Colored paper with controlled tint penetration

Abstract

A premium colored paper having high contrast suitable for high-end packaging applications is produced through a controlled penetration of a coloring formulation through the paper. The paper is coated on a first side with a first coloring formulation. Then, a second coloring formulation is applied to a second side (i.e. opposite side) of the paper such that the coloring agent in the second coloring formulation penetrates through the paper sheet but does not significantly interfere with the color or brightness of the first coated side of paper. When desired, the first coloring formulation may be applied on the paper on-line during papermaking process.

1 . A method of producing a colored paper-based product, comprising steps of:
 (a) providing a paper-based substrate having a first side and a second side;   (b) coating the first side of the substrate with a first coloring formulation to afford a whiteness L* value of L1; and   (c) coating the second side of the substrate having a whiteness L* value of L2 with a second coloring formulation to provide the colored paper-based product characterized by a whiteness L* value of the coated first side of L3 and a whiteness L* value of the coated second side of L4,   wherein L1 is no more than 8 points higher than L3 and L2 is at least 30 points higher than L4, and the whiteness L* value is determined using CIE L*a*b* color specification having D65 Illuminant lamp and at 10 degree observer.   
     
     
         2 . (canceled) 
     
     
         3 . The method of  claim 1 , wherein L1 is no more than 3 points higher than the L3. 
     
     
         4 . The method of  claim 1 , wherein L2 is at least 40 points higher than L4. 
     
     
         5 . (canceled) 
     
     
         6 . (canceled) 
     
     
         7 . The method of  claim 1 , wherein the second coloring formulation comprises a second coloring agent, and a color intensity of the second coloring agent in the colored paper-based product decreases gradually from the second coated side to the first coated side. 
     
     
         8 . The method of  claim 1 , wherein the second coloring formulation comprises a coloring agent that colors from about 10% to about 100% of a thickness of the colored paper-based product. 
     
     
         9 . The method of  claim 1 , wherein the first coloring formulation includes a clay-based coating. 
     
     
         10 . The method of  claim 1 , wherein the first coloring formulation is applied onto the substrate during a papermaking process. 
     
     
         11 . The method of  claim 1 , wherein the second coloring formulation comprises, based on the formulation weight:
 ( 11 .a) from about 1% to about 10% by weight of a coloring agent; and   ( 11 .b) from about 1% to about 5% by weight of a surfactant.   
     
     
         12 . The method of  claim 11 , wherein the second coloring formulation comprises, based on the formulation weight:
 ( 12 .a) from about 1% to about 10% by weight of the coloring component, and   ( 12 .b) from about 0.1% to about 3% by weight of the surfactant.   
     
     
         13 . The method of  claim 11 , wherein the second coloring formulation is absence of a binder. 
     
     
         14 . A colored paper-based product obtained from a process comprising steps of:
 (a) providing a paper-based substrate having a first side and a second side;   (b) coating the first side of the substrate with a first coloring formulation to afford a whiteness L* value of L1; and   (c) coating the second side of the substrate having a whiteness L* value of L2 with a second coloring formulation, wherein   (i) the coated first side of the product has a whiteness L* value of L3 and the coated second side has a whiteness L* value of L4,   (ii) L1 is no more than 8 points higher than L3 and L2 is at least 30 points higher than L4, and the whiteness L values are determined by CIE L*a*b* color specification having D65 Illuminant lamp and at 10 degree observer.   
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . The product of  claim 14 , characterized by an increase in Parker Smoothness value of no more than 1 point after an application of the second coloring formulation in step (c). 
     
     
         18 . The product of  claim 14 , characterized by an increase in caliper value of no more than 1 point after an application of the second coloring formulation in step (c). 
     
     
         19 . The product of  claim 14 , wherein the second coloring formulation comprises a second coloring agent, and the product further characterized by a gradual decrease in an color intensity of the second coloring agent from the second coated side to the first coated side. 
     
     
         20 . The product of  claim 14 , wherein the second coloring formulation comprises a second coloring agent, and the product further characterized by from about 10% to about 100% of its thickness being colored by the second coloring agent. 
     
     
         21 . The product of  claim 14 , wherein the first coloring formulation includes a clay-based coating. 
     
     
         22 . The product of  claim 14 , wherein the first coloring formulation is applied onto the substrate during a papermaking process. 
     
     
         23 . The product of  claim 14 , wherein the second coloring formulation includes a black coloring agent. 
     
     
         24 . The product of  claim 14 , wherein the second coloring formulation comprises, based on the formulation weight:
 ( 24 .a) from about 1% to about 10% by weight of a coloring agent; and   ( 24 .b) from about 1% to about 5% by weight of a surfactant.   
     
     
         25 . The product of  claim 24 , wherein the second coloring formulation is absence of a binder.