The Importance of Curing Conditions in Overall ... - ACS Publications

6 The Importance of Curing Conditions in Overall Energy

Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on November 11, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch006

Requirements for Organic Coatings V. D. McGINNISS and L. J. NOWACKI Battelle, Columbus Laboratories, Columbus, OH 43201 S. V. NABLO Energy Sciences, Inc., Woburn, MA 01801

Coatings for industrial finishing have been formulated over the years with only minor consideration given to the energy requirements for preparation, application, and curing. However, in recent years cost and availability of energy has become a very important consideration. Natural gas, which has been the common source of energy for curing coatings in convection ovens, has become short in supply necessitating industry shut downs for substantial time periods in some areas. (1-6) Coil coating is one of the large segments of our industrial finishing industry. The coil coaters might more readily change to alternative methods for curing coatings than are open to other segments of the metals finishing industry. For example, coil coaters might change to induction heating or radiation curing (either infrared or electron beam) both of which use electricity as the energy source. The application of these methods to preformed metal objects, on the other hand, would be very difficult if not impossible because of the shapes of the objects. (4) T h i s paper examines the p o t e n t i a l f o r energy savings o f f e r e d to c o i l coaters by using e l e c t r o n c u r t a i n f o r c u r i n g i n s t e a d o f n a t u r a l gas. I t a l s o examines the comparisons i n cost f o r the two methods i n c l u d i n g comparisons o f cost o f the a l t e r n a t i v e c o a t i n g materials. R a d i a t i o n Curing Coating

Technology

R a d i a t i o n curable coatings technology u t i l i z e s e l e c t r i c a l energy and converts i t e i t h e r i n t o l i g h t energy or an a c c e l e r a t e d e l e c t r o n beam. The 1 0 0 percent r e a c t i v e l i q u i d c o a t i n g systems a s s o c i a t e d with t h i s technology absorb converted electrical energy from the processor u n i t (Light Source or E l e c t r o n Acc e l e r a t o r ) and undergo conversion t o a s o l i d matrix or cured finish. In the case o f l i g h t - e n e r g y - c o n v e r t i b l e coatings a photoactive c a t a l y s t i s r e q u i r e d i n order t o i n i t i a t e the c u r i n g mechanism. With e l e c t r o n beam the energy output i s s u f f i c i e n t to cause d i r e c t i o n i z a t i o n - r a d i c a l formation and subsequent i n i t i a t i o n c u r i n g r e a c t i o n s o f the c o a t i n g system. 0-8412-0509-4/79/47-107-051$05.00/0 © 1979 American Chemical Society

Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

52

ENERGY

CONSERVATION

IN TEXTILE

A N D POLYMER

PROCESSING

The m a j o r i t y o f r a d i a t i o n curable m a t e r i a l s are d e r i v e d from or c o n s i s t o f a c r y l i c and m e t h a c r y l i c unsaturated monomers, o l i gonomers, and polymers ( i n c l u d i n g unsaturated polyethers) which cure through f r e e r a d i c a l a d d i t i o n - p r o p a g a t i o n r e a c t i o n s .


Energy Comparisons i n Manufacture o f R a d i a t i o n Curing vs Conventional Coatings Most o f the r a d i a t i o n curable raw m a t e r i a l technology i s based on a c r y l i c or m e t h a c r y l i c a c i d d e r i t i v e but may a l s o i n c l u d e modified epoxies, p o l y e s t e r s , and polyurethanes. Thus the backbones o f r a d i a t i o n c u r i n g and conventional coatings are s i m i l a r . Conventional i n d u s t r i a l coatings m a t e r i a l s o f the thermoset type a r e u s u a l l y a c r y l i c , p o l y e s t e r , epoxy, polyurethane or s i l i cone r e s i n s dispersed or d i s s o l v e d i n organic or water/ethera l c o h o l c o u p l i n g s o l v e n t s . They a r e cured with gas convection or e l e c t r i c IR ovens. The raw m a t e r i a l s f o r the polymers come from petroleum feedstocks which a r e processed or manufactured i n t o a f i n i s h e d c o a t i n g system. Examples o f some t y p i c a l prepolymer m a t e r i a l s and t h e i r raw m a t e r i a l d e r i v a t i v e s are given i n Table I . Polymer manufacture schemes f o r r a d i a t i o n curable and conventional coatings a r e i n F i g u r e s I and I I . Q u a l i t a t i v e comparison o f a r e l a t i v e energy input i n t e n s i t y f o r p r e p a r a t i o n o f r a d i a t i o n curable and convent i o n a l coatings are given i n Tables II, I I I , and IV. The p o i n t to be made i s that most c o a t i n g b u i l d i n g blocks, conventional or r a d i a t i o n curable, come from approximately the same raw m a t e r i a l s sources. The o v e r a l l energy input f o r a manufacturing process i n v o l v i n g conventional polymers i s very s i m i l a r or can be equivalent t o manufacture o f a r a d i a t i o n curable polymer system. In some cases there may be, however, an added p r o c e s s i n g step f o r the r a d i a t i o n curable polymer i n order t o include reactive functionality. R a d i a t i o n curable c o a t i n g polymer systems are simple m o d i f i c a t i o n s of e x i s t i n g conventional solvent-based r e s i n technologies. A solvent-based, standard h y d r o x y l - f u n c t i o n a l p o l y e s t e r r e s i n can become a r a d i a t i o n curable r e s i n through d i r e c t e s t e r i f i c a t i o n o f a c r y l i c a c i d . Processing time (manufacturing) can be the same or s l i g h t l y longer f o r r a d i a t i o n curable polymers but the only s i g n i f i c a n t d i f f e r e n c e i s a t t r i b u t e d t o a c r y l i c a c i d content and i n c r e a s e d raw m a t e r i a l cost (RMC). A c r y l i c a c i d m o d i f i c a t i o n o f 1000 grams o f a hydroxyl f u n c t i o n a l l i n e a r p o l y e s t e r r e s i n (1000 molecular weight) would r e s u l t i n approximately $0.10/lb p r i c e i n c r e a s e (RMC) based on a c r y l i c a c i d cost of $0.40/lb (Cost comparisons are developed l a t e r ) . In almost a l l cases a r a d i a t i o n curable polymer can be manufactured under the same c o n d i t i o n s as conventional s o l v e n t based coatings except f o r s p e c i a l handling o f p o s s i b l e t o x i c materials. Thus, d i f f e r e n c e s i n t o t a l energy requirements f o r both manufacturer and use ( a p p l i c a t i o n and cure) are d i r e c t l y r e l a t a b l e t o the energy consumed i n a p p l i c a t i o n and c u r i n g .


