1800
INDUSTRIAL AND ENGINEERING CHEMISTRY CONCLUSION
Vol. 44, No. 8
Boyer, R. F. (to Dow Chemical Co.), U. S. Patent, 2,500,149 (March 14, 1950). (3) D'iilelio, G. F. (to General Electric Co.). U. S. Patent
(2)
The advantages of physically stable ion exchange resin particles are well known and some of the techniques involved in the preparation and maintenance of the spherical product have been shown. Especially, the need for swelling agents prior to sulfonation, sulfonation techniques, dilution techniques, and operating techniques have been shown, as well as the results of improper methods. LITERATURE CITED
(1) Bauman, W. C. (to Don, Chemical Co.), 2,466,675 (April 12, 1949).
U. S. Patent
2,366,007 (Dec. 26, 1944).
Lindsay, F. K., Wirth, L. F., and Durinski, A. M., IND.ENG. CHEM.,43, 1062 (1951). ( 5 ) Partridge, S.M., Brimley, R. C., and Pepper, K. W., Biocham. J . . (4)
46, No. 3 , 334 (1950). (6) Pepper, K. W., J. Applied Chem., 1 ,
Part 3, 124 (1951).
RECEIVED for review November 3, 1951. ACCEPTED April 7 , 1952. Presented before the Division of Paint, Varnish, and Plastics Chemistry a t the 120th Meeting of the AMERICAN CHEMICAL SOCIETY,New York, N. Y.
Teflon Tetrafluoroet
J
esin Dispersion A NEW AQUEOUS COLLOIDAL DISPERSION OF POLY TETRAFLUOROETHYLENE JOHN F. LOKTZ AND WILLIAM B. HAPPOLDT, JK. Polychemicals Department, E. I . du Pont de Nemours &2 Co., Inc., Wilmington, Del.
T
EFLON tetrafluoroethylene resin is noted for its outstanding heat resistance, chemical inertness, antiadhesiveness, and extremely low dielectric loss properties. It was first observed and characterized as a powdery product by Plunkett (5), who obtained it as a residue from the storage of tetrafluoroethylene monomer under superatmospheric pressures. Subsequently, Hanford and Joyce (5) described the polymerization of the monomer under controlled conditions in aqueous systems using hydrogen peroxide initiator and discussed the structure and properties of the polymer obtained in the form of nonwetting white granules. Later, Renfrew (6) prepared the polymer in the form of dilute aqueous dispersions by using his( P-carboxypropiony1)peroxide as a polymerization catalyst in an aqueous system, while Berry ( 1 ) described methods for concentrating the dilute product into higher solids dispersions. The unique propertie8 of the granular polymer along with a description of its fabrication into useful articles have been outlined by Renfrew and Lewis (7). As polytetrafluoroethylene has an extraordinarily high melt viscosity and lacks the flow characteristics of thermoplastics when heated above the softening point, the methods of fabricating the granular form of polymer are somewhat limited. On the other hand, the aqueous dispersion is especially suited to forming films, to coating and impregnating applications, and to preparing mixtures with a variety of fillers such as carbon, silica, and clay for molding purposes. This paper describes the general dispersion properties and film-forming characteristics of the dispersion form of polymer.
are more amenable to the preparation of t>hinfilm under conditions described later.
