I/Ec
September 1956
One foam manufacturer's timetable for rigid, foamed-in-place urethanes
URETHANE PLASTICS
-
Polymers of Tomorrow
BASIC
isocyanate chemistry goes back to 1848, when Wurtz prepared methyl and ethyl isocyanates by reacting potassium cyanate and alkyl iodides. T h e following year he hydrolyzed these isocyanates, forming methylamine and ethylamine, now considered a classic work. Industrial research first went into high gear in the late 1930's with Bayer's work in Germany on urethane formation : R-N=C-O isocyanate
+ alcohol HORl+ R--NH-CO-O-R1 urethane
T h e hydrogen atom from the alcohol's hydroxyl group adds to the nitrogen atom of the isocyanate. This is the funda-
The Society of the Plastics Industry has adapted the name "urethane foam" for what used to be known as isocyanate, polyurethane, or polyester foam.
mental reaction in the field of urethane chemistry. When the simple alcohol is substituted with longer chain materials bearing a multiplicity of hydroxyl groups, such as polyesters and polyethen, and the isocyanate is replaced by a diisocyanate, chain extension and cross linking result by this reaction, producing poly(esteror poly(ether-urethanes). urethanes) Depending on the presence and type of additional ingredients in the polymerization recipe, solid or foamed polymers result, ranging in consistency from liquid elastomers to rigid solids. Bayer workers found that rigid urethane plastic foams could be produced with relatively high strength and a wide range of elasticity. Prior to World War 11, they had a product with compressive strength of 140 lb./sq. in., heat resistance to 212' F., and a specific gravity less than 0.1, produced from toluene diisocyanate and a polyester prepared from adipic acid, trimethylolethane, and ethylene glycol. In this country, Du Pont was issued basic patents during 1937-39 covering the
s of pounds sol t's the urethane Once atmost without consideration as a commercial materiat, isocyanates today are used to make a great variety of useful products: foams, fibers, coatings, adhesives, textile auxiliaries, and leather tanning agents, to name a few. Some marketing crystal ball gazers talk in terms of a 100 million pound urethane foams' market in the United States within 5 years. This i s only a guess, not based on broad market experience, for these products are simply too recent an innovation. The flgure has as much chance of being Coo low us it hos of being too high. Most authorities agree that 1956 produclion will double 1955's, and 1958 figures shouid be 1Wold or more over last year's rate. The editors know that I&EC's readers are keenly interested in this newer material, which i s so filled with potential. More than a dozen o# the leading isocyanate, polyof, and finished foam producers have helped J&EC's editors present this detaiied picture of rhe urnthanes to you.
VOL. 48, NO. 9
SEPTEMBER 1956
1383
reaction of diisocyanates and polyols, and polyamides. United States manufacturing interest in this field was not kindled to any marked degree until the postwar years, when Allied Military Intelligence reports showed the potential of the German ideas and just how far they had advanced by war’s end. When the Cnited States Air Force indicated its interest in rigid urethane foams by placing development contracts with several organizations, urethane product research in this country went into high gear. At that time work was being conducted by D u Pont, Monsanto, Princeton University. Goodyear Aircraft, and Lockheed Aircraft. Lockheed chemists developed and patented a foamed-in-place rigid polyurethane technique which is one of several being used today; but, in 1950 company officials decided to have a licensee further develop and produce foam products using this technique. Here American Latex Products Co. entered the picture. By 1951 urethane protective coatings, and later flexible urethane foams, were a commercial reality in Germany through Bayer’s continued research and development. Du Pont and Monsanto were producing pilot plant quantities of diisocyanates by 1950 in the United States, and other companies such as National Aniline and B. F. Goodrich soon initiated or expanded their research programs. Since Bayer had made the most rapid advances in the field, several American companies obtained Bayer license agreements. After long negotiation, in 1954 Bayer and Monsanto jointly formed Mobay Chemical Co. Together with Lockheed’s and Du Pont’s. Mobay’s licensees comprise virtually the entire industry.
