Vinyl Resins Used in Coatings - American Chemical Society

50 Vinyl Resins Used in Coatings RUSSELL A. PARK

Downloaded by CORNELL UNIV on May 13, 2017 | http://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch050

PVC Resins and Compounds Division, Occidental Chemical Corporation, Pottsdown, PA 19464

Historical Polymerization Techniques Polymers Formulation Considerations Application Techniques Today and Tomorrow

Historical Poly(vinyl chloride) i s over 100 years o l d . M. V. Regnault (1) i s credited with discovering the basic building block, vinyl chloride, in 1835. He obtained the vinyl chloride by chlorinating ethylene to give 1,2-dichloroethane, which was later treated with an alcoholic caustic potash solution to y i e l d the monomer plus water and potassium chloride. When heated 4 days later, he noted that a white powder was formed under the influence of sunlight. It took 40 years before additional conversion of vinyl chloride was investigated. In 1912 Zacharias and Klatte carried out the commercial preparation of vinyl chloride by the addition of hydrogen chloride to acetylene in Germany. In 1914 F. Klatte and A. Rollet described the first polymerization of vinyl acetate to poly(vinyl acetate). In 1921 Herman Plausen of Hamburg, Germany, described the polymerization of vinyl chloride. The copolymerization of v i n y l chloride and v i n y l acetate was disclosed in the United States in 1928. " I m i t a t i o n " or s u b s t i t u t e products made from poly(vinyl chloride) did not have much commercial acceptance after World War I, probably due to the poor quality of war-manufactured goods. During 1928-32 compositions were made by dissolving polymers of v i n y l halides i n a number of high-boiling esters at elevated temperatures to form rubberlike materials. The development of compounding principles (still felt to be an art by many) and the a v a i l a b i l i t y of new raw material sources produced from natural and cracked petroleum gases brought the 0097-6156/85/0285-1205$06.75/0 © 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


i n d u s t r y out of i t s i n f a n c y . World War I I pushed i t i n t o a d o l e s cence when t h e need f o r new sources of e l e c t r i c a l i n s u l a t i o n , w a t e r p r o o f i n g , and c o r r o s i o n p r o t e c t i o n developed as a m i l i t a r y necessity. Of the more than 30 b i l l i o n pounds of ethylene consumed i n the U n i t e d S t a t e s i n 1980, over 17% was used i n the p r o d u c t i o n of ethylene d i c h l o r i d e / v i n y l c h l o r i d e monomer and v i n y l acetate. The major feedstock f o r ethylene production i s ethane (47%), with other major feedstocks being gas o i l , naphtha, and propane. In the oxychlorination process, ethylene i s f i r s t converted to ethylene d i c h l o r i d e as f o l l o w s :

CH =CH + 2

2HC1

2

ethylene

catalyst 250-315 °C > 1 atm

+ i0

2

hydrogen chloride

oxygen

CH C1CH C1 2

vapor phase +

2

H0 2

ethylene d i c h l o r i d e water The ethylene d i c h l o r i d e i s then dehydrochlorinated by p y r o l y s i s as follows: catalyst 480-500 °C CH C1CH C1 2

>

2

CH =CHC1

+

2

HC1

3 atm ethylene d i c h l o r i d e

v i n y l chloride

hydrogen chloride

Seventy-five percent of ethylene d i c h l o r i d e consumption i s converted to the v i n y l c h l o r i d e monomer (VCM). A minor process f o r VCM p r o d u c t i o n i s based on a c e t y l e n e as follows: catalyst 100-210 °C HC=CH

+

HC1

>

CH =CHC1 2

1 atm vapor phase acetylene

hydrogen chloride

v i n y l chloride

V i n y l acetate production i s mostly based on acetylene as f o l l o w s : catalyst 210 °C HC=CH + CH3COOH > CH3COOCH = CH over 1 atm vapor phase acetylene a c e t i c acid v i n y l acetate 2

The newer plants mostly use the f o l l o w i n g ethylene route:


50.

CH =CH 2


ethylene

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Vinyl Resins Used in Coatings

PARK

2

+

CH3COOH

+

io

a c e t i c acid

•> CH COOCH=CH +

H0

v i n y l acetate

water

3

2

oxygen

2

2

A p p r o x i m a t e l y n i n e t y percent of the world's o r g a n i c c h e m i c a l p r o d u c t i o n i s petroleum based. A p p r o x i m a t e l y 8% of the U.S. production of petroleum products w i l l go to the chemical industry (a s i g n i f i c a n t part of t h i s comes from the natural gas reserves of the United S t a t e s ) . V i n y l c h l o r i d e i s one of many "monomers" t h a t can be made to form a l a r g e m o l e c u l e by s u c c e s s i v e a d d i t i o n s to i t s e l f . The v i n y l c h l o r i d e "polymer" thus formed can be represented as shown below. P o l y ( v i n y l c h l o r i d e ) i s a l i n e a r , t h a t i s , s t r a i g h t c h a i n thermoplastic. CH =CHC1 + CH =CH-C1 + CH =CH-C1 + etc. 2

2

2

> -[CH -CH-Cl]2

n

When v i n y l acetate i s introduced i n t o the reactor i n the presence of v i n y l c h l o r i d e , a "copolymer" i s formed: CH =CH-C1 + CH =CH0-C-CH 2

2

3

I

0

> -[CH -CHC1-CH -CH(0-C-CH )]2

2

3

n

0

Four commercial methods are used to polymerize v i n y l c h l o r i d e . These are emulsion polymerization, suspension polymerization, bulk polymerization, and s o l u t i o n polymerization. The f i r s t two are the only techniques of s i g n i f i c a n c e with respect to f l u i d v i n y l systems. Polymerization Techniques Many s o l u t i o n r e s i n s used today are produced v i a suspension polymerization techniques. I t i s the most widely used process f o r making p l a s t i c r e s i n s , i n terms of both the number of polymer products and the tonnage production. P r a c t i c a l l y a l l of the newer polymers are made by t h i s method. With t h i s p o l y m e r i z a t i o n technique v i n y l c h l o r i d e d r o p l e t s are "suspended" throughout the water phase. P r o t e c t i v e c o l l o i d s or suspending agents are added to p r e v e n t a g g l o m e r a t i o n of the PVC d r o p l e t s due to the a g i t a t i o n achieved i n the reactor. The suspending agents are s o l u b l e i n water but i n s o l u b l e i n v i n y l c h l o r i d e . As the polymer molecules form, the organic phase increases i n v i s c o s i t y . A polymer phase i s produced i n the dispersed organic d r o p l e t s due to the polymer being i n s o l u b l e i n v i n y l c h l o r i d e monomer. As with a l l polymerization process raw materials, the water and monomer must be i n an extremely pure state. Suspension polymerization i s considered one of the most economical methods of polymerization since water i s g e n e r a l l y the suspension medium. T h i s a l s o a s s i s t s i n the removal of exothermic heat of polymerization. F i g u r e 1 shows the t y p i c a l s t e p s i n the m a n u f a c t u r e of suspension ( s o l u t i o n type) r e s i n s . The v i n y l c h l o r i d e and v i n y l acetate monomers are "charged" (added) to a pressure v e s s e l . Water and suspending agent, etc., are added, the a c t u a l p o l y m e r i z a t i o n being c a r r i e d out under c o n d i t i o n s of c o n t r o l l e d pressure and temperature.



