Two-pack polyurethane paints

Two-pack polyurethane paints exhibit film properties comparable to those of solvent-borne polyurethane coatings (Bittner and Epple, 1996 Mirgel, 1993). 

The effect of silanes on the bond strength of a two-pack polyurethane paint Direct pull-off, silane on surface... 

Reference to Table 7 will show the data for the two-pack polyurethane paint, and indicate a similar improvement to that of the epoxide paint due to the use of silanes. Although there are differences in the values for particular silanes on the different substrates and surface treatments, the general picture is that AAMS and MPS are the most effective in epoxide and polyurethane paints. 

Bittner and Epple (1996) reported the development of aqueous and high-solid two-pack polyurethane paint which is useful as industrial finishing. 

Polyurethane systems based on hydroxypolyester resins and free polyisocyanate resins (two-pack polyurethane paints. Section 2.9) are used particularly for finishes of road vehicles, railroad vehicles, aircraft, and plastics. Blocked polyisocyanate resins are available for formulating one-pack stoving enamels which are particularly suitable for coil and can coatings [2.83]. 

Poiyisocyanate Resins. Hydroxy-functional polyester resins play a significant role in two-pack polyurethane paints. Combinations with nonblocked poiyisocyanate resins are discussed in Section 2.9. 

Two-Pack Polyurethane Paints. Polyester-polyurethane paints are described in detail in Section 2.9. Polyester polyols for polyurethane systems are generally adjusted to be softer than those used for stoving enamels. Their hydroxyl number and degree of branching are adapted to the recommended polyisocyanate cross-linking agent. 

Polyisocyanates differ as regards their chemical structure, reactivity, functionality, and isocyanate content. They are the principal curing constituent of two-pack polyurethane paints. Curing agent solutions have an isocyanate content of 5-16 wt%. Solvent-free, liquid curing agents may contain up to 30 wt% isocyanate. 

Polyols. In conventional two-pack polyurethane paints, high molecular mass compounds containing hydroxyl groups form the base that cross-links and hardens... 

Two-pack polyurethane paints can be applied by all conventional methods apart from dipping. Curing takes place at ambient temperature, but can be accelerated if necessary by heat. Stoving is not necessary (energy saving). 

Aqueous two-pack polyurethane paints are obtained by combining, for example, hydroxyl-containing polyacrylate dispersions with water-emulsifiable, low-reactive aliphatic polyisocyanates. 

Catalysts also include accelerators for two-pack polyurethane paints (e.g., tin and zinc compounds, tertiary amines) and initiators for unsaturated polyester resins that act as radical-forming agents. 

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. 

Solvents containing moisture-cured or two-pack polyurethane resin paints are also used extensively. They... 

Certain components of domestic appliances are also coated with electrodeposition paints. Two-pack polyurethanes are applied if the dimensions of the parts are too large for the electrodeposition bath. These paints dry at ambient temperature to give films with similar properties to stoving acrylic enamels. Solvent-free powder coatings are also used to coat domestic appliances. Nowadays powder coatings and precoated metal (coil coating) are gaining more importance. 

Pigmented, two-pack, waterborne epoxy resin coatings (garages) or one-pack waterborne acrylic resin emulsion paints are used for areas that receive less wear (e.g., cellars). Wooden parquet floors are coated with one- or two-pack polyurethane varnishes that can be applied by spraying or brushing. Acrylate-based waterborne parquet varnishes are also used because they are environmentally friendly. 

Easton et aV modified the waterborne alkyd with sihcon intermediates to improve weathering resistance in paints for exterior apphcatioa Organosilane incorporation in alkyds became the first choice in systems for protecting metal surfaces on bridges, railways and towers. Today they compete with other coating types, including two-pack polyurethane coating, which perform extremely well. 

Abstract— The use of organosilanes as adhesion promoters for surface coatings, adhesives and syntactic foams is described and reviewed in the light of published work. Data are presented on the beneficial effect of silanes, when used as pretreatment primers and additives, on the bond strength of two pack epoxide and polyurethane paints applied to aluminium and mild steel. It is shown that silanes when used as additives to structural epoxide and polyurethane adhesives are less effective than when used as pretreatment primers on metals but are highly effective on glass substrates. The compressive properties of glass microballoon/epoxide syntactic foams are shown to be markedly improved by the addition of silanes. 

Depending on their chemical composition, polyurethane paints are formulated as two-component (two-pack) or one-component (one-pack) mixtures. They are applied from the liquid phase, which may be solvent-containing, aqueous, or solvent-free, or from the solid phase as a powder coating. They may be cured under a wide range of conditions drying above to stoving at ca. 200°C. 

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. 

Although two-pack epoxy primers and polyurethane intermediate coats have high solids contents, they still contain significant amounts (20-30 wt%) of organic solvents. In polyurethane topcoats, the VOC is even higher. Anticorrosive, waterborne primers based on aqueous dispersions of two-pack epoxy resins and one-pack acrylic resins have been developed to decrease solvent emission. Waterborne, one-pack acrylic topcoats are also used. All of these waterborne paints contain 2 - 5 % organic cosolvents that are required for film formation. 

Chem. Descrip. Polyurethane in water and emulsifier Uses Thickener, rheology control agent, flow aid for aq. coatings, acrylic gloss paints, anticorrosion paints, styrene-acrylate, S/B, water-emulsifi-able two-pack systems, air- and force-drying water-emulsifiable binders Features Low-vise. 

Chemical reaction between paint ingredients low or very low medium to high, 30-100% cross- linked fair-poor fairly fast varies 10-15° C common two-pack or short shelf-life, unless stoving or radiation curing type Industrial stoving finishes acid-catalysed, polyurethane and polyester wood 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... 

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