6.

Organic

MCGINNISS ET AL.

53

Coatings

TABLE I. RAW MATERIAL SOURCES FOR SELECTED CHEMICAL INTERMEDIATES USED IN THE COATINGS INDUSTRY


Compound Name and Formula Acry1amide

Sources of compound

CHCHCONH

Acrylonitrile, Cone sulfuric

(C^NO)

Acid, amonia or

2

2

Process Hydration

Total Production (MilIons of Kilograms (lb) - year) 18.2 (40)1973

Sodium hydroxide ditto

See above

Acrylonitrile

Direct hydration

water

over catalysts

Acrylic acid

Ethylene oxide,

Addition, Hydro-

C H COOH

Hydrogen cyanide,

lysis (Addition

(131.6)-

(C H 0 )

Sulfuric acid

& Oxidation)

1973

(Process consi-

431

2

3

3

4

2

dered obsolete)

59.7

(948.)1974

ditto

Propylene-air

Oxidation

(includes esters) See above 614.8 (1354.2)-

Acrylonitrile

Ethylene

CHCHCN

cyanohydrin

1973; 642

(C H N)

Acetylene,

1974

HCN

552

2

(1412)3

3

(1215)1975 Adipic acid

Cyclohexane

COOHCCH^COOH

air, catalyst

(1567)-

nitric acid

1973 764

CC

H

6 10V

Oxidation

711

(1630)1974 668 (1470) 1975



RADIATION

CURABLE

S o l v e n t , Water Based o r Powder

CONVENTIONAL

MATERIALS

MATERIALS

RAW

Polyester manufacture

Acrylic Acid Esterification

Esterification ( S o l v e n t and Stripping, Fusion Cook)

MANUFACTURING

Amine A d d i t i o n

NEUTRALIZATION

Esterif ication (Solvent, Solvent and S t r i p p i n g , F u s i o n Cook)

MANUFACTURING

MATERIALS

Figure 1.

Acid

MATERIALS

Acrylic

RAW

G l y c o l , Anhydrides, Unsaturated Acids

RAW

G l y c o l , Anhydrides, Unsaturated Acids

RAW

Reactive

-3H A c r y l a t e Solvents

SOLVENT REDUCTION

Water

Hydrocarbon

SOLVENT REDUCTION

100% S o l i d s t o Be C o o l e d and Ground f o r Powder C o a t i n g s



Water Powder

RADIATION CURABLE

Solvent, Based o r

CONVENTIONAL

^

MATERIALS

MATERIALS

Optional Acrylate

Figure 2.

Glycidyl

Acrylic Acid, Methacrylic Acid and A l c o h o l Esters, Styrene, Hydroxyl Containing Acrylate Esters

RAW

O p t i o n a l Hydroxy1 Containing Acrylic] Ester

Acrylic Acid, Methacrylic Acid and A l c o h o l E s t e r s , Styrene

RAW

\f E s t e r i f i c a t i o n With A c r y l i c Acid or Reaction With G l y c i d y l Acrylate, Isoc y a n a t e s , Epoxy R e s i n s

SOLVENT REDUCTION

~ά

Water

Hydrocarbon

RAW

>

Acrylate Solvents

1\

Reactive

SOLVENT REDUCTION

MATERIALS

Addition

NEUTRALIZATION Amine

Addition Polymerization ( F u s i o n Cook, S o l v e n t S t r i p or P r e p a r a t i o n in Reactive Solvent for Other Polymer Systems)

Acrylic manufacture

>

MANUFACTURING

100% S o l i d s F o r Powder Coating

F i l t r a t i o n and D r y i n g i n the Case o f S u s p e n s i o n

Addition Polymerization (Solvent, Suspension, F u s i o n Cook)

MANUFACTURING


Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979. RMC f o r w a t e r - b a s e d systems a r e g r e a t e r as w e l l as p r o c e s s i n g time

Same as (A) b u t added second r e a c t i o n s t e p + cost of a c r y l i c acid

100-200°C 30-100°C

200-300°C

1 day s o l v e n t cook and 1/2-1 day n e u t r a l i z a t i o n

1 day F u s i o n cook f o l l o w e d by r e a c t i v e s o l v e n t a d d i t i o n and low-temperature e s t e r i f i c a t i o n 1/2 day 1 day s o l v e n t cook and e s t e r i f i c a t i o n

