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The Pfund Glossmeter Applied to Paints and Lacquers’ George S. Haslam and Lester D. Grady, Jr. THE SEW JERSEY ZINC COMPANY, PALMERTON, PA.
FUSD ( I ) , in describing a new glossmeter, has
P
An apparatus is described that measures objective gloss, the property dependent on the degree of surface perfection. It has been possible to eliminate color and brightness differences entirely from the measurement. A method of numerically evaluating gloss so that gloss retention may be followed has been suggested. Data illustrating the adaptability of the apparatus to paint and lacquer problems are presented.
presented two definitions of “gloss.” The psgchological sensation is called “subjective gloss,” whereas that property dependent on surface perfection is “objective gloss.” Subjective gloss is defined as the ratio of the amount of light reflected specularly from the film to the total reflected light, both specular and diffuse. Objective gloss is here defined as the ratio of the intensity of the light reflected specularly from the film in question to the intensity of the light reflected speculnrly from a perfectly polished glass surface a t the same angle of incidence. The paint and lacquer industries have been measuring and observing subjective gloss and interpreting their results as objective gloss, a situation which has led to considerable confusion. The confusion has resulted primarily from the fact that subjective gloss may be largely influenced by color and diffuse reflection, while objective gloss is quite independent of these factors. If two surfaces, one black and one white, have the same objective gloss, the black will nppeor to hal-e the higher gloss.
Figure 1-Diagram of Glossmeter
It is obvious that, from t.he standpoint of smoothness, shiny appearance, and ease of washing and repainting, the white surface is as satisfactory as the black. I n considering automobile lacquers, for instance, it is certainly the objective gloss that should be measured. If a dark green lacquer gave the same gloss sensation as a light tan, i t would mean that the surface perfection of the tan was far superior to that of the dark green. The instrument described b y Pfund measures objective gloss 1 Received April 16, 1930. Presented before the Division of Paint and Varnish Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930.
and some results 011 paper, glass, and textiles are included in his paper. H e has suggested its adaptability to enamels and lacquers. The present article js a description of this apparatus, with a few minor changes, and some results that hai-e been obtained with it in this field.
Description of Apparatus
A diagram of the apparatus is shown in Figure 1, and a photograph of the apparatus as used in this investigation is shown in Figure 2. I n Figure 1, A is a substantial vertical post bearing a fixed pivot, D, and movable collar, E . Attached to these are two equal adjustable triangles, DBB‘ and DCC’, pivoted a t all corners. Illumination of the panel, H, is affected b y a single ribbon filament lamp. F . The pivot, D, is level with the top of the panel, H, so that if the angle of incidence is changed by moving E, the beam reflected specularly from the sample will always lie in the direction of the arm, C. The panel holder, L , consists of a brass frame, with adjustable screws for holding the panel in place during rotation. By a system of bevel gears a small motor, M, rotates the panel holder in a horizontal plane. The light is reflected from the panel a t a point s/4 inch (19 mm.) from the center of rotation. The panel is rotated in order to integrate the gloss over a considerable area of the panel. The panels used are regular 4 by 4l/2 inch (10.2 by 11.4 cm.) panels, prepared by priming white pine with one coat of shellac and two coats of flat white. T h e paint being tested is subsequently applied by spinning, brushing, or spraying. The panel holder and type of panel differ from the cylinders originally described by Pfund, because i t was found impracticable to expose the cylindrical panels uniformly, and the experimental work in mind included weathering exposure.* To measure the intensity of the image of F formed by reflection from the panel surface, a small optical pyrometer, K , supplied with red filter, R , is used. The specular image of elongated form is focused in the eyepiece b y means of cylindrical lens, 4V, and is brightest in the middle. The eyepiece is adjusted so that the pyrometer lamp filament crosses the specular image transversely. The current through the lamp can be regulated so that the filament disappears at the brightest portion of the image. Readings are taken on the milliammeter, T , connected in series with the pyrometer lamp, battery, and rheostat. CBLIBRATIOY--~~ glass panel is mounted in posit’ion and movable collar E is set so that the arms of the instrument 2 The panel holder for use with regular exposure panels was substituted at the suggestion of A. H. Pfund.
July 15, 1930
IiVDUSTRIAL A N D ENGINEERING CHEXISTRY Table I-Gloss
347
Measurements of Various Painted Panels ZISC OXIDE
1
Aged
ged and exuosed
AVERhOES
Aged and exposed $30 650
lged
A" c,c
Linseed Linseed-soya (1-1) Linseed-tung (3-1) Linseed-soya-tung (3-3-2) Perilla Perilla-soya (1-1) Perilla-tung (3-1) Perilla-soya-tung (3-3-2) Perilla-linseed (1-1) Perilla-linseed-soya (1-1-1) Perilla-linseed-tung (3-3-2) Perilla-linseed-soya-tung (1-1-1-1) Soya Soya tung (3-1)
1.7 2.6 1.l
1 1 6 1 4 2 1 2.9 2 1.7 1.7
69 49.5 30 3 5 j.8 4.6 17 15.5 14
26 6 14
42 9 33
34 7.5 18.5
3.0 11 4.5
2.3 6.8 3.1 . . 1.1 21 13.5 1 . 3 1.35 3.4 2 . 7 2.4 2 6 3 2.5 1 . 4 1.55 1.51.6
. . 1
..
