Fillers and Reinforcements for Plastics

2 The Coatings Industry Looks at Fillers FRED

B. S T I E G

Downloaded by NORTH CAROLINA STATE UNIV on December 23, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch002

Titanium Pigment Division, Ν L Industries, Inc., South A m b o y , N. J. 08879

Pigment packing characteristics have become an important formulating consideration in the paint industry. The binder demand of any given combination of pigments and/or fillers can be determined from its oil absorption, and it can be expressed as its critical pigment volume concentration (CPVC). A relationship exists between the CPVC of a pigmentation and the viscosity that it will produce in a given vehicle system: Ρ

η R =

CPVC

—

Ρ

where is the relative kinematic viscosity, and Ρ is per cent pigment and/orfillerby volume. Sincefillerscan be blended to maximize CPVC, it follows that maximumfillercontents in polymer systems can be increased by a similar procedure. ηR

' T p h e materials k n o w n i n t h e plastics i n d u s t r y as fillers a r e defined b y A S T M ' s Committee

D - 2 0 as " r e l a t i v e l y i n e r t m a t e r i a l a d d e d

to a

p l a s t i c t o m o d i f y its strength, p e r m a n e n c e , w o r k i n g properties, o r other q u a l i t i e s , or to l o w e r fibrous

cost"

( J ) . This

definition

includes,

however,

materials a n d f a b r i c s , s u c h as those u s e d i n p l a s t i c laminates,

w h i c h p r i m a r i l y accounts f o r a n y reference to the m o d i f i c a t i o n of strength or p e r m a n e n c e .

T h e materials w h i c h are sometimes r e f e r r e d to i n t h e

coatings i n d u s t r y as

fillers—but

more commonly

as extenders—are t h e

nonfibrous, inert, i n o r g a n i c p i g m e n t s most f r e q u e n t l y u s e d i n the plastics i n d u s t r y solely to r e d u c e cost. T y p i c a l l y they i n c l u d e c a l c i u m

carbonate

( o r w h i t i n g ) , b a r i u m sulfate, c a l c i u m sulfate, s i l i c a , c h i n a clay,

mag

n e s i u m silicate, p o w d e r e d m i c a , d i a t o m a c e o u s s i l i c a , a n d so f o r t h . T h e c o m m o n use o f t h e t e r m extender n o d o u b t o r i g i n a t e d f r o m t h e Webster's

D i c t i o n a r y i n t e r p r e t a t i o n , " t o increase t h e b u l k of a p r o d u c t 7

In Fillers and Reinforcements for Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8

FILLERS AND

R E I N F O R C E M E N T S FOR PLASTICS

b y the a d d i t i o n of a c h e a p e r substance : a d u l t e r a t e . "

I n t h e e a r l y days

of the coatings i n d u s t r y , fillers or extenders w e r e b r a n d e d as adulterants b y l e g a l statutes, a n d e a r l y l a b e l i n g l a w s w e r e d e s i g n e d to f o r c e p a i n t manufacturers

to disclose

the use of a n y materials other t h a n

linseed oil, white lead, and zinc oxide i n their products.

"pure"

Such

early

attempts b y the f e d e r a l g o v e r n m e n t to regulate p r i v a t e i n d u s t r y specified the use of those same l e a d p i g m e n t s that today's g o v e r n m e n t

regulations


are d e s i g n e d to e l i m i n a t e . T h e coatings i n d u s t r y , h o w e v e r , has h a d m a n y reasons to t h i n k of fillers as s e r v i n g some p u r p o s e other t h a n a d u l t e r a t i o n . A s e a r l y as 1907, Perry (2)

h a d d r a w n an a n a l o g y b e t w e e n p a i n t a n d concrete ( r e f e r r i n g

to a p a p e r b y T a y l o r a n d T h o m p s o n , W a t e r t o w n A r s e n a l ) a n d h a d d e v i s e d a so-called " l a w of m i n i m u m v o i d s " i n w h i c h h e c o n c l u d e d t h a t " t h e r e q u i s i t e thickness of a p a i n t film, together w i t h the utmost

attainable

strength a n d i m p e r m e a b i l i t y , c a n best b e o b t a i n e d b y a p r o p e r l y t i o n e d b l e n d of p i g m e n t s

propor-

of t h r e e or m o r e d e t e r m i n a t e sizes."