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" S l u r r y " from more than one r e a c t o r i s "dropped" i n t o a " s t r i p p e r " t o remove unreacted monomer and then t r a n s f e r r e d t o a l a r g e " b l e n d tank." The suspended polymer p a r t i c l e can e a s i l y be separated from the water phase by f i l t e r i n g or c e n t r i f u g i n g . The "wet cake" i s then sent to a rotary k i l n type dryer and bagged. The p a r t i c l e s i z e of polymers obtained i n t h i s manner are u s u a l l y much l a r g e r than those obtained with emulsion polymerization. They can be d e f i n e d by a c o n v e n t i o n a l screen a n a l y s i s w i t h r e s p e c t t o p a r t i c l e size. Some s o l u t i o n r e s i n s a r e made v i a s o l v e n t o r s o l u t i o n polymerization. This technique of polymerization has been performed i n many media t h a t a r e s o l v e n t s f o r monomer but not polymer. S o l v e n t s may i n c l u d e methyl a l c o h o l , d i e t h y l e t h e r , dioxane, t o l u e n e , benzene, acetone, etc., which may be used s i n g l y or as b l e n d s . A s u i t a b l e c a t a l y s t f o r use w i t h methyl a l c o h o l , f o r example, would be benzoyl peroxide. Hydrogen peroxide may be used with acetone. The r e s i n i s separated as a s o l i d by f i l t e r i n g and/or water quenching. This method i s u s u a l l y used f o r copolymers because of the poor s o l u b i l i t y of p o l y ( v i n y l chloride). The c o s t of the s o l v e n t s used i n the p o l y m e r i z a t i o n make t h i s process uneconomical except f o r some of the more e x p e n s i v e v i n y l c h l o r i d e copolymers and terpolymers used i n s o l u t i o n , f o r example, coating a p p l i c a t i o n s . Emulsion p o l y m e r i z a t i o n i s c o n s i d e r e d the g e n e r a l l y accepted technique to produce dispersion ( p l a s t i s o l ) resins and v i n y l latexes today. The monomers a r e made d i s p e r s i b l e by e m u l s i f i e r s i n a c o n t i n u o u s water phase. The i n i t i a t o r s or c a t a l y s t s a r e water s o l u b l e while the emulsifying agents s t a b i l i z e the emulsion formed when the system i s a g i t a t e d . G e l l n e r (2) c i t e s t h e f o l l o w i n g advantages of emulsion polymerization over other methods: "1. R e l a t i v e l y high molecular weight polymers can be produced at a h i g h r a t e of reaction... 2. E x c e l l e n t heat transfer i s r e a l i z e d with water as the continuous phase... 3. R e l a t i v e l y low v i s c o s i t y a t high polymeric s o l i d s i s of substant i a l advantage i n many applications..." To these advantages must be added the a b i l i t y t o produce a v e r y s m a l l p a r t i c l e s i z e t h a t i s e s s e n t i a l t o p r e p a r i n g an adequate dispersion of r e s i n i n p l a s t i c i z e r s . A m o d i f i c a t i o n of t h i s technique would be t o use a monomers o l u b l e c a t a l y s t and use an homogenization s t e p t o form the dispersion. Figure 2 shows t y p i c a l steps i n the manufacture of an emulsion r e s i n . B a s i c a l l y , the v i n y l c h l o r i d e monomer i s added to a pressure v e s s e l ( r e a c t o r ) where i n c o n t a c t w i t h the e m u l s i f i e r and t h e i n i t i a t o r the p o l y m e r i z a t i o n i s c a r r i e d out under c o n d i t i o n s of c o n t r o l l e d p r e s s u r e and temperature. Since i t i s uneconomical to c a r r y out the r e a c t i o n t o 100% c o n v e r s i o n , unreacted monomer i s removed i n a s t r i p p i n g v e s s e l . I f the polymer i s to be applied v i a the l a t e x (water-based coating) technique, the manufacturing process can now be c o n s i d e r e d complete. I f a d i s p e r s i o n r e s i n i s t o be produced, then l a t e x from the blend tank i s transferred to a spray dryer where water i s removed. These very small polymer p a r t i c l e s


50.

PARK


n


Vinyl Chloride Tank Cor

Suspending Agent, tCatalysf

Figure 1. Suspension polymerization.

Figure 2. Emulsion polymerization. Tess and Poehlein; Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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1210


have a tendency to agglomerate d u r i n g the spray d r y i n g o p e r a t i o n . T h i s i s counteracted by p a s s i n g the r e s i n through a hammer m i l l before i t i s bagged. The average p a r t i c l e s i z e v a r i e s from approximately 2 to 8 ym i n diameter with extremes f a l l i n g below 0.6 and above 20 ym. Note that average opening of a 325-mesh screen i s 43 |Jm. This means that a l l the dispersion r e s i n p a r t i c l e s would show up as 100% through the 325 mesh i n a conventional screen a n a l y s i s . With b u l k p o l y m e r i z a t i o n the o n l y m a t e r i a l s present i n the r e a c t o r are monomer and c a t a l y s t . The polymer formed from v i n y l c h l o r i d e , as mentioned p r e v i o u s l y , i s not s o l u b l e i n i t s own monomer. Very high f l u i d v i s c o s i t i e s are encountered i n the reactor w i t h t h i s technique. U n t i l i t s recent development i n Europe, a commercial process f o r producing bulk polymers did not e x i s t . This European technique has been l i c e n s e d to a few domestic U.S. r e s i n producers who use i t to produce "large p a r t i c l e " type resins. Polymers The use of the v i n y l polymer i n f l u i d form o f f e r s d i s t i n c t advantages to the manufacturer of v i n y l products. The most important obvious advantage i s the r e l a t i v e l y lower cost of l i q u i d processing equipment and accessories as compared to those required f o r p r o c e s s i n g of s o l i d or powder t h e r m o p l a s t i c s . For example, a spread c o a t i n g l i n e , f o r example, k n i f e or r o l l c o a t e r , even w i t h appropriate unwind and takeup accessories, i s l e s s expensive than a banbury-mixer-mill calender configuration. F o r t u n a t e l y or u n f o r t u n a t e l y (due to the many v a r i a b l e s t h a t have to be c o n s i d e r e d ) , the l i q u i d v i n y l s come i n a v a r i e t y of forms. One can use a 100% s o l i d system or a system w i t h v a r y i n g amounts of a v o l a t i l e component. The v o l a t i l e component can be an organic solvent or water, and the solvent may be a f a s t evaporating or a slow evaporating type. One of the f i r s t uses of v i n y l polymers as c o a t i n g s was i n the form of a s o l u t i o n ; f o r example, the r e s i n was d i s s o l v e d i n a pure solvent. V i n y l s o l u t i o n r e s i n systems are defined as lacquers with v a r y i n g amounts of s o l i d c o n t e n t s . When d i s s o l v e d i n s u i t a b l e s o l v e n t s , these r e s i n s g i v e c o a t i n g s with e x c e l l e n t chemical and weathering r e s i s t a n c e upon e v a p o r a t i o n of the s o l v e n t — a i r dry c o a t i n g s are o b t a i n a b l e . The s o l u t i o n polymers a v a i l a b l e today i n c l u d e homopolymers (high p h y s i c a l p r o p e r t i e s but w i t h very low s o l i d s — 5 - 1 0 % ) , v i n y l acetate copolymers ( s t i l l high p h y s i c a l s but with conventional lacquer s o l i d contents of 10-35%), and terpolymers ( w i t h metal adhesion p r o p e r t i e s t h a t most o t h e r s do not have and very high s o l i d s of 30-40%). V i n y l c h l o r i d e has a l s o been r e a c t e d w i t h o t h e r monomers c o n t a i n i n g c a r b o x y l , h y d r o x y l , a c e t a t e , maleate, and v i n y l i d e n e groups. Some of these r e a c t i v e groups permit c r o s s - l i n k i n g w i t h o t h e r polymers such as a l k y d s and melamines. T y p i c a l s o l u b i l i t y c h a r a c t e r i s t i c s are shown i n Figure 3. With s o l u t i o n v i n y l s we can obtain very low f l u i d v i s c o s i t i e s and very hard and t h i n c o a t i n g s . These p r o p e r t i e s have to be balanced against dangers of using v o l a t i l e , flammable s o l v e n t s and the i n a b i l i t y to produce t h i c k c o a t i n g s w i t h these systems. S o l u t i o n polymers are the most expensive of the f l u i d v i n y l s .



50.

PARK

1211


High Sokibiity Copolymer

Metal Adhesion Terpolymers

Solids (Per Cent by Weight)

Figure 3. S o l u b i l i t y c h a r a c t e r i s t i c s B r o o k f i e l d LVF viscometer.

of v i n y l polymers i n MEK.



