In many packaging applications, it is useful to be able to modify the behavior of materials that come in contact with one another. For example, blocking in a roll of the film decreases our ability to unwind and use it. If a plastic part tends to stick to the mold, the molding process will be slower and less efficient. Friction between plastic and the barrel of the extruder is desirable. But friction between the plastic and the screw inside the barrel is not. In this section, we will discuss various additives that, in one way or another, modify these behaviors.

Anti-blocking agents additives

Blocking is the tendency of two adjacent layers of a material, such as a polymer film, to stick to each other by simple physical contact. It is particularly a concern for polyolefins such as PE and PP, soft PVC films, and PET. Blocking tends to increase with increasing temperature and pressure. The degree to which a film is susceptible to blocking is mainly determined by the smoothness of the surfaces; the smoother the surface, the greater is the degree of intimate physical contact, and therefore the greater the blocking. To reduce blocking, the smoothness of the surfaces may be reduced by incorporating tiny particulates into the polymer. These anti-blocking agents produce irregularities on the film surface, which reduce the amount of contact between the layers of material.

In films packaging

In packaging films, synthetic or natural silica and minerals are common anti-blocking agents. Performance is affected by both the shape and size of the particles. As a rule, finer particle sizes are used in thin films and larger particle sizes in thicker materials. The preferred average particle size for anti-blocking agents in LDPE and PP films is 6 to 20% of the film thickness.

Synthetic silicas such as “micronized” silica gel, fumed silica, and zeolites are often used in high-quality packaging films. While naturally occurring silica and minerals such as clay, diatomaceous earth, talc, and quartz predominate in lower-quality materials. Diatomaceous earth is a compact, granular, or amorphous mineral composed of hydrated silica formed of fossil diatoms. Talc is a soft mineral of fine colloid particles with a soapy feel, made of hydrated magnesium silicate, 4SiO2–3MgO–H2O. Talc has some advantages over diatomaceous earth as an anti-lock for PE films. It includes platelet morphology, particle size distribution, and the possibility of being coated to make it more compatible with PE. Levels used typically range between 0.1 and 0.5% of the resin weight.

In PE films

When anti-blocking 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 a 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.

Slip agents additives

Slip agents are related to anti-blocking agents, but instead of decreasing surface contact, they reduce blocking by introducing a thin, low-friction coating between the plastic materials. These additives are usually mixed into the polymer film but have a strong tendency to migrate to the film surface (“bloom”), where they perform their function. Slip agents are often used in polyolefin films. Common choices are oleic acid amide for polyethylene and erucamide for polypropylene.

Combinations of a slip and an anti-blocking agent can improve performance through the more rapid development of slip properties and more efficient use of the anti-lock; in both cases, this is the result of improved dispersion of the additives. These agents are commonly added to a resin in the form of a multicomponent masterbatch which also includes other additives. The amounts of anti-lock in the masterbatch commonly range from 5 to 50%.

Antislip agents additives

While blocking is a concern in many applications, at other times, there is a need to increase blocking. For example, a common problem in stacking plastic sacks is a tendency for the sacks to slide off one another. An antislip agent can be used to combat that problem by increasing friction between the surfaces, or by increasing the attractions between nearby surfaces. Common antislip agents include ethylene/maleic anhydride copolymers, colloidal silica, and finely powdered sand or other minerals. These agents may be compounded into the plastic or sprayed on surfaces. The particle sizes are generally less than 1 micron, and concentrations of the agents are usually under one percent by weight.

Lubricants additives

Lubricants are materials that promote flow and reduce the tendency of plastics to stick to surfaces. Slip agents, and mold release agents, can be regarded as examples of special types of lubricants. These materials can be used to promote the flow of plastics over or through surfaces of dies, mold cavities, and so on. Common lubricants include fatty-acid esters and amides, paraffin and polyethylene waxes, stearates, and silicones. These and other lubricants can be compounded into the plastic resin or applied externally.

In the flexible PVC film, waxes and low molecular weight polyethylene are often used as external lubricants, and fatty acids, esters, and metallic soaps are often used as internal lubricants. As the names suggest, external additives, including lubricants, are applied to the surface of the film or other plastic articles. While internal lubricants are blended into the polymer before it is formed.

Mold release agents additives

Mold release agents are often used to facilitate the removal of plastic parts from molds by acting to decrease the adhesion between the plastic and the mold. These additives may be sprayed or otherwise applied to the mold surfaces, as an alternative to, or in combination with, compounding the additives into the resin. These agents may be liquids that provide lubrication, such as those mentioned previously, or maybe fine solids such as dusting powder.

Fillplas has additives materials. Please kindly contact us for more information.