Urethane Chemistry and Applications - ACS Publications - American

32 Specialty Urethanes for Solventless Coatings and Adhesives CLAIRE BLUESTEIN

Downloaded by UNIV LAVAL on October 30, 2015 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch032

Captan Associates, Inc., Rutherford, NJ 07070

This paper is a commercial survey covering recent developments i n urethane coatings and adhesives with reduced solvent contents. There are many aspects of urethane chemistry which make polyurethanes an i d e a l base f o r nonsolvent coatings developments. However, i n order to achieve p r a c t i c a l handling behavior for coatings & adhesives, modifications of c l a s s i c a l urethane chemistry are needed.

The major commercial market i n polyurethanes, foam, has always been predominantly non-solvent. Solvents had only entered the commercial picture i n urethanes i n the 1960's when early e f f o r t s to make s p e c i a l i z e d coatings out of state of the art urethanes required a free flowing form. The sizes and distribution of these and other polyurethane commercial markets have been discussed i n papers presented e a r l i e r i n t h i s symposium. In the United States alone, t o t a l urethane consumption i s presently over 2 billion pounds. The polyurethane derivatives used i n solventless coatings and adhesives systems form a r e l a t i v e l y small part of the market. There were about 50 m i l l i o n pounds sales i n 1979, however, the solventless segment can be expected to grow at more than the 10% rate expected f o r all polyurethane coatings & adhesives. Our problem i s that these numerous v a r i e t i e s of commercial polyurethane materials are very s l i p p e r y to define, p a r t i c u l a r l y i n a chemical sense. The name polyurethane attached to a coating or adhesive has a good public r e l a t i o n s image, one that generates the impression that i t has superior properties. Are a l l urethane coatings equal, either chemically or property0097-6156/81/0172-0505$05.00/0 © 1 9 8 1 American Chemical Society In Urethane Chemistry and Applications; Edwards, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

URETHANE CHEMISTRY AND APPLICATIONS

506


wise? C e r t a i n l y not. Does the purchaser or user of the coating or adhesive know this? Yes he does, but he does not always know how to select from what i s a v a i l a b l e . Further, how much polyurethane must a coating contain to exhibit so-called "polyurethane properties?" There i s no industry guide to answer these questions. T h i s has l e d many users of both solvent containing and solventless technology to h i r e t h e i r own polyurethane chemical experts and to produce t h e i r own multitude of proprietary variants. Classification We believe i t i s a good time to i n i t i a t e a comprehensive c l a s s i f i c a t i o n system. The system would be oriented to the commercial user and not i n tended to be l i m i t e d by chemical considerations, because i n the p r a c t i c a l world frequently more than one composition w i l l perform an equivalent job. We also believe that such a system would encourage a h e a l t h i e r i n d u s t r i a l growth s i t u a t i o n . The present ASTM urethane coatings c l a s s i f i c a t i o n (1) covers c h i e f l y the solvent types and i s thus an extremely l i m i t e d one from the viewpoint of the new developments i n the past ten years. Thus, we are proposing such a c l a s s i f i c a t i o n system here. The system presented appears broad enough to encompass a l l s p e c i a l i z e d i n d u s t r i a l urethanes, including elastomers & moldings and also the solvent containing urethanes. But f i r s t , we must define the base polyurethane. 1. D e f i n i t i o n . A polyurethane i s a polymeric product which has been formed by the r e a c t i o n of a d i or polyisocyanate and a d i - or polyhydroxyl bearing molecule (Equation 1). Equation 1 shows i n theory what might happen i f precise equimolar amounts of hydroxyl and isocyanate terminated intermediates were reacted. In the p r a c t i c a l manufacturing s i t u a t i o n i t i s more complex. Many of the i n t e r e s t i n g propert i e s and varying behavior of polyurethanes are f e a s i b l e because a wide range of mole r a t i o s can be used. We believe that the lowest molecular weight range of polymers i s about 600. Commercially a v a i l able materials below that range should be c l a s s i f i e d as intermediates.

