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Comparison of the Advantages and Disadvantages of Four Commonly Used Plastic Colorants, the Secrets that Colorists Need to Master

April 26,2022

Colorants are mainly divided into two types: pigments and dyes. Pigments are colorants that cannot be dissolved in common solvents, so to obtain ideal coloring properties, it is necessary to uniformly disperse the pigments in the plastic by mechanical methods. Dye is an organic compound that can be used in most solvents and dyed plastics. It has the advantages of low density, high tinting strength and good transparency, but its general molecular structure is small and it is easy to migrate during coloring.

Today, I will take you to understand the advantages and disadvantages of 4 kinds of plastic colorants, so as to better select and use different colorants in production.

There are four types of plastic colorants, according to their physical form:

Powdered colorants – toners;

Solid colorant – masterbatch;

Paste colorants – colorants;

Liquid colorants – color oils;

In the coloring of the plastics industry, toners and masterbatches are relatively widely used.

Toner Coloring

The method of coloring plastic particles directly with toner (pigments or dyes) and adding appropriate amount of powder additives, also known as dry coloring.

01. Advantage
1. Good dispersion;

2. Suitable for small batch plastic processing;

3. The cost is low, which saves the consumption of manpower and material resources in the processing of color masterbatch and color paste.

02. Shortcoming
1. Flying dust pollution, pigments will fly during transportation, storage, weighing and mixing, resulting in pollution and seriously affecting the working environment;

2. The hopper of the extruder is not easy to clean, and the toner used for coloring adheres to the inner wall of the barrel (and even the screw) under the action of wetting agents such as white oil. When the material needs to be changed, cleaning the barrel becomes a difficult problem for the on-site operator;

3. Film blowing and spinning products are not practical, and color powder is used for coloring. Since the pigment powder is evenly distributed in the resin to be colored, its dispersibility is good. This conclusion can only be applied to injection molding products, especially thick-walled products. In other words, it is another matter for blown film and spinning products. Because the toner is generally not pretreated, when it is mixed with the resin, it is only necessary to make the pigment powder by the distance from the extruder feed port, screw, to the discharge port and such a short plasticizing mixing time. The molecules of the pigment and the pigment molecules to be colored go hand in hand very well – full combination is completely impossible, and there will be a phenomenon of “inclusion”. However, this “cracked” phenomenon will be masked in thick-walled products, and it is obvious in blown film and spinning products. Therefore, the coloring method of the latter is still dominate d by color masterbatch.

Masterbatch Coloring

Using a certain process and corresponding equipment, under the action of additives, the pigment (or dye) is mixed into the carrier, and finally the molecules of the pigment powder and the molecules of the carrier resin are fully combined by heating, plasticizing, stirring and shearing. up, and then made into pellets similar in size to resin pellets.
01. Advantage

1. Improve the environmental pollution caused by flying toner;

2. It is easy to change the color during use, and it is not necessary to carry out special cleaning on the extruder hopper;

3. Strong pertinence, simple color matching, and easy quantification;

4. Compared with batch resin dry dyeing and granulation before making plastic parts, the use of color masterbatch can reduce the resin performance aging caused by secondary processing of plastic products, which is beneficial to the improvement of the service life of plastic products;

5. In the process of processing, under the action of additives, the color masterbatch is fully mixed with the carrier resin. When in use, it is placed in the resin to be processed according to a certain proportion, and the compatibility is obviously better than that of toner coloring.

02. Shortcoming

1. The dispersibility is poor. Due to the small amount of addition, the processing time of plastic products is short. Due to the limitation of the length-diameter ratio ofthe extruder screw, the dispersibility of the color masterbatch is often not as good as that of the toner;

2. The cost is high, and there is one more manufacturing process, and the cost of dyeing is higher than that of toner coloring;

3. The performance requirements of the color masterbatch are high. When the performances of the carrier in the masterbatch and the resin to be colored are different, undispersed spots, stains and patterns often appear on the surface of the plastic product. Therefore, the use of the masterbatch is due to its phase. Capacitance and dispersion are limited.

Color Paste

Color paste is a semi-finished product made of pigments and fillers dispersed in the paint. According to the classification, it can be divided into paint color paste, tape color paste, papermaking color paste, textile color paste, mechanical color paste, toy color paste, latex product color paste, etc.

01. Advantage

1. It is easy to use and can be directly used in the processing process for forming and sheet coloring;

2. Generally, it has good high temperature resistance, convenient storage and no precipitation;

3. It can reduce the problem of dust pollution in the use of toner, and can also solve the lack of compatibility and dispersibility of color masterbatch;

4. The color paste is easy to control the input amount in use, reduce the color difference, and improve the tinting strength and color brightness;

5. The environmental protection type meets the requirements of EU REACH and other regulations.

02. Shortcoming

1. At present, the biggest restriction on the development of color paste is the production process of domestic color paste. High-quality color paste has higher requirements on process and raw material quality, and its cost will be higher than that of color masterbatch and toner;

2. When the addition amount is large, the screw may slip;

3. When stored for a long time, precipitation will occur, and it is better to stir before use.

Color Oil

Color oil is a liquid pigment concentrate without a resin carrier. At present, color oil is mainly used on bottle embryos in my country.

01. Advantage

1. Low addition ratio, usually 0.1-0.5% for transparent series, 0.3-3.0% for pearlescent/solid color series;
2. Excellent dispersibility, more uniform color, brighter color, higher gloss of the product; stable color, reduce coloring defects;

3. The material only undergoes a high temperature process, keeping the physical properties of the raw resin unaffected;

4, the best inventory management, only need a small space to complete the storage of color oil. Compared with color masterbatch, it saves three-quarters of storage space. Reduce overall inventory and working capital pressure;

5. The color oil adding equipment is simple, the cost is low, the color changing process is simple and fast, the freedom of production scheduling is improved, and the labor time, machine and energy consumption are saved;

6. Applicable to all polyolefins (such as PP/PE), polystyrene resin (PS), PET resin and other engineering resins.

02. Shortcoming

1. Do not add antistatic agent to the color oil, so that the product cannot be dustproof on the shelf or in storage;

2. The shelf life of color oil products is shorter than that of color masterbatch products;

3. The color oil needs special color oil adding equipment, that is, the color oil metering pump can supply the color oil to the injection molding machine to produce the product of the desired color.

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