Applied Polymer Science - ACS Publications - American Chemical

51 Bituminous Coatings STEPHEN H. ALEXANDER

1

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 1, 2018 | https://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch051

Gulf States Asphalt Company, Inc., Houston, TX 77002

Availability of Raw Materials Manufacturing Processes Processes for Coal Tar Mining of Gilsonite Properties Chemical Properties Physical Properties Types of Coatings by Use The Future

The two main raw materials used in the production of bituminous coatings are asphalt and coal tar; a third is a native bitumen, gilsonite. The petroleum industry, from which asphalt is derived, was born in this country on August 27, 1859, when Colonel Drake drilled 69.5 ft. near Titusville, Pennsylvania, to bring in a producing well of 30 bbl/day (1). Until 1908, the emphasis on products from petroleum was for kerosene used as an illuminating oil. In 1908, Henry Ford began mass-producing his Model "T" Ford, and as automobile production rapidly increased, the emphasis changed from illuminating oil to motor fuel (2). The coal tar industry began in this country when a horizontal retort was installed in Baltimore in 1816 (3). Not much attention was given to the recovery of coal tar until World War I proved our great dependency on European sources for chemicals available from coal. The shortages r e s u l t i n g from our being cut o f f from European supplies caused a rapid growth i n production of c o a l t a r and r e l a t e d chemicals during and f o l l o w i n g World War I (4). 1C u r r e n t address: 13826 Kingsride, Houston, TX 77079

0097-6156/ 85/0285-1229S06.00/0 © 1985 American Chemical Society

Tess and Poehlein; Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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APPLIED POLYMER SCIENCE

G i l s o n i t e was d i s c o v e r e d i n 1882 by S. H. G i l s o n of S a l t Lake C i t y , who a l s o l a t e r c o m m e r c i a l i z e d i t . I t i s a n a t u r a l bitumen found i n Utah near the C o l o r a d o border. I t i s a m a t e r i a l of good uniformity, occurring i n veins from a f r a c t i o n of an inch to 18 f t . thick. The veins are g e n e r a l l y more or l e s s v e r t i c a l (5).


A v a i l a b i l i t y of Raw Materials The p r o d u c t i o n of a s p h a l t has i n c r e a s e d g r e a t l y as the amount of crude o i l processed has r i s e n to meet growing demands f o r petroleum f u e l s and p e t r o c h e m i c a l s . From 1925 to 1950, the annual r a t e of production doubled each decade. A f t e r 1950, the rate of growth of asphalt production declined. In 1960, the annual rate was 180% that of 1950, and i n 1970, the annual rate was 140% that of 1960. The f a c t o r s that have affected the a v a i l a b i l i t y of c o a l t a r are quite d i f f e r e n t from those a f f e c t i n g the a v a i l a b i l i t y of a s p h a l t . The i n t e r r u p t i o n of a v a i l a b i l i t y of c o a l tar-derived chemicals from Europe during World War I provided i n c e n t i v e f o r a rapid increase i n p r o d u c t i o n of coke and a g r e a t e r emphasis on the r e c o v e r y of the coproduct, c o a l t a r . P r o d u c t i o n of c o a l t a r doubled i n the f o u r years from 1914 t o 1918 and doubled again i n the nine years from 1918 t o 1929. P r o d u c t i o n r a t e s decreased d u r i n g the d e p r e s s i o n years but i n c r e a s e d s i g n i f i c a n t l y during World War I I ; production r a t e s peaked i n 1957. S i n c e 1957, t h e r e have been s u b s t a n t i a l r e d u c t i o n s i n the amount of coke needed t o produce a ton of i r o n through increased e f f i c i e n c y by higher b l a s t furnace temperatures, oxygen enrichment, h u m i d i f i c a t i o n , and i n j e c t i o n of supplemental fuel. In Table I data are given on production of asphalt and c o a l t a r . Data have not been given on volume of coatings produced from these bitumens because of a l a c k of a v a i l a b i l i t y of data. Doerr and Gibson p u b l i s h e d some i n f o r m a t i o n on the use of c o a l t a r f o r pipe coatings, which i s i n the range of 200 m i l l i o n lb/year f o r the years 1950 to 1964 (7). They a l s o indicated that about 30 m i l l i o n lb/year were used f o r other c o a t i n g uses (8). These data i n d i c a t e t h a t approximately 3% (230 m i l l i o n l b ) of the c o a l t a r produced i s used for coatings manufacture. Figures show that i n 1970 the amount of asphalt used for paving and r o o f i n g (6} was 78% and 14.5%, r e s p e c t i v e l y . T h i s l e a v e s 7.5% f o r a l l other miscellaneous uses. From knowledge of the industry, i t i s estimated t h a t a t l e a s t 10% of t h i s 7.5% goes i n t o c o a t i n g s uses. For the year 1970, t h i s would be 460 m i l l i o n l b . Data on the p r o d u c t i o n of g i l s o n i t e and the amount used i n c o a t i n g s were not a v a i l a b l e to the author. G i l s o n i t e was a s i g n i f i c a n t factor when the a v a i l a b l e grades of petroleum asphalt were l i m i t e d . Gilsonite's importance f o r coatings manufacture began to fade i n the 1940s, and i t s use f o r coatings i s now quite l i m i t e d . Manufacturing

