The Saran coating latices are colloidal dispersions of solid polymer in water. The particle size, observed with an IlCA type B electron microscope, is uniform and ranges from approximately 0.08 to 0.15 micron (Figure 1). The solids content can be made as high as 607, without sacrifice of particle size or distribution. Figures 2 and 3 show the variation of specific gravity and viscosity, respectively, with increasing solids content. Thc specific gravities were determined with standard hydrometc:rs and the viscosities by the capillary method. Tlie Saran coating latices are somewhat sensitive to coagula1ion by electrolytes and water-miscible organic liquids:
Applications, formulation techniques, and physical properties are presented for a new Saran coating latex. It is characterized by ease of application, rapid drying, and low cost; the resulting coatings are outstanding for such properties as high gloss, clarity, toughness, fireproofness, unrestricted color possibiIities, and high degree of resistance to water, oils, acids, alkalies, and organic solvents.
T
HE copolymers of vinylidene chloride are prominent in the field of thermoplastics for their high degree of resistance to a wide variety of chemicals and their very low rate of transmission of gases and vapors as well as for their excellent mechanical properties and fireproofness. These properties exist through a wide range of polymer structure from crystalline, fiber-forming molding powders to amorphous, readily soluble coating resins, which permits their utilization in a variety of application. The latex discussed here furnishes a further means of making use of the qualities of the Saran type resins-namely, through their use as film-forming and coating compositions in which water is the dispersing and carrying phase. These water dispersions are the newly developed Saran coating latices and their utilization eliminates the costs, toxicity, and fire hazards which accompany the use of organic solvents formerly required for the application of similar coatings.
Sample (100 Grams) Unplasticized l a t e x 25% plasticizer in latex
Cc. of 5% Salt Soln. Required t o Produce Faint Trace of Coagulation iXh;aCln MpCh Alt(BO4)s MeOH 44 10.5 2.5 75 2c 0.4 0.1 5
P"C',;
These concentrations are much higher than need be encountercd in normal practice. Infinite dilution of the latex with hard watvr produces no coagulation or unstabilizing effects. I n common with other water dispersions, the Saran latices s h o ~ ' greater stability in contact with certain metals than with otlicrs. The order of preference of representative metals found t o be satisfactory for processing and handling the latices (pH adjusted between 5 and 8) follows: stainless steel, chromium, tin, bronze,
468
May, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
brass, nickel, aluminum. Metals, such as black iron and mild steels, which are readily corroded are unsatisfactory; however, these surfaces are satisfactory if coated with a water-impermeable finish, such as one of the Saran coating resins i n the form of a latex or in organic solvent solution. The p H of the latex as normally furnished is in the range 6.5 t o 7.5. This may be raised t o 12 by addition of ammonia, although some discoloration may occur i n the higher range. Likewise, the p H may be lowered t o 2 by adding a monobasic acid such as hydrochloric or nitric; coagulation begins a t a p H below 2. FORMULATION TECHNIQUES
No extraordinary technique is required for incorporating various ingredients into Saran latices. Any precautions t o be observed are the same as would be employed in handling any colloidially dispersed system. The viscosity of the latex usually marketed (Figure 3) is approximately 22 centipoises a t 57% solids. This can be raised t o any desired viscosity by the addition of small amounts of available thickeners, typical examples being hydroxyethylcellulose, carboxymethylcellulose sodium salt, and sodium or ammonium alginate. As the viscosity is increased by addition of thickener, some degree of thixotropy is encountered which makes accurate determination of viscosity by the capillary method impossible. Several types of viscometers are available which measure viscosity by the drag exerted against a rotating spindle, immersed in the liquid and driven a t constant speed or constant torque. The Brookfield Syncro-Lectric viscometer (Figure 4), which operates. on this principle, has been found satisfactory for determining viscosities of thickened latices and was used for all such determinations in this work. Figure 5 shows the increase in viscosity produced by the addition of increasing concentrations of thickening agent t o a 57% solids latex. The thickening agent employed was 100-centipoise-
469
type hydroxyethylcellulose added as a 10% aqueous solution. The concentrations are expressed as hydroxyethylcellulose solids based on total latex solids. The viscosity of the latex may be readily increased to approximately 5000 centipoises by adding small concentrations of thickener. Higher viscosities show marked thixotropy and poor flow characteristics, and are therefore less applicable t o most coating operations. Hydroxyethylcellulose is available in various viscosity types, ranging from 10 t o 500 centipoises, measured as a 5% aqueous solution at 25' C. At a given conceetration a higher viscosity type hydroxyethylcellulose produces a higher latex viscosity. The data plotted in Figure 6 piere obtained by adding a 0.2% concentration, calculated as just described, of various viscosity types of hydroxyethylcellulose t o a 57% solids latex and determining the resulting viscosity. Viscosity V L refers to t h e viscosity of the thickened latex; W T refers t o the viscosity type of the thickener. The plot shows the relatively lower efficiency of the viscosity types above 200 centipoises. Plasticizers, stabilizers, resins, and other water-insoluble cgmpatible materials are best added by emulsifying the addition agent. A few typical suitable emulsifying agents follow: ~
Name Aerosol MA Alkanol W X N Aquarex D Daxad 11 IZuponol M E Naocolene F Nopco 1156 Triton 720
Chemical Type Dihexyl ester of sodium sulfosuccinic acid Sodium hydrocarbon sulfate Lauryl and myristyl sulfates Polymerized sodium salt of alkyl naphthalene-sulfonio acids (alkyl short chain) Alkyl sulfate Modified alkyl aryl sulfonate Sulfonated natural oil Sodium salt of aryl alkyl polyether sulfonate
A variety of plasticizers have been found suitable, either singly or in combination, for use with the Saran latices. A wide range of formulations is thus available t o meet a given combination of requirements. Those found t o be most widely useful are organic esters of phthalic, glycolic, sebacic, and phosphoric acids.
