The coloring methods of rubber grommets mainly include surface coloring and coloring of the mixture. The surface coloring is to spray the coloring agent onto the surface of the rubber grommets to color the rubber product. The method has a certain effect on static grommets. For dynamic products, the colorant is easily peeled off and easily fades. Mixing coloring is currently the main method of rubber coloring, divided into two methods: solution method and mixing method. Among them, the mixing method has several methods such as dry powder coloring, color paste coloring, pellet coloring and masterbatch coloring.

1. Solution Coloring

The method is to dissolve the rubber into a certain concentration of the solution, and then add the coloring agent and the rubber compounding agent other than sulfur to the solution, stir and mix uniformly, dry and remove the solvent at a certain temperature, and then add on the rubber mixing machine. Sulfur. The coloring method is complicated in operation, the coloring agent and the compounding agent are unevenly dispersed, the color difference is poor, the solvent is difficult to be recycled, and the environment is polluted, which has been less used at present.

2. Mixing Method Coloring

This method is currently the most commonly used method for coloring rubber grommets. The coloring agent is added directly or mixed with the carrier and then added to the rubber compound, and evenly mixed by the rubber mixing machine to color the rubber grommets. The specific method is as follows.

(1) Dry powder coloring This method directly adds the powdery coloring agent to the rubber together with the small material, and kneads it on the open mill. The method has the advantages of simple operation and low cost, but the dust is large during the mixing, pollutes the environment, and is not easy to disperse uniformly, and has a color difference. If the particles are too thick and too thick, the quality problems such as color point, stripe or chromatogram may be caused to be contaminated. It has been used less frequently. For ease of use, powdered colorants can be prepared as pre-dispersed colorants together with stearic acid, sulfates, and the like, and are commercially available.

(2) Color paste coloring method is to first mix the coloring agent with a liquid compounding agent (such as a plasticizer), grind it into a paste or a slurry by a three-roller machine, and then add it to the rubber in a certain proportion. Mixing. This method can avoid dust flying, and is also beneficial for the colorant to be dispersed in the rubber grommets and the color is uniform. However, the content of the coloring agent in the color paste is low, the coloring is not high, the transportation amount is large, the loss is large, and the user is inconvenient to use.

(3) There are two main methods for preparing the pellet coloring agent pellets. The first method is the same as other powder compounding granulation methods, in which the powdery coloring agent is first impregnated with a surfactant, and then waxed or melted and extruded with a resin to be granulated; the second method is to use a coloring agent. After the surfactant is infiltrated, the colorant particles are refined by mechanical force to form a dispersion of a certain concentration, and then mixed with the latex, and dried and then granulated. Most of the surfactants are anionic and nonionic, such as fatty acid salts, sulfonates, etc., and latex is usually a natural latex. The granular coloring agent is convenient to use, has good dispersibility, no dust flying, does not pollute the environment, has bright color, uniform hair color and no color difference, and is a promising coloring method. However, the preparation process of the granular coloring agent is complicated and the cost is limited, which limits its wide application.

(4) Masterbatch coloring This method is to mix the coloring agent, part of the plasticizer and other rubber compounding agent with the raw rubber by an open mill to prepare a colorant masterbatch with a concentration of about 50%, and then scale. Coloring is added to rubber grommets. This method is effective for coloring fine particles and difficult to disperse colorants, and has uniform color development and no color difference. Pay attention to the concentration of the colorant in the masterbatch and the amount of other compounding agents in the masterbatch.

Reprinted from：https://rubber-grommet.com/color-rubber-grommets-manufacturing-method/