Energy Conservation in Textile and Polymer ... - ACS Publications

9 New Energy Saving Reactive Acrylic Liquid Polymers for the Pressure Sensitive Adhesives Industry Y.-S. LEE

Downloaded by CORNELL UNIV on October 23, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch009

BFGoodrich Company, R&D Center, 9921 Brecksville Road, Brecksville, OH 44141

A large volume of solution adhesive is consumed in the pressure sensitive adhesive (PSA) converting industry. This requires vast quantities of energy for drying and for incineration or solvent recovery. The well-publicized natural gas shortage of the winter of 1976-1977, the energy crisis, and the tightened EPA emission control regulations make the solventless and high solids PSA systems very attractive. Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar® 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. Results and D i s c u s s i o n Emission and Economic Advantages. The use of Hycar 2100R s e r i e s polymers o f f e r s a s i g n i f i c a n t r e d u c t i o n i n solvent emission over conventional 40% s o l i d s system (by wt.). An 83% r e d u c t i o n i n s o l v e n t emission ( f i g u r e 1) r e s u l t s when the 80% s o l i d s Hycar system i s used. Further r e d u c t i o n i s obtained f o r 90% and 100% s o l i d s systems. The solvent content of the 90% s o l i d s system i s so low that n e i t h e r i n c i n e r a t o r nor heat exchanger may be needed - a very good p o s s i b i l i t y f o r smaller PSA c o n v e r t e r s . F i g u r e I I shows a comparison of the energy needed and energy cost f o r a system using a solvent i n c i n e r a t o r with a heat exchanger i f needed. The energy needed to make 1000 m2 of adhesive

0-8412-0509-4/79/47-107-097$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.

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i s about 2.1X109 Joules f o r 40% s o l i d s conventional system and i s about 3.5X108 Joules f o r the 80% s o l i d s system. T h i s i s about an 80% energy saving f o r the 80% s o l i d s system when compared with

H9

40%

40h

8

m

-30|-

6 § 9

co Downloaded by CORNELL UNIV on October 23, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch009

C

7 S χ*

1

CO

Ï20I-

4 5

5

l*J

CO

80%

1

90%

CONVENTIONAL SYSTEM Figure 1.

1

CO CO

I

I

I

100% 0

BF6 SYSTEM

Effect of total solids on solvent emission

ENERGY COST

ENERGY

-40

200

40%

~400H 40%

«Γ

c

00

-30»

CO

S

«ι

-2θ8 60%

H80

Π w w » CONVENTIONAL BF6 SYSTEM SYSTEM Figure 2.

iooh

80%

90% 00% π η Π CONVENTIONAL BFG SYSTEM SYSTEM

Energy and energy cost with incinerator and heat exchanger (if needed)


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the 40% conventional system. Based on a n a t u r a l gas p r i c e of $2.00/1000 f t . 3 , i t would cost almost $4.00 to make 1000 m of adhesive f o r the 40% s o l i d s system and only about $0.80 f o r the 80% s o l i d s system. The savings i n energy and energy cost would, of course, be even higher f o r the 90% and 100% s o l i d s systems. F i g u r e I I I shows the same comparison when no p o l l u t i o n c o n t r o l system i s incorporated. A s u b s t a n t i a l r e d u c t i o n i n energy usage 2

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ENERGY COST

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40%

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1 - sU H -

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S 41 00% 90%

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90%

100%

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CONVENTIONAL BFG SYSTEM SYSTEM Figure 3.

90%

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CONVENTIONAL BFG SYSTEM SYSTEM

Energy and energy cost without pollution control

and energy cost can be r e a l i z e d by ths high s o l i d s or 100% s o l i d s system. The model that was chosen f o r the c a l c u l a t i o n s i s the following: % S o l i d s of conventional system by wt. Dry adhesive f i l m thickness Substrate Solvent S p e c i f i c g r a v i t y of adhesive L i n e speed of coater Web width Oven length Oven width Oven height Oven temperature Combustion e f f i c i e n c y Heat exchanger e f f i c i e n c y N a t u r a l gas cost

40 0.025 mm (1 m i l ) 0.05 mm (2 m i l s ) Mylar toluene 1.05 1.5 m/s (300 fpm) 1.52 m (60") 45.7 m (150 ) 3.1 m ( 1 0 ) 3.1 (10') 149°C (300°F) 65% 43% $7.06Χ10" /1 ($2.00/M f t 3 ) ?

