October 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
creasing the glycol content above about 50%, the decrease in wlubility with temperature increase tends to become a little larger w e n though the actual solubility value is decreasing. h large n u n h e r of aqueous glycol solvents was employed in order to establish definitely whether there is a reversal of the dupes of the inverted solubility curves. The decrense in solubility with increase in temperature over a wide middle portion - vertical for solut'ions with 40 weight % or higher glycol as solvent. The approximate boiling points included in Table I V are intended to indicate the degree to which these limiting temperatures were approached. LITERATURE CITED
(1) Berkeley, Trans. Rog. SOC.(London),203, 189-215 (1904). (2) Fisrlier, Karl, Anww. Chem., 48, 304-6 (1935). (3) Fleurs, P.. and Marque, J., J . p h a r m . ch,im., [ 8 ]10, 241 (1929). (4) kltiller, B.. Chem.-Ztg., 44, 513-16 (i920). ( 5 ) Phipus. H. E., and Reedy, J. H., J . Phz/a. C h r m . , 40, 89-100 (1986).
SchTeineinskers, F. A. K.. Z. phuisil. Chem., 43,671-88 (1903). Seidell, ;\,, "Sclubilitiec of Incrganic and Metal-Organic Conipounds," 3rd ed., Vol. I, pp. 1300-2, New York, D. Van Nostrand Co., 1940. (5) Spanglei. J., snd Davies, F., IXD.ENG.CHEM.,.IXAL. ED.,15, 96-9 (1943). - - , -
\
(9) Thompson, A. R., and Mclstsd, Id.C., ISD. E ~ GCHEN., . 37, 1244-5 ( 1 9 4 3 , (10) Thompson, A , R., and \-ener, R. E., Ihid., 40, 478-51 (1948). RECEI\-GD S?ptnnher 24, 1948. Based o n a dissertation presented by Rayinond E. Vener to t h e Gredlintr School, University of Pennsylvania, in partial frilfillinent of t h e reqiiiremrnCP for t h r cirgrer of d o r t n r of philosophy.
Tack of Butyl and Natural Rubbers R . I l compounds.
I
N THE manufacture of Butyl inner tubes one of the major
problems is the making of a satisfactory butt splice. The Goodyear splicing machine shown in the adjacent photographs is in general use in the industry for hutt splicing. The tube lengths which are cut sonicivhat longer than required are placed in position by the operator a3 shown in Figure A. The splicing is then done automatically as follon-s: (1) the clamp arms close down upon the tube cnds and flatten them int,o the clamp dies; (2) a pair of heated knives descend vertically onto a cutting anvil ttnd trim off both tube endi, leaving clean and tacky faces ready for splicing together; ( 3 ) the knives and anvil then move out of the way (Figure B ) ; (4)t h r clamps move linrinontally toward
each other, pressing forcibly together the two freshly cut tube ends and holding them so for a short interval of time; ( 5 ) after which the clamps open up and return t o their ready position (Figure C), completing the cycle. The tiinkg end pressures of any operation in the cycle can be varied brit the full cycle completes a splice in about 30 seconds. While it has been clearly shown that niechanical improvements in the splicing machine are effective in reducing rejects a t the butt splicer, there has been a general feeling that Butyl h m a lower margin of safety for splicing than has natural rubber. Furthermore, it has been reported that Butyl shon-r, quite erratic results in the splicing operation. I n vien. of these difficulties, it was felt t,hat a !aborntory Btudy of the factors influencing the tack ol" Butyl would be helpful in understanding the splicing problem. Since natural rubber is considered to have good tack, Butyl and natural rubtler n-ere compared under t,hesame test conditions in so far as possilile. EXPERIMENTAL METHOD
The esperiniental technique which was used in this study i,. based on a method for quantitatively measuring tack in e l a s tomers which was used by Buise et (11. ( 1 ) . Certain mndifcntions were made in order to coiitribute as much information to the prohlrni of eplicing Butyl as possible. h diagrammatic sketch of the unit is presented in Figure 1 . It coiisists essentially of a platform scale for measuring pressure and tension and a moving arm for Contacting the rubber samples pnclosrd in an oven For temptri>:igtl~ i:, the ratio bet,\veen tlie tack ytreiigth arid the raw 3tnrli SI rcTlpth cxpre T h e ftictors affecting the, measured tack values liavt. I ~ t x i clivitlrd a i io1lom-s int,o t,lirw groups: External factors, thc condit,ionu unrlcr which the p o l ~ - m t ~ are r s contacted and sep:iratod : irihereri t polymer factors, such as molecular weight, molccular 5r-eight di~trihution,and unsaturation; and compounding factors, inclutling hlacli~,plasticizers, and accelerators. ,set, oi'c~oritlitions.
