Color shifting multilayer polymer fibers and security articles containing color shifting multilayer polymer fibers

An optical body, comprising:

• a first polymer fiber comprising a reflecting arrangement of substantially concentric, alternating layers of a first polymer material having a first refractive index and a second polymer material having a second refractive index different from the first refractive index;
• and
• at least a second polymer fiber comprising an arrangement of substantially concentric layers comprising alternating layers of a third polymer material having a third refractive index and a fourth polymer material having a fourth refractive index different from the third refractive index, a first portion of the first fiber being attached to the second fiber;
• wherein the portion of the first fiber attached to the second fiber reflects light of a first color different from a second color of light reflected from a second portion of the first fiber not attached to the second fiber, and wherein at least the first polymer fiber comprises polymer materials wherein at least one of the first and second polymer materials being birefringent;
• and wherein thicknesses of the layers of the first polymer material and the layers of the second polymer material are selected so that the first multilayered polymer fiber reflects visible light within a selected portion of the visible spectrum in a first polarization state and incident perpendicular to a fiber longitudinal axis and transmits visible light in the first polarization state that lies outside the selected portion of the visible spectrum and incident perpendicular to the fiber longitudinal axis.

A method of making a polymer fiber, comprising:

• forming a polymer fiber having an arrangement of substantially concentric layers comprising alternating layers of a first polymer material having a first refractive index and a second polymer material having a second refractive index different from the first refractive index, the polymer fiber having a first cross-sectional shape;
• and
• changing the first cross-sectional shape of the polymer fiber to a second cross-sectional by elongating the cross-section of the polymer fiber along a first cross-sectional axis, wherein at least one of the first and second polymer materials is birefringent;
• and wherein the thicknesses of the layers of the first polymer material and the layers of the second polymer material are selected so that the first multilayered polymer fiber reflects visible light within a selected portion of the visible spectrum in a first polarization state and incident perpendicular to a fiber longitudinal axis and transmits visible light in the first polarization state that lies outside the selected portion of the visible spectrum and incident perpendicular to the fiber longitudinal axis.

A polymer fiber, comprising:

• a first multilayered fiber comprising
• a central core formed of a polymer material;
• and
• reflecting layers of at least a first polymer material and a second polymer material, layers of the first polymer material being disposed between layers of the second polymer material, at least one of the first and second polymer materials being birefringent;
• wherein thicknesses of the layers of the first polymer material and the layers of the second polymer material are selected so that the fiber reflects visible light within a selected portion of the visible spectrum in a first polarization state and incident perpendicular to a fiber longitudinal axis and transmits visible light in the first polarization state that lies outside the selected portion of the visible spectrum and incident perpendicular to the fiber longitudinal axis.

A secure article, comprising:

• a member having a first surface;
• and
• a first multilayer polymer fiber on the first surface, the first polymer fiber comprising an arrangement of substantially concentric layers comprising alternating layers of a first polymer material having a first refractive index and a second polymer material having a second refractive index different from the first refractive index, and wherein the first multilayered polymer fiber comprising an arrangement of substantially concentric layers comprises reflecting layers of at least a first polymer material and a second polymer material, layers of the first polymer material being disposed between layers of the second polymer material, at least one of the first and second polymer materials being birefringent;
• wherein thicknesses of the layers of the first polymer material and the layers of the second polymer material are selected so that the first multilayered polymer fiber reflects visible light within a selected portion of the visible spectrum in a first polarization state and incident perpendicular to a fiber longitudinal axis and transmits visible light in the first polarization state that lies outside the selected portion of the visible spectrum and incident perpendicular to the fiber longitudinal axis.

A method of verifying an article, comprising:

• illuminating with light a multilayer polymer fiber attached to the article;
• detecting a wavelength range of light in at least a first polarization state of light reflected or transmitted from the multilayer polymer fiber;
• and
• verifying an spectral fingerprint of the detected light;
• wherein the multilayered polymer fiber comprises an arrangement of substantially concentric layers comprises reflecting layers of at least a first polymer material and a second polymer material, layers of the first polymer material being disposed between layers of the second polymer material, at least one of the first and second polymer materials being birefringent;
• wherein thicknesses of the layers of the first polymer material and the layers of the second polymer material are selected so that the first multilayered polymer fiber reflects visible light within a selected portion of the visible spectrum in a first polarization state and incident perpendicular to a fiber longitudinal axis and transmits visible light in the first polarization state that lies outside the selected portion of the visible spectrum and incident perpendicular to the fiber longitudinal axis.