i
Y
Acid Pulping of Southern Pine Sulfite Pulps for Viscose Manufacture
The suitability of bleached southern pine sulfite pulp for viscose was demonstrated on a laboratory scale. Suitable pulp was cooked in 11 to 13 hours at yields of 41 to 42 per cent of the dry weight of the wood. Adequate purification was secured within 4 to 8 hours at 40" C.through application of 3 per cent or less of chlorine as sodium hypochlorite.
CHARLES CARPENTER AND FRANK McCALL Pulp and Paper Laboratory of the Industrial Committee of Savannah, Inc., Savannah, Ga.
R
ESEARCH concerning the suitability of pine sulfite pulp for viscose began in 1934 at the Pulp and Paper Laboratory of Savannah. I n that year Rasch (4) pointed out the possible significance and the proposed scope of this research. A year later Herty and Rasch (3) gave the first description of the experimental work. It was reported then that the chemical characteristics of bleached pine pulps compared well with those of commercial rayon pulps; furthermore, small-scale conversion of bleached pulps into viscose had been performed satisfactorily in two commercial laboratories. Processing and testing of pine sulfite yarns a t the Savannah laboratory were announced later by Herty ( 2 ) . He showed that the yarns from pine compared well with yarns from commercial rayon pulps when produced under the same conditions. Detailed information regarding the laboratory processing of bleached pine sulfite into viscose was given by Itasch ( 5 ) in 1936. I n this more comprehensive article Rasch indicated that satisfactory viscose could be made and spun into yarn from the very dense wood of the longleaf pine as well as from the less dense wood of loblolly pine. I n these publications only fragmentary information regarding the cooking and bleaching of pine was included. The purpose of this paper is to present cooking and bleaching data of pine sulfite pulps and to attempt to correlate these data with the characteristics of the viscose and yarn.
reproduced in Figure 1. A was that from which the springwood and summerwood were isolated. The wood data are assembled in Table I. I n general, 5/s-inch green chips of approximately 55 per cent oven-dry weight were employed. The cooks of springwood, summerwood, blue-stained longleaf pine, and slash pine were carried out with smaller amounts of wood held in perforated alloy steel containers. During the cooking the containers were suspended in the digester.
Pulping
Pulping was carried out in a 60-cubic-foot alloy steel digester equipped with an external heat interchanger and circulating pump. The heater and pump were employed throughout. Cooks 444,445, and 447 were of longleaf pine. Each charge was pulped a t a different maximum temperature to approximately the same bleachability and yield. Cooks were blown by color. Charge 453, consisting of loblolly pine and baskets KO. 2 (springwood), No. 5 (summerwood), and No. 6 (slash Wood pine), was cooked similarly to charge 445 but to a somewhat lower bleachability. Cook 454 (longleaf) and basket No. The wood of young longleaf, loblolly, and slash pines, and 2 (blue-stained longleaf) were made with soda base acid. isolated springwood and summerwood were employed. These The complete curves of cook 445 and the temperature woods varied markedly in density, growth rate, and relative curves of cooks 444, 447, 453, and 454 are reproduced in percentages of springwood and summerwood. RepresentaFigure 2. Pressure and acid curves of cooks 444, 447, 453, tive cross sections of the loblolly and longleaf pulpwood are and 454 were similar to those of 445. Cookine: and pulp