Description of paint products

1.1.1 Introduction

The term organic coating encompasses conventional paints, varnishes, enamels, lacquers, water-emulsion and solution finishes, nonaqueous dispersions (organosols), plastisols, and powder coatings. The following definitions have been used commonly, although not always in a consistant manner (IARC, 1989a; Stoye & Freitag, 1998; Brock et al., 2000; Goldschmidt & Streitberger, 2002). Glossaries for short explanations of paint and painting terms are available on the internet (e.g. www.occa.org.za/paintopedia/glossary.htm

# Sect. S).

Paint is a suspension of finely divided pigment particles in a liquid composed of a binder (resin) and a volatile solvent or water, normally with additives to impart special characteristics. The volatile components evaporate from the drying film after application, while the binder holds the pigment in the dry film, causing it to adhere to the substrate.

Some high quality, hard gloss paints are referred to as enamels.

Lacquer is defined as a coating that dries primarily by evaporation rather than by oxidation or polymerization. Because the solvents or water used in lacquers are relatively volatile and no chemical change is required for formation of the film, lacquers dry very rapidly.

Varnish is defined as a homogeneous, transparent or translucent liquid that is converted to a solid transparent film after being applied as a thin layer.

The basic components of paints vary widely in terms of chemical composition, depending on the colour, durability, and other properties required from the paint. Table 1.1 lists the main substances and classes of substances present in paints and to which workers may be exposed in the painting trades.

44 IARC MONOGRAPHS VOLUME 98

At the time of writing, solvent-borne paints contain much less solvent (high-solids paints) and less hazardous solvents than a decade ago. Sometimes, the solvent content is reduced to such an extent that volatile organic compounds (VOCs) emission levels are similar to those of waterborne paints.

Waterborne paints are used for private end consumers, as well as in several industries, including:

- the construction industry, for interior and exterior decoration - the metal industry,

- the wood industry, including the furniture-making industry, - the car industry, and

- the plastics industry.

Research and development for higher performance focuses on faster drying, and decrease of the residual solvents used in formulation. In countries where the ambiant air temperature is high together with elevated air humidity, waterborne paints are less convenient because of their very slow drying time. In these environments, high-solids paints or powder coatings are preferred.

The quality of powder coatings has much improved since their introduction, and now often reaches that of conventional paints. Future developments will allow their application onto heat-sensitive substrates such as wood-fibre plates or plastics.

1.1.2 Pigments and extenders (fillers)

Pigments can be classified as (i) inorganic, and (ii) organic pigments (Bentley &

Turner, 1998; Stoye & Freitag, 1998; Brock et al., 2000; Smith, 2002). They can also be classified into whites, colours, and effect pigments. Pigments are generally added in considerable proportion (3–60% by weight) to paint formulations and are used to provide colour, opacity, and sheen. They also affect the viscosity, flow, toughness, durability, and other physical or chemical properties of the coating, such as corrosion protection. The physical properties of pigments (particle shape and size) vary; the diameter of pigment particles is mostly <3 µm, and for special performance up to 15 or 20 µm. The particles in dry pigment powders are 0.5–10 µm in diameter (Oyarzún, 2000).

Dyes (soluble in paint medium, unlike pigments) are used only in very few instances or products because they provide much less long-term stability against light and other influences. Examples of use are the extremely transparent wood stains (see 1.3.2) (Zollinger

& Iqbal, 2003), and the limited use of transparent colorants in automotive clear coats for special effects in Japan (Streitberger & Dössel, 2008).

Hazardous pigments and fillers, especially chromate- or lead-based products, are being increasingly replaced even though many of the new products possess lower performance in coloristics, corrosion protection or mechanical properties of paint layers. The speed and type of changes depends mainly on local legislation, costs, suitability and simplicity of substituting for the newer products. Many paint systems for industrial or individual use are

OCCUPATIONAL EXPOSURE AS A PAINTER 45 free of lead and chromate, especially in western Europe, but the situation is extremely heterogeneous across countries worldwide.