1212


V i n y l s o l u t i o n r e s i n s are u s u a l l y made v i a suspension or s o l u t i o n p o l y m e r i z a t i o n techniques. P l a s t i s o l s are d e f i n e d as suspensions of homopolymers or copolymers i n nonaqueous l i q u i d s . The l i q u i d s , which are normally v i n y l p l a s t i c i z e r s , are selected so t h a t they do not s o l v a t e the polymer to any extent at room temperature. The suspension i s maintained by r e s i d u a l e m u l s i f i e r l e f t on the p a r t i c l e , and the very s m a l l p a r t i c l e s i z e of the polymer i t s e l f ( a l l pass through a 200-mesh screen). A f i n i t e q u a n t i t y of p l a s t i c i z e r must be present i n order to form the p l a s t i s o l or "paste": no p l a s t i c i z e r , no p l a s t i s o l . As w i t h a l l v i n y l systems, consideration may have to be given to p l a s t i c i z a t i o n , heat and l i g h t s t a b i l i z a t i o n , pigmentation, etc. The f i r s t reference to the term v i n y l dispersions i s claimed to have occurred i n J u l y 1944 (3). P r i o r to t h i s landmark, the use of these high polymers r e q u i r e d e i t h e r a l o w - s o l i d s o l u t i o n of the r e s i n i n an e x p e n s i v e s o l v e n t or the use of heavy-duty, h i g h pressure equipment to move the polymer i n i t s hot m e l t (molten) s t a t e . I n i t i a l l y , p o l y ( v i n y l c h l o r i d e ) r e s i n s were ground i n an organic media. This required the l i q u i d phase to be polar enough to s l i g h t l y s o l v a t e the r e s i n but not s t r o n g enough to a c t u a l l y dissolve i t . In 1947 the f i r s t true dispersion resins were introduced i n the United States. These emulsion-type polymers could be prepared with 100% s o l i d s with r e l a t i v e l y simple " s t i r - i n " techniques. Paste-type dispersions are noted to have been developed somewhat e a r l i e r and independently i n Europe. M e c h a n i c a l i n c o r p o r a t i o n of a i r i n t o the paste or the use of chemical "blowing agents" i n t o the formulations a l l o w s foam products to be produced. P l a s t i s o l s are not " a i r - d r y " systems; that i s , they r e q u i r e f u s i o n temperatures of at l e a s t 250 °F f o r the copolymers and 300 °F for the homopolymers. P l a s t i s o l s e n a b l e us to o b t a i n very low durometer hardness, t h i c k fused s e c t i o n s , and e x c e l l e n t c h e m i c a l r e s i s t a n c e . High durometer hardness values are d i f f i c u l t to obtain. Organosols are p l a s t i s o l s that contain a v o l a t i l e d i l u e n t . The v o l a t i l e component i s u s u a l l y selected from true nonsolvents f o r PVC r e s i n s such as the a l i p h a t i c hydrocarbons—the main purpose of the v o l a t i l e i n g r e d i e n t i s to lower the v i s c o s i t y of the paste by contributing more l i q u i d to the formulation. Very low p l a s t i c i z e r l e v e l s are then p o s s i b l e , and higher durometer hardness values are a t t a i n a b l e (as compared to p l a s t i s o l s ) . Generally, the same heat h i s t o r y requirements are required f o r the f u s i o n or development of p h y s i c a l s w i t h o r g a n o s o l s and p l a s t i s o l s . On the other hand, an organosol may require more heat i n p u t s i n c e some of t h e a p p l i e d h e a t i s used o n l y f o r t h e v o l a t i l i z a t i o n of the d i l u e n t . The v o l a t i l e component p r e v e n t s fusing thick sections without the danger of bubble formation. Dispersion or p l a s t i s o l resins are made e x c l u s i v e l y by emulsion polymerization techniques. A v i n y l l a t e x i s a c o l l o i d a l suspension (emulsion) of the homo-copolymer p a r t i c l e i n water. (The 0.2 ym average p a r t i c l e s i z e i s s m a l l enough to be i n Brownian movement.) Soaps are g e n e r a l l y used to form a p r o t e c t i v e c o l l o i d around the p a r t i c l e , and they are surrounded by a negative e l e c t r i c a l charge. In some cases a i r - d r y film-forming systems are possible.



50.


PARK

1213

Because water i s the f l u i d component, very low v i s c o s i t i e s a t r e l a t i v e l y high s o l i d s (50%) are a t t a i n a b l e . Latexes are u s u a l l y cheaper than s o l u t i o n v i n y l s but s i m i l a r i n c o s t to d i s p e r s i o n resins. As with organosols and s o l u t i o n v i n y l s , coating thickness i s l i m i t e d due to the evaporation of the f l u i d component. Note that more heat i s u s u a l l y required to remove water than organic s o l v e n t s , and corrosion of equipment must be considered. One of the l a t e s t c o a t i n g techniques to f i n d commercial acceptance i s "powder c o a t i n g . " In t h i s process the c o a t i n g i s i n the form of a f i n e powder t h a t i s l a t e r fused i n p l a c e to d e v e l o p the p r o t e c t i v e f i l m . I t s advantages include e l i m i n a t i o n of waste i n spraying, since overspray can be c o l l e c t e d and used again, r e l a t i v e low p l a s t i c i z e r l e v e l s , e l i m i n a t i o n of v o l a t i l e s o l v e n t s , and improved long-term storage s t a b i l i t y . These advantages must be weighed a g a i n s t the c r i t i c a l c o a t i n g a p p l i c a t i o n parameters, s o p h i s t i c a t e d c o a t i n g p r e p a r a t i o n techniques, and lower molecular weight l i m i t a t i o n of the polymers. Formulation

Considerations

P l a s t i c i z e r s have enabled the v i n y l compounder to o b t a i n such diverse properties as resistance to e x t r a c t i o n by many chemicals to e x t r e m e l y low temperature f l e x i b i l i t y . They contribute not only d e s i r a b l e properties i n the f i n i s h e d product but a l s o appreciably toward improved p r o c e s s a b i l i t y . P l a s t i c i z e r s can be c l a s s i f i e d as e i t h e r solvent type (primary) or nonsolvent or poor s o l v e n t type (secondary). A s p e c i a l category of the nonsolvent type would include polymeric and epoxy polymeric plasticizers. P l a s t i c i z e r s such as the p h t h a l a t e s , phosphates, etc., are considered the most important. Other monomerics such as adipates, a z e l a t e s , sebacates, g l y c o l a t e s , c i t r a t e s , etc., are u s u a l l y c l a s s i f i e d as s p e c i a l t y types. The p h t h a l a t e s are c o n s i d e r e d the most w e l l balanced " p r o p e r t y - w i s e " of a l l the p l a s t i c i z e r s available. The polymeric p l a s t i c i z e r s are used where permanence i s of prime importance. The molecular weights of these p l a s t i c i z e r s vary quite e x t e n s i v e l y . V a r i a t i o n s from under 850 to 8000 are not uncommon. The cost of polymeric p l a s t i c i z e r s i s u s u a l l y i n excess of that of the normal monomeric types. R e s i s t a n c e to e x t r a c t i o n by soapy water, o i l s , and m i g r a t i o n i n t o n i t r o c e l l u l o s e , p o l y s t y r e n e , and rubber are u s u a l l y s u p e r i o r w i t h p o l y m e r i c p l a s t i c i z e r systems. Because of t h e i r higher v i s c o s i t i e s , they are u s u a l l y more d i f f i c u l t to handle. Where low-temperature f l e x i b i l i t y i s of importance, adipates, azelates, sebacates, and the epoxidized stearates and t a l l a t e s are used. Care must be e x e r c i s e d when u s i n g these p l a s t i c i z e r s i n regard to c o m p a t i b i l i t y l i m i t s . The low-temperature p l a s t i c i z e r s are u s u a l l y l e s s c o m p a t i b l e than the p h t h a l a t e s because of t h e i r lower solvent power for the r e s i n . This condition u s u a l l y requires more heat and/or higher temperatures to obtain adequate fusion. The primary reason f o r u t i l i z i n g a dispersion r e s i n system i s to o b t a i n the b e n e f i t of f l u i d p r o p e r t i e s . With v i s c o s i t y c h a r a c t e r i s t i c s i n mind, we must consider t h i s q u a l i f i c a t i o n f o r the p l a s t i c i z e r s used i n p l a s t i s o l s .


