Two-pack paints

These requirements are usually met with two-pack paints based on hydroxyl-rich polyester or acrylic resins in the pigmented pack and aliphatic polyisocyanates in the activator pack. Cure with this type of finish is relatively fast and complete even at low ambient temperatures. An alternative finish is an acrylic lacquer, similar to the lacquer used for refinishing motor cars. These finishes are applied to the assembled aircraft by operators protected by air-fed hoods and using airless or conventional spray guns. High durability pigments are included. 

Two-Pack a paint or lacquer the materials for which are supplied in two parts which must be mixed in the correct proportions before use. The mixture will then remain in a usable condition for a limited time only. The two parts of a two-pack paint are often (though not necessarily) supplied in the correct relative proportion either in entirely separate containers of appropriate sizes or in a single container divided into two compartments the term dual-pack is often used to describe the latter type of container. 

Tyrer FH Hazards of spraying with two-pack paints containing isocyanates. Soc Occup Med 29 22-24, 1979... 

Esters, ketones, and ether esters of polyurethane grade (i.e., absence of reactive constituents and a maximum water content of 0.05%) are required for solvent-containing paints. Aromatic hydrocarbons are suitable as diluents. High-solids two-pack paints containing 30-40 wt% of volatile components are becoming more popular on account of their low solvent emission. 

The solvents, dilute hydrochloric acid, and ethyl silicate are mixed and stirred and the temperature rises an upper limit of 25-30 C is often recommended. The second component of the two-pack paint is the pigment-extender mixture. The binder can be used after 1 - 3 d the storage stability is limited and is generally specified by the manufacturer. In the above example it is ca. one year. 

The contents of two-pack paints must be constantly stirred after mixing to prevent settling. The pot lives are ca. 8 h. With one-pack paints, layer thicknesses of up to 200 pm can be obtained in a single application. Pot life is unlimited provided moisture is excluded. 

In two-pack paints both the binder and the hardener have to be mixed before application. In paints with a short pot life the paint must be metered and mixed in the atomization equipment immediately prior to use. The two reactive components are normally mixed in static mixers after metering. 

Solventhorne paints are mainly alkyd paints with mineral spirit as solvent. Paints based on synthetic resins and two-pack paints with hydrocarbon, ester, or ketone solvents are, however, also used. Gloss ranges from silk-matt to high gloss. 

Uses Binder, film-former in paints (printed circuit board coatings, coil, container, conosion-protection, marine, metal, plastics, sealers, tarp, wood varnishes), printing inks (screen printing), primers (adhesion pro-motion/corrosion protection), ceramic compds., sealers, heat-sealable lacquers, two-pack paints, resinous/polymeric food-contact coatings reactive resin in two-pack systems, e.g., crosslinked with melamine/phenolic resins... 

Chem. Descrip. Vinyl chloride/acrylates copolymer Uses Binder, film-former for surf, coatings, two-pack paints, primers, undercoats, alkyd paints, stoving finishes, adhesives Features Contains hydroxyl groups char, by exc. toughness, permanent flexibility, abrasion resist., low swelling in presence of water, low gas permeability produces highly water-resist, films with exc. resist, to oils, greases, dil. aq. acids, alkalis, etc. 

An activator may be one portion of a two pack paint, one reactant of the resin-forming ingredients. In this instance the activator can hardly be called an additive. The true additive activator is a chemical which, when added as a minor ingredient, sparks off the chemical reaction in the paint. Such an additive is usually a chemical which decomposes to give free radicals which, in turn, initiate an addition polymerization Peroxides, Chapter 16). 

Since there is a variety of isocyanate reactions, the formuiator has considerable scope. So far, five different approaches have been used three have led to one-pack paints and two to two-pack paints. 

Two-pack paints, now known generally as 2K coatings, are the largest volume urethane coatings produced, of which those under the second heading below are most popular. The term 2K comes from the German for 2-pack (2 komponenten) in Germany the term IK is used for one-pack finishes. 

Amoebae Animal protein Enzymes Isocyanates Moulds Air conditioning (humidifier fever) Hair cutting, veterinary work Raw cotton Used in belt-joining glues, two-pack paints, manufacture of foam and polyurethane rubbers Hay, grain, cheese... 

Isocyanates are volatile organic compounds widely used in industry for products such as printing inks, adhesives, two-pack paints (particularly in vehicle body shops) and in the manufacture of plastics (polyurethane products). They are irritants and sensitizers. Inflammation of the nasal passages, the throat and bronchitis are typical reactions to many isocyanates. When a person becomes sensitized to an isocyanate, very small amounts of the substance often provoke a serious reaction similar to an extreme asthma attack. Isocyanates also present a health hazard to fire fighters. They are subject to a workplace exposure limit (WEL) and respiratory protective equipment should normally be worn. Two-pack polyurethane paints and varnishes are used in construction as surface coatings. 

Paints, whose curing is provoked by chemical reaction, including two-pack paints... 

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