Coloring method of rubber products

Coloring method of rubber products

The coloring methods of rubber products mainly include surface coloring and compound coloring

1. Surface coloring

It is to spray the colorant on the surface of the rubber product to color the rubber product.

This method has a certain effect on static products, but on dynamic products, the colorant is easy to peel off and fade.

2. Mixed coloring

It is the main method of rubber coloring at present, there are two kinds of solution method and mixing method.

The mixing method includes several methods such as 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 coloring agent and rubber compounding agents except sulfur to the solution, stir and mix evenly, dry at a certain temperature to remove the solvent, and finally in the Add sulfur to the rubber mixing machine. This kind of coloring method is complicated to operate, the colorant and compounding agent are dispersed unevenly, there is color difference, the solvent is difficult to recycle, and it pollutes the environment. It has been seldom used at present.

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 first mix it with the carrier and then add it to the rubber material, and mix it evenly through the rubber mixer to make the rubber color. The specific method is as follows:

(1) Dry powder coloring

This method is to directly add the powdery coloring agent together with the small material into the rubber, and mix it on the open mill. The advantages of this method are simple operation and low cost, but the dust is large during mixing, polluting the environment, and it is not easy to disperse evenly, and there is color difference. If the particles are too hard and too thick, it will also cause quality problems such as color points, streaks, or mutual pollution of chromatograms. Currently less used.

For ease of use, powdered colorants can be made into pre-dispersed colorants together with stearic acid, sulfate, etc., which have been sold in the market.

(2) Color paste coloring

This method is to first mix the coloring agent with a liquid compounding agent (such as a plasticizer), grind it with a three-roller machine to make a paste or slurry, and then add it to the rubber in a certain proportion for mixing.

This method can avoid flying dust, and is also conducive to the dispersion of the colorant in the rubber, and the color is uniform. However, the content of colorant in the color paste is low, the coloring is not high, the transportation volume is large, the loss is large, and the user is inconvenient to use.

（3）Pellet coloring

There are two main methods of preparing colorant pellets.

The first method is the same as other powder compounding agent granulation methods. Firstly, the powder colorant is infiltrated with surfactant, then melted with wax or extruded with resin, and then granulated;

The second method is to infiltrate the colorant with a surfactant, and then use mechanical force to refine the colorant particles to make a dispersion with a certain concentration, then mix it with latex for co-precipitation, and roll it after drying Granulate. Among them, the surfactants are mostly anionic and nonionic, such as fatty acid salts, sulfonates, etc., and the latex is usually natural latex.

This granular coloring agent is easy to use, good in dispersibility, free from dust, does not pollute the environment, bright in color, uniform in color, and free of color difference. It is a promising coloring method. However, the preparation process of granular colorants is complicated and the cost is high, which limits their wide application.

(4) Masterbatch coloring

This method is to mix the colorant, some plasticizers and other rubber compounding ingredients with the raw rubber through an open mill to make a colorant masterbatch with a concentration of about 50%, and then add it to the rubber in proportion. medium coloring.

This method is more effective for coloring the colorants with fine particles and difficult to disperse, with uniform color development and no color difference. When compounding, pay attention to the concentration of the colorant in the masterbatch and deduct the amount of other compounding agents in the masterbatch.

With regard to the selection of pigments and pigments, the selection of appropriate and suitable color pigments depends on the previously described processing requirements and the end use of the product, of which the latter is more important. The following factors must be considered:

Fade resistance, caused by factors such as sunlight, heat or natural aging;

Resistance to bleed and detrimental effect on the aging properties of the base compound, avoid copper orRed is a kind of pigment with superior performance but expensive price. It is mostly used in mixing pigments, and it is only used when obtaining special shades.

Different salts of naphthol red can form orange red, blue red and other different shades of light. Similar to Permanent Red 2B, it is an expensive pigment.

Lithor Red, Golden Crimson C, and Lithor Scarlet are all lower cost pigments. These 3 pigments have been used in large quantities in the past. Their technical characteristics are relatively poor, and as people pay more and more attention to the quality and service life of rubber products, these 3 pigments are used less and less.

Organic orange pigment

There are 2 main types of organic orange pigments: dianisidine and benzidine orange.

Dianisidine gives a clean reddish shade and Benzidine Orange gives a bright, clean yellow shade, both of which have very good color fastness properties, with Benzidine Orange having the best light fastness some.

Phthalo blue

It is the preferred colorant for blue rubber products. There are many shades, among which the red shade (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.

Green Light Phthalocyanine Blue is fairly weak in strength, but very thermally stable and more expensive than other grades. Phthalocyanine blue pigments are difficult to disperse and should be used in the form of rubber master mixes or color pastes.

Phthalo green

This pigment can produce several shades, a yellowish green shade, a bluish green shade. Although many green rubber products are made with a mixture of yellow, blue or green, phthalocyanine green is the most widely used single-species color pigment in green products.

All shades of phthalocyanine green have good technical properties and are difficult to disperse. The masterbatch method is recommended and its properties are similar to those of other colors.

In fact, very few rubber products are made from a single pigment, either 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 the successful production of rubber products. Moreover, colored products are related to fashion, and merchants or buyers always ask for new colors.

In summary, 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 the shades produced are not too bright and clean.

For brighter, cleaner colors, organic pigments must be used. They have stronger coloring ability, but the thermal stability, light resistance and bleeding resistance of organic pigments are not as good as inorganic pigments, and they are more expensive to use. Generally speaking, organic pigments are difficult to disperse in rubber compounds, and they are more dusty when applied. In fact, they are usually used as rubber color matrix mixtures.