Document pLnMx0DdR2dE411npNN21GJD

ALLIED RESEARCH BULLETIN NUMBER RC-SZ SUBJECT PHYSICAL PERFORMANCE OF PAINT PRIMERS Prepared by: C. D. Holley Fc M. Nelson August 10, 1939 L ' 9 9i ALLIED RESEARCH LABORATORIES CHICAGO, ILLINOIS N12513 - Physical Performance of Paint Prliters <? ' , ; kyer'd -Statement. Very little is known of the physical performance of paint pri: Tirs and' undercoaters on application to wood surfaces, Hie following data was ob tained to furnish inform. ticn which could he used in publicising the superiority of 450 Undercoafcer. It is recognized that the figures given in the following tables are not fixed quantities, but will vary somewhat according to the porosity of the wood on' which the paints are applied. By selecting a well known type of wood of medium porosity - Uhite Pine - we obtained a reasonable basis of comparison. It is natural to think of the composition of en applied Paint Primer or Finish Coat as being similar in composition to. the formulas from which made. The results given herewith show that the dried paint films can be quite different. Purpose. The purpose of this investigation was to ascertain* the effect of differ ent oils and pigments, as to amount of the oil retained in the film and the amount absorbed into the wood and finally the same information with a number of different types of ready to use Primers. Such information should furnish an excellent back ground for future changes in Paint Primer formulations. . Procedure. Rex 450 - SIP Ondercoater was taken as the basic formula. The Primers were spread at 500 sq. ft. per gallon on selected Ifaite Pine. The paints in each group were applied on the same board, allowed to stand for about five hours or until the paint became pasty. The paint then removed and the residual oil content deter mined and the amount of oil absorbed calculated. Hie application of the Finish Coats over the Primers was at 625 feet per gallon and the residual oil contents determined as above, the Primer being allowed to dry two days. 0007-SWP-000006689 -2- ' / ertain diffi-sbltiee were. experienced in determining the individual per-, forsonca of two cons'llturn ts of the 450 Undercoater. The Amorphous. Silica, 1552 dry, would not mix or grina satisfactorily alone, hence was determined in admixture with Asbestine and then the Asbestine separately, from which an approximation of the behavior of the Silica was calculated. It became necessary to deal with the {281), a bodied Tung Oil, in a simi lar manner, because of rapid surface drying after application. Its behavior in com bination with Linseed Oil was determined and a calculated value obtained. Effect of Polymerized Oils . It has been commonly believed that there was a marked degree of selective absorption on wood surfaces, of polymerized oils as compared with raw oils, the polymerized oils having little penetration. This may be true where the oils are present in large volumes per unit of area of application. On a paint primer coating where a substantial volume of the oil is bound to the pigment, there is only sufficient "free" oil to penetrate the wood to the depth of 1 or 2 cneithousandths of an inch. In this short distance, there appears to be only a very limited selective absorption, almost none with Linseed and some with Tung Oil. An admixture of 50 parts of a 12 minute bodied Linseed with 50 parts Raw Linseed applied in thin layer on White Pine after & two hour period, showed a com position of 52 parts bodied oil to 48 parts raw oil as determined by change in Refractive Index. A similar test was made barely saturating saw dust and removing a small portion of the oil with hydraulic pressure. The results were similar to those above. It is possible that the presence of pigments might have influenced the selective absorption. 