October 15, 1930
INDUSTRIAL A N D EYGINEERING CHEVISTRI-
heated to 60" C. One cubic centimeter of this solution will precipitate 2.9 mg. of alumina and approximately equal quantities of ferric and titanium oxides. T o prepare rosolic acid indicator solution, dissolve 0.080 gram of the solid in 100 cc. of 1:I ethyl alcohol. Literature Cited (1) Berg, Z . anal. Chem., 70, 341 (1927); 71, 23, 171, 321, 369 (1927); l a , 177 (1928); 76, 191 (1929). (2) Britton, Analyst, 46, 359, 437 (1921); 47, 50 (1922).
407
(3) Gmelin, Pogg. Ann., SO, 176 (1840). (4) Hahn and Vieweg, 2. m o l . Chern., 71, 122 (1927). ( 5 ) Havens, A m . J . Scr., 4, 111 (1897). ( 6 ) Kolthoff and Sandell, -7. A m . Chem. Soc., SO, 1900 (1928). (7) Lundell and Knowles, Bur. Standards J . Research, 3, 91 (1929) (8) hloser and Niessner, dlonatsh., 48, 113 (1927). (9) Parsons and Barnes, J . A m . Chem. Soc., 28, 1589 (1906). (10) Penfield and Harper, A m . J . Sci.. 32, 107 (1886). (11) Robitschek, J . A m . Ceram. Soc., 11, 587 (1928). (12) Schaffgotsch, Pogg. Ann., SO, 183 (1840). (13) Wunder and Wenger, Z . anal. Chem., 51, 470 (1912). (14) Zimmerman, Ibid., 27, 61 (1887).
Lacquer Studies I-Development of an Abrasion Test for Use with Nitrocellulose Lacquers* William Koch HERCLLES PollDER
co%lP?'IY,
EYPERIVHVTAL S T & T I O V K E V X I LhT J
The equipment, theory of development of the test, The regulated air stream is HE measurement of the and the Practical use of the proposed method for measobtained by introducing air resistance of a protective coating t o &brauring abrasion of lacquer films are described in this from a pressure line into the paper. Practical results are included, not only on glass equalizing reservoir. sion or wear is of practical experimental laboratory lacquers, but on a variety of One outlet tube from this significance whenever such a coating is subject to \Tear. commercial products as well. reservoir leads to the adjustIt has theoretical interest able water leg through which when the results are correlated with the results of other a small constant stream of excess air is bubbled. Regulation methods of test. Wear resistance aids in studying the by this means is accurate within + Z mm. of water. The relation of the different components of the protective coating other outlet tube leads the regulated air stream t o the abrasion to one another in affecting the properties of the final coating, apparatus past the manometer openings. The colored-water and thus assists in determining proper formulation. This will manometer is the only one used a t present and is simply a be the subject of another paper. means of checking the constancy of the air pressure. Other physical tests, such as hardness, mandrell, tensile Figure 2 illustrates the appearance of a lacquer film on its strength, and elongation, do not give results which can be glass support with duplicate abrasion patterns after the end interpreted easily in terms of wear resistance. point has been reached. Figure 3 is a n enlargement of a Sward has given a review of numerous tests which have single pattern with the arrow pointing t o the tiny holes actubeen described in recent years ( 2 ) . His considerations led ally worn through the lacquer film. When following an abrahim to choose loose sand falling under the force of gravity in a sion determination, no difficulty is experienced in observing coniined tube. The simple and practical features of his test the first appearance of these ciny holes, which constitutes the appealed to the author. It mas desired, however, to make end point. The entire pattern becomes frosted almost imthe test more rapid by having the abrasive strike the film mediately and the tiny holes when they appear (always in under the increased force of an air blast. This necessitated the same position) are very clear and sharp. constructing an enclosed apparatus with access to a regulated The abrasion factor or index is obtained by weighing the air stream. Experiments also indicated the desirable features abrasive in the container before starting and again a t the of using a finer abrasive. The construction of such an ap- end of the determination. A small constant correction is paratus does not detract from the simple and practical plan subtracted from the weight of the abrasive used to allow for of Sward's instrument. I n addition i t is more compact, more the quantity of abrasive in the constricted tip below the rapid, and accurate. cut-off after the abrasive stream has been shut off.
