In the plastic processing and molding process, granules are produced by compounding the required additives and fillers with a small amount of carrier resin. These granules consist of three components: carrier resin, fillers, and various additives, with their performance and cost primarily determined by the carrier resin.

Masterbatch Overview

Filler masterbatch refers to a granular or powdered material produced by blending and compounding various additives and fillers with a small amount of carrier resin during plastic processing and molding, for the convenience of handling. This blended material is known as a masterbatch.

Filler masterbatches are composed of a carrier resin, fillers, and various additives. The levels of additives or the filler content in the masterbatch are typically several to more than ten times higher than the amounts required in the final plastic product. During molding and processing, the ratio of the masterbatch to the base resin must be adjusted based on the concentrations of the relevant components in the masterbatch and the quantities that need to be incorporated into the finished product. Masterbatches are generally classified into standard filler masterbatches (referred to as filler masterbatches) and functional masterbatches, such as color masterbatches and anti-fogging masterbatches. The primary component of filler masterbatches is filler, and they are mainly used in the processing and molding of polyolefins (polyethylene and polypropylene), hence the alternative name “polyolefin filler masterbatch.”

Raw and auxiliary materials

Polyolefin filler masterbatches consist of three main components: a carrier resin, fillers, and various additives, with fillers constituting the major portion—up to 90% by weight. These masterbatches are primarily used in the production of polyolefin plastics such as polyethylene and polypropylene, including hollow blow-molded polyethylene products, injection-molded polyethylene articles, polyethylene films, polypropylene woven bags, woven fabrics, and strapping tapes. When selecting raw and auxiliary materials for olefin filler masterbatches, it is generally important to prioritize good processing performance and low cost.

Filler

The primary filler used in polyolefin masterbatches is heavy calcium carbonate, followed by talc, kaolin, calcium powder, and other inorganic fillers. For any inorganic filler, particle size and particle-size distribution are critical technical parameters. Generally, the smaller the particle size and the narrower the distribution, the better the filling performance. In addition, filling efficiency is also influenced by dispersibility: the smaller the particles, the more difficult it is to achieve uniform dispersion, and the higher the cost. Purity is another important technical parameter for inorganic fillers; the lower the impurity content and the higher the purity, the better. When selecting heavy calcium carbonate, its content and whiteness should be as high as possible, typically requiring a minimum of 94%. Once all other specifications are met, the price should be kept low to help reduce the overall cost of the masterbatch.

Carrier resin

The performance and cost of polyolefin-filled masterbatches are primarily determined by the carrier resin; typically, the carrier resin content ranges from 10% to 20%, depending on the intended application of the masterbatch. The carrier resin used in polyolefin-filled masterbatches should exhibit good compatibility with the base plastic resin being filled. From this perspective, the carrier resin is generally selected as the same resin as the base matrix. In addition, when choosing a carrier for the masterbatch, its melting point and melt flow properties must also be taken into account; the melting point of the carrier resin must not exceed that of the base resin. Some companies still use LDPE (1F7B) as the carrier resin, mainly because this grade has a low melting point and a high melt flow rate (7 g/10 min). However, due to the higher melt temperature of polypropylene—typically 20 to 40°C higher than that of conventional polyethylene—its use in polyethylene-based formulations is limited. By contrast, random polypropylene or powdered polypropylene produced via the liquid-phase bulk polymerization process has a melting point no higher than 100°C, making it widely employed as the carrier resin in polyolefin-filled masterbatches.

Using LDPE (1F7B) as the carrier resin for polyolefin-filled masterbatches offers advantages such as a low melting point, high melt flow rate, and high melt strength; however, its major drawback is its high cost. If a lower-cost, lower-melt-flow low-density polyethylene resin—such as 1I2A-1 or 2F2B—is selected, its relatively low melt flow rate, typically around 2 g/10 min, necessitates the addition of more wax-based additives during processing to ensure better dispersion of the filler in the base resin. In general, fillers formulated with polyethylene as the carrier are most suitable for polyethylene plastic products, primarily because the carrier resin and the base resin have similar properties and exhibit excellent compatibility. For fillers used in polyethylene films, the requirements for the carrier resin are even more stringent.

For filler masterbatches used in polypropylene products, polypropylene is selected as the carrier resin. In theory, random polypropylene is preferable because it has a lower melting point, better melt flow, and superior dispersibility. However, given China’s specific national conditions, it is more appropriate to use powdered polypropylene synthesized via the liquid-phase bulk polymerization process, as it is cost-effective and, being in powder form, mixes very easily and uniformly with inorganic fillers—without layering even in the feeding hopper. When polypropylene is used as the carrier, its poor thermal stability necessitates the simultaneous addition of antioxidants and lubricants. To ensure that these additives, which account for only a few parts per thousand of the total resin content, are evenly distributed throughout the resin, the resin is first thoroughly blended with all the additives, and then compounded with the filler at a specified ratio before pelletizing.

To enhance versatility, polypropylene and polyethylene with similar melt indices can be blended in specific proportions to serve as the carrier resin. When used in combination with polyethylene, the masterbatch can further improve certain properties; when combined with polypropylene, it can increase elongation at break.

Recycled polystyrene is widely used in the manufacturing process of synthetic leather. Even when the compatibility between the carrier resin and the matrix resin is suboptimal, the impact of the carrier resin on the performance of plastic products is far less than that of fillers, resulting in significant economic benefits. When preparing filled masterbatches using other resins as carriers, a small amount of recycled polystyrene is often added to enhance the processing flowability of the masterbatch and its dispersion within the matrix resin.