0007-SWP-000006690 The cumulated value obtained for Taag.Oil (see table S) slows a definite tegraa of selective absorption. Very little difference. ms observed' between .Raw ptaseed Oil and the mildly bodied (785). Behavior of Different Primer Types. Table 1 show the relative performance of dif ferent types of primers compared with White Lead in Oil, SHP - Outside White, and a Krebs paint as reduced for first coat work. The results show that the wood surface could easily take up much greater quantities of oil than were taken up from the prepared Primers, indicating that in primer formulation we should consider two kinds of oil - "ffcee" oil and "bound1* oil. The final Pigment Volume Relationship of White Lead and of SUSP being similar to that of the vaxdous Primers. Table 1 , Paint Primers ... ... Distribution of Oil Between Wood and Paint Film Formula Krebs1 1st coat Total Oil Gals. Gals Gals. P.V.C. P.V.C. % Oil Vol. of Per 100 - Abs. in Pig- ' Paint Film Abs. Film - Gals. Film meat Gals. 68.3 50.5 17.8 18.1 21.056 50.556 74.0% 55.9 SIP Outside White 1st coat reduction 66.6 49.5 17.1 19.1 22.356 53.056 74.4% 36.2 White Lead in Oil 1st coat 58.5 45.7 12.8 17.9 23.056 58.056 78.0% 30.4 Hew Jersey Zincs Primer 450 Undercoater Lowe s Primer M5S 401 (Devoe Type) 58.9 47.3 46.5 39.7 55.0 25.1 28.6 22.2 23.9 22.2 17.9 17.5 25.6 25.7 23.9 25.8 30.256 35.256 33.956 39.656 51.7% 53.756 57.256 59.5% 59.5% 49.5 53.0% 47.9 61.5% 41.8 55.8% 43.5 0007-SWP-000006S91 It is. interesting to .rote that the relation of. oil to' pigment in the 450 4v Undercoater paint film is similar to that of the film of SWP White reduced for X-. first coat work or 54 to 55 (Fig. ol. Bel.). . " It is also worthy of note that the 450 Undercoater retains more oil in . the fils and gives more to the wood than the Devoe type of Primer and presumably imparts a greater margin of safety to the 450 Undercoater to meet varying types of wood surfaces, as contributing to durability. The 450 Undercoater at a spreading rate of 500 sq. ft. per gallon has about 10$ greater "build" - thickness of film - than Devoe and about 13$ more than Lowe Brothers. (See last column.) The Hew Jersey Zinc Primer based on US-150 and 15$ Leaded Zinc as the pigment and with 75$ of the total oil as & medium bodied Tung - Linseed Oil shows " - an excellent build, an excellent relationship between oil absorbed and oil retained. In comparative exposure tests it has shown better durability than the Devoe type - of Primer. ' Adequate film. _ thickness Jg j., 2 .coat .ay-stay is, vitally...important.Sd&'s. - ""450 Undercoater is the only commercial Primer we have found which has -the required "build" accompanied by the proper through drying of the film. Behavior of Individual Pigments. Taking Rex 450 as the basic formula, the perform- ance of individual pigments was observed, in which the volume of the given pigment \ | used was the same as of the combined pifpnents in Rex 450. :- Table 2. Effect of Individual Elements in 450 Undercoater Type of Formulation \ Piemenfc Total Oil Gals. Gals. Gals. P.V.C. P.V.C. $ Oil per 100 Abs. in Pig- in in Absorbed Gals. Film ment Paint Film a\ *KO> o 0o Tit&nox B White Lead Leaded Zinc 35/65 Asbestine' Asbestine - 75$) Amorphous Silica - 25$) Amorphous Silica (calc.) Titanium Oxide 47.3 47.3 47.3 47.3 47.3 47.3 47.3 26.7 22.5 21.0 13.72 14.75 17.9 5.91 20.6 24.8 26.3 33.58 32.55 29.4 41.39 25.7 25.7 25.7 25.7 25.7 25.7 25.7 35.2$ 35.2$ 35.2$ 35.2$ 35.2$ 35.2$ 35.2$ 55.6$ 50.8$ 49.5$ 43.0$ 4&.3$ 46.6$ 38.8$ 56.5$ 47.5$ 44.4$ 29.0$ 31.2$' 37.8$ 12.5$ 1 CO o o Die similarity of performance cn tin' equivalent volume basis of Halts Lean. and. Oslo Leaded Zinc .55/65 is particularly noticeable. The high oil retaining characteristic of Titanium Oxide in the film, is a factor of importance. '- The recent replacement of 25% of the Asbestine with'Amorphous Silica shows little effect as to oil performance. Effect of Individual Oils. The effect of polymerisation was discussed briefly ; under a previous caