A Simplified Distinctness-of-Image Glossmeter ROBERT J. MYERS, Resinous Products 8; Chemical Co., Inc., Philadelphia, Penna. is usually avoided by preparing a new standard with each batch of paint pastes under tests. Such a method is expensive and time-consuming, the paints are still rated in relation to a single standard, and a comparison between different paints made a t separate times is difficult, if not open to question. Any method which would yield a numerical quantity capable of being recorded as a permanent value for the observed gloss of a paint film would be of great practical value.
A simple glossmeter capable of measuring a distinctness-of-image gloss value was designed on the basis of an optical principle. Trials with paint and enamel films indicate that the instrument is well suited for the measurement of a gloss value associated with distinctness-of-image gloss as observed by the eye. It is simple in construction and operation, and is capable of yielding a reproducible gloss value in numerical form.
T
H E measurement of the gloss of a paint or enamel film has been the subject of many extensive investigations. The definition of the term “gloss” has been discussed a t length by various investigators; recently, Hunter and Judd (3) showed that it might well involve considerations of specular and diffuse reflections, sheen, absence of bloom, and distinctness-of-image gloss. On the basis of studies correlating observation by eye with measurements made on an instrument designed to measure mainly specular gloss, Hunter ( 3 ) has proposed a method of rating painted surfaces in five classes: high gloss, eggshell to high gloss, eggshell, flat to eggshell, and flat. Hunter previously (1) had proposed a method of measuring sharpness-of-image gloss by means of a groundglass screen which caused the image of a standard target to become diffuse, and comparing the character of the surface under observation with the obscured target. Different types of surfaces may, however, demand different methods of gloss measurement, and particular problems may warrant other approaches to the problem of gloss measurement.
FIGCRE 2. REFLECTIONOF LIGHT RAYFROM OBSTRUCTION ON SURFACE
K i t h this thought in mind, the construction of a simple instrument which would measure a quantity related to the distinctness-of-image as measured by the eye, and which T o d d record the relative degrees of such a gloss observation in numerical form, was undertaken. The glossmeter described below was constructed and based on a theory concerned with the effect on gloss of irregularities in, on, or beneath the surface of the paint film. It has been successfully used to record as a numerical value the degree of distinctness-of-image gloss as observed by the eye and target-pattern lamp. While the data collected to date do not justify a definite conclusion regarding the substructure of paint films, the instrument is felt to be unique and interesting in that it is simple and cheap in construction, simple in operation, and capable of rapidly determining a particular kind of gloss value in a numerical form.
Theory and Construction of Glossmeter -4s a fundamental postulate prefacing the construction of the instrument, it was assumed that the degree of distinctnessof-image gloss was directly related, in this particular problem, to the size of the pigment agglomerates lying just below the surface of the paint film. Thus, the condition existing in the immediate neighborhood of the film surface was pictured as in Figure 1. It was assumed that the pigment particles served as the major reflecting surface and that in inferior wetting, certain clumps of pigment extended above the effective depth of the clear resin layer and served to form a “rough” reflecting surface. Hence, a machine designed to determine a quantity proportional to the roughness or discontinuous character of the reflecting surface should give values in agreement with those obtained by the eye and target-pattern method, if the above postulate is reasonably correct and if the gloss observed is a function of pigment wetting, other things being equal. Such an instrument was easily constructed, based upon the well-known principle of physical optics that a diffusely reflecting surface assumes the properties of a specularly reflecting surface when the angle of incidence approaches grazing incidence-that is, the diffuse reflection caused by irregularities in the surface is in fact caused by the angle of incidence being less than a minimum value. If the angle of incidence
FIGURE1. DIAGRAMMATIC REPREBENTATIOK OF CONDITIOX OF PIGMENT NEAR PAINT FILMSURFACE About two years ago, a problem dealing with the relative pigment-wetting action of various metallic soaps was under investigation in the author’s laboratory. The preliminary experiments corroborated the widely prevalent view that the pigment-wetting action was largely the dispersion (either spontaneous or aided by mechanical action) of pigment agglomerates and the formation of a stable dispersion of the pigment. The studies were continued on the paint mill and on sprayed panels made from paints containing various quantities of different wetting agents. Since it was desired to correlate good pigment-wetting n-ith improved gloss in the final paint film, the sprayed panels were first evaluated by simple observation with the eye, aided by the familiar target-pattern lamp ( 2 ) . However, as is well known, the gloss of many paint films is not a permanent quantity and decreases with time. This difficulty in the evaluation 678
ANALYTICAL EDITION
NOVEMBER 15, 1940
FIGURE 3. GLOSSMETER COXSTRUCTION Scale, approximately
1/1
is equal to or greater than the minimum, specular reflection will result. This is illustrated in Figure 2. A B P is the path of a ray of light reflected from the surface of the pigment agglomerate, X. ABCP is the path the ray would have taken if the light had been able to proceed to C, the effective depth of the layer (or the “base line” of the surface). It can easily be shown that if distance h is not great compared to the wave length of light, the reflected ray, BP, proceeds to P without appreciable displacement from CP. Thus, if the height of the irregularities is not too great, specular reflection will result. If h is large compared to h, the wave length, then the incident angle must be increased to a more grazing value when specular reflection occurs.
679
The paint panel, held in a bedlike frame (not, shown) could be tilted about an axis through point 0, which was also the center of curvature of a flat strip, RAF, of urea-formaldehyde-impregnated paper. The translucent strip was mounted on a semicircular frame and was illuminated by diffuse light through frosted (or opal) glass from the small bulbs, L. Along the axis of the strip of paper, a series of concentric crossed circles was drawn and these could be seen at B by specular reflection when the panel was observed through the eyepiece. As the panel was tilted about 0, the distinctness of the crossed circles became greater, proceeding from A to F , or less, proceeding from A to R. The eyepiece slit opening vias 0.156 inch (3.62 mm.) high and 2.873 inches (7.3 cm.) wide, and was so placed that only one crossed circle at a time came into view as the panel was tilted. At a fairly well-defined position, the reflection of the crossed circle then observed v a s just clearly visible. The angle at which the panel was tilted was read from a graduated drum mounted outside the instrument and on the shaft about which the panel rotated. The angle at which the crossed circles were just clearly visible was readily determined to within *2.5“, and was taken as a measure of the distinctness-of-image gloss of that panel. The completed instrument is shown in Figures 4, 5, and 6.
Testing the Instrument I n order to test the instrument as a possible measure of the type of gloss observed by the eye and target-pattern lamp method, a series of samples of black paints, identical in composition except for the presence of 0.1 per cent of wetting agent on the paste, was examined by both methods. The results are indicated in Table I. It is evident that the glossmeter rated the panels in almost the same order as they were rated by eye. Furthermore, the glossmeter readings were reproducible over various portions of the same panel and on different batches of the same paste. The numbers served not only as a numerical index of the relative rating of the gloss observed by eye but also as a permanent record of the degree of this particular type of gloss. I n this vehicle, with carbon black as pigment, the metals examined rated in the relative order lead, barium, nickel, zinc, and aluminum.
c
FIGURE 4. UNASSEYBLED GLOSSMETER Showing panel bed, graduated drum, eyepiece, observation compartment (blackened), illumination compartment (painted white), opal glass, and tracing cloth atrip of crossed concentric circles
The angle of incidence, the height, h, and the wave length are related as follows: p x = 2 h cos i
(1)
where pX is a small fraction of the wave length. For ordinary yellow light the presence of irregularities of the order of 0.5 to 1.0 micron produces such a n effect, which suggests that the fundamental postulate given above is a t least reasonable. Actually, as Hunter (3) has indicated, the eye would probably be incapable of distinguishing differences or displacements in the reflected beam, provided that the displacement a t the eye was less than one minute of arc. Hence, though the disturbances might easily be of the order of several microns, “specular reflection” would still be observed. The instrument which was constructed serves to determine quantitatively the angle at which a paint film must be viewed in order to obtain a definite minimum of specular reflection. The principle of operation is apparent from Figure 3.
FIGURE 3. SIDEVIEW OF GLOSSMETER
INDUSTRIAL AND ENGINEERING CHEMISTRY
680
VOL. 12, NO. 11
TABLE 111. DATAON CURVES IN FIGURE 7 (Duraplex C-48 architectural whites) Yehicle, Duraplex C-48, 42.9% (Mineral Thinner), viscosity, E-(Gardner-Holt Varnish Scale) Drier, 0.3% cobalt Pigmentation, 1 : l ,on regin, Rayox FF 787,, Panels, flowouts, air-dry Timonox 1570, zinc oxide 10% Agent, 0.5yo metal on pigment
No. 1 2
3
4
5
6
Agent
Other Changes
S o n e , blank
Zinc alkoxyacetate Xone T i n alkoxl-acetate None Sone
TABLE IV.
Remarks
...... ., ...
....
......
..,. Fresh paste Old paste
Low acid number resin S o zinc oxide N o zinc oxide
.... ,...
LEAD18s. ZISC SO.IPS
Type of enamel Black Architectural white Toluidine red Pigmentation See Table I See Table I1 See Table I1 2" 28 6 Zinc alkoxyacetate Lead alkoxyacetate 37 26 12 Zinc naphthenate 18 27.5 14 a Arbitrary units on a preliminary scale. .4pproximatcly 1 unit = 2 . 2 5 ' .