In Urethane Chemistry and Applications; Edwards, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

32.

BLUESTEiN

507

Specialty Urethanes

η (0CN-C-—C-NCO) + η (H0-C--C?0H) - » R2

Re

R4

Rs

(1)

OCfi-JL/ L-?--.|ZoL^--?4-NHLc---C^OH NH

N


«2

R4

1

5

Re

R5

Rs

R2

R4/ n-1

Re

Rs

Polyurethane intermediate chemicals have been thoroughly studied and described with regard to the commercial markets ( 2 ) . They should be incorporated i n t h i s c l a s s i f i c a t i o n system, but we do not plan to devote much space to t h e i r description i n t h i s paper. However, the growing markets f o r polyurethanes have helped encourage the chemical manufacture of a wide v a r i e t y of intermediates. The isocyanates most r e a d i l y a v a i l a b l e are TDI, M D I and polymeric MDI, but hydrogenated MDI, IPDI, HDI, and t h e i r d e r i v a t i v e s are frequently chosen f o r use i n coatings. The most economical hydroxyl bearing intermediates are the polyether p o l y o l s based on polyethylene and polypropylene oxide, but there are also the polyadipate p o l y g l y c o l s (polyesterpolyols). These commodity materials are widely a v a i l a b l e because they form the basis of the major p o r t i o n of polyurethane foams. Yet, f o r the reasons stated above, there are presently many sources of s p e c i a l t y p o l y o l materials f o r syn t h e s i z i n g polyurethanes. 2 . Coreactive and prereacted. A l l polyurethanes can be subdivided into two broad categories, using the reactive isocyanate f u n c t i o n a l group to d i s t i n g u i s h them. Those that have a v a i l a b l e NCO ( f o r further reaction) can be c a l l e d coreactive and those that have e s s e n t i a l l y no pendant NCO are prereacted. Table I contains an outline and d e s c r i p t i o n of some of the a v a i l a b l e materials that f i t each type. I t should be noted that some of the prereacted urethanes do contain other chemical f u n c t i o n a l groups that may be a v a i l a b l e f o r non-urethane forming reactions. 3 . System design. A l l commercial coatings and adhesives are prepared with some p a r t i c u l a r applica t i o n system i n mind. The system design i s a highly




TABLE I

POLYURETHANE CLASSIFICATION BASED ON RNCO A, NCO

COREACTIVE TERMINATED

B, PREREACTED 1.

PREPOLYMERS

THERMOPLASTIC URETHANES SOLIDS

BLOCKED

PREPOLYMERS

BLOCKING PHENOLS OXIMES NCO

IN

AGENTS:

TERMINATED

IN

SOLVENTS OTHER

DILUENTS

2,

URETHANE

3.

URETHANE

ACRYLATE

HYDROXYL

TERMINATED

ALKYD

(ASTM I)

ISOCYANURATES 4,

URETHANE URETHANE

EPOXY


32.

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Specialty Urethanes

TABLE

509

II

SYSTEM DESIGN A, ONE COMPONENT


1.

2,

CONTAINS

COREACTIVE

A,

TO

BE

MOISTURE

B,

TO

BE

HEAT

CONTAINS A.

TOGETHER AND

C.

CURED

WITH

(INCLUDES B.

CURED

PREREACTED

TOGETHER

URETHANE

III)

URETHANE

SOLVENT

OR

INERT

DILUENT

ASTM VI) WITH

WITH

INTERMEDIATE

B, COMPONENT

ASTM

(INCLUDES

REACTIVE

PHOTOINITIATOR

TOGETHER

7

AST!! II)

(INCLUDES

DILUENTS

FOR

REACTIVE

UV

CURE

DILUENTS

AND CATALYST

FOR

AND/OR

HEAT

OTHER

CURE

TWO COMPONENT COMPONENT. R

A

1.

COREACTIVE

URETHANE

CATALYST

(ASTM IV)

2.