1

5


ENERGY CONSERVATION IN T E X T I L E A N D P O L Y M E R PROCESSING

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Note that the d i f f e r e n c e i n c a p i t a l and operating costs between the conventional system and the BFG 80% s o l i d s and 90% s o l i d s systems due t o the s i z e d i f f e r e n c e of the p o l l u t i o n cont r o l equipment has not been considered, and that none of t h i s equipment i s needed by the 100% s o l i d s system. Also note that the energy cost c a l c u l a t i o n s a r e based on n a t u r a l gas. I f o i l or e l e c t r i c i t y i s used, the cost would be even higher. Owing to the n a t u r a l gas shortage, a number of converters have switched from n a t u r a l gas to o i l , thus the d i f f e r e n c e i n energy cost of using o i l i s about twice that of using n a t u r a l gas. Materials. T h i s paper i s mainly concerned w i t h two Hycar 2100R polymers, Hycar 2103 and Hycar 2106. These a r e c h a r a c t e r ized i n Table I. Isocyanate Prepolymer C i s used as the c u r a t i v e I t s t y p i c a l p r o p e r t i e s are summarized i n Table I I . TABLE I - T y p i c a l P r o p e r t i e s of Hycar 2100R Polymers Hycar 2103 100%_Solids 70% S o l i d s

Hycar 2106 100% S o l i d s 70% S o l i d s

Clear;Light Yellow

Sp. Gr. @ 24°C

1.05

0.996

1.05

0.996

OH Value, meq./g.

0.53

0.37

0.75

0.53

OH Number, mg KOH/g

30

21

42

29

Viscosity Brookfield Pa-s (cps), @ 24°C 700(7x105) Flash °C

1.7(1700)

Clear;Light Yellow

Clear;Light Yellow

Clear;Light Yellow

Appearance

400(4x105)

0.9(900)

Point, 7

8

TABLE I I - T y p i c a l P r o p e r t i e s of Isocyanate Prepolymer C Free NCO, wt. % Sp. Gr. @ 24°C V i s c o s i t y , B r o o k f i e l d , Pa-s (cps), @ 24°C

4.3-4.7 1.09 24 (24000)


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PSA Formulation and P r o p e r t i e s . The formulations used i n t h i s study f o r the Hycar 2103-Prepolymer C and Hycar 2106-Prepolymer C PSA c o n t a i n OH/NCO r a t i o s of 1.7 and 1.3, r e s p e c t i v e l y . D i b u t y l t i n d i l a u r a t e c a t a l y s t i s used a t a 0.2 wt.% l e v e l based on the t o t a l adhesive s o l i d s . PSA samples are made from an 80% s o l i d s s o l u t i o n (by wt.) with a dry solvent system (27/73 by wt. of e t h y l acetate-toluene) and cured a t 150°C f o r 45 seconds. The samples are then evaluated by running 180° p e e l , s t a t i c shear, r o l l i n g b a l l tack, and v i n y l f i l m shrinkage t e s t s . These adhesive systems g i v e an e x c e l l e n t combination of s t a t i c shear (at both room temperature and 70°C) and r o l l i n g b a l l tack along with e x c e l l e n t v i n y l f i l m shrinkage r e s i s t a n c e . The r e s u l t s of these t e s t s a r e summarized i n Table I I I . TABLE I I I - T y p i c a l PSA P r o p e r t i e s Hycar 2103 Clear,Colorless

Adhesive F i l m Appearance 180° P e e l S t r e n g t h ' , N/m (oz./in.) S t a t i c S h e a r l * , h, 70°C 24°C Rolling b a l l t a c k ' , cm ( i n . ) V i n y l F i l m Shrinkage^, cm 1

Clear,Colorless

2

3

1

Hycar 2106

438 (40) >100 (no creep) >1000 (no creep)

569 (52) >100 (no creep) >1000 (no creep)

2.3 (0.9) 0x0

2.8 (1.1) 0x0

4

^Test with 1-mil adhesive c o a t i n g on 2-mil Mylar. PSTC-1, overnight dwell on SS panel. .PSTC-7, 6.45 cm (1 i n c h ) contact area on SS panel, 1 Kg l o a d . ^PSTC-6 5-mil v i n y l f i l m used, t e s t run f o r 24 h a t 70°C - 10.16 cm χ 10.16 cm (4"x4") samples used. 3

2

2

Performance F l e x i b i l i t y . F i g u r e IV i l l u s t r a t e s the e f f e c t of the 0H/NC0 r a t i o of 180° p e e l s t r e n g t h and r o l l i n g b a l l tack f o r both the Hycar 2103-Prepolymer C and Hycar 2106-Prepolymer C adhesive systems. P e e l s t r e n g t h values o f 493 N/m (45 oz./in.) or lower are p o s s i b l e f o r the Hycar 2103 system simply by a l t e r i n g the OH/NCO r a t i o . Likewise f o r the Hycar 2106 system, peel strengths of 657 N/m (60 oz./in.) or lower a r e p o s s i b l e . In both cases, r o l l i n g b a l l tack remains r e l a t i v e l y constant unless the OH/NCO r a t i o becomes too low. In a d d i t i o n , no creep i n s t a t i c shear i s observed a t room temperature or 70°C a t the r a t i o shown. High p e e l s t r e n g t h w i t h cohesive f a i l u r e i s p o s s i b l e by i n c r e a s i n g the OH/NCO r a t i o . At a higher r a t i o , s l i g h t creep i s observed a t room temperature i n the s t a t i c shear t e s t . , OH/NCO r a t i o s above 2.0 f o r Hycar 2103 and 1.8 f o r Hycar 2106 r e s u l t i n adhesives having incomplete cures with low peel values and poor s t a t i c shear s t r e n g t h .


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1.2 Figure 4.

1.3

1.4 1.5 1.6 OH/NCO RATIO

PSA properties vs. OH/NCO ratio: ( 2106.

1.7

1.8

) Hycar 2103; (

) Hycar

Figure V demonstrates the e f f e c t of adhesive d r y c o a t i n g weight on 180° peel strength and r o l l i n g b a l l tack w i t h OH/NCO r a t i o s of 1.7 and 1.3 f o r Hycar 2103 and Hycar 2106, r e s p e c t i v e l y . S t a t i c shear t e s t s run both a t room temperature and 70°C show no creep f o r both systems throughout the thickness range t e s t e d . Only a t low adhesive coating weight does the r o l l i n g b a l l tack begin to increase s l i g h t l y .

THICKNESS (mil) Figure 5.

PSA properties vs. adhesive thickness: ( _ 1.7; ( ; Hycar 2106, OH/NCO

) Hycar 2103 — 1.3.

y

OH/NCO



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Processing. The 80% s o l i d s systems are compatible with conventional c o a t i n g equipment such as k n i f e - o v e r - r o l l and reverse r o l l . P r i o r to c o a t i n g , the use of i n - l i n e meteringmixing equipment i s recommended to accommodate the mixing of the 2-component system. A 90% s o l i d s Hycar 2106-based PSA system has been s u c c e s s f u l l y processed by a reverse r o l l coater i n c o r porated with a Twinflo® metering-mixing equipment (manufactured and sold by L i q u i d C o n t r o l Corp. of W i c k l i f f e , Ohio). Encouraging r e s u l t s have a l s o been obtained by processing a s o l v e n t l e s s Hycar 2100R PSA system with a d i f f e r e n t i a l r o l l coater (manufactured by Egan Machinery Co.). The r a t i o of the Hycar 2100R polymer to isocyanate prepolymer can be adjusted to ?,ive a f a m i l y of products with a range of p e e l strengths while r e t a i n i n g e x c e l l e n t s t a t i c shear strength and tack (see Figure IV). This f a m i l y of products can be produced at the "touch of a d i a l ' with i n - l i n e meteringmixing equipment. The c a t a l y s t may be added to the Hycar 2100R polymer before mixing; however, a prolonged storage of Hycar 2100R polymer with c a t a l y s t should be avoided. Figures VI and VII i l l u s t r a t e the i n i t i a l v i s c o s i t y of both the Hycar 2103 and Hycar 2106 systems as w e l l as the v i s c o s i t y increase with time due to the r e a c t i v e nature of the 2-component system. These f i g u r e s w i l l help i n determining the percent s o l i d s necessary f o r processing on a given p i e c e of equipment depending upon i t s v i s c o s i t y handling c a p a b i l i t y . Since the 100% s o l i d s PSA systems have high i n i t i a l v i s c o s i t i e s of over 100 Pa*s (100,000 c p s ) , the conventional k n i f e - o v e r - r o l l and reverse r o l l coaters can not process them. r

