Paints, Coatings and Solvents Episode 3 potx

2.7.3. Cross-Linking of Polyester Resins Amino Resins. Formaldehyde-modified amino resins (i.e., melamine, benzoguanamine, and urea resins) are the most important resins for the heat curing of hydroxyfunctional polyester resins. These resins are readily available with a low molecular mass (very good polyester compatibility, but less reactive) or in precondensed form (limited compatibility, but very reactive). In order to prevent premature reaction in the wet paint, the amino resins are blocked by etherification with, for example, methanol or butanol. Sulfonic acids (e.g., p-toluenesulfonic acid, dodecyl- benzenesulfonic acid) have proved suitable for accelerating the deblocking of amino resins during heat curing. These acids must also be used in blocked form (ammonium salts, thermolabile adducts). The polyester-amino resin ratio is generally in the range 90: 30 to 70: 30. High molecular mass polyester resins can be cross-linked with hexamethoxymethylme- lamine resins (HMMM) above ca. 190°C. Amino resins undergo selfcondensation above this temperature [2.82]. Low molecular mass linear polyesters react above 160'C, and branched types above ca. 100°C. The latter generally contain acid groups (acid number 5-25 mg KOH/g) in addition to the hydroxyl groups to en- hance reactivity with amino resins. Stoving enamels based on high molecular mass polyester resins and HMMM or benzoguanamine resins have excellent flexibility and surface hardness as well as outstanding adhesion to metal substrates [2.88], [2.89]. Low molecular mass linear polyesters combined with HMMM resins have lower flexibility, but have the advantages of higher reactivity, better pigmentability, and higher paint solids content [2.90], [2.91]. Low molecular mass branched resins form particularly reactive stoving enamels, but the resulting films are less flexible and do not adhere as well to metal substrates. Polyisocyanate Resins. Hydroxy-functional polyester resins play a significant role in two-pack polyurethane paints. Combinations with nonblocked polyisocyanate resins are discussed in Section 2.9. Storage-stable one-pack polyester stoving enamels can be formulated with polyisocyanate resins that are thermoreversibly blocked. Tin catalysts (e.g., dibutyl tin dilaurate) are particularly suitable for accelerating hardening with hydroxypolyester resins. Although linear polyester resins do not readily undergo heat curing, they form extremely flexible paint films with excellent adhesion to metal substrates. Polyisocy- anate resins are more resistant to hydrolysis than amino resins, Polyester- polyurethane paints therefore exhibit improved resistance to moisture and weathe- ring but are more expensive. Epoxy Hardeners. The heat curing of carboxy-functional polyester resins with epoxy resins is mainly used in powder coatings. Catalysts (e.g., benzyltrimethylam- monium chloride or 2-methylimidazole) are used to accelerate the reaction during heat curing. Triglycidyl isocyanurate plays a special role as cross-linking agent. Powder coatings with outstanding weather resistance and very good mechanical 2.7. Suturured Polrester Couritigs 55 properties are obtained [2.84]. Hybrid powder coatings based on epoxy resins of the bisphenol A type should also be mentioned. Radiation Curing. The cross-linking of acrylate-modified polyester resins with UV radiation or an electron beam is an energy-saving alternative to the heat-curing systems. Reactive diluents (e.g., polyfunctional acrylates) are required to adjust the viscosity for application; although they increase reactivity, they reduce the flexibility and substrate adhesion of the paint film. 2.7.4. Uses Coil Coating. On account of their outstanding hardness-elasticity balance, good adhesion to metals, good application properties, and favorable cost, paints based on saturated polyester resins represent the most important system for coil coating. On account of their insensitivity to solar radiation, some polyester resins are particularly suitable for weather-resistant topcoats (e.g facade claddings. blades of shutters and venetian blinds, vehicle claddings, metal signs). Melamine-formulated paints are economical and have a well-balanced property profile. Polyurethane-formulated paints have an even better processability and weather resistance (colorfastness, chalking resistance) [2.92]. Specially