Document N2xb91nREow8NQex7a0RXrVV8

/ indexed CCs 0* H. Bullitt, lr, Exp* 3ta., Wilts* R* B. Davis, Lab. Patent Section, Lab* 10 Marshall Lab. Library (5) R* Nforgan, Lab. p. B. Evans, Lab* S. C. Horning, Lab* M* P* Morse, Lab. K. 0* Lamport, Lab. D. t. Herndon, Lab* Files 1810 MARSHALL LABORATORY November 23, 1953 .MEMORANDUM REPORT #M-655 . PREPARED BY: B. M* lOHICPATRlOK COP^ Ig} J CllClllUlSi INSTRUMENTAL METHOD FOR MEASURING INITIAL EASE OF BRUSHING OF INTERIOR ENAMELS AND INTERIOR MATER OLSIOI PAINTS BITRODtJCTIONi Research Report No* 1252 and .feraorandum Report #M-629 explain the details involved In the development of a new instrumental method for measuring the initial ease of brushing of ex* terlor house paints and oil base flat wall paints, 'respectively. The method has now been adopted for Interior enamels and interior water emulsion paints (wall paints). Separate rating charts are necessary for each class of paints* In this .report the term ''initial ease f brushing** means ease of wetting and spreading* In the past, this rating was determined by the pinion of the painter making the brushouts * At its best, this opinion .Involved considerable error and was usually reported on a relative basis* The new instrumental method reported here eliminates this personal error end provides better precision* SUMMARY; Cl) The initial ease of brushing of interior enamels and interior water emulsion paints {wall paints) can be determined by means of a recently developed instrumental method* lie method is based on the use of plastic viscosity and yield value, as. deter** mined with the Interchemical Rotational Viscometer. (2) Separate rating charts are required for the Interior enamels (Fig* 4} and for water emulsion paints (Fig* 5) * It should be noted that the limits of good, fair, and poor brushing N35484 -2- vary for these two types of products. ;(3) lost methods have been written to explain the details of the test. TD-508-H explains the method of obtaining plastic viscosity and yield value oh the Interchemical Rotational Viscometer. TD-516-B and TD-516-C explain the methods of determining initial ease of brushing for interior enamels and ilnterior water emulsion paints, respectively. (4) TD-527-A covers the details for determining the "drag at lip" of architectural finishes. This term is defined as the resistance encountered in pulling a brush from an unpainted area to a jfreshly painted area. This value, plus the Initial ease of brushing value, gives a more complete rating for "brushabillty". STATUS: m the past, ease of brushing ratings have been based almo# entirely on the opinions of a master painter. The develop ment bf the instrumental method provides better precision and provipes the fonnulator with a concrete "target area" for good initial ease of brushing. ACTION TAKEN: Test Methods (TD-508-H, TD-516-B, TD-51S-C) have been issueft, giving the procedures for determining initial ease of brushing ineitrumentally. 1 DISCUSSION AND EXPERIMENTAL: I Ir. discussing initial ease of brushing with professional painters and in analyzing the problem from a theoretical aspect, it became apparent that at least two values were required from rheological measurements, namely one to measure the vehicle viscositjr and one to measure the puffiness or structure of the paint. Plastic viscosity and yield value, respectively, as determined on the literchemical Rotational Viscometer, met these requirements. Furthermore, it was believed that, besides the effeots of temper ature IJ on ease of brushing, (Research Report #1252), penetration into ihe substrate and (in the case of water emulsion paints) surface tension might have some effects over porous substrates. 1. Mastic Viscosity and Yield Value: By definition, yield value is the minimum force re quired to produce laminar flow in a plastic material, expressed in dyies/cm2. Plastic viscosity is the resistance to flow of ' a nonfNewtonlan system in excess of its yield value, expressed in dynes sec,/cm2, or poises. These values are obtained by DUP030003608 -3- measuring shearing stress as a function of shear rate on a rotational viscometer. Figure 1 shows the type of curve commonly found In interior enamels and In water emulsion paint!. It is noted that, as is generally the case, the plastic viscosity of the enamel is greater than that of the water!emulsion paint. This is evident from the difference obserfed In the slopes of the two curves. Actually the ocal of the slope of the straight portion of the down curve Is a measure of the plastic viscosity. While the intercept < \t the extrapolation of this straight portion of the down < iurve to the shearing stress axis is a measure of the yield lvalue. The yield value is a function of the structure or flocculation of the system. The formulae for calculating plastic viscosity and y:(eld value are as follows: U where F * shearing stress (dynes/cm2) S * rate of shear (sec.