Coatings, talc

U.S. Pat. No. 6,255,368 [114] describes plastic cellulosic composite pellets comprising 20-60% by weight of polyethylene, polypropylene or polystyrene, 40-80% of cellulosic fiber (jute, kenaf, sisal, bamboo, rice hulls, corn husks, wood fiber, and wood flour) with an aspect ratio of between 2 and 20 and a trace of mineral coating (talc) dispersed on the surface of the pellet. 

The sixth and seventh steps involve treatment of certain talcs. Some talc grades are silane surface-treated for the rubber industry. Others are treated with glycol stearate to improve dispersibUity and processing. Amine-coated talcs are used for fertilizers and cationic talcs for pitch control in papermaking. The surface treatment also helps vrith compatibihzation reactions of certain components of polymer blends [1, 4]. 

In pultmsion process, thermoplastic polymer is deposited between multifilaments. The polymer comprises additives which do not adversely affect activity of catalyst of covalent bond formation between mnltifilaments and polymer coating. Talc was found to be snitable nncleating agent. Talc is also used in pnltmsion process of sizing glass fibers. ... 

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. 

Certain raw materials can be coated (talc, mica, serecite, pigments, pearls, etc.) or micronized (talc, mica, serecite, pigments) to modify or amplify an aspect. Globally speaking, they may facilitate pigment dispersion, compacting, skin adhesion, softness and wet and dry apphcation. 

K.-J. Kim, J.L. White, S.E. Shim, S. Choe. Effects of stearic acid coated talc, CaC03, and mixed talc/CaC03 particles on the rheological properties of polypropylene compeimds.. Appl. Polym. Sci., 93,2105-2113, 2004. 

Sheet form, composed of organic roofing felt, saturated with asphalt and coating on both sides with asphalt compound that may or may not contain mineral stabiHzer, surfaced with powdered talc, mica, or other tine mineral matter to prevent sticking. Classified, in mineral net mass per unit area of roofing, as Type I, 1943 g/m (39.8 lb/100 fC) Type II, 2666 g/m (54.6 lb/100 fC) Type III, 2495 g/m (51.1 lb/100 fC) and Type IV, 1943 g/m (39.8 Ib/lOOfC). 

Paper. Paper is the principal apphcation for talc throughout the world. It is used as a filler, a coating pigment, and a process aid in pulping and de-inking for pitch and stickies control. As a paper filler, talc is used because of its platiness, softness, whiteness, abiUty to space Ti02, and ink receptivity. 

Cordierite [12182-53-5] Mg Al Si O g, is a ceramic made from talc (25%), kaolin (65%), and Al O (10%). It has the lowest thermal expansion coefficient of any commercial ceramic and thus tremendous thermal shock resistance. It has traditionally been used for kiln furniture and mote recently for automotive exhaust catalyst substrates. In the latter, the cordierite taw materials ate mixed as a wet paste, extmded into the honeycomb shape, then dried and fired. The finished part is coated with transition-metal catalysts in a separate process. 

Most talc sold to paper, ceramics, and other industrial customers is manufactured to specifications agreed to between the producer and consumer. In paper, properties such as color, abrasion, surface area, and tint ate most important, whereas in ceramics, oxide chemistry, fired color, pressing characteristics, and alkaH metal content ate mote important. There ate some military specifications for talc used in corrosive coatings (6) and for cosmetic talc products used for cleaning of personnel in chemical warfare zones (7). 

Chisso-Asahi uses a spouted bed process for the production of their coated materials (12). A 12,000 t/yr faciHty is located in Japan. The semicontinuous process consists of two batch fluid-bed coaters. A dilute polymer solution is prepared by dissolving 5% polymer and release controlling agent into a chlorinated hydrocarbon solvent such as trichloroethylene. The solution is metered into the spouted bed where it is appHed to the fertilizer core. Hot air, used to fluidize the granules, evaporates the solvent which is recovered and reintroduced into the process. Mineral talc, when used, is either slurried into the polymer solution or introduced into the fluidizing air. 

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

The layers in the plate-like structure of talc are Joined by very weak van der Waals forces, and therefore delamination at low shear stress is produced. The plate-like structure provides high resistivity, and low gas permeability to talc-filled polymers. Furthermore, talc has several other structure-related unique properties low abrasiveness, lubricating effect, and hydrophobic character. Hydrophobicity can be increased by surface coating with zinc stearate. 

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