E X T E R N L FACTORS
Contact Pressure. Figure 2 presents data for the variation of the tack of Butyl with prepsure, and Figure 3 presents hiniilar (or Hevea. The tack of Butyl rises sharply as the presswe rises to lxtn.con 10 and 20 pounds per square inch; the tack then inc r e a x s ninre slowly as the pressure i. increased. \\-hen cut \vitli :ikniCr. at room temperature, Butyl reaches its nixximum t:ic*kitrcsiigth l)clo~v50 pounds per square inch applied 11 \T'hen twt ivith a hot knife (approximately 426" F.), Butyl requii,c,s a prcwure soiiie\vliat highcr than 100 pounds pcir q u a r e inrh 1)eiorc its maximum tack strcngth is rcachcd. Ht tlie otl1t.r hand, ~vliencut 11-ith a kriife a t room tcmperat :I tack stwngtli n-hich is lower than that of Butyl under thc same conditions. However, if IIcvea is cut Tvith the hot' lctiife (approximately 426' F.) thc tack strength rises sharply with increasing contact pressure. T h e upper limit of SO pound? pt'r
square inch is the value at which the sample tore from the clamps, the true stock strength not being reached. JT-hen a hot lalife is used for cutting, the tack strength of €€even exceeds that of Butyl. The effect of increasing pressure can bc understood iis an irnprovc:iwnt of molecular contact with a rciultant incr
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
Polymer Temperature.
2249
-1s the temperature of the polymer
rises, the tack strength decreaws fur both Butyl and IIevea. Figure 5 shows that above 150' F. the tack strength and the raw
TAG K M E T ER
Figure 1
effectiv(~nessof niolccular forces of atrriwtion: and an iricrcxiisiiig degree of intermingling of polymer chain segmcntq. Thc vffect of cutting kiiife temper:iture caiinut be so readily exp1:iiiiuI. The following section offers adtlitioii:tl data on thi? point. Cutting Knife Temperature. Figure 4 prese1its data f i ~ l ,t l i i a effect of cutting knife teriiperature on the tack of Butyl and I-Ievea. The tests were coriducted :it pressures of 50 and 30 pounds per square inch for Ilevea and Butyl, respectively. .kt these pressures the change of tack with pressure !vas relatively small. The tack of Butyl decreases regularly as t,he knife rises from 75 to 400' F., goes through a minimum at about 500 F.. and appeal's to rise again as the knife temperature reaches 600" I:. The trick of Hevea increases rapidly as the knife temperature is increased up to about 300" F.; further taniperat,urc rise has little effect in increasing tack. Won-ever, the liiiiitiiig value io^ Hevea shown in Figure 4 may he due t o clamp hrexli.. a . ~it3 ultiniatt. stock strcngth could not be measured.
stock strength of Butyl fall sharply, but teiid to level off above 200 F. Hevea (Figure 6) also loses tack strength and raw stock strength, the ran- s t o c k strt:iigtli falling rapidlj- Ixtn.ccri 80' and 120' F., aticl then, with tlic tiirk strength, dcei~(~:ihiiig 11101~~ slo\vIy aliove that tc~niperaturc. tlic higlirr tcnipc~r:iturc~sused, tlic polyriiers hati ION raw stock sti,cwgth aiid therefore ?-ieltled a t a rclntively Ion- tviisiori. Time of Contact. Figuix, 7 pr'ezents the data for tht: effect oi' time of contact on tack ,-trength. T h e t ~ l $trength i of both Butyl arid Hevea rises as the time of contact increasw uiitil the limiting stock strength is reached. At a higher preswrt', I3utyl i,eaches iti limiting strength more rapidly and a similar cffect \vould tic anticipated foi, Hrvcn. A4 greater Ic,ngth of time prrniits tlit: flow to a greater eyttxnt, thcrebv inipiwviiig molecular contact. Rate of Pull. Figui,es 8 and '3 give the data for tlic c4fcsct of late of pull on the appai'eiit stock and tack strc~rigtlicof Butyl and Hrvea, renpecti\--rly. For both polyniew the apparent, as tlic rate of pull iri tack strength iiicrea of cuttiiig knife temperature is the saiiic a' previously rioted. The relativel?. Ion- tack shown for Hcvea in Figure 9 results from the lo^ black loading. Humidity. T h e data in Table I slion. that the tack strength I J f Butyl is virtually unaffected by humidity ov(!r a range of 25 to 90'; rclative liuniitlit>-.
T.\Rr.D
E o s T.\CKO F BUTYL I. EI'FECTOF I ~ : L < T I \ -HUMIDITY Relatiw Humid1t y ,
Tack, Lb. In.
