- April 01, 2003, David J. Bentley Jr., RBS Technologies
Anyone who has been in the converting business and uses adhesives and coatings has — at some time or another — asked (or heard someone else ask) the question, “Can we add color to our adhesive or coating?” The immediate and easy answer is yes. In fact, a colored adhesive or coating is an ink. Obviously, inks find use in the converting industry daily for a multitude of applications.
Let's think about the basic qualities of ink for a moment. They provide a wide variety of colors; that is their primary claim to fame. A second factor is that inks are also coatings. They are coated onto a substrate so the material has the color of that ink. A third factor is that inks are also adhesives. An ink coated onto a substrate that doesn't adhere to that substrate certainly is not going to be a very effective ink.
If inks inherently are adhesives and coatings, we noted above we can color adhesives and coatings, at least theoretically. Inks contain pigments and dyes that give them their ability to act as colorants. We can add pigments and dyes to adhesives and coatings, too. We probably could make them any color we wished.
The only trick would be to use the necessary amount of the proper blend of pigments and dyes. Voilà, we have a colored adhesive or coating!
Or do we? Looking at the material, we can see it has the color we desire, but does it still maintain the desirable properties of the initial adhesive or coating?
It probably does not, because the amounts of pigment or dye we needed to add were so excessive, they essentially negated the characteristics of the original adhesive or coating.
Consider for example a pressure-sensitive adhesive. If we added titanium dioxide or some other pigment in large enough quantities to obtain a white color, the titanium dioxide would act as an inert filler that would decrease the tack and adhesion properties of the p-s material.
The same phenomenon would occur with a heat seal adhesive. To make a colored heat seal adhesive, we would need to add sufficient pigment to provide the desired color. Again this addition would detract from the ability of the finished adhesive to perform properly. Because of the level of pigment necessary, attempts to seal the adhesive with heat would fail because the actual amount of adhesive present would be considerably less.
The point is that someone indeed can add pigments and dyes to an adhesive or coating. They will mix in well and provide a material that probably has an attractive color. However, doing so will change the properties and performance of the adhesive or coating drastically, to such an extent that it will no longer function as originally intended.
One instance where coloring an adhesive or coating is possible might be tinting. Some converters have done this for identification purposes. A small quantity of a soluble dye at a level that does not detract from the final properties of the adhesive or coating can provide a tinted material. This might be useful to indicate the presence of the material when coated onto a substrate, to differentiate it from another adhesive or coating, etc.
Anyone attempting this definitely should test the tinted product to ensure the addition of the dye does not change the properties of the adhesive or coating. At the small levels necessary for tinting, probably no change will occur. Nevertheless, one should be safe rather than sorry.
For those applications in the converting industry that require color, use an ink. Rarely add coloring agents to adhesives or coatings to provide color. Use the adhesives and coatings to provide the adhesion, cohesion, slip, COF, etc., designed into them.
David J. Bentley Jr. is a recognized industry expert in polymers, laminations, and coatings with more than 30 years of experience in R&D and technical service. Contact him at firstname.lastname@example.org.