1 384
Most foam manufacturers arc licensed by Du Pont, including many of those manufacturing under Mobay license arrangements. Two companies have made it known that they are licensed by all three: Nopco Chemical Co. and .American Latex Products Co. Another foam producer, Hudson Foam Plastics Corp., has been manufacturing a polyester foam in this country since 1953, and is attempting to establish a patent position for its particular type of foam. Aside from supplying polyesters and isocyana tes, Mobay furnishes machinery (based on original Bayer developments) for foam production to its licensees, while National Aniline is supplying blueprints of foam machines developed in its Buffalo laboratories to interested customers. No one has to ask where urethane plastics’ markets are. Much publicity has been given to their foams-an application which probably will prove to be the major tonnage consumer. There are many other significant urethane-based products: surface coatings, fibers, liquid and solid elastomers, electrical insulation, fabric finishes, adhesives, tanning and waterproofing agents, small drive belts, oil and abrasion resistant tubing, and special grars, gaskets, diaphragms, and valves.
Reaction Technology I s Complex Vrethane polymer formation is based, rather simply, on the avidity of the isocyanate group for active hydrogen. The multiplicityofways in which this reactivity may be used to advantage is what makes the technology of urethanes complex. Fundamentally, a polyurethane results from the reaction between a diisocyanate and one or more polyfunctional reactive hydrogen compounds. These latter in-
INDUSTRIAL AND ENGINEERING CHEMISTRY
gredients may include low molecular weight (500 to 4000) blocks of hydroxylterminated polyesters or polyethers, modified castor oils, and/or simpler substances such as water, diamines, glycols, and triols. The combination of a polyester 01 polyether with a diisocyanate is the foundation of polyurethane technology and leads to a polymer chain containing numerous urethane groups:
60. , , . O B + OCN-R--NCO
go.. , .U-R-[U..
-P
. .U-R]z-NCO
(1)
0
6 It
where U = urethane = (N-C-0) and the labile hydrogen has been circled If water is included in a formation it will react with isocyanates, yielding carbon dioxide and an amide which, being very reactive, quickly unites with another NCO group forming a urea linkage :
K--N-8
-+
\
COI t
+ K--N
6 6
These latter reactions are of primary importance to foam technology because the carbon dioxide evolved is the blowing agent which generates the foam. The reactions shown in Equations (1) and (2) yield linear polymers which would be thermoplastic. Cross linking to a cured
Household products
Quilting and other insulation
Y
to suit the customer
manufacturers can tailor state can be effected in several ways. One technique, highly important to solid polymers, takes advantage of the less active, labile hydrogen of the urea and urethane groups, and by heating or catalysis forces them to react with excess isocyanate included in the formulation :
o=c @k-R? T h e cross link so formed is a n allophanate when the urethane group is involved, or a biuret in the case of urea. I n the manufacture of foams and some solid polymers, a cross-linked network is developed by starting with a polyester which contains more than two reactive OH groups (via a triol built into its structure) :
Du Font, Mobay, and t t o p c ~
setting, elastic or brittle, soft or hard, resilient or loggy, solid or foam. Take, for example, the variations possible with just one of the possible starting materials used, polyesters. Generally, the polyester is made from dicarboxylic acids, glycols, and usually tribasic alcohols, and is hydroxyl-terminated. These acids are used : adipic, phthalic, sebacic, succinic, oxalic, and ricinoleic. Glycols used include : ethylene, diethylene, propylene, and butylene glycols, and 1,4-butanediol. Triols used are glycerol, trimethylol propane and ethane 1,2,6-hexanetriol, and 1,2,4-butanetriol. The molecular weight, amount of, and distance between branch points, and structure of the hydrocarbon portion of the polyols and acids are a few of the more important features of the polyesters which
affect the nature of the urethane polymers. Low molecular weight or a large amount of branching leads to more rigid structures, while increasing molecular weight and distance between branching leads to softer polymers. Inclusion of inflexible aromatic hydrocarbon between ester links stiffens the polyurethane. The particular diisocyanate employed in a formulation has a smaller, but still vital, effect on the properties of the finished polymer. While the only isocyanate now used in large-scale commercial quantities in this country is toluene diisocyanate (primarily the 80/20 isomeric mixture), other isocyanates have been thoroughly studied [IND. ENG. CHEM.48, 794 (195G)l and may go into commercial products soon, particularly in the application of solid polyurethanes.
Here’s the w a y flexible urethane foams change with formulation, even with the same ingredients
A
Batch, Parts by Weight B C
n
Formulation 80/20
OH
OH OCP;-R--U.
,
. .U-R--U.
,
. , .OH
OH U-R-L’.