Preparing Test Bags by Heat-Sealing Paper, Coated with Saran F-122 Latex, to Be Used for Chemical Reqistance Determinations
470
INDUSTRIAL AND ENGINEERING CHEMISTRY
E
0 1.1
Vol. 38, No. 5
I
Y v1
~
I
1.0
1
_I
0
10
20
30
J
50
40
60
P E R CENT SOLIDS
Figure 2.
Figure 1. Electron 3Iicrograph Showing Particle Si& a n d Size Distribution of Solid S a r a n F-122 Resin Dispersed i n t h e Aqueous P h a s e (XU.;,OOO) \Yater-solublt. n i a t i - i i : i l a ,-ucli :i,- (Lyt'b, lubririints, c o i ~ r i ~ i o i i inhibitors, etc., may tw added tis ~ XV IT' solutioris or stirred directly into the latex. Chutioii must tic. i ) l ~ ~ r v as e d to thr electrolytic nature of the additioii :+gent siiic-e e ivc. eluctrolytt, ooiitent disturbs or coagulates such i~olloitlalsystems, as discuswd eariier. Kater-illsoluble exteiidrrs tinct modifiers, such as pigments, filiers, cliiys, etc., cnii hest i ~ iiwoi.porated r in the form of water sliirrics or pmtes. AIatiy \\-:it i x i ' clisprr*ihlr carbon bincks. pigments, clay.. etc., are availahlta from pigment nianufactui'ers and diatrihn-
Increase in Specific Gr?\ity of Latex with Variation iii Solids C o n t e n t
tors. In gerioral i t may be said that, for incorporating watci emulsions, slurricac, and pastes, thosr, y 10 methods will be most 0 successful which proc 4 duce the most urri1 1 5 form and smalleet U I piwticle size. > c X typical f o r m u h U 0 tion for a coating c composition t o deposit a colorless, glossy, transparent, I 0 IO 20 33 40 50 60 flexible finish 011 P E R CENT SOLIDS paper, cloth, n~ood, etc., is as folloTr: Figure 3. Increase in \ iscosit > of Idatex with Variation i r i +)lids 100 parts Saran latm Conten I (57YG salids), 23.X parts dibutyl flhthalate eniulsion (605; dibutyl phth'ilat?), and 1.7 pait- hydroxj ethylcellulose solution (5ycsolidri. Thr coating aii-dxics*rapidl) S o elevated temperature ib required t o produce a contiiiuoui film having excellent moisture and chemical rt.'sistance. ' A superior water paint mag be obtained by incorporating 20 t o 40 parts of titanium dioxide pigment in the above formulatiini. Water-dispersible tit anlum dioxide may bt stirred directly into water t o give a smooth slurry whirh requires no grinding anti which
10,000
1,000
s I
.-
>
- -_- -
5 Y .05 .IO .I5 .20 ,725 .30 PER C E N T H Y O R O X Y E T H Y L CELLULOSE B A S E D O N T O T A L L A T E X SOLIDS
Figure 4. Determining Latex Viscosity in Brookfield Syncro- Lertric Viscometer
Figure 3. Increase in Viscosity of a 57% Solids Latex, w i t h Increasing C o n c e n t r a t i o n of Hydroxyethylcellulose Solids, Based o n T o t a l Latex Solids
100 10
100 VISCOSITY
-
1,ooa 7 7
Figure 6. Viscosity of S a r a n F-122 Latex, Produced b y Adding 0.20% Hydroxyethylcellulose of Various Viscosity Grades
May, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
may be added d i r e c t l y into the latex t o produce glossy or flat finishes de-
471
TABLE I. EFFECT OF PLASTICIZER ON CHEMICAL RESISTANCE OF FILMS
-
pending on the pigment Saran ratio.