data are given in Table 11. The yields of screened and washed pulp were TABLE I. WOODDATA nearly identical (41 to 42 per cent), regardless Weight Ovenof the cooking schedule or wood species. All per Growth D f y Species Densitya Cu. Ft. Kateb (Chips)C Condition Cook KO. pulps except basket cooks were washed over the Lb. % inclined wire to remove pitch. As the washing Longleaf ( P . palustris) 0.55 34.3 4.1 55 Fresh * 444,445, 447, 434 over the inclined wire entailed a fiber loss of apLoblolly (P.laeda) 0.45 28.1 2.4 52 Fresh 433 Longleaf 0.58 36.2 4.3 55 Blue stainedd 454, basket No. 2 proximately 4 per cent, the reported yields from Slash ( P . heterophulla) 453, basket No. 6 0.45 28.1 2.3 82 Air dry the baskets were correspondingly higher, Pulps SDringwood 0.28 ,.. 82 17.5 Air dry 453. basket No. 2 SLmKerwood 0.54 33.7 .., 82 Air dry 453, basket S o . 5 washed on the inclined wire had ether-soluble a Based on oven-dry weight and green volume. contents of 0.4 or 0.5 per cent; the basket cooks 6 Nuniher of annual rings of a given cross section divided b y the diameter (in inches) of that section. had ether-soluble contents of 0.6 to 0.9 per cent. Over>-dry weight as per cent of wet or green weight. (Data relative to the operation of the inclined d Blue-stained wood is pulpwood discolored b y Ceratostornella sp. wire were reported by Carpenter, 1 . ) u
0
15
INDUSTRIAL AND ENGINEERING CHEMISTRY
16
VOL. 30, N O . 1
The yields of oven-dry pulp per cord of 78 solid cubic feet varied considerably with the density of the wood cooked. Dense longleaf pine yielded approximately 1100 pounds of pulp per cord; the less dense loblolly yielded only 900 pounds. This difference was reflected in the yields per unit digester volume (Table 11).
Bleaching Single-stage soda-base h y p o c h 1or i t e bleaching was employed throughout except for two two-stage bleaches of pulp 445. The bleaching was performed with 2 to 4 pounds of pulp in a laboratory bleacher equipped with a water bath and paddle agitation (56 r. p. m.). The single-stage bleaching data are given in Table 111. I n the case of pulps 445, 447, and 453, two or more batches of each pulp were bleached under varying conditions of hydrogen-ion concentration, time, or temperature. Yields of bleached pulp were approxim a t e l y 98 p e r c e n t (oven-dry basis). Brightness values' increased with increased c h l o r i n e c o n s u m p t i o n wherever two bleaches were made from the same unbleached pulp. Copper numbers were lower as the final pH values of the bleach liquor were higher. Cuprammonium viscosities of the bleached pulps were lower as the 1 Courtesy of the Pulp and Paper Department, New York State College of Forestry.
( Ab0Ve)FLABORATORY SHREDDER SHOWIXG SODA CELLULOSE (Below)
L.4BORATORY XANTH.4TIOK R.4RETTE
(Left) SPISNIXG VISCOSE OX EXPERIMENTAL BOBBIN SPIKXING M.4CHINE
(Right) REELINGUNBLEACHED RAYOS Photographs by R. H . Rasch
INDUSTRIAL AND ENGIUEERING CHEMISTRY
JANUARY, 1938
A.
Loblolly
17
when the purificationi. e., c h l o r i n e c o n sumption--was m o s t vigorous. A two-stage, c h l o rination-hypochlorite purification and a twostage high-low density hypochlorite bleaching were carried out with pulp 445. Bleaching conditions a n d p u l p data are given in Table 1V. I n both cases the total percentage chlorine consumed was 1.9, and the total bleaching time was 6.5 hours. The bleached p u l p s B . Lon#l,ieo/ C. Lobloilv had s i m i l a r chemical constants. The twcFieim: 1. Cnoss SECTIONS 01 Pumr-oon ( X 'I3 stage bleaching represented a considerable saving in chlorine over the single-stage bleaching.
