Polymeric Reactions in Magnetic Recording Media - American

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Downloaded by CORNELL UNIV on October 7, 2016 | http://pubs.acs.org Publication Date: March 15, 1984 | doi: 10.1021/bk-1984-0242.ch032

Polymeric Reactions in Magnetic Recording M e d i a LESLEY J. GOLDSTEIN Department of Chemical Technology, Graham Magnetics, Inc., North Richland Hills, TX 76118 Magnetic recording tape is a complex interaction of select chemicals designed for peak recording capabil ities in a durable, reliable package. Commonly, mag netic Fe O particles are mixed in a binder system composed of solvent, polymer, isocyanate, catalyst and other components. The media is coated onto a base film, oriented, dried, and calendared to enhance recording quality. The oxide adheres to the sup porting base film via a polyurethane-isocyanate re action to yield a strong, flexible material similar to a crosslink thermoset. Actually, a "pseudo" crosslink mesh is formed from interpenetrating units. The main polymer is an ester based polyurethane with hydroxyl termination. Water also reacts with iso cyanate and its abundance in a production environment may cause improper cure of the tape. A study was done on the reaction rates of isocyanate and polyurethane including a change in catalysts and alternating func tionalities. Looking at these variations, the chemical composition of the recording media can be modeled to a top quality, low contaminant, complete cure system. 2

3

"Polymer in Electronics" is designed to discuss innovative ways polymeric materials can be used in the growing electronics field. This paper discusses specific polymer reactions in mag netic recording media. Magnetic properties originate from in organic transition metal-oxides ( jFe 0 , CrCL, cobalt-modified JFeJL) or metal powders. These particles offer the charac teristic of acting as tiny bar magnets and containing magnetic moments. When a magnetic field is impressed upon a metal par ticle, the electron spin will alter the surface charge for the bar magnets to align with the field. Using a strong in duced field, the spins orient themselves to a degree ideal for magnetic recording. As shown in Figure 1. 2

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0097-6156/ 84/ 0242-0409S06.00/ 0 © 1984 American Chemical Society Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

410

POLYMERS IN ELECTRONICS

sag Η = 0


Figure

H = Weak 1. P a r t i c l e

H = Strong alignment

H = Saturation

i n various

magnetic

H = 0, fields.

Removing the magnetic f i e l d , the p a r t i c l e s w i l l e i t h e r return t o the o r i g i n a l , nonoriented pattern or continue to remain oriented. In the l a t e r c a s e , a remanent magnetization remains. There e x i s t s a unique r e l a t i o n between magnetic f i e l d strength and degree o f p a r t i c l e o r i e n t a t i o n . For the magnetic p a r t i c l e s to remain in a d e s i r e d p a t t e r n , an organic binder system i s used. The magnetic p a r t i c l e s are dispersed in a polymer system and coated onto a supporting b a s e f i l m . The polymers used can be n i t r i l e rubber, polyurethane, n i t r o c e l l u l o s e or p o l y e s t e r . In t h i s i n v e s t i g a t i o n , the r e a c t i o n s discussed i n v o l v e a polyurethane system. Figure 2 represents a t y p i c a l polyurethane compound used in magnetic media. This polymer i s a product from an i s o c y a n a t e g l y c o l ether r e a c t i o n , and has terminal carboxyl groups.

H E 0 - ? f C H

2

) J ^

Carboxyl

Urethane

Figure

2.

Urethane

T y p i c a l polyurethane

Carboxyl structure.

To c o n t a i n the magnetic p a r t i c l e s , the base polymer must be crosslinked. In t h i s s t u d y , the polyurethane r e a c t s with a prepolymerized i s o c y a n a t e . There i s a question as to the exact s i t e where the isocyanate r e a c t s . Isocyanate r e a c t s with an " a c t i v e hydrogen" on a compound as in the f o l l o w i n g example:

R-N=C=0 + Η - A — > R - N - C - A ή Aromatic isocyanate tends to r e a c t f a s t e r than a l i p h a t i c i s o cyanate. The r e a c t i v i t y i s a l s o dependent on f a c t o r s such as s t e r i c hinderance, temperature, c a t a l y s t s and competing r e a c tions. Isocyanate r e a c t i o n s found in a urethane system are shown on Table 1 .

Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


-U-N-R'H

R-N-C-N-R' H H

+ R"0H

R-N=C=0 + R'N-?—NR H ή (urea)

M

N-R'—* R-N=C=0 + H-N-R' H (primary amine)

m

v w

Determined by d e s i r e d needs.

160-190°C

RN-C-OR" + R'NH, H

Urea d i s s o c i a t e s to i s o c y a nate to r e a c t wi th al c o h o l .