Curing occurs at elevated temperatures as the solvent i s being evaporated. Various oven temperatures and a i r v e l o c i t i e s can be used depending on the substrate being coated. The c u r i n g temperature vs. c u r i n g time i s summarized i n Table IV. I f d e s i r e d , p a r t i a l c u r i n g may be performed i n the oven and then completed i n the r o l l . TABLE IV - Curing Temperature v s . Curing Time

Curing Temp.

Curing Time Hycar 2103/ Hycar 2106/ Prepolymer C Prepolymer C

150°C (302°F) 120°C (243°F) 93°C (200°F)

45 sec. 1.25-1.5 min. 4 min.

30 sec. 1 min. 2.5 min.

Acetates, such as e t h y l acetate and 2-ethoxyethyl* a c e t a t e , hydrocarbons, such toluene and heptane, c h l o r i n a t e d hydrocarbons, such as methylene c h l o r i d e and 1,1,1-trichloroethane, and mixtures of them, such as the mixture of toluene and e t h y l acetate have been screended as solvents f o r the Hycar 2100R-based PSA. Good PSA p r o p e r t i e s are obtained using any of these s o l v e n t s . How-


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ever, the solvent used has to be reasonably dry due to the reactive nature of the isocyanate prepolymer with water. The viscosity of the PSA system in the different solvents may not be the same due to the difference in the initial solvent viscosity and the solubility of the polymers. In summary, BFG has developed a series of new reactive acrylic liquid polymers for the PSA industry. The PSA converters can process BFG 30% solids system with their existing equipment without modification and obtain superior PSA properties, such as excellent static shear (at R.T. and 70°C) and rolling ball tack, good peel strength and low vinyl film shrinkage. They will also be able to conform to the more stringent requirements of reducing energy consumption and meeting EPA emission standards with only very minimum capital outlay. Abstract Energy consumption and EPA standards are becoming important considerations to pressure sensitive adhesive (PSA) converters. The BFGoodrich Hycar® 2100R series of polymers is a new product concept designed to fulfill the changing needs of the PSA industry. These polymers are designed specifically to conform to those more stringent requirements while maintaining superior performance properties and minimizing equipment additions or modifications. The Hycar 2100R products are reactive acrylic liquid polymers and are furnished as 70% solids solutions which when combined with Isocyanate Prepolymer C and catalyst give a PSA formulation of approximately 80% solids. This high solids system is compatible with conventional coating equipment such as knife-over-roll and reverse roll. A 90% solids Hycar 2106-based PSA system has been successfully processed by a reverse roll coater incorporated with a Twinflo metering-mixing equipment. This paper covers: (1) the economic advantages of this high solids system due to reduced solvent requirements and reduced energy needs to evaporate solvents, when compared with conventional acrylic solution polymer PSA systems; (2) the PSA properties attained including a combination of excellent static shear and rolling ball tack, good peel strength, and excellent vinyl film shrinkage resistance; (3) the property changes that occur by varying the ratio of Hycar 2100R polymer to isocyanate prepolymer resulting in a family of products; and (4) the processing parameters. References (1)

R. G. Marchessault and A. P. Plummer, Adhesive Age, 20, No. 4, April, 1977, p. 34.

RECEIVED March 12, 1979.


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