FIGL-RE 6. FROSTV I E W O F GLOSShfETER, ISTERIOR ILLUMISATED
TABLE I. GLOSSMETER RE.4DINGS US. EYERATINGS, BLACK EKAMEL Vehicle, Amberol ST-137 varnish, 38 gallons of tung oil, 2 gallons of linseed oil Pigmentation, carbon black (Super Spectra) : 12.5 pounds of carbon per 100 gallons of varnish Agent, 0.7% o n pigment Milling, agent added t o paste before milling on stone buhr mill Panels, 3 X 10 inch flowouts (hrushed or sprayed, same relative position) Drier, 0.03% cobalt, air-dry Eye-Lamp Rating Glossmeter Ratingo Lead alkoxyacetateb Lead alkoxyacetate 37 Barium alkoxyacetate Barium alkoxyacetate 37 Sickel alkoxyacetate Zinc naphthenate 18 Zinc naphthenate Nickel alkoxyacetate 11 Zinc resinate Zinc resinate 11 Zinc alkoxyacetate Aluminum alkoxyacetate 4 Blank (no agent) Zinc alkoxyacetate 2 Aluminum alkoxyacetate Blank 0 Arbitrary units, on a preliminary scale. Approximately 1 unit = 2.25'. b Alkoxyacetate: typified by "Oilsolate" driers of Resinous Products & Chemical Co.
apparent loss of gloss F i t h age could be readily followed and recorded in a quantitative manner by the glossmeter. Figure 7 and Table I11 illustrate this particular application. Figure 7 indicates that the relative rates of loss of gloss could be readily followed in a numerical manner with the aid of the glossmeter. The loss of gloss due to mixtures of zinc oxide and titanium dioxide (but not zinc oxide or titanium dioxide alone) was readily measured. The instrument was also used to compare the effect of lead and zinc soaps in three types of paint vehicles. The gloss of the final films mas quantitatively evaluated by means of the glossmeter. The results are listed in Table IV. The familiar specificity of wetting agents is again encountered, as the data indicate that lead is better than zinc
Q
TABLE 11.
(;LOSSMETER
KE..XDIS(:S u,s. EYEfiansc:s, K E D
Esa.?lEr.
Vehicle, Amberlac 80-X, 43.5Cc i n xylene (viscosity, E) Pigmentation, 1 5 % on resin Agent, 0.1% on resin, 2.05$ on pigment Panels, flowouts, baked 2 hours, 2?5O F. E y e Rating Glossmeter Ratinga Zinc resinate Zinc resinate 17 Nickel alkoxyacetate 1w 1-ickel alkoxyacetate 17 Zinc naphthenate Zinc naphthenate 14 Lead alkoxyacetate Lead alkoxyacetate 12 Barium alkoxyacetate ' Zinc alkoxyacetate 6 Zinc alkoxyacetate Barium alkoxyacetate 3 Blank Blank 3 a Arbitrary units, o n a preliriiinary scale. Approximately 1 unit = 2 . 2 3 "
A second series of experiments, using a toluidine red baking enamel, showed the same concordance between the glossmeter ratings and the ratings by eye (Table 11). On the basis of these results, the instrument was adjudged a satisfactory device for the evaluation of distinctness-of-image gloss as usually observed by the paint and varnish formulator, A Hunter glossmeter of the type proposed in 1935 ( 1 ) was not available for comparison with the instrument described here. Comparisons with other types of commercially al-ailable glossmeters mere not made, as distinctness-of-image gloss is included with other types of gloss in results obtained lyith such instruments, or the results are not expressible in numerical form.
Applications The instrument was used to study the effect of various iiietallic soaps on the gloss of architectural n-hites. Here the
E
16 ACE,
24
32
DAYS
FIGURE 7. Loss OF GLOSSOF ARCHITECTUR.AL WHITE ESAMELS, AS OBSERVED TVITH GLOSSMETER 1. Blank
2 . Zinc alkoxyacetate
:I. Low acid number resin 4 . Tin alkoxyacetate 5 , 6 T o zinc oxide
ANALYTICAL EDlTION
NOVEMBER 15, 1940
681
and the glossmeter has been found a valuable aid in the study TABLE V. GLOSSMETER RATINGSOF BAKEDUREA-FORMALDE- of alkali-resistance of baked urea-formaldehyde finishes, HYDE FINISHES I S .4LKALI TEST Typical data are listed in Table V. Vehicle, 40% urea formaldehyde, 60% As Table V indicates, the glossmeter recorded in numerical alkyd Alkali, 3% NaOH Pigmentation, 1:l on resin solids, 5% form the progressive loss of gloss produced by the attack of zinc oxide, 9570 Ti03 Panels, on glass 3 X 5 inches the alkali. Also, the improved resistance to alkali attack Film, 0.003 inch (Filmograph), 55% solids under longer baking conditions )vas readily measured. Since Gloss, Gloss, Resin Gloss, Gloss, Gloss, So. 1 Hour 2 Hours 4 Hours 5 Hours 6 Hours the alkali test undoubtedly is based upon the loss of gloss due Baked 30 minutes a t 200' F. to pitting of the surface, this instrument, designed to measure 1 Over SOa Over 90 32.5 l5b .. surface irregularities, is excellently adapted for application 2 Over 90 80 30 25b 3 Over 90 Over 90 40 30 3Ob in such a test. 4 5
1 2
3 4 5 0
b
Over YO Over 90
Over 90 50 Over 90 Over 90 Over 90
Over 90 60 SO Over 90 Baked 45 minutes a t 200' F.