ELECTRON MICROGRAPHY. In preparing the electron micrographs of the polymer particles, the aqueous dispersions were diluted to about 0.02% solids with distilled water, placed on a supporting transparent film, and then dried. The dilution avoids agglomeration which would obscure good definition of the individual particles. Under a magnification of 25,000, the particles were compared against a 1-micron wale, classified, and counted. To avoid distortion of the particles, the electron micrograph studies were necessarily restricted to dispersions containing no added dispersing agents. PARTICLE S l Z E DISTRIBUTION. Thc clcctron photomicrographs Kere used for the determination of the frequency distribution of the particles based on a statistical technique described by Watson ( 8 ) . -4number count for a typical dispersion is shown in Table I, the data from which were used to indicate graphically the distribution shown in Figure 3. TABLE I. FREQUESCY DISTRIBUTION OF PARTICLES IN POLYTETRAFLUOROETHYLENE DISPERSIONS Dialnetera, Ma
Numerical Count
Percentage of Total Count
Distribution, %, Up t o and Including Stated Diameter
PARTICLE CHARACTERISTICS
Teflon tetrafluoroethylene resin dispersions, prepared according to the method described by Renfrew (6),consist of colloidalsized, negatively charged particles suspended in water. Electron micrographs reveal particles that are predominantly spherical ranging from 0.05 to 0.5 micron in diameter, with a minor proportion of elongated forms as shown in Figure 1. In the presence of dispersing agents the polymer particles, as shown in Figure 2, appear somewhat enlarged and more rounded, presumably because of surface adsorption; in this form the particles
Average diameter estimated visually as most closely representing, t h e diameters of t h e individual particles using a reference micron scale divided into 16 units. b Particles at least twice as long as wide. Q
The data in Table I plotted on the Hazen logarithmic probability grids show a geometric mean diameter of 1 4 5 ~ . A particle diameter of 148p was calculated from the specific surface deter-
August 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
1801
impregnating in order to ensure thorough wetting and penetration. Generally, in applications involving fusing the dried polymer dispersion, it is not desirable t o use more than 12%, as this increases the time required to bake out the dispersing agent. Furthermore, high concentrations of dispersing agents tend to render the dispersions too viscous for many coating and filmforming applications. The stabilized dispersions have an indefinite shelf life as long as they are stirred occasionally. SPECIFIC GRAVITY, SOLIDS CONTENT, AND VISCOSITY
The approximate linear relationship between the specific gravity and solids content is indicated in Table 11. Solids content was determined by the complete evaporation of the water and weighing the residual solids.
TABLE11. RELATIONSHIP BETWEEN SPECIFIC GRAVITYA N D POLYMER CONCENTRATION EQUIVALENTS OF UNSTABILIZED DISPERSIONS Polymer Solids,
%
Figure 1. Electron Micrograph of Spherocolloidal Polytetrafluoroethylene Dispersions, Unstabilized
mined by the nitrogen absorption method on the dried coagulated powder, The two values are in good agreement. With a specific gravity of 2.2 to 2.3 (7) the polymer particles of the dispersion tend to settle on prolonged standing with some classification of sizes. Figure 4 shows the particle sizes determined, from electron photomicrographs, on samples taken from the top, middle, and bottom portions of the dispersion stored for a period of 1 month. It is evident that classification of the particles can be utilized to a limited extent either to deplete the dispersions of the fine particles or to concentrate them by simple decantation. Prolonged storage up to 6 months is generally accompanied by progressively increasing clarification of the water phase at the top of the container. Although most of the settled dispersion can be redispersed b y gentle agitation, prolonged storage of the unstabilized dispersion beyond 6 months without occasional stirring results in the formation of some caked sediment which is irreversibly coagulated.
5 10 15 20 25 30 35 40 45 50 55 60 65
Spec. Gravit.y,
n; I 1,0325 1 ,0628 1.0945 1,1288 1.1650 1.2035 1 ,2445 1 ,2885 1.3355 1.3870 1.4420 1.5025 1 ,5665
G. Polymer/ M1. 0.0516 0.1063 0.1642 0.2258 0.2913 0.3611 0.4356 0.5154 0.6010 0.6935 0.7931 0.9015 1.0182
Lb. Polymer/ Gal. 0.431 0.887 1.370 1.884 2.431 3.014 3.635 4.301 5.016 5.788 6.619 7.523 8.479
COAGULATION AND STABILITY
The unstabilized dispersions are irreversibly coagulated by the addition of electrolytes and many water-miscible solvents such as alcohol and acetone. Coagulation is also caused by violent mechanical agitation, freezing, or boiling. During the coagulation, the polymer generally separates first as a water-wet white sediment which, on continued agitation, becomes completely hydrophobic. The coagulated polymer is a light, feathery, highly absorptive powder which is readily wetted by a variety of organic fluids. Mechanical coagulation of the dispersions in the presence of certain organic liquids yields lubricated mixtures that have an unusual coalescing property which can be utilized for molding, calender-rolling, and extrusion into all kinds of fabricated articles. This property is described in another paper ( 4 ) dealing with the extrusion characteristics of the lubricated mixtures. The addition of small amounts of either anionic or nonionic surface-active dispersing agents renders the dispersion more stable toward coagulation by mechanical agitation, sedimentation, or admixture with water-miscible solvents. The effective lower limit for the adequate stabilization of the dispersion is approximately 1yoof dispersing agent based on the polymer content. Higher proportions of stabilizers (up to 10% based on the polymer) are required for most applications involving coating or
Figure 2. Electron 3Iicrograph of Spherocolloidal Polytetrafluoroethj lene Dispersions. Stabilized with Triton x-100
The relationship between specific gravity and polymer solids. can be expressed by the equation
+
V = P ( A - B/lOOAB) 1/A (1) where V = specific volume of dispersion, P = per cent by weight of polymer solids, A = specific gravity of water (0.9985),and B = specific gravity of polymer solids (2.25). Aqueous dispersions of polytetrafluoroethylene show the usual viscosity-solids relationship common t o suspensions of fine particles (9). The viscosity of the aqueous dispersions can be readily determined by means of a MacMichael or equivalent type o f
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1802
PARTICLE
Figure 3.