adapted polyester resins are available for topcoats for interior architectural use (e.g., underfloor ceilings. light fittings), for appliance claddings (e.g., domestic appliances. hifi equipment), or for automobile fittings. Hard. high molecular mass copolyesters are suitable for primers containing corrosion protection pigments on account of their low oxygen permeability and very good adhesion to metals [2.93]. Can Coating. Polyester stoving enamels are widely used for coating can exteriors (metal decorating) but also for protecting can interiors. Polyester resins are available that satisfy the FDA regulations for internal coatings of cans used for food packaging [2.94]. Polyester coatings do not affect the taste of the food. High molecular mass polyester resins, cross-linked with benzoguanamine and melamine resins, are particularly suitable for highly drawable, sterilization-resistant decorative stamping enamels [2.88], [2.89]. Low molecular mass polyester resins also exhibit good processability and sterilization resistance in polyurethane formulations. Automotive Finishes. Important industrial automotive topcoats are produced from alkyd resins. Two-coat metallic finishes consist of an acrylic clearcoat and a metallic basecoat. Solventborne basecoats are generally composed of cellulose acetobutyrate and a low molecular mass, branched polyester resin which exhibits high reactivity with precondensed melamine cross-linking resins. Surfacers are mainly produced from low molecular mass polyester resins cross- linked with amino resins. Blocked polyisocyanate resins may also be used for high stone chip resistance. Water-soluble polyester resins are increasingly used for water- thinnable stoving surfacers. Spray and dip paints based on polyester resins are used to coat automobile accessories (e.g., windscreen wipers, axle parts). 56 2. Ttprs of’Piiinrv nnd Cocitingc (Bijiderx) Industrial Paints. Stoving enamels used to spray or dip-coat machinery, domestic appliances, vehicles, and office furniture are termed industrial paints. On account of their good adhesion and resistance to hydrolysis, polyester - melamine stoving enamels provide very good protection of metal surfaces against undercoat corrosion creep. Polyester resin grades are available for special mechanical requirements (high impact resistance, hardness, abrasion resistance) or for exterior use (weather resis- t ance) . Polyester paints with high solids contents (65-75 wt % at application viscosity) can be produced from very low molecular mass resins [2.95]. Low-pollution paints can also be produced from water-soluble polyester resins [2.85]. On account of their good water solubility, HMMM resins are particularly suitable for cross-linking these resins. Organic cosolvents (mostly glycol ethers) must be added to waterborne polyester paints to control their viscosity and applicability (leveling, substrate wet- ting). Two-Pack Polyurethane Paints. Polyester ~ polyurethane paints are described in detail in Section 2.9. Polyester polyols for polyurethane systems are generally adjust- ed 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. Polyester resins combined with aliphatic polyisocyanate resins have outstanding weather resistance, good substrate adhesion, and high flexibility even under very large temperature changes (aircraft finishes). Polyester ~ polyurethane paints are particularly suitable for coating plastics (max- imum drying temperature generally 80 “C) on account of their very high flexibility and good adhesion. Powder Coatings. Polyester resins are available for two different reactive powder coating systems: 1) Hydroxy-functional resins for combination with blocked polyisocyanate resins 2) Carboxy-functional (acid) resins for combination with triglycidyl isocyanurate or (based on isophorone diisocyanate) [2.96] epoxy resins The resulting powder coatings have good weather resistance as well as excellent impact strength and adhesion to metals (even under humid conditions) and are therefore suitable for many uses (e.g., in exterior and interior architectural applications, for coating machinery, domestic appliances, steel furniture, garden tools). Radiation-Curable Polyester Coatings. Radiation-curable polyester paints (see also Section 3.7) are particularly suitable for coating flat surfaces (strips, boards, sheets) and for temperature-sensitive substrates (paper, plastics). Acrylate-modified polyester resins are used for UV printing inks, UV varnishes for paper and plastics, as well as for pigmentable, electron beam-curable gloss and matt paints [2.86]. Radiation-curable polyester paints are also suitable for metal coatings with good elasticity. 