A Method of Preparing Thin Films E. L. KALLANDER, Dennison Manufacturing Co., Frarningharn, Mass.
A
MODIFICATION of the method recently described by Sager (1) for the preparation of thin films has been used in this laboratory for some time, and is applicable to the spreading of aqueous or nonaqueous dispersions of film-forming materials upon a variety of sheet materials. The dried films from most aqueous dispersions map be readily peeled
Shims of suitable thickness are most conveniently selected by trial and error; a starting point may be arrived at by calculating the thickness of the liquid film which it is desired to apply, and then selecting sheets of paper having suitable caliper. For reproducible results, the following requirements must be met: 1. The bed plate and the bottom of the spreader bar must be ground in so that, when shims are inserted, the slit between them is of uniform thickness. 2. Durable shims must be provided. Steel feeler gage stock of precise thickness may be obtained from the Starrett Company, Athol, Mass. 3. The viscosity and solids content of the film-forming dispersions must be controlled.
Literature Cited (1) Sager, T.P., IND. ENG.CHEM., Anal. Ed., 9,156 (1937). RECEIVEDSeptember 18, 1937.
Apparatus for Testing Crushing Strength of Granules
S H I U y $ l
FIGURE 1. APPARATUS
from a base of moisture-proofed regenerated cellulose, whereas the films from nonaqueous solutions might well be stripped from a sheet of plain cellulose, as Sager has described. I n the author’s laboratory the method has been used principally for the preparation of samples of coated papers and other sheet materials. The method dispenses with equipment for stretching the regenerated cellulose base, permits contraction of the film during drying and thus eliminates drying strains, and facilitates the production of films of essentially reproducible thickness. It is convenient to spread films from aqueous dispersions upon a moisture-proofed regenerated cellulose sheet, using a device (Figure 1) which consists of a steel bed plate 12 X 4 X 1.25 inches and a spreading bar 10 X 3 X 0.5 inches. This device is used by resting the spreader bar on its edge, with its face perpendicular to the bed plate and separated from it by the use of thin shims, the thickness of which will regulate the amount of coating applied. The cellulose sheet is placed under the spreading bar between the shims, and an excess of the film-forming solution is poured on i t and spread with a spatula across the width of the sheet. The sheet is drawn between the plates with a uniform motion and the coating is permitted to dry. The thickness of liquid film applied has been found to approach the difference in thickness between the shims and the base sheet, but never to equal it. The contraction is probably due to the formation of a stationary film in contact with the spreading bar. With bases that tend to pucker or curl, i t has been found advantageous t o use solutions of appreciable viscosity and to pull the sheet through with a rapid motion. The base material should be pulled through straight and parallel with the base plate in order to avoid wrinkling the sheet or interfering with the thickness of liquid film applied, as determined by the spacing of the spreader bar.
E. F. HARFORD E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.
T
HE increasing interest in granulation of various materials has created a need for methods of production control and evaluation of granule characteristics. One of the chief properties with which both producer and consumer are concerned is the hardness of the individual granules-i. e., the resistance to destruction during normal shipping and handling. An instrument for quantitative expression of granule crushing strength therefore should serve a useful purpose. Previous methods employed in this laboratory for the determination of ultimate compression lacked the desired speed and accuracy. The simplest determination of granule crushing strength is accomplished by placing the grain between plates and piling weights on the top plate until failure occurs. Materials of construction such as concrete, cast iron, etc., are tested for ultimate compression in such equipment as the Adie (8) or Wicksteed (1) single-lever testing machine. However, no instruments of this type have been constructed to operate within the range desired for the granules or briquets made from finely divided materials. The present apparatus was designed as a simple compression tester without sacrificing the necessary speed, convenience, and reproducibility.
Description of Apparatus As shown in Figure 1, the apparatus consists of a first-class lever, pivoted in the center. The applied force acting upwards on one end is a direct function of the granule resistance to crush-
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JANUARY 15, 1938
ANALYTICAL EDITION
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Reproducibility of Determinations Kumerous samples of widely differing materials were s e lected for testing the reproducibility of the crushing strength determinations. The reproducibility of determinations d e pended on the number of granules included in the average, It was found that maximum deviations from the averages of fifteen granules of each material tested were approximately * 8 per cent. Still closer agreement was obtained by crushing 20 granules, which resulted in reduction of the maximum deviation to around *6 per cent. For example, a material with a crushing strength around 850 grams gave averages ranging from 800 to 930 grams with 15 granules and from 830 to 930 Kith 20 granules. This small increase probably cannot justify the extra time required to crush larger numbers of granules. Although crushing strengths of individual granules varied from 480 to 1560 grams, in the above example the averages of 15 t o 20 granules were satisfactorily reproducible. The accuracy of the method.also depends on close grading of the granules by screening. A relationship between granules of different screen sizes probably may be determined from the formula P = Cd“ (6),where P is the load on a single grain and C is a coefficient having a value which may be determined experimentally. The value of 11-for ball bearings is 2 but for granular materials it may vary from 1 to 2 depending on the material and method of granulation. -4pplication of the Tester This apparatus should be useful in investigating the influence of absorbed moisture, compounding, mechanical methods of production, and other factors on the crushing strength and handling or storage characteristics of granular or briquetted pharmaceuticals, foods, fertilizers, and fuels.
FIGURE1 ing on the other. A granule is placed on the plate, A , directly beneath one end of the lever, B , and the load is applied on the opposit’e end a t a uniform rate by winding the string on a small reel, C, until failure occurs. 9 spring balance, D, connected in the reel system and sliding in upright supports, registers the amount of load applied a t that end of the lever. It was found convenient to use lever arm ratios of 4 and 8 to 1 and consequently the balance reading was multiplied by 4 or 8 as the case may be. The capacity of the instrument illustrated was 2000 grams with a lever ratio of 4 to 1 and 4000 grams ivith a lever ratio of 8 t o 1.
Literature Cited (1) Batson and Hyde, “Mechanical Testing,” Vol. I, p. 48,New Ycrk, E P. Dutton & Co., 1922 (2) Marks, “Mechanical Engineers’ Handbook,” pp. 716-16, New York, McGraw-Hill Book Co., 1916. (3) Morley, “Strength of Materials,” pp. 619-20, London, Longmans, Green & Co. 1921. RECEIVEDOctober 6 1937.
Courtesy, Lilly Research Laboratories, Indianapolis, Ind.
GENERAL VIEW OF ONE OF
THE
PHARMACOLOGIC RESEARCH LABORATORIES
Operating table and large variable-speed kymograph apparatus for recording the effects of drugs over several hours. Changes in blood pressure, respiration, etc.. can be permanently recorded in this manner.