SIZE
-
MICRONS
Frequency Distribution of Particle Sizes of Spherocolloidal Dispersions E.
Elongated Forms
viscosimeter. With dispersions containing no added dispersing agents, the viscosity increases gradually in proportion t o the solids content up to approximately 30 to 35%. Beyond this concentration, as shown in Figure 5 , the viscosity increases rapidly with increasing solids content. A parallel relationship is evident in dispersions containing dispersing agents except for a noticeable upward displacement of the curve which depends upon the amount and type of dispersing agent added. Thus, in Figure 5 it is evident that the viscosity increase in the presence of the nonionic dispersing agent, Triton X-100 (alkyl aryl polyether alcohol, Rohm & Haas), is slight compared t o that caused by the presence of an equivalent proportion of the anionic agent Duponol M E (sodium lauryl sulfate, D u Pont). I n particular, Duponol ME, added in proportions greater than 6% based on polymer content, forms thixotropic dispersions above 60% resin solids. I n addition to stabilizing the dispersions against coagulation, the dispersing agents serve t o impart the necessary wetting characteristics t o ensure uniform spreading of the dispersion over such surfaces as metals, glass, ceramics, and polytetrafluoroethylene substrates.
Vol. 44, No. 8
dispersion through loose-woven cloth which served to hold back the foam. To prepare films thicker than the critical value (0,0015 inch) it was necessary to apply several coatings. This was readily accomplished by repeating the casting operation with subsequent drying, baking, and cooling until the desired thickness was attained. Each casting required baking above the transition temperature of the polymer at 327” C. in order to sinter the particles before applying a succeeding casting. In applying successive coatings, the dispersions required suitable formulation with dispersing agents in order to wet or spread out on the Teflon surface, otherwise the casting failed to spread evenly over the polymer film surface and formed a spotty deposit. In general, a minimum of 3% dispersing agent, based on the polymer, was found necessary to ensure satisfactory wetting of the casting surface and a minimum of 6% for the succeeding castings. Table 111 describes the wetting characteristics obtained with Triton x-100. TABLE 111. TIONS OF
a b C
WETTING CHARACTERISTICS AT v A R I O V S PROPORNONIONIC DISPERSING AGEXT(TRITONX-100)
(38% solids, Teflon tetrafluoroethylene resin dispersion) Triton Wetting on Rewetting on X-looa, % Clean Surfaceb Baked CoatC 0 Poor, spotty Poor, drains off 1 Poor, spotty Poor, drains o f f 2 Fair Poor, drains off 4 Excellent Fair 6 Excellent Excellent 8-12 Evcellent Excellent Based on polymer content in dispersion. Chrome-plated steel test plate, 2 X 2 X 0.040 inch. Tested on air-cooled coatings.
