Coatings Technology Handbook 2010 Part 9 pps

Krister Holmberg Chalmers University of Technology DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM Oil Length and Type of Oil • Percentage of Phthalic Anhydride • Actual Functiona

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Polyesters 50-13

47 D Stoye and J Dörffel, in Organic Coatings, Science and Technology, Vol 6 New York: Dekker,

1984, pp 257–275

48 L W Hill and K Kozlowski, J Coat Technol., 59, 63 (1987).

49 F N Jones and D D -L Lu, J Coat Technol., 59, 73 (1987).

50 K H Albers, A W McCollum, and A E Blood, J Paint Technol., 47, 71 (1975).

51 M R Olson, J M Larson, and F N Jones, J Coat Technol., 55, 45 (1983).

52 K L Payne, F N Jones, and L W Brandenburger, J Coat Technol., 57, 35 (1985).

53 H Müller et al., U.S Patent 4,668,763 (1987); Dynamit Nobel

54 M Schmitthenner, paper presented at the ECCA Annual Congress, Brussels, 1983

55 R R Robertson, paper presented at the 1982 Fall Technical Meeting, NCCA

56 M Schmitthenner, paper presented at the Fourteenth International Conference on Organic Coat-ings Science and Technology, Athens, 1988

57 Federal Register, Vol 21, Section 175.300 [Food and Drug Administration].

58 S Harris, Polym Paint Color J., 174 (4114), 162–164 (1984).

59 E Bodnar and P Taylor, Pigment Resin Technol., 15(2), 10–15 (1986).

60 R Gras, F Schmitt, and W Wolf, U.S Patent 4,246,380 (1981); Hüls

61 R Gras et al., U.S Patent 4,413,079 and 4,483,798 (1984); Hüls

62 P L Heater Jr., EP Patent 0 056 356 (1985); Goodyear

63 Ciba-Geigy Bulletin, Araldit PT 810 Ciba-Geigy, Basel, Switzerland

64 W Marquardt and H Germeller, Farbe und Lack, 86, 696–698 (1980).

65 J W Saracsan, EP Patent 0,089,913 (1983); Goodyear

66 Dynapol Coatings Bulletin L-650 (product information), Hüls AG, Marl, West Germany.

67 Polyester Resins, Adhesives and Coatings (brochure), Dayton Chemical Division of Whittaker Corp.,

West Alexandria, OH

68 H F Huber and H Müller, Conf Proc Radcure, 86, 12–23 (1986).

69 H F Huber and H Müller, Conf Proc Radcure, 87, 8–35 (1987).

DK4036_book.fm Page 13 Monday, April 25, 2005 12:18 PM

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51

Alkyd Resins

51.1 Classiﬁcation 51-1

51.2 Principle of Alkyd Synthesis 51-2 51.3 Functionality and Prediction for Gel Point 51-4 51.4 Raw Materials 51-6 51.5 Manufacturing Process 51-7

51.6 Alkyds for Reduced Solvent Emission 51-9

51.7 Modiﬁed Alkyds 51-10

51.8 Uses 51-11 References 51-11

Alkyd resins represent a class of polymers that are used in surface coating formulations because of their low cost and versatility The term “alkyd” was coined by Kienle and Ferguson1 and is derived from “al”

of alcohol and “cid” of acid; “cid” was later changed to “kyd.”

Alkyd resins in a broad sense refer to polymers By convention, however, polyesters with unsaturation

in the backbone are not referred to as alkyds but are termed “unsaturated polyesters.”

The specific definition of alkyds that has gained wide acceptance is that alkyds are polyesters modified with fatty acids The nonmodified resins are then called saturated polyesters Terms like “oil-free alkyd” and “oil-modified polyester” can also be found in the literature

51.1 Classification

Alkyds are synthesized from three basic components: polybasic acids, polyols, and (except for oil-free alkyds) fatty acids The nature and proportions of these components control the properties of the resin The amount of combinations is enormous, and speciﬁcation of an alkyd resin must involve several parameters The most important ways of classifying are given below

51.1.1 Oil Length and Type of Oil

Depending on the weight percentage of fatty acid in the resin, alkyds are referred to as short oil (<45%), medium oil (45 to 55%), or long oil (>55%) However, some confusion exists regarding the terminology

Krister Holmberg

Chalmers University of Technology

Oil Length and Type of Oil • Percentage of Phthalic Anhydride •

Actual Functionality • Gel Point • Alkyd Calculations Acid Value and Hydroxyl Number