.,I’
H 0’
(41
T h e physical properties of the finished urethane polymer depend on the nature and ratios of the starting materials and can be varied widely. T h e large variety of raw materials which can be used enables the preparation of polymers which are thermoplastic or thermo-
TDI
Polvester “A” Dispersing agent Water N-methylmorpholine or Dimethylethanolamine Physical Properties Density, lb./ cu. ft. Tensile strength, p.s.i. Compression set, o/o Compression to produce 25 % deflection, p.s.i. Resilience, o/o Elongation, %
45 100 4.2 6 .O 2.5
39 100 2 .o
5 .O 2.7
(1 .o>
(1 .O)
1.6 19
10 0.8 25 398
39 100 1.o 2.5 1.3
31 100 1.o 1.8 1.3
(0.5)
(0.5)
25
3.1 29
10
5
3.7 30 10
1.6 25 400
1.9 25 350
2.1
0.9
22 450
VOL. 48, NO. 9
SEPTEMBER 1956
1385
with a diol, triol, diamine, or water to make a finished polymer. The simplest way to handle the polymerization is to mix all the ingredients more or less simultaneously, a n ideal solution that is not always practical. Because of effect on competing reactions, manufacturing technique has a large influence on the properties of the products. The latter two methods above are applicable to foam technology, while all are useful in preparing solid products. Polyether foams are somewhat more complicated to process than polyester foams. They can be made successfully only by partially reacting the isocyanate and glycol as a separate step and then reacting this product with water and catalyst to produce the foam. This technique necessitates the handling of viscous materials and requires slower cures than polyester foams.
Coloring Techniques
The Foam Spotlight The various reactive ingredients may be combined in several ways. 4 thermoplastic “millable gum” is made by reacting a polyester or polyether and water with a nearly equivalent amount of diisocyanate. This gum stock can be compounded on a rubber mill u i t h an
additional amount of a reactive diisocyanate and subsequently cured by heating. X second method is to prereact the poly01 with a considerable excess of diisocyanate to yield a liquid “prepolvmer.” This can then be treated
Courtesy Dayton Rubber Co. Finished flexible urethane foam a t the end of the production cycle. capacity of this imported machine i s 8 million pounds
1 386
INDUSTRIAL AND ENGINEERING CHEMISTRY
Annual
Foams are divided into two major groups: flexible and rigid, including semirigid. The flexible field has both rubber and plastic products in competition, while the rigid group is composed of lightweight woods (balsa), as well as honeycomb and other cellular plastics. Urethane foams are the latest plastic materials to enter the field and are becoming increasingly applied. Urethane foams can be made with an almost infinite number of raw material combinations-each product with different properties from the next. While this great flexibility of characteristics is actually urethane’s greatest virtue, it is too often used to cloud the picture. It may not be incorrect to speak of these foams in general as having or lacking a certain qualitv, but it may often be misleading. A particular urethane foam could have many times the resistance to a certain test than that of a sister urethane which does badly on it. The criterion is the individual formulation. General attributes of urethane foams include light weight, high heat and electrical insulation value, extreme toughness, and resistance to vermin, rot, water, and many chemicals and solvents. Aging resistance is very good, and while many urethanes yellow on aging, it is not a sign of physical deterioration in this case L4ost urethane materials can be easily and effectively colored. and have fine radar, radio. and x-ray transmission properties. These foams are available in a wide range of densities. T o illustrate their strength one urethane foam 1 , ’ 3 ~ the density of water (lighter than foamed rubber, foamed vinyl, or cellular sponge) has tear resistance many times that of foam rubber. But rubber’s elongation qualities are generally superior. Sound and vibrationalabsorption ofurethane foams are equal or superior to those
of most known materials a t standard frequencies. A typical urethane formulation has a sound absorption coefficient of 0.99 a t 2 lb./cu. ft. foam density, which varies to 0.22 a t 10 1b.jcu. ft. Heat resistance is to above 250' F. (some urethane manufacturers claim as high as 400" F). At the opposite extreme many urethane foams cannot be shattered a t -50' F.? while some producers cite results as low as -80' F. Typical urethane formulations have far better resistance than natural rubber to petroleum ether, benzene, and lubricating oils, although rubber is superior in resistance to acetone and ethyl acetate. r r e t h a n e foam formation involves the liberation of carbon dioxide within the body of the mixture. This release can be well controlled? and a high degree of cell size and density uniformity realized. Most foam rubber is not foamed chemically. I n the widely used Dunlop process air is mechanically beaten into a latex made of varying amounts of natural and synthetic rubber. Although bubble control can be difficult: a major foam rubber manufacturer states that latex foam density can be controlled within &2.5y0uniformity. In the Tallalay process for foam rubber, a chemical agent in the mix releases a gas, leading to excellent density and bubble control. Both open- and closed-cell urethane foams can be made within wide limits of density, flexibility, and mechanical strength. In contrast, foam rubber's flexibility is largely dependent upon density and the quantity of butadiene: resin used in the mixture.
