Antiblocking applications

MAJOR PRODUCT APPLICATIONS paints, coatings, rubber, abrasive polishes, cleaning waxes, seed coatings, anticaking agent, antiblock applications, pesticide formulations, asphalt extender, automotive windshields, catalyst support, concrete additive, dental molds, drilling mud, filter papers and pads, specialty p ers, paperboard, foundry, waste disposal aids, stucco, battery boxes, plastic film... 

Fine silica particles are incorporated in the surface of plastic films to prevent the adhesion of two sheets in contact with one another. The application is called antiblocking. The relatively low refractive index of the silica particles makes them more difficult to detect. 

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). 

In judging the suitability of a common filler such as CaCOs as an antiblock in PO film applications, researchers have noted complicated relationships between... 

Chem. Descrip. Behenamide CAS 3061-75-4 EINECS/ELINCS 221-304-1 Uses Lubricant, slip, antiblock, and mold release agent for plastics, crayons, petrol, prods., asphalts, inks, metals, textiles mold release agent for thermoplastic resins in inj. molding defoamer and water repellent in industrial/household applic. corrosion inhibitor pigment grinding aid and dyestuff dispersant in paints, enamels, varnishes, and lacquers intermediate for textile emulsifiers and softeners foam stabilizer in household detergents... 

Food contact packaging film can also contain antiblocks. The additives must not only achieve regulatory approval, but must minimise taint and odour and maximise colour stability. Nippon Shokubai developed crosslinked PMMA particles called Epostar MA about five years ago, as a food contact antiblock for polyethylene. The company was claimed at the time to have been the first to have an antiblocking agent approved by the EU for food contact applications with polyethylene. 

Apart from packaging applications, another opportunity for antiblocking agents is in medical gloves. The users traditionally employ talc or a similar powder to facilitate donning, but some recent designs have incorporated an antiblocking composition. 

Kaolin or china clay, like many minerals, is used much more widely outside the plastics industry than within it, especially in the paper industry but also to a lesser extent in paint, rubber and pharmaceuticals. It is currently used to improve the electrical properties of PVC wire and cable insulation. Other applications are in automotive parts and as an antiblocking agent in plastic films. It can benefit thixotropy, and calcined kaolin can improve dimensional stability. (Calcined kaolin is also competing with silica in the antiblocking agent market.) Polarite 102A from Imerys is an example of a premium kaolin product, targeted at polyamide automotive applications. 

Antiblocking agents are used in polyolefin films in conjunction with slip agents in such consumer items as trash bags, shipping bags, and a variety of packaging applications... 

In many cases blocking may be counteracted by incorporation of antiblocking agents in the plastic. These are generally fine-particle silicas and silicates or certain paraffin and waxes. Where applicable, suitable modification of processing conditions... 

Primary fatty amides are the preferred slip agents and are added at an approximate level of 0.1% during the production of LDPE film materials (in the USA, PE film production was 6.3 billion poimds (lbs) in 1991) [46]. They are less frequently used as antiblock and mould release agents in the manufacture of other flexible and rigid plastic products. EA, OA and SA are very cost-effective for these applications and hence are widely used however, other saturated and unsaturated amides with a chain length of 18-22 carbon atoms may be equally effective [47]. 

For resins with completely imknown compositions, this method is not applicable because the analyst cannot determine the possible interferences. For instance, the Si-O band in silica and silicates, often used as antiblock agents, overlaps the C-O-C band in PEG. As the crystallinity in HDPE can also vary, spectral subtraction could cause some imcertainty from incomplete removal of the PE crystallinity band absorption at 1075 cm. ... 

A fine-particle silicone additive has been developed by GE Silicones to improve the surface and surface Interaction characteristics of polymers, rubbers and similar materials. A key application for the additive (Tospearl) is an antiblocking agent for thin plastics film. Added to the resin during compounding, the fine particle spheres (0.5 12 pm) protrude from the surface of the blown film to form a uniformly uneven surface that prevents adhesion between film layers. The particle size is selected depending on film thickness. The spherical shape of the particles, combined with good inherent lubricity of silicone, also improves the slip characteristics of the film. 

Highly cross-linked spheres with an average particle size from 0.5 to 12.0 /rm have been produced. Extremely narrow particle size distributions are possible. The particle size and degree of monodispersivity are controlled by kinetic factors during the hydrolysis. Applications for Tospearl powders include wear resistance, antiblocking properties, light-diffusion control, and lubrication (542). 

China clay is a widely used white filler in the rubber industry. Depending on particle size, it can be used as a semi-reinforcing filler (hard clay) or a non-reinforcing filler (soft clay) in such applications as chemical liners, bicycle tyres, conveyor belts, shoe soles, gaskets and flooring. Its use in plastics is much more limited. In thermoplastics it is used for speciality antiblocking, in thermosets it is used in urea-, phenol- and melamine formaldehyde, in unsaturated polyesters, and in epoxy resins. 

Tospearl particles are crosslinked siloxanes made by the controlled hydrolysis and condensation of methyltrimethoxysilane. Their spherical nature, narrow particle size distribution and chemical and thermal stability make them ideal for use in wear resistance, antiblocking and light diffusing applications. 

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