Polybasic Acids • Polyols • Fatty Acids and Oils

Fusion Method versus Solvent Method • Monoglyceride versus

High Solids Coatings • Emulsion-Based Coatings • Powder Fatty Acid Process

Coatings Polyamide Modification • Vinyl Modification • Other Modifications

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Alkyd Resins 51-3

reactivity of the functional groups in the growing polyester chain is independent of the degree of polymerization In other words, at all stages of polymerization, the reactivity of every functional group

is the same This principle of equal reactivity of functional groups, ﬁrst demonstrated by Flory,4,5 is important for alkyd synthesis because it permits the application of statistical considerations to the problem of distribution of the bonds formed during polymerization

Polyesteriﬁcation carried out in the absence of an added catalyst has been found to follow third-order kinetics.5,6 The carboxyl groups act as catalyst, and the mechanism involved is the following:

The second step is believed to be rate determining.7 In reaction media of low dielectric constant, such

as esters and polyesters, the ions are probably associated as ion pairs The decrease in concentration of carboxyl groups can be expressed as follows:

If the polyesteriﬁcation is performed in the presence of an acid catalyst, the reaction becomes second order.6,7 At high degrees of conversion, however, the reactions become sluggish This has been ascribed

to depletion of the catalyst; at low concentration of remaining carboxyl groups, a catalyst, such as p -toluenesulfonic acid, may compete favorably in reacting with hydroxyl groups, thus acting as a chain-terminating additive.8,9

TABLE 51.1 Effect of Oil Length and Type of Oil on the Properties and Uses of Alkyds

Oil Type

Oil Length

Oxidizing ≥ 60 Linseed, safﬂower, soybean, tall oil

fatty acids; wood oil in blends with other oils; dehydrated castor oil

Soluble in aliphatic solvents; compatible with oils and medium oil length alkyds; good drying characteristics; ﬁlms are ﬂexible, with reasonable gloss and durability

Oxidizing 45–55 Linseed, safﬂower, soybean, tall oil

fatty acids; wood oil in blends with other oils

Soluble in aliphatic or aliphatic–aromatic solvent mixtures; good drying characteristics, durability, and gloss

Oxidizing ≤ 45 Linseed, safﬂower, soybean, tall fatty

acids; wood oil in blends with other oils; dehydrated castor oil

Soluble in aromatic hydrocarbons; low tolerance for aliphatic solvents; usually cured at elevated temperatures either by heating with manganese driers or with urea or melamine formaldehyde resins

Nonoxidizing 40–60 Coconut oil, castor oil, hydrogenated

castor oil

Soluble in aliphatic–aromatic solvent blends; usually used as a plasticizer for thermoplastic polymers such as nitrocellulose

Nonoxidizing ≤ 40 Coconut oil, castor oil, hydrogenated

castor oil

Soluble in aromatic solvents; used as a reactive plasticizer that chemically combines with other resin entities (e.g melamine–formaldehyde resin)

Source: From Solomon, D H., The Chemistry of Organic Film Formers. New York: Krieger, 1977, p 91.

2

H

H O

2

←

COOH

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TABLE 51.3 Typical Fatty Acid Composition (%) of Vegetable Oils

Fatty Acid

Vegetable Oils Castor Coconut Linseed Olive Palm Palm Kernel Peanut Safﬂower Soybean Sunﬂower Tall Tung

C18 Ricinoleic

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51-12 Coatings Technology Handbook, Third Edition

28 S Paul, Surface Coatings: Science and Technology, 2nd ed New York: Wiley, 1996.

29 A G North, J Oil Colour Chem Assoc., 39, 695 (1956).

30 E F Redknap, J Oil Colour Chem., Assoc., 43, 260 (1960).

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52

The Polyurea Revolution: Protective

Coatings for the 21st Century

52.1 History 52-1 52.2 Polyureas versus Polyurethanes/Chemistry 52-1 52.3 Application Characteristics 52-2 52.4 General Performance 52-2 52.5 Weathering Characteristics 52-2 52.6 Chemical, Water, and Corrosion Resistance 52-2 52.7 Safety 52-3 52.8 Conclusion 52-4

Welcome to the new world of polyureas In the time it is taking you to read this sentence, a polyurea elastomeric coating, mixed and sprayed onto a surface, will have reached its initial set