Perry

c o n c e i v e d of the largest p a r t i c l e s i n s u c h a b l e n d of p i g m e n t s as piers, a c t i n g as p h y s i c a l supports

for the d r y p a i n t

film,

w h i c h he

further

d e s c r i b e d as a series of flat arches. T h e r e is no r e c o r d of a n y e x p e r i m e n t a l w o r k ever h a v i n g b e e n d o n e to s u p p o r t these conclusions, b u t i n the e a r l y 1900s a n extensive series of coatings w a s e x p o s e d o n the test fences of the N o r t h D a k o t a E x p e r i m e n t a l S t a t i o n to establish the v a l u e of fillers i n exterior h o u s e paints. T h e results a p p e a r e d to s u p p o r t P e r r y ' s hypothesis i n that m a n y p a i n t films c o n t a i n i n g coarse

fillers

proved

to be

more

d u r a b l e t h a n those p i g m e n t e d o n l y w i t h t h e s o - c a l l e d " p u r e " p i g m e n t s . A

statistical analysis of t h e N o r t h D a k o t a d a t a b y

s h o w e d that p a i n t films c o n t a i n i n g less t h a n 2 6 %

Calbeck

pigment by

volume

w e r e significantly less d u r a b l e t h a n those c o n t a i n i n g 2 6 - 3 0 % by volume.

(3)

pigment

A b o v e this v a l u e , d u r a b i l i t y w a s a g a i n i m p a i r e d .

T h e s e findings d i d not specify that a n y of this p i g m e n t v o l u m e n e e d necessarily be c o m p o s e d of

filler,

b u t e c o n o m i c considerations

dictated

that a n y q u a n t i t y of p i g m e n t a b o v e that r e q u i r e d to p r o d u c e a c c e p t a b l e brightness a n d o p a c i t y w o u l d b e just that. pure pigments—white

F u r t h e r m o r e , the

so-called

lead and zinc oxide—were chemically

reactive

w i t h c o m m o n p a i n t vehicles, so that a n excess h a d to be a v o i d e d to p r e v e n t p a i n t failures s u c h as a l l i g a t o r i n g , c h e c k i n g , a n d c r a c k i n g . o n the other h a n d , w e r e i n e r t a n d c o u l d i n h i b i t s u c h f a i l u r e s , i f

Fillers, fibrous

or p l a t y , b y a p p a r e n t l y r e i n f o r c i n g the film against the m e c h a n i c a l stress f r o m p o o r d i m e n s i o n a l s t a b i l i t y of w o o d substrates. w e r e necessary

to p r o d u c e lusterless,

flat

finishes.

In addition,

fillers

T h e i r larger, more

i r r e g u l a r l y s h a p e d particles w e r e f a r m o r e efficient i n p r o d u c i n g a l i g h t d i f f u s i n g surface t h a n w h i t e l e a d or z i n c oxide. frequently called

flattening

I n fact, s u c h fillers w e r e

agents.


2.

STIEG

Titanium

Coatings

9

Industry

Dioxide

W i t h the appearance of a new, non-reactive white pigment, titanium d i o x i d e , n e w emphasis w a s p l a c e d u p o n t h e use of

fillers.

Titanium pig

ments w e r e so m u c h m o r e o p a q u e t h a n w h i t e l e a d o r z i n c o x i d e t h a t s u b s t a n t i a l q u a n t i t i e s o f filler c o u l d b e a d d e d .