Viscose Several of the bleached pulps were converted into viscose and spun. The data pertaining to the viscose processing and spinning are given in Table V. The procedure was as follows: Two pounds of conditioned pulp sheets (10 per cent moisture) were steeped in 18 per cent rayon-grade sodium hydroxide for 1.5 hours. A nickel steeping tank and wire cage were employod. After steeping, the sheets WPM allowed to drain 5 minutes. They were then pressed t,o a ratio of cellulose :oailstic equal to approximntely 2 : 1. After pressing, the sheets were shredded 3 hours in a cast-iron Werner-Pfleiderer shredding machine of 4gnlIon capacity. The alkali cellulase vas then aged at 21.5' C. for 48 to 72 hours, aceording t o the cuprammonim viscosity of the bleached
T ~ B L11. E COOKING A N D PI~LP DATA Cook Nu. Wood
Cooking acid: Base GaI./lOO Ib. wood Initial so1.0 %: Total Combined SO* s t blow. % : Total Combined Cooking: Tots1 time. hr. Mar. tern".. " c.
X a r . preraure. Ib./rq. i n .
P u b yield: Screened and washed, %
screenings. % I.h./eord (oven-dried) d Lb./lOU c u it. o h i m (oven-dried)
RleeehnbiIiLy : Peima".a"ste N0.I 70ciz (1Wp"olrlorite)o
444 I.o"glea! ra
(i7 3.1 1 2
0 8
I"
10.5 147 95 4lb 0.6 1100
475 .5 . 5
2.2
445 Lon.leaf
('%
iia
i'B
64
,5 . 2 1.2
10.8 142 90
1;s
i. 2 1 ~ 3
1.0
I"
cs
1.1
I"
12.9
337 90
1.4
{
Ilsrket
Basket
oook
cook 453
No. 2,
4.53
No. 8.
Basket No. 8 . oook
433
13.
1
N* 62 4.7 1.2
1.6
in
10 0 I42 90
Basket No. 2 cook 454
11.0 I42
...
42b 1 1 1150 490 i. 0 2 5
4.6
80 I on 2.9
8* 100 2.8 11.5 0.8 ti8
2.0
3.6 I .0
4.0
1.8
a.8 1.7
8.8
4,s
1.8
2.0
4.4 2.0
03 ti0 2.7
2.7
PUIP:
n-ceilulune. %h viseurity, eent*poiaeri Comer No.< Ether-sol.. %i
Aah. %i 13iiphtnessi
110
Ion
2 .a 0.4
0 3
...
0.5 11.2
ti7
* Sander'a teat. b Yield oven-dry ~ u l p screened and waphed O D ioolined wire. Yield oven-dry pulp srreened only. d Based on 78 cu. ft. solid wood i n standard w r d of unbaiked a.ood. ' Rnaed on ohqervation with tiO-eu.-ft. digester.
00 h0
2.9 0.4 0.3
63
'I0 a0
2.5
?.>a ! 2.8
0.12
0.6
0.2
0.3
...
...
!a ,XI
2.5
0.9
0s
...
0.5
0.2
io
0.7
0.3
...
I Pulp Blenohine C o i ~ u i a l i o nnumber. 0 Peroeotqe of GI, as iiypoohiorite to bleach to 82 brightness i i n one stsgc h V o l u r r l ~ t i i roxidation metbod. i T.I.P.P.I. standsid methods. I Hiegins 0"I"l ana1yser.
1 NDUSTRIAL AND ENGINEERING CHEMISTRY
18
r'
tions were made with humidified representative samples of t,he twisted and undesulfurized yarn. Physical tests were performed on a Suter single-strand tensile and elasticity tester.
40'C, SXCONSISTENCY 5 6 R . P
tn,+t5; ,454
A 4t7-I
TEMPERATURE
i
Splitting of sheets during pressing was infrequent with pine. In the past, splitting of commercial rayon pulps had been experienced. This difference was probably due to the greater length of the pine fibers. The hemicellulose content from the drain and press liquors varied from 6.2 to 8.6 per cent. No correlation between wood species, cooking or bleaching procedure, and hemicellulose content could be observed. The hemicellulose value, 6.6 per cent (average of nine batches), for commercial rayon pulps fell within these limits. The shredding of the pine pulps was satisfactory in all cases. The xanthated crumbs from pine did not tend to ball any more or less than those of spruce have done. Two-stage bleached pulps gave alkali celluloses superior to one-stage pulps in color.