';
Teat Conditions
i ~1
1
0
10
7t
13
40
50 60 PRESS8RE.PSI
I
I
70
80
1
90
1
1
I00
Figure 2 I ~
I
EFFECT OF KNIFE TEMPERATURE CN TACK
L
6
POLMY
1 0
I 10
i PO
I 30
40
50
I
1
60
70
PRESSURE,PSI.
Figure 3
I
80
1
90
I
100
J
SRF
ioo14o-so .hiooriEr) 50
I
i
1
Vol. 41, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
2250
higher stork strength, are subject to further improvement in tack. Tack Strengtlibr ___ Unsaturation and Molecu60 scc. a t 12-10 sec. a t 33.6 lb./sq. in. lh./sq. in. lar Weight Distribution. 4 4 . 7 =t 0 . 9 4 3 . 9 =t 1 . 3 Table I1 presents the data for 49.2 = 1 . 4 40.0 1.4 47.7 = 0 . d 45.9 * 0 . 3 tack strength of a number 46.0 * 1 . 4 4i.7 * 0.4 of Butyl polymers having 4'3.8 - 0 . 9 44.9 -0.7 4.5.2 0.5 43.3 * 0.6 different unsaturations and 41.0 * 0.7 40.6 t 0 . 7 molecular weight distributions. Neither unsaturation nor m e lecular weight distribution within the range tested seems t o have much effect on the stock strength or the tack of the polymer. Scorch. Table I11 presents tack data for a sample of Butyl, compounded in an inner tube formulation, which has been quite scorched (precured) as indicated by the Killiams plasticity.
STREXGTH O F VARIOUS BUTYLPOLYMERS TABLE 11. TACK
dample 1 2 3
Relative hIol. K t . Distribution Sorinal Xarrow Kido Very wide Wide Kormal Normal
Polymer
GR-I R-3 R-4
R-5
4
5 6
R-6 Y-15 Y-25
7
Mole "c Unaatd. 1.6 1.6 1.6 1.0 2.4 2.3 3.3
\Iooney" Viscosity at 10 l o C., 8 Alin, 43 47 46 43 46 43 43
Stock Strrngthb, Lb./Sa. In. 48.4 * 1 . 3 M . 3 = 1.4 51.1 t 0.2 5U.2 f 0 G 33.1 - 0 . 5 47.fi * 0 . 6 47.8 * 0.2
Piire gum.
b Baaed o n original cross-sectional area.
Compound: polymer 100, S R F 30, EPC 20; hot knife.
10. As the IIooney viscosity increases from 38 t o 73, the stock strength increases continuously, whereas the tack strength goes through a maximum between 50 and 60 Mooney. The tack strength is limited in the low llooney range by the lox stock strength, but the high Xooney polymers, having appreciably
C
f
f
PRESSURE
10
__
2OPSl
I
I
I 60
80
100
120 140 160 I80 200 T E M P E R A T U R E OF STOCK,*F.
220
I
240
10
0
I
20 RATE
Figure 5
40
30
OF P U L L
I N /MIN
Figure 8 E F F E C T OF R A T E OF P U L L N A T U R A L RUBBER
60
~~
I 50
I
t
pI--
HOT K N I F E
COLD KNIFE
COMPOUND
20
60
80
100
I20
140 I T E M P E R A T U R E OF STOCK,*F.
IO0 1 4 5 M O O N E Y l
HEVEA PRESSURE
(0
~~
30 P S I
I
Figure 6 20 JO RATE O F PULL, IN./MIN.
IO
0
40
Figure 9
100 1 4 0 - 5 0 MCQNEYI 30
POLYMER SRF
70
0 Y
30 20
I OR-l
1
100
B U T Y L A N D N A T U R A L RUBBER
IO 1
I
20
40
I
I
60 80 CONTACT TIME.SEC.
Figure 7
I
,
100
120
,
Mor
KNIFE (4es'~IJ
I
1
I 30
35
40
45 SO 55 60 65 P U R E OIJM 8 ' U O O N E I AT 212.F
Figure 10
I 70
October 1949 ~ A B I X111.
INDUSTRIAL AND ENGINEERING CHEMISTRY
EFFECT OF SCORCH 0s T A C K STRENGTH OF
TFBESTOCK
2251
knife temperature (Figure 4) is not attributed to scorch in thr normal sense because the presence or absence of curatives hnp little effect on this phenomenon.