N o t o n l y c o u l d fillers b e

a d d e d , t h e y w e r e necessary f o r m a x i m u m efficiency i n m a n y types of f o r m u l a t i o n s . T h i s w a s c a u s e d b y a p e c u l i a r i t y of w h i t e h i d i n g p i g m e n t s Downloaded by NORTH CAROLINA STATE UNIV on December 23, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch002

that h a d never b e e n n o t i c e d b e f o r e because of t h e l o w o p a c i t y o f t h e o l d e r types. A s t h e c o n c e n t r a t i o n o f t h e h i d i n g p i g m e n t w a s i n c r e a s e d i n a p a i n t film, t h e a m o u n t of h i d i n g p o w e r c o n t r i b u t e d p e r p o u n d of p i g m e n t b e c a m e s m a l l e r . T h i s is i l l u s t r a t e d i n F i g u r e 1 f o r r u t i l e t i t a n i u m dioxide.

T h i s effect is a t t r i b u t e d to t h e fact that l i g h t scattered b y a n

i n d i v i d u a l p a r t i c l e w i l l encounter interference f r o m l i g h t scattered, o u t of-phase, b y adjacent p a r t i c l e s , a n d t h e m o r e closely s u c h p a r t i c l e s a p p r o a c h e a c h other, t h e m o r e t h e interference, a n d t h e less t o t a l l i g h t scattered f r o m t h e film to p r o d u c e whiteness, b r i g h t n e s s , a n d o p a c i t y . 180 160

I

140

oc LU

°- 120 t "

100

I oc LU

g

CL eu S

t—ι

80

60 40

10

20

30

40

50

60

PIGMENT VOLUME CONCENTRATION

Figure

1.

Hiding power curve for rutile Ti0 2

T h e use of m o r e t h a n 3 0 v o l % t i t a n i u m d i o x i d e i n a p a i n t

film

results i n a n a c t u a l loss of o p a c i t y b e c a u s e o f this i n t e r f e r e n c e effect

(4),

yet m a n y types o f coatings m u s t c o n t a i n s u b s t a n t i a l l y m o r e p i g m e n t t h a n this to d e v e l o p d e s i r e d p e r f o r m a n c e characteristics. F l a t w a l l p a i n t s , f o r example, typically contain 5 5 - 6 5 % pigment b y volume (dry-film basis),


10

FILLERS AND R E I N F O R C E M E N T S FOR PLASTICS

a n d c e i l i n g paints m a y c o n t a i n m o r e t h a n 7 0 % . can be titanium dioxide, the balance must be

If no more than 3 0 %

filler.

I n p r a c t i c e , the use

of m o r e t h a n 2 1 % t i t a n i u m d i o x i d e b y v o l u m e is u n e c o n o m i c a l i n terms o f h i d i n g p o w e r p e r d o l l a r of t o t a l cost. W h e n l a r g e amounts of filler b e g a n to be u s e d , i n t e r e s t i n g effects of p a r t i c l e size w e r e noted.

F o r e x a m p l e , the c o m b i n a t i o n of t i t a n i u m

d i o x i d e w i t h t h e types of coarse filler c o m m o n l y u s e d i n flat w a l l p a i n t s


to p r o d u c e a lustreless finish r e s u l t e d i n a n u n e x p e c t e d loss of h i d i n g power.

T h i s was the result of the p a c k i n g p h e n o m e n o n n o t e d 50 years

earlier b y P e r r y . T h e fine t i t a n i u m d i o x i d e p a r t i c l e s w e r e b e i n g p a c k e d i n t o the v o i d s of the coarse extender system b y the forces of film f o r m a t i o n , a n d t h e i r p r o x i m i t y w a s e x a g g e r a t i n g the i n t e r f e r e n c e effect.

This

u n d e s i r a b l e c o n d i t i o n c o u l d b e a l l e v i a t e d b y a d d i n g a p o r t i o n of

filler

of average p a r t i c l e d i a m e t e r of t h e same o r d e r of m a g n i t u d e as t h a t of titanium dioxide.