Same as conven t i o n a l + amine and c o u p l i n g s o l vent costs amine = 0.40/lb s o l v e n t = 0.35/lb

Same as conven tional + acrylic a c i d = 0.40/lb

anhydride + propylene oxide addition + acrylic acid

Water 30-60% s o l i d s

Radiation curable 100% reactive

Radiation curable 100% r e a c t i v e

100-200°C

E q u a l t o low energy s t a n d a r d (B) e x c e p t f o r added c o s t o f a c r y l i c a c i d

RMC e q u a l but p r o c e s s s l i g h t l y g r e a t e r than energy i n p u t s t a n d a r d and much g r e a t e r than

200-300°C 0°to room temp.

1 day F u s i o n cook and 1/2 day c o o l i n g / g r i n d i n g

Same as conventional

Powder 100% s o l i d s

l e s s than 130°C

(B) Low energy i n p u t

(B) 100-200°C

is high (A) (B)

(A) H i g h energy i n p u t

(A) 200-300°C

1 day F u s i o n cook (8-16 h r ) o r 1 day S o l v e n t cook

Manufacturing Procedure

A c i d , Anhydrides 0 . 2 8 — 0.50/lb glycols alcohols 0.25-0.50/lb

Raw Materials

Conventional solvent-based systems 30-80% s o l i d s

Technology

R e l a t i n g Energy and Raw M a t e r i a l Cost (RMC) Input f o r New T e c h n o l o g y V e r s u s Standard

Temperature Requirements i n Manufacture

TABLE I I . ENERGY INPUT FOR POLYESTER MANUFACTURE


M

ι

2

1

η ο 2

M

Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979. RMC a r e e q u a l t o t h e s t a n d a r d (A) b u t p r o c e s s i n g i s s l i g h t l y more energy i n tensive RMC i s e q u a l but p r o c e s s i n g time i s much g r e a t e r than s t a n d a r d system (B) RMC f o r water-based system are g r e a t e r as w e l l as i n c r e a s e i n p r o c e s s i n g times

Same as (A) but added second r e a c t i o n step + cost of a c r y l i c acid

(B) 80-200°C 200-300°C

80-100°C

80-200°C

200-300°C

1 day s o l v e n t

1 day s o l v e n t cook and 1/2 t o 1 day n e u t r a l i z a tion—let-down

F u s i o n cook 1 day f o l l o w e d by r e a c t i v e s o l v e n t r e d u c t i o n and subsequent a c r y l i c a c i d e s t e r i f i c a t i o n (1/2 day)

Same as convent i o n a l + amines and c o u p l i n g s o l v e n t s 0.30-0.60/lb

Same as conventional + acrylic acid or glycidyl a c r y l a t e 0.40 s o l i d s water based system w i l l present a removal burden o f 68.4 g a l l o n s to the oven. T h i s represents 570 pounds/hour which must be removed, or a heat input of 0.74 χ 10 BTU/hr f o r evaporation. The exhaust volume r e q u i r e d t o provide a dry oven environ ment at t h i s l e v e l of water removal, w i l l be 5700 cubic feet/hour of a i r at 70 F, or a thermal input of 3.26 χ 10 BTU/hr t o e l e v a t e t h i s 5700 cubic f e e t of a i r to a temperature of 600 F (see Appendix). As i n the s e c t i o n above, the oven input w i l l be made up of the energy investment i n the metal, the oven panel l o s s , the opening l o s s , the exhaust a i r l o s s and the heat input to evaporate the water: Q

= (2.45 + 0.41 + 0.17

Q

+ 3.26 + 0.74)

10

6

BTU/hr

6

= 7.03 x 1 0 BTU/hr The power requirements of the fans are estimated t o be 30 hp f o r the c i r c u l a t i o n volume of 42,600 cfm, and 10 hp f o r the exhaust of 11,400 cfm. Hence, the fan power requirements Q are 40 hp or 29.8 kW. As before, the gross energy input per hour f o r the water based system can be estimated: f

Q

tot

=

Q

+

Q

0 f = 7.03 x 1 0 fi

b

+ (29.8 χ 10,500)

= (7.03 + 0.3D

10

6

6

= 7.34 χ 1 0 BTU/hr At a gas cost of $2.50 per 1000 f t and power c o s t s of 30/kWhr one a r r i v e s at an hourly energy cost of the system f o r water based p a i n t of: 3

tot

gas elec = (7.03 x $2.50) + (29.8 χ = 17.58 + = $18.47

.03)