Besides nanoparticle-based pigments (see below), new colour-effect pigments are being developed, such as interfering mica pigments, liquid-crystal pigments, inorganic or organic pigments with better performance in colour or stability, and corrosion-protection pigments with better corrosion effects for chromate substitution. New fillers with better mechanical properties are also being formulated and produced.

(a) Inorganic pigments and fillers

Inorganic pigments are an integral part of numerous decorative, protective and functional coating systems, as found in automobile finishes, marine paints, industrial coatings, traffic paints, maintenance paints, and exterior and interior oil, alkyd and latex house paints. Inorganic pigments belong to several different chemical classes, i.e. primary elements, oxides, carbonates, chromates, phosphates, sulfides and silicates (Brock et al., 2000; Smith, 2002; Buxbaum & Pfaff, 2005).

Many forms of lead have been used for over 200 years in pigments including: carbonate (white lead), oxides (litharge, red lead), sulfate, oxychloride (Turner's yellow), acetate, borate, and chromates (IARC, 2006a). During the last few decades, they have been substituted to a large extent by organic pigments or lead-free inorganic pigments.

Alternatives to lead are the very resistant and insoluble mixed-phase oxide pigments such as nickel (or chromium) titanium yellow (NiO.Sb₂O₅.20TiO₂), and bismuth vanadate (BiO₄V^-5). New oxide pigments include the spinel-structured cobalt blue Co(Al,Cr)₂O₄ and cobalt green (Co,Ni,Zn)₂(Ti,Al)O₄ (Winkler, 2003; Buxbaum & Pfaff, 2005).

Zinc chromate was widely employed to protect against rust formation on all sorts of equipment until recently (Buxbaum & Pfaff, 2005). Currently, its use is restricted to a few applications such as in primer formulations for airplanes. Other chromium pigments that had been used in paint for many years included lead chromates, barium chromate and chromium oxide (see IARC, 1990). Cadmium sulfide, cadmium sulfoselenide and antimony trioxide are now substituted with various grades of naturally occurring, or synthetic, ferric oxide which provide yellow, red and brown pigments (Buxbaum & Pfaff, 2005).

Today, the most common pigment employed in paint is the white pigment titanium dioxide, TiO2 (IARC, 2010a), produced in two different crystal forms – rutile and anatase – with distinct colour properties. The rutile crystal structure has an almost 25% greater opacity than the anatase form. Because of its chemical inertness, extreme whiteness, excellent covering power and lack of toxicity compared to white lead, titanium dioxide is the dominant component in the manufacture of white paint, and represents 90% of all pigments on the market worldwide. Lithopone, a coprecipitate of 28–30% zinc sulfide and 70–72%

barium sulfate (Buxbaum & Pfaff, 2005) introduced before the First World War, is hardly ever used any more.

46IARC MONOGRAPHS VOLUME 98 Table 1.1 Main substances (and classes of substances) which workers may be exposed to in the painting trades^a

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Acrylates (e.g., ethyl acrylate, methyl

methacrylate) Acrylic resins, ultraviolet

curing paints Ethyl acrylate Acrylic acid Methyl acrylate Methyl methacrylate

IARC (1999a) IARC (1999a) IARC (1999a) IARC (1999a)

2B 3 3 3

Acrylic resins Binders As above

Alcohols, aliphatic (e.g., methanol, isopropanol, n-butanol)

Solvents (lacquers), paint removers

Methanol Ethanol Isopropanol n-Butanol

– –

IARC (1999a) –

– – 3 – Alkalis (e.g., sodium hydroxide, potassium

hydroxide)

Paint removers – – –

Alkyd resins Binders – – –

Aluminium, powder Pigment – – –

Amides, aliphatic (e.g., dimethylformamide) Solvents Dimethylformamide IARC (1999a) 2A Amines (mono), aliphatic (e.g., diethylamine) and

alkanolamines (e.g., 2-amino-2-methyl-1-propanol)

Water-based paints Triethanolamine IARC (2000) 3

Amines (poly), aliphatic (e.g., diethylenetriamine)

Curing agents (epoxy resins) – – –

Amines, aromatic (e.g., meta-phenylenediamine, 4,4-methylenedianiline)