PRESSURE
8
E 1
I
2
+
FIGURE 2.
\
6
0
IO
12
14
HaRS
COOKING CURVES
VOL. 30, NO. 1
FIGURE 3. BLEACHING CURVESFOR PULP447, BATCHES1, 2, AND 8
TABLE 111. SINGLE-STAGE BLE.4CHING Pulp No. Bleach No.
7
444 5
---4452
c
5
1
2
447
-4541
5
8
2 (bluestained)
1
3
453
(spring 4
(summer5
(slash)
wood)
wood)
98
99
99
2
Bleaching: Clz applied, % Cl? constmed, % Temp., C. Consistence, %a Time, hr. Initial p H Final p H Yield, % b
...
97
98
98
98
...
98
99
99
98
98
Bleached pulp: m-Cellulose, % C o m e r No. VisXosity, centipoises Brightness Ether-sol., % Ash, % a Grams oven-dry nulp per gram liquid. b Laboratory bleaching; no fiber loss.
pul . After aging, the crumbs were transferred to a waterlacfeted Baker-Perkins 5-gallon hexagonal xanthating barette. Carbon disulfide (37 per cent of the cellulose in the alkali cellulose) was then introduced under vacuum. Xanthation continued for 3 hours at a controlled temperature. At the end of the 3-hour period the barette was evacuated for 30 minutes and dumped. The charge was then incorporated in an aqueous solution of sodium hydroxide of such volume and strength as to give a viscose solution of approximately 7.2 per cent cellulose and 6.8 per cent sodium hydroxide. A 3-hour mixing period followed. At the end of the mixing period the viscose solution was transferred to a pressure vessel preparatory to filtration. The viscose was then forced three successive times through media identical for each viscose batch. The medium of the first filtration consisted of four layers of Canton flannel, four layers of cotton batting, and two layers of cambric. For each subsequent filtration the cotton batting was increased by two layers. For filtering, the media were clamped in a two-plate filter press 325 sq. cm. in are'a. An air pressure of 95 pounds per Equare inch was maintained throughout. The filtered viscose was placed under vacuum and allowed to ripen at 21.5' C. The solution was spun a t proper maturity. The spinning machine was a five-spool, 125-mm. bobbin laboratory machine. The bobbins of freshly spun viscose were washed overnight on a suction washer. Bobbins and yarn were dried in a rotarytype dryer equipped with an exhaust fan and heater. After humidification the yarn was twisted (3.5 r. h. turns per inch) on a Fletcher laboratory twisting machine. Determinations of denier, dry and wet strengths, and elonga-
TABLE IV. TWO-STAGE OF PULP445 BLEACHING Bleach No. Bleaching: Chlorination: Clz applied clz c o n y m L Z % Temp., C. Consistence, % Duration, hr. pH Hypochlorite: C h applied, % Cl? consumed, % Temp., O C. Consistence, yo Duration. hr. Initial p H Final p H Total Clz, % Total time, hr. Yield, % Bleached pulp: m-Cellulose, % Copper No. Viscosity, centipoises Brightness Ether-sol., % Ash, %
4
1
1st stage 1.3 1.2 25 3 0.5 2.4
.. ..
2nd stage
1st stage
, .
98
..
89
.. ..
2.9
28 85
0.1 0.18
..
2nd stage
98
91
2.9
31 83
0.1 0.20
JANUARY, 1938
P u l p No. Bleach No. Viscose No. Steepingl.5hr.at21"C.: Hemicellulose, %" Shredding, 3 hr.: Temp. C. NaOH: % Cellulose, 70 Aging a t 21.5' C., hr. Xanthation 37.5%b CSz: Temp., C. Filtration rating C Ripening a t 21.5' C., hr. Spinning (40-filament sninnerette) :
INDUSTRIAL AND ENGINEERISG CHEMISTRY
444 3
220
-
2 224
TABLE V. 5 225
8.6
6.8
7.6
24-6 13.8 30.4 72
26-7 13.8 32.2 48
25-6 14.2 28.9 72
. ..
