How to design colored toothpaste? Why can't colors mix together? Why can toothpaste squeeze out colored stripes? I had the same problem before. Later, I bought a toothpaste and cut it with a knife. I see a partition inside. That is to say, there is a partition in the toothpaste of two colors, which is equivalent to two toothpastes, but there is no partition in the mouth of the toothpaste, so it will be a beautiful and smooth toothpaste color, and three colors are three partitions. Cut a toothpaste and you will understand. Inside the toothpaste are four small bags filled with toothpaste of different colors. The small bags are all the same length, stuck together side by side, and the tail end is fixed at the tail end of the toothpaste tube. The openings of the small bags are fixed together and attached to the openings of the toothpaste skin. So a striped toothpaste is actually four small toothpastes with different colors. Wrap it in a toothpaste bag outside.

Toothpaste is a Bingham fluid, a non-Newtonian fluid and usually a viscoplastic material. Under low stress, it behaves as a rigid body, but under high stress, it will flow like a viscous fluid, and its fluidity is linear. That is, toothpaste can be fixed without force. The color strips of toothpaste are all pastes composed of polymers, and polymer pastes are incompatible. In addition, toothpaste manufacturers usually wrap dyes with polyethylene to make the colored paste more stable.

There is already a colored grid in the nozzle for pouring toothpaste. For example, there is red paste imported and blue paste imported, so the colors have been divided in the toothpaste pipeline. At the same time, because toothpaste itself is a non-Newtonian fluid and has a solid-liquid network thickener, the paste mixed with pigment in advance will not easily penetrate into another paste that is evenly mixed. Of course, if the formula of this toothpaste is not good, it is too solubilized, or the thickener of this toothpaste is too weak, it will lead to the mutual penetration of two colors of paste. So sometimes you will see that the boundary between the two colors is blurred when some color stripes are extruded.