0.89



62

ENERGY CONSERVATION IN TEXTILE AND POLYMER PROCESSING

The Water Base Paint i n an 80/20 Blend. In t h i s case, a 45Î s o l i d s c o a t i n g w i l l be u t i l i z e d with an 80% water and 20% s o l v e n t base. As before, 68.4 g a l l o n s of water and s o l v e n t w i l l be removed per hour of o p e r a t i o n f o r a t o t a l of 45ό pounds of water. T h i s , i n t u r n , w i l l r e q u i r e a heat input of 0.59 x 10 BTU/hr f o r evaporation. The exhaust r a t e r e q u i r e d to provide a s a f e and dry oven atmosphere can then be determined f o r each component of the c o a t i n g . I f , as i n the f i r s t case, one u t i l i z e s a f i g u r e o f 166 cfm per g a l l o n of s o l v e n t / h r removed, the 13.7 g a l l o n s of solvent per hour r e q u i r e s : 2271 of cfm of 70 F a i r . I f one assumes a f i g u r e of 10 cfm/lb of water/hr, the 456 l b s of water r e q u i r e s : 4558 cfm of 70 F a i r . The energy r e q u i r e d to heat the replacement a i r to the 600 F r e q u i r e d a t t h i s r a t e (6829 cfm), from a 70 F ambient temperature, can be c a l c u l a t e d t o be 3.91 χ 16 BTU/hr. As before, the oven input w i l l then be made o f the energy investment i n the metal, the oven panel l o s s , the opening l o s s , the exhaust a i r l o s s and the energy r e q u i r e d t o evaporate the water: Q

= (2.45 + 0.41

Q

+ 0.17

+ 3.91

+ 0.59)

10

6

BTU/hr

6

= 7.53 x 1 0 BTU/hr The power requirements f o r the fans are estimated t o be i d e n t i c a l to that of case 3 or 29.8 kW (Appendix) As before, the gross energy input per hour f o r the 80/20 system can be estimated as: Q

tot

Q

+

Q

= 0 F , = (7.53 x 10 ) b

= 7.84 χ At a gas cost 30/kWhr, one a r r i v e s of: C. . = C + tot gas

+ (0.3) x

, 10 )

1 0 BTU/hr of $2.50 per 1000 f t and power cos.ts of at an hourly energy cost f o r the 80/20 system 3

C , elec

= (7.53 x $2.50) + (29.8 χ = 18.82

+

b

6

.03)

0.89

= $19.71 E l e c t r o n Curing of a 100% S o l i d System. In order to assess the comparative m e r i t s of an e l e c t r o n c u r i n g system, i t i s f i r s t necessary to s p e c i f y the energy investment to cure (or dose to cure) requirements of the coatings. At the present time, the e l e c t r o n c u r a b l e 100% s o l i d s systems s u i t a b l e f o r i n t e r i o r metal d e c o r a t i n g a p p l i c a t i o n s possess cure doses i n the range of 2.5 megarads (6 cal/gm or 26 BTU/lb). — I t i s l i k e l y that r a d i a t i o n curable coatings with e x t e r i o r d u r a b i l i t y w i l l soon become a v a i l able with energy investments to cure not much i n excess of t h i s figure. }



6. MCGIXNISS ET AL.

Organic

Coatings

63

Under these c o n d i t i o n s , a s i n g l e c u r i n g s t a t i o n a t an e l e c t r o n beam power output of approximately 300 watts per i n c h i s adequate t o cure such a coating a t a l i n e speed o f 300 f e e t / minute. For the a p p l i c a t i o n t r e a t e d here, a 175 kV χ 155 cm u n i t operating a t a beam current o f 100 MA would s u f f i c e - t h i s i s the CB 175/155/100 u n i t - i t provides a beam output of 17.5 kW a t an input power of 21.5 k i l o w a t t s . The coatings c u r r e n t l y a v a i l a b l e f o r e l e c t r o n c u r i n g a r e f r e e r a d i c a l i n i t i a t e d a d d i t i o n polymerized systems - u t i l i z i n g unsaturated oligomers and a c r y l i c moraomers. Since these r e a c t ions are oxygen i n h i b i t e d , i n e r t i n g o f the process zone i s u s u a l l y r e q u i r e d , although n o n - a c r y l i c coatings chemistry i s now w e l l developed which shows near term promise of non 0^ i n h i b i t e d systems. In order to present a r e a l i s t i c comparative a n a l y s i s , the cost of i n e r t gas should be i n c l u d e d . Current i n e r t i n g systems i n commercial p r a c t i c e are based upon i n e r t gas genera t o r s which (simply) provide a d r i e d , compressed source o f the products of combustion. The f u e l source f o r these generators i s t y p i c a l l y n a t u r a l gas or f u e l o i l . The former w i l l . b e considered here s i n c e i t i s the most p e r t i n e n t to the present a n a l y s i s . For a 5 f o o t l i n e running a t 300 f e e t per minute, an i n e r t gas supply of ^50 cfm or 3000 c f h w i l l be r e q u i r e d using the present coating systems (which w i l l cure weLI i n a few thousand ppm of 0 ) . Such a generator w i l l r e q u i r e 12% o f t h i s output i n n a t u r a l gas, or ^400 c f h to f i r e i t . Some o f ,the important operating parameters f o r such an i n e r t gas system — (Selas SGV 100) are as f o l l o w s : 2

3

Output Volume:

3540 c f h or 100 m /hr

Gas (Methane):

414 c f h or 11.7 m /hr

Cooling Water:

1980 gph or 7.5 nr/hr

3

Power*: 20 kW •Includes 15 hp compressor f o r p r o v i d i n g ouput a t 100 p s i . The t o t a l energy requirements f o r t h i s system w i l l be made o f the input to the e l e c t r o n processor, the f u e l f o r the i n e r t gas system and i t s compressor power: Q

tot

=

Q

eb

+ Q

i g

= (21.5 x 10,500) + (414 χ 1000) + (20 χ 10,500) = 0.23 + 0.41 + 0.21 6

= 0.85 x 1 0 BTU/hr At a gas cost o f $2.50/1000 f t and power costs o f 30/kWhr, one a r r i v e s a t an hourly energy cost f o r the 100$ s o l i d s c u r i n g system o f : c. . = C + C tot gas elec 3