S i n c e i t w a s s i m i l a r i n size, it f o u n d its w a y i n t o the

same voids a n d p r o v i d e d a b e n e f i c i a l p h y s i c a l d i l u t i o n of the t i t a n i u m dioxide. Critical

Pigment Volume

Concentration

T h e e v i d e n c e t h a t s u c h p a c k i n g effects w e r e t a k i n g p l a c e l e d to extensive i n v e s t i g a t i o n of the v o l u m e r e l a t i o n s h i p s i n d r y p a i n t

films.

It

w a s f o u n d t h a t e v e r y c o m b i n a t i o n of t i t a n i u m d i o x i d e a n d filler h a d a c h a r a c t e r i s t i c " b i n d e r d e m a n d " that w a s a f u n c t i o n of the difference i n p a r t i c l e size b e t w e e n the t i t a n i u m p i g m e n t a n d the filler, a n d t h e p a r t i c l e size d i s t r i b u t i o n of the

filler.

T h e v o l u m e r e l a t i o n s h i p of

pigment-to-

b i n d e r w h i c h just satisfied this b i n d e r d e m a n d w a s d e s c r i b e d as the c r i t i c a l P V C , o r C P V C , P V C b e i n g the c o m m o n l y u s e d a b b r e v i a t i o n for pigment volume concentration.

It was p o s s i b l e to i d e n t i f y the

CPVC

for a n y c o m b i n a t i o n of p i g m e n t s b y d e t e r m i n i n g the m i n i m u m a m o u n t of l i n s e e d o i l t h a t w o u l d f o r m a d r y b u t coherent mass w h e n a d d e d to a g i v e n w e i g h t of the p i g m e n t a n d w o r k e d v i g o r o u s l y w i t h a s p a t u l a — t h e s o - c a l l e d s p a t u l a r u b - o u t o i l a b s o r p t i o n test ( A S T M M e t h o d D 2 8 1 ) . CPVC

=

v o l of p i g m e n t v o l . of p i g m e n t + v o l . of o i l

F u r t h e r m o r e , b y v a r y i n g the percentages

of fine a n d coarse

com-

ponents, it w a s possible to s h o w the v a r i a t i o n of p a c k i n g w i t h c o m p o s i t i o n o n a C P V C c u r v e a n d to i d e n t i f y the c o n d i t i o n of m a x i m u m p a c k i n g (5).

T h i s is i l l u s t r a t e d i n F i g u r e 2 for r u t i l e t i t a n i u m d i o x i d e i n c o m b i -

nations w i t h three c a l c i u m c a r b o n a t e fillers of v a r y i n g p a r t i c l e size.

The

coarser the filler, the m o r e p r o n o u n c e d t h e p e a k i n the c u r v e r e p r e s e n t i n g



2.

STIEG

Coatings

11

Industry

a c o n d i t i o n of m a x i m u m p a c k i n g . F o r t i t a n i u m d i o x i d e a n d most l a r g e p a r t i c l e size fillers, this p e a k t y p i c a l l y occurs at a c o n c e n t r a t i o n

(v/v)

of a b o u t 2 0 % t i t a n i u m d i o x i d e . T h e e v i d e n c e of s u c h o i l a b s o r p t i o n e n d points c a n also b e i n t e r p r e t e d i n terms of the m a x i m u m a m o u n t of filler t h a t c a n b e i n c o r p o r a t e d i n t o a fixed a m o u n t of b i n d e r . n / ι resin · = g a li f i filler/gal F o r the coarser c a l c i u m c a r b o n a t e

(^pyQ) C

P

V

C

of F i g u r e 1, f o r e x a m p l e ,

the

t o t a l l o a d i n g for t h e p u r e filler c a n b e i n c r e a s e d f r o m 1.82 g a l p e r g a l of r e s i n to 3.02 g a l b y u s i n g a b l e n d w i t h 2 0 % T i 0 . 2

increase of almost 6 6 %

in maximum loading.