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Since they vary q u i t e e x t e n s i v e l y i n o i l v i s c o s i t y and i n s o l v e n t power, paste v i s c o s i t y w i l l vary. Because of the influence of v i s c o s i t y s t a b i l i t y upon commercial acceptance, p l a s t i c i z e r s such as the long-chain phthalates are common. With s o l u t i o n v i n y l systems the q u a l i f i c a t i o n s of p l a s t i c i z e r s c i t e d p r e v i o u s l y a p p l y w i t h t h e f o l l o w i n g two a d d i t i o n a l considerations. 1. 2.

The o i l v i s c o s i t y of the p l a s t i c i z e r may now be i n s i g n i f i c a n t due to the high concentration of solvent. Most s o l u t i o n v i n y l r e s i n s are more s o l u b l e than the powder coating or dispersion grade v i n y l resins. They w i l l , therefore, r e q u i r e much l e s s p l a s t i c i z e r to reach any s p e c i f i c l e v e l of "softening. The compounder has to be extremely c a r e f u l that he does not over p l a s t i c i z e and obtain a "tacky" or " s o f t " f i l m .


11

The basic p r i n c i p l e s regarding the s e l e c t i o n of a p l a s t i c i z e r remain the same w i t h a l a t e x system as w i t h the other polymer systems i f o n l y end p r o p e r t i e s of the f i n a l f i l m are to be considered. The v i n y l latexes require very l i t t l e r e o r i e n t a t i o n of thought with respect to compounding philosophy. As the copolymers are i n t r o d u c e d , each system w i l l have to be considered on i t s own merits based on the chemistry of the polymers under study. With few exceptions, the p l a s t i c i z e r must be added to the l a t e x as an o i l - i n - w a t e r emulsion. T h i s o p e r a t i o n r e q u i r e s high-speed, high shearing action equipment. Some l a t e x systems r e q u i r e a p l a s t i c i z e r to make them f i l m formers at room temperature. One polymer l a t e x system can sometimes be used to p l a s t i c i z e another. Another modifier for v i n y l polymer systems frequently used i s a stabilizer. Polymers of v i n y l c h l o r i d e , under prolonged heat and/or l i g h t exposure, may change c o l o r and increase i n hardness. Heat can cause the s p l i t t i n g out of HC1 from the m o l e c u l e , causing conjugated polymer unsaturation and a color-bearing group. Light can cause a simultaneous oxidation at the point of unsaturation. Light e f f e c t s , however, are g r e a t l y reduced i n pigmented systems. Vinyl s t a b i l i z e r s react u s u a l l y i n one of the f o l l o w i n g ways: 1. 2. 3. 4.

They possess r e a c t i v e d i e n o p h i l i c molecules that break up c o l o r forming polyene systems. They are HC1 acceptors that react with the HC1, removing i t as an i n s o l u b l e product. They are s e l e c t i v e u l t r a v i o l e t absorbers, thus reducing t o t a l u l t r a v i o l e t energy absorbed. They are antioxidants and i n h i b i t carbonyl formation from oxygen and polyenes.

The m e t a l l i c soaps of barium, cadmium, l e a d , and c a l c i u m are commonly used as s t a b i l i z e r s . They are HC1 a c c e p t o r s , but t h e i r r e a c t i o n products o f t e n cause c l o u d i n e s s i n c l e a r f o r m u l a t i o n s . A l k y l and a r y l phosphates are o f t e n used w i t h them to i n h i b i t p r e c i p i t a t i o n of i n s o l u b l e c h l o r i d e s . Tin complexes have a l s o been used s u c c e s s f u l l y .



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Opaque s t a b i l i z e r s c a n be used i n pigmented and f i l l e d compounds. Many of the m e t a l l i c compounds and organic a u x i l i a r i e s used as heat s t a b i l i z e r s a l s o a s s i s t i n regard to l i g h t s t a b i l i t y . There are a number of s p e c i f i c compounds that are used as l i g h t s t a b i l i z e r s only. They have been c l a s s i f i e d chemically as s a l i c y l i c esters, hydroxybenzophenones, and benzotriazoles. Because of the requirements f o r f l u i d properties i n a p l a s t i s o l , the l i q u i d s t a b i l i z e r s are most o f t e n encountered. The c h e m i c a l nature of the s t a b i l i z e r i s based on the p h y s i c a l p r o p e r t i e s and processing requirements of the system. S o l i d s t a b i l i z e r s are encountered o c c a s i o n a l l y when they can contribute to increasing the y i e l d or r a i s i n g the v i s c o s i t y of the paste, i f these p r o p e r t i e s are r e q u i r e d . S o l i d s t a b i l i z e r s a r e added, i n most cases, a f t e r they have been e f f e c t i v e l y dispersed i n p l a s t i c i z e r on a t h r e e - r o l l paint m i l l . The UV absorbers i n use today a r e s o l i d s thus r e q u i r i n g dispersion v i a the t h r e e - r o l l paint m i l l technique. S t a b i l i z e r s are not used as frequently with the s o l u t i o n v i n y l systems as with the dispersion r e s i n systems. The reasons f o r t h i s are as f o l l o w s : 1. 2.

Air-dry systems do not require heat s t a b i l i z e r s . When heat i s a p p l i e d t o a s o l v e n t v i n y l system, i t i s of low magnitude; that i s , i t i s used j u s t to d r i v e o f f solvent.

When an a c t u a l "bake" i s r e q u i r e d i n order t o produce a h i g h g l o s s or due to the treatment of some other part of the item coated, the s e l e c t i o n of the s t a b i l i z e r i s very d i f f i c u l t . As mentioned e a r l i e r , the copolymer may depolymerize before HC1 degradation takes p l a c e . T h i s l i m i t s the s e l e c t i o n of the s t a b i l i z e r . The s u l f u r c o n t a i n i n g o r g a n o t i n type s t a b i l i z e r s appear to be more e f f e c t i v e with respect to improving the heat s t a b i l i t y of the s o l u t i o n v i n y l r e s i n systems. The UV absorbers are used to a greater extent with the s o l u t i o n v i n y l s than with the general-purpose and dispersion resins. This i s due t o the s o l u t i o n v i n y l systems h a v i n g been used t o a g r e a t e r e x t e n t outdoors than any of t h e other systems. The h i g h c o l o r pigment l o a d i n g s used w i t h s o l u t i o n v i n y l o f t e n a c t l i k e UV screeners and protect the v i n y l r e s i n from attack. As with a l l compounding ingredients used i n l a t e x systems, the s t a b i l i z e r should be emulsified p r i o r to addition to the latex. L i q u i d s t a b i l i z e r s c o n t a i n i n g m e t a l l i c s a l t s or soaps may be s o l u b l e i n water-based systems. When s o l u b i l i t y occurs, m e t a l l i c c a t i o n s may be formed t h a t can i n j u r e the s t a b i l i t y of the r e s i n emulsion. Various l i q u i d epoxy compounds and organotin s t a b i l i z e r s have been used s u c c e s s f u l l y . The use of i n e r t materials i n v i n y l s i s widely practiced. The f i l l e r can be used t o lower c o s t and i n c r e a s e hardness. The most common types of f i l l e r s i n use today include the calcium carbonates and s i l i c a t e types. A l s o a v a i l a b l e a r e v a r i o u s s i l i c a g e l s , barytes, gypsum, alums, wood f l o u r , and antimony oxide. Depending upon the o i l absorption value of the i n e r t m a t e r i a l , a f i l l e r w i l l (1) lower t e n s i l e p r o p e r t i e s , (2) i n c r e a s e hardness, (3) lower f l e x i b i l i t y , and (4) increase processing temperatures.