2.8. Unsaruratrd Poljv.cter Coatings 57 Special Uses. High molecular mass copolyester resins are used in the manufacture of flexible packaging. Terephthalate resins are particularly suitable as adhesion promotors for printing inks, lacquers, and adhesives on poly(ethy1ene terephthalate) films. Some polyester printing inks adhere directly to these sheets. Lacquers that can be heat sealed at relatively low temperature can be produced from high molecular mass, soft copolyester resins. Special linear copolyester resins are used for magnetic tape coatings [2.97]. 2.8. Unsaturated Polyester Coatings Unsaturated polyester coatings are used on, for example, furniture, vehicles and mineral substrates. They are formulated using unsaturated polyester (UP) resins, stabilisers, accelerators, hardeners and, possibly, pigments, extenders, barrier agents, promoters, deaeration agents, flow promoters, thixotropic agents and photoinitiators. The coatings primarily contain monomers. In addition to styrene, the most frequently used monomer, it has become increasingly common in recent years to use acrylates as the copolymerisable monomers, especially in coatings for UV curing. However, monomer-free UP resins have also gained some significance ~ either 100 YO or dissolved in, for example, butyl acetate or dispersed in water [2.98]. Coatings containing styrene cure in virtually any thickness as the styrene which initially acts as a solvent polymerises with the double bonds of the UP resin and is incorporated into the paint film. As only a small proportion of the styrene evaporates, this virtually “solvent-free” coating yields films with extremely good body [ 2.991. 2.8.1. Unsaturated Polyester Binders UP resins are soluble linear polycondensation products made from polyvalent - usually unsaturated - acids (e.g. maleic or fumaric acids) and bivalent alcohols (e.g. ethylene glycol and/or 1,2-propylene glycol). For special applications, it is common to substitute some of the ci, P-unsaturated dicarboxylic acids with phthalic acid and/or adipic acid. Seminal work on unsaturated polycondensation products made from maleic acid, maleic acid anhydride and glycols and on their copolymerisation with styrene is listed in [2.100]. The wide range of UP resins on the market covers products which require the addition of paraffin wax through air-drying, UV-curing, amine-accelerated or flexibilising products to styrene-free and/or water-dispersible resins. World production of UP resins in 1995 - including those for captive use - is estimated at around 200,000 tonnes. Of this amount, 60,000 tonnes are produced in western Europe where roughly two-thirds are used in furniture coatings and the remaining one-third in fillers. Commercial Products. UP resins are supplied by the manufacturers under the following trade- names [2.101]: Alpolit (Hoechst), Crystic (Scott Bader). Distroton (Alusuisse), Estratil (Rio Ro- dano), Gohselac (Nippon Gohsei). Ludopal (BASF), Poloral, Verton (Galstaff), Polylite (Reich- hold). Unidic (Dainippon Ink), Roskydal (Bayer). Silmar (Silmar), Synolite (DSM). Vestopal (Hiils), Viapal (Vianova). The testing of UP resins is governed by, for example, DIN 53 184. Paraffin-type UP Resins. In the case of the UP resins described above. atmospheric oxygen inhibits polymerisation by chain rupture, with the result that the paint film remains tacky. The addition of small amounts of paraffin wax [2.102] eliminates the inhibiting effect of atmospheric oxygen. Initially, the paraffin wax dissolved in the UP coating loses its solubility as polymerisation progresses. It accumulates on the film surface and forms a layer which prevents contact with oxygen. Coatings containing paraffin wax can be force-dried under heat once they have gelled at room temperature. A further advantage of using paraffin wax is that the wax layer on the surface of the paint film reduces the evaporation of styrene to less than 5% [2.103]. This is of particular significance given the low threshold values which now apply for styrene. UP Resins for Fillers. Tack-free films are also