Processes

The f i r s t step i n the manufacture of asphalt-based coatings c o n s i s t s of the d i s t i l l a t i o n of crude petroleum, which r e s u l t s i n d i s t i l l a t e f r a c t i o n s ( g a s o l i n e , naptha, kerosene, d i e s e l f u e l , and gas o i l ) . The f r a c t i o n of crude o i l that b o i l s above approximately 300 °C i s not d i s t i l l e d , but i s withdrawn from the bottom of the d i s t i l l a t i o n



51.

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Bituminous Coatings

ALEXANDER

Table I . Asphalt and Coal Tar Production i n the United States (6)

Year

Asphalt (million pounds)

1925 1930 1940 1950 1960 1970 1980

4,800 6,000 12,400 24,000 43,600 60,900 64,100

Coal Tar

3,150a 7,800 6,733 7,400 6,880 7,609 534(gal.) b

c

d

a

For year 1918 For year 1929 From Energy Information Administration, U.S. Department of Energy d From Synthetic Organic Chemicals P u b l i c a t i o n (the number shown i s m i l l i o n gallons)

b

c



1232


tower. T h i s i s petroleum a s p h a l t . I f the c o r r e c t crude o i l has been selected and the r i g h t processing conditions have been used, i t i s p o s s i b l e to get an asphalt f o r use i n coatings from the crude o i l d i s t i l l a t i o n step. I f an a s p h a l t d i f f e r e n t from t h a t produced i n the crude o i l d i s t i l l a t i o n step i s desired, further modification can be accomplished by a i r blowing, by a i r blowing with a c a t a l y s t , by s o l v e n t p r e c i p i t a t i o n , or by a combination of these. A i r b l o w i n g i s c a r r i e d out a t about 240-270 °C by i n t r o d u c i n g s m a l l streams of a i r i n t o the bottom of the a s p h a l t - c o n t a i n i n g v e s s e l , and a l l o w i n g s m a l l a i r bubbles to r i s e through the asphalt. This process increases i t s s o f t e n i n g p o i n t by dehydrogenation and condensation polymerization reactions. The asphalt can be further modified i n the a i r blowing process by the use of a c a t a l y s t , such as phosphorus pentoxide or f e r r i c chloride. These are u s u a l l y used i n concentrations from 0.5 to 3%, and they are not c a t a l y s t s i n the true sense because they enter i n t o the r e a c t i o n and are at l e a s t p a r t i a l l y i n c o r p o r a t e d i n t o the asphalt. Sometimes these c a t a l y s t s change reaction rate, but they are used p r i m a r i l y to modify properties. S t i l l another method of m o d i f y i n g the p r o p e r t i e s of a s p h a l t i n v o l v e s the use of s o l v e n t p r e c i p i t a t i o n . This i s done by charging the asphalt i n t o a v e s s e l of propane, butane, or a mixture of these or s i m i l a r s o l v e n t s . T h i s v e s s e l i s then h e l d a t about 70 °C and 400 psia. The s o l v e n t s d i s s o l v e an o i l y f r a c t i o n , and the remaining asphalt p r e c i p i t a t e s . Thus, an asphalt of a higher softening point and greater hardness i s produced. Asphalt produced i n t h i s manner can be f u r t h e r m o d i f i e d by a i r blowing. A b l o c k diagram showing these manufacturing steps appears i n Figure 1. These s e v e r a l processes can be used i n series. The composition of t h e a s p h a l t c o n t a i n e d i n t h e c r u d e o i l i s an i m p o r t a n t c o n s i d e r a t i o n . However, the s e p a r a t i n g and m o d i f y i n g processes a l l o w the p r o d u c t i o n of a s p h a l t s of a f a i r l y wide range of properties from a given crude o i l . Processes f o r C o a l Tar. C o a l t a r i s produced by the d e s t r u c t i v e d i s t i l l a t i o n of c o a l to give coke and a vapor stream from which the c o a l t a r i s condensed. This crude c o a l t a r can be further d i s t i l l e d to o b t a i n d i s t i l l a t e o i l s and a c o a l t a r p i t c h . The p i t c h can be used f o r the manufacture of coatings or can be further modified by a i r blowing. A i r blowing i s not as commonly practiced i n modifying c o a l t a r p i t c h as i t i s f o r m o d i f y i n g a s p h a l t . A b l o c k diagram showing these manufacturing steps appears i n Figure 2. Mining of G i l s o n i t e . G i l s o n i t e i s obtained by s t r i p mining. I t i s u s u a l l y blended with other bitumens to produce a coating base. No p r i o r processing i s required. Properties Chemical Properties. The chemical makeup and some of the properties of the three bitumens used i n the manufacture of coating are shown i n Table I I . The f i v e elements commonly contained i n these bitumens i n s i g n i f i c a n t q u a n t i t i e s are carbon, hydrogen, oxygen, n i t r o g e n , and s u l f u r . Several metals are frequently present i n trace amounts; n i c k e l and vanadium are the most prevalent.



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Bituminous Coatings

ALEXANDER

Distillation

DISTILLATE

Solvent Precipitation

Air Blowing

A i r Blowing With C a t a l y s t

HEAVY OIL

Air Blowing

Figure 1.

Manufacturing steps and coproducts i n producing asphalt coating base.


1234



COAL

Destructive Distillation

COAL TAR

COKE

Distillation

DISTILLATE OILS

Air Blowing

COATING BASE

Figure 2· Manufacturing steps and coproducts i n producing c o a l t a r p i t c h coating base.


Bituminous Coatings


ALEXANDER

Table I I . Typical Properties of Asphalt, G i l s o n i t e and Coal Tar P i t c h Asphalt

Gilsonite

Coal Tar

84.5

85.5

89.3

Hydrogen, wt%

9.8

8.4

4.8

C/H r a t i o

0.72

0.85

1.54

Oxygen, wt%

1.6

1.0

3.2

Nitrogen, wt%

0.9

2.4

1.6

S u l f u r , wt%

2.7

0.4

1.1

Property Elemental a n a l y s i s Carbon, wt%

Molecular weight

450 to 5000

Density,

1.02

g/mL

Flash point COC, °C.

