Five Carrier Selection Principles That Must Be Followed in Masterbatch Formula Design

In the process of using color masterbatch, the biggest difficulty is how to properly add it to the material. The two main factors are the carrier resin used to produce the color masterbatch and its molecular weight, and they often cannot be purchased from the color masterbatch. The company can decide.

Therefore, masterbatch companies need to consider the impact of the selection of carrier resin on later sales and applications when designing formulas.

The amount of color masterbatch added to the final resin is generally 2%-5%. If the color masterbatch is mixed and added correctly, the content of the carrier resin in the final mixture will account for 1%-3% or more. This makes it the most abundant additive in the additive family, so some details should be paid attention to when selecting the carrier resin. For example, users' requirements for color, color stability, environmental requirements, and the role of masterbatch in the final product, etc., make the formulation of masterbatch increasingly complex.

Masterbatch generally chooses the same resin as the product resin as the carrier. The two have the best compatibility. However, in complex cases, the fluidity of the carrier and the pigment dispersion and mixing and distribution after selecting this carrier must also be considered. , only by uniformly balancing these complex characteristics can the most suitable masterbatch formula be obtained.

Specifically, the five major principles for carrier selection in masterbatch formulations are compatibility, fluidity, processability, high viscosity, and applicability.

Compatibility

The so-called compatibility refers to the ability of two substances to accommodate each other. According to the principle of similarity and compatibility, the masterbatch carrier resin and the colored resin have the same or similar structure. Its compatibility is good. Under normal circumstances, the same type of polymer should be selected for the masterbatch carrier resin and the matrix resin of the product, in order to ensure that the carrier resin and matrix resin have good chemical compatibility.

For example, AS resin can be used as the carrier of ABS masterbatch, and PBT can be used as the carrier of PET masterbatch. However, if the same type of resins are incompatible, it will affect the quality of the colored products. For example, although polyethylene and polypropylene are both olefins, there is no problem in using polyethylene as the carrier of masterbatch for injection molding, film blowing and other products, but Using polyethylene carrier color masterbatch for polypropylene spinning will affect the spinnability. When used for high-brightness injection molding products, there will be flow marks on the product. It also shows that although polyethylene and polypropylene are both olefin resins, the two resins The compatibility is not very good.

Even the universal color masterbatch that uses polyethylene wax as a carrier will inevitably have defects when faced with engineering plastics, and the surface is prone to "peeling". Therefore, the existing market size of universal masterbatch is far from reaching the expected goal.

Fluidity

The so-called fluidity means that the fluidity of the masterbatch carrier resin itself is better, and the carrier melt flow rate is higher than that of the colored resin. If the same polymer as the plastic that needs to be colored is used as the carrier, its molecular weight should be lower than the colored plastic (i.e. The melt flow rate of the carrier is greater than the melt flow rate of the plastic to be colored). In this way, the high melt flow rate masterbatch can more easily flow ideally in the coloring screw and be dispersed more easily in a large amount of resin.

However, this method often has drawbacks. After all, the connection between melt index and molecular weight cannot be ignored at any time. In the final analysis, the molecular weight determines the performance of the resin, and the carrier resin with high melt flow rate may not be easily processed during final processing. It will lead to a decrease in product performance, especially the coloring of engineering plastics. If you choose a carrier resin with a molecular weight similar to that of the resin to be colored, you can use an appropriate amount of lubricant to improve the fluidity of the overall masterbatch, that is, to increase the melt index of the masterbatch; otherwise, low molecular weight resins are prone to degradation. What's more, it will seriously affect the appearance of the product.

However, sometimes, in some colored products, it is clearly required that dispersants are not allowed to be added to the masterbatch. At this time, it is even more important to choose a suitable carrier resin.

High viscosity

High resin viscosity and good fluidity may be a contradiction. However, if the melt viscosity of the carrier resin is high, the shear viscosity of the system will also be high. The shear force transmitted from the molten resin to the pigment particles will be greater, which is beneficial to the pigment particles. of dispersion. Therefore, how to unify contradictions requires comprehensive consideration in carrier selection.

For example, the molecular structure of conventional LLDPE is characterized by its linear main chain with few or no long branches, but it contains short branches and the absence of long branches makes the polymer more crystalline. Under the same molecular weight, the melt viscosity of LLDPE with linear structure is higher than that of LDPE with non-linear structure. Under the same melt flow rate, the melt viscosity of LDPE is also significantly lower than that of LLDPE. Therefore, it is not surprising that high melt flow rate linear low density polyethylene (LLDPE) is chosen to be used or partially used as a carrier for polyolefin masterbatch.

Processability

The so-called processability refers to meeting the production process requirements. Many practical experiences and statistical results show that the final dispersion properties obtained by using powdered resin for production are better than using granular resin. An obvious difference is that the powdered resin can quickly complete the melting process in the equipment due to its small particle size, which means that the pigment particles can be infiltrated relatively early and enter the wetting and dispersing process. At the same time, the mixing uniformity between the powders is also extremely high, which also effectively increases the wetting speed.

In order to improve the quality of masterbatch, masterbatch manufacturers need to take into account the morphological differences of different carrier resins when formulating. However, not all resin products on the market are supplied in powder form. At the same time, masterbatch manufacturers should prepare their own grinding equipment. If necessary, part or all of the resin used can be ground into powder before being used in the production of masterbatch. , in order to improve and ensure the quality of products.

Applicability

Applicability means that the carrier needs to meet the production needs of customers and the needs of the product, without affecting the surface and internal quality of the product. When masterbatch is used for plastic coloring, improper use of carriers should not affect the mechanical properties of plastic products. For example, when selecting masterbatches for degradable plastic products, avoid using masterbatches that use non-degradable materials as carriers to prevent them from affecting the determination of the properties of the degradable products.

For example, the PPR pipe masterbatch uses LLDPE as the carrier resin, which has good compatibility with PPR. However, the high melt index of LLDPE means that the molecular weight is too low and cannot withstand the pressure of hot water; the HDPE carrier resin also has good compatibility with PPR. But the heat resistance time is very short.

Resins for spray-free plastics also need to pay attention to this problem. The more transparent the resin, the better the silver effect of the product. For example, with the same silver addition, the effect of transparent ABS is more vivid than that of PP. In addition, the carrier and material are required to have high fluidity, low thermal stability and low volatile content. Too high a melt viscosity will be detrimental to the movement of metallic pigments and affect dispersion, and too low a melt viscosity will have weak shear properties. , the dispersion and distribution of the pigment will also become worse.

All in all, when designing the masterbatch formula, it is necessary to fully consider the performance of the target matrix resin and select an appropriate carrier resin. Masterbatch manufacturers can design different masterbatch carrier formulas according to whether the product processing process is injection molding or extrusion, the flow of the matrix resin, the final use conditions of the product, etc.

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