Analysis of The Reasons for Poor Color Dispersion After Using Color Masterbatch

Masterbatch is the most common plastic coloring method and is widely used in the plastic processing industry. Dispersion is one of the most important performance indicators of masterbatch. So, what is the dispersion of masterbatch?

Dispersion refers to the uniform dispersion of masterbatch in plastic materials. Whether it is injection molding products, extrusion or film blowing processes, if the dispersion is not good, the final product may show uneven color distribution, irregular lines of varying depths, or quality abnormalities such as pinhole-shaped powder spots.

Obviously, dispersion has a vital impact on the quality of plastic products. So, what are the reasons for poor color dispersion?

Poor dispersion of color powder

Color masterbatch is a highly concentrated pigment aggregate. A large amount of powder aggregated together will inevitably affect the dispersion of the color masterbatch. Many color powders have particularly strong agglomeration properties, such as the most common titanium dioxide and carbon black, which are extremely easy to clump together. According to the customer's final product and process, choosing the appropriate color powder type and the appropriate particle size of the color powder has an important impact on the final dispersion of the color masterbatch.

Static electricity effect

Many masterbatches do not contain antistatic additives. When using masterbatches, customers often mix the masterbatches and raw materials together, which can easily generate static electricity, causing uneven distribution when the masterbatches are mixed with the raw materials, resulting in inconsistent colors before and after the product.

The melt index of the masterbatch is not suitable

Usually, when selecting a carrier, the masterbatch supplier will choose a resin with a higher melt index as the carrier. However, it is not the higher the melt index is, the better it is. It is necessary to fully consider the physical properties of the final product, the surface requirements and the good processability of the masterbatch. A too low melt index can easily cause poor dispersion of the masterbatch in the product. The melt index of the masterbatch needs to take into account the conditions of the carrier and the powder. Designing a suitable melt index is of great help to the dispersion of the masterbatch.

The addition ratio of masterbatch is too low

Considering the physical properties of the final product and the total cost of the coloring solution, some masterbatch suppliers will design a lower masterbatch addition ratio, resulting in poor dispersion of the masterbatch in the finished product.

Inappropriate dispersion system of masterbatch

In order to break up the agglomerated powder in the masterbatch, some dispersants and lubricants are added during the masterbatch processing to assist in the dispersion of the powder in the masterbatch. If the dispersant is not selected appropriately, the masterbatch will inevitably have poor dispersion.

Influence of Masterbatch Density

Density-rich colorants are often added to masterbatch. For example, in order to achieve a strong hiding power of the masterbatch, a large amount of titanium dioxide is added. The density of titanium dioxide is about 4.0g/cm³ (3.8g/cm³~4.4g/cm³), which is greater than the density of many resins. Therefore, the density of the masterbatch may be quite different from the density of the resin. When mixing, the masterbatch is more likely to settle at the bottom of the mixer, resulting in inconsistent color before and after the product.

Improper selection of carrier for masterbatch

The carrier of masterbatch is used to carry color powder and other functional additives. The type, quantity, model, melting index and even form of the carrier will greatly affect the processability and dispersibility of the masterbatch. For example, for masterbatch used in polyolefin products, whether the carrier is PP, PE or EVA, whether it is a single carrier or a mixture of several carriers, which brand, how much melting index is selected, whether it is powder or granular, etc., will affect the final performance of the masterbatch.

Masterbatch processing

The masterbatch processing is a combination of multiple processes. What kind of mixing equipment should be selected? How to design the mixing process? What kind of granulation equipment should be selected? What kind of screw combination should be selected? What kind of granulation process should be selected? Even what kind of cooling process should be selected will affect the final performance of the masterbatch.

Influence of process

The plastic molding process has a certain influence on the dispersion of masterbatch. As far as the injection molding process is concerned, temperature, pressure and holding time will affect the dispersion of masterbatch.

Influence of equipment

Plastic molding equipment will also have a certain impact on the dispersion of masterbatch. For example, if the screw is severely worn, the shear force will be greatly reduced, which will weaken the dispersion of masterbatch.

Influence of molds

For injection molding, mold structures such as the location of the mold inlet will have a certain impact on the molding of the product and the dispersion of the masterbatch. For extruders, the flow channel structure and slope of the mold will affect the dispersion of the product.

The temperature setting of extrusion, etc., will also have a certain impact on the dispersion of the final product. In many cases, the dispersion problem is not a simple material problem or process problem. It may require all relevant parties to work together to analyze the problem, find the problem, and finally eliminate the problem.

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