I
L. E. ROBB' Manufacturing Co., St. Paul, Minn.
D. A. STIVERS, F. J. HONN, Minnesota Mining and
and
For High Temperature Operation
A Fluid-Resistant Fluorocarbon Elastomer
.
resists heat up to 600" F., compression set at 500" F., and loss of properties caused by normal swelling and deterioration effect of many corrosive fluids at lesser temperatures LASTOMISRS which are resistant to solvents and functional fluids a t high temperatures will be increasingly important in the aircraft, missile, automotive, and chemical industries. This report describes a linear fluorocarbon (Fluorel), composed of vinylidene fluoride and hexafluoropropylene, which resists heat and compression set in the presence of destructive fluids.
Because of its excellent mechanical properties and chemical resistance, this fluorocarbon elastomer is expected to find wide application in mechanical seals, fuel cells, fire walls, air ducts, fuel and hydraulic hose, sealants, diaphragms, liners, and similar usage.
Table I.
Typical Raw Gum Properties
Conventional processing equipment can be used
1.85 >60 Off-white 40
Sp. gr.
F, wt. 5% Color Shore A hardness Mooney viscosity ML-4/ 212' F. Embrittlement temp.,
135
F.
- 50
Low temp.
stiffness ASTM D 1053-52T) Gchman T2, F.
++155
5"s Tlo Storage stability Solubility
to 320' F. followed by an oven postcure of 24 hours at 400' F. is adequate for most parts. Mold shrinkage folloxving post-cure will average 2%. Metal Bonding. Adhesion to metals such as steel, copper, brass, and alumi-
$2
Excellent Esters and ketones
Table II. This General-Purpose Compound Has Good Mechanical Properties Recipe Compound A, pt. by wt. Base Elastomer Maglite E;" Thermaxb HMDA carbamate
100 20 15 1
Cure
fully extruded in standard rubber tubers. Because the viscosity is higher than that of conventional rubbers, the heat build-up within the barrel must be controlled by lowering the extrusion speed and maintaining adequate cooling
1-hr. press, F. 24-hr. oven, F.
300 400
Mooney ScorchC Minutes to 10-point rise Minimum reading
8
53
Properties
IO0
Present address, Pennsalt Chemicals Gorp., Philadelphia, Pa.
90
80
t;
m z:
SP
2HR. AT 700°F. 16 HR. AT 600'F. 3 DAYS AT 550'F. 10 DAYS AT 500°F.
I
30 DAYS AT 450°F. ORIGINAL 2500
2OQO
1500
500
I
30
0
20 IO
I 1000
50
40
* s
I I
60
u o 05s
%ti
I
70
100
200
300
VOL. 51. NO. 12
DECEMBER 1959
1465
n u m can be obtained with Chemlok 607 (Lord Mfg. Co., Erie, Pa.). Vulcanization. The gum and its compounds can be vulcanized by organic amines, peroxides, and controlled dosages of irradiation. The most practical vulcanizates are those obtained with a blocked polyamine such as hexamethylenediamine (HMDA) carbamate (Minnesota Mining and Manufacturing Co.) along with various metallic oxide acid acceptors (Table 11). Should the physical properties of the fully cured stock be significantly lower than the standards, poor dispersion of H M D A carbamate should be suspected as a possible cause. Improved dispersion may be obtained by remilling the stock a t a tight gage after allowing it to stand for 4 to 16 hours. Stabilization. Ten parts each of zinc oxide and Dyphos can be used as a stabilizer during cure, but magnesium oxide is preferred because of its superi-
Table I l l .
ority against heat degradation. When properly compounded and cured, stocks can be rated for continuous long-time service above 400' F. without marked degradation of either the molecular structure or its related mechanical properties (Figure 1). Because of its resistance to compression set, this elastomer is excellent for seals and closures in mechanical goods (Figure 2).
Resistance of the elastomer to a wide variety of hot oils, fuels, organic solvents, and strong inorganic acids and bases is excellent. Of particular interest is its stability to almost all of the fuels, lubricants, and hydraulic fluids being used or developed for application in aircraft and missiles. These fluids include hot diester-based lubes, aromatic-containing aviation gasolines, and high energy fuels of the boron type.
Immer-
'F.