Ί

= (0.41 χ $2.50) + (41.5 x .03) = 1.03 + 1.24 = $2.27



64


In a comparative cost a n a l y s i s o f the e l e c t r o n vs. thermal c u r i n g stystems, a maintenance cost should be assigned t o each system. In the case of the eb u n i t , i t i s about one d o l l a r per hour; f o r thermal ovens of t h i s s i z e , i t i s of the same order. Water costs f o r the i n e r t gas generator are not included, but would add about 400/hr. A summary o f these comparative e n e r g e t i c s i s tabulated below Cost "($/hr)

T o t a l Gnii (iOOOcfh)

Method

Coating

Afterburner

Totn] Knor^y

Thermal

Solvent

No Preheat Preheat

15.7 10.7

15.4 10. A

AO.03 26.78

Thermal

Water

7.3

7.0

18.A7

Thermal

80/20

7.8

7.5

19.71

Electron

100% S o l i d s

0.85

.A

2.27

* Using 1 kUhr = 10,500 BTU f o r e l e c t r i c a l power:

thermal energy conversion.

Comparisons i n Cost o f E l e c t r o n Curing Coatings M a t e r i a l s vs Conventional Coatings The cost o f r a d i a t i o n curable coatings i n l a r g e volume can be equivalent t o , or s l i g h t l y more expensive than conventional coatings depending on the polymer desired, the cost o f the s t a r t i n g m a t e r i a l s and added manufacturing processes. This conclusion i s based on h y p o t h e t i c a l comparison's of costs as discussed below. A sample c a l c u l a t i o n f o r raw m a t e r i a l costs (RMC) o f a conventional p o l y e s t e r r e s i n s y n t h e s i s i s shown below. 5 moles o f p h t h a l i c anhydride = (5 moles) (148.12 g/mole) = 740.6 g 740.6 g/454 g / l b = (1.63 l b ) ($0.26/lb) = $0.42 6 moles o f ethylene g l y c o l = (6 moles) (62.07 g/mole) = 372.42 g 372.42 g/454 g / l b = (0.082 l b ) ($0.25/lb) = $0.21 Molecular wight o f the p o l y e s t e r r e s i n = (5 moles p h t h a l i c anhydride) + (6 moles ethylene g l y c o l ) - (5 moles o f H 0 ) . 740.6 + 372.42 - (5) (18) = 1023.02 gms/mole T o t a l l b o f p o l y e s t e r r e s i n made = 2.45 l b Minus water o f r e a c t i o n - 0.20 l b 2.25 l b T o t a l cost = $0.63 f o r 2.25 l b m a t e r i a l = $0.63/2.26 l b = $0.28/lb The above c a l c u l a t i o n s a r e based on a t h e o r e t i c a l molecular weight o f 1000 with p r i c e s o f bulk monomer q u a n t i t i e s taken from CMR, February 27, 1978, r e s u l t i n g i n a t o t a l m a t e r i a l cost f o r the f i n a l product o f $0.28/lb. (RMC p h t h a l i c anhydride, $0.26/lb; RMC ethylene g l y c o l , $0.25/lb). Manufacture i s by simple f u s i o n cook or s o l v e n t a z e o t r o p i c water removal. ?

S i m i l a r c a l c u l a t i o n s are shown below f o r a r a d i a t i o n curable p o l y e s t e r but i n c l u d e d i s the cost o f a c r y l i c a c i d (0.37/lb) and


6.

MCGINNISS ET AL.

Organic

Coatings


an e x t r a manufacturing cost step polymer e s t e r i f i c a t i o n .

65

(0.1071b) f o r the a c r y l i c a c i d -

5 moles of p h t h a l i c anhydride = (1.63 l b ) ($0.25/lb) = $0.42 6 miles of ethylene g l y c o l = (0.82 l b ) ($0.25/lb) = $0.21 2 moles of a c r y l i c a c i d = (0.32 l b ) ( $ 0 . 3 7 / l b ) = $0.12 Molecular weight of the p o l y e s t e r r e s i n = (5 moles p h t h a l i c anhydride) + (6 moles ethylene g l y c o l ) + (2 moles a c r y l i c acid) - (7 moles of H 0) = 9 8 7 . T o t a l l b of a c r y l a t e d p o l y e s t e r r e s i n made = 2.17 l b . T o t a l cost = $0.75 f o r 2.17 l b . $0.75/2.17 l b = $0.34/lb. Added manufacturing cost f o r a c r y l i c a c i d r e a c t i o n $0.10/lb. T o t a l cost of r a d i a t i o n curable r e s i n = $0.44/lb. The t o t a l RMC plus e x t r a manufacturing cost f o r the polymer ( r a d i a t i o n curable) i s $0.44/lb. This i s approximately $ 0 . l 6 / l b more i n cost f o r the same molecular weight polymer as used i n conventional c o a t i n g systems. The i n d i v i d u a l RMC f o r polymer m a t e r i a l s i s not the only f a c t o r i n cost a n a l y s i s of a c o a t i n g system. In order t o make a f a i r comparison between conventional and r a d i a t i o n curable coat ings one must consider the e n t i r e coatings formulation. Shown below i s a cost range c a l c u l a t e d f o r a conventional solventc o n t a i n i n g r e s i n (excluding pigmentation) using the $0.28/lb p o l y e s t e r r e s i n cost c a l c u l a t e d e a r l i e r . 2

Low Solvent

Range

?

