Coatings Technology Handbook Episode 2 Part 5 pptx

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 resistan

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53-4 Coatings Technology Handbook, Third Edition

gloss.12 Parasubstituted phenolic novolak resins that have been modified with rosin make excellent ink additives Rosin modification of the phenolic resin raises the melting point and gives the phenolic excellent oil solubility The formulations consist of a phenolic resin, oils, pigments or dyes, driers, and lubricants

or plasticizers.13 The proper balance of ingredients gives the desired combination of hardness, viscosity, penetration, and drying rate

53.4 Epoxy Hardeners

Phenolic resins may be combined with epoxy resins for use in protective coatings Phenolic–epoxy products are also used in laminates, prepreg manufacturing, molding materials, and electrical insulation coatings The phenolic resin is used as a coreactant to produce thermoset systems with improved heat and chemical resistance Non-heat-reactive (novolak) resins are used to cross-link the epoxies The epoxy resins are typically epoxy–phenolics or bisphenol A-based resins.14 The reaction mechanism is different from the resole–epoxy reactions The coating is heat-activated and uses a base catalyst such as an amine,

polyether structure, which has an advantage, because no volatiles are released during cure This allows for thick films to be produced with low shrinkage and no voids from volatile emission The phe-nolic–epoxy reaction using a base catalyst can be demonstrated as follows:

For critical electrical applications, “high purity” resins are used These products are made according

to stringent specifications limiting the amount of water, ions, and free monomers present in the resin

53.5 Summary

Phenolic resins were one of the first synthetic polymers to have widespread commercial importance Their outstanding performance properties have given them a permanent role in the coatings industry They are used in applications ranging from railroad tank cars to carbonless copy paper Phenolic resins are also used on a wide variety of substrates including metal, wood, paper, and ceramics There are so many types of phenolic resin available to the marketplace that a particular resin can be selected for virtually any application

Phenolic resins should not be overlooked when choosing a high performance polymer Phenolics currently do not receive the same attention as some of the more recently developed polymers, but for many applications, there is simply no substitute for phenolic resins Phenolics will continue to have an

OH OH

CH2 CH2

CH2

H2C CH.CH2O-R OCH2-CH CH2

n

Base

∆

OCH2CH(OH)CH2O-R OCH2-CH(OH)CH2O

OCH2CH(OH)CH2O-R OCH 2 -CH(OH)CH2O

DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM

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Phenolic Resins 53-5

References

1 J S Fry, C N Merriam, and W H Boyd, Chemistry and Technology of Phenolic Resins and Coatings,

1985, p 1147

2 R T Morrison, and R N Boyd, Organic Chemistry, 3rd ed Boston: Allyn and Bacon, 1973, p 1147

3 J S Fry, C S Merriam, and W H Boyd, Chemistry and Technology of Phenolic Resins and Coatings,

1985, p 1149

4 Union Carbide Corp., Formulation Suggestions — Durable Phenolic Baking Coatings for Rigid Metal Substrates (F-60675), 1988

5 A Knop, and L Pilato, Phenolic Resins. Berlin: Springer-Verlag, 1985, p 247

7 R W Martin, The Chemistry of Phenolic Resins. New York: Wiley, 1956, p 203

9 R W Martin, The Chemistry of Phenolic Resins. New York: Wiley, 1956, p 205

11 S H Richardson, Paint Varnish Prod., August (1955)

1979, p 192

14 J S Fry, Ucar Phenolic Resins for Epoxy Hardeners. Union Carbide Corp (P-)-3(57)

15 U S Patent 3,493,630, Union Carbide Corp

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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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55 Vulcanizate Thermoplastic

Elastomers

55.1 Introduction 55-1 55.2 Properties 55-1 55.3 Processing 55-2 55.4 Uses of TPV 55-2

55.1 Introduction

A thermoplastic elastomer (TPE) is a material that is processed in the same manner as a conventional thermoplastic but gives a finished article with properties and performance similar to those of a thermoset rubber Thermoplastic vulcanizates (TPVs, referred to as elastomeric alloys in some earlier literature) are

a generic class of TPEs with a chemically cross-linked rubber phase in a continuous matrix of thermo-plastic TPVs thus have properties significantly better than those of the same rubber/thermoplastic composition with little or no cross-linking of the rubber phase (i.e., and olefinic blend)

performance, moderate cost TPEs They have performance and cost higher than those of the styrenic and olefinic blend TPEs and lower than those of the polyurethanes, copolyesters, and polyamides