-
FILM-FORMING PROPERTIES
Dispersions of the colloidal polymer, suitably formulated with 6 t o 10% dispersing agents, spread out on smooth surfaces as deposits which can be converted into tough, thin films. The preparation of these films involves four distinct steps-namely, casting (dipping or flowing out) on a supporting surface, drying to remove the water, baking, and cooling the baked films. Each of these operations involves certain specific features that are essential to the successful preparation of high quality films. Like many suspensions or slurries of organic and inorganic materials, the dispersions on drying in comparatively thick deposits develop fissures or cracks, reminiscent of the well-known mudcracking. These cracks cannot be eliminated by fusing, even on prolonged baking. Frequently, the cracking may not be noticeable in the dried casting, but becomes evident after baking. Under optimum conditions of casting, this cracking does not occur below an average layer thickness of 0.0015 inch but limits the amount that can be laid down in a single application. This limit, referred to as the critical thickness and described in a later section, is dependent on several factors, notably particle &e range, amount of dispersing agent used in the dispersion, and solid content or concentration. CASTINGOPERATIOX.Castings were made by flowing out the dispersion on flat metal surfaces or by dipping a metal plate into the dispersion. Ordinarily, plain nickel- or chrome-plated steel surfacee were satisfactory for this application, but it was found necessary to have the surface substantially free from grease and dust particles which caused incomplete wetting and uneven castingb. The casting was carried out so as to ensure uniform spreading, with due care to avoid the formation of “is1ands” which later appeared as craters, pinholes, and cracked imperfections in the sintered a m . Often the craters were caused by the foam produced by excessive agitation : this was avoided by filtering the
-
PARTICLE
0 .I
SIZE
0.2 PARTICLE
SIZE
0.2 PARTICLE
SIZE
--
- MICRONS
0.3
- MICRONS.
0.4
E
-
0.4
E
40 W (3
Z
a
30
K
f 3
20 10
Q. I
Figure 4.
0.3
MICRONS
Frequency Distribution of Particle Sizes Resulting from Settling (1 Month) E.
Elongated forms
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1952
DRYING. The dispersion cast on a metal, glass, or ceramic surface dried with the gradual appearance of a smooth, opaque, and enamel-like glaze in 10 to 20 minutes, depending upon the ambient temperature and humidity. The drying could be further accelerated at higher temperatures to approximately 2 to 3 minutes a t 110" C. Heating by means of infrared lamps provided a convenient method for drying continuous lengths of coated strips. The dried casting is sufficiently strong to withstand some flexing of the support but it can be rubbed off easily and is sensitive t o water. Recoating without baking destroyed the casting and ubually deposited a layer in excess of the critical thickness. For this reason, it was necessary to submit each dried casting t o a baking operation before recoating. BAKING. One factor controlling the baking time necessary t o remove the dispersing agent was found t o be the type of agent employed. In general, nonionic dispersing agents such as Triton X-100 were removed more readily than the anionic types such as Duponol ME. Temperatures above the transition point a t 327' C. were required to fuse the polymer particles. At these temperatures the greater portion of the dispersing agent volatilized rapidly aa degradation products, but a small amount of decomposition, indicated by discoloration, formed carbon residues which required further thermal exposure for their removal. Other factors affecting the time necessary t o bake a coating completely free of the dispersing agent included thickness of the film, stabilizer content, baking temperature, and air circulation efficiency in the oven. The time necessary to bake the castings to clarity, or the point at which no discoloration was visible in the baked film, is shown in Table IV. From Figure 6, plotted from Table IV, it is evident that the baking time increases linearly with the film thickness up to 0.0012 inch (1.2 mils). Beyond this thickness, the linear relationship no longer prevails, as presumably the diffusion of the thermal decomposition products of the dispersing agent through the sintered Teflon layer becomes an important factor. Film thicknesses greater than 0.0012 inch required less total baking time when applied from two or more castings. Thus, it is not neceesary to exceed the critical thickness, 1.5 mils, or to attempt
0 UN STABILIZED DISPERSION
8 WITH 6 % " T R I T O N " X - 1 0 0 0 W I T H 6 % "DUPONOL" ME
TABLE IV.
1803
TIMENECESSARY TO BAKEFILM TO CLARITY VERSUS THICKNESS
(Temperature 350' t o 370' C . , dispersing agent 12% Triton X-100) Thickness, Time, Mils Min. 3.0 72
_2.5 _ 10
1 9
1.2 1.0 0.7 0.3
8
5
1.5
w u)
f
60
f 1 ,
zI-
40
-:: 20 Q
t
m
0 0
0.5
I O
1.3
FILM THICKNESS
Figure 6.
-
2 .o
2.5
3.0
MILS
Film Thickness us. Time Required to Bake Out Dispersing Agent Dispersing agent, 12% Triton X-100 Temperature, 306' C.
to develop a dispersion with a critical thickness greater than 1.5 mils for thick coatings. COOLING AND STRIPPING. On completion of the baking cycle, the resulting films were either cooled rapidly by quenching in water to impart the maximum toughnebs, or cooled slowiy to room temperature to give filmb that were more easily wetted on succeeding castings, In mu1 tiple castings, it was therefore important to allow the films to cool slowly after each application except, the final one, which was quenched rapidly. The final film was readily stripped with slight forcing t o give nearly transparent sheets, slightly bluish in appearance.