Curing agents (epoxy resins) meta-Phenylenediamine 4,4-Methylenedianiline

IARC (1987) IARC (1987)

3 2B Amino resins (e.g., urea-formaldehyde resins,

melamine-formaldehyde resins)

Binders See Formaldehyde

OCCUPATIONAL EXPOSURE AS A PAINTER 47 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Ammonia Water-based paints – – –

Anhydrides, organic (e.g., maleic anhydride, phthalic anhydride, trimellitic anhydride)

Alkyd resin synthesis, curing agents (epoxy resins)

Succinic anhydride IARC (1987) 3

Antimony compounds (e.g., antimony trioxide) Pigments, fire retardant pigments

Antimony trioxide Antimony trisulfide

IARC (1989a) IARC (1989a)

2B 3 Arsenic compounds (e.g., copper aceto-arsenate) Antifouling agents – IARC (1987) 1

Asbestos Filler, spackling and taping

compounds, talc Asbestos IARC (1987) 1

Barium compounds (e.g., barium sulfate, barium carbonate)

Pigments – – –

Benzoyl peroxide Catalyst Benzoyl peroxide IARC (1999a) 3

Bisphenol A Epoxy resins IARC (1999a) 3

Cadmium compounds (e.g., cadmium sulfide, cadmium sulfoselenide)

Pigments Cadmium and Cadmium

compounds

IARC (1993) 1

Calcium compounds (e.g., calcium sulfate,

calcium carbonate) Fillers – – –

Camphor Plasticizer – – –

Carbon black Pigment Carbon black IARC (2010a) 2B

Cellulose ester resins (e.g., cellulose nitrate, cellulose acetate)

Binders – – –

Chloracetamide Fungicide (water-based paints) – – –

48IARC MONOGRAPHS VOLUME 98 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Chlorofluorocarbons Spray-can paint propellants Chlorofluoromethane IARC (1999a) 3 Chromium and chromium compounds (e.g.,

chromic oxide, chromates)

Pigments Chromium (III) compounds

Chromium (VI) compounds Chromium, metallic

IARC (1990) IARC (1990) IARC (1990)

3 1 3

Clays (e.g., bentonite) Fillers – – –

Coal-tar and asphalt Special waterproof coatings

(ships, tanks, pipes) Coal tar Coal-tar pitches Bitumen extracts Bitumen refined

IARC (1987) IARC (1987) IARC (1987) IARC (1987)

1 1 2B 3 Cobalt compounds Pigments, driers Cobalt and cobalt compounds

Cobalt, metallic

IARC (1991a) IARC (2006a)

2B 2B Copper and copper compounds (e.g., bronze

powder, cuprous oxide)

Pigments, antifouling agents – – –

Dyes and pigments, organic (e.g., aromatic azo dyes, phthalocyanines, rhodamine)

Pigments CI Basic Red 9 } Magenta production } 2-naphthylamine } 4-aminobiphenyl } Auramine production } Benzidine } Benzidine-based dyes }

IARC (1982) IARC (2010b)

2B 1 1 1 1 1 1

Epichlorohydrin Epoxy resins Epichlorohydrin IARC (1999a) 2A

Epoxy resin Binders – IARC (1976) –

Esters, aliphatic (e.g., ethyl acetate, isopropyl acetate)

Solvents – – –

OCCUPATIONAL EXPOSURE AS A PAINTER 49 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Ethers, aliphatic (e.g., isopropyl ether,

tetrahydro-furan) and glycol ethers (e.g., methyl cellosolve) Solvents 2-Butoxyethanol 1-tert-Butoxypropan-2-ol IARC (2006b)

IARC (2006b) 3 3 Formaldehyde Amino resin varnishes, biocide

(water-based paints)

Formaldehyde IARC (2006b) 1

Gasoline Solvent Gasoline IARC (1989b) 2B

Glycidyl ethers (e.g., n-butyl glycidyl ether and bisphenol A diglycidyl ether)