340

_ 1.06 345

220 to 1000 1.24 245



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The carbon/hydrogen r a t i o s are s i m i l a r for asphalt and g i l s o n i t e (0.78 i s t y p i c a l ) , thereby i n d i c a t i n g a s i m i l a r d i s t r i b u t i o n of p a r a f f i n i e , napthenic, and aromatic compounds i n these two bitumens. Coal t a r s have a much higher carbon/hydrogen r a t i o (1.5 i s t y p i c a l ) , thereby i n d i c a t i n g a high degree of condensed aromatic compounds. Most of the compounds making up asphalt f a l l w i t h i n a molecularweight range of 450 to 5000. The range f o r c o a l t a r compounds i s somewhat lower: 220 to 1000. The density of asphalt and g i l s o n i t e i s s l i g h t l y over 1 g/mL whereas 1.24 g/mL i s t y p i c a l f o r c o a l t a r . F l a s h p o i n t by the C l e v e l a n d Open Cup method i s i n the range of 340 °C f o r a s p h a l t and g i l s o n i t e and 245 °C f o r c o a l t a r . C o a l tar's lower molecular weight and high aromaticity account f o r t h i s low f l a s h point. P h y s i c a l P r o p e r t i e s . Some p r o p e r t i e s of s p e c i f i c i n t e r e s t i n the coating f i e l d are: adhesion; w e a t h e r a b i l i t y ; m o i s t u r e permeation and a b s o r p t i o n ; i n e r t n e s s to c h e m i c a l environments; c o l o r ; and s e r v i c e temperature range. Bitumens e x h i b i t good adherence to almost any surface. Coatings with e x c e l l e n t weathering properties can be obtained by proper s e l e c t i o n of the bitumen and formulation with other materials. Low p e r m e a b i l i t y and low water absorption are two outstanding f e a t u r e s of bitumens f o r use i n c o a t i n g s manufacture. T a b l e I I I gives permeability data on four bitumens and uses neoprene and v i n y l c h l o r i d e f o r comparative purposes. These data demonstrate the r e l a t i v e l y low permeability of bitumens. The use of added f i l l e r s i n the manufacture of c o a t i n g s g e n e r a l l y i n c r e a s e s p e r m e a b i l i t y . For some s p e c i a l uses, h i g h permeability i s d e s i r a b l e and can be accomplished by s e l e c t i o n of f i l l e r s as shown by the example i n T a b l e I I I . Permeation r a t e i n use depends on the permeability constant of the coating and on the c o a t i n g t h i c k n e s s . Permeation decreases with increasing thickness of the coating. For example, vulcanized neoprene has a permeability constant of 26 which i s 6.5 times t h a t of c o a l t a r p i t c h , which has a permeability constant of 4. Coal t a r coatings are t y p i c a l l y used 90 m i l s t h i c k as compared t o neoprene f i l m at 34 m i l s . T h i s i s a t h i c k n e s s r a t i o of 2.6. Combining these two f a c t o r s (6.5 χ 2.6) makes neoprene f i l m 18 times more permeable than a c o a l t a r coating i n a t y p i c a l use s i t u a t i o n . More extensive data on permeability and water absorption can be found elsewhere (9). Bitumens a l s o have good resistance to attack by most inorganic s a l t s and weak i n o r g a n i c a c i d s . In a d d i t i o n , bitumens are dark brown or b l a c k and these c o l o r s are very d i f f i c u l t to mask w i t h pigments; therefore, t h e i r use should be r e s t r i c t e d to a p p l i c a t i o n s where these c o l o r s are not objectionable. Colored overcoats can be used when a d u a l c o a t i n g system can be j u s t i f i e d . Bitumens are t h e r m o p l a s t i c and have a r a t h e r narrow s e r v i c e temperature range unless modified with fibrous f i l l e r s and/or synthetic resins. Types of Coatings by Use Bituminous c o a t i n g s can be d i v i d e d i n t o two major c l a s s e s by a p p l i c a t i o n c h a r a c t e r i s t i c s : hot a p p l i e d and c o l d a p p l i e d . The hot-applied coatings can be subdivided by composition: nonfilled and f i l l e d ( u s u a l l y f i n e l y d i v i d e d m i n e r a l ) . The c o l d - a p p l i e d


51.