1 1
..
1
1
3.1
a r e a t the desired angle. The glass panel is taken aq having 100 per cent gloss. Points on tlie calibration curves (Figure 3) are obtained by reducing the intensity of the incident beam in various known ratios by the introduction of a rotating sector with a variable aperature betveen the source of illurnination and the panel. Thus, b y reducing the illumination 50
1.3 1.4 1.4 1.0 3 1.4 2 1 1.7 1.4 1 1 1.3
I
1.7 1.5 3.0 2 . 2 1 . 9 1.65
...
8
1 4 2 5 2.3 1 . 0 1.35 . ., 1.4 . . , 1.1 . . . 1.3
...... ...
1,2
!.?. J
il
1 1.0
..
1 105
1.7
28 33 46 14 .j0 36 45
39 50 71 21 62
52
72 60 GO 68
32 4: 42
;16
62
33.5 41.5 58.5 17.5 56 46 53.5 63 46 52 j 55
11 19
1:
17
26'5
36
23 25 43 12 57 35 33 43 45 42 42
41.7
9
ij
Azed and exposed 1':
21.5 15.4 24., 13 8 28.8 16. 1 IC3.9 20.4 20.1 19 n 101
33 28 37 31 68 5 5 . 5 23 1 7 . 5 7 3 65 53 44 45 39 62 5 2 . 5 60 5 2 . 5 60 5 1 62 52
22.9 19.6 25.5 15.8 27.8 17. 1 25.2 25.0 19.0 20.1 20.3
15 12
3 2 . 2 2:j.o 3.4 A3 1 4 . 3 1.i.l
,j
26 40 0
difference. did not affect the g l o s as measured by this apparatus. A large number of painted panels were measured and the results tabulated in Table I. These panels represent a part of a series of pigment-1-ehicle mixtiires being studied in another connection, in which the nieasurement of gloss and gloss retention under exposure n-ere desired to complete the data. These paints were all made u p a t pigment-vehicle ratio of 30:'iO by volume. The oils used vere all heat-bodied a t 280" C. to the same viscosity and contained the same amount of drier and volatile. The panels were aged in a cabinet a t 100 per cent humidity and 42' C., half of the panel being covered and the other half exposed to the light of a 75-watt bulb. Measurements similar to those shown in this table will be made at regular intervals as the aging and exposure progresses. Discussion
It is not the purpose of this paper to discuss these paints, but the data are presented to gii-e some idea of the type of results that can be obtained. These panels v-ere all read a t two angles of incidence-45 and 65 degrees. The instrument r a s calibrated in such a manner that, in the case of a film of the same physical perfection as the 3tandard glass plates, the Figure 2-Assembled
Glossmeter
per cent, a niilliainmeter reading is obtained n.hicli is that to be expected with a panel of 50 per cent gloss receiving full illumination. This is repeated for a series of angles between normal and grazing incidence. Experimental
Tno standard glass panels were prepared, one white and t h e other black, and readings made with them a t a large nuniber of angles and various intensities of illumination. The readings obtained were the same for both panels in every case. Since there was considerable diffuse reflection froin the n hite panel and none from the black, it was apparent that the diffuse reflection was not affecting the measurement. This was clue to the fact that. because of the closely restricted field and the high intensity of the reflected beam, the increinent in the reflected beam due to the diffuse reflection was insensible even in tlie case of the white glass panel. The glass panels were prepared b y painting the under side with a white enamel in one case and black enamel in the other. Highly polished black glass and opalite glass surfaces gal-e similar results. From similar measurements on panels prepared with red and green backgrounds. it was found that color
percentage of objective gloss would be the sanie regardless of the angle a t which it is determined. It will be observed that the values for objective gloss when determined a t the two angles is quite different, being greater a t 65 degrees. This difference is due to the physical imperfections of the surface which becomes less effective in causing departure froin the
dS A L Y TI CAL EDI TI 01;
348
regular reflection of a perfectly polished surface as the angle of incidence is increased. It has been possible to use the average of these readings and get quite consistent results. I n order to get more accurate values it would be necessary to make measurements for a large number of angles and average the results, but it is questionable whether the amount of work involved would be warranted b y the increased accuracy to be obtained. Table I indicates that, in the vehicles studied, zinc oxide gives the highest gloss and that in general the vehicles containing perilla oil give the best results with any of the three pigments. It will be noticed that in several instances higher
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gloss readings were obtained on the exposed panels than on the unexposed. This was checked visually and found to be t r w . although no explanation is offered for the phenomena. Average results indicate a loss of gloss on exposure. Acknowledgment The authors wish to acknowledge the helpful criticism of A. H. Pfund and the assistance of Victor Bachman in making. the measurements. Literature Cited (1) Pfund, J. Optical SOC.A m , 20, 23 (1930).