COREACTIVE

URETHANE

REACTIVE

INTERMEDIATE

3.

COREACTIVE

URETHANE

PREREACTED

4.

PREREACTED

URETHANE

CROSSLINKING

5.

PREREACTED

URETHANE

REACTIVE (FOR

URETHANE

(ASTM V)

AGENT

INTERMEDIATE

GROUPS

IN

FABLE


IV)

510



important f a c t o r , and when a user ignores t h i s , he w i l l not obtain s a t i s f y i n g r e s u l t s from the polyure thane coating. This i s not molecular behavior, but processing behavior. I n i t i a l l y we must d i s t i n g u i s h between one and two-component systems. In each of these categories we can further subdivide systems performance. A number of examples are shown i n Table II. 4. Backbone elements R-NC-Q-R'. In order to assess the general p r o p e r t i e s a polyurethane f i l m exhibits one must i d e n t i f y the backbone elements: the R and the R' i n the t i t l e formula. This harkens back to the o r i g i n a l intermediate chemicals. But, i t has been found i n the r e a l world of a p p l i c a t i o n s that some reasonably s i m i l a r combinations are v i r t u a l l y i d e n t i c a l . In Table I I I , therefore, we are able to estab l i s h some generalized categories. 0

TABLE I I I

R-N-fi-O-R* BACKBONE ELEMENTS R ATTACHED TO Ν

R ' ATTACHED TO 0

aromatic aliphatic non carbon

polyether polyester polycaprolactone hydrocarbon non carbon

However, i d e n t i f y i n g the general category of backbone element i s not the only thing that should be c l a s s i f i e d . We should be able to estimate the average molecular weight, or, r e a l l y better, the NCO to OH r a t i o used i n the urethane synthesis, the o v e r a l l fo

9, -N-C-0- i n an average molecule, and whether i t i s a l i n e a r , branched, or c r o s s l i n k e d polyurethane. These are more e a s i l y said than done. In pure chemical and model compound studies, these q u a n t i t i e s can be con t r o l l e d quite c l o s e l y , but i n the manufacturing k e t t l e , c o n t r o l , though not that precise, w i l l make a r e a l difference i n use properties. A r e a l i s t i c system f o r assessing c l a s s i f i c a t i o n of these f a c t o r s may take further time to develop. In current p r a c t i c e , a competent a n a l y t i c a l chemist derives most of t h i s information v i a spectrometry, usually i n f r a r e d and NMR. A d d i t i o n a l d e t a i l s of backbone elements are shown i n Tables IV and V.


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Urethanes

511

TABLE IV Bi Ε Χ A M l 1.1. S OF Downloaded by UNIV LAVAL on October 30, 2015 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch032

~

h -C—C-

J

~

R2

R4

(toiuylene )

(A)

( h ex ante t η ν 1 ene ]

(CH ) -

(B)

2

6

?j

(C)

( h e x a m e t h y 1ene

-(CH ) -N"'Y(CH ) 2

6

2

i socv v, n u r d t e trimer )

6

o=c

1=0 (CH ) 2

6

40*3 (polymeric

MDI )


512


Table IV shows some examples of what might be i n the molecule i n place of the generalized grouping R

l

-C R

R

3

C2

i n Equation 1.

Table Y shows some examples

R4

of what might be i n the molecule i n place of the gene r a l i z e d grouping -C---C i n Equation 1. 1