15% D.P.O in Film Physical Appearance properties No change No change No change No change Opaque, white Nb change
Material HCl concd.) HCl h 3 X I HNO: (concd.)
PHYSICAL PROPERTIES
“08
Hap04 Hap04 NaOH NaOH
Free films were prepared from commercially available Saran F-122 latex by adding 5 to 2570 of plasticizer in water emulsion and sufficient thickener t o give a good casting viscosity, approximately 1000 centipoises. The latex was then poured onto a glass plate, knifed evenly over the surface, and allowed to air-dry until clear. Films containing 15% or less of plasti-
Slight haze No change
(10%) (siru Y) (408 30 )
NaCl {satd.) Acetio acid (glacial)
Black Brown, transparent No change Slight haze
Ethanol (95%)
Slight haze
Turpentine
No change
~lO%l
Peanut oil No change Petroleum na htha No change (100-140° boiling range) CClr No change
8.
.......... ..........
Methyl ethyl ketone Butyl acetate Toluene No change a D.P. dihutyl phthalate.
-
No change No .change No change Brittle Slight loss of flexibility No change No change Slight loss of flexibility No change
No change No change Sli h t loss of %exibility Dissolves Softens No change
20% D.P. in Film 25% D.P. Physical Appearance properties Appearance Slight haze No change Slight haze No change Slight haze Opaque, white Opaque, white Slight, loss of Opaque, white flexibility 0 aque, white No change Opaque, white Hazy, cloudy &zy, cloudy No change No change No change No change Black Black Brittle Brown, trans- No change Brown, transparent parent No change No change No changeSlight loss of Slight haze Slight haze flexibility Slight haze Slight loss of Slight haze flexibility No change Slight loss of No change flexibility No change No change No change No change Slight loss of Slight haze flexibility
in Film Physical properties No change No change Slight loss of flexibility No change No change No change Brittle No change
Slight loss of flexibility Dissolves. Softens No change
Slight loss of flexibility Dissolves Softens No change
No change
.......... .........
No change
Slight haze
..........
..........
Hazy, cloudy
No change Slight loss of flexibility Slight loss of flexibility Slight loss of flexibility No change Slight loss of flexibility
physical properties if heated
a few minutes a t 100’ to 110’ C.; those containing more plasticizer are not markedly improved by heating. Clarity of film, however, indicates complete removal of water; this is confirmed by analyses showing air-dried clear films to contain O . O l ~ oor less of water. After drying, the film was stripped from the glass plate for testing. The data following were determined on films approximately 0.002-inch thick. The tensile strength and elongation were determined with a Scott IP-4 Tensilgraph at 25’ C. and 50% relative humidity, using samples 1 inch wide and 2 inches long. These results show good agreement with those obtained on films deposited from solution in organic solvents when. the plasticizer content is 15% or higher. The dotted line extrapolated t o lower per cent plasticizers on the tensile strength plot (Figure 7) is that obtainable from solvent cast films. The solid curves obtained from the latex cast films indicate nearly constant tensile strength and a rapidly increasing elongation from 5 t o 15% plasticizer, as Figure 8 shows. The moisture vapor transmission was determined by the General Foods method; i.e., the test sample is sealed as a diaphragm over the open top of a cup containing a desiccant, and air at 100’ F. and 95% relative humidity is circulated around the cup. The amount of moisture transmitted through the sample is measured by the weight increase and calculated t o some standard unit of weight/unit area/unit time. Figure 9 shows the variation of moisture vapor transmission with film thickness for films cast from latex containing 15% dibutyl phthalate. The transmission is almost inversely proportional to the film thickness over the
z
f
range of thickness 0.5 to 6.0 mils according to the following equation: T = 2.6/t
T = moistuie vapor transmission, grams/100 sq. in./24 hr. t = film
thickness, mils (0.001 inch)
Chemical resistance was determined by suspending strips of free film partially immersed in the test liquid for 2 weeks at 25” C. The strips were removed -and were examined visually and manually by Dullinn. -, tearinn. -, and iolding, TableI gives the results.
300
z 0 4:
8 200 w J I-
Y a
w
a I00
I i _ _
5
10
15
---I 20
Figure 8. Variation of Elongation with Plasticizer Content of Saran F-122 Latex Cast Free Films
7 000
Oo0
5000
c I
‘8
4 000
E
I
5 3 000
u
I
A
\-
W
2000.