Each flexible foam has its selling points
. ..
Foam Rubber Advantages
Disadvantages
High resilience Flammability Low price Low chemical resistance Long production background and experi- Oxygen and ozone deterioration (direct ence sunlight) Good elongation Low tensile and tear strength Easily molded Natural rubber price fluctuation Customer acceptance
Foamed Vinyl Advantages
Disadvantages
Low price Easily heat sealed or embossed Easily fused electrically Guod chemical resistance (except organic solvents) Flame retardance Resistance to tearing, aging, and abrasion High thermal insulator Good tensile strength
Slight objectionable odor Low compression set resistance Limited temperature performance range Solubility in chlorinated hydrocarbons and ketones; attracted by other organics Poor low temperature resilience Dimensionally unstable during aging
Urethqne Foam Advantages
Disadvantages
Wide temperature and density range Chemical resistance Tear a n d abrasion resistance Good adhesion High compression-densityratio Downward price structure Good thermal insulating properties Goad tensile strength Easily heat sealed and embossed Easily fused electrically
Yellowing (but no deterioration) with age Recency of development
Not All Foams Are Flexible Disregarding degree of rigidity, flexible and rigid foamed urethanes can have similar chemical and physical properties. The contrast between rigid urethanes and The polystyrene foams is interesting. latter cannot be used with temperatures over 150' F., and have very poor solvent resistance-two points in which many urethanes excel. But there's one place where polystyrene wins hands downcost. Until recently only preformed polystyrene foam was available. This forced a user to buy large sheets and then fabricate his design. Within the past few years a new polystyrene material was introduced which could be formed in place. This material, in bead-like form, ivas inserted in the cavity to be filled, then heated to fusion temperature. Rigid urethanes are most often used as foamed-in-place, two-component liquid systems. But Where Are Foamed Urethanes Being Used? The scores of products presently being manufactured from urethane foams in this country represent only a fraction of European applications. But as we be-
coavudrac. is o h tha d.tidin@fscrsr. butEach rigid ryrtpm had advanlager
..,
,
Potystynne Foam Advantages
Disadvantages
High moisture resistance Low price Odorless Vermin resistance Low thermal and electrical conductivity Easily machinable High strength-to-density ratio
Poor solvent resistance High temperature (1 50" F.) deterioration
Rigid Urethane Foam Advantages
Disadvantages
High moisture resistance Mechanical mixing and spray e q u i p Odorless ment only recently available Resistance to vermin, fungus, oils, and Recencyofdevelopment many chemicals Outstanding thermal and ekctricgl insulation Radar and x-ray transmitter Adherewe to all nonwaxy, nongreasy surfaces when foamed-in-place Easily machinable
VOL. 48, NO. 9
SEPTEMBER 1956
1387
DllSOCYANATE PREPARATION
nitrate Mixture of mononitrotoluene isomers crystallization
nitrate
1
1
I
I
807, 2,4-Dinitrotoluene
o-Nitrotoluene
+-+I
crystallization I
20% 2,6-Dinitrotoluene
I
nitrate
nitrate
I
reduce
I
phosgenate
I
reduce
I
phosgenate
bimolecular reduction
reduce
I
I
react with formaldehyde
benzidine rearrangement
I
I
phosgenate
phosgenate
condensation
I
phosgenate
1388
INDUSTRIAL AND ENGINEERING CHEMISTRY
come increasingly adept a t modifying basic formulations, authorities agree that this number will snowball. Immediately seen is urethane foam's application in the aircraft industry. Cored, flexible urethanes are being introduced very successfully for airplane seat cushioning. Having both long life and weight saving attributes, some urethanes have ideal ventilating and seating properties. Weight saving alone is said to cut Los Angeles to New York costs $100 per flight. Rigid urethane foams are used in actual aircraft construction. Light weight, foamed-in-place urethanes not only increase the rigidity of control surfaces by filling cavities in ailerons, rudders, and similar parts, but also their buoyant effect helps keep downed aircraft afloat. Some urethanes are used for aircraft insulation. The well-publicized near-perfect radar transmission properties of urethane foams allow them to serve well as materials to fabricate radomes for aircraft and guided missiles. The same factors making flexible urethane ideal for aircraft seats would make it fine for auto seats and other cushioning. Some authorities feel that these foams will largely replace sponge rubber and vinyl foams in a major part of the automotive industry. Information is that the end cost of urethane foams is equal to or less than that of its two competitors. Most auto manufacturers are noiv specifying foamed urethanes for crash padding. Lt'ith