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Very high f i l l e r loadings w i l l cause a whitening e f f e c t upon the compound when i t i s bent. Since f i l l e r s are bought by the pound and many f i n i s h e d goods s o l d by the yard, i t i s important to use pound volume f i g u r e s when using a high-density f i l l e r f o r cost reduction purposes. The a d d i t i o n of a f i l l e r w i l l g e n e r a l l y i n c r e a s e the paste v i s c o s i t y of a p l a s t i s o l . To what extent i s determined by the o i l absorption value, density, p a r t i c l e s i z e , shape, and d i s t r i b u t i o n . The high o i l a b s o r p t i o n f i l l e r s i n c r e a s e the y i e l d v a l u e i n addition to r a i s i n g the ultimate v i s c o s i t y of the paste. F i l l e r s are used frequently with s o l v e n t v i n y l systems i n order to lower c o s t , i n c r e a s e h i d i n g power of the c o a t i n g , and i n c r e a s e the t o t a l s o l i d s of the system. They may d e t r a c t from u l t i m a t e d u r a b i l i t y due to impurities that are present i n the f i l l e r . This may manifest i t s e l f as poor l i g h t s t a b i l i t y or f i l m porosity due to w a t e r - s o l u b l e i n g r e d i e n t s present. B a s i c i n g r e d i e n t s may be r e a c t i v e w i t h c a r b o x y l - c o n t a i n i n g (metal adhesion type) r e s i n s . I r o n contamination may cause poor l i g h t and heat s t a b i l i t y of the system. The word " f i l l e r " i s normally associated with v i n y l compounding and the word "extender" w i t h l a t e x compounding. They both denote i n e r t materials used to reduce the cost of the coating or compound and provide opacity. An important feature of general concern to the v i n y l p l a s t i s o l compounder i s the o i l a b s o r p t i v i t y of the i n e r t and i t s e f f e c t on the rheology of the dispersion. A p a r a l l e l property known as water a b s o r p t i v i t y or water demand i s of prime importance to the l a t e x compounder. The water demand of an i n e r t f i l l e r i s determined by many v a r i a b l e s such as p a r t i c l e s i z e , shape and d i s t r i b u t i o n , moisture l e v e l of the i n e r t , e t c . As a r e s u l t , each f i l l e r must be g i v e n a separate i d e n t i t y and treated as such. The f i l l e r s h o u l d be added to the l a t e x as a water-based dispersion. The most important properties of a c o l o r pigment to be used i n a v i n y l system are (1) resistance to bleed i n s o l v e n t s , p l a s t i c i z e r s , s t a b i l i z e r s , and other a d d i t i v e s ; (2) heat s t a b i l i t y ; both h i g h heats f o r short durations and long-term low heat s t a b i l i t y may have to be considered; (3) inertness to the polymer and other formulation i n g r e d i e n t s ; (4) r e s i s t a n c e t o m i g r a t i o n ; (5) r e s i s t a n c e t o c r o c k i n g ; (6) l i g h t s t a b i l i t y ; (7) c h e m i c a l r e s i s t a n c e ( s t a i n i n g , etc.). C o l o r pigments can best be i n c o r p o r a t e d i n t o a p l a s t i s o l formulation by means of a p r e d i s p e r s e d p i g m e n t - p l a s t i c i z e r paste. This paste can be prepared on a t h r e e - r o l l paint m i l l using a s m a l l q u a n t i t y of a p o l y m e r i c type p l a s t i c i z e r as the g r i n d i n g media to g i v e m i l l tack. The higher v i s c o s i t i e s of polymeries are b e l i e v e d necessary i n order to increase the shearing action, thus achieving a b e t t e r dispersion. Many c o l o r pigments can cause a l t e r a t i o n of r h e o l o g i c a l properties f a r i n excess of what t h e i r concentration would indicate. Pigments such as p h t h a l o c y a n i n e greens and b l u e , and some blacks, may cause high paste v i s c o s i t i e s . In addition to the pigment c h a r a c t e r i s t i c s mentioned p r e v i o u s l y , we have to c o n s i d e r very c r i t i c a l l y the s o l u b i l i t y of the c o l o r



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pigment i n s o l v e n t s when using s o l u t i o n v i n y l s . Pigments containing i r o n and z i n c have t o be e v a l u a t e d c a r e f u l l y because o f t h e i r p o s s i b l e adverse e f f e c t s upon heat s t a b i l i t y . The dispersion of the c o l o r pigment becomes more d i f f i c u l t since the q u a n t i t y o f p l a s t i c i z e r r e q u i r e d f o r a t h r e e - r o l l p a i n t m i l l d i s p e r s i o n may be i n excess of t h a t p e r m i s s i b l e i n t h e f i n a l c o a t i n g . I t i s f r e q u e n t l y d e s i r a b l e t o add t h e c o l o r pigment d i r e c t l y t o the r e s i n i t s e l f . I n t h e case of t h e n o n r e a c t i v e pigments, i t may be p o s s i b l e t o m i l l f u s e the r e s i n and add t h e c o l o r pigment d i r e c t l y t o the r e s i n upon the m i l l . C o l o r " c h i p s " are obtained i n t h i s manner. The c h i p s can l a t e r be i n c o r p o r a t e d i n t o the s o l u t i o n during mixing. I t may be p o s s i b l e t o d i p e r s e t h e pigment i n a s l o w l y evaporating s o l v e n t such as isophorone or Solvesso 150 by using a d i f f e r e n t i a l t h r e e - r o l l m i l l . T h i s technique i s s i m i l a r t o the p l a s t i c i z e r dispersion technique except the p l a s t i c i z e r i s replaced by a solvent. When r e a c t i v e ( c a r b o x y l groups present) r e s i n s are used, t h e pebble m i l l , or c o l o r chip techniques are most frequently encountered. (The c o l o r chip i s prepared with a nonreactive resin.) The a c i d i c condition of the r e s i n reduces the c o m p a t i b i l i t y with many pigments, e s p e c i a l l y those made w i t h b a s i c m e t a l s , such as z i n c , l e a d , e t c . Some a p p a r e n t l y i n e r t pigments c o n t a i n s m a l l amounts of i m p u r i t i e s that are basic, thus causing r e a c t i v i t y with the resin. Phthalocyanine blue i s an example. This means that only the purest pigments should be used. The c h o i c e of c o l o r pigments i s extremely broad i n the l a t e x systems. Many of the processing considerations c i t e d under f i l l e r s with l a t e x systems w i l l apply to c o l o r pigments a l s o . C e l l u l a r v i n y l s can be produced by t h r e e b a s i c techniques. These a r e mechanical, p h y s i c a l , or c h e m i c a l methods. I n t h e mechanical method, a foam i s produced by the vigorous a g i t a t i o n of a f l u i d producing f r o t h that i s l a t e r g e l l e d and fused. In t h e p h y s i c a l method, an i n e r t gas i s i n c o r p o r a t e d i n t o a f l u i d by mechanical means. Upon fusion, a foam or c e l l u l a r product i s formed. Chemical blowing agents are inorganic or organic m a t e r i a l s that decomposed under heat to y i e l d at l e a s t one gaseous decomposition product. About a dozen or more have commercial s i g n i f i c a n c e . The most commonly encountered today i s azodicarbonamide (a h i g h temperature blowing agent). V o l a t i l e i n g r e d i e n t s , c a l l e d d i l u e n t s , are used t o lower t h e v i s c o s i t y of a p l a s t i s o l . By d e f i n i t i o n , t h e use o f a d i l u e n t converts the p l a s t i s o l to an organosol. The main reason f o r using a d i l u e n t i s t o lower the v i s c o s i t y of the paste. The d i l u e n t w i l l modify the wetting and s o l v a t i n g c h a r a c t e r i s t i c s of the p l a s t i c i z e r (dispersant). Since v i s c o s i t y c o n t r o l i s one of the primary reasons for using a d i l u e n t , i t i s u s u a l l y of an a l i p h a t i c or nonsolvating nature. Each d i s p e r s a n t - d i l u e n t system s h o u l d be a c c u r a t e l y i n v e s t i g a t e d because t h e r e i s u s u a l l y a c r i t i c a l point or composition where a minimum v i s c o s i t y i s obtained. Organosols, being complex c o l l o i d a l systems, d i f f e r from s o l u t i o n s i n that the i n d i v i d u a l r e s i n p a r t i c l e i s dispersed i n the suspending l i q u i d , but not d i s s o l v e d . F o r m u l a t i o n s low i n d i s p e r s a n t tend t o agglomerate, a r e u n s t a b l e on a g i n g , and may