40 DETERMINATION OF CRlTICAL THICKNESS 0
To determine the critical thickness, 50 to 100 ml. of the dispersion, suitably formulated with a dispersing agent, was poured into a 12 X 14 inch metal tray so as to cover the entire surface. After excess dispersion was drained off, the tray was placed a t an angle to dry in order to obtain a casting of varying thickness, in effect a. wedge. The angle of inclination was adjusted to produce a mud-cracked region in a t least one third of the casting. The angle was found to depend upon the consistency of the dispersion, which in turn depended upon the solids content and the proportion of the dispersing agent used. Usually, an angle of 45 degrees from the horizontal produced a baked film varying in thickness from about 0.8 to 1.0 mil a t the top of the tray to approximately 2.6 to 3.4 mils a t the bottom with a dispersion containing 50.% solids and 6% of a nonionic dispersing agent. Critical thickness was measured on the baked, stripped film across the boundary between the cracked and noncracked regions of the baked film. The critical thickness measured a t numerous points often showed a spread of from 0.0003 to 0.0005 inch. This spread in values is believed to be due to some stratification of the colloidal particles in different size ranges along the inclined planes resulting in different critical thickness values.
3 0
v) (u
-3 0 (0
w
2
0
P
52 0 w
0
I
* c (010 0
0
4 >
I
I
30
Figure 5.
I
40 ! PERCENT S O L I D S Viscosity us. Solids Content
EFFECTOF PARTICLE SIZE RANGE. A definite disparity waa found to exist in the particle size distribution in the top, middle, and bottom portions of samples stored for 30 days without agitation, as shown in Figure 4. Using these fractionated dispersions
INDUSTRIAL AND ENGINEERING CHEMISTRY
1804
TABLE1 ' .
EFFECTO F
0
Vol. 44, No. 8
SIZE RANGEO N CRITICAI. THICKNESS
PARTICLE
(Formulation: 9 % added dispersing agent based on polymer) Critical Thickness Mean Mils, with Varied Particle GeoFormulations Size metric Range, Size, Solids, Triton Duponol Fraction Micron Micron % X-lOOG hlEb Original composite 0.05-0.4 0,145 34.3 1.5-1.8 1.5-1.8 0.05-0.4 0.125 33.7 1.5-1.8 1.5-1.8 TOP hliddle 0.10-0.4 0.135 35.0 1.8-2.0 1.8-2 0
I
I-
-I
a
0
Figure 7.
Critical Thickness versus Solids Content
TABLEVI.
W i t h 6 % T r i t o n X-100
EFFECT
SOLIDS CONTEXT THICKNESS
OF
OX
CitITIC.4L
( Formulation: 9 % Triton X-100 on polymer basis)
Casting Angle from Horizontal, Degrees
Solids,
%
5
33 40 45 48 50 53 55 60
TABLE VII.
5 5 15 60 60 60 75
Thickness Range, Mils 0.8-3.6 1.0-3.6 1 .O-3.O 1.0-2.6 0.8-2.2 1.0-2.2 1 .o-2.2 1.2-2.2
Critical Thickness, Mils 1.8 1.8 1.8 1.8 1.8 1.5 1.5 1.5
EFFECT O F ADDED DISPERSING AGEXTO N CRITICAL THICKNESS
(Solids conrent: 50%) Critiral Thickness, Mils
Triton, X-100,
% 0
n
1.O:l.z 1.0-1.2 1.2 1.5-1.8 5 1.8 6 1.8 8 1.8 1.8-2.2 12 Not measurable, does not form continuous nonporous film. 1 2 3 4
Figure 8.