T
Discussion of Test
LVeight of abrasive used in grams Abrasion factor = Figure 1 shows the assembled apparatus. The abrasive Film thickness in cm X 1000 in the weighed container at the top flows in a fine stream under It should be noted that the pattern is very symmetrical the force of gravity through a constricted orifice into the &m7s a spot wear. The shape and sJmmetry of the and confining tube. Here it meets the air stream introduced 1 ) ~ of the insealed side tube and is distributed Over the pattern are governed entirely by the design and construction entire cross section of the confining tube. It leaves the con- of the apparatus. I n prelimillary work a large number of fining tube with definite force and strikes the lacquer film on different construction designs were tried. The present type the glass plate supported in a plane whose inclination is 45 %'as finally chosen because of the very symmetrical pattern, degrees from that of the descending abrasive. The abrasive Figure 4 shows the constricted tip fitted to the confining tube by means of a rigid ground-glass joint. The air-inlet tube is then falls into a container in the confining box below. The sharply defined abraded area is easily observed through fused into the confining tube and this whole assembly iS rigidly the glass window in the door, because the inside of the box is clamped in a fixed position with a clamp attached to the backilluminated by a small shielded light bulb fastened in the back board (see Figure The actual dimensions of these members are unimportant of the box. and can be adjusted to meet the needs of the individual user. 1 Received July 15, 1930. Presented before the Division of P a i n t and constriction be adapted The diameter Of the Varnish Chemistry a t t h e 80th Meeting of t h e American Chemical Society, to the size of the abrasive used. -4170- to ZOO-mesh CarCincinnati, Ohio, September S t o 12, 1930
AXALY TICAL EDITION
408
Vol. 2, No. 4
These results indicate the necessity of regulating the particle size of the abrasive. Lacquer Films
Experience has shown that the only satisfactory method of obtaining a lacquer film on a support of equal thickness throughout is the spinning disk method ( 3 ) . The range of thickness desired (0.0015 to 0.0025 cm.) can be readily obtained by this method, and the thickness can be controlled. Smooth films free from ridges and orange peel are necessary. These undesirable factors can be completely eliminated by controlling spinning time and rate of evaporation while spinning. A variable-speed attachment controls film thickness for lacquers of different viscosities. Film thickness must be measured very accurately, because abrasions are reported as grams of abrasive per unit of film thickness. The measuring instrument finally selected for this purpose is a specially constructed paper gage micrometer with ratchet stop capable of measuring accurately to 0.0001 inch. The advantages embodied in this instrument are: (1) The point of contact is very large and minimizes the error of squeezing the film. (2) The micrometer has sufficient depth so that any point on the plate can be measured. (3) Measurement is accurate.
Figure 1-Assembled
Abrasion Apparatus
borundum dust, which requires a constriction 1.5 mm. in diameter, was used. Smaller constriction does not permit even flow and larger openings allow too fast a flow. A number of constricted tips of the same design have been made for substitution in case the present one becomes broken or badly abraded. It is of interest, however, that the original tip is still in perfect condition after more than 6 months of constant use.
The numbers shown in Figure 2 are thickness measurements of the glass plate made in adjacent circles where abrasion takes place. These measurements are constant and were scratched on the back of the plate permanently for convenience. The advantage of measuring film thickness a t the point of abrasion is obvious. Four points on each plate are measured in order to insure a sufficient number of points a t which abrasion can be run and duplicated. Oftentimes dust
Abrasive
The abrasive adopted is Carborundum poTvder of 170 to 200 mesh which is obtained by screening. Other abrasives were tried, but they did not flow so freely. Carborundum powder apparently is unaffected by adsorption of moisture or humidity conditions, because substantially the same quantity flowed through the tip in the same time on a number of different days having differing humidity conditions. The cleanness of the abrasive has not yet become a factor. This is connected somewhat directly with the problem of reuse of the abrasive many times. The present abrasive has been used a t least fifty times without rescreening or cleaning and the same factor can be duplicated a t Jvill a-ith any given lacquer film. The abrasion factor was found to be inversely proportional to the particle size. A lacquer film formulated to contain 45.5 per cent 1j2second nitrocellulose, 36.4 per cent tricresylphosphate, and 18.1per cent glycerin-phthalic anhydride resin (lacquer type) was used to obtain the data in Table I. Figure 2-Duplicate Table I-Abrasion 140-170 MESH 160.3 158.2 164.1 161.4 158.7 Av. 160.5
Factor for Differing Abrasive Size 170-200 MESH ZOO+ MESH 142.1 135.8 142.9 139.6 148.3 130.3 133.2 146.9 147.7 136,9 142.6 135.4 Av. 1 3 5 . 0 141.5 14.5.2 146.5 146.9 144.3 145.1 148.1 145.2
Abrasion Patterns
particles settle on the drying films, and when this occurs within any of the circular areas accurate thickness cannot be obtained and that area is not used. Plate glass has been chosen for the foundation support of all films for abrasion because it is clear and the least technical difficulties are experienced in determining an end point. I t is also very even in thickness and is very smooth and level. Film age for these very thin films was found to have no effect on the abrasion factor after 24 hours of aging (Table 11).