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Bituminous Coatings

ALEXANDER


Table I I I . Permeability of Various Organic Films to Water Vapor

Typical Usage Permeability Constant Thickness Perms χ 10* (in.) 3

Film Asphalt, oxidized

8

0.050

0.023

Coal t a r p i t c h Asphalt f i b r a t e d coatings (conventional f i l l e r s ) Asphalt f i b r a t e d coatings ( s p e c i a l f i l l e r to increase permeability)

4

0.090

0.006

20

0.060

0.048

200

0.060

0.475

Neoprene, vulcanized

26

0.034

0.109

P l a s t i c i z e d v i n y l chloride

38

0.019

0.286

Permeability constant i s based on Fick's law of d i f f u s i o n , which states that the amount of vapor which d i f f u s e s through a membrane i s proportional to the area of the membrane, the pressure gradient of the d i f f u s i n g vapor, and time. I t i s i n v e r s e l y proportional to the thickness of the membrane. Mathematically i t i s expressed as W = k(APT/L), where A i s the area of the membrane i n square centimeters, Ρ i s the pressure d i f f e r e n t i a l of the vapor i n mm Hg, Τ i s the time of d i f f u s i o n i n hours, W i s the weight of gas d i f f u s e d i n grams, L i s t h e t h i c k n e s s o f t h e membrane i n centimeters, and k i s the permeability constant. Thus, the u n i t s of k a r e g - cm/cm - mm Hg - h. 2

A perm expresses permeation rate i n the u n i t s of grains per square foot of membrane, per inch of Hg pressure d i f f e r e n t i a l , per hour of time elapsed. (The perm measure does not include the thickness which i s p a r t of the p e r m e a b i l i t y constant formula. Thus, a membrane of a given material w i l l have a d i f f e r e n t "perm" value f o r each t h i c k n e s s o f membrane measured.) The u n i t s a r e g r a i n s / f t . - i n . Hg - h. 2