25-7 Fair
28-7 Fair
Poor
48
46
42
6.6 7.0 43 44 11.0 8.2
6.7 8.3 71 75 9.6 8.2
6.6 7.0 105 20 10.5 8.2
445---
1 223
4 227
VISCOSE
-4471 221
19
DATA
2 230
-
1 222
2 229
453 3 232
4 240
5
231
. Commercial spruce 228
6.5
6.4
6.2
6.7
6.2
6.7
7.5
6.2
5.7
26-7 14.1 29.4 72
23-6 14.5 29.6 72
26-8 14.6 30.3 72
26-7 14.2 29.8 72
25-8 14.2 29.9
26-7 14.3 28.4 72
26-6 14.4 29.2 72
26-6 14.1 28.2 72
25-6 14.1 29.6 72
24-8 15.3 30.5 72
26-7 Excellent 45
28-7 Good
Fair
Fair
Good
44
45
45
24-6 Very poor
27-6 Excellent 4.5
26-7 Fair
45
28-7 Excellent 45
27-7 Excellent 69
6.6 7.1 71 29 10.4 8.3
6.6 7.2 100 37 9.3 8.1
6.6 7.0 78 41 10.8 8.2
6.8 7.1 142 31 10.3 8.2
6 6 7.2 40 45 10.2 8.1
6.7 7.1 57 26 10.2 8.2
...
2.7 I .2 30 42 10.2 8.3
...
78
. ..
...
...
...
... ... ...
46
6.8 7.1 47 47 10.2 8.4
6.6 7.2 27 21 10.4 8.2
Yarn (undesulfurized): Stretched Denier 140 156 154 152 149 143 156 140 147 . . . 159 164 156 154 Strength, grams/denier: 1 37 1.51 1.52 1.45 1.50 1.55 1.48 1.60 1.49 ... 1.50 1.47 1.85 1.48 Dry 0.50 0.43 0.57 0.61 0.57 0.63 0.55 0.68 Wet 0 58 , . , 0.63 0.59 0.83 0.60 Elongation, 70: 14 13 11 15 13 15 14 13 15 ... Dry 22 16 12 23 21 25 20 23 20 Ret ... 0 Volumetric oxidation method; 1 gram KzCrzOi 3 0.1375 gram hemicellulose. e Falling sphere method, '/s-inch steel ball, 10 inches,, 21' C. b By weight of the oven-dry cellulose in alkali cellulose. / Hottenroth method, 10 per cent NHhC1, 20 grams viscose a n d 30 cc. 0 Excellent = 15 min. for first filtration, no changes of filterine media: good = water. over 15 min. f o r first filtration, no changes; fair = one change of-filteringmedia; Adjusted t o approximately 8.2 per cent HzSOh before each spinning; poor = two or more changes; very poor = not spun. NazSO1, 22.8 per cent; ZnSOa, 0.8 per cent; glucose, 4 per cent; 14 inches d Maximum depth of viscose permitting resolution, b y Iiessler tube method. in depth, 40' C.