obtained if phthalic acid anhydride is substituted with tetrahydrophthalic acid anhydride [2.104]. The addition of en- domethyl tetrahydrophthalic acid anhydride (a cycloaddition product of maleic acid and cyclopentadiene) also has a positive effect on the air-drying properties [2.105]. Both product classes have become popular above all in the manufacture of binders for highly extended fillers for vehicle repair applications. Air-drying UP Resins. Air-drying UP resins, also known as gloss polyesters, are produced by incorporating b, p-unsaturated ethers such as the diallyl ether of glyc- erol or trimethylol propane and the di- and triallyl ethers of pentaerythrite, in the polymer network. These cure to yield a tack-free film. Investigations of the drying mechanism of this significant class of resins have been undertaken t2.1061 (more at ”Polyesters”). 2.8.2. Other Raw Materials The formulation of coatings must be matched to the required property profile in terms of the resin/hardener system as well as the additives which influence the rheology, flow, deaeration, mechanical and chemical properties, resistance to yel- lowing and film colour. Hardeners. The polymerisation reaction is initiated by peroxide radicals. Typical examples are cyclohexanone peroxide and methyl ethyl ketone peroxide (hydroper- oxides), benzoyl peroxide, perbenzoates and peroctoates (acyl peroxides). It is standard to use around 4% (calculated on the resin and styrene content) of a desensitised supply form (e.g. 50 YO peroxide in flexibiliser). The manufacturer’s instructions are to be observed in handling peroxides. 2.8. Uri.satirruted Polj~rster Cootings 59 Accelerators. To allow the degradation of the peroxides at room temperature, the activation energy must be reduced. This is done by adding accelerators. Hydroper- oxides are cleaved by heavy metal salts and acyl peroxides by tertiary aromatic amines. Up to 2% of the latter are added by the manufacturers to resins for fillers. These are known as amine-accelerated UP resins. It is common to add 0.02-0.05% cobalt (calculated as cobalt metal) in the form of cobalt naphthenate or cobalt octoate dissolved in aromatics (not white spirit) to the systems hardened with hy- droperoxides. The accelerator should only be added shortly before application for reasons of storage stability and drift. Promoters. Substances such as acetyl acetone, ethyl acetoacetate, amides of ace- toacetic acid [2.107], acetyl cyclopentanone [2.108] or tertiary aromatic amines have an accelerating effect on the curing reaction initiated by the hydroperoxide/cobalt octoate. Ethyl acetoacetate is most frequently used. The amount added is 1 -3%, calculated on the resin supply form. Photoinitiators. Derivatives of benzoin and benzil are added in amounts of 1 - 3 YO as photoinitiators in UV-curing systems. These have differing effectiveness in the UP systems [2.99]. Special initiators are available for pigmented systems. The UV light splits them into radicals which in turn initiate polymerisation. The UV radiation is generated using superactinic fluorescent lamps and/or high-pressure mercury vapour lamps [2.109]. Special fluorescent lamps or gallium-doped high-pressure lamps are available for pigmented systems. Stabilisers. If stabilisation is necessary, e.g. to prolong the pot life or increase the storage stability, 0.01 -0.03 YO (solid) hydroquinone or tertiary butyl catechol can be added as a 1 to 5% solution in a suitable solvent. It should be borne in mind that the use of such substances has an effect on the drying time of the coating. Barrier agents. To prevent inhibition by air, it is common practice to add special paraffin waxes which are suitable for UP resins [2.110]. Paraffin waxes with a high melting point are used at higher application temperatures (max. 40 C) and products with a low melting point at low ambient temperatures (min. 15'C). The melting points are between 40 and 70'C. The usual addition is around 0.1 YO (solid, calculated on the coating). preferably as a 10% solution in toluene. When coatings and fillers containing paraffin wax cool, there is the risk of crystallisation. The paraffin wax solution is usually added with the cobalt accelerator (as a solution) just before application. Deaeration Agents and Flow Promoters. Because of the many potential formulations and applications, the type, amount and time of