b


1238


c o a t i n g s can a l s o be s u b d i v i d e d by composition: those containing s o l v e n t or those containing water. Both of these subclasses can be further subdivided i n t o nonfibrated or f i b r a t e d types. A major use of h o t - a p p l i e d , n o n f i l l e d a s p h a l t c o a t i n g s i s f o r c o a t i n g metal highway c u l v e r t s . The l a r g e s t use of h o t - a p p l i e d , f i l l e d , bituminous c o a t i n g s i s t o coat pipe f o r b u r i e d p i p e l i n e s . P i p e l i n e s so coated a r e used t o t r a n s p o r t n a t u r a l gas, p e t r o l e u m products, petroleum crude o i l , s l u r r i e d c o a l , and carbon dioxide. Some other major uses, by types, a r e as f o l l o w s : Solvent cutback and water e m u l s i o n , n o n f i b r a t e d c o a t i n g s a r e used as p r o t e c t i v e c o a t i n g s f o r m e t a l and masonry. S o l v e n t cutback and water e m u l s i o n , f i b r a t e d c o a t i n g s a r e used i n r o o f i n g , waterp r o o f i n g , and i n d u s t r i a l i n s u l a t i o n , and i n a u t o m o b i l e s f o r protection and sound deadening. Aluminum pigments are compounded with solvent cutback bitumens to produce a v a r i e t y of c o a t i n g s f o r v a r i o u s uses. A f t e r a s h o r t weathering period, they produce b r i l l i a n t aluminum coatings. Major uses are i n roofing, metal protection and i n s u l a t i o n protection. A block diagram showing the manufacturing steps used to produce these c o a t i n g s i s shown i n F i g u r e 3, and T a b l e IV shows three types of asphalt roof coatings. Each c o a t i n g has i t s s p e c i a l use. The s o l v e n t type has an e x t r e m e l y low p e r m e a b i l i t y and i s e s p e c i a l l y s u i t e d f o r new c o n s t r u c t i o n . The aluminum type i s heat r e f l e c t i v e and decreases the a i r c o n d i t i o n i n g l o a d on a b u i l d i n g . The e m u l s i o n type has a high permeability and i s e s p e c i a l l y suited as a maintenance coating where the roofing components have absorbed moisture that needs to be e x p e l l e d without causing b l i s t e r i n g of the coating. With t h i s type of coating, the heat of the sun w i l l d r i v e the moisture out, and i t can be e x p e l l e d through the coating at a s u f f i c i e n t l y rapid rate to prevent pressure buildup and b l i s t e r i n g from occurring. T a b l e V shows p r o p e r t i e s f o r two a s p h a l t and two c o a l t a r c o a t i n g s used t o coat pipe f o r b u r i e d p i p e l i n e s . Because of i t s aromaticity, c o a l t a r i s more temperature susceptible (changes more i n v i s c o s i t y w i t h a g i v e n temperature) than a s p h a l t . This d e f i c i e n c y i s overcome t o a l a r g e degree by compounding w i t h p l a s t i c i z i n g o i l s and c o a l dust t o produce a c o a l t a r c o a t i n g denoted as "wide range". The s e r v i c e temperature range of the nonmodified c o a l t a r i s 33 °C vs. 94 t o 100 °C f o r the two a s p h a l t and the "wide range" c o a l t a r c o a t i n g s . Again, because of g r e a t e r a r o m a t i c i t y , t h e c o a l t a r c o a t i n g s a r e 20% more dense than the asphalt coatings. Table VI shows three types of asphalt-weather and vapor-barrier c o a t i n g s used t o p r o t e c t thermal i n s u l a t i o n . These examples i l l u s t r a t e that a wide range i n moisture vapor permeability can be accomplished. The low-permeability m a t e r i a l has a r a t i n g of .003 perra-in. and i s e s p e c i a l l y u s e f u l f o r p r o t e c t i n g i n s u l a t i o n on v e s s e l s operating at very low temperature. This condition produces d r i v i n g f o r c e s t h a t cause m o i s t u r e t o migrate i n t o the thermal i n s u l a t i o n . I f t h i s i s a l l o w e d t o happen, i c e b u i l d s up i n the i n s u l a t i o n , and i t s e f f i c i e n c y i s g r e a t l y r e d u c e d . For i n s t a l l a t i o n s operating at higher temperatures, the heat prevents a m o i s t u r e b u i l d u p problem, but p r o t e c t i o n from weathering and b l i s t e r i n g resistance i s needed. Here a solvent cutback formulated to have 10 times the permeation (.03 perm-in.) or an e m u l s i o n type


51.

ALEXANDER

1239

Bituminous Coatings


COATING BASE

Filler Addition

Solvent Addition

HOT APPLIED

Fiber Addition

Emulsific at i o n

EMULSION COATING

Aluminum Pigment Addition

Fiber Addition

Fiber Addition

ALUMINUM MASTIC COATING

Figure 3. M a n u f a c t u r i n g s t e p s t o p r o d u c e v a r i o u s t y p e s o f bituminous coatings.


1240


Table IV.

Asphalt Roof Coatings

Solvent Type


Description

Aluminum Pigmented

Emulsion Type

Typical properties B l i s t e r i n g and sagging on metal at 30° angle i n 71 °C oven

none

none

none

pass 52--71

pass 52--71

pass 43--54

45--55

40--50

30--40

Asbestos f i b e r content, wt%

8--16

8--16

7--15

Mineral f i l l e r , wt%

5--15

0--20

—

—

15--25

Bend t e s t of coated panel over a 1-in. mandrel a t 0 °C Asphalt softening point (R&B), °C Typical composition Asphalt content, wt%

Aluminum pigment, wt% a

3

Over a 2-inch diameter mandrel

Table V*.