Epoxy resin diluents and constituents

Phenylglycidyl ether Triethylene glycol diglycidyl ether

Bisphenol A diglycidyl ether

IARC (1999a) Glycols (e.g., ethylene glycol) Polyester resins, water-based

paints

– – –

Hydrocarbons, aliphatic (e.g., hexanes, heptanes) Solvents (naphthas, white spirits)

– – –

Hydrocarbons, aromatic (e.g., benzene, toluene, xylenes, trimethylbenzene)

Solvents (naphthas, white spirits), paint removers

Benzene Hydrocarbons, chlorinated

(e.g., dichloromethane, 1,1,1-trichloroethane, carbon tetrachloride, trichloroethylene)

Solvents, paint removers, metal degreasers Hydrochloric acid (hydrogen chloride) Catalyst (amino resins) – IARC (1992) 3 Iron compounds (e.g., iron oxides, ferric

ferrocyanide)

Pigments Ferric oxide IARC (1987) 3

50IARC MONOGRAPHS VOLUME 98 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Isocyanates (e.g., 1,6-hexamethylene diisocyanate, toluene diisocyanate)

Two-component polyurethane resins

Toluene diisocyanate IARC (1999a) 2B

Isothiazolones (e.g., 1,2-benzisothiazolin-3-one) Biocides in tinned foods – – –

Kerosene Solvent Jet fuel IARC (1989c) 3

Ketones, aliphatic (e.g., acetone, methyl ethyl ketone, cyclohexanone, isophorone, diacetone alcohol)

Solvents, lacquers, paint removers

Cyclohexanone IARC (1999a) 3

Lead compounds (e.g., lead chromate, lead oxides, basic lead carbonate, lead naphthenate)

Primers, pigments, driers Lead

Lead compounds, inorganic

IARC (1987) IARC (2006c)

2B 2A Magnesium compounds (e.g., magnesium

carbonate)

Fillers – – –

Manganese naphthenate Drier – – –

Mercury compounds (e.g., mercuric oxide, phenyl mercuric acetate)

Fungicides (water-based paints) Mercury and inorganic mercury compounds

IARC (1993) 3

Methyl cellulose Thickener (water-based paints) – – –

Mica Filler – – –

Molybdenum compounds (e.g., lead molybdate) Pigments – – –

Nickel, metal powder Pigment Nickel compounds

Nickel, metallic and alloys

IARC (1990) IARC (1990)

1 2B 2B Nitroparaffins (e.g., nitroethane, 2-nitropropane) Solvents 2-Nitropropane IARC (1999a) 2B

Oils, vegetable (e.g., linseed oil, tung oil) Binders – – –

OCCUPATIONAL EXPOSURE AS A PAINTER 51 Table 1.1 (Contd)

Material Principal uses or sources of

emissions Agent evaluated IARC

Monographs Evaluation Oximes (e.g., methyl ethyl ketoxime) Anti-oxidants, anti-skinning

agents

– – –

Petroleum solvents (e.g., Stoddard solvent, VM & P naphtha)

Solvents, paint removers Petroleum solvents IARC (1989a) 3

Phenol Phenol-formaldehyde resins,

paint remover (formerly) Phenol IARC (1999a) 3

Phenol-formaldehyde resins Binders See Phenol, and Formaldehyde

Phenols, chlorinated (e.g., pentachlorophenol) Fungicides (water-based paints) Polychlorophenols and their sodium salts

Pentachlorophenol

IARC (1999a) IARC (1991b)

2B 2B Phosphates, organic (e.g.,

tricresyl-ortho-phosphate, tributyl phosphate)

Plasticizers – – –

Phthalate esters (e.g., dibutyl phthalate, dioctyl phthalate

Plasticizers Di(2-ethylhexyl)phthalate Butyl benzyl phthalate

IARC (2000) IARC (1999b)

3 3 Polychlorinated biphenyls Plasticizers Polychlorinated biphenyls IARC (1987) 2A Polycyclic aromatic hydrocarbons Special waterproof coatings

(ships, tanks, pipes)