T h i s amounts to a n

T h e discovery that o i l

a b s o r p t i o n effects w e r e n o t s i m p l y a d d i t i v e p r o v i d e d a n e x p l a n a t i o n for m a n y p h e n o m e n a that h a d p u z z l e d p a i n t f o r m u l a t o r s . Particle Size

Distribution

A v e r a g e p a r t i c l e size a n d C P V C

w e r e not sufficient i n f o r m a t i o n ,

h o w e v e r , to e x p l a i n the shape of m a n y of these C P V C curves. P a r t i c l e -


12

FILLERS AND R E I N F O R C E M E N T S FOR PLASTICS

s i z e d i s t r i b u t i o n h a d a m a r k e d effect.

T h e C P V C h a d been defined b y

A s b e c k a n d V a n L o o ( 6 ) as t h a t p i g m e n t - t o - b i n d e r r a t i o w h i c h p r o v i d e d just e n o u g h b i n d e r to satisfy the p i g m e n t surface a n d to fill the v o i d s b e t w e e n p i g m e n t p a r t i c l e s . E x p r e s s e d as a n e q u a t i o n , this b e c a m e CPVC


where Ρ =

=

(7):

P+a+b

v o l % of p i g m e n t

a =

v o l % of a d s o r b e d b i n d e r

b =

v o l % of b i n d e r i n v o i d s

T h e t e r m a c o u l d b e e x p e c t e d to v a r y w i t h surface area a n d therefore w i t h a v e r a g e p a r t i c l e size, b u t b d e p e n d e d u p o n p a r t i c l e - s i z e d i s t r i b u t i o n . T o g e t h e r a - f b w e r e n u m e r i c a l l y e q u i v a l e n t to the v o l u m e of b i n d e r r e q u i r e d to w e t Ρ v o l u m e s of p i g m e n t .

I t is therefore q u i t e p o s s i b l e for

t w o v e r y different fillers to possess s i m i l a r o i l absorptions ( a n d C P V C ' s ). A l a r g e - p a r t i c l e - s i z e filler w i t h a v e r y u n i f o r m p a r t i c l e - s i z e d i s t r i b u t i o n w i l l h a v e a n o i l a b s o r p t i o n m a d e u p of a s m a l l a c o m p o n e n t b u t a l a r g e b component

( because of the a b s e n c e of p a c k i n g ), w h i l e a

fine-particle-

size filler w i t h a w i d e p a r t i c l e - s i z e d i s t r i b u t i o n w o u l d h a v e a n o i l a b s o r p t i o n c o m p o s e d of a l a r g e a c o m p o n e n t the s u m of a +

a n d a small b component.

Yet

b c o u l d t h e o r e t i c a l l y b e the same for b o t h . T h e C P V C

c u r v e w o u l d disclose the difference, h o w e v e r , because the l a r g e v o i d s of the coarser

filler

w o u l d p e r m i t a m u c h h i g h e r percentage

of t i t a n i u m

d i o x i d e to b e p a c k e d i n t o t h e m w h i l e t h e v o i d s of the finer filler w o u l d be essentially filled t o b e g i n w i t h . Table I.

Effect of Particle-Size Distribution Oil

Type of Filler

No Ti0

2

Unclassified C a C 0 Classified C a C 0

3

3

a

Absorption"

1

20%

17.3 18.8

Ti0

2

14.0 10.6

Lbs of oil per 100 lbs of pigment ( A S T M Method D281).

T h e difference i n p o t e n t i a l p a c k i n g is i l l u s t r a t e d i n T a b l e I for t w o calcium carbonates—one

a n o r m a l d r y g r o u n d m a t e r i a l , t h e other

classified f r a c t i o n of the first w i t h the fines r e m o v e d .