Since the production cost of filler masterbatches is primarily determined by the carrier resin, and given that the carrier resin constitutes only a small fraction of the masterbatch, its impact on the performance of typical filled and modified plastic products is relatively minor. To reduce masterbatch costs, waste polyethylene, polypropylene, or edge and corner scrap from polyethylene–polypropylene composite films are often selected as the carrier resin.

Additive

The primary additives used in polyolefin-filled masterbatches are dispersants and surface modifiers. Dispersants enhance the processability of the masterbatch by improving its flow characteristics, thereby facilitating more uniform dispersion within the base resin. Commonly used dispersants include white oil (liquid paraffin), paraffin wax, dioctyl phthalate (DOP), low-molecular-weight polyethylene (polyethylene wax), and stearic acid. The selection of an appropriate dispersant should be based on the specific properties of the filler and the carrier resin. Surface modifiers alter the surface activity of inorganic fillers, converting their hydrophilic nature to lipophilic, which promotes better compatibility and mixing with the carrier resin; these typically include coupling agents and stearic acid. To further improve product dispersibility and gloss, additives such as EBS and flow modifiers may also be incorporated.

Processing technology

The processing technology and associated equipment for polyolefin-filled masterbatches evolve in tandem with continuous changes in the carrier resin.

The carrier resin used in the first-generation polyolefin-filled masterbatch (APP masterbatch) is domestically produced random polypropylene (which is, in fact, a byproduct of polypropylene production). The processing procedure consists of mixing, open-roll sheeting, and water-cooled pelletizing, and is carried out in a batch mode using a internal mixer, an open mill, and a flat-die pelletizer.

The second-generation polyolefin-filled masterbatch uses LDPE (1F7B) as the carrier resin; the resulting masterbatch is referred to as PEP masterbatch. To achieve optimal performance, this process must employ a specially designed single-screw extruder with a high length-to-diameter ratio and superior mixing capabilities.

Filler masterbatches using polypropylene powder as the carrier—known as PPM masterbatches—are regarded as China’s third-generation filler masterbatches. Typically, excellent performance is achieved by using a polypropylene–polyethylene blend as the carrier resin. Such products not only retain the distinctive characteristics and broad application scope of PPM masterbatches but also lend themselves to die-face hot-cutting with air cooling, thereby enhancing production efficiency and reducing raw-material costs.

The equipment used to produce filled masterbatches is a co-rotating twin-screw extruder. Its advantages include continuous production, stable product quality, high production efficiency, low energy consumption, reduced labor intensity for operators, and a favorable operating environment.

Filler masterbatches contain high concentrations of fillers and additives; therefore, a certain amount of base resin must be added during use, followed by compounding and subsequent processing into finished products. The primary function of the filler is to provide bulk. Fillers and additives can impart specific functionalities to plastic products, such as optical, electrical, flame-retardant, and biodegradable properties, and are thus referred to as functional filler masterbatches. Functional masterbatches typically include color masterbatches, photoconversion masterbatches, thermal-insulation film masterbatches, anti-fogging masterbatches, and biodegradable masterbatches, among others.

Color masterbatch is a specialized granular material used for coloring plastic products. Depending on the type of plastic being colored, it can be classified into polyolefin-based, ABS-based, PS-based, and AS-based types, among others. The production process of color masterbatch typically consists of two steps: first, preparing a pigment pre-dispersion by surface-treating the pigment with dispersants or other additives; second, melt-blending the pigment pre-dispersion with a carrier resin and then pelletizing to obtain the final color masterbatch. Color masterbatch is composed of pigments, dispersants, carrier resins, and appropriate amounts of additives. The primary function of the dispersant is to ensure thorough and uniform dispersion of the pigment within the carrier resin and the base resin, thereby producing plastic products with consistent coloration. The carrier resin used in color masterbatch should first exhibit good compatibility with the resin being colored; second, its flowability should exceed that of the resin being colored, so as to facilitate better pigment dispersion. The composition of the color masterbatch, as well as the selection and dosage of pigments, depend on the properties of the plastic being colored; typically, for color masterbatches used in coloring polyolefin plastics, the pigment content ranges from 20% to 40% by mass.

Application Fields

Filler masterbatches are suitable for processing plastic films, garbage bags, shopping bags, vest bags, packaging bags, and other applications. They exhibit excellent dispersibility, produce blown films free of white and black spots, and deliver high fineness, thereby ensuring superior gloss and toughness of the finished products. These masterbatches are primarily used for filler modification of woven bags, strapping tapes, hollow articles, pipes, sheets, injection-molded parts, and plastic fast-food containers, which can enhance the performance of plastic products while reducing production costs.

How to use

Simply mix this masterbatch uniformly with moistened plastic raw materials, and the finished products can then be processed and manufactured.

Used in blow-molding and drawing production, with an addition level of 1.0–3.0%.

Used in sheet and injection molding production, with an addition level of 2–5%.

The specific addition ratio may be adjusted by the user based on the degree of moisture absorption in the plastic.

Precautions

1. Avoid exposure to moisture before use; use the ingredients immediately after preparation.

2. Do not heat and dry together with damp plastics to avoid product quality defects.

3. Before opening the package, inspect it for integrity, and promptly reseal any unused masterbatch to maintain its freshness.

4. Do not allow the masterbatch packaging to be damaged or stored with the opening exposed; avoid direct sunlight and rain.

5. Prior to bulk procurement, a small-scale trial must be conducted to confirm that compatibility and other relevant parameters meet production requirements.