Selected polycyclic aromatic hydrocarbons

IARC (2010c) –^b

Polyester resins Binders – – –

Polyurethane resins Binders Polyurethane foams IARC (1987) 3

Polyvinylacetate resins Binders Polyvinyl acetate IARC (1987) 3

52IARC MONOGRAPHS VOLUME 98 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Pyrolysis fumes Removal of paint by burning;

heat-curing operations

– – –

Rosin Binder – – –

Rubber, synthetic (e.g., butyl rubber, styrene-butadiene rubber)

Binders (special paints, water-based paints)

Rubber industry IARC (1987) 1

Shellac resin Binder – – –

Silica, amorphous (e.g., diatomaceous earth) Filler Silica, amorphous IARC (1997) 3 Silica, crystalline (e.g., quartz) Filler, sand-blasting operation Silica, crystalline IARC (1997) 1 Silicates (e.g., sodium silicate, aluminium

silicate)

Fillers – – –

Stearates (e.g., aluminium stearates, zinc stearates)

Soaps, flattening agents – – –

Strontium compounds (e.g., strontium chromate, strontium sulfide)

Pigments Strontium chromate see Chromium and chromium compounds

Styrene Polyester resins Styrene IARC (2002) 2B

Styrene oxide Diluent (epoxy resins) Styrene-7,8-oxide IARC (1994) 2A

Sulfuric acid Metal cleaner – – –

OCCUPATIONAL EXPOSURE AS A PAINTER 53 Table 1.1 (Contd)

Material Principal uses or sources of

emissions

Agent evaluated IARC Monographs

Evaluation

Talc Filler Talc containing asbestiform

fibres

Talc, not containing asbestiform fibres

IARC (1987) IARC (2010a)

1 3

Tin, metal powder Lacquers (tinplate containers) – – –

Tin, organic compounds (e.g., tri-n-butyltin oxide, dibutyltin laurate)

Antifouling agents, catalysts – – –

Titanium dioxide Pigment Titanium dioxide IARC (2010a) 2B

para-Toluenesulfonic acid Catalyst (amino resins) – – –

Turpentine Solvent – – –

Vinyl acetate Polyvinylacetate resins Vinyl acetate

Vinyl chloride – vinyl acetate copolymers

IARC (1995) IARC (1987)

2B 3

Zinc and compounds (e.g., zinc metal powder, zinc oxide, zinc chromate)

Pigments, catalysts, bodying agents

Zinc chromate see Chromium and chromium compounds

a Updated from IARC (1989); –, not evaluated by IARC

b Groups 1–3, see IARC Monographs Volume 92 for details

54 IARC MONOGRAPHS VOLUME 98

The use of iron-blue pigments M^I[Fe^IIFe^III(CN)₆] (Milori blue, Vossen blue, Berlin blue, Prussian or Turnbull´s blue) is in decline as they are too sensitive to chemicals and alkaline water.

The term earth pigments is obsolete, as these iron or chromium(III) oxide pigments (Fe2O3, Fe(O)OH, Cr2O3) are now produced synthetically from ores in a similar manner to titanium dioxide, the most widely used of the coloured pigments derived from natural sources (Buxbaum & Pfaff, 2005). Natural iron oxides are processed from several different ores, including haematite (see IARC, 1987), limonite, siderite and magnetite, and provide a range of reds, yellows, purples, browns and blacks. Iron oxide particles of around 10 nm are highly transparent and additionally, offer good ultraviolet (UV) protection of wood.

Bismuth vanadate pigments are a relatively new class of pigments that have steadily gained importance over the last three decades. Formulations range from BiO₄V^-5 to the mixed pigment 4BiVO₄x3Bi₂MoO₆. The pigments are lead- and chromate-free inorganic yellow pigments used to manufacture high-peformance brillant yellow, orange, red, and green shades. Bismuth vanadate has become an increasingly important substitute for lead chromate in the last 10–20 years. Nevertheless, lead chromate and lead wolframate are still used in some countries (Smith, 2002).

Traditionally, the most important black pigment, carbon black (microcrystalline carbon, graphite-similar), belongs to inorganic pigments (Buxbaum & Pfaff, 2005). The small particles (10–40 nm) can have surface areas as large as 1000 m²/g.