Both could

a be

c a l l e d c o a r s e — i n the 5 - 1 0 m i c r o n average p a r t i c l e - s i z e r a n g e — b u t the classified m a t e r i a l h a d a n a r r o w e r p a r t i c l e - s i z e d i s t r i b u t i o n . T h e u n c l a s s i f i e d filler h a d a l o w e r o i l a b s o r p t i o n t h a n the classified m a t e r i a l b e c a u s e of the p a c k i n g of its w i d e r r a n g e of p a r t i c l e sizes.


The

2.

Coatings

STiEG

13

Industry

a d d i t i o n of 2 0 % t i t a n i u m d i o x i d e p r o d u c e d a l o w e r o i l a b s o r p t i o n w i t h t h e classified m a t e r i a l , h o w e v e r ,

because of the a v a i l a b i l i t y of

larger

v o i d s not present i n the u n c l a s s i f i e d m a t e r i a l because of p a c k i n g .

The

t i t a n i u m d i o x i d e p r o d u c i n g this effect h a d a n o i l a b s o r p t i o n of 21.2, yet it w a s a b l e to increase p a c k i n g because of its s m a l l e r p a r t i c l e size w h e n a d d e d to t h e coarser extenders. S i n c e coatings are s o l d o n a v o l u m e basis, the v o l u m e r e l a t i o n s h i p


C P V C is of m o r e interest t h a n the o i l a b s o r p t i o n w e i g h t r e l a t i o n s h i p . T h e C P V C i n coatings is closely associated w i t h a t r a n s i t i o n p o i n t for m a n y film p r o p e r t i e s , a m o n g t h e m w a s h a b i l i t y a n d s t a i n r e m o v a l , e n a m e l h o l d - o u t , color u n i f o r m i t y o v e r surfaces of v a r y i n g p o r o s i t y , v a p o r p e r m e a b i l i t y , a n d b l i s t e r i n g . C o n s e q u e n t l y , c o n t r o l of

filler

p a r t i c l e size has

b e c o m e a significant factor i n p a i n t f o r m u l a t i o n . Maximum The

Packing relationship between

pigmentation

CPVC

and P V C which

has b e e n d e s c r i b e d as the p o r o s i t y i n d e x , P I , has b e e n u s e d to p r e d i c t the d r y h i d i n g p o w e r of p o r o u s coatings, as w e l l as film p o r o s i t y ( 8 , 9 ) : CPVC

(1-PVC)

P V C (1-CPVC) I n l i q u i d coatings w i t h n o p i g m e n t / b i n d e r i n t e r a c t i o n s , v i s c o s i t y has b e e n s h o w n to b e r e l a t e d to the p a c k i n g characteristics of t h e p i g m e n t a t i o n , as w e l l as to its v o l u m e c o n c e n t r a t i o n , b y the e q u a t i o n :

log VR where η

η

=

Ρ =

=

cpvc-P

r e l a t i v e k i n e m a t i c v i s c o s i t y of p i g m e n t paste to clear v e h i c l e percent pigment b y volume

B e c a u s e of this r e l a t i o n s h i p of v i s c o s i t y to the C P V C — a n d

therefore

to p i g m e n t p a c k i n g — i t is possible to increase the m a x i m u m a m o u n t of p i g m e n t that c a n b e i n c o r p o r a t e d i n a g i v e n v e h i c l e b y

deliberately

s e l e c t i n g a c o m b i n a t i o n of l a r g e a n d s m a l l p a r t i c l e size p i g m e n t s ( a n d / o r fillers)

to p r o d u c e m a x i m u m p a c k i n g . B y a s i m i l a r t e c h n i q u e , v i s c o s i t y

c a n b e r e d u c e d at a fixed p i g m e n t l o a d i n g . I n plastics systems w h e r e the v o l u m e of t i t a n i u m d i o x i d e u s e d is v e r y s m a l l c o m p a r e d w i t h coatings, the use of a b l e n d of l a r g e a n d s m a l l p a r t i c l e size filler m a y b e d e s i r a b l e . W h i l e l o w o i l a b s o r p t i o n m a y h a v e