increased public safetyconsciousness this trend will continue, and it is believed that all automotive manufacturers will incorporate these crash pads in 1957 models as optional equipment. Crash pads other than dash and sun visor types will be introduced. Automotive people are showing interest in these foams for interior insulation and other uses not yet publicized. Inside the home these foams are having ever-increasing application. The great resilience of some urethane foams when used as carpet underlay makes any rug feel luxurious. This use has great potential, especially if a foamed-in-place technique is developed for applying the underlay directly to the rug by the manufacturer. Great strength and tear resistance help make it a n ideal underlay. Sheets from l,'g to '/4 inch thick are competitively priced. Urethanes are expected to find wide use as furniture upholstery. A complete spectrum of seating characteristics should be available soon. In addition, most forms are self-extinguishing, and cannot be ignited by a burning cigarette. Several companies have adopted urethane foams, especially for casual and outdoor lines. At present, the low density products are preferred, and even here the foams are cored for softness.
When slit into very thin pieces, the foam can still act as a n excellent heat insulator. Coat manufacturers are expected to make wide use of this property for linings. T h e thin films can he hand or machine sewn, and manufacturers claim that jackets with as little as a 1 / 1 ~ inch thick urethane foam liner are warm enough for Arctic temperatures. Detergents and cleaning solvents do not attack some urethane, leading to its use in shoulder pads that need not be removed \vhen the garment is cleaned. Urethane sponges are much tougher than conventional types, combining strength with resilience. However, current major urethane foam formulations do not have the water absorption properties of the cellulosics, although special formulations may approach them. In both tear resistance and resistance to rot and vermin, urethane sponges are generally superior. Expected markets are household and industrial sponges, mops, and related products. Foamed urethanes will find application as acoustical material. Preliminary tests and trial installations show them to be as effective a t most frequencies as any other material on the market. Urethane foam is presently more expensive than conventional material, but other factors often lead to a lower finished application cost using the urethanes. These factors are ease of fabrication and installation, and the use of le% urethane material per unit. Many urethane foam applications are based on its excellent adhesive and bonding properties. Aside from its use to fill aircraft structural cavities, it is used as a low-density core in p l y o o d manufacture. Rigid foamed-in-place urethanes again simplify a n operation often requiring a costly bonding and curing process. These are only a few of the applications of urethane foams. Blades for wind tunnels, aircraft models, crash helmets, sports equipment, defense usesthe list is long, and additions are accelerating. Urethane foams show great promise, but the dominance of foamed latex together with the much smaller tonnage of foamed vinyl is far from over. A new product is unlikely ever fully to replace the older forms, except in those applications in which it has extreme advantage, either in chemical and physical properties, or in reduced costs. Cutting fabrication costs is one of the great advantages of rigid, foamed-in-place urethanes, and is a major reason why they are expected to find increasing use in assembly line manufacture of automobiles and appliances, and in related operations such as railroad refrigerator car fabrication. Some authorities feel that urethanes are likely to replace older forms to a considerable degree as soon as toluene
Courtesy American Latex Products Co.
Both rigid and flexible urethane foams find application in the aircraft industry. Here Lockheed Constellation seats are fabricated from urethane foam diisocyanate (TDI) prices drop below 65$ per pound. Today’s price ranges from 85b per pound up, n i t h no expectations of a 2 5 7 ~drop in the near future; yet finished urethane foams are very competitive on a unit rather than pound basis. Further development and applications of urethanes will be forthcoming, as realization of new advantages arrives and is utilized by developers.
based wire coatings is the relative ease of making soldered connections. Unlike conventional wire enamels the urethane products do not require wire ends to be stripped and cleaned before soldering. The elimination of this step saves time, trouble, and money for the manufacturer. Mobay’s technical bulletins suggests the following as simplified typical wire enamel formulations:
What about Urethane Coatings?