Biuret reaction. Moderate rate.

Strong bases. Metal compounds.

Most r e a c t i v e . needed.

Not

0-25°C

100°C

Rapid r e a c t i o n . Expels C 0 . 2

Fast r e a c t i o n .

Determined by d e s i r e d needs.

M i l d and strong bases. Metal compounds.

Allophanate reaction. Reacts slow.

T e r t i a r y amines. Strong bases. Metal compounds.

25-50°C

25-50°C

COMMENTS

CATALYST

RN-ίί- NHR" =0 HR'

R-N-Î-NR' H H (urea)

9

1

R-N-C-0(CH ^- OCN-R' UN-R' H H 2

120-140°C

R-jj-jj-OR" NHR'

PREFERRED TEMPERATURE

PRODUCT

REACTIONS IN A URETHANE SYSTEM

R-N=C=0 + H , 0 « ^ [ R N - C - 0 H ] - ^ RNH + CO 2 2 (amine) H

m

R-N=C=0 + H-~0(CH,K (primary alcohol)

R-N=C=0 + R'fu-OR" — * H (urethane)

FUNCTIONAL GROUP

Table 1


412



Looking at Figure 2, an isocyanate w i l l react with (1) a v a i l able H O , (2) primary alcohol or carboxyl groups, and (3) urethane groups. Under the r i g h t c o n d i t i o n s , c e r t a i n c a t a l y s t s can i n f l u e n c e the r a t e o f the r e a c t i n g i s o c y a n a t e . For example, t r a n s i t i o n metal complexes are used to i n i t i a t e isocyanate-hydroxyl or isocyanate-urethane r e a c t i o n s . Examples are metal a c e t y l a c e t o n a t e s , napthanates and o c t o a t e s . The isocyanate w i l l r e a c t with terminal carboxyl groups and any a v a i l a b l e water, c r e a t i n g unwanted s i d e r e a c t i o n s . Without the urethane-isocyanate l i n k a g e , a " p s e u d o - c r o s s l i n k " occurs as i n Figure 3. It i s hypothesized that r e a c t i n g isocyanate with the urethane g r o u p s , thus u t i l i z i n g more r e a c t i o n s i t e s , would promote a f a s t e r cure and a more durable polymer s t r u c ture.

Figure 3 . Interpenetrating structure.

Experimental Saunders and F r i s c h (2) c i t e c e r t a i n c a t a l y s t s used to induce an isocyanate-urethane (allophanate) r e a c t i o n . They are z i n c o c t o a t e , c o b a l t napthanate and c o b a l t octoate and are claimed to y i e l d 95% allophanate. An experiment was designed observing the c a t a l y t i c e f f e c t o f these metal complexes under v a r i e d concentrations and over time. Ferric acetylacetonate, a catal y s t known to i n f l u e n c e an isocyanate-carboxyl r e a c t i o n , was included in the study. The c a t a l y s t s were added i n d i v i d u a l l y and in combinations o f two into a polyurethane-polyisocyanate system. Concentrations v a r i e d from 1.50% to 8.00% by weight. The i n g r e d i e n t s were mixed together, c a s t onto supporting b a s e f i l m , and subjected to 70°C f o r 10, 30 and 60 minute periods. The t e s t method used was a s o l v e n t wipe t e s t where s p e c i f i e d pressures and s o l v e n t concentrations are a p p l i e d to each coated sample. Data generated was number o f seconds to pinhole d i s t o r t i o n which r e l a t e s to amount o f c u r e . Figure 4 e l u c i d a t e s the r e s u l t s .


32.