Cost($)

Cost/lb($)

30? p o l y e s t e r r e s i n 50? solvent 20? melamine r e s i n

(0.30) (0.50) (0.20)

(0.28) (0.06) (1.00)

0.08 0.03 0.20 0.31/lb

High Solvent Cost Range 30? p o l y e s t e r r e s i n 50? solvent 20? melamine r e s i n

(0.30) (0.50) (0.20)

(0.28) (0.55) (1.00)

0.08 0.28 0.20 0.56/lb

Low range = ($0.31/lb cost) (9 l b / g a l ) = $2.79/gal High range = ($0.56/lb cost) (9 l b / g a l ) = $5.04/gal. These coatings formulations are 50? s o l i d s and t h e i r coatings coverage i s only 650 t o 800 f t / g a l l o n . For comparison, the cost of a comparable r a d i a t i o n c u r i n g c o a t i n g i s shown below: Cost($) 0.13 0.22 0.22 0.57/lb of the r a d i a t i o n curable coatings f o r m u l a t i o n i s ($0.57/lb χ 9 l b / g a l = $5.3/gal: at 100 percent This c o s t / g a l l o n i s comparable bo the high range

30? a c r y l a t e d p o l y e s t e r r e s i n (0.30) 50? 2-ethyl hexyl a c r y l a t e (0.50) 20? m u l t i f u n c t i o n a l a c r y l a t e (0.20) The cost $5.13/gal solids).

Cost/lb($) (0.44) (0.44) (1.10)

= = =



66


solvent-based system, but the coverage i s now 1600 to 1625 f t * . In d i r e c t comparison to the conventional systems, r a d i a t i o n curable coatings formulations can be constructed with lower cost than conventional s o l v e n t systems on a square f o o t of coverage basis. I t takes $2.79 to $5.04 of coatings m a t e r i a l ( t h i s i s range i n cost per g a l l o n of m a t e r i a l ) x>f solvent-based convent i o n a l coatings to cover 650 to 800 f t . Since coverage of the r a d i a t i o n curable c o a t i n g system i s 2 to 2.5 times greater than the 50% s o l i d s coatings, the a c t u a l cost f o r equal coverage of the r a d i a t i o n curable m a t e r i a l i s $5.13/gal τ2 or 2.5, r e s u l t i n g i n $2.05/gal to $2.56/gal f o r equal coverage. This savings, amounts to about $0.23 to $0.74/gal i n the low s o l v e n t range, and about $3.00/gal i n the high s o l v e n t cost range. Comparisons i n Cost of Equipment Amortization f o r R a d i a t i o n Curing vs. Conventional C o i l Coatings The aforementioned model of a c o i l c o a t i n g l i n e provides f o r a cost a n a l y s i s of e l e c t r o n c u r i n g compared to conventional c u r i n g of coatings on a c o i l c o a t i n g l i n e . For t h i s a n a l y s i s c e r t a i n assumptions have been made. (1) Two s h i f t s , 5 day/week operation (2) Coating c a p a c i t y - 12,000 f t /day (3) Coating thickness - 0.001 i n c h on 0.020 i n c h s t e e l (4) C a p i t a l expenditures under a mortgage at 15% f o r 10 years making annual payments of 20Î of i n i t i a l cost f o r each of the f i r s t 10 years (5) Cost of f l o o r space - $10/ft . I f a g a s - f i r e d oven costs $200,000, and an i n c i n e r a t o r f o r emission c o n t r o l costs $75,000, t h i s r e s u l t s i n an hourly c o s t of: ($200,000) (0.20/yr) (10 y e a r s ) * (10 years) (50 weeks/yr) (5 days/wk) (16 hr/day) = $10/hr ($75,000) (0\20) (10) * $40,000 = $3-75/hr An E l e c t r o c u r e r a d i a t i o n c u r i n g u n i t could cost up t o $400,000 or a c a p i t a l expenditure cost of $20/hr. R a d i a t i o n curable systems a l s o r e q u i r e more maintenance and an i n e r t atmosphere ( n i t r o g e n blanket) to ensure e f f i c i e n t c u r i n g operations. Summary of Cost Comparisons f o r Radiation-Cured Coatings on a C o i l Coating L i n e

vs.

Conventional

The previous s e c t i o n s have shown that c o n s i d e r a b l e energy savings can be accomplished by s u b s t i t u t i n g r a d i a t i o n c u r i n g f o r conventional ovens i n a c o i l c o a t i n g l i n e . The c o i l coatings management today i s c e r t a i n l y i n t e r e s t e d i n saving energy, but i t s major concern i s the cost of the c o a t i n g , assuming equal performance f o r the f i n i s h e d product. Thus i t i s important to examine c a r e f u l l y the o v e r a l l costs of c o i l coatings when cured by r a d i a t i o n and n a t u r a l gas. These costs are t a b u l a t e d below:



6.

MCGINNISS

ET

AL.