Formula A Isocyanate blocked adduct Polyester Cresylic acid Methyl glycol acetate Butyl acetate Toluene
Urethane’s use in both electrical insulating and protective and decorative coatings has received widespread acclaim for a long Tvhile in Europe, and recently in this country. .4pplication in electrical insulating coatings is apparent from urethane’s properties. These coatings protect well. even under high temperature and humidity conditions. Used as impregnating varnishes for woven glass and cotton fabric, dip varnishes for paper and foil, they are currently the most \videly used magnet wire coatings in Europe, and are receiving detailed attention in this country’s electronic and television manufacturing industries. One big advantage in using urethane-
% 33 17 21
14 3 ~
12 100
7i 32.5 15.5
Formula B Isocyanate blocked adduct Polyester Pol yamid Cresylic acid Hi-flash naphtha
2
35 15 __ 100
Great interest in urethane-based protective coatings is being shown in this
Bond strength of urethane foams Foam density, Ib./cu. ft. Bond strength,. p.s.i. (without special surface preparation) To aluminum To glass To steel To wood
2
5
10 9 12
27
17
10
20
25
56 50
29 29
62 62
158 142 146 170
VOL. 48, NO. 9
SEPTEMBER 1956
1389
5% olyurethanes will be one of the highlights of the program a i the 130th National Meeting of the American Chemical Society, Sept. 1 6-2 1, 1956, Atlantic City, N. J. The Division of Paint, Plastics, and Printing Ink Chemistry will present a 22-paper symposium on isocyanate polymers. Germany’s Otto Bayer, pioneer in this field, will speak on “Polyurethane in New Plastics.”
country, in view of the product’s acclaim in Europe. Field tests have been very successful, and proponents consider them equal or superior to any type of organic coating except in heat resistance? where only silicone coatings are superior. Products can have extreme hardness. flexibility, and very high resistance to impact, solvents, and abrasion. Americans report these coatings are finding much use in Europe under severe conditions. A s a n illustration, they say that! in one sulfuric acid plant, urethane coatings, after a year’s exposure to sulfur di- and trioxide fumes at elevated temperatures, still had good gloss and were adequately protecting against corrosion. These coatings are not limited to metal application-similar coatings are formulated for wood. plaster, concrete. rubber, and paper. Air-dry and baking finishes are available, and both clear and pigmented coatings are formulated. Most dry pigments are suitable for dispersion. One supplier suggests that the folloiving pigments may be used Ivith urethanes :
Red Orange Yellow Green Blue Black Brown White
.
Cadmium red, iron oxide red, molybdate red Cadmium orange Cadmium yellow, yellow iron oxide Chrome oxide green, phthalocyanine green Manganese blue, ultramarine blue, phthalocyanine blue Iron oxide black? bone black, some carbon black Iron oxide brown, ocher, umber Rutile titanium dioxide, lithopone, antimony oxide
Various purpose vehicle modifications may be made with proper plasticizers. Dependent on the degree of modification, some desirable property, such as extreme hardness, may be lessened. Here’s Mobay’s simplified formula for a typical urethane coating: 1390
Pigment Isocyanate adduct Polyester B u t y l acetate E t h y l acetate Toluene
22 28 16 12 11 11
of its toxic properties, and, as yet, no completely satisfactory replacement has been developed.
F-I-P-Cost-Cutter
I
100
Most manufacturers offer complete technical data sheets to interested parties.
