INDUSTRIAL AND ENGINEERING CHEMISTRY
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in Figure 12 for the group of plasticizers examined. Average values are given for each of the plasticizer types in white and black formulations. All the natural samples had degraded a t the end of 2000 hours' exposure t o the point where they had no measurable elongation. None of the plasticizers conferred any significant weatherability t o the natural PVC compositions. The addition of titanium dioxide and carbon black improved the weatherability of all of the plasticized systems. The improvement with black is much more pronounced and general than with titanium dioxide. Where white or nonblack coatings are required, dioctyl phthalate would be the best plasticizer to use. Where black compounds may be employed, any one of the types examined can be formulated into coatings with outdoor weatherability, but the polyesters and the acrylonitrile copolymer deserve special consideration. CONC LU SIOXS
Natural and accelerated weathering tests show that polyvinyl chloride compositions can be formulatcd that are suitablc for long-time outdoor service. The exclusion of sunlight from the body of the plastic represents the maior formulation problem. Unprotected polyvinyl chloride systems degrade rapidly when exposed to the weather. This degradation may be retarded through the incorporation of suitable basic lead salts capable of acting as light screens. A relationship has been demonstrated to exist between light absorption of lead stabilizers and the improvement in weathering that is obtained. The use of lead salts alone is not believed t o be sufficient to sustain polyvinyl chloride compositions for long-time outdoor service in all climates. Further protection through light-shielding pigments is considered necessarv. The best protection is provided by a small particle size carbon black. This pigment gives protection t o compositions prepared from a variety of plasticizers. Where color is important, a rutile titanium dioxide treated with aluminum, zinc, and silicon gives a white base with good weatherability to which colorants may be added. Titanium dioxide is most effective with octyl phthalate type plasticizers. ACKNOW'LEDGMENT
It is a pleasuie to acknowledge the assistance of G. F. Brown, who prepared most of the compositions tested, and of Patricia
as
Vol. 47, No. 2
Langille and Margaret Woodring, !Tho obtained most of the phlsical test data. H. V. \J7adlow carried out the microanalytical work involved. R. H. Eiickson and W. L. Hawkins furnished the oxidation data that have been presented. The authors also received much encouragement from discussion of this work a i t h B. S.Biggs and W.0. Baker. LITERATURE CITED
(1) Biggs, B. S., Bell System Tech. J . , 30, 1078 (1951). (2) Biggs, B. S., and Hawkins, W. I,.,Modern Plastics, 31, 121 (September 1953). (3) Boyer, R. F., J . Phys. & CoIZoid Chem., 51, 80 (1947). (4) Clark, F. G., h a . ENG.CHEM.,44, 2697 (1962). (5) Decroes, G . C., and Taniblyn, J. Til', Alodern Plastics, 29, 127 (Aoril1952'r. (6) Drk&edow, D., and Gibbs, C. T., I h z d . , 30, 123 (June 1953). (7) Escales, E., Kunststoje, 41, 327 (1951). (8) Fox, V. W., Hendricks, J. G., and Ratti. H. J., IKD.EXG.CHEM., 41,1774(1949). 19) Haine, W. A,, Smith, E. F., and Smith, N. K., Am. Inst. Eleo. Engrs., Misc. Paper 52-205, presented at general meeting, Ninneapolis, Minn., June 1952. (10) Hendricks, J. G., U. 8. Patent 2,579,572 (December 25, 1951). (11) Hendricks, J. G., White, E. L., I Y D . ENG.CHCM.,43, 2336 (1951). Hendricks, J. G., a n d White, .:1 I,., Wire and W i r e I'~oduct8, 27,1053 (1952). Hendricks, J. G., White, E. L.. and Bolley, D. S.,1x0. EXQ. C ~ ~ ~ . , 4 2 ,(1950). 899 Jaeobsen, A. E.,Ibid., 41,523 (1949). Mack, G. P., Modern Plastics, 3 1 , 160 (Sovember 1963). Vol. Mattiello, .J. J., "Protective and Decorative Coatings." 11, pp. 372, 423, Wiley, New York, 1942. (li) Ilosenberg, A., Kunststofe, 42, 41 (1953). (18) Scarborough, A . L., Kellner, TT. L.. Rizao. P. W., Modern Plastica,29,111 (May 19521. (19) Society of Plastics Industry, Group 111, Committee on Exposure Test Methods, prelirninaiy report, Oct. 1, 1963. (20) U. S. Dept. of Commerce, Bureau of Census, Statistical Abatract of the United States, p. 148, 1952. (21) Wallder, V. T.. Clarke. 1%'. (J., aiid coworkers, Isn. ENG.CHEM., 42,2320 (1950). 0 1 , Paint & Varnish Production ( 2 2 ) Werthan, P., Ofic. Dig. Ped c l u b s . 2 9 2 , 3 1 1 (1949). (23) Yustein, S. E., Winans, It. R.. and Stark, H. J., Am. S o r . Testing Materials, preprint KO. 89, 1953. RECEIVED for review April 30, 1954. ;ICCEPTED October 19, 1954. Presented a t 11Ieeting-in-hliniature, North .Jersey a n d S e w York Sections, ACS. Neiyarlc, N . J . , Jan. 25, 1964, and L-e\\. Y o l k , N . Y., Feb. 12, 1954.
sins Co
ELECTRICAL AND PHYSICAL PROPERTIES OF FTV-2.5 AND OTHER RESINS PAUL EI-IRLICII1, R. W. TUCKER, AXD P. $. FRANIBLIN Diamond Ordnance Fuze Laborutories, Pushington 25, D . C .