GOLDSTEIN

Polymeric Reactions in Magnetic Recording Media

413


Evaluating a s i n g l e c a t a l y s t , the f a s t e s t cure r a t e i s when f e r r i c acetylacetonate i s used in the system. In high concent r a t i o n s , c o b a l t napthanate alone and combined with c o b a l t octoate, offer a fast reaction rate. Y e t , when f e r r i c a c e t y l acetonate i s combined with c o b a l t napthanate or c o b a l t o c t o a t e , the r e a c t i o n r a t e i n c r e a s e s . For t h i s system, the increased amount o f c a t a l y s t y i e l d s a decrease in cure time. There i s no d i r e c t c o r r e l a t i o n between length o f time specimens were was subjected to heat and cure r a t e . When using c a t a l y s t s which i n f l u e n c e the allophanate r e a c t i o n , one would expect a decrease i n r e a c t i o n r a t e . Y e t , as seen in Figure IV, the f e r r i c acetylacetonate o f f e r s the f a s t e s t r e a c tion rate. It i s concluded t h a t the f i r s t c r o s s l i n k i n g r e a c t i o n i s between isocyanate and the terminal carboxyl groups. The c o b a l t or z i n c complexes do not have the c a t a l y t i c e f f e c t o f Fe(AAL. S u r p r i s i n g l y , when combined with e i t h e r o f the c o b a l t complexes, the f e r r i c a c e t y l a c e t o n a t e s c a t a l y t i c e f f e c t i s r e duced. This suggests t h a t c o b a l t napthanate and c o b a l t or z i n c octoate may indeed i n f l u e n c e the allophanate r e a c t i o n l e a v i n g a l i n k a g e so weak i t impairs the physical c h a r a c t e r . Another explanation i s t h a t the metals c o b a l t and z i n c and t h e i r ligands i n t e r f e r e with the f e r r i c acetylacetonate c a t a l y t i c e f f e c t and very l i t t l e c r o s s l i n k i n g o c c u r s . 1

To draw a c o n c l u s i o n , one needs to observe the allophanate formation, but u n f o r t u n a t e l y there i s not a t e s t method a v a i l able to i d e n t i f y t h i s r e a c t i o n . To evaluate whether the ligands do e f f e c t c a t a l y t i c cure r a t e , an experiment was designed keeping the base metal constant while varying the l i g a n d s . F e r r i c acetylacetonate and f e r r i c napthanate were used under the same t e s t c o n d i t i o n s as the previous experiment. Results are given in Figure 5. Fe(AAL has a greater c a t a l y t i c e f f e c t , y e t when combined with f e r r i c napthanate, i t s r e a c t i v i t y decreases. Thus, the ligands do i n f l u e n c e how the c a t a l y s t s d r i v e a r e a c t i o n . In t h i s system acetylacetonate y i e l d s the f a s t e s t cure r a t e . The napthanate may induce the allophanate r e a c t i o n , but again there i s no way to prove t h i s . An experiment was done keeping the l i g a n d constant and varying the base metal. This was to evaluate whether the metal has an i n f l u e n c i n g f a c t o r on the o v e r a l l cure r a t e . The c a t a l y s t s used were c u p r i c , manganic and f e r r i c a c e t y l a c e t o n a t e s . The concentration o f c a t a l y s t v a r i e d from 1.50% to 8.00% by weight and were added alone and i n combinations o f two. The experiment c o n s i s t e d of v i s c o s i t y measurements over time using a B r o o k f i e l d Viscometer. Figure 6 i l l u s t r a t e s the change in v i s c o s i t y o f 1.5% by weight c a t a l y s t c o n c e n t r a t i o n s . Cu(AA) had v i r t u a l l y the same e f f e c t 2


414



Number of

seconda

Catalyst*

F i g u r e 4. RXN w i t h m e t a l c a t a l y s t s . K e y : 1, Co n a p t h a n a t e ; 2, Co o c t o a t e : 3, F e ( A A ) ^ ; 4, Zn o c t o a t e ; 5, Co n a p t h a n a t e + Co o c t o a t e ; 6, Co n a p t h a n a t e + F e ( A A ) ; 7, Co n a p t h a n a t e + F e ( A A ) ~ ; 3 , Co o c t o a t e + Zn o c t o a t e ; Zn o c t o a t e ; 8, Co o c t o a t e and 10, no c a t a l y s t .

Number of

seconds

LOW CONCENTRATION

HIGH CONCENTRATION

Γ773

2 Catalysts

F i g u r e 5. RXN w i t h i r o n c a t a l y s t s . K e y : 1, F e ( A A ) ^ ; Fe n a p t h a n a t e ; and 3, F e ( A A ) ^ + Fe n a p t h a n a t e .


2,

32.

GOLDSTEIN

Polymeric Reactions in Magnetic Recording

415

Media

as no c a t a l y s t . At 1.5% c o n c e n t r a t i o n , Mn(AAL caused a rapid increase i n v i s c o s i t y , so f a s t that data points could not be collected.


The e f f e c t o f v a r i e d f e r r i c and manganic acetyl acetonate c o n c e n t r a t i o n s with r e s p e c t to v i s c o s i t y i s shown on Figures 7 and 8. Of note i s the l i m i t i n g f a c t o r F e ( A A L has on the system, where 3.0% r e a c t s f a s t e r the 4.5% c o n c e n t r a t i o n . This i n d i c a t e s a unique c a t a l y s t concentration i s needed f o r t h i s system to have an optimum e f f e c t . Manganic acetylacetonate has even a g r e a t e r c a t a l y s t i n f l u e n c e in t h i s system. At 0.75%, Mn(AA) r e a c t s f a s t e r than elevated concentrations o f e i t h e r o f the acetylacetonates.