55.2 Properties

The cross-linking of a TPV rubber phase gives improvement to a number of properties of a specific rubber/thermoplastic composition, such as EPDM rubber/polypropylene (PP) These property improve-ments include tensile strength, tensile and compression set resistance, stress relaxation, fluid resistance, and retention of properties at elevated temperature These improvements qualify TPVs for many uses where a simple rubber/polyolefin blend would be inadequate

Key parameters for the premium performance of a TPV are (1) the degree of cross-linking of the rubber phase, (2) the degree of dispersion of the rubber phase in the thermoplastic phase, and (3) the thermody-namic compatibility of the polymers present TPV performance is known to be improved by greater cross-linking, dispersion, and polymer compatibility TPVs with high polymer compatibility have no need for a compatibilizer; those with low compatibility (e.g., NBR rubber/PP) will need one to stabilize the intermin-gling of the rubber and thermoplastic chains The mutual compatibility of the rubber and thermoplastic polymers will increase as the difference in their solubility parameters (i.e., cohesive energy density) decreases The hardness of TPVs ranges from 35 Shore A up to 50 Shore D EPDM/PP TPVs are generally suitable for use in air from –60°C to 135°C, and those from nitrile rubber/PP have a range in air from –40°C to

Charles P Rader

Advanced Elastomer Systems, L.P.

Figure 55.1 compares the generic classes of TPEs by performance and cost The TPVs are medium

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Vulcanizate Thermoplastic Elastomers 55-3

Perhaps the principal reasons are (1) TPVs are the closest approach of any TPE to the properties and performance of a conventional thermoset rubber, and (2) TPVs permit close-to-optimum exploitation

of the economic advantages inherent in the processing of a TPE

Today’s applications of TPVs number well into the thousands, penetrating virtually all major uses of rubber — but with one massive exception, that of penumatic tires, which consume slightly more than one-half of the rubber produced in the world In other rubber application areas, TPVs have been eminently successful A leader in this success has been the automotive segment, where these materials enjoy uses in convoluted protective boots, seals, jacketing, hose, grommets, weather stripping, and numerous other specific parts TPVs function well in under-the-hood uses where other TPEs are inad-equate for the service temperature, which continues to progress upward

Architectural uses also provide a ready market for TPEs Hundreds of large buildings around the world now employ window glazing and/or chemical expansion joints extruded from an EPDM/PP TPV Mechanical rubber goods embrace those uses in which a molded or extruded rubber article is a component part of a useful assembly Major TPV uses in this area include household appliances, office equipment, toys, and other items requiring the use of boots, bushings, seals, tubing, and other rubber articles EPDM/PP TPVs have excellent electrical insulating properties — dielectric constant, resistivity, dielec-tric strength, power factor — that render them quite suitable for use as primary insulators or as jacketing materials Electrically conducting wire can readily be coated by crosshead extrusion of a TPV for use in automotive, construction, industrial, appliance, and many other applications

EPDM/PP TPVs have unusually low toxicity for a rubber This explains their broad utility for direct contact with foods and potable water TPVs have also found use in health care applications in hospitals and physician’s offices and in pharmaceutical applications involving direct contact with preparations to

be taken orally or injected into the bloodstream

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56 Olefinic Thermoplastic

Elastomers

56.1 Introduction 56-1 56.2 Properties 56-2

Limitations of TPOE Compounds

56.3 Usage 56-2

56.1 Introduction

Olefinic elastomers based upon ethylene-propylene and/or ethylene-propylene-diene monomer rubbers (EPR or EPDM) are thermoplastic by virtue of their alloying with isostatic crystalline polypropylene and/or high-density polyethylene (HDPE) These products are produced by high intensity mixing in Banburies continuous mixers, and extruders

The olefin plastics are either pellets or reactor beads, while the rubber can be in bale form for mixing

in a Banbury For mixing in an extruder or continuous mixer, the rubber must be converted to a pellet

or granular particle The high intensity mixing results in a simultaneous comminution of the polymers, with the olefin as the continuous phase and the rubber the dispersed phase Thus the blend is thermo-plastic: the blend viscosity is largely controlled by the choice of polyolefin, and the elasticity is controlled

by the rubber segment of the blend

Thermoplastic olefinic elastomers (TPOEs) can be manufactured by blending alone, which limits the

com-pounding operation When the compounds are cross-linked, the elevated temperature properties are enhanced The processing “nerve” of the blend is reduced, and thinner, more complex extruded products are possible

The polymer compound is made broadly versatile by the inclusion of a great variety of additives In addition to the initial choice of polymers, the ratio of plastic to rubber (hard to soft segment) controls the hardness of the compound to some degree The use of high permanence petroleum oils that function

as permanent plasticizers assists in the control of hardness Flexural modulus or toughness is more readily controlled by the rubber polymer The combined use of these ingredients results in a wide variety of physical properties