EVELOPMENT of resins lor casting or potting electronic equipment has been a continuing project of the National Bureau of Standards. As described in a preceding publication ( 7 ) , the requirements for these resins include. first, lorn7 electrical losses over a wide range of frequencies and temperature and, secondarily, low viscosit,y in the monomeric form: low curing temperatures and times? low shrinkage on polymerization, small coefficient of thermal expansion, high tensile, compressive, and impact strength, nonc.orrosiveness, and chemical stability. Crosslinked polystyrene has many of the required properties but is slow in curing and exhibits high shrinkage during polymerization. In order to overcome these limitations, a t least in part, the National Bureau of Standards has developed several casting 1 Present address, Plastics Division, Monsanto Chemical Co., Springfield, Mass.
irsin8 which are essential13 copol? i i i c i b of styrpne with the comonomer chosm to acceleiate cuniig The first of the copolymers develsped, NBS casting resin, uses 2,5-dichlorostyrene, which has a higher polymerization rate than styrene, as the comonomer. The formulation consists of 33% 2,5-dichlorostyrene, 21.5% poly-2,5-dichlorostyrene,and 11% polystyrene which keep the shrinkage on polymerization to a minimum; 21 % styrene, 13 % hydrogenated terphenyl n-hich reduces brittleness; 0.5% of a 40% solution of divinylbenzene which prevents melting a t elevated temperatures, and a catalyst. The method of preparation and some of the properties of this resin have been described ( 7 ) Because inhibitom have been removed, batches of the resin mixture require refrigeration for storage.
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1955
323
e100 C.P.S. alOOO C.P.S. 0 l O o o O C.P.S.
OlOOOOO c.cs
0 100 c
120
80
40
160
200
160
200
PS.
e 1000 C.P.S. 4
10000 C.P.S. 0 100000 C.P.S. 0
8
80 120 TEMPERATURE, OC.
40
160
2b
A s a function of temperature a t several frequencies
Figure 2.
The second of the copolymers developed, AN-5 casting resin, uses acrylonitrile as the comonomer. The formulation consists of 5% acrylonitrile, 50% styrene, 30% polystyrene, 13% hydrogenated terphenyl, 2% of a 40 to 50% solution of divinylbenzene, a cobalt naphthenate drier, and a catalyst. The increased amount of divinylbenzene in this formulation increases crosslinking but tends to require increased polymerization temperatures and to produce a proliferous polymer. The method of preparation and some of the properties of this resin have also been described (10,If). It does not require refrigeration for short-term storage. I n recent work, a third copolymer, FN-2.5 casting resin, which uses fumaronitrile as the reactive comonomer has been prepared. This resin was modeled after AN-5 casting resin and differs from it only in that the 5% of acrylonitrile has been replaced by 2.5% fumaronitrile. Like other unsaturated nitriles, fumaronitrile should be handled with caution. I t s vapors and dust are irritating to the mucous membranes and are both vesicant and lachrymatory. I n the event of contact with the skin, the area should be washed promptly and thoroughly with soap and water to avoid irritation and blistering. Fumaronitrile gave a copolymer which promised lower dipolar losses a t high temperatures than those of AN-5. The electrical properties of this resin have been found to differ sufficiently from those of the other two resins to warrant description. This report presents detailed data of dielectric constant and dissipation factor over a wide range of frequencies and temperatures for these resins, as well as for polystyrene, their chief constituent. As far as is possible, these data are correlated with the chemical nature of the ingredients of the formulations and several generalizations emerge which suggest means of exerting some control over the electrical losses of these materials.
Table I.
80 I20 TEMPERATURE , T
40
Figure 1. Dissipationf actor, tan 6, of pure polystyrene
eJ/4
Dielectric constant, K , and dissipation factor, tan 6, of NBS casting resin
A s a function of temperature at several frequencies
3.30-
100 C.P.S. 0 0
10000 C.P.S. 100000 C.P.S.
r
2.90-
2.50;
40
80
I20
1
I60
Figure 3. Dielectric constant, K , and dissipation factor, tan 6, of AN-5 casting resin As a function o f temperature at several frequencies
Dissipation Factor Maxima and Temperatures of Occurrence for All Materials Considered
Pure Polystyrene Frequency, Tan 6 , 0.p.s. max. 102 0.0026 4 X 102 0.0027 103 0.0027 0.0032 4 x 103 104 0 0031 4 X 104 0.0031 103 0.0031 4 x 103 0.0032
NBS Casting Resin Tmex,
c.