Typical Properties of Pipe Coatings

Asphalt Property Softening point, °C Mineral f i l l e r content, wt% Service temperature range, °C Density A p p l i c a t i o n Temperature, °C

Regular

High Temp.

Coal Tar Narrow Wide Range Range

115

132

93

110

25

25

25

30

-29 to 65

-18 to 82

4 to 37

-29 t o 65

1.20

1.20

1.45

1.45

245 to 260

255 t o 275

176 to 204


218 t o 246


Yes

Other f i l l e r s usually present

2

10-20

Asbestos f i b e r content, wt% Yes

10-20

30-40

63-88

0.03

60

Solvent-Type Med-Permeability

A perm-in. i s the same as perm except that i t i s expressed per inch of thickness of the membrane. (To convert a perm value to perm-in. value, multiply by the thickness of the membrane i n inches.) Units are g r a i n - i n . / f t . - i n . H g - h .

50-65

Asphalt content, wt%

a

71-93

0.003

72

Solvent-Type Low-Permeability

Typical composition Asphalt softening point (R&B), °C

a

Water Vapor Permeability (perm-in. )

Typical properties Solids content, wt%

Description

Table VI. Asphalt Weather and Vapor-Barrier Coatings

Yes

7-15

30-40

43-54

0.15

58

Emulsion-Type High-Permeability



1242


of 50 times the permeation (.15 perm-in.) of the c o n v e n t i o n a l c o a t i n g can be used. [See f o o t n o t e s f o r T a b l e s I I I and VI f o r d e f i n i t i o n s of perm and perm-in.) T a b l e V I I shows t h r e e a s p h a l t c o a t i n g s used i n t h i c k n e s s e s comparable to i n d u s t r i a l paints. F i l m thicknesses are from 0.7 to 3 mils. These coatings f i n d wide use i n industry f o r the protection of s t r u c t u r a l s t e e l , f o r the p r o t e c t i o n of metal p a r t s i n s t o r a g e (removable w i t h s o l v e n t s ) , and as pipe and tank c o a t i n g s . The aluminum pigmented c o a t i n g has two main advantages: aluminum appearance i s more d e s i r a b l e "than b l a c k , and the pigment p r o t e c t s the bitumen from the a c t i n i c rays, thereby extending the l i f e of the coatings. T a b l e V I I I g i v e s data on a r a i l r o a d c a r and t h r e e a u t o m o t i v e c o a t i n g s . These are combination p r o t e c t i v e c o a t i n g s and sounddeadening materials. A s i g n i f i c a n t property of these compositions i s t h e i r d e c i b e l decay r a t e at 10 °C. These r a t e s range from 8.2 f o r the standard automotive undercoating to 10.1 f o r mediume f f i c i e n c y sound deadening and 15 f o r h i g h - e f f i c i e n c y sound deadening. Also, the f i l l e r content i n the h i g h - e f f i c i e n c y deadener i s i n the range of 45-60%. I t contains only 16-22% asphalt and i s a very dense material of about 12.3 l b / g a l . In recent years, the bituminous coatings have been modified with epoxy r e s i n s , urethane polymers, and v a r i o u s rubbers. The epoxies and urethanes have made p o s s i b l e the f o r m u l a t i o n of c o a t i n g s c o n t a i n i n g over 50% bitumens. These c o a t i n g s have low s h r i n k a g e during cure and widely varying cure times. M o d i f i c a t i o n with these resins and rubbers a l l o w s t a i l o r i n g of performance c h a r a c t e r i s t i c s for s p e c i f i c a p p l i c a t i o n s . T a b l e IX g i v e s a t y p i c a l f o r m u l a t i o n f o r c o a l t a r epoxy. I t c o n t a i n s a p p r o x i m a t e l y 30% epoxy and 25% c o a l t a r . T h i s type of c o a t i n g w i l l perform b e t t e r than e i t h e r the pure c o a l t a r or the pure epoxy c o a t i n g s i n s e v e r a l a p p l i c a t i o n s . Because of the r e l a t i v e l y low c o s t of c o a l t a r p i t c h , the raw m a t e r i a l c o s t i s s i g n i f i c a n t l y l e s s than f o r a pure epoxy. The