addition must be tailored to the individual system. The storage of coatings containing special silicones may result in cratering. Solvents and Other Binder Constituents. Coatings based on UP resins generally contain no solvents with the exception of the solvents used in the cobalt, paraffin 60 2. Tvpes of Paints arid Coorings (Binders) wax or peroxide solutions. In special cases where inert or co-reacting binders are to be used, low-boiling solvents are required. The type and quantity must be selected according to the application and curing conditions. In thin-coat varnishes containing nitrocellulose or cellulose acetobutyrate, the solvent content can be as high as 75 YO and special attention should be given to compatibility. In the case of high-build coatings, the solvent content should not exceed 4%. To improve the chemical resistance and the adhesion to the substrate, small amounts of polyisocyanate can be added to UP systems. The changes to the pot life must be borne in mind. Pigments and extenders. The only pigments and extenders which can be used are those which have virtually no effect on the curing process. The influence on storage stability, shade and surface structure must also be considered. Extenders have the primary task of reducing the shrinkage which occurs during curing to between 7 and 10%. This also improves the adhesion. Talc, barytes, chalk and dolomite are normally used as extenders. It should be ensured that the formulated fillers and coatings have adequate storage stability. So that coatings based on UP resins can be applied on vertical surfaces, they are made thixotropic. This is done either by using thixotropic resins or by combining standard resins with, for example, highly disperse silicic acid, bentonite and/or hydrated caster oil derivatives. To produce matt coatings, waxes (polyethylene and polypropylene waxes) and/or silicic acid are added in amounts up to 10%. 2.8.3. Formulation, Application, Use, Properties Fillers and Putties for Wood Materials. Fillers are highly extended (resin/extender ratio, 1 : 2.5) compounds of high viscosity which are applied to cover any unevenness in a substrate such as chipboard. Putties contain less extender (1 : 1.5) and are normally used as an intermediate coat between the filler and the top coat. Fillers and putties are formulated using dissolvers, butterfly mixers or attrition mills. Whereas fillers are applied using a roller machine, putties are usually applied by reverse roller, spray gun or curtain coater. Depending on the substrate, the application rate is between 50 and 200 g/m2. Fillers are mainly formulated with paraffin- type UP resins or air-drying types which are UV-cured. For fillers cured with hydroperoxide/cobalt, air-drying UP resins are normally used in combination with flexibilising resins. UV curing is carried out at a conveyor speed of approximately 3 m/min. The conveyor speed is usually calculated on the basis of a high-pressure mercury vapour lamp with an output of 80 W/cm. Conventional curing of spray fillers in a circulating air oven takes 10 min at 80°C. These systems provide virtually ideal substrates for a number of top coats as, unlike other systems, they have good hold-out. Roller, Curtain and Spray Coatings for Laminated Panels and Films (Thin-coat). Laminated panels which are to be given an open-pored coating are first primed and sanded. 2.8. Unsuturoterl PolJ.ester Couriiigs 61 Priming process: a) With UV-curing roller primers: based on an air-drying UP resin applied at a rate of 20-40 g/m2; curing at a conveyor speed of 3 m/min. b) With solvent-borne UV-curing spray primers: like a) with a solids content of < 30% applied at a rate of 50-70 g/mZ; flash-off for 4-5 min at 50’C followed by UV curing at a conveyor speed of 3 m/min. Because their solvent content is as high as 75 YO, varnishes containing cobalt/hydroperoxide have a pot life of several hours. The reduction in the solids content is achieved primarily through the addition of highly viscous nitrocellulose. The storage stability must be tested if styrene resins are used. Given flow times of 20-40 s (DIN 4 cup), an application rate of 20- 100 g/m2 is used. The drying time at room temperature is approx. six hours. After flash-off of the solvent (4-5 min at 50“C), the coating can be cured in approx. 