52.1 History

Polyureas were first developed in the 1970s, but the development of any practical application was impeded

by their extremely short set times of 1 to 3 sec In the early 1980s, sophisticated, plural-component heated equipment was able to mix quickly and dispense the polyureas into a usable form Throughout the 1980s and 1990s, improvements in polyurea chemistry led to products with set times that ranged from 3 sec

to 25 min This led to a wide variety of practical applications

52.2 Polyureas versus Polyurethanes/Chemistry

Polyureas, as the name suggests, are closely related to polyurethanes Both polyureas and polyurethanes are based on a two-component system, with one component being an isocyanate material Polyureas’ second component is a polyether polyamine, whereas polyurethanes’ second component is a polyether polyol Polyurethanes require a catalyst to speed up the reaction time of the components, whereas polyureas do not The polyurethane reaction is sensitive to low temperatures and moisture due to the addition of catalysts Low temperatures inhibit the reaction time Moisture interferes with the reaction

by creating carbon dioxide, which causes blistering in the polyurethanes Polyureas, on the other hand, require no catalyst, so they are able to cure at any temperature and in the presence of moisture The fast curing ability of polyureas is inherent in their chemistry, which gives them several unique advantages

Bruce R Baxter

Specialty Products, Inc.

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53

Phenolic Resins

53.1 Rigid Packaging 53-2 53.2 Maintenance Primers 53-3 53.3 Printing Inks 53-3 53.4 Epoxy Hardeners 53-4 53.5 Summary 53-4 References 53-5

Synthetic phenolic resins were developed and commercialized in the early 1900s by Leo Baekland.1 The reaction of phenol and formaldehyde produces a product that forms a highly cross-linked three-dimen-sional polymer when cured The resins have found use in various applications in the coatings industry because of their excellent heat resistance, chemical resistance, and electrical properties They also offer good adhesion to many substrates and have good compatibility with other polymers

Phenolic resins have two basic classifications: resoles and novolaks Resoles, or heat-reactive resins, are made using an excess of formaldehyde and a base catalyst The polymer that is produced has reactive methylol groups that form a thermoset structure when heat is applied

Novolaks are made using an excess of phenol and an acid catalyst Reaction occurs by the protonation

of the formaldehyde,2 and the intermediate is characterized by methylene linkages rather than methylol groups These products are not heat reactive, and they require additional cross-linking agents such as hexamethylenetetramine to become thermosetting These reactions can be thought of as nucleophilic attack of phenoxide ion on the formaldehyde, or electrophilic substitution by protonated formaldehyde

on the aromatic ring.3

Both polymerization reactions evolve water during cure This condensation reaction serves to limit film thickness to approximately 3 mils, because the volatiles will cause blistering while curing takes place Baking temperatures are generally 300 to 400°F with a bake time of 10 to 30 min

Phenolic resin polymers have been used in the coatings industry for many years because of their excellent performance properties and their relatively low cost Some of the major applications are in rigid packaging, maintenance primers, printing inks, and epoxy hardeners A brief discussion of these appli-cations follows

Base Formaldehyde

H2C

CH2OH

OH

CH2 CH2OH OH

Kenneth Bourlier

Union Carbide Corporation

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54

Coal Tar and Asphalt Coatings

54.1 Coal Tar Types 54-1 54.2 Asphaltic Types 54-3 Bibliography 54-4

Coal tar coatings have been used for many centuries because of their resistance to water and biological organisms Coatings based on asphalt have been developed for over a century This is a brief review of the materials

54.1 Coal Tar Types

Bituminous coal, a very complex chemical mixture, decomposes into simpler components when heated

in retorts without air above 700°C (1292°F) Gas, aqueous vapor, and coal tar are driven off, leaving coke

as residue The coat tar is dehydrated and heated in stills to yield oil and coal tar pitch Depending on the source of the coal tar and the amount of heat applied, pitches of different characteristics are obtained When used as bases for superior coatings, coal tar pitches are reprocessed, and any corrosion-accelerating substances are removed Various types of coal tar pitches are then blended together

The outstanding quality of coal tar paints is their extremely low permeability, their high electrolytic resistance, and their remarkable resistance to the disintegrating action of water There are hardly any materials, old or new, that are as water resistant as properly compounded coal tar coatings They will not be affected by mineral oil but may be dissolved by vegetable and animal oil, grease, and detergents,

if they are in direct contact with them Their resistance to weak mineral acids, alkalis, salts, brine solutions, and other aggressive chemicals is good Furthermore, coal tar paints give more value per dollar than any other protective coating This fact should not be overlooked when selecting paint for a certain job Coal tar paints are made by dissolving the processed pitch or blend of pitches in suitable solvents Skill and experience are essential in compounding coal tar paints because similar physical characteristics of raw materials do not necessarily mean similar behavior of the finished product under exposure The raw materials selected for the blending, the degree of refining, and the addition of other modifiers, often in small quantities, decide the final merit of the coating