Nanoparticles, mostly inorganic, are chemically similar to pigments and fillers, but they are discussed together with additives because of their special additive-like functions, and the low contents at which they are used in formulations.

(i) Lustre pigments (effect pigments)

This group includes metallic, pearlescent and iridescent pigments. The most common metallic dusts and powders used in paint are aluminium powder or fine flakes and bronze powders, which consist of metals in a finely divided state; e.g. gold bronzes are alloys of copper with varying proportions of zinc or aluminium (Glausch et al., 1998; Wissling, 2006).

Additional effect pigments developed for new optical effects include mica plates, which have been increasingly used over the last 20 years (often inorganically coated with silicium dioxide, iron(III)oxide, chromium(III)oxide or aluminium oxide). The thickness and the kind of metal oxide used has an impact on the optical effect, especially the colour and the interference effect [where the angle of watching determines the colour]. Other plate-like effect pigments are based on silicium dioxide, thin polymer flakes or haematite (Wissling, 2006).

(ii) Fillers

Materials used as fillers (extenders) are not pigments as they do not contribute to the coloristic or functional properties of the coating (Stoye & Freitag, 1998; Brock et al., 2000;

OCCUPATIONAL EXPOSURE AS A PAINTER 55 Nanetti, 2000). Typical fillers are barium sulfate (barytes), calcium carbonate (ground limestone and chalk), silica (diatomaceous or amorphous, pyrogenic or precipitated; see IARC, 1997), clays (hydrated aluminium silicate), talcum (hydrated magnesium silicate; see IARC, 1987) and mica (hydrated potassium aluminium silicate). Fillers are often added to paint to reduce cost, improve physical characteristics, and increase resistance to wear; their effects are largely governed by their average particle size. This size is normally about 1–

10 µm, and under 0.1 µm for special performances.

(b) Organic pigments

Hundreds of organic pigments, comprising a broad spectrum of structural classes, are used in the paint industry (Brock et al., 2000; Smith, 2002; Zollinger & Iqbal, 2003). The most important and established uses for organic pigments include the coloration of coating compositions for interior, exterior, trade and automotive applications, including oil and water emulsion paints and lacquers. Azo pigments are formed by successive diazotization of a primary amine and coupling.

After the discovery of Perkins’ mauve in 1856, the development of synthetic colouring materials continued with the discovery of fuchsin in 1858 and of other triphenylmethane dyes, such as alkali blue, methyl violet, and malachite green. Large amounts of these dyes were used as the first synthetic organic pigments. The largest single advance in pigment technology after the First World War was the discovery in the 1930s of phthalocyanine blue and, later, its halogenated green derivatives, which are still widely used in automotive finishes. Other main categories of organic pigments used in paints and related products include quinacridones, thioindigos, perinones, perylenes, diketo-pyrrolopyrroles and anthraquinone.

Organic effect pigments have reached some commercial significance. In particular, liquid crystals (spiro compounds), fixed in the binder matrix by polymerization, permit extreme colour changes depending on the viewing angle.

In the 1960s, there were probably more than 200 different organic pigments used in paints. At the time, azo pigments such as Benzidine Yellow were considered to have relatively low toxicity, and were widely used. These pigments are of relatively low solubility, and although they are based on the aromatic amine 3,3′-dichlorobenzidine, the free amine is not bioavailable. IARC (1982) identified eight pigments based on 3,3′-dichlorobenzidine. Three 3,3′-dichlorobenzidine-based paint pigments were commonly used in architectural finishes in the mid-to-late 1960s. Benzidine was used as the basis for the paint pigment pyrazolone maroon (see IARC, 2010b).

Free aromatic amines used in the synthesis of azo pigments can be found in trace amounts as impurities. The aromatic amines 4-aminobiphenyl, benzidine, 2-naphthylamine and 2-methyl-4-chloroaniline [4-chloro-ortho-toluidine] have been found in azo pigments (see IARC, 2010b).

56 IARC MONOGRAPHS VOLUME 98

Im Dokument IARC Monographs on theEvaluation of Carcinogenic Risks to Humans (Seite 53-66)