Additive for invisible flexographic inks

A method of manufacturing an ink additive for enhancing the stability and color change properties of water-based flexographic ink, comprising:

• solubilizing at least two binders in distilled water by
• (i) mixing distilled water at low speed with a wetting agent, antibacterial agent and propylene glycol to form a first mixture,
• (ii) adding a first binder to the first mixture at low speed and mixing until solubilized to form a first binder mixture, and
• (iii) adding a second binder to the first binder mixture at low speed and increasing the speed until the first and second binders are fully solubilized to form a binder mix;
• adding a color developer activator to the binder mix at high speed to form a color developer activator/binder mix mixture, and passing the color developer activator/binder mix mixture through a wet micronizer machine to achieve a particle size with a mean of about 1 micron to about 3 microns, to form a binder mix with micronized color developer activator;
• and
• adding a wax emulsion and dispersant to the binder mix with micronized color developer activator.

An improved invisible ink that displays color in response to heat, comprising:

• a first ink combined with a second ink and an ink additive;
• the first ink comprising a color developer activator without a color former leuco dye in an amount of from about 30% to about 40% by weight of the first ink, a binder in an amount of from about 2% to about 15% by weight of the first ink, one or more components selected from the group consisting of a dispersant and a wetting agent, the one or more components being present in an amount of from about 1% to about 5% by weight of the first ink, the remainder of the first ink being water;
• the second ink comprising a color former leuco dye without a color developer activator in an amount of from about 30% to about 40% by weight of the second ink, a binder in an amount of from about 2% to about 15% by weight of the second ink, one or more components selected from the group consisting of a grind aid, a dispersant and a defoamer, the one or more components being present in an amount of from about 1% to about 5% by weight of the second ink, the remainder of the second ink being water;
• and
• the ink additive comprising a color developer activator in an amount from about 5% to about 25% by weight of the ink additive, an antibacterial agent in an amount from about 0.009% to about 2% by weight of the ink additive, a wetting and grinding agent in an amount from about 0.01% to about 2% by weight of the ink additive, a first binder in an amount from about 1% to about 5% by weight of the ink additive, a second binder in an amount from about 0.35% to about 2% by weight of the ink additive;
• a wetting agent and evaporation retardant in an amount from about 3% to about 10% by weight of the ink additive, a wax emulsion and dispersant in an amount from about 3% to about 10% by weight of the ink additive, and distilled water in an amount from about 50% to about 90% by weight of the ink additive.

A method of preparing an improved invisible ink that displays color in response to heat, comprising:

• preparing a first ink comprising a color developer activator without a color former leuco dye in an amount of from about 30% to about 40% by weight of the first ink, a first ink binder in an amount of from about 2% to about 15% by weight of the first ink, one or more components selected from the group consisting of a dispersant and a wetting agent, the one or more components being present in an amount of from about 1% to about 5% by weight of the first ink, the remainder of the first ink being water;
• preparing a second ink comprising a color former leuco dye without a second ink color developer activator in an amount of from about 30% to about 40% by weight of the second ink, a second ink binder in an amount of from about 2% to about 15% by weight of the second ink, one or more components selected from the group consisting of a grind aid, a dispersant and a defoamer, the one or more components being present in an amount of from about 1% to about 5% by weight of the second ink, the remainder of the second ink being water;
• preparing an ink additive comprising a color developer activator, an antibacterial agent, a wetting and grinding agent, a first binder, a second binder, a wetting agent and evaporation retardant, and distilled water;
• and
• combining the first ink, the second ink and the ink additive prior to color development.

An improved invisible ink product, comprising:

• a print medium upon which an improved invisible ink has been applied;
• the improved invisible ink comprising a first ink combined with a second ink and an ink additive;
• the first ink comprising a color developer activator without a color former leuco dye in an amount of from about 30% to about 40% by weight of the first ink, a binder in an amount of from about 2% to about 15% by weight of the first ink, one or more components selected from the group consisting of a dispersant and a wetting agent, the one or more components being present in an amount of from about 1% to about 5% by weight of the first ink, the remainder of the first ink being water;
• the second ink comprising a color former leuco dye without a color developer activator in an amount of from about 30% to about 40% by weight of the second ink, a binder in an amount of from about 2% to about 15% by weight of the second ink, one or more components selected from the group consisting of a grind aid, a dispersant and a defoamer, the one or more components being present in an amount of from about 1% to about 5% by weight of the second ink, the remainder of the second ink being water;
• the ink additive comprising a color developer activator in an amount from about 5% to about 25% by weight of the ink additive, an antibacterial agent in an amount from about 0.009% to about 2% by weight of the ink additive, a wetting and grinding agent in an amount from about 0.01% to about 2% by weight of the ink additive, a first binder in an amount from about 1% to about 5% by weight of the ink additive, a second binder in an amount from about 0.35% to about 2% by weight of the ink additive, a wetting agent and evaporation retardant in an amount from about 3% to about 10% by weight of the ink additive, a wax emulsion and dispersant in an amount from about 3% to about 10% by weight of the ink additive, and distilled water in an amount from about 50% to about 90% by weight of the ink additive;
• and
• wherein heat generated by rubbing and/or scratching the improved invisible ink on the print medium activates the color former leuco dye and activator to change the color on the printing medium.

An improved invisible ink scratch pad, comprising:

• a plurality of sheets of paper arranged in a stack;
• each sheet of paper having a top surface and a bottom surface;
• the bottom surface of each sheet having an adhesive applied to at least a portion thereof to releasably secure the sheets of paper to the stack;
• the top surface of each sheet having an improved invisible ink applied thereto, the improved invisible ink comprising a color developer activator, a color former leuco dye and an ink additive;
• wherein the ink additive comprises a color developer in an amount from about 5% to about 25% by weight, an antibacterial agent in an amount from about 0.009% to about 2% by weight, a wetting and grinding agent in an amount from about 0.01% to about 2% by weight, a first binder in an amount from about 1% to about 5% by weight, a second binder in an amount from about 0.35% to about 2% by weight, a wetting agent and evaporation retardant in an amount from about 3% to about 10% by weight, a wax emulsion and dispersant in an amount from about 3% to about 10% by weight, and distilled water in an amount from about 50% to about 90% by weight, and
• wherein heat generated by rubbing and/or scratching the invisible ink on the top surface of one of the sheets activates the color former leuco dye and activator to change the color on the sheet.