Organic

Coatings

67

Cost Breakdown ($/hr) Cost Breakdown ($/hr) of of Radiation Solvent-Based (Electron Curtain) Conventional Coating Cured Coating System System 20.00 Cure Equipment 10.00 Aux. Equipment 3.75 N a t u r a l Gas 10.50 0.70 Electricity 0.35 System Space 0.75 0.03 Storage Space 0.50 Labor 10.00 15.00 37.96 to Coating Cost 51.62 t o 93.24/650 t o 800 f t * 47.45/650 t o 800 f t * 1.50 Maintenance 0.50 Nitrogen 1.20 T o t a l Operating Cost $92.97 t o $134.59/hr. $71.39 t o $80.88/hr. The coatings m a t e r i a l cost c a l c u l a t i o n s shown above were developed e a r l i e r f o r an i d e a l i z e d c o i l c o a t i n g o p e r a t i o n . The method o f c o i l coatings o p e r a t i o n a l c a l c u l a t i o n s were taken from References J7, j3, 9. and 1Ό and a p p l i e d to the present coatings c o s t comparisons. Coatings consumption i s 18.5 g a l / h r and s o l v e n t based coatings average cost range i s $2.79 to $5.04/gal, g i v i n g a t o t a l c o s t of $51.62 to $93-24/hr. The cost of the r a d i a t i o n curable coatings f o r m u l a t i o n i s $ 5 . 1 3 / g a l , but i t covers 2 t o 2.5 times more s u r f a c e area than the solvent-based c o a t i n g . The c o s t f o r equal coverage o f r a d i a t i o n c u r a b l e c o a t i n g i s $18.50 g a l / h r τ 2 or 2.5 times $ 5 . 1 3 / g a l = $37.96/hr to $47.45/hr. Thus, under i d e a l c o n d i t i o n s , r a d i a t i o n curable coatings might be formulated or designed to show a lower or equal c o s t per square f o o t of coverage when compared with solvent-based coatings without even c o n s i d e r i n g energy and space savings c a l c u l a t i o n s . In a l l of these c a l c u l a t i o n s there has been no added value (profit, r e s e a r c h d o l l a r spending, etc.), attached to the figures. These c a l c u l a t i o n s are i d e a l i z e d and t r y to r e f l e c t p o s s i b l e raw m a t e r i a l s cost at the present time. I t i s t h e o r e t i c a l l y p o s s i b l e at the present time t o formu l a t e ( r a d i a t i o n cured) coatings systems with almost e q u i v a l e n t RMC (raw m a t e r i a l s cost) a t equal coverage as conventional sys tems. As the use o f RC systems becomes more widespread the c o s t f o r expensive r e a c t i v e monomer, prepolymer components should a l s o drop. T h i s would occur as l a r g e s c a l e e f f i c i e n t manufacturing processes are adopted t o handle l a r g e r volumes. T h i s lowering o f p r i c e f o r RMC of the i n d i v i d u a l RC coatings components as w e l l as energy and space savings w i l l a l s o be a t t r a c t i v e t o end users. One of the major disadvantages of RC versus conventional coatings, at the present time, i s the f i n a l coatings p r o p e r t i e s obtained under a given s e t of cure. This i s especially true i n c o i l coatings operations where the r e q u i r e d performance charac-


ENERGY

68

CONSERVATION

IN

TEXTILE

AND

POLYMER

PROCESSING

t e r i s t i c s are extreme and d i f f i c u l t to obtain, and the subt s t r a t e / c o a t i n g throughput i s very f a s t . Much more research i s s t i l l needed on RC systems i n order to match d i v e r s e c o i l c o a t i n g product l i n e s and complex c o a t i n g performance c h a r a c t e r i s t i c s .


Appendix Estimates of the Heat Input f o r the Afterburner f o r the Conventional Solvent c a l c u l a t e d exhaust r a t e of 11,350 cfm estimate the r e q u i r e d hourly heat input Q

Operation o f the Paint. Based upon the of 70 F a i r , one can from the r e l a t i o n : Q =

Q = mcA t where m i s the mass of a i r moved per hour, c A t the temperature change. For the case 1400 F burner temperature i s assumed. The Q = 9.99 x 10° BTU/hr Since the i n c i n e r a t i o n process i s only 75%

i t s s p e c i f i c heat and of the a f t e r b u r n e r , a t h e o r e t i c a l input i s

t

efficient,

6

Q

= 13.32 χ 1 0 BTU/hr a Now the s o l v e n t (e.g., cyclohexanone) w i l l y i e l d 14,000 BTUs/lb upon i n c i n e r a t i o n , so that the 68.4 g a l l o n s of s o l v e n t burnt per hour have a thermal y i e l d of Q

= 7.52

s

χ 10

6

BTU/hr

The net heat input to the Q

= Q

afterburner

- Q

a s r = 5.81 χ 10 BTU/hr In order to i n c r e a s e the a f t e r b u r n e r e f f i c i e n c y , preheat zone e l e v a t e s the input a i r from 600 F t o 900 F.

a single For t h i s

condition: Q

1 t

= 6.24

χ 10

6

BTU/hr

1

Q = 8.33 x 10g BTU/hr And the net input to the a f t e r b u r n e r with a s i n g l e preheat zone i s now reduced to: a

Q

l

n

=

Q a

"

Q

o

a 3 r = 0.81 χ 10° BTU/hr Estimate of the Heat Input f o r the Exhaust A i r f o r Water Base Paint With No Solvent. The a i r exhaust r a t e r e q u i r e d t o provide a dry oven atmosphere i s determined by the amount of water r e l e a s e d i n t o the oven. Using a f i g u r e of 10 cfm of a i r per pound o f water per hour, the 570 pounds of water per hour w i l l r e q u i r e approxi mately 5700 cfm of a i r at 70 F. As i n the example above, the hourly heat input r e q u i r e d to heat t h i s amount of a i r i s : Q = mc Δ t


6.