PERCENT "TRITON" X - 1 0 0 Critical Thickness versus Amount of Dispersing Agent Used
a
use Of more than 12% dispersing agent 'vas not 'Onsidered in a series of castings, the results, as indicated in Table V, showed Of the prolonged baking required to Obtain that higher thicknesses are obtained as the proportion of practical films free of decomposition residues. ' larger Dartides increases. -~ EFFECTOF SOLIDSCONTENT. It is conceivable that the ultiPHYSICAL AND DIELECTRIC P R O P E R T I E S OF BAKED FILMS mate deposition of the dispersed particles should be more orderly Polytetrafluoroethylene films prepared by the described casting in dilute than in concentrated dispersions. This was demonstrated procedures, especially by multiple coating methods, showed high by actual castings a t various solids contente, as shown by the physical strength and good dielectric properties snd were found data given in Table VI and plotted in Figure 7 . The data showed to be suhstantially free of pinholes. A wide range of properties that the higher critical thickness was obtained a t lower solids was obtained by varying the time and temperature of baking. contents and that as the solids content was increased t o approxiTable V t l l illurt,rates the physical properties obtained wing a mately 53% a definite lowering in critical thickness occurred. 2-mil film prepared by four successive castings with a baking EFFECT OF DISPERSING AGENTS. On progressive addition of the nonionic dispersing agent, Triton X-100, a marked increase in critical thickness was TEMPERBTURE TABLE VIII. PROPERTIES O F 2-MIL CAST FILMVERSUS BAKIXG obtained, as shown in Table Baking Temperature, C. ~_.__ VI1 and Figure 8, with a typiASTlI Property Method 350 370 390 410 430 cal 50% solids dispersion. I n this case, the critical thickness "echanical Tensi1.e strength, properties lb./ sq. in. D 412 3810 4010 3490 2420 1710 increased as more dispersing Elongation, % D 412 330 370 390 420 100 agent was added but reached Elmendorf tear, g./ mil .... 6 8 9 14 ... a constant value at approximately 5% dispersing agent properties Dielectric constant based on solids content. As ClOOO,~ D 150-47T 2.14 2.14 2.14 2.14 2.14 Dissipation factor the proportion of the dispers(1 000-) D 150-47T 0.0002 0.0003 0.0002 0.0002 0.0003 Volume resistivity, ing agent was increased t o ohm-cm. D 257-46 1014 1014 10" 1014 1014 12% there was a slight increase Dielectric strength, short time, volts/ in the critical thickness. HOWmil D 149-44 3740 4090 2600 2250 3160 ever, as mentioned earlier, the O
August 1952
1805
INDUSTRIAL AND ENGINEERING CHEMISTRY
period of 5 minutes after each casting, These data indicate that the optimum properties are obtained a t a temperature of 370" C. with a 5-minute baking period. With higher sintering temperatures, Le., above 400" C., the films showed a marked decrease in tensile and dielectric strength. With sintering times longer than 5 minutes, optimum properties were obtained a t kmperatures slightly lower than 370" C. The properties obtained in the optimum sintering temperature ranges were equivalent to those of the polymer fabricated by molding techniques (7). MISCELLANEOUS APPLICATIONS
In addition to the preparation of thin films, Teflon tetrafluoroethylene resin dispersions wcre found suitable for impregnating woven fabrics and mat structures to render them chemically more resis tant. These were further laminntcd by compression molding at temperatures above the transition point a t 327' C. into useful products having excellent resistance to corrosive
chemicals and excellent dielectric properties. Combinations of the dispersion? with stable fillers, such as titanium dioxide, carbon, silica. talc, calcium silicate, and mica, were also found useful foi coating and impregnating applications. Dispersions of the Teflon resin could also be applied by spraying onto various surfaces within the limitations of the critical thickness disrussed above, but for arceptable adhesion to metal and ceramic suifaces special formul~tionsare recommended. The various properties of the Teflon tetrafluoroethyl~neresin in its dispersed form as described in this paper involv? numeroue theoretical considerations bearing on colloid chemistry which warrant further investigation for this unueually inert fluorine polymer. RECEIVED for review October 26, 1951. ACCEPTED April 3, 1952. Presented as part of the Svmposium on Fluorine-Containing Polvmers before the Division of Polymer Chemistry a t t h e 120th Meeting of t h e AhfERIcaN CHEMICAL SOCIETY, New York, September 1951.
(Teflon Tetrafluoroethylene Resin Dispersion)
EXTRUSION PROPERTIES OF LUBRICATED RESIN FROM COAGULATED DISPERSION JOHN F. LONTZ, JOSEPH A. JAFFE, LESTER E. ROBB, AND WILLIAM B. HAPPOLDT, JR. Polychemicals Department, E. I . d u Pont d e Nemours & Co., Inc., Wilmington, Del.