R

6

R

8

5. Other f u n c t i o n a l moieties. Other f u n c t i o n a l moieties that are i n the polyurethane coating or adhesive w i l l have a large e f f e c t on i t s p r o p e r t i e s . These exert both a q u a l i t a t i v e and a quantitative e f f e c t . T h i s means that as the r e l a t i v e r a t i o of urethane moiety diminishes, the coating w i l l behave more nearly l i k e the c l a s s of coating as defined by the major f u n c t i o n a l moiety content. Table VI provides a l i s t i n g together with each formula. 6 . Multiphase d e s c r i p t i o n . The nature of polyurethane requirements f o r a coating or adhesive makes i t highly u n l i k e l y that we are t a l k i n g about simple homopolymers. Thus we are more l i k e l y to have copolymers, segmented copolymers, g r a f t s , block copolymers, polyblends, networks, and even other complexes. Whatever i s i n the coating s o l u t i o n i s l e s s important than what happens when i t dries or cures to i t s f i n a l f i l m . What w i l l the morphology of the f i l m be? W i l l i t become c r y s t a l l i n e , have domains, form networks, or be amorphous? These would be good and h e l p f u l to know, but i t u n l i k e l y that anything beyond hypothesis can be determined f o r the commercial systems. Nevertheless, the numerous exc e l l e n t studies on model systems i n recent years Q ) have helped to shape the path of development f o r i n d u s t r i a l chemists to improve f i l m formation i n polyurethane coatings and adhesives. 7· Catalyst content. The c a t a l y s t content does make a s i g n i f i c a n t difference i n a p p l i c a t i o n s propert i e s of coatings and adhesives. T h i s i s e s p e c i a l l y true where the user i s seeking a long wearing f i l m . Where multistage preparations have been made, the cumulative e f f e c t s of c a t a l y s t s used i n each stage have been known to cause s t a r t l i n g r e s u l t s i n usage, because each stage was done independently of the others without being aware of p r i o r c a t a l y s t content. For urethane reactions, the c a t a l y s t s are e i t h e r m e t a l l i c or t e r t i a r y amine or a combination of both.


BLUESTEiN

32.

513

Specialty Urethanes

1 ABLE V


EXAMPLES

(A)

(B)

(C)

OF

-C---C-

CII-, -CirCIL-0-

0 0 •(CHp.OiCH^^O-C-ÎCHJ^'-O-CCH^./KCH.,)^-

•C-(CII;,) -0-(î-(CH ) 5

2

5

CH

(D)

•4-CH-CI!-.0-i-4-CH7CH—> X

T i l

81 2

(E)

CHoNHR •C-CH.

CH C— CH 3

3

CN

y

-CHoC-CMHR

COHÎCH=CH. (F) — C

CH < r

CH C-


514

URETHANE CHEMISTRY AND APPLICATIONS TABLE VI

OTHER FUNCTIONAL MOIETIES

0

NH-C-NH-

UREA


0 ESTER

C-C-OC-

0 C-O-C-O-C-

CARBONATE

ο EPOXY

-C-C-

OR - C = C - UNSATURAT ION

-OC-

CH =CHC2 '

ALLYL

CH =C2 '

VINYL

0

II

I

CH =CHC-0C2 '

ROSO - C 2 '

ACRYLIC

SULFONATE

0 -C-C-NHC-

AM IDE

-C-C-O-Si-0

SILICONE

-cIn Urethane Chemistry and Applications; Edwards, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

32.