-1) U * Plastic Viscosity (poises) f Yield value (dynes/cm. Tlie size of the hysteresis loop formed between the up curve land the down curve is an Indication of the degree of thixo tropy,,. si. Effects of Surface Tension of Water Emulsion Paints on Ease of Brushing over Porous Substrates? From the results, shown in Table I, it is concluded erences in surface tension do not affect the initial rushing of water emulsion paints when brushed over porous 3. The range of surface tensions studied is greater than entered in actual paints. It is seen that, in going from substrate to an unsealed substrate, the painter*a rating tslightly in all but two cases. These two paints were too a sealed substrate, but Just right for unsealed surfaces, t reduction in initial ease of brushing of the majority was attributed to loss of vehicle into the substrate. In , with one exception, the painter claimed the initial over porous substrates was good, but that the paints needed speed up the work. DUP030003609 -4> TABLE I Code -Surface Plastic Yield Initial Ease of Brushing Tension Vise. Value sealed substrate porous substrate 391-004 391-019 391-005 31 1, 31 31 0.8 1.1 0,9 55 Ex. (thin, not sloppy) 138 Ex. 55 Thin Perfect, Just right V.G.-Goodj Slow, needs water Perfect; not sloppy. 391-014 391-002 32 ji , 34 5J i 1.1 1.5 133 V. Good 260 Ex. V. Good; Nseds a little water. V. Good? needs a little water. 389-001 48 1 2.8 166 Pair Pair-Poor; needs water p-100-063074A.. r-100-063074 51 1 0.7 i1 53 1i ] 2.1 39 Thin 89 Ex.-V.Oood Ex,; Hot sloppy V.Oood; needs water. P-100-U- 53 i 63095A JI 1.3 55 Ex.-V.Good P-100-0- 55 '! 1.7 89 Ex.-V.Oood 6307? i\1 " P-100-U63072A p-100-0630E___ 59 j 2.0 J........... - - 1 61 1 1 _______________ 116 116 Ex. Ex.-7.Good 3. Initial Ease of Brushing Charts: V.Oood; needs water. V.Oood; needs water. V. Good; needs water V.Oood: needs water figure 4 shows the limits which have been set up for interior enamels, ml general, an enamel with good initial ease of brushing has a plastic viabosity between 2.5 and 5.7 poises and a yield value in excess of 55 dyneajfcin*. Plastic viscosity and yield value data for 75 interior DUP030003610 -5- la are plotted in Figure 2 together with their ease of ihing ratings. Classes of good, fair and poor are design on this chart. An area marked too thin for trim work so Included. This means that, although the paint produoes under the brush, it is too sloppy to apply by brush on surfaces. In like manner. Figure 5 is a chart for deter- the initial ease of brushing of interior water emulsion s. These limits were determined from a plot of plastic sity and ease of brushing data for 70 water emulsion It may be possible to thin paints falling in the or poor range (marked with an asterisk) in Figure 4 and that they will fall in a better brushing area. This reon teat should be tried before a paint la condemned for al ease of brushing for commercial sale. A further interpretation of Figure 2 and 3 in terms Low properties can be generalised! as the yield value sases from a low value to & high value, the false body taaes and the overall effect is good slip under the brush, _~,flow, and heavy brush marks. Below a minimum yield value (50-$5 dynes/cm.2) brush marks are less pronounced, but sagging say result. Also, at a constant yield value, inplaatic viscosity above 3.7 poises for enamels >ve 2.2 poises for water emulsion paints results In loss se of brushing! below 2.3 poises (enamels) and below 0.3 : olse (water emulsion paints; there is a danger that the pain er cannot apply the necessary film thickness fur dur ability purposes, due to the thinners and aloppiness of the paints. MARSHALL LABORATORY Mr R. M, KIRKPATRICK RMKtHLM iiAs|7h DUP030003611 **MCTfU fi**m**f DUP030003612  *.t t r Pi.*sTt<: / wi7y DUP030003613  *0C lit V DUP030003615 Puirit iri*cmty- DUP030003616