Discussion In t h i s polyurethane-prepolymerized isocyanate r e a c t i o n , the f a s t e s t c a t a l y s t are the acetylacetonate complexes. Looking a t the molecular s t r u c t u r e s i n v o l v e d , an octoate i s a 2-ethylhexoate, having the s t r u c t u r e

The napthanate i s derived from naphthenic a c i d and i s a mixture o f molecular weight a c i d s . No chemical s t r u c t u r e i s a v a i l a b l e . Metal acetylacetonates a r e i l l u s t r a t e d

as: (3)

Studying the a c e t y l acetonate mechanism in the presence o f i s o cyanate, a carboxyl w i l l e x h i b i t an interchange o f oxygen atoms. The acetylacetonate l i g a n d separates from the base metal and i s replaced with isocyanate to form a charge d i s t r i b u t i o n between the oxygen and carbon. Having a c a t i o n i c c h a r a c t e r , the carbon r e a d i l y accepts the i o n i c carboxyl group. At completion o f the r e a c t i o n , the isocyanate-carboxyl group d i s s o c i a t e s from the metal complex and the ligand resumes i t s o r i g i n a l s t r u c t u r e (Figure 9 ) .


416



Figure A ,

7. RXN w i t h F e ( A A ) « c a t a l y s t . Key(7 F e ( A A ) ^ ) : 3.0· Q , 4.5; ana , no c a t a l y s t . 0

-f"


,

1.5:


32.

GOLDSTEIN


Figure 8.RXN with Mn(AA)^ catalyst. Key(7 Mn(AA)^) : ^ , . 7 5 ; and Q , no catalyst. 0

Δ ,


417

.375;



Figure

9.

Reaction

mechanism


32. GOLDSTEIN


In the system studied, the order of reactivity for the acetyl acetonate complexes is: Mn > Fe > Cu In the late 1950*s, Weisfeld (4) studied certain metal acetyl acetonate in a polyester/disocyanate system. He found the order of reactivity of the metal complexes to be:


Cr> Cu> Co>Fe> V"?Mn Weisfeld's order of reactivity is directly opposed to the order studied in this work, although the same test method was used in both experiments. Weisfeld used monomeric isocyanate and poly ester while this study included carboxyl terminated polyurethane and prepolymerized isocyanate.(5) This distinction between mono meric and polymeric materials could explain the distinct contrast in catalytic activity. In line with this study, Mel lor and Maley proposed a list of diyglent ions and their tendency towards coordination. Here, Cu tends to chelate sponger than Fe which is a stronger chelating agent than Mn This neatly çelates to the second ionization potentials Cu = 20.2ev, Fe = 16.2ev, and Mn 15.7ev. (6) This also correlates to the catalytic activity of the metal ions used with acetylacetonate in this work. + 2

+

Conclusion The onset of this study includes promoting the allophanate reac tion in a polyjrethane-polyisocyanate syste.i. Using catalysts sited to influence this reaction (metal napthanates and octoates), test results show either (1) the allophanate reaction did not occur, or (2) the reaction did occur resulting in a weak linkage. Of interest, the allophanate promoting catalysts disrupted reac tivity of catalysts known to influence the isocyanate-carboxyl reaction. Further studies were done to isolate whether the base metal or the ligand dictates the catalyst's effectiveness. Re sults show the catalyst reactivity is dependent on the metal, ligand and chemical composition of the ingredients. Literature cited 1. Jorgensen, F., The Complete Handbook of Magnetic Recording; Tab Books, Inc: Blue Ridge Sumitt, PA, 1980; pp. 34-36. 2. Saunders, J. H. and K. C. Frisch. "Polyurethane Chemistry and Technology"; Robert Krieger Publishing Company: Huntington, NY, 1978, p. 197.



420

3. Allinger, Norman L., Organic Chemistry; Worth Publishing; N.Y., NY, 1976, p. 174. 4. Farkas, A. and G. A. Mills. "Advances in Catalysis and Related Subjects." 1962, 13. 5. Weisfield, L.B. "The Estimation of Catalytic Parameters of Metal Acetylacetonates in Isocyanate Polymerization Reaction." Journal of Applied Polymer Science; 1961, vol. 5, pp. 424-427.


6. Gould, Edwin S. Inorganic Reactions and Structures; Hole, Rinehart and Winston, N.Y., NY, 1965, pp. 342-3. RECEIVED

December 19, 1983


Polymeric Reactions in Magnetic Recording Media - American

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