Coloring of rubber productsMethods
The coloring methods of rubber products mainly include surface coloring and mixture coloring
1. Surface coloring
The colorant is sprayed onto the surface of rubber products to color the rubber products.
This method has a certain effect on static products. For dynamic products, the colorant is easy to peel off and fade.
2. Mixed coloring
It is currently the main method for rubber coloring, divided into two types: solution method and mixing method.
The mixing methods include dry powder coloring, color paste coloring, pellet coloring and masterbatch coloring.
Solution coloring
This method is to dissolve the rubber into a solution of a certain concentration with its good solvent, then add the colorant and rubber compounding agents except sulfur into the solution, stir and mix evenly, dry at a certain temperature to remove the solvent, and finally in Add sulfur to the rubber mixing machine. This coloring method is complex to operate, the colorants and compounding agents are unevenly dispersed, there is color difference, the solvent is difficult to recover, and it pollutes the environment. It is rarely used now.
Coloring by mixing method
This method is currently the most commonly used method for coloring rubber products. It is to add the colorant directly or mix it with the carrier first and then add it to the rubber compound, and mix it evenly through the rubber mixer to color the rubber. The specific methods are as follows:
(1) Dry powder coloring
This method is to directly add the powdery colorant together with the small materials into the rubber and mix it on the open mill. The advantages of this method are simple operation and low cost, but the dust during mixing is large, pollutes the environment, is not easy to disperse evenly, and has color difference. If the particles are too hard and too thick, it will also cause quality problems such as color spots, stripes or mutual contamination of the chromatogram. It is rarely used now.
For ease of use, powdered colorants can be combined with stearic acid, sulfate, etc. to make pre-dispersed colorants, which are already on the market.
(2) Color paste coloring
This method is to first mix the colorant with a liquid compounding agent (such as a plasticizer), grind it with a three-roller machine to form a paste or slurry, and then add it to the rubber in a certain proportion for mixing.
This method can avoid dust flying, and also helps the colorant disperse in the rubber and make the color uniform. However, the colorant content in the color paste is low, the coloring is not high, the transportation volume is large, the loss is large, and it is inconvenient for users to use.
(3) Pellets coloring
There are two main methods for preparing colorant pellets.
The first method is the same as other powdery compounding granulation methods. The powdery colorant is first soaked with surfactant, and then melted with wax or melted with resin and extruded for granulation;
The second method is to infiltrate the colorant with surfactant and then use mechanical force to refine the colorant particles to make a dispersion of a certain concentration, then mix it with latex and co-precipitate, dry and roll into sheets Granulation. Among them, surfactants are mostly anionic and nonionic, such as fatty acid salts, sulfonates, etc., and latex is usually natural latex.
This granular colorant is easy to use, has good dispersion, no flying dust, does not pollute the environment, has bright color, uniform color development, and no color difference. It is a promising coloring method. However, the preparation process of granular colorants is complex and the cost is high, which limits its wide application.
(4) Masterbatch coloring
This method is to first mix the colorant, some plasticizers and other 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 rubber in proportion. Medium coloring.
This method is more effective for coloring fine-particle, difficult-to-disperse colorants, with uniform color development and no color difference. When mixing, pay attention to the concentration of the colorant in the masterbatch and deduct the amount of other compounding agents in the masterbatch.
Concerning the selection of pigments, the selection of appropriate color pigments depends on the processing requirements previously described and the end use of the product, with the latter being more important. The following factors must be considered:
Anti-fading ability, caused by factors such as sunlight, heat or natural aging;
Resistance to bleeding and harmful effects on the aging properties of the base compound�Taste.
Sulfur red is an expensive pigment with superior performance. It is mostly used in mixed pigments, and is only used to obtain a special color.
Different salts of naphthol red can form different colors of light, such as orange red, blue red, etc. Similar to Permanent Red 2B, it is an expensive pigment.
Lisol Royal Red, Golden Red C and Lisol Red are all lower cost pigments. These 3 pigments have been used extensively in the past. Their technical properties are relatively poor. As people increasingly emphasize the quality and service life of rubber products, these three pigments are used less and less.
Organic orange pigment
There are 2 main types of organic orange pigments: dianisidine and benzidine orange.
Dianisidine can form a clean reddish shade, while benzidine orange can form a bright, clean yellow shade. They both have good non-fading properties, among which benzidine orange has better light fastness. some.
Phthalocyanine blue
It is the preferred pigment for blue rubber products. There are many kinds of light, among which red light (RS) is the most used in rubber. At the same time, its thermal stability is also the worst, so the vulcanization temperature must be considered when using this phthalocyanine blue.
The intensity of green light phthalocyanine blue is quite weak, but its thermal stability is very good, and it is more expensive than other grades. Phthalocyanine blue pigments are difficult to disperse and should be used in rubber color master mix form or color paste form.
Phthalocyanine green
This pigment can produce several colors of light, including slightly yellowish green light and slightly bluish green light. Although many green rubber products are made from a mixture of yellow, blue or green, phthalocyanine green is the most widely used single color pigment in green products.
All shades of Phthalocyanine Green have good technical properties and are difficult to disperse. It is recommended to use the master mix method, whose properties are similar to those of other colors.
In fact, very few rubber products are made from one type of pigment, whether inorganic or organic. The final color of a rubber product is matched to a specific color approved by the buyer or seller of the product. Therefore, color matching becomes a major requirement in successful rubber product production. Moreover, colored products are related to fashion, and merchants or buyers are always asking for new colors.
In short, inorganic pigments can provide rubber compounds with good heat resistance, light resistance and bleeding resistance at low cost. These colorants are mostly used as powder pigments and produce shades that are not very bright and clean.
For brighter, cleaner colors, organic pigments are necessary. They have stronger coloring ability, but the thermal stability, light resistance and bleeding resistance of organic pigments are not as good as those of inorganic pigments, and they are more expensive to use. Generally speaking, organic pigments are difficult to disperse in rubber compounds and are dusty when applied. In fact, they are usually used as rubber color master mixtures.