Filtration of the viscose solutions was from poor to ex- * cellent. I n general, the two-stage bleaching yielded pulps with better filterability. With single-stage bleaching the filtration improved with increasing purification of the pulps. This was best exemplified by batches 1 and 2 of pulp 447 and by batches 1 and 2 of pulp 453, where increases in the bleach consumption resulted in considerable improvement in the filterability of the viscoses. The springwood pulp filtered much easier than the summerwood pulp. This was in accordance with earlier observations relative to the comparative filterability of pulps from . denser woods-i. e., high summerwood content (1ongleaf)and from less dense wood-i. e., high springwood content (loblolly). Microscopical examination of the summerwood viscose showed a number of swollen, undissolved, thickwalled fibers. The behavior of batch 1 of pulp 445 and batch 2 of pulp 447 demonstrated, however, that excellent filtration of dense-wood viscoses could be assured through adequate purification of the pulps. The clarity of the viscose solutions was a function of the ether-soluble content of the bleached pulps. The clearer solutions were obtained from those pulps having low (0.1 to 0.2 per cent) ether-soluble contents. The more turbid solutions were from the basket-cooked pulps which had not been washed on the inclined wire. The commercial pulp with an ether extract of 0.4 per cent gave the lowest clarity value. No well-defined correlation could be found between yarn strength and any one factor of cooking or bleaching, as shown in Table VI, where cooking, bleached pulp, viscose, and yarn data are summarized. For each cook the averages of the batches bleached and processed are given.
Summary Sulfite pulps of 1.5 to 2.5 per cent chlorine consumption were obtained a t yields of 41 to 42 per cent from the wood of young trees of longleaf, loblolly, and slash pines. The unbleached pulps were characterized by a-cellulose contents of 89 to 93 per cent, cuprammonium viscosities of 50 to 100 centipoises, copper numbers of 2.5 to 2.9, and brightness values of 63 to 68.
.
Portions of each of these pulps were purified according to one or more different procedire;. Data bf the bleached p i l p s were: per cent a-cellulose, 87 to 91; copper number, 1.6 to 3.1; cuprammonium viscosity, 19 to 31; percentage ethersoluble content, 0.1 to 0.7; and brightness, 80 to 86. Each bleached pulp was converted into viscose under uniform conditions. Significant characteristics of the viscose batches were : hemicellulose from drain and press liquors, 6.2 to 8.6 per cent; filtration, poor to excellent; and clarity, 30 to 142 mm. The tensile strength of the unstretched yarns varied from 1.37 grams per denier dry and 0.43 wet, to 1.60 dry and 0.68 wet. Average strength was 1.50 grams per TABLE VI. SUMMARY Wood
Longleaf Longleaf Longleaf Loblolly
Commercial rayon Pulp
Cook No. 444 445 447 453 .. Max. temp., C . 147 142 137 142 .. Yield. %. a41 42 42 41 Unbleached pulp: Viscosity, centipoises 100 100 100 50 ,.. 2 2 2.5 2.0 1.7 ... Clz, % Bleached pulp (av. of pulps processed) : No. batches 1 4 2 4 1 a-Cellulose, % 89 90 90 91 90 Copper S o . 2 6 2.9 2.6 2.7 1.8 Viscosity centipoises 27 25 24 23 22 Ether-sol., % 0.2 0.2 0.2 0 4 0.4 I-ield, 70b 98 ... 98 98 Yield bleached pulp from woodb . . , 41 41 40 Viscose (av. of pulps processed) : Hemicellulose, yo 8.6 6.9 6 3 5.9 5.7 Clarity, mm. 43 87 1,lO 44 27 Filtration Fair Satisfactory Excellent Yarn (av. of batches processed) : Denier 140 I53 150 152 154 Strength, gram/denier: 1 52 1.46 1.52 1,52 1.48 Dry Wet 0.57 0.53 0,59 0.62 0.60 Elongation, yo: 14 13 15 16 16 Dry Wet 22 18 23 23 21 a Oven-dry basis; screened a n d washed pulp. b Oven-dry basis; based on laboratory yields of bleached pulp. Mill yields would be 2-4 per cent lower.
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
20
denier dry and 0.58 wet at 15 per cent and 21 per cent elongation, respectively. Significant data of a commercial rayon piilp processed and spun at the same time were: hemicellulose content, 5.7 per cent; filtration, excellent; clarity 22 mm.; tensile strength, 1.48 grams per denier dry and 0.60 wet at 16 and 21 per cent elongation, respectively.