Fillers, such as fine particle calcium carbonates, clays, talc, and silicas are all usable TPOE compounds cannot be made to be clear; but very pale, pastel colors are possible Translucent colors are possible in thin sections For outdoor use, protection against ultraviolet radiation is needed The general-purpose compounds are not flame retardant inherently and require a package of halogen donor additives to pass any necessary specifications

Jesse Edenbaum

Consultant

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57 Ethylene Vinyl Alcohol Copolymer

(EVOH) Resins

57.1 Polymer 57-1 57.2 Barrier Properties 57-1 57.3 Regulatory Approval 57-4 57.4 Fabrication Methods 57-4

57.1 Polymer

Ethylene vinyl alcohol (EVOH) resins are hydrolyzed copolymers of vinyl acetate and ethylene The vinyl alcohol base has exceptionally high gas barrier properties, but it is water soluble and difficult to process

By copolymerizing ethylene with vinyl alcohol, the high gas barrier properties are retained and significant improvements are achieved in moisture resistance and processibility

reaction yields a copolymer that is more than 99% hydrolyzed

57.2 Barrier Properties

EVOH copolymers are highly crystalline, and their properties are highly dependent on the relative concentration of the comonomers Generally speaking, as the ethylene content increases, the gas barrier properties decreases, the moisture barrier properties improve, and the resins are processed more easily The presence of a hydroxyl group in the molecular chain renders the gas barrier properties of the properties decrease However, by proper use of companion materials in a multilayer structure, this effect can be minimized

content of the EVOH and maintain superior gas barrier properties In this article, any aqueous-based food is considered to be 100% relative humidity; the storage environment is shown at relative humidities

of 65 and 85%

R H Foster

Eval Company of America

Table 57.1 lists the range of EVOH resins presently available

(see Table 57.2)

EVOH resins sensitive to moisture As the moisture content of the resin increases, the gas barrier

Table 57.3 shows how the combination of different materials can be used to minimize the moisture

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Ethylene Vinyl Alcohol Copolymer (EVOH) Resins 57-3

In addition to being outstanding as barrier properties, EVOH resins offer excellent barriers to a variety

of flavors, aromas, and solvents (see Table 57.4 and Table 57.5)

TABLE 57.4 Flavor Barrier Data (Citrus and Tropical Flavors) a

Film b

Thickness ( µ m)

Duration

1 h 2 h 15 h 1 Day 4 Days 35 Days EVOH-32 15 A A A A A A EVOH-44 15 A A A A A A

BO EVHO 15 A A A A A A

BO Nylon 15 A A B B B B OPP 20 B B C C C C PVDC 25 A A B B B B LDPE 50 D D D D D D

a Key: A, no detection; B, faint flavor; C, partial flavor; D, flavor clearly distinguished.

b BO EVOH, biaxially oriented EVOH; BO Nylon, biaxially oriented nylon; OPP, ori-ented polypropylene; PVDC, polyvinylidene chloride; LDPE, low density polyethylene.

TABLE 57.5 Flavor, Aroma, and Solvent Barrier Properties a

Resin b

Allyl Sulfide:

Garlic-Food Type (Croutons, Snacks, Salad Dressins)

Acetic Acid Vinegar-Food Type (Cheddar Cheese, Snacks, Condiments)

Ethylene Acetate:

Laminating Adhesive Solvent Residual

Toluene:

Printing Ink Solvent Residual

Methyl Ethyl Ketone Printing Ink Solvent Residual HDPE-Nylon-EVa 0.00008 0.92 0.03 0.02 0.005 HDPE-EVOH-EVA 0.00075 0.035 0.0043 0.007 0.035 PVDC-PP-PVDC 0.0068 1.98 0.34 0.22 3.09 OPP-HDPE-EVOH-EVA 0.00076 1.40 0.15 0.00003 0.09 EVA-Glassine-PVDC 0.50 4.18 6.47 3.15 15.1

a g/24 h, m 2 , 100 pm at 70 ° F.

b HDPE, high-density polyethylene; EVA, ethylene vinyl acetate; PVDC, polyvinylidene chloride; OPP, oriented polypro-pylene.

+

C

x C

—

H H

C

y C

—

H H

H O

— (CH2— CH2)x— (CH2— CH)y—

O

O C

CH3 Ethylene Vinyl Acetate Copolymer Vinyl Acetate

Monomer

Ethylene Monomer

(CH2— CH2)x— (CH2— CH)y (CH2— CH2)x— (CH2— CH)y

O

C C

CH3 Ethylene Vinyl Acetate Copolymer Ethylene Vinyl Alcohol Copolymer

(EVOH)

Heat Catalyst

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