10 min at 80 C in a circulating air oven, in 1-2 min under IR radiation or at a rate of, for example, 3 m/min under UV radiation. Coatings applied in this way have outstanding properties such as good scratch resistance, adhesion and resistance to household chemicals. In the case of film coating (application using doctor blades), aqueous and/or solvent-borne UP coatings containing no monomers and dried by conventional means are becoming increasingly significant. The high-gloss or matt coatings have a long pot life (several hours or days) and cure in approx. 30 s at 150 C. Aqueous UV-curing UP spray coatings can be recycled t2.1111. They can be recovered by ultrafiltration, wet-on-wet or scraping techniques. Roller, curtain and spray coatings for wood and wood materials (high-build). When working with conventional curing processes, UP resins requiring paraffin wax are normally used for high-build coatings, either clear or pigmented, with or without matting agent. In many cases, gloss polyesters are used. After the films have been stored overnight or longer, they are sanded and polished. This yields films with high gloss, hold-out and body. For this reason, these systems are favoured as base coats for top coats based on polyurethanes or other binders. Because of their rapid curing, UV-curing UP resins are being used increasingly for clear high-build coatings, either gloss or matt. Pigmented UV-curing coatings can be applied using either the mono- or double-cure process t2.1121. When using the double-cure process, the pigmented coating is first pre-gelled using conventional cobalt/peroxide accelerators. The film is then cured under UV lamps. In the mono- cure process, the paint film is cured directly (after flash-off) under special UV lamps or specially formulated coatings are used. An overview of the applications of UP and UA resins in wood and furniture coatings is given in [2.112]. Depending on the application process, the viscosity of the coatings varies from 20- 100 s (DIN 4 cup). UP coatings which cure conventionally can be applied at a rate of 500 g/mZ and UV-curing systems at a rate of 250 g/m’. The following application processes are employed industrially. a) Roller coating. Up to around 150 g/m’ of coating are applied using a reverse roller. As styrene evaporates on the roller, UP systems containing reactive thinners are being used increasingly. 62 b) Curtain coating. When applying UP formulations on a curtain coater, the main problem of the short pot life is overcome by separating the cobalt and hydroperoxide. For example, in the active primer process which is normally used [2.113], nitrocellulose coatings containing peroxide are applied first. These may also contain styrene-free UP resins. The primer is applied either by roller or curtain coating. Once the solvent has evaporated, the UP coating containing cobalt is applied. Other less frequently used processes are the double-head (1 : I), sandwich and transfer processes [2.1 141. As UV-curing coatings (one-pack systems) do not have a pot life, they are ideally suited for application by curtain coating. 2. T\prs ot' Puin1.r utid Coutirip I Bitrclrrs) c) Spraying. UV-curing coatings without a pot life can be applied using conventional spray equipment. Two-component units are used for the application of coatings containing cobalt/ hydroperoxide which have a short pot life. Curing. When applied at a rate of 450 g/m2, coatings containing paraffin wax gel after approx. 20 min at room temperature. They are wipe-resistant after approx. 1 hour and can be stacked after approx. 3 hours (see also 2.8.1.2). In contrast, air-drying UP coatings can be force-dried after a brief flash-off at room temperature and without pre-gelling. UV-curing coatings are cured at a rate of 1.25-3 m/min per 80 W lamp after 30-90 s (curtain coatings) or 5 min (spray coatings) flash-off at room temperature. Knifing, Spot and Spray Fillers for Metal and Marble (here also coatings). Knifing and spot fillers are especially suited for filling large areas of unevenness in just a few operations in quick succession. Knifing resins (hard to flexible) are mixed to a paste-like consistency with the extenders described. Benzoyl peroxide and tertiary aromatic amine are used as the hardener system (the latter is usually a component of the resin supply form). Before application, the necessary amount (2-3 YO) of benzoyl peroxide paste is mixed in well and the formulation applied with a knife. The pot life is usually around 5 min. The curing time is approx. 