Non-chemical thermally printable film

Abstract

A two-layer mono-axially oriented film includes a first layer of an opaque beta-nucleated microvoided propylene-based polymer; and a second layer containing a dark pigment that is adapted for use in a thermal printer in which the thermal print-head contacts the exposed surface of the first layer. The dark pigment of the second layer pigment has a color contrasting with the color of the first layer and can contain a carbon black. The first layer includes microvoids and may be made transparent upon the application of heat by collapsing the voids of the first layer or upon the application of ultra-sonic energy.

What is claimed is: 
     
         1 . A multilayer film comprising at least a two-layer film comprising: a first layer comprising an opaque beta-nucleated polypropylene-based polymer; and a second layer comprising a dark pigment; wherein the multilayer film forms an image without using an ink or a dye. 
     
     
         2 . The multilayer film of  claim 1 , wherein the dark pigment of the second layer pigment has a color contrasting with the color of the first layer. 
     
     
         3 . The multilayer film of  claim 1 , wherein the first layer comprises a propylene-based polymer and an amount of a beta-nucleating agent or beta-nucleated propylene polymer. 
     
     
         4 . The multilayer film of  claim 3 , wherein the second layer comprises a propylene-based polymer and an amount of carbon black pigment in propylene-based polymer carrier resin. 
     
     
         5 . The multilayer film of  claim 1 , wherein the dark pigment of the second layer comprises a carbon black. 
     
     
         6 . The multilayer film of  claim 1 , wherein the first layer comprises micro-voids. 
     
     
         7 . The multilayer film of  claim 1 , wherein the first layer comprises a beta nucleating agent selected from the group consisting of pimelic acid supported on nano-CaCO.sub.3; amides of dicarboxylic acid including N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide and aryl dicarboxylic acid amide, two-component beta nucleating agents of organic dibasic acids selected from the group consisting of pimelic acid, azelaic acid, o-phthalic acid, terephthalic acid and isophthalic acid; oxide, hydroxide, or acid salts of Group II metals; gamma-crystalline forms of quinacridone colorants; aluminum salt of 6-quinizarin sulfonic acid; and bisodium salt of o-phthalic acid. 
     
     
         8 . The multilayer film of  claim 1 , wherein the first layer can be made transparent upon the application of heat by collapsing the voids in said first layer. 
     
     
         9 . The multilayer film of  claim 1 , wherein the first layer can be made transparent upon the application of ultrasonic energy. 
     
     
         10 . The multilayer film of  claim 1 , wherein the first layer comprises a transparent dye. 
     
     
         11 . The multilayer film of  claim 10 , wherein the second layer comprises a transparent dye that is of a different hue or color than that of the first layer. 
     
     
         12 . An imageable multilayer film comprising:
 a polypropylene first layer that is clear or comprises a pigment or colorant; and   an image-side tie layer comprising a cavitating agent.   
     
     
         13 . The multilayer film of  claim 12 , wherein colorants, pigments, and opacifying agents are substantially absent from the image-side tie layer. 
     
     
         14 . The multilayer film of  claim 12 , wherein the image-side tie layer has contacted to within the range of from 0.1% to 15% of its original thickness upon collapse of the voids created by the cavitating agent in the areas where an image is effected. 
     
     
         15 . The multilayer film of  claim 12 , wherein the image-side tie layer comprises a material having a density in the range of 0.9 g/cm 3  to 1.13 g/cm 3 , a DSC melting point in the range of 40° C. to 165° C., and a melt flow rate in the range of 1.6 dg/min to 4 dg/min. 
     
     
         16 . The multilayer film of  claim 12 , wherein the film is treated with a device that imparts selective physical or thermal treatment to the image-side of the multi-layer film to affect an image. 
     
     
         17 . The multilayer film of  claim 12 , wherein the multilayer film is biaxially oriented. 
     
     
         18 . A method of forming an image on a multilayer film comprising the steps of:
 co-extruding at least a first layer, and an image-side tie layer;   orienting the multilayer film in at least one direction; and   imparting selective physical or thermal treatment to the image-side of the multilayer film to effect an image thereon.   
     
     
         19 . The method of  claim 18 , wherein the first layer comprises a colorant or pigment. 
     
     
         20 . The method of  claim 18 , wherein colorants, pigments, and opacifying agents are substantially absent from the image-side tie layer. 
     
     
         21 . The method of  claim 18 , wherein a colored coating or metal coating is placed on the multilayered film surface opposite the image-side tie layer. 
     
     
         22 . The method of  claim 18 , wherein the imparting causes the image-side tie layer to contract within the range of from 0.1% to 15% of its original thickness upon collapse of the voids created by the cavitating agent in the areas where an image is effected.