5
10
P E R C E N T DIBUTYL
I5
80
25
PHTHALATE
Figure 7. Variation of Tensile Strength of Films with Plasticizer Content Solid curve, latex cast filmm; dotted curve, solvent cast films
25
PER CENT O l 8 U T Y L P H T H A L A T E
T H I C K N E S S - THOUSANDTHS
INCH
Figure 9. Decreasing Rate of Moisture Vapor Transmission with Increasing Film Thickness
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 38, No. 5
sion was determined n-ith the General Electric recording spectroTABLE 11. EFFBCTOF PLASTICIZER ON PHYSICAL PROPERTIES photometer. OF F I L ~ I S 15% D 2 . o
Test Elmendorf tear Fold endurance,, cycles
Light transmission througl
3-mil film, 4000 A. 5000 A. 7000 A. a D.P. dibutyl phthalate
-
20% D.P.
25% D.P.
100 88.000
850
77.0 86.0 89.5
69.0 81.5
62.5 78.0
89.0
86.5
Table I1 shows the effect of plasticizer on other physical properties of films. Block temperature was determined by folding a strip of cast film lengthwise upon itself, applying a load of one pound per square inch upon the film, and placing the sample in a forceddraft hot air oven for one hour. The temperature a t which the film adhered to itself so that marring or defacing resulted from pulling the halves apart is considered the block temperature. Heat-seal temperature was determined on the continuous-belt Saran sealer (15 feet per minute), inm-hich the sample to be sealed is carried between two continuous belts through a heated zone and a cooling zone. The heat-seal temperature is taken as that point which produces a seal stronger than the film surrounding it. Elmendorff tear tests were run on the standard tester of that name by the recommended technique. Fold endurance was determined a t 25’ C. and 50y0relative humidity in the Tinius Olsen model 31633 by the recommended technique. Light transmis-
USE APPLICATIONS
The Saran coating latices h a w been found useful in a broad range of applications. As coatings on paper, cloth, leather, plastics, and foils they provide heat-sealable finishes of excellent appearance, resistant t o water, greases, oils, and a wide variety of chemicals, and cxhibit low rates of vapor transmission. Latexcoated paper was until recently being used for packaging foodstuffs and small parts for the armed forces. I t is now available for civilian applications. As base resins for water paints these latices appear promising. Among the outstanding characteristics for this application are the rapid drying rate of successive coats and the resistance t o scrubbing after a one-hour drying period. This is of particular interest t o bakeries, laundries, and brevieries where the rapid application of a maintenance paint having good resistance to water is paramount. The finish may be applied by either brushing or spraying. Free films and tapes cast from the latices are of interest in the packaging field. Excellent adhesives ranging from rigid to flexible have been prepared for paper, cloth, leather, conveyor belts, belt drives, etc., and have shovn high strength and durability in use. Other uses include binders for materials such as cork, clays, mica, yarn floes, etc., in insulation, wallboard, and floor coverings. Because of the recent introduction of this type of latex and allocations which restricted use t o the war effort, the wide and varied fields of application are still unexploited. Development work is continuing to provide improved formulations for specific applications.
Construction of Nornographs with “YP erbolic Coordinates WALTER HERBERT BURROWS State Engineering Experiment Station, Georgia School of Technology, Atlanta, G a .
E
ARLY treatises on nomography, such as the works of d’Ocagne (5) and Lipka (S), were largely investigations of the equation forms arising from various arrangements of scales and index lines, with applications of these forms to t h e solution of engineering formulas. There was much duplication, and the same formula might fall into a number of different forms. The tendency among more recent authors, such as Sllcoclr and Jones (1) and Navis ( I ) , has been to devote primary interest t o the single case of three scales cut by one index line, with the various modifications and extensions possible within this form. The defining equation for nomographs ef this form is the equation of the straight line (index line) through points on the three scales. I n determinant notation this equation is
yu
xu xo
f/w
xw
=
0
(1)
1
where x is the Cartesian abscissa and the y is the Cartesian ordinate of the scale points employed in constructing the U , V , and W scales. If all z values are constants, the three scales are straight and parallel. If any y = 0, the scale lies on the base line of the chart. If any y is a function of the corresponding z,
the scale may be curved. Thus, a wide variety of equation forms may be accommodated by this general nomographic form. When vie add the device of “variable Constants”, giving rise to “network scales”, thc form becomcs very versatile. The difficulties in constructing a nomograph to represent a given formula are not primarily those of converting the formula to the form of Equation 1 but of constructing the scales in such a manner as to yield a well-balanced and accurate chart. Two factors are involved in this step-the moduli of the scales and the angle between the coordinate axes. The latter factor has never presented any difficulty, since oblique coordinates are as easy to use as rectangular coordinates. On the other hand, it is not possible to change the modulus of any scale without simultaneously changing both the modulus and the position of a t least one other scale. Xomographs constructed without due consideration to the best relative positions and moduli of the scales are frequently impractical from the standpoint of ease of reading and interpolation, as indicated in Figure 5. I t is necessary, therefore, to devise means of varying the moduli and posltions of the scales. Earlier texts employed formulas relating these factors; later