Standard Methods (Revised) for Determining Viscosity and Jelly Strength of Glue Adopted by t h e National Association of Glue Manufacturers Atlantic City N J October 10, 1923. Published i n Industrial and Engineering Chemistry, Vol. 16, j l 0 (1924). Redsidn adopted April 10, 1930.
(A) Sampling a n d Preparation of Sample 1. GROUND GLUE OR
EQUIVALENT-A grab sample in the
ratio of 1 ounce per 100 pounds (28 grams per 45 kg.) shall be taken at random from not less than 20 per cent of the containers, except that the total number of samples so taken shall not be less than ten. When the number of containers in the shipment is less than ten, samples shall be taken from each container. GLUE,ETC.-sample shall be taken as out2. SHEET,FLAKE lined for ground glue, except in cases of large lots, where the entire sample drawn will amount to more than 10 pounds (4.5 kg.), in which cases the portion taken from each container shall then be reduced proportionately so that the total sample drawn shall not exceed 10 pounds (4.5 kg.). 3. GRINDINGOF SHEET, FLAKEGLUE, ETc.-The entire sample as drawn above shall then be ground in any suitable manner, to a t least 4 mesh, or finer if in the judgment of the operator it appears necessary, so as to minimize weighing errors and to shorten the soaking period. FOR TEsT-The entire ground sample as drawn 4. SAMPLING and prepared above is then thoroughly mixed and quartered down until reduced t o two 1-pound (454-gram) samples, which shall be placed in air-tight containers. One of these is to be used for test and the other shall be held as a reserve sample.
(B) Testing of Sample
I, COXCENTRATION AND QUANTITY OF SoLuTIoK-samples are made up in duplicate a t a concentration of 12.5 per cent by weight. Since a minimum of 100 cc. of solution a t 60" C. is required for the viscosity determination, 15.00 =t 0.03 grams of commercially dry glue are weighed out and transferred without loss to the standard container (described in D-2), and 105 * 0.25 grams of distilled water at approximately 15" C. are added while the glue is being thoroughly stirred with a thin metal rod. A metal rod is preferable to one of glass, since small glue particles will not adhere to the former when it is wet. If the end of the rod is pointed, particles in the comer of the container can be reached. The container is now closed with the perforated stopper. 2. SOAKING TEMPERATURE-The samples are then placed in a cooler, ice box, or other compartment held at a temperature of 10' to 15" C. PERIOD-In view of the variations in subdivision 3. SOAKING and grade of glue samples, the committee does not consider it
advisable to fix the exact length of the soaking period. It must, however, be long enough to soften the glue thoroughly. Soaking overnight is sufficient for all glues. It has been demonstrated that shorter time is permissible for some samples, but such a change in procedure should only be made in the light of experience justifying same. 4. PROCEDURE FOR MELTINGOF SAMPLES-In order not t0 crack the thick-walled containers, they should be placed for a few minutes in water of 20" to 30' C. before being put into the melting bath. The sample is then placed in the melting bath, the temperature of which is not allowed to exceed 70' C., and brought to a temperature of 62" C. as determined by an accurate thermometer placed in the glue solution and carrying one of the stoppers described but with a small perforation off center. The stopper originally closing the container is placed aside until after the viscosity determination has been made, when it is again used to close the bottle. The time required to bring the sample up to temperature should not exceed 15 minutes and, having attained the required temperature, there should be no delay in transferring the sample to the viscosity pipet. After closing the container with the stopper carrying the thermometer and before reaching the final temperature, the solution must be made thoroughly uniform, preferably by swirling the container a number of times. Any motion that will produce violent agitation of the solution should be avoided. In order to keep the supply of samples to the pipet continuous, several samples will have to be in the process of melting at the same time. Moreover, they should leave the bath in the same order that they entered it, so that all samples will have been subjected to as nearly identical thermal conditions as possible. The maximum number of samples present in the bath at any one time will depend largely upon the speed with which the subsequent viscosity determinations are made. A short trial will determine the correct number. Samples of low-grade glues heat through more rapidly than the more viscous high-grade ones and can be brought to temperature faster than the latter. The time required to make the viscosity determination varies in the same direction; hence the number of samples in the melting bath at any one time becomes fairly constant. (C) Viscosity Determination 1. VISCOMETER-The committee has adopted a pipet form of viscometer for glue solutions, which is a modiiied Bloom viscosity pipet. This type of viscometer furnishes a rapid and, when used