14

FILLERS A N D R E I N F O R C E M E N T S FOR PLASTICS

b e e n t h e basis f o r o r i g i n a l l y selecting a p a r t i c u l a r filler, i t is q u i t e p o s s i b l e , i n d e e d p r o b a b l e , that its l o w o i l a b s o r p t i o n is m o r e t h e result o f v e r y l a r g e p a r t i c l e size ( a n d therefore l o w surface a r e a ) t h a n of a p a r t i c l e s i z e d i s t r i b u t i o n specifically d e s i g n e d to r e d u c e v o i d v o l u m e .

VOLUME PERCENT ASP-100 0

20


I

»

40

60

1

1

I

1

1

100

80

60

1 40

80

100

1

1

i

1

20

0

VOLUME PERCENT L0RITE

Figure

3.

CPVC

curve for filler blend

B y d r y b l e n d i n g fillers i n v a r i o u s p r o p o r t i o n s b y v o l u m e a n d determ i n i n g t h e s p a t u l a r u b - o u t o i l a b s o r p t i o n f o r t h e b l e n d s , i t is p o s s i b l e to i d e n t i f y t h e c o m b i n a t i o n of m a x i m u m p a c k i n g , as i l l u s t r a t e d i n F i g u r e 3. F o r t h e fillers i n v o l v e d i n this e x p e r i m e n t , t h e C P V C of m a x i m u m p a c k i n g (55.4) represents a n increase o f almost 2 3 % i n t h e a m o u n t of filler that m a y b e u s e d p e r 100 lbs of r e s i n c o m p a r e d w i t h the l o w e r o i l a b s o r p t i o n filler

( L o r i t e , a p r o d u c t o f N L I n d u s t r i e s , I n c . ) alone.

A s i n coatings,

the p a r t i c l e size of t h e largest filler u s e d m a y b e l i m i t e d b y film t h i c k n e s s , surface texture, m i l l a b r a s i o n , or other considerations.

T h i s imposes a

l o w e r l i m i t o n t h e o i l a b s o r p t i o n of t h e filler since, as a g e n e r a l r u l e , o i l a b s o r p t i o n tends to increase as p a r t i c l e size is r e d u c e d . I t w i l l u s u a l l y b e possible, h o w e v e r , to find a n e v e n finer filler t h a t w i l l r e d u c e t h e o i l a b s o r p t i o n w h e n a d d e d i n s m a l l amounts. A n excellent source of d a t a o n s u c h fillers is t h e " R a w M a t e r i a l s I n d e x , P i g m e n t S e c t i o n , " p u b l i s h e d b y the N a t i o n a l P a i n t a n d C o a t i n g s A s s o c i a t i o n , 1500 R h o d e I s l a n d A v e . , N.W., Washington, D . C .


2.

STIEG

Coatings

Industry

15

Literature Cited ASTM Standard D883, Committee D-20, ASTM, Philadelphia, Pa. Gardner, Η. Α., "Paint Technology and Tests," p. 105-200, McGraw-Hill, New York, 1911. 3. Calbeck, J. H., Ind. Eng. Chem. (1926) 18, 1220. 4. Stieg, F . B., Off. Digest (1957) 29, 439. 5. Stieg, F . B., Off. Digest (1956) 28, 695. 6. Asbeck, W. K., Van Loo, M., Ind. Eng. Chem. (1949) 41, 1470. 7. Stieg, F . B., J. Paint Technol. (1967) 39, 703. 8. Stieg, F . B., Ensminger, R. I., Off. Digest (1961) 33, 792. 9. Stieg, F . B., J.O.C.C.A. (1970) 53, 469.


1. 2.

RECEIVED October 11, 1973.


Fillers and Reinforcements for Plastics

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