MCGiNNiss E T A L .

Organic

Coatings

69

where m = (5700 χ 60) c f h χ (0.075 pounds/ft ) c = 0.24

BTU per l b per F

t = 600 - 70 = 530 F So the heat input 4

Q = (34.2 x 10 )


= 3.26 χ 1 0

6

(0.018) (530)

BTU/hr

E s t i m a t i o n o f the C i r c u l a t i o n Fan Power f o r the Water Base P a i n t . Consider f i r s t the heat input r e q u i r e d f o r the metal, the water removal, the end l o s s e s and the oven panel l o s s e s . Call this Q made up of: 1?

Q

= (2.45 + 0.74

x

+ 0.41

+ 0.17)

10

6

BTU/hr

6

= 3.77 x 1 0 BTU/hr We can now c a l c u l a t e the a i r volume V, i n cfm r e q u i r e d t o provide t h i s input at 70 F from Q±

= νλ

p c so V±

A t 60

= 1^/(60 A t ρ

c)

where ρ i s the a i r d e n s i t y i n l b / f t ^ , and c i t s s p e c i f i c heat and A t the o p e r a t i n g head temperature d i f f e r e n t i a l o f 200 F. V±

= 3.77

6

x 10 /2.16 4

= 1.74 χ 10 cfm at 70 F Secondly, the a d d i t i o n a l heat input per hour f o r the exhaust air, Q = 3.26 χ 10 BTU/hr. In the same manner, one can calculante the t o t a l heat f o r i t s d e l i v e r y from: 2

= Q /(60 νλ

At

2

pc) 6

= (3.26 χ 10 )/(60 χ 1.74

χ ΙΟ

4

χ 0.018)

= 173 F Operating head (200 F) + oven temperature (600 F) = d e l i v e r y temperature (800 F) and d e l i v e r y temperature - t o t a l head = mixed temperature. Hence

800 F - 173 F = 627 F The c i r c u l a t i n g volume at 70 F, hence the c a p a c i t y o f the c i r c u l a t i n g fan at that temperature, i s V, c o r r e c t e d t o the mixed temperature o f 627 F, or 2.05

ν

χ

= 2.05

x 1.74

χ 10

4

= 35,800 cfm The exhaust volume, c a l c u l a t e d t o be 5700 cfm at 70 F, w i l l provide the exhaust blower requirement of 600 F a i r , or 2.00 χ 5700 = 11,400 cfm. In order t o achieve a c i r c u l a t i n g volume o f 35,800 cfm at a s t a t i c pressure of 2.5 inches, 2 χ 21,000 cfm fans with 15 hp motors are needed. T h e i r power consumption i s t h e r f o r e 22.4 kilowatts.


70

ENERGY

CONSERVATION

IN TEXTILE

A N D POLYMER

PROCESSING

In order t o achieve an exhaust volume o f 11,400 cfm a t a s t a t i c pressure o f 2.5 inches, an 11,700 cfm blower with a 10 hp d r i v e motor i s r e q u i r e d . I t s power consumption i s t h e r e f o r e 7.46 kilowatts.


Acknowledgement Thanks are expressed t o Mr. H. R. Powers and The SherwinWilliams Company f o r permission t o use cost i n f o r m a t i o n developedl i n - h o u s e d VÎU.

Literature Cited 1. Editorial, "Paint Curing: Saving 27.8 Billion BTUs/Year". Products Finishing, March 1977, pp 77-79. 2. David, Mary P., "Energy Consumption Outlook for the Printing Industry". Inland Printer/American Lithographer, February 1977, p. 60. 3. Toronto and Montreal Societies for Coatings Technology, Joint Symposium, Sept. 14, 1977. "Energy Conservation in Paint Production". American Paint and Coatings Journal, August 15, 1977, p. 9. 4. Anderson, R. J., "The Energy Reason for Using Coated Coil". Metal Finishing, November 1977, pp. 20-22. 5. Dekoker, Neil, "Energy Conservation in Manufacturing". Industrial Engineering, December 1977, pp. 20-26. 6. Evaluation of the Theoretical Potential for Energy Conservation in Seven Basic Industries. Battelle Columbus Laboratories Report to FEA, January 31, 1975. 7. Powers, H. R., "Electron Beam Curing for Coil Coatings, A Study of The Energy Requirements". Sherwin-Williams Company, 1975. 8. Powers, H. R., "Comparison of Energy Requirements for Various Methods of Curing Coil Coatings". Sherwin-Williams Company, 1973. 9. Rothchild, R. D., Painting Highlights, Nov./Dec., 1977, p. 16. 10. Product Data Sheets of following companies: Electron Beam Curable Coatings of Interior and Exterior Durability, Sherwin Williams Co., Chicago, Il., 1977; UCARV-280 and 281, Radiation Curable Coatings for Metal Decoration, Union Carbide Corporation, 270 Park Ave., New York, 1976; Reactomer Monomers for Radiation Cured Coatings, Thiokol Chemical Div., Thiokol Corp., Trenton, N. J., 1976; Coatings for Aluminum Coil Mobil Chemical Co., Edison, N. J. RECEIVED

February 12, 1979.


The Importance of Curing Conditions in Overall ... - ACS Publications

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