMPLE 1 Sample 1 consisted of polybutylene terephthalate and polymethyl methacrylate, and sample 2 of polyethylene naphthalate and polybutylene terephthalate. The surface layer of both samples was polybutylene terephthalate. The samples were processed using two-stage Marshall-Williams equipment and stretched at various orientation temperatures. Effective draw ratios varied from 1.8 to 2.6:1 at temperatures ranging from 110 to 145° C. At the predetermined ultimate gauge, color measurements were taken across the web to determine the uniformity of color. There was no indication of non-uniform draw of the individual microlayers in the plane perpendicular to the moving web. This was later confirmed with photomicrographs of the sample cross section. Mechanical properties were tested using an Instron model 5500. The force required to break a 6 mm wide strip of post-stretched film exceeded 5 kgf of force in all cases, as compared with less than 2 kgf for the typical non-oriented structure. Apart from the 10-20% of the edge material which remained too thick for color measurement, the primary samples exhibited satisfactory color intensity. The products can be slit into a microfilament thread having a width of about 0.13-0.3 mm. 
 EXAMPLE 2 Three film samples were produced with optical cores containing approximately 100 alternating layers. Sample 1 consisted of polybutylene terephthalate and polymethyl methacrylate, sample 2 of polyethylene terephthalate and polymethyl methacrylate, and sample 3 of a copolyester ether and glycol modified polyethylene terephthalate. All samples were between 0.03 and 0.06 mm in thickness. The samples were processed using custom machine direction compression rolling equipment. Effective draw ratios varied from 1.7 to 3.0:1 at mill roll temperatures ranging from 100 to 110 deg C. Mill roll pressures ranged from 1300 psi to 1900 psi. Due to the magnitude and direction of the force vectors deployed, it was anticipated that some degree of thickness gradient would be imparted to the microlayer stack. By using tension adjustments and draw ratios to control thickness (and thereby color), the thick samples were oriented to predetermine target thickness having peak reflection curves in the 540-600 nm range. There was no evidence of non-uniform draw in the individual microlayers indicated by spectrophotometric readings. This was later confirmed with photomicrographs of the sample cross sections. Mechanical properties were tested using an Instron model 5500. The force required to break a 6 mm wide strip of post-stretched film exceeded 5 kgf of force. The products can be slit into a microfilament thread having a width of about 0.13-0.3 mm. Various changes and modifications can be made in the process and products of this invention without departing from the spirit and scope thereof. The various embodiments disclosed herein were for the purpose of illustrating the invention but were not intended to limit it.