T
HE extrusion of Teflon above its transition temperature at ability of these lubricants depends upon the extrusion conditions 327 C. involves certain mechanical and thermal problems to which the compositions are subjected. Thus, the boiling which limit to some extent the rates by which such fabricated point of the organic compound must be above room temperature t o avoid evaporation from exposed surfaces. The boiling point articles as rods, tubes, sheets, and wire coverings can be made. I n an attempt to circumvent some of the difficulties involved in high temperature extrusion, an investigation of the extrusion properties of the TABLE I. EXTRUSION QUALITYOF VARIOUSORGANICLIQUIDSAS lubricated polymer resin was undertaken. LUBRICANTS FOR COAGULATED DISPERSION POLYMER In studying the properties of the aqueous dis[Die, 0.010-inch (lO-mi!) tape die, 1% inches wide: lubricant concentration, 18 t o 20% by persions of the resin described in the preceding weight of mixture; temperature, 20' t o 25' C. (room temperature)] Viscositya paper, it was discovered that the colloidal form of Pressure Temp., Range, Extrusion polymer forms a polymer-in-oil composition when Organic Compounds Cps. ' C. Lb./Sq. 1n.b Qualityc coagulated in the presence of organic lubricants. Hexane 0.326 20 18,000 Poor, does not extrude Further work indicated that these polymer-in-oil Octane 0.542 20 Fair 18,000 (approx.) compositions could also be prepared by mixing Decane 22.3 0.77 Excellent 6,000-10,000 Dodecane 23.3 1.26 4,000 the dry coagulated polymer with a variety of Hexadecane (cetane) 22.2 3.59 2,000- 4,000 Excellent Evcellent Hydrocarbon oil (Primof C)d 2,000- 4,000 .. organic compounds, some of which act as lubriBenzene 0 . bb4 20 2,000- 5,000 Excellent cants. These compositions can be extruded into Toluene 0.590 20 2,000- 5,000 Excellent 0.648 20 Excellent Fair 5,000- 9,000 various forms at room temperature at rates apKxiY 2.0 25 4,500- 5,000 Decalin 2.41 25 5,500- 6,000 Fair preciably higher than those attainable by the Chlorobenzene 20.1 0.80 12,000-15,000 Fair high temperature extrusion of the nonlubricated Chlorinated biphenyl (Aroclor 1242) 6 .. Excellent 2,0004,000 polymer. Ethanol 1.20 20 4,000- 7,000 Excellent Fair O
LUBRICANT COMPOSITIONS
Teflon tetrafluoroethylene resin particles obtained from the coagulated aqueous dispersion are readily wetted by organic compounds. It was found that compounds which act as lubricantb are not limited t o any specific chemical structure. Thus, representative members of such organic classes as hydrocarbons, both aliphatic and aromatic, halogenated hydrocarbons, alcohols, glycols, esters, ethers, ketones, silicone oils, tricresyl phosphate, and fluorocarbon oils are effective lubricants for the coagulated polymer. The suit-
tert-Butyl alcohol Ethylene glycol But l a c e t a t e MetK yl benzoate Djbutyl phthalate Di-n-propyl tetrachlorophthalate Aniso1e .Tricresyl phosphate (tech.) Silicone DC-500 (50 cts.)f Perfluoro lube oil, FC-3328
2.95 2.18
20 0
2.067
..
20
1.'ii
20
..
..
..
vi'shous oil
..
..
..
11,000-14,000 4,000- 6,000 6,000-1 1,000 14 000-18 000 4:OOO-
6,'OOO
4,000- 8,000
6,000-12.000 4,000- 6,000 10,000-12,000
16,000-18,000~
Fair Evcellent Fair Excellent Fair Excellent Excellent Exrellent Fair
Taken from "International Critical Tables" and other reference sources. b Force applied on a ll/r-inch ram (Carver press). 0 Rated in the order: excellent. fair, and poor, as a oomposite rating of smoothness, absence of strains, and flexibility. d Standard Oil Co. of New Jersey. Monsanto Chemioal Co. f Dow-Corning Corp. 9 Organic Chemicals Department, E. I. du Pont de Nemours 8. Co., Inc. Requires a minimum temperature of 160" C. t o extrude a t this pressure range,