128 131 133 138 143 152 157 174
Freauenoy, 0
P.S.
102 4 X 102
IO3
4 X 10s IO4
4 X 104 10’
3 X 106 106 3 . 8 X 108
IO’
Tan 6, mrtx. 0.0042 0.0043 0.0047 0.0044 0.0048 0.0048 0.0049 0.0052 0.0050 0.0048 0.0052
Tmax,
c. 99
I07 108.5 117.5 129 136 143.5 150 162.5 182.5 194
AN-5 Casting Resin Frequency, Tan 6, Tmex, C.P.8. max. C. 102 0.037 92 105 0.044 102 104 0.047 110 10s 0.050 128
FN-2.5 Casting Resin Frequency, Tan 6, Tmar, C.P.8. max. c. 102 0.0178 140 108 0.0188 148 104 0.0212 160 10s 0.0248 178
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
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Vol. 47, No. 2
ELECTRICAL PROPERTIES
Table XI. Dissipation Factor Maxima in AN-5 Casting Resin and Tenrperatiire of Occurrence as Function of ancentration of Crosslinking ..igent Concn. of 40% DVB Solutions,
Frequency, C.P.S. 102 10s 10'
% 0
103
2
102 103 104 105
G
102
103 104 106 10% 103
12
104 a
105
Divinylbenaene.
T a n 6, Max. 0.038 0.042
Trnax,
c.
90 95
...
...
0.037
92 102 110 128 100 110 120 137.5 115 128 137 1.55
0.044 0.047
0.050 0,036 0.035 0.038 0.043 0 018 0.021 0,023 0.032
D a t a for some physical properties of NBS, AN-5, arid FN-2.5 casting resins are also included. EXPERIMENTAL METHODS
Methods of preparation of NBS and AN-5 casting resins have been desc-nbed (5, 7 , 10, 11:. FN-2.5 casting resin n-as prepared by a procedure similar to that used for AN-5 casting resin. Electrical data were obtained by means of a commercial Schering-type bridge and ot,her standard equipment. Rleasurements above room temperature were made on sample holders: designed for high-t,emperature work. The sample holder had a spring-loaded positive drive on the ground electrode. The inotion of the ground electrode was monitored wit,h a, dial indicator. The setting of the ground electrode was adjusted until minimum pressure was applied to the sample. Thus, although the plast,ics became flexible a t elevated temperatures, they did not deform seriously. Electrical dat,a for AN-5 casting resin have been presented ( 6 , IO),but are included for comparat'ive purposes. Physical properties of FN-2.5 casting resin were measured according to Federal Specification L-P-406, where applicable. 2.9W
B
r
Low-Frequency Behavior, 102 to 105CyclesperSecond. EFFECT TYPEAND CONCESTRATIOX OF I ~ P O L E S All . resins under consideration, including polystyrene, showed dipolar losses. I n polystyrene and XBS casting resin, the dipole moments are very small and the resultant dipolar losses never became large. Figure 1 shows the dissipation facto? as a function of temperature for a very pure polystyrene (3). Qualit,atively, ail other resins under consideration behaved simila,rly. Their main points of difference were: the magnitude of the loss peaks JThich depended on the proportion of dipoles present in the polymer chain and on the magnitude of their moments, and the temperatures a t which these losses became operative. Table I gives tho dissipationfactor (tan 6 ) maxima and the temperatures a t which these occurred for the various resins. Figures 1, 2, 3, and 4 give complete data on dielectric constant and dissipation factor for all these resins up to elevated temperatures. >laking alloa-ance for the proportion of dipoles present in the polymer chain; it is immediately clear from an inspection of Figures 1, 2, 3, arid 4 that the dipole moments of the nitrile groups in AN-3 and in FK-2.5 casting resins must, he large compared to those of the phenyl groups present in polystyrene and to those of the 2,5-dichlorophenyl groups present in NBS casting resin, as v a s to be expected. The t,emperatures at which these dipolar losses became operative depended on the second-order transition point,-i.e., approximately the temperature a t which the samples begin to exhibit rubberlike behavior-and this temperature varied for the different resins, as: shown by the different temperatures a t which the different resins have their loss maxima (Table I). It follows that, ahhough a material may have considerable dipolar losscs, these losses may not occur a t temperatures to which the material is subjected in ordinary usage. If 85' C. is the peak t.emperature which has to be withstood in ordinary use, then NBS and FN-2.5 casting resins, but not AN-5 casting resin, would be fairly good dielectrics in the frequency range considered (Figure 5). .It still higher temperatures, only OF
.o
100C IO00 c P s IO000 c P s
\
3 AN-5 C A S T I N G R E S I N
2 70-
.o
3
FN-2.5 C A S T I N G RESIN
@
N B S CASTING RESIN
9
I
z /-----
\
;r .o
.o
.
F R EQUE NCY, C B.S
Figure 4. Dielectric constant, I