Future

During the l a s t 10 years, the c o s t of a s p h a l t and c o a l t a r has increased s i g n i f i c a n t l y more than the cost of most other coating raw m a t e r i a l s . T h i s i s because t h e i r c o s t i s so c l o s e l y r e l a t e d to energy costs, which have increased approximately 10-fold (1000%) i n the l a s t 10 years (much f a s t e r than g e n e r a l i n f l a t i o n which increased 130% over the same period of time). The cost of energy now appears to have s t a b i l i z e d such that i t w i l l more n e a r l y approximate t h a t of g e n e r a l i n f l a t i o n i n the immediate f u t u r e . T h e r e f o r e , the c o s t of bituminous c o a t i n g s as r e l a t e d to other c o a t i n g types i s a l s o expected to s t a b i l i z e . In l i g h t of these f a c t o r s , the bituminous c o a t i n g s and m o d i f i e d bituminous coatings are expected to maintain t h e i r market share f o r the immediate future.



51.

ALEXANDER

Table V I I .

1243

Bituminous Coatings

Asphalt Protective Coatings, Thin-Film Type f o r Above-Ground Service Chassis and Frame Paint

Solvent Type Nonfibrated

Solids content, wt%

45-60

53-67

60-70

Film thickness, mils

0.7

3

2

-18 to 71

-18 to 71

-18 to 77

Description

Aluminum Pigmented

Typical properties

Service temperature range, °C Typical composition Asphalt softening point (R&B), °C

82-104

82-104

77-104


45-60

57-67

17-30

Aluminum pigment, wt%


14-20


Finely divided heavy, nonabrasive mineral f i l l e r , wt%

9-18

0-15

10-20

25-50

8-16

45-60

6-12

16-22 22-32

28-40

40-50


Asbestos f i b e r content, wt%

60-82 60-82

71-93

12.3 10.8

8.6

71-93

8.0

10.4 15.0 6.8

50°

80

Automotive High Efficiency Deadener

15.9 10.1 3.9

70°

78

Automotive Undercoating Deadener

13.6 8.2 3.8

70°

65

Automotive Undercoating

T y p i c a l composition Asphalt softening point (R&B), °C

Weight, l b / g a l

2

—

70°

Cold adhesion t e s t , -23 °C, angle

Sound deadening properties, 0.5 l b / f t , decibels Decay per second at -18 °C +10 °C +43 °C

64

Typical properties S o l i d s content, wt%

Railroad Car Coating

Asphalt Coatings and Sound Deadeners f o r Transportation Vehicles

Description

Table V I I I .



51.

1245

Bituminous Coatings

ALEXANDER

Table IX. Typical Formulation (Coal TarEpoxy Coating) Component

Wt%

Base component (20 parts by volume) Liquid epoxy r e s i n

30

Soft coal t a r p i t c h

25

Xylene

20

Pulverized t a l c

25

Curing agent (1 part by volume) Diethylenetriamine Xylene

70 30

Literature Cited 1. Oil and Gas Journal, Petroleum Panorama--An Issue to Commemorate Oil's First One Hundred Years, 1959, 57, 5, A-3. 2. Ibid., A-20. 3. Rhodes, E. O. Bitum. Mater. 1966, 3, 14. 4. Ibid., 16. 5. Broome, D. C. Bitum. Mater. 1965, 2, 3. 6. Minerals Year Book, U.S. Bureau of Mines. 7. Doerr, J. S.; Gibson, P. B. Bitum. Mater. 1966, 3, 129. 8. Ibid., 133. 9. Alexander, S. H.; Tarver, G. W. Bitum. Mater. 1965, 2, 223.


Applied Polymer Science - ACS Publications - American Chemical

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