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e x h i b i t f a l s e body. Resin s o l v a t i o n may be e x c e s s i v e when the d i s p e r s a n t l e v e l i s h i g h , c a u s i n g poor paste v i s c o s i t y s t a b i l i t y (i.e., increase i n v i s c o s i t y ) on aging. L i q u i d s w i t h poor s o l v e n t a c t i o n upon the r e s i n make the best d i l u e n t s . H i g h - s o l v e n t power d i l u e n t s produce sharp, t h a t i s , c r i t i c a l v i s c o s i t y composition curves and may cause a rapid increase of paste v i s c o s i t y during aging. The e f f e c t s of various v o l a t i l e ingredients upon the r h e o l o g i c a l p r o p e r t i e s of a p l a s t i s o l are shown i n F i g u r e 4. The d i l u e n t s s t u d i e d i n c l u d e (1) t o l u e n e (an a r o m a t i c ) , (2) S o l v e s s o 150 (aromatic but h i g h i n C\Q aromatic and above p l u s indenes and heavier aromatics), and (3) APCO thinner. In a l l cases, an a p p r e c i a b l e drop i n paste v i s c o s i t y was observed upon the addition of the v o l a t i l e ingredients. Ketones are t r u e s o l v e n t s f o r v i n y l r e s i n s w i t h the s o l u t i o n r e s i n system. The s o l v e n t power of the s o l v e n t w i l l depend upon many p r o p e r t i e s of the v o l a t i l e , i n c l u d i n g m o l e c u l a r weight and chemical configuration. Depending upon the s o l u b i l i t y of the r e s i n , v a r i o u s v o l a t i l e s such as a c e t a t e s , n i t r o p a r a f f i n s , etc., may be considered primary solvents. The m o l e c u l a r and c h e m i c a l composition of the polymer w i l l i n f l u e n c e i t s s o l u b i l i t y c h a r a c t e r i s t i c s . Park (4^) has d i s c u s s e d the s o l v e n t - r e s i n r e l a t i o n s h i p s i n d e t a i l i n "Advances i n Chemistry Series 124." They can be summarized as f o l l o w s : Aromatics such as toluene and xylene are primary s o l v e n t s f o r only the most s o l u b l e of the v i n y l r e s i n s . The homopolymers have very s l i g h t aromatic tolerances. A l i p h a t i c - t y p e s o l v e n t s are not c o n s i d e r e d good s o l v e n t s f o r v i n y l s . As with the aromatics, the extremely s o l u b l e r e s i n s w i l l t o l e r a t e a l i p h a t i c s o l v e n t s i f a s t r o n g ketone i s present. Only f a i r a l i p h a t i c t o l e r a n c e i s obtained w i t h the low m o l e c u l a r weight h i g h v i n y l c h l o r i d e content s o l u t i o n polymers. A l i p h a t i c t o l e r a n c e of the homopolymers i s p r a c t i c a l l y n i l . The a l c o h o l tolerance of v i n y l r e s i n s i s very l i m i t e d . Recent studies w i t h the high s o l u b i l i t y type metal adhesion copolymers i n d i c a t e that appreciable q u a n t i t i e s of 2-propanol may be used, i f a strong ketone s o l v e n t i s used. Other f a c t o r s , besides s o l u b i l i t y , to be c o n s i d e r e d when s e l e c t i n g a s o l v e n t include evaporation rate, density, f l a s h point, b o i l i n g range, etc. Much data of t h i s nature are a v a i l a b l e i n the l i t e r a t u r e a l o n g w i t h t e s t methods f o r a d d i t i o n a l s o l v e n t properties. Three basic methods are used to manufacture dry powders. There are (1) dry-mix blending, s i m i l a r to conventional dry blending; (2) hot m e l t b l e n d i n g , f o r example, the i n g r e d i e n t s are blended ( v i a regular dry blend procedures), fused or melted down and cooled and then ground t o f i n a l p a r t i c l e s i z e ; and (3) wet p r o c e s s i n g , f o r example, mixing i n a l i q u i d phase f o l l o w e d by spray d r y i n g , evaporation, and p r e c i p i t a t i o n . The r e s i n and r e s u l t i n g p a r t i c l e s i z e of the f i n a l compound must be h e l d w i t h i n vary narrow l i m i t s . A l l l i q u i d s must be absorbed uniformly and a l l s o l i d ingredients thoroughly dispersed.


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50.

Figure 4. O r g a n o s o l v i s c o s i t y viscometer.

stability.

Brookfield


RVF

1220



Application Techniques The f l u i d v i n y l s are extremely v e r s a t i l e with respect to a p p l i c a t i o n techniques. Dipping i s one of the e a r l i e s t and simplest methods to apply a coating. Figure 5 i l l u s t r a t e s a t y p i c a l l i q u i d v i n y l process. In t h i s case, i t i s designed to handle p l a s t i s o l s . A l l of the l i q u i d v i n y l systems are candidates i n dipping. Very t h i c k p l a s t i s o l c o a t i n g s can and are o f t e n a p p l i e d . Coating thickness c o n t r o l can be achieved f i r s t through c o n t r o l l i n g the flow c h a r a c t e r i s t i c s of the p l a s t i s o l and preheating the objects to be coated. P o s s i b l e l i m i t a t i o n s to the use of hot d i p p i n g i n c l u d e danger of hot forms r a i s i n g the d i p tank paste v i s c o s i t y , t h a t i s , destroying i t s v i s c o s i t y s t a b i l i t y , and damage to the object being coated by the preheated oven. I f c o n d i t i o n s l e a d i n g to these l i m i t a t i o n s are present, one must r e l y c o m p l e t e l y on the f l o w c h a r a c t e r i s t i c s of the paste to c o n t r o l the amount of "pickup" i n a c o l d d i p tank. Objects c o m m e r c i a l l y a v a i l a b l e made by p l a s t i s o l dipping include coated gloves ( f a b r i c ) , disposable s u r g i c a l gloves, t o o l handles, seat springs, g l a s s b o t t l e s , and lamp sockets. I f an o r g a n o s o l i s used, lower p l a s t i c i z e r l o a d i n g s are p o s s i b l e , but they w i l l l i m i t the thickness of the applied coating. At the same time the v o l a t i l e s o l v e n t s force one to s e l e c t a lower i n i t i a l preheat temperature of the object to be coated. I t should be noted that both p l a s t i s o l s and organosols have no natural adhesion to metal or g l a s s . I f the generic configuration of the item to be coated i s inadequate to ensure a locked on coating, a primer coat may have to be a p p l i e d . T y p i c a l primers f o r t h i s a p p l i c a t i o n are of a buna-phenolic or epoxy nature. A s m a l l amount of v o l a t i l e d i l u e n t i n the coating w i l l help to obtain a t i g h t f i t due to the shrinkage of the coating when the solvent i s driven o f f d u r i n g fusion. S o l u t i o n v i n y l systems have been used f o r many years to coat m e t a l p a r t s . Since we have a v o l a t i l e o r g a n i c s o l v e n t i n the system, we have to ensure t h a t (1) the tank remains c o o l and (2) we have a s m a l l l i q u i d s u r f a c e to p r e v e n t premature s o l v e n t evaporation. The carboxyl-containing v i n y l terpolymers do not need an a d d i t i o n a l v i n y l - t o - m e t a l primer. H i g h - s o l i d v i n y l l a t e x e s can " s k i n o v e r " i n a d i p tank i f a g i t a t i o n i s not p r o v i d e d . (Note many metal pretreatments make metal surfaces hydrophobic, i.e., i t w i l l not be wet out r e a d i l y by a water-based system). Powder coatings are used i n dipping operations v i a f l u i d i z e d bed and e l e c t r o s t a t i c f l u i d i z e d beds. I t i s the oldest form of powder application. I t was f i r s t used i n Germany i n 1950 and was introduced to North America i n 1955 (5). Large i r r e g u l a r - s h a p e d o b j e c t s t h a t are impossible to coat by dipping can be protected by spraying. A l l the l i q u i d v i n y l s can be handled i n t h i s manner. Low-viscosity systems such as the s o l u t i o n v i n y l s and latexes can be handled e a s i l y on conventional suction feed equipment. Because of the a c i d i c nature of v i n y l latexes, the m a t e r i a l s of c o n s t r u c t i o n of the spray equipment w i l l have to receive s p e c i a l consideration. Pressure pot type guns and a i r l e s s spray equipment enable much h i g h e r v i s c o s i t y l a t e x e s , v i n y l s o l u t i o n s , and p l a s t i s o l s to be sprayed. Hot a i r l e s s spraying i s d e s i r a b l e f o r very high s o l i d s or



