Antiblocking additives diatomaceous earth

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 are additives that inhibit the stickiness (blocking) of polymer surfaces. Blocking is most apparent in films, particularly blown films. After a blown film bubble has passed through the nip roller and the two halves have been pressed together, they may tend to block. Antiblocks help the film to be easily pulled apart. Diatomaceous earth is a commonly used antiblock additive. 

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. 

Additives used in final products Antistatics carbon black, copper complex of polyacrylic add, ethoxylated amines, fatty diethanol amines, glycerol monostearate, graphite, ionomer, lauric diethanolamide, polyethylene glycol, quaternary ammonium compound, trineoalkoxy zirconate Antiblocking diatomaceous earth, natural silica, slloxane spheres, synthetic silica, talc, zeolite Blowing agents Release stearyl erucamide Slip erucamide, ethylene bisoleamide, oleamide Process aid Thermal stibullzers UV stabilizers ... 

Additives used in final products Fillers carbon black, china clay, fly ash, mica, nano-calcium carbonate, nano-magnesium hydroxide, zinc oxide Plasticizers chlorinated paraffins, dioctyl sebacate, dibuthyl phthalate, dioctyl phthalate, paraffinic, aromatic, or naphthenic mineral oils, polyisobutylene Antiblocking diatomaceous earth Release liquid polybutadiene Slip erucamide+stearamide ... 

Additives used in final products Fillers antimony trioxide, aramid, barium sulfate, boron nitride, calcinated kaolin, carbon black, carbon fiber, glass fiber, glass spheres, mica, montmorillonite, talc, titanium dioxide, zinc borate Antistatics antimony-doped tin oxide, carbon nanotubes, polyaniline, polyisonaphthalene Antiblocking calcium carbonate, diatomaceous earth, silicone fluid, spherical silicone resin, synthetic silica Release calcium stearate, fluorine compounds, glycerol bistearate, pentaerythritol ester, silane modified silica, zinc stearate Slip spherical silica, silicone oil ... 

Additives used in final products Fillers barium and strontium ferrites, boron carbide, calcinated clays, calcium carbonate, carbon black, carbon-silica dual phase filler, clays, dolomite, fumed silica, iron oxide, magnesium aluminum silicate, magnesium carbonate, mica, montmorillonite, nickel zinc ferrite, nylon fibers, pulverized polyurethane foam, quartz, silica carbide, soapstone, talc, zinc oxide Plasticizers naphthenic oil, polybutene, aromatic oil, esters of dicarboxylic acid Plasticizers adipates, aromatic mineral oil, paraffin oil, phosphates, phthalates, polyethylene glycol, processing oil, sebacates Antistatics dIhydrogen phosphate of 8-amlnocaprolc add. Iodine doping Antistatics carbon black, quaternary ammonium salt, zinc oxide whisker Antiblocking diatomaceous earth Release propylene wax Slip erucamide+stearamide ... 

Additives used in final products Plasticizers polyethylene glycol, polypropylene glycol, partial fatty ester, glucose monoester, citrate, adipate and azelate esters, epoxidized soybean oil, acetylated coconut oil, linseed oil, acetyl tributyl citrate, glycerol triacetate, glycerol tripropionate Antistatics ethoxylated fatty amines, polyethylene glycol ester, quaternary ammonium salt Antiblocking diatomaceous earth, talc Slip erucamide ... 

About one third of all minerals belong to the silicate class, but only three types of natural silica are in popular use, and these are included in the table above. Diatomaceous earth is one of the most frequently used antiblocking agents. Its range of applications has recently decreased, when it was discovered that diatomaceous earth absorbs process additives used in extrusion. 

The most relevant drawback in talc applications is caused by its absorption of polymer process additive. This is a subject of intensive research and patent activity. The treated talc inhibits the adsorption of plastic film additives onto the talc. Surface treating means coating, partial coating, or using an effective amount of modifier to inhibit the adsorption of other additives. A functionalized polydialkyl, preferably polydimethylsiloxane is used for surface treatment. Bis-(12-hydroxystearate) terminated polydimethylsiloxane, is a preferred agent used for the surface treatment of talc (but can also be used in conjunction with other antiblocking agents, such as, diatomaceous earth, calcium carbonate, and synthetic silica). 

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. 

Figure 10.8. Blocking force of LLDPE containing 5,000 ppm of antiblocking additives (DE = diatomaceous earth) vs. temperature. [Data from Radosta, J. A. Deutsch, D. R. Drummond, D. K., AddCon Asia 97, International Plastics Additives and Modifiers Conference, Singapore, Oct. 28-29,1997, paper 18,1-6.]...

Adhesion of ink to LDPE film containing erucamide is very poor even after corona treatment (Figure 10.44). Modification of erucamide into a more polar compound (better compatibility with a polar corona treated surface) improves adhesion (Figure 10.45). The antiblocking force and coefficient of friction typical of N-(2-hydroxyethyl) erucamide may be further reduced by addition of 1,500 diatomaceous earth. Combination of 2,000 ppm N-(2-hydroxyethyl) erucamide and 1,500 ppm diatomaceous earth satisfies the requirement of printed film. 

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 11.8 shows the influence of several antiblocking agents on the performance of a fluoroelastomer process aid. Talc and diatomaceous earth have no treatment, which results in a more pronounced absorption of the additive. Siloxane-coated talc has reduced interference with the additive, as does S5mthetic silica. 

Figures 11.9 and 11.10 show that melt ftacture is improved and die pressure reduced with time of extmsion. This is due to accumulation of the additive and more complete coating of the die. Siloxane coating improves performance of the additive by reducing its absorption. Diatomaceous earth releases the additive, eliminates melt fracture, and reduces die pressure. The die pressure is a good predictor of antiblock performance related to absorption of the additive and influence on melt...

Figure 11.11 summarizes influence of various antiblocking additives on blocking force of polyethylene film. It is pertinent from the data that the 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, diatomaceous earth are usually used at concentrations of 5,000 ppm in order to give performance similar to silica. 

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