15 min at room temperature. The filler can then be dry-sanded. The shrinkage of the cured filler is 1-2%. This means that the system adheres on metal. To ensure the complete absence of pores, a spray filler and a non-sanding sealer must be applied over the knifing filler. The spray filler (based on an air-drying UP resin and cured with hydroperoxide and cobalt octoate) serves to fill the marks left by sanding. The polyurethane-based non-sanding sealer prevents blistering after application of the top coat, especially in warm and humid climates. Knifing and spray fillers have been used for many years in vehicle repair and machine finishing (on sanded or sandblasted iron). The cured fillers are characterised by their very good adhesion (even if the surface is extremely uneven), good through-curing in both thick and thin coats and rapid curing (even at temperatures down to 0 "C). The system described above (knifing/ spot filler, spray filler and non-sanding sealer) can be overcoated with any type of coating. One application for special UP resins is in stone putties, marble fillers and coatings. The consistency of the formulations ranges from paste-like to pourable. They are cured with benzoyl peroxide and tertiary aromatic amine and can be sanded and 2.Y. Polwrerhane Corrritigs 63 polished after 15-20 min. It is important that these hard reactive formulations discolour minimally on curing and have good mechanical properties. The top coats (applied by spray or curtain coating) are based on air-drying UP resins. Coatings containing paraffin wax do not adhere on marble. The coatings are cured with cobalt/hydroperoxide to yield gloss films. 2.8.4. Storage, Transport, Toxicology UP resins do not have unlimited storage stability. When protected from light and heat, the manufacturers generally guarantee storage stability of 6 months (33 C). UP resins are supplied in hobbocks, drums, containers and road tankers made from stainless steel, aluminium, tinplate or sheet iron - sometimes coated inside. Depen- ding on the styrene content, the flash point of UP resins is 28-35-C. The necessary precautions must be taken to prevent electrostatic pick-up. The following regulations apply for the transport of UP resins: GGVSee/IMDG code: 3.3; UN No.: 1866; MFAG: 310; Ems: 3 05; GGVEiGGVS: Class3 No. 31 C; RID/ADR: Class 3 No. 31 C; ADNR: Class 3 No. 31 C, Cat.; ICAO/IA- TA-DGR: 3, 1866 111; exception can be applied for viscous substances in accordance with note re. margin no. 301 E (GGVE/RID) / 2301 E (GGVS/ADR, ADNR). When formulating, handling and applying coatings based on UP resins dissolved in styrene, particular attention should be paid to the toxicology of styrene. Styrene is harmful when inhaled. It irritates the skin and the eyes. The widely varying threshold values in individual countries must be observed. To prevent inhalation of the coating aerosols during spray application. face masks must be worn. 2.9. Polyurethane Coatings [2.1151-[2.11~1 The term polyurethane paints (coatings) originally referred to paint systems that utilized the high reactivity of isocyanates groups with compounds containing acidic hydrogen atoms (e.g., hydroxyl groups) for chemical hardening (curing). However, this term now includes a large variety of binders. The amount of polyurethane raw materials processed into coatings is steadily increasing, and was estimated to be more than 500000 t worldwide. Polyurethane paint films all have a polymeric structure with urethane, urea, biuret, or allophanate coupling groups. Coupling can occur during paint hardening (curing) as the result of polyaddition of relatively low molecular mass starting products. Alternatively the paints may already contain high molecular mass polymers synthe- sized by the coupling of appropriate monomers. High molecular mass adducts with excess isocyanate groups or adducts in which curing occurs via oxidation of conju- gated double bonds are also common. [...]