Baked 90 minutes a t 200' F Over 90 80 l5b 30 40 Over 90 Over 90 72.5 Over 90 Over 90
40 47.5
50 b
40 72.5 90
32.5 32 5
45
.. 55 90
Over 90 indicates specular reflection a t normal incidence Film failure.
with carbon black as pigment, but zinc is equally effective with titanium dioxide. Lead and zinc are about equally effective in a toluidine red baking enamel. A third use of the instrument has been in following the loss of gloss of a baked urea-formaldehyde finish as observed during the alkali test, This application of the instrument, which approaches most closely the fundamental theory of the observation and measurement, was developed by K. E. Martin and W. H. Graeff in this laboratory. The test is in daily use
Summary
A glossmeter has been designed and constructed to measure the distinctness-of-image gloss of painted surfaces. While the theory of the instrument is based upon the existence of minute irregularities on, in, or beneath the surface of the paint film, the data collected thus far do not prove that distinctness-ofimage gloss is solely affected by the presence of such irregularities. The instrument is flexible in its application and has been found valuable in various problems dealing n-ith a gloss denoted as distinctness-of-image gloss. Its chief points of advantage are : simplicity of construction, simplicity of operation, and capability of yielding a reproducible gloss value in numerical form. Literature Cited (1) Hunter, R. S., K'atl. Paint, Varnish Lacquer bssoc., Sci. Sect., CZ'TC. 493, 268-80 (1935). (2) Zbid., 503, 141-53 (1936). (3) Hunter, R. S., and Judd, D. B., Am. SOC. Testing Materials, BUZZ.97, 11-18 (1939). PRESENTED before t h e Division of Paint and Varnish Chemistry at the 9 9 t h Meeting of t h e American Chemical Society, Cincinnati, Ohio.
Precision Feed Device for Catalytic Experiments ROBERT L. BLRWELL, JR.', Trinity College, Hartford, Conn.
W
ITH increasing frequency, the necessity of employing
rare or expensive chemicals in catalytic experiments is arising. This article describes an apparatus designed for the precise feed of liquids on a semimicro scale, though i t may find application for ordinary feed rates where the precision of flow achieved would u-arrant the increased complication. The following characteristics were required for t h e author's purposes: ready setting of feed rate to any predetermined value, ready change of this rate, ready use of the apparatus at any pressure from atmospheric t o about 50 mm., provision for evacuating the catalyst under high vacuum, and absence of stopcocks in the feed line. Devices in which the feed liquid is displaced b y mercury flowing in through a capillary have been widely used in experiments with ordinary feed rates. These may be modified for use a t lower rates, as has been done, for example, by Goldwasser and Taylor (1). Such apparatus fails to meet all the above requirements. Furthermore, the achievement of uniform flow of mercury through fine capillaries is difficult if the mercury becomes in the slightest fouled. The device described in this article satisfies the conditions named above. The feed is positive in action and yields very 1
Present address, Northwestern University Evanston, I l l .
even and very reproducible result's. It could be simplified for purposes in which all the itemized characteristics were not required.
Description of Apparatus The apparatus is illustrated herewith. hIercury is displaced by the gas evolved by the electrolysis of a 30 per cent potassium hydroxide solution. The displaced mercury forces the feed liquid into the preheater. An electric current from a storage cell is passed through a 4-decade resistance box, &, and through the cell, K. The voltmeter, R, allows a check upon the potential fall through the cell. The cellis provided xith two nickel electrodes brazed or spot-welded to the tungsten rods sealed into the apparatus. It would probably be satisfactory, however, to replace the tungsten seals with leads passing through a rubber stopper. The gas evolved in K is fed to the container, H . Mercury is forced from H up into the calibrated 10-cc. buret, F , which is surrounded by a water jacket, E. The feed liquid passes into the capillary, C, and thence through the finer capillary, B, into the preheater, A , the jacket of which should be heated at least 40' above the boiling point of the liquid. The liquid volatilizes within the fine capillary at the edge of the preheater. In the author's experiments, the meniscus of the feed liquid would not vary 1 mm. from this point during an experiment. The proper diameter for the fine capillary depends upon the desired range of feed rates and upon the viscosity of the feed liquid. With a