Other N o n f o a m e d Uses A r e o n the Way
Coatings are only a fe\v of the nonfoamed urethane products. Some of the more \videly used applications include adhesives, rubber, and, in Europe. as a molding material. Adhesives. The combination of polyol and diisocyanate is used for bonding a variety of materials such as paper. glass, tvood, aluminum. and resins to themselves and to each other. Both castor oil and polyesters are used, and one of the recommended diisocyanates is diphenylmethane-4,4’-diisocyanate. Excellent bonds are obtained Lvith thr application ol‘ only contact pressure and room temperature cure. according to industry officials. Rubber. IVhile several technical problems related to high-temperature properties and urethane rubber-ordinary rubber adhesion exist, urethane rubber shows great promise. I n Europe, Bayer‘s “Yulkollan“ cast elastomers have found Pont’s \vide industrial use. Du “Adiprene B” resembles commercial diene hydroca.rbon polymers, but is much tougher. stable TO storage. and soluble only in certain polar solvents. Properly compounded vulcanizates have high tensile strength, good resilience, lowtemperature properties, and resistance to oxygen, ozone, and abrasion. Tires manufactured with urethane rubber wear far longer than convcntional tires. Manufacturers feel that the great application \vi11 not be in tires to last 100>000miles? but in thinner 40,000-mile tires, which would develop less heat and be far safer and more resistant to blowout. Urethane rubber should also find application in solid rubber tires for industrial vehicles such as fork trucks. Molding Compounds. During World \Var 11, the Germans developed an outstanding urethane injection molding compound (Perlone U) based on hexamethylene diisocyanate, which became a substitute for nylon. The Germans found that polyurethane compounds used in injection molding produced materials Tvhich had higher moisture resistance, abrasion resistance, and tensile strength than conventional materials. However, American manufacturers have shied aivay from this isocyanate because
INDUSTRIAL AND ENGINEERING CHEMISTRY
Flexible urethane foams dominate the picture today. but rigid foams account for an ever-increasing volume of business. Foamed-in-place urethanes have proved very versatile as techniques have been perfected. The greatest single attribute of the foamed-in-place product is its ability to cut fabricating costs. For example, the General Motors “Frigifrater” railway car’s insulation is foamed in less than 5 hours. Sormally, using conventional insulation application techniques, 6 to 7 days are required. Diisocyanate and resin may be combined in two Lvays to form the rigid foam-merely by mixing the tclo ingredients together with Tvater and catalyst; or by reacting the dry resin with an excess of diisocyanate: forming a “prepolymer“ to which can be added Lvater and a basic catalyst. Tertiary amines are often used as catalysts in urethane formation. I n both systems one or more surface active materials may be added to regulate miscibility and control bubble formation. Either technique can be utilized as a two-component, foamed-in-place system. The first method (commonly called the “one-shot” method) calls for blending a highly branched polyol with a diisocyanate, catalyst? water: and modifiers (if any). The ingredients, other than the diisocyanate, may be masterhatched Lvith the polyester; or \vhen a continuous mixer is used, the polyol and catalyst-\vater mixture may be metered separately to the mixing head, and there mixed simultaneously. \+’hen handmixed: several minutes are required to achieve a uniform blend of the fluid isocyanate and viscous polyol masterbatch. As blending takes place, the reactions begin, the mixture becomes lvarm Xvith an attendant momentary decrease in viscosity. and foaming begins. As in all foam technology, the reaction rates must be so regulated that the polymer \vi11 be viscous enough initially to hold the gas bubbles in their desired size: yet retain sufficient fluidity a t the end of the foaming to allow full expansion without splitting the foam. The “batter” is poured into the cavity. filling it with foam in a few minutes. Much heat is evolved, and the foam sets u p quickly. The second, or ”prepolyrner” method was independently developed by Du Pont and Bayer. As the prepolymer has been made by reacting the polyol lvith a considerable excess of diisocyanate, it can be regarded as the resin terminated Ivith reactive N C O groups. Dur-
ing foam formation these groups, under the influence of a basic catalyst, react with lvater (as does the free isocyanate in the first method) splitting out carbon dioxide and tying the resin molecules together through urea linkages. During the foam expansion, the viscosity of the
that lend themselves to automation. The automotive industry is making use of this concept, according to reports. Price depends in large part on raiv material cost: especially isocyanate cost. Typical manufacturer’s breakdowns for different poly01 systems look like this:
Polyester, 50C/lb. 1
Resin
70
Toluene diisocyanate (95c/Ib.)
30
Catalyst, etc. Approx. raw material cost/lb.
.. ..
cost
c
Pol yet her, $l/lb. cost
$0.35 0.285 0.015
70 30
..
$0.70 0.285 0.015
0.65
..
1.00
prepolymer foams generally rises more slowly than the viscosity of the foams from the first method. The prepolymer foam also blows more slowly and develops less heat because much of the exothermal heat has been removed during the prepolymer preparation. This second method produces a polymer of greater chain length and. consequently, a foam with some different properties. Because of the lo\ver temperature reached, cure rate is sloiver, so that the foaming is usually followed by a heat treatment o r “post cure” to obtain the best physical properties. I t is impossible to rate one system over the other-the choice is often one of applicability. Du Pont points out that basically properties are very similar. T h e prepolymer is easier to handle Lvhen one must resort to hand mixing in small batches, and was the first system used by Bayer. As soon as they developed automatic mixing equipment and machinery for continuous foaming, Bayer engineers went over to the one-shot system. which, under machinc operation, they felt gave better control and a Lvider property range.
