The anti-block additives are used to reduce blocking which is a common problem faced by manufacturers in the case of polyolefin films as well as coatings. An anti-block additive occurs in form of the resin which has a microscopic protrusion coming out from the surface of a film. The irregularities in the surface help in reducing the film-to-film surface contact which ultimately helps in increasing the gap between 2 layers and ultimately reduces blocking (Blong et al., 1989).
The anti-blocking efficiency of these anti-blocking additives majorly depends on the particle size as well as the shape of the additive being added along with the quality of dispersion and the gauge (thickness) of the film. The various additives for preventing blocking are calcined kaolin, cristobalite, precipitated silica as well as talc, along with diatomaceous earth, calcium carbonates, mica, calcium sulphate (anhydrite) along with magnesium carbonate (Fink, 2018) feldspars and magnesium sulphate.
Working of the anti-blocking additive:
The use of anti-block additive helps in reducing the film-to-film coefficient of friction as well as based on measuring the relative difficulty as per which one surface slides over the adjoining surface. Thus anti-blocking refers to describing measures for avoiding the film sheets from sticking together. Majorly these additives work on van der Waals interaction as well as electrostatic charges due to close contact between various films in case of adjacent layers. Thus the anti-blocking agents help in avoiding the adherence of various layers due to close proximity. Majorly particulate matter is put inside the film which is present in a much diluted concentration. This particulate matter creates a micro-rough surface and ultimately reduces the contact area between various layers of film (Sankar et al., 2017). Also, the distance between the layers is increased to a maximum limit with a subsequent reduction in the adherence capacity. But an important property for this is the type of mineral particulate matter being used and it must not alter the mechanical properties or any other intrinsic properties of the polymer.
These antiblocking additives are compatible with the various processes in film-processing such as extrusion and injection moulding. Majorly the various types of minerals that are used as anti-block additives are calcined kaolin as well as talc, cristobalite along with precipitated silica, calcium carbonates, diatomaceous earth, mica, and calcium sulphate which is in anhydrite form along with magnesium carbonate as well as magnesium sulphate along with feldspars.
Various types of antiblockingadditive:
The major classification for the anti-blocking additives are based on their origin is organic as well as inorganic anti-blocking additives.
- Inorganic anti-blocking additives: These anti-block additives are majorly non-migratory in nature and used in case of high-temperature applications. Also, these additives are used as they melt at much higher temperatures as compared to typical polyolefin extrusion temperatures (Maltby et al., 1999). The inorganic anti-blocking additives are cost-effective in nature along with the best positioning for comparatively large volume commodity-like applications.
- Organic anti-blocking additives: The organic anti-blocking, as well as anti-stick additives, are amides as well as fatty acid amides along with fatty acids. In addition to this, the salts of fatty acids and silicones serve as potential anti-blocking additives. Their mechanism of action is distinct from that of inorganic anti-blocking additives as they are migratory in nature and migrate to the outer film surface upon cooling which results in the formation of the release layer. But the organic anti-blocking additives have a lower anti-blocking ability as compared to inorganic anti-blocking additives whereas they have a better slip effect than the inorganic additives. Also, Organic antiblocking additives crystallize on the film surface which ultimately forms interfering layers between the adjacent film layers (Maltby et al., 1998). They are high clarity films as well as release applications such as use for rubber bales as well as sticky food items. They are more costly than inorganic additives along with possessing more utility in higher value-added applications.
Advantages of using anti-blocking additives:
- Theseadditives help in preventing the Prevention of film blocking during as well as after the processing process.
- It helps in optimizing the performance as well as the production process.
- It has a very narrow particle size distribution in comparison to other such products and high-efficiency anti-blocking activity (Van et al., 2000).
- These additives have high film clarity as well as low use levels.
- In addition to this, they offer positive effects on slipping solutions.
- These are homogeneous in nature and have a narrow particle distribution optimal for various films.
- Most of the additives are highly transparent and do not interfere with the intrinsic properties of film and no impact on product optical properties.
- These additives have a wide range of compatibility.
- They can be easily incorporated into the manufacturing of various products and films and show good performance at high temperature and thus show temperature resistance.
Applications of anti-blocking additives:
- They are used in manufacturing and providing anti-locking activity to rubber bales as well as sticky food items.
- Also, it is used in improving performance and used in process of fabrication as well as downstream packaging equipment.
- Also, it is used in polymer manufacturing by improving its end-use performance.
- It is used as an additive for water-based as well as solvent-based paints along with improving properties of external coatings by improving their stackability in the end products.
Frequently Asked Questions:
Q1: What are Anti-blocking additives?
Ans: The Anti-blocking additives are used as polymer additives which help in reducing the blocking at the polymer surface films as well as in the case of plastic products which ultimately helps in improving the processing as well as handling.
Q2: What is the difference between organic and inorganic polymers?
Ans: The inorganic anti-blocking additives show anti-blocking activity by decreasing the polymer to polymer contact as well as improves the micro-roughening of the surface. But the organic anti-blocking additives work by reducing the surface friction which ultimately helps the polymer surfaces to separate out easily.
Q3:What are the most commonly used anti-block agent?
Ans: Ethylene bisstearamide, Stearyl erucamide, glycerol monostearate, Zinc stearate, silicone PTFE, natural silicone in form of natural silicone, talc in form of magnesium Silicate, calcium carbonate, Aluminium silicate as well as Aluminium potassium silicate along with ceramic spheres, kaolin, clay and mica.
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