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high v i s c o s i t y solvent v i n y l systems. Equipment of t h i s type with p l a s t i s o l s i s not normally considered since heat causes g e l a t i o n of the p l a s t i s o l , which i s an i r r e v e r s i b l e process. E l e c t r o s t a t i c spraying of powders i s now a commercial r e a l i t y . G o l o v o y (6) c i t e s p a r t i c l e s i z e , s p h e r i c a l p a r t i c l e shape, and e l e c t r i c a l s u r f a c e r e s i s t i v i t y of the powder b l e n d as important factors i n deposition e f f i c i e n c y . Most of the f l u i d v i n y l s f i n d a p p l i c a t i o n v i a spread coating of v a l u e . Spread c o a t i n g has many a p p l i c a t i o n s . T y p i c a l spread coating equipment would i n c l u d e k n i f e coaters, blade coaters, r o l l coaters (direct and reverse r o l l , gravure, transfer r o l l , cast), bar or rod c o a t e r s , and c u r t a i n c o a t e r s . F i g u r e 6 shows the b a s i c c o n f i g u r a t i o n f o r a spread c o a t i n g l i n e . A u x i l i a r y trimming and embossing equipment can be included i n the l i n e , and a l l the f l u i d v i n y l systems described above can be used i n these systems. The 100% s o l i d system of p l a s t i s o l s a l l o w s very t h i c k coating weights to be a p p l i e d . Because i n c r e a s e d p l a s t i c i z e r l o w e r s v i s c o s i t y and a s s i s t s i n coating a p p l i c a t i o n , very high p l a s t i c i z e r l e v e l s ( f o r very s o f t f i l m s ) are e a s i l y handled. The use of chemical blowing agents and mechanical a i r incorporation are e a s i l y adaptable to p l a s t i s o l systems. An organosol w i l l e n a b l e the use of a much lower p l a s t i c i z e r l e v e l . Low l e v e l s of v o l a t i l e d i l u e n t s w i l l enable one to produce tough coatings as i n the c l e a r wearlayer sheet goods f l o o r i n g f i e l d . Depending upon the d i l u e n t l e v e l s , fused f i l m t h i c k n e s s e s of approximately 10 m i l s can be obtained. With both the p l a s t i s o l and o r g a n o s o l , f u s i o n temperatures i n the range of 290-400 °F are required. Other a p p l i c a t i o n s of organosols include aluminum s i d i n g , tapes, and s k i n coats on upholstery and handbags. C o i l coating (of aluminum s i d i n g and s t e e l products f o r example) i s a fast-growing a p p l i c a t i o n of t h i s technique. A s o l u t i o n v i n y l system would enable one to deposit and a i r - d r y a spread coat f i l m . For p r a c t i c a l production rates, forced s o l v e n t e v a p o r a t i o n a t about 120-180 °F i s p r a c t i c e d . Completely u n p l a s t i c i z e d c o a t i n g s are a t t a i n a b l e , but w i t h a l i m i t a t i o n on coating thickness of 0.1-4.0 m i l s . Less l a t i t u d e i s a v a i l a b l e with s o l v e n t systems than i s a v a i l a b l e with p l a s t i s o l s and organosols with respect to increasing coating v i s c o s i t y or y i e l d value of the r e s i n . T y p i c a l a p p l i c a t i o n s of s o l u t i o n v i n y l s include wallpaper, can coatings, aluminum s i d i n g , and tapes. The organic s o l v e n t s are flammable (as are the o r g a n o s o l d i l u e n t s ) ; t h e r e f o r e , one needs explosion proof and p o s s i b l y v o l a t i l e s c o l l e c t i o n equipment. Some of the s o l u t i o n polymers are c r o s s - l i n k a b l e , e n a b l i n g t h e r m o s e t - l i k e p r o p e r t i e s , such as s o l v e n t r e s i s t a n c e , to be obtained. The low s o l u t i o n v i s c o s i t i e s c h a r a c t e r i s t i c s of a s o l v e n t system g e n e r a l l y c o n t r i b u t e toward good coating properties. This can be a d i s a d v a n t a g e , however, when a porous or l o o s e weave substrate i s to be coated. The v i n y l l a t e x systems are s i m i l a r to the solvent v i n y l systems with respect to coating c h a r a c t e r i s t i c s ; that i s , they both have low coating v i s c o s i t y . Removal of at l e a s t 50% of the coating weight as water requires ovens with minimum a v a i l a b l e temperatures of 212 °F. Since organic s o l v e n t s are not present, f i r e hazards are diminished. The h i g h e m u l s i f i e r l e v e l s i n these systems w i l l l i m i t t h e i r a p p l i c a t i o n s where water c o n t a c t or s e n s i t i v i t y are important



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COOLING SYSTEM POSSIBLE WITH HOT DIPPED FORMS

RAW MATERIAL RECOVERY

* PREHEAT OVEN NOT NECESSARY FOR COLD DIPPING OPERATIONS

Figure 5. Application of v i n y l p l a s t i s o l s by dipping.

UNWNCMNG (SPLICING UNIT

TENSION CONTROL

INCLUDED)

WEB* GUIDES

FUSION OVENS (SOLVENT REMOVAL)

COOLING ROLLS

SUCTION ROLLS APRONS.OR DRUMS

AUTOMATIC COATING WEIGHT CONTROL

TRIM SLITTERS

CUTTER AND LAYBOY

Figure 6. A p p l i c a t i o n of f l u i d v i n y l r e s i n s i n a spread c o a t i n g line.



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factors. They have found a p p l i c a t i o n s on wallpaper, window shades, w e a r l a y e r s i n yard goods f l o o r i n g p r o d u c t s , and drapery backing (crushed foam). F i r e retardant properties are considered e x c e l l e n t with the v i n y l l a t e x polymers. Unplasticized and p l a s t i c i z e d f i l m s are produced. Slush molding i s used mainly with p l a s t i s o l s . I t i s u s u a l l y a continuous operation. The mold (female) i s f i l l e d above a s p e c i f i c p a t t e r n mark and passed through an oven t h a t s e t s or g e l s the m a t e r i a l i n c o n t a c t w i t h the metal mold s u r f a c e . These molds are electroformed copper or cast aluminum. The material i n the center of the mold that i s s t i l l a f l u i d i s poured out of the mold with the mold returning to an oven f o r f i n a l fusion. Upon removal from the fusion oven, the mold i s cooled and the f i n i s h e d product i s stripped from the mold. Vacuum or compressed a i r can be used w i t h l a r g e p a r t s or w i t h those of a complex geometry to a s s i s t i n product removal. One p a r t of the mold must be open t o the atmosphere to permit pouring and product removal. The l o w - s o l i d content o r , more e x a c t l y , the l a r g e amount of v o l a t i l e components that cannot r e a d i l y be r e m o v e d — e s p e c i a l l y i n t h i c k e r molded p a r t s — c o m p l e t e l y e l i m i n a t e s s o l u t i o n v i n y l s and latexes from s l u s h molding operations. I t i s conceivable that low d i l u e n t loading organosols could be used, but commercially t h i s i s a rare occurrence. P l a s t i s o l s , almost by the process of e l i m i n a t i o n , have the f i e l d to themselves. P l a s t i s o l objects produced i n t h i s manner include r a i n shoes (transparent), hip boots (foam l i n e d based on slushing d i f f e r e n t pastes containing blowing agents i n s e r i e s ) , and d o l l parts. With r o t a t i o n a l molding, a closed mold i s rotated i n two or more planes during fusion or s o l i d i f i c a t i o n of the f l u i d polymer system. The action of the r o t a t i o n deposits an even coating of polymer upon the inside of a "clam s h e l l " type mold. After a predetermined time under heat, the molds are removed from the oven and cooled, and the f i n i s h e d product i s removed whereupon the c y c l e i s s t a r t e d a g a i n . C o n v e n t i o n a l gas f i r e d ovens or hot s a l t bath s p r a y s are used f o r heat t r a n s f e r , and c o o l i n g i s u s u a l l y e f f e c t e d by s p r a y i n g or immersion i n c o l d water. This technique i s w e l l suited to molding completely hollow objects. S o l u t i o n v i n y l s and l a t e x e s are r e s t r i c t e d from r o t a t i o n a l m o l d i n g f o r the same b a s i c reason as c i t e d i n s l u s h molding o p e r a t i o n s , t h a t i s , the problems connected w i t h removing l a r g e volumes of v o l a t i l e components. P l a s t i s o l s have the f i e l d again nearly to themselves, but low d i l u e n t l e v e l s i n an organosol may be t o l e r a t e d . I t should be noted that r o t a t i o n a l molding i s adaptable to powder t e c h n o l o g y a l s o . Dry b l e n d PVC systems, low m o l e c u l a r weight p o l y e t h y l e n e , and now other r e s i n s have been s u c c e s s f u l l y r o t o c a s t e d . P l a s t i s o l b a l l s , dashboard pads, auto arm r e s t s , t r a f f i c cones, hobby h o r s e s , and d o l l p a r t s have been made commercially f o r many years. For c a v i t y and i n p l a c e molding p l a s t i s o l s are m a i n l y used. F l u i d s are i d e a l f o r the encapsulation of i n t r i c a t e mold i n s e r t s . They can be poured i n t o p l a c e by g r a v i t y or i n j e c t e d a t low pressures, thus enabling r e l a t i v e l y low cost, l i g h t l y constructed molds t o be used. Due to the problems i n h e r e n t i n s o l v e n t or v o l a t i l e r e m o v a l , the p l a s t i s o l s have t h i s f i e l d n e a r l y t o