Don’t Figure Cost/Pound Everyone asks-what \vi11 it cost? I t is common kno~vledge that urethane foam production has been increasing beyond the expectation of many observers during the past few years. This is equally true of nonfoamed applications. As production continues to rise. hopes are that urethane foams \vi11 sell at approximatel). $1 .00 per pound in large quantities ivithin the next year. Some manufacturers are not so optimistic, but others are planning to achieve the goal. But price per pound figures do not tell the entire story. Interest should be centered around the finished per-unit cost. Urethane foams often have loxver application costs: and ivith a much lower density, it is very realistic to say that a pound goes a long \vay. >loreover, and far more important, urethane foams permit bold neiv types of assembly
c
Castor Oil 18c/lb. cost
50 50
..
$0.09 0.475 0.015
..
0.58
The important question is hon. far does a pound go? The key is per-volume cost. The loivest known figures, not taking coring into account, give minimum densities as : Foam rubber Foamed vinyl Foamed urethanes
5 Ib. ’cu. ft. 4 Ib. cu. ft. 1.5 Ib. ’cu. fr
Polyester urethanes account for the major part of the industry. Ra\v material costs range from about $0.62 to $0.80 ’lb., depending on the resin used. -4s diisocyanate production increases, its price should drop somewhat, leading to a lower raw material cost.
Who leads the Field? i\t present. Du Pont, hfobay, and rational .Aniline are in the forefront as producers of basic chemicals. Each has the advantage of years of background and has a n intensified research program to keep abreast of the situation. Du Pont is not manufacturing any urethanes, but is limiting its operation to supplying isocyanates. a new polyether glycol, and technical kno\v-ho\v. The nelvly erected plant at Chambers TVorks. across the river from Tl’ilmington, has an annual capacity of 25 million pounds of isocyanates. hlobay does not make finished products either, but is concentrating on isocyanates and polyesters, as \vel1 as offering technical aid and machinery to customers ivho manufacture foams under its license agreements. I t also administers Bayer licenses in this country. Materials are supplied from recently completed Seiv hlartinsville. TV. \’a,: facilities. Kational Aniline supplies a variety of isocyanates from neiv plants a t Moundsraiv materials ville: \V. \-a.-necessary supplied to it through the .4llied organization. Until the neiv plant \vas completed, materials and technical service \\’ere supplied through Buffalo, S. Y. TVho are the actual foam producers? Some like .American Latex. .Armour,
Goodyear, and Kopco have many years of research and production experience, while others are comparative newcomers. A partial list of commercial foam producers licensed under the various systems includes : American Collo Armour B Co. Cur tiss-IVright Dryden Rubber Firestone B. F. Goodrich Isocyanate Products C . S. Rubber
American Latex LV. T. Burnett Dayton Rubber Emerson B Cuming General Tire & Rubber Goodyear Nopco
Other companies. rather than producing finished foams, are producing a specialty. For example, Atlas Mineral Products produces prepolymers. Still other licensees such as Chrysler are experimenting but not producing foams commercially.
1960-?? Already stated is the fact that many people are looking for annual urethane production figures to hit the 100-millionpound mark by 1960. Feeling exists that this seemingly large figure is actually conservative, but no one really has sufficient market experience to know. Rigid urethane foams \vere originally expected to amount to no more than 2070 of the market, with foamed-in-place urethanes a large part of that figure. Today the view of the future is changing. S o t all companies expect this to be the case by 1960. Nopco Chemical, originally subscribing to the general view: nokv expects foamed-in-place rigid urethanes to amount to a t least half the total market. Their planned timetable for the foamed-in-place rigid part of the industry may be very accurate. Year 1955 1956 1957 1958 1959 1960
Pounds 300,000 10,000,000
20,000,000 30,000,000 40,000,000 50,000,000
The 10-million pound figure for 1956 appears high in the light of first-half figures. but may be reached by year’s end. depending in large part on automotive production. Xmerican Latex. ivith three automated production lines and a n annual capacity of 25 million pounds, predicts the industr)- \vi11 show a total urethane production of 30 million pounds in 1356. In truth. any rstimate ma); be too lo\v.. Only recently has full-scale commercial production been operating in this country. LVith a supply of raw materials noiv assured, and new applications continually being developed. there is no predicting just lio\v large this new plastics field \vi11 be. The only sure thing is-IT‘S BIG! VOL. 48, NO. 9
SEPTEMBER 1956
139 1