Acknowledgment The authors wish to express their appreciation to C. H. Herty, director of the laboratory, for his interest and advice during the execution of the work. They also acknowledge the assistance rendered by the staff of the laboratory. To
VOL. 30, NO. 1
J. S. Fox for the bleaching and the chemical analyses of the pulps and to W. L. Hendrix for the cooking of the pulps special acknowledgment is due.
Literature Cited (1) Carpenter, C . , Tech. Assoc. Papew, 20, 371 (1937). (2) Herty, C . H., Texiile FVmZd, 85. IS40 (Sept., 1935). (3) H e r t y , C. H., and Res& R. H., Raym and Melliand Tcztilc Monthly. 16, 107-8 (1935). (4) Raseh, R. H., Manufa~turersRecord, Nov.. 1934. ( 5 ) Rasch. R. H., Paperlnd., 17, 948-53 (1936). R E C E ~ VSeytemher E~ 10, 1937. Presented before the Diviaion of Cellulosa Chemistry at the 94th Meeting of the hmeriean Chemioal Society ,Rocheater N . Y . . September B to 10, 1937.
MASTIC FLOOR TILE --CARLETON ELLIS Ellis-FosterCompany , Montdair., N. J.
FIGURE1.
APPEARANC~ OF TILES CONTAINING A SULPURRESINBINDER AFTER A YEAR'SSERYICE
T h e rirela xhows tile in
vestibule: the other oietuie ii a s l e ~tread exposed out of doois.
B
LL flooring material can be classified under the headings of textile, wood, plastic, or ceramic. Plastic floor compositions include linoleum, rubber, cork, and mastic coverings. Each type of floor has its particular good features. The present outline deals with only one phase of the plastic floor-covering field. The main advantages of mastic flooring are its cheapness and acceptable durability. The material is not as hard and cold as ceramic, and feels more resilient underfoot. Rubber and cork compositions are much more expensive; this is also true of ceramic tile, which comes in a class nith marble. Disadvantages of present mastic products are susceptibility to solvents and grease, more or less eold flow which causes slow indentation when heavy objects are placed on the floor, and liability to scratching. At present, about 12,000,000 pounds of asphalt tile are used yearly in the United States; one company alone is in a position to produce 15,000,000 square feet a year.
Asphalt Tile Early plastic floor making involved a heavy asphalt solution containing mineral fillers which was troweled smooth and allowed to harden by evaporation of the solvent. Later
the making of separate tiles to lay in place was introduced, the binder being hot-mixed with the fillers. Production of individually molded tiles mas first practiced, hut this was superseded later by the present process oi sheeting and cutting to size. As long as asphalt was used as the binder, colors were limited to blacks, although the duller shades of red, green, and brown were possible by heavy pigmentation (8). Candle tar or stearin pitch, mixed with sufficient hard asphalt to give i t the right body and consistency, was the usual hinder. Asphalts such as gilsonite, whose dominant color is brown instead of black, were preferred, since a somewhat wider range of colors W B S then possible. A representative formula is: 25 parts Vegetable itch 25 Asbeatup f i f e 120 Coloring matter to shade GiI8O"ite
The ingredients are mixed a t an elevated temperature and shaped (6).
Light-Colored Tile With the trend in all industries towards lighter and brighter colors, the tile manufacturer in seeking to satisfy this preference turned to materials of lighter color than asphalt. Coumaron resin was a more or less natural choice not only on account of its color but also of its unsaponifiable nature (3). At present the demand for this resin for tiles taxes the supply. Since it is thermoplastic, no change in process was required and the only problem was to find a plasticizcr that would give the right consistency. Fatty acid pitch was selected of necessity since i t imparted a toughness not obtainable with other cheaply available softeners. However, the inherent brown color of fatty acid pitches is a disadvantage, and cheap tiles of very light color are still not possible. The following is an example of such a composition: Vegetable pitoh
