What is bentonite?

2021-11-08   Pageview:509

Bentonite is a non-metallic mineral with montmorillonite as the main mineral component. The structure of montmorillonite is a 2:1 crystal structure consisting of two silica-oxygen tetrahedra interspersed with a layer of aluminum-oxygen octahedra.













After the coating is added with polysiloxane and coated and cured, the polysiloxane can migrate to the surface of the coating film, and it is easy to aggregate to form a uniform and extremely thin monomolecular layer. The surface of the film has a very low surface tension, which acts as a slip layer, giving the bed film lubricity.

The polysiloxanes used as slip and anti-scratch agents are all liquids, and there are the following types. ①The structural formula of polydimethylsiloxane (i.e. methyl silicone oil) is:

The special Si-0 and Si-C bonds in the molecule reduce the steric hindrance between the methyl group (CH2) and the adjacent silicon (Si), and the semi-ionic Si-0 bond makes Si A 0-Si can bend to 120~145 in the middle, so that the steric hindrance is reduced again, so it has a very low surface tension, second only to fluorocarbon polymers. On average, its surface tension is 20mN/m, which is at least 10mN/m lower than general organic oxidized ft wax adhesive polymers. The average surface tension of common solvents and polymers.

Average surface tension of common solvents and polymers
O-xylene 30.0 epoxy resin 46.0
Toluene 28.4 Urea-formaldehyde resin 45.0
Methoxypropyl acetate 26.4 Vinyl chloride resin 42.0
Butyl acetate 25.2 Polymethyl methacrylate 41.0
N-butanol 24.6 polyvinyl acetate 36.5
Methanol 22.6 Alkyd resin 33.0

In the structural formula, polydimethylsiloxane of 45~230 provides slippage, but its wetting compatibility with the coating base material is very poor. Low molecular weight polydimethylsiloxane is slightly miscible with the coating base material. Soluble, when the chain is long, it is practically immiscible with all organic coating base materials, and the amount to be added is small, and the control range is very narrow. For example, if it is added at the recommended concentration (average 0.05%%), there is almost no slippage. Effect. If this amount is exceeded, or the operation is slightly careless, the washing solvent with polydimethylsiloxane, the pollution of the spray gun and the equipment will easily cause shrinkage, shrinkage, shrinkage and other side effects of the coating film. Use is restricted. For this reason, polydimethylsiloxane is modified so that part of the -CH: group is replaced by the polymer chain, only at the expense of part of the reduction of surface tension, and greatly improves its compatibility with various coating materials.


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