... via hydroxyl group I solid type 1 solid, type 2 solid, type 3 solid solid, solid, solid, type 6 type 7 type 8 type 9 71 1000 industrial maintenance and marine coatings powder coatings can coatings and finishes 4000 coil coatings can coatings and finishes two-pack polyurethane 5000 paints high molecular primers (cold curing) 10000 can and coil coatings mass epoxy resins 1-9 indicate increasing molecular... low-solids coatings and 35 -40 O h in high-solids coatings The cure temperature for most amino-resin-based automotive coatings is 120150°C In end-of-line repair applications the same coatings are cured with addition of acid catalyst at 80-90°C Amino resins are also employed in waterborne systems used in industrial coatings (e.g.?automotive spray primers and basecoats, can and coil coatings) Stable coatings. .. coating industry where coatings containing > 50% silicone have retained their gloss and color for more than ten years [2 .34 0] Other ~ 80 2 Ti!pes of' Puin1.Y and Coatings (Binder.7) applications include appliance finishes, exterior cookware coatings, and colored maintenance and architectural paints Curing Curing cycles are primarily determined by the silicone content of the resin [2. 139 ] A typical cure... binders produce coatings with outstanding resistance to chemicals and solvents Cross-linking takes place primarily via the free hydroxymethyl groups of the resols The disadvantage of the low flexibility of these coatings has to be borne in mind Coatings for Sheet-Metal Cans and Containers By far the most important area of use is the coating of sheet-metal containers and cans for the storage and preservation... including solvent-based, waterborne, high-solids, and powder coatings 2.12 Urea, Benzoguanamine, and Melamine Resins for Coatings Alkylated urea -, benzoguanamine - and melamine- formaldehyde resins represent a versatile group of cross-linking agents for hydroxy-, amide-, and carboxyfunctional polymers They are used in both waterborne and solventborne coatings, including high-solids industrial coating... degree of alkylation and polymerization, and its residual hydroxymethyl and amino content, all of which can significantly affect physical and chemical properties Environmental Protection The potential release of formaldehyde during application and cure is a serious problem in the handling of amino resins Depending on the structure and the conditions of manufacture a resin can contain 0.25 -3% free 2.12, Ureu,... Acids and Carboxy-Functional Polyesters Curing of epoxy resins with acids and carboxy-functional polyesters requires heat Industrially, these systems are most important in the formulation of powder coatings: more than 70% of powder coatings are based on epoxy resins and carboxy-functional polyesters (see also Sections 3. 4.2 and 3. 4 .3) Polyphenols Polyphenols react with epoxy resins on heating, but require... requirement profile can be developed by suitable formulations 2. 13 Plietiolic Resins for Coatings 87 2. 13. 1 Resols Resols are phenolic aldehyde resins that undergo self-cross-linking catalyzed with bases or basic salts Their structure depends on the choice and molar ratios of the raw materials (e.g., phenols and cresols), the solvents, and the type and amount of catalyst used Resols have free hydroxymethyl... combinations cure more rapidly and at lower temperature than epoxy resins cured with polyamines Anhydrides Polyanhydrides and not monoanhydrides must be used to cure epoxy surface coatings They are used in powder form for powder coatings and in solution for can coatings; both forms are hot curing The films have a good acid resistance, and do not impart an undesirable taste to foods Acids and Carboxy-Functional... Blocked isocyanates are usually used for curing [2. 133 ] Waterborne coatings are increasingly used for can coatings The binders are mainly based on epoxy resins High molecular mass epoxy resins ( M , 30 00-4000) can be made waterborne by graft polymerization with acrylates, methacrylates, and/ or acrylic or methacrylic acid in the presence of styrene, and subsequent neutralization with amines These waterborne . code: 3. 3; UN No.: 1866; MFAG: 31 0; Ems: 3 05; GGVEiGGVS: Class3 No. 31 C; RID/ADR: Class 3 No. 31 C; ADNR: Class 3 No. 31 C, Cat.; ICAO/IA- TA-DGR: 3, 1866 111; exception can be applied for. coil coatings solid, type 9 can coatings and finishes can coatings and finishes two-pack polyurethane 5000 paints high molecular primers (cold curing) mass epoxy 10000 can and coil coatings. transition temperature and good resistance to aqueous and acid solutions of the coatings. The chemical structure and high functionality lead to coatings with limited flexibility and a somewhat lower

Định dạng
Số trang	35
Dung lượng	2,71 MB