BLUESTEiN

Specialty Urethanes

515


The m e t a l l i c c a t a l y s t most widely employed i s some form of t i n . However, some s p e c i a l i z e d uses of titanium, mercury, and even lead e x i s t i n industry. Based on my i n d u s t r i a l experience I do not recommend the use of t i n i n a coating or adhesive that i s de signed f o r long ageing or wearing. I f c r o s s l i n k i n g or other f u n c t i o n a l moieties are designed i n t o the coating, most frequently the same classes of c a t a l y s t s are employed. However, i t i s f e a s i b l e to expect that a manufacturer might use another c a t a l y t i c material. With respect to catalysts, i d e n t i f i c a t i o n and c l a s s i f i c a t i o n should be easy. 8. Nonresinous compounding ingredients. Τ hough the polyurethane r e s i n or blend with other r e s i n s determines the key properties of a coating or adhe sive, i t s a p p l i c a t i o n u t i l i t y i s not evident u n t i l the proper compounding ingredients are added. The supplier may or may not add a l l of the necessary compounding ingredients and thus, one might argue that these may not be necessary to include i n a c l a s s i f i c a t i o n system. Nevertheless, i t should be pointed out that i n current applied polyurethane coatings and adhesives, the polyurethane r e s i n con tent can range anywhere from 1 5 to 9 5 $ · Further, i t requires much probing on the part of the user to determine what l e v e l he i s buying. Evan a guess based on p r i c e may be misleading. We f e e l that t h i s percentage should be an important part of an industry designation. The classes of compounding ingredients that may be present as follows*. A. Diluents - solvents, water, monomer, crossl i n k i n g agents B. F i l l e r s , r e i n f o r c i n g agents, flame retardants C. Pigmentation and gloss modifiers D. Surfactants and coupling agents E. S t a b i l i z e r s and antioxidants Commercial materials used are selected from those that are a v a i l a b l e f o r compounding use with a l l of the major p l a s t i c s materials (4). The r e s i n manufacturer normally takes r e s p o n s i b i l i t y f o r designating to formulators which materials are more compatible with his products. But the formulator of a coating i s frequently l e s s informative on which of these classes of additives are present. A yes or no answer to each c l a s s , A through E, should thus be included i n the comprehensive d e s c r i p t i o n .


516



Review We have shown eight f a c t o r s which could be used to characterize polyurethane coatings and adhesives: Intermediate chemicals, coreactive and prereacted, system design, backbone elements, other f u n c t i o n a l moieties, multiphase d e s c r i p t i o n , c a t a l y s t content, and compounding ingredients. D e s c r i p t i v e terms f o r subcategories have been given as examples under each f a c t o r . The tabulation and organization of a more complete set of terms can now be set up and appropri ate code l e t t e r s and numbers assigned so that industry could be encouraged to c l a r i f y to i t s customers the products that are a v a i l a b l e . Much of the terminology i s presently i n use informally. We hope that a good system w i l l develop communication which encourages users to f e e l they have a sensible way to s e l e c t an appropriate product. Conclusions We have described the current state o f the industry market i n solventless polyurethane coatings and adhesives. There i s a wide v a r i e t y of s p e c i a l t y materials a v a i l a b l e , a l l s e l l i n g f o r widely d i f f e r e n t p r i c e s and c o n s i s t i n g of a wide v a r i e t y of chemical compositions. We are proposing a c l a s s i f i c a t i o n system which could form a guide to the purchaser and user of these products. We hope that such a system could help eliminate confusion that presently e x i s t s among many purchasers of these products. L i t e r a t u r e Cited 1. 2.

ASTM D-3726-9, "Annual Book of ASTM Standards," American Association for Testing and M a t e r i a l s , P h i l a d e l p h i a , P A . , 1980, V o l . 29. a. P i g o t t , K . A . , Polyurethanes, "Encyclopedia of Polymer Science and Technology," Interscience D i v i s i o n , J . Wiley, New York, 1969, V o l . 11, pp. 506-563. b. B u i s t , J.M., Crowley, G . P . , & Lowe, Α . , Polyurethane Technology, "Encyclopedia of Polymer Science and Technology," Interscience D i v i s i o n , J . Wiley, New York, 1971, V o l . 15, pp. 445-479.


32. BLUESTEIN

3.


4.

Specialty Urethanes

c. Cooper, S . L . , Seymour, R.W., and West, J.C., Polyurethane Block Polymers, "Encyclopedia of Polymer Science and Technology," Interscience Division, J . Wiley, New York, 1976, Suppl. I, pp. 521-543. d. Patton, J.T., Chemtech, 1976, 6, pp. 780-4. Cooper, S.L. & Estes, G.M., Eds., "Multiphase Polymers," American Chemical Society, Washington, D.C., 1979. Agranoff, J., E d . , "Modern Plastics Encyclopedia." McGraw-Hill Publication, New York, 1979, pp. 152229.

RECEIVED April 30,

1981.


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Urethane Chemistry and Applications - ACS Publications - American

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