GR-I
Extrusion Time a t 375’ F. S.Iin.n 0.5
Formulation -of Williams _ Stock Plasticity Tackb Parts 22.1 * 0 . 3 138-1 Polymer, GR-I 100 3.0 136-3 22.0 * 1.5 Black, SRF 50 1.0 137-2 20.4 f 1 . 0 ZnO 5 6 . (1 145-3 20.3 * 1.3 Sulfur 2 8.0 174-46 19.0 * 1.0 Tuads 1 Y.2 215-113 (19.0) Captax o.5 Stock scorched by recycling through extruder. Pressure 10 lh./sq. in., contact time 6 s e e . , rate of pull 10 in. j m i u .
COMPOUNDING FACTORS
Carbon Black. Table I V presents data for the effect of different types of carbon black on the apparent tack of Butyl. -4s the particle size of the carbon black increases, the stock strength and the tack strength both decrease. T w o mixtures of different blacks have an effect which would be anticipated by interpolation b between the values obtained €or Butyl containing only the individual blacks in question. Since ratio of the tack strength to TiR,,E IV. E~~~~~OF caRBoN B~~~~~~O N T~~~ O F B~~~~ the stock strength is reasonably constant, it may be concluded Tack, Lb./Sq. In.6 . t h a t the type of carbon black affects the tack strength only in so 33.6 17 Ib,/sq. in. Stock .~ ~ 60-min. - lb./sq. in. far as it changes the ram stock strength. Strength, 30-min. 10-min. ! > > e of Black“ Lb./Sq. I n . contart contact contact Plasticizers. D a t a for the effect of various plasticizers (3 56.6 3 P C (WYEX) 43 1 $8.4 47.1 parts per 100 parts gum) on the tack of Butyl are given in Table H M F (Philblaok) 54.6 42.2 47.4 45.8 33., 37.9 35.2 V. Of the plasticizers listed, only two seem to have a pronounced 4 R F (Gaster) 43.5 \IT (Tlirrinax) 38.1 31! 8 3-1.9 :33 1 effect on the relative tack strength. Paraffin v.-as and stearic acid 1 Forinulation: OR-I 100, h!acii 5U. lower tlw tack of Butyl to Rate of pull 13 in./min., hot knife. less than 53yo and less that. SS%, respectively, of its ino s TAU,r ) F Br.mI. TABLE 1.. E:I..~F:cT O F PLASTICIZERS herent tack strength under -T a c k * (12 Lb./Sq. In.: . ‘ [ a c k a 133.8 Lt,,,’sI1. I ~ . : the same conditions. None 30-min. contact 60-min. rontact I n - V i n . Contart RelatirTe-Relative of the others raise the tack Relativr Stock Strenrttr, strength, Lb./sq. in. atrength, % Lh./Pq. in. strength, % s t r e n g t h b y a significant Plaat !ciLerQ Lb. Sq. I n . LG., sq. i n . 5; amount although they alter the :lycerol ‘48.3*(!.4 36:.6r1.4 75.8 41.7*0.8 86.3 11.1*0.6 85.1 .Foruin 20 .lil*O.L’ 33.6*0,8 74.5 39.911.3 88.5 3Y.lf0.8 86.7 shape of the contact time or Petrolatum 42,5f0,2 33.8-0.9 79.6 36.711.0 86.4 36.0i.O.O 84.7 pressure against tack curve Dibenzyl ether 4%.6*0.4 36.4-1.3 81.6 39.8*0.5 89.2 37.8f0.8 81.8 3araffin wax 42.0 f O . 0
f
f
f
*
*
*
The n-urd “tack” (as used in the subject of the foregoing paper) does not occur often in the titles of 1.hE.C. papers. I t is hoped that as this report is channeled through records and indexes it will shox. up in the proper subject categories and that cross references will not be misleading. In addition to its other general meaningsa small nail, a course over land or sea, loose stitching, a fastening or attachment--“tack” is used in a number of technical applications to describe stickiness and/or adhesion. For example, in the paint and varnish industry, tack, measured in dynes, is a function of viscosity and especially refers to a state of drying betiveen application of a layer of paint and its final drying. I n the rubber industry, tack refers to the adhering property of raw rubber, measured in pounds per square inch of stress required to separate layers; in the splicing operation there is of course a double connotation as ‘‘a tack is achieved as the result of tackiness.” “Tack” has also been used to describe the stickiness of some overcured rubbers. However, the rubber industry prefers to reserve “tack” to designate the natural adhesiveness of m w rubber which is a great asset in f:thricating, and to call t,hr other stickiness “degradation”. TTelch, ?;elson, and Wilson h a w reported further work on Butyl rubber in 3 paper, “Effect of Diolefin TJ pe and Concentration on Properties of Butyl Rubber,” which will be published in the December issue of 1.kE.C. The properties of Butyl rubbers made with diolefins other than isoprene were tested to determine the suitability of Butyl polymers for the production of mechanical goody tires, and other products.
