Antiblocking additives silica

Antiblock additives are often incorporated into packaging films to prevent them sticking together. Their effectiveness relates directly to the roughness they impart on a film surface while minimising loss in optical properties. They are often used in association with slip additives such as erucamide. Common antiblock additives include crystalline silica, diatomaceous earth and talc (magnesium silicate). 

Antiblocking agents, slip additives Silica, amide waxes, oleamide... 

The choice of antiblocking additive depends on the polymer, the desired film quality, and whether there is a pigment. Several inorganic substances are used, including synthetic amorphous precipitated silica, diatomaceous earths, nepheline syenite, calcined clay, coated calcium carbonate, magnesium carbonate, magnesium sulphate, mica, talc and various zeolites. Calcium carbonate particles are approximately spherical, but silica ones are irregular mica forms sheets and talc is plate-like. 

Typically, injection molding grades are used for masterbatches. One of the main masterbatches used in the polyolefins industry is LDPE-based silica masterbatches, since Si02 is used in film applications as an antiblocking additive. 

Fluorocarbon additives are added to polyolefins to prevent melt fracture during film extmsion. The efficiency of these additives depends on composition, especially in respect to fillers and antiblocking additives (e.g., diatomaceous earth, synthetic silica, and talc). Studies of antiblocking compounds with fluoro-... 

Masterbatching is one of the favored techniques, considering that not only quality of mixing with resin is important, but also proper and fast distribution of small amount of additive in usually very viscous material. Synthetic silica master-batch usually contains from 5 to 20 wt% of silica, but modified natural products such as talc, diatomaceous earth, or zeolites may constitute up to 50 wt% of mas-terbatch. The selection of concentration is usually determined by the effect of additive on the melt flow index. The concentration in masterbatch is also determined by the concentration of antiblocking additive in the final product, which varies widely depending on polymer and product type, from 500 to 5,000 ppm. 

Low density polyethylene, LDPE, containing erucamide and silica antiblocking, was analyzed for odor formation in food-contact applications. Cg unsaturated aldehydes are most likely to be produced in LDPE as a result of reactions involving polymer, erucamide, and silica antiblocking additive. The exact nature of these reactions is still under study. ... 

F igure 11.8. Effect of various antiblocking additives on melt fracture during extrusion of polyethylene tape. SS - synthetic silica, DE -diatomaceous earth, SCT - sUoxane coated talc. [Data from United States Patent 6,593,400, July 15,2003.]... 

Figure 11.11 summarizes the irrfluence of various antiblocking additives on the blocking force of polyethylene film. It is pertinent from the data that synthetic silica is the most efficient antiblocking additive, usually used in concentrations of up to 2,000 ppm. Talc, zeolites, and, not represented on the diagram, diatoma-ceous earth are usually used at concentrations of 5,000 ppm in order to give performance similar to silica. 

All three antiblocking additives included in Figure 11.12 have a similar influence on haze, but silica is usually used at lower concentrations, which means that some synthetic silicas are most useful in applications which require good optical properties. At the same time, talc manufacturers make extensive efforts to make their products more suitable for such applications. ... 

All three antiblocking additives included in Figure 11.12 have similar influence on haze, but silica is usually used at lower concentrations which means that... 

Polyethylenes are susceptible to oxidative degradation at processing temperatures, therefore antioxidants are added. Silica is sometimes added to LDPE as an antiblock to prevent films sticking and N,N-bis(2-hydroxyethyl)alkyl(C8-C18) amine (BEA) as an additive to reduce a build up of static charge (antistat). Table 10.2 gives commonly used substances in polyethylenes. 

When antiblocking agents are incorporated into PE films, other important properties of the polymer are also affected. These include an increase in stiffness, a decrease in the coefficient of friction, and an increase in haze. Interaction effects with processing aids can also result, especially with fluorocarbon elastomers that are added to prevent melt fracture in the blowing process of films. Worker exposure to dust generated by these additives can be hazardous if impurities such as crystalline silica or asbestos are present. 

Synthetic silica is another high-clarity antiblock, but as with DE, it has the highest hardness of these additives and thus can easily damage metal tool surfaces. It also tends to absorb slip agents and can be hard to disperse, and, like DE, it absorbs moisture and is expensive [7-20]. 

Several inorganic fillers/organic additives, such as silica, talc, kaolin, CaC03, titania, zeolites, cross-linked acrylic copolymers, spherical silicon beads, and so on, are employed in the plastics/coatings industry to attain the desired blocking performance. Some of these fillers are discussed elsewhere in this book in terms of their primary function only amorphous silica forms (natural and synthetic), used for antiblocking, will therefore be discussed in this chapter. 

Silicas, which are in competition with carbon blacks as functional fillers for plastics and rubbers, have one significant advantage their white color [62]. The most important role of silicas is as elastomer reinforcements, inducing an increase in the mechanical properties. Other functions, in addition to their use as antiblocks for PE, PP, and other films, are (a) to promote adhesion of rubber to brass-coated wires and textiles, (b) to enhance the thermal and electrical properties of plastics, (c) in accumulator separators, and (d) as rubber chemical carriers. 

Surface Property Modifiers with further division into a) solid lubricants/tribological additives that include molybdenite, graphite, PTFE and boron nitride and b) antiblocking fillers such as silica. Chapter 19. 

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