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Table I.


Physical Properties of F l u i d Coating Systems

Physical Properties

Plastisols

Molecular weight of polymers

Low t o

Organosols Low to very high

very high Downloaded by CORNELL UNIV on May 13, 2017 | http://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch050

VC/VA Copolymers a v a i l a b l e

VC/VA

P l a s t i c i z e r l e v e l (range) (phr)

35-100+

Fusion temperatures (°F)

250-400

Film thickness ( M i l )

0.5-250+

Metal primer required ( f o r adhesion)

Yes^

25-70 300-400 0.5-8 Yes

b

Gloss range a v a i l a b l e

Low t o high

Low to high

Chemical resistance

Excellent

Excellent

Water resistance

Good t o excellent

Good to excellent

Percent s o l i d s

100

50-95

E l e c t r i c a l properties

Poor to f a i r

Poor t o fair

Outdoor d u r a b i l i t y (pigmented systems)

F a i r to good

Good

Normal v i s c o s i t y range Brookfield 20 rpm (cps)

2000-10,000

500-4000

Nature of v o l a t i l e

None

Aliphatic, naphtha

l

Plus VC/vinylidene c h l o r i d e , VC/maleates, terpolymers (C00H, OH types).

'Limited self-priming formulas a v a i l a b l e .


50.


PARK

Solutions

Latexes

Low to medium

Low to high

Low

VC/VA

VC/acrylates

No

0-25

0-40

0-60

Air-dry

230-400

400-600

0.25-5

0.25-5

1.5-100

No

Yes

Yes

Low to very high

Low to high

Low to high

Good to excellent

Good to excellent

Excellent

Excellent

Poor to f a i r

Good to excellent

10-50

40-50

100

Good to excellent

Poor

Good to excellent

Good to excellent

Poor to fair

Good to excellent

40-3000

40-3000

Not applicable

Ketone, aliphatic, aromatic, naphtha, esters

Water

None


a

Powder Coatings


1225

1226


themselves. Encapsulated e l e c t r i c a l and e l e c t r o n i c parts, p r i n t i n g p l a t e s , automotive a i r cleaner s e a l s , c l a y pipe gaskets, etc., are t y p i c a l products made with these techniques. T a b l e I c i t e s the p h y s i c a l p r o p e r t i e s than can be a n t i c i p a t e d from f l u i d coating systems.


Today and Tomorrow Today's market areas f o r v i n y l c h l o r i d e dispersion r e s i n s , s o l u t i o n r e s i n s , and l a t e x e s are centered around c o a t i n g (wearing a p p a r e l , u p h o l s t e r y , shoe uppers), molding and d i p p i n g ( s u r g i c a l g l o v e s , toys, p l a t i n g racks, t o o l handles), b o t t l e closures, c o i l coating i n d u s t r i e s , beverage can c o a t i n g s , p r o t e c t i v e and d e c o r a t i v e lacquers, and nonwoven bindings. High energy c o s t s encourage polymer compositions that require fewer BTUs for conversion. The use of copolymer dispersion resins o f f e r s d e f i n i t e advantages over homopolymers. Figure 7 i l l u s t r a t e s t h i s c h a r a c t e r i s t i c of the v i n y l c h l o r i d e / v i n y l acetate dispersion r e s i n s . I n t h i s i n s t a n c e , the 5% v i n y l a c e t a t e copolymer o f f e r s d i s t i n c t t e n s i l e s u p e r i o r i t y t o the high molecular weight homopolymer u n t i l f u s i o n temperatures of 185 °C are exceeded and then the s u p e r i o r i t y of the homopolymer i s very s l i g h t . Reactive d i s p e r s i o n r e s i n s ( f o r metal and polymer adhesion) are c u r r e n t l y being given commercial e v a l u a t i o n s . R e l i a n c e upon b a t c h p o l y m e r i z a t i o n techniques by polymer manufacturers w i l l a l s o be given c l o s e scrutiny. Higher s o l i d latexes w i l l help to lower BTU costs f o r d r i v i n g o f f the water used i n latex-based coatings. Formulation Resin 100 OOP 60 Thermolite 20"! 20 mil films fused on glass plate.

Vinyl Chloride/ Vinyl Acetate Copolymer

DOOf-

TENSILE

DEVELOPMENT of

DISPERSION

110

120

130 140 BO

160

170

180

RESINS

190 200 210 220

Temperature (°C)

Figure 7. Tensile development of dispersion r e s i n s . Tess and Poehlein; Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

50.

PARK


1227

Both polymer manufacturers and polymer converters w i l l continue to i n v e s t i g a t e new monomers, p l a s t i c i z e r s , and a d d i t i v e s . Greater use o f o l e f i n s , maleates, and a c r y l a t e s as comonomers w i t h v i n y l c h l o r i d e w i l l occur. Regulations and r e s t r i c t i o n s on s o l v e n t use w i l l continue t o encourage use o f r e s i n s t h a t have g r e a t e r s o l u b i l i t y i n order t o a c h i e v e h i g h e r s o l i d s and/or t o t o l e r a t e poorer solvents. C e l l u l a r products (foams and f r o t h s ) w i l l c o s t l e s s through greater coverage per pound. This approach i s c u r r e n t l y being used to advantage i n the s e a l i n g and gasketing area. The years ahead o f f e r g r e a t c h a l l e n g e s but a l s o g r e a t rewards for those with the v i s i o n t o take advantage of the v i n y l polymers greatest a s s e t — t h e i r v e r s a t i l i t y and a d a p t a b i l i t y . Downloaded by CORNELL UNIV on May 13, 2017 | http://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch050

1

Literature Cited 1. Regnault, M. V. Ann. Chimi Phys. 1838, 69(2), 151. 2. Gellner, O. Chem. Eng. 1966, 73(16), 74. 3. Whittington, L. R. "A Guide to the Literature and Patents Concerning Polyvinyl Chloride Technology," 2nd ed.; Society of Plastics Engineers, Stamford, Conn. 1963; p. 232. 4. Tess, R. W. "Solvents Theory and Practice"; American Chemical Society: Washington, D.C., 1973; pp. 186-218. 5. Levinson, S. B. J. Paint Technol. 1972, 44(570), 38. 6. Golovoy, A. J. Paint Technol. 1973, 45(580), 42.


Vinyl Resins Used in Coatings - American Chemical Society

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