ISDCSTRIAL A S D ENGIYEERIXG CHE,VIXTRY
October 15, 1930 T a b l e 11-Effect TIMEAFTER PREPARATION
of F i l m Age on Abrasion Factor ABRASION FACTOR 1st Set 2nd Set
Hours 24 4s 72 96
145.2 148,s 145 9 145 1
145.5 144.6 144.3 148.1
148.3 141.3 140.6 144.8
146.9 143.3 140.8 143.7
Table 111-Hardness
409
a n d Abrasion D a t a f o r Some Representative Nitrocellulose Products AsRASIOlr
SAMPLE
INDEX
HARDNESS
INDEX
COMMERCIAL P R O D U C T S :
No. 1, recommended by makers for exterior application No. 2. a furniture lacquer No. 3, a sanding sealer
168.4 106.8 73.4
10 241 356
EXPERIMENTAL LACQUERS’
Other Factors Air pressure is very important because the force with which the abrasive strikes the film determines how rapidly abrasion will take place. A variable pressure gives results entirely unreliable. The water leg and equalizing reservoir adopted to regulate pressure are simple, easily adjusted, and operate very accurately. Air temperature varies from time to time during the year. It is important because the lacquer film assumes the same temperature as that of the in-rushing air stream. This factor has not been regulated by the use of any apparatus. A simpler procedure which has been found to work very satisfactorily is as follows: An experimental lacquer is chosen whose formulation is known and can be duplicated a t will. This is arbitrarily established as a standard for all reference and a film of this standard is prepared and run every time that unknowns are to be determined. For accurate work duplicate checks are recommended, but a single determination can be relied upon to be within * 5 per cent of the correct abrasion factor.
No. 1, 34.17, ‘/*-second nitrocellulose, 36.356 * dewaxed dammar, 29.67, dibutyl phthalate No. 2 34.17, l/*-second nitrocellulose, 46.2% dewaxed dammar, 19.7% dibutyl phthalate No. 3, 34.17, ‘/*-second nitrocellulose, 60.07, dewaxed dammar, 5 9% dibutyl phthalate
113.5
52
136 6
286
75.0
325
Actual experience with the three commercial products has yielded the following data: No. 1 exhibits excellent resistance t o outdoor weathering. No. 2 is a satisfactory furniture lacquer in every respect. No. 3 exhibits excellent sanding qualities.
Figure 4-Assembled T i p a n d Confining Tube
The three experimental products were chosed because of their great similarity to the commercial products in hardness and abrasion, with no particular interest at the time of choice in any other property. An examination of each in comparison with the corresponding commercial product does bring out the following interesting facts:
Figure 3-Enlarged
Pattern S h o w i n g T i n y Holes Worn t h r o u g h Film
This method can be used for any type of protective coating material which can be applied on a glass plate, either clear or pigmented. Drying time, of course, must be suitably chosen for the type being tested. The method as developed is practical and simple. It is also rapid and accurate. Representative Data Although a full discussion of data cannot be given at this time, a few results on some commercial nitrocellulose products and some experimental products may be helpful and illustrative. Abrasion data, together with the Pfund hardness index ( I ) , are presented in Table 111. The results given are the averages of check determinations in each case.
No. 1 possesses good resistance to outdoor weathering, but not to the extent that commercial No. 1 does. No. 2 is satisfactory as a furniture lacquer. No. 3 sands as well as commercial No. 3.
These data clearly illustrate the relation of these two measurements t o each other for the three types of products chosen. Acknowledgment The author wishes to express his appreciation for some basic ideas obtained from the Bell Telephone Laboratories while on a visit there, and for permission to use these ideas in developing the present method. H e also wishes to acknowledge his appreciation for the great assistance and suggestions rendered by Mr. Speaker of this laboratory. Literature Cited (1) Pfund, Proc. A m . Soc. Testing Materials, 25, Pt. 11, 392 (1925). (2) Sward, Am. Paint and Varnish Mfrs.’ Assocn., Cwc. 353, 625 (1929). (3) Walker and Thompson, I b i d , 22, Pt. 11. 465 (1932).