Oil a n d fuels ASTM No. 3 GE 81406 M I L - 0 5606 M I L - 0 7808 OS-45 M I L - 0 8200 Type A transmission Skydrol 500 Tricresyl phosphate Pyranol JP-4 aromatic fuel Ref. fuel B High energy fuel 3 High energy fuel 3 Solvents Acetone Aniline Benzene
csz
cc14 Cyclohexanone Dimethyl formamide Dioxane Ethyl acetate Ethyl alcohol Methylene chloride Petroleum ether Trichloroethylene Acids and bases Acetic acid (glacial) Concd. HC1 (37'%) H F (48%) "03 (90%) Red fuming "01 HaPOa (85%) Fuming H2S01 N a O H (50%) Steam (ZnO, Dyphos, H M D A carbamate) (ZnO, Dyphos, H M D A carbamate) (MgO, H M D A carbamate) a
Volume Swell, %
300 350 350 400 400 300 212 300 300 300 77 77 77 325
3 0
6 12 3 3 3 320 22 5 0 3 0 8
77 77 77 77 77 77 77 77 77 77 77 77 77
374 5 22 3 2 350 375 205 375 2 30 3 6
77
180 32 12 24 64 0 12
77 77 77 77 77 77 77 212 300a 212 3OOa
io-hour immersion.
1466
D.c. resistivity At 50% R.R., ohm-cm. 2 x 1013 At 90% R.H., ohm-cm. 1 . 5 x 1013 Dielectric strength (short time), volts/mil 630 Dielectric constant, 100 c.P.s., 250 c. 11.4 Dissipation factor, 100 c.P.s., 25' C. 0.0125
Properties
The Elastomer Shows Good Chemical Resistance to Aircraft and Missile Fuels and Lubricants (Immersion time, 7 days) sion Temp.,
Table IV. Electrical Properties Are Comparable to Those of Electrical Grade Vinyl Chloride
INDUSTRIAL AND ENGINEERING CHEMISTRY
Tensile Strength,
Elong.,
Hardness Shore
P.S.I.
70
A
2520 2170 1750 2180 2180 2400 2600
360 300 265 265 295 340 345
58 58 50 59 60 60 57
1450 2575 2160 1980 1620 1830
320 350 3 10 335 280 180
...
...
1725 1980 2100 1940
... ... ... ...
...
...
280 300 370 315
... ... ... ...
1920 775 2150 1840
360 240 320 355
... ...
...
... 50 58 60 62 63 68
20 57 49 63 65 25 25 28 30 60 42 63 59
0
2200 2000 1020 2700 1780 2600
360 340 520 375 290 335
30 48 69 52 66 62 60 67
3 6 12 12
1600 1700 1820 1880
245 345 300 300
60 66 90 80
9 . .
Table V.
Low Temperature Properties
Embrittlement occurs below the point where stiffness increases
F. Gehman stiffness" T? T6
TIo Tioo Temperature reaction test TR 10 TR 30 T R 50 TR 70 Brittle pointb 0,075-in. thickness 0.025-in.thickness a hSTM D 1053-62T. 52T.
+c 177 t
3
- 11
--P
- 1 4 5 13
+
- 30 - 40 .ISTM D 746-
Low molecular weight carbonyl or carboxyl compounds, such as organic acids, ketones, aldehydes, and ethers are solvents for the raw gum, and cause excessive swelling of its vulcanizates. Table I11 shows the volume swell and tensile properties following a seven-day immersion in various types of chemical compounds. This new elastomer is highly resistant to weathering and ozone, showing no change in physical properties after one year of outdoor exposure and no cracking in ozone a t 150 p.p.m. after 200 hours. It has moderate resistance to radiation. and because of its high fluorine content. does not support combustion. Electrical properties are comparable to those exhibited by the electrical grade vinyl chloride polymers (Table IV). T h e flexibility and elasticity a t low temperatures are only fair, yet the elastomer compares well with other highly fluid resistant, special purpose synthetic rubbers. Stocks tend to stiffen rapidly a t 0' F., which approximates the glass transition temperature. Thin sections may be bent without F., showing that cracking a t -50" embrittlement takes place a t temperatures much lower than the point where stiffness increases sharply (Table V). Acknowledgment
T h e authors are grateful for the assistance of Galen R. Meier and Don L. Peterson in obtaining the data. RECEIVED for review July 8, 1959 ACCEPTED August 31, 1959 Division of Rubber Chemistry, Los Angeles, Calif., May 1959.
