There are two coloring methods for silicone rubber products: surface coloring and mixing coloring.Surface coloring refers to spraying colorant on the surface of the product to make it colored.The act for liquid products, colorants are easy to fall off and fade, solid products have a certain effect.Mixing method is the main method of silicon rubber coloring at present, which is divided into liquid phase method and mixing method.Another method of mixing is dry powder dyeing, color paste dyeing, granule dyeing and base glue dyeing.
1. Solution staining method
The method is to dissolve silicone rubber and other solvents into a solution of a certain concentration, then add the colorant and devulcanizing agent complex to the solution, stir and mix uniformly, dry and remove the solvent at a certain temperature, and finally add the vulcanizing agent to the rubber mixer . The dyeing method is complicated to operate, uneven distribution of dyes and compounding agents, bright colors, difficult to recycle solvents, and environmental pollution, so it is rarely used at present.
2. Mixing and coloring
This method is currently the most commonly used method for coloring silicone rubber products, that is, adding the coloring agent directly or mixing with the carrier and then mixing with the rubber compound, and mixing and coloring uniformly through a rubber mixer.
There are four specific methods:
a. Dry powder dyeing
In this method, the powder colorant and the small materials are directly added to the silicone rubber for mixing on an open mill. The method is simple to operate and low in cost, but the dust during mixing is large, pollutes the environment, and is not easy to be dispersed and uniform, the color is not good, the particles are too coarse, and it can also cause quality problems such as color dots, streaks, and mutual contamination of chromatograms. use. For convenient use, the powder colorant can be mixed with stearic acid, sulfate, etc. to make a pre-dispersed colorant and sell it on the market.
b. Dyeing of color paste
In this method, the coloring agent is mixed with a liquid compounding agent (such as a plasticizer) first, and then made into a paste or slurry through three-roll grinding, and then added to the silicone rubber in a certain proportion for mixing. This not only avoids the flying of dust, but also facilitates the dispersion and uniformity of the colorant in the silicone rubber. But the colorant content in the color paste is low, the coloring rate is not high, the conveying volume is large, the loss is large, and the user is inconvenient to use.
c. Pellet coloring method
There are two main methods for preparing colorant pellets. As with other powdery compounding agent granulation methods, the first method is to infiltrate the powdery colorant surfactant first, then melt it with wax or melt it with resin to extrude into granulation. The second method is to infiltrate the colorant surfactant, and then use mechanical force to refine the colorant particles to make a dispersion with a certain concentration, and then co-precipitate with the emulsion, and then flaked into granules after drying. Among these substances, surfactants are mainly anionic and non-ionic, such as fatty acid salts, sulfonates, etc., and natural rubber latex is usually used. This product is easy to use, high dispersion, no dust, no pollution, bright color, uniform color development, and no color difference. It is a promising coloring method. However, the preparation process of the granular pigment is complicated and the cost is high, which limits its application.
d. Masterbatch coloring
The method is to first mix the colorant, part of the plasticizer and other silicone rubber compounding agents with the raw rubber through an open mill to make a colorant masterbatch with a concentration of about 50%, and then mix it into the silicone rubber in proportion. Coloring. This method has a good coloring effect for dyes with fine particles and difficult to disperse, with uniform color development and no color difference. Pay attention to the concentration of the colorant in the masterbatch when adding, and deduct the amount of other complexes when adding.