There are five main types of coal tar coatings:

1 Thin coal tar pitch solutions without any filler

2 Heavy coal tar pitch solutions with inert fillers added

3 Very heavy coal tar pitch coatings containing inert fillers possessing a thixotropic gel structure but only medium inherent viscosity

4 Heavy coal tar emulsions containing inert fillers and having low inherent viscosity

5 Hot applied coal tar coatings

Henry R Stoner

Henry R Stoner Associates

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54-2 Coatings Technology Handbook, Third Edition

The first three types are solutions and have about the same chemical and water resistance They vary mainly in the thickness of the film that can be laid down in a single coat The fourth type, coal tar emulsions, consists of dispersions of coal tar pitch in water and are inferior in corrosion resistance to the solution type This is not a fault of the pitch itself but is caused by the higher permeability of the applied film Pitch particles dispersed in water are relatively large and do not coalesce as completely after drying as the much smaller dissolved pitch particles do But coal tar emulsions have other very good features that will be mentioned later

The fifth type, coal tar pitch reinforced with inert filler and applied in a molten state over a primer, is called in the trade, coal tar enamel These enamels have all the good qualities of coal tar paints, but in a higher degree, because the coating is very thick and does not depend on the evaporation of solvent to set Type 1 is a thin coal tar solution of low viscosity with a solids content of 60 to 70% and a spreading rate of 300 to 400 square feet per gallon, and it gives an approximate thickness of 1 to 2 mils per coat This thickness cannot be increased because the thin solution cannot be applied at a lower rate without sagging Type 2 is designed to achieve a heavier coat; a filler coal tar solution must be used, which, in addition to its higher solids content, can be applied at approximately 180 square feet per gallon without sagging This produces an approximate dry film thickness of 6 mils To apply even heavier coatings by brush, a gel must be selected that can be applied at the low rate of 75 square feet per gallon without sagging This will produce a dry film thickness of approximately 16 mils in one coat Coal tar emulsions will not sag at a coverage of 75 square feet per gallon and will give approximately a 12 mil dry film thickness in one coat

Coal tar paints afford protection by the mechanical exclusion of moisture and air If they are applied

as a continuous film without holidays, they give almost perfect protection As it is impossible to avoid pinholes and flaws in a one-coat application, more than one coat will be necessary They dry by solvent evaporation only

Concrete, as a rule, can be protected with thin coal tar solutions, but steel requires heavier coatings that will form an almost impervious barrier against severe corrosive influences

All coal tar paints “alligator,” more or less, in the sun The paint will look like an alligator skin, and hence, the name alligatoring This alligatoring is a surface defect It is brought about by the hardening

of the upper layer of the film, stimulated by the sun’s rays This causes the upper layer to contract, crack, and slip over the lower stratum which is still soft If not enough coats are applied, these alligator marks can go right down to metal, opening the path for atmospheric corrosion Alligatoring does not (or only

to a limited degree) occur under water, where the coating is protected from the rays of the sun Coal tar emulsions do not produce this phenomenon, probably because the pitch particles are not fused as tightly

as in solution types; therefore, coal tar emulsions can be used as topcoats over badly alligatoring heavy coal tar paints Bear in mind that these emulsions have less protection capabilities in immersion service and are not recommended for such use

There are several popular methods to prevent alligatoring of heavy coal tar coatings, which are temporarily exposed to sun and air before submersion The older method uses a whitewash Add slowly and simultaneously 150 lb of processed quicklime and 1 gal of boiled linseed oil to 50 gal of water, containing 10 lb of salt dissolved therein While being mixed and for 15 min thereafter, the mixture shall

be stirred continuously and allowed to cool It shall be free from lumps and foreign matter The whitewash shall be aged for at least 3 days before application (NAVDOCKS Specification 34 Yc)

A more current approach is to use an acrylic latex paint, or a similar emulsion paint applied to the surface of the coal tar coating However, note that discoloration of this paint’s film by the oils in the coal tar coating is not deemed as a cause for failure

The solvents used in coal tar pitches are strong in odor, and adequate ventilation is necessary during applications and drying Coal tar emulsions, which use water as a volatile thinner, are in this respect superior and should be used where proper ventilation is not possible

Coal tar paints give excellent protection at low cost in dam and flood control installations, penstocks, piers, marine work, etc

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