Antiblocking effect

Antiblocking, matting and texturing properties are obtained by introduction of irregularities. Particles, which are firmly embedded in the product, cause small elevations at the surface. Small amounts of Vinnolit pol5miers (K and C) produce matting and antiblocking effects. 

Two parameters, namely the particle size and the number of antiblock particles on the film surface, dominate the antiblocking effect, besides other factors such as type of film material. It has been shown that the higher the surface roughness (i.e., the more particles that there are on the surface) the better the antiblocking performance. 

An antiblocking effect in polymer films can apparently be attained by adding fine silica to the mixed monomers before polymerization. Hoppe and Behn claim that around 0.5% silica based on polymer gives a 50% reduction in adhesion (586). The nature of the film containing silica was examined by scanning electron microscope and it was found that the polymer around the particle protuberances was less soluble. Film separation was observed by Newton s rings in reflected light (587). 

Diatomaceous earth also influences optical properties of films such as haze and optical clarity. The abrasive nature of diatomaceous earth is another reason for its diminishing use. Abrasion of machine parts requires replacement, and it is a substantial part of expenditures. Finally, crystalline forms of silica, also present in diatomaceous earth, are considered to be dangerous for human health, which further decreases interest in its application. Section 12.11.3 contains comparison of the most important antiblocking agents from the point of view of optical properties, antiblocking effect, and health and safety. 

Kaolins are used in PET and polyolefins to provide a balance of antiblocking effect and clarity. Imerys is the supplier of these kaolins. 

The HDPE resin contributes antiblocking effect without resulting in a deterioration in the clarity, the gloss, the color, the appearance, or the mechanical strengths of the film. HDPE should have a specific gravity greater than 0.940 and a narrow molecular weight distribution." ... 

While pure erucamide does not exhibit absorption in the 250-280 nm range all commercial products showed UV absorption maxima at 230, 257, 267 and 278 nm (with variable intensities), indicative of the presence of oxidation products (up to 8 wt%) as impurities with chromophoric groups. Colourless impurities do not have an interference effect. 1JV/VIS was also used to evaluate discoloration of 50wt/wt% mixtures of commercial erucamide and inorganic antiblock agents [59]. Apart from the interference by impurities from solvents chemical methods suffer from lengthy procedures. 

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). 

The optimal quantity of additive formulated into the resin varies with the type of polymer, the specific additive and its desired effect. For example, the amount of antiblock additives can be as high as several percent for some applications. ("Blocking" may be defined as the tendency of sheets of polyethylene film to "stick" together.) However, in most cases, the quantities of additives needed to achieve its function are in the range of 0.05 to 1% (500 to 10,000 ppm). 

Whereas bis(stearoyl)ethylenediamine (EBS), generally known as amide wax, shows an unusually high melting point of 140°C and has a good balance of internal and external lubricating properties for PVC, the fatty acid monoamides, more particularly oleamide, stearylamide, and erucamide show a pronounced external effect. They are more particularly used as lubricants, mould release and antiblocking agents in polyolefins. 

The presence of stabilizer has little effect on poly (vinyl chloride) carboxylation (Table VIII). Since the other polymers were also subjected to the carboxylation process without removing commercial additives such as antioxidants, UV and thermal stabilizers, antiblocking agents, etc.—the additives inhibit neither the polymerization of the styrene-maleic anhydride complex nor the grafting reaction. 

Antiblock Agent. Antiblocking is the prevention of the adhesion of two plastic films in contact with one another. This effect can be achieved by incorporating fine silica particles in the surface of the film. The relatively low refractive index of silica makes the particles less easy to see. 

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. 

Slip, antislip, and antiblock agents [30, 31] do not facilitate molding or semifinished product manufacture as do lubricants. What they do is to simplify further processing - of foils in particular. Foil bags that have been stored in stacks cannot be readily picked up or opened, problems that are particularly noted with LDPE and PP. An effective slip agent with LDPE is addition of 0.05 % oleic acid amide and with PP the same amount of eruca acid amide. Additive manufacturers supply concentrates of these compounds in granulate form for addition to molding compounds [50]. 

Chem. Descrip. Micronized PTFE-modified polyethylene wax Uses Surf, modifier for a variety of baking and air-dry coating and ink applies., plastics, esp. for food-contact coatings provides exc. slip, water-repelling props. improves scratch/scuff/abrasion resist., antiblocking props. enhances meat release effective in polyesters, acrylics, epoxies, PU, alkyds, PVC... 

Uses Surf, conditioner, mar resist, aid, scuff resist, aid, abrasion resist, aid, antiblocking agent, slip agent for coatings, plastic clear coats, inks, overprint varnishes Features Very little effect on gloss... 

Blocking is a surface effect between adjacent film layers that stick to one another. Blocking is quantified by the force needed to separate two film layers under controlled conditions. Two situations where blocking is an issue are the opening of blown film tubes after extrusion and film layer separation after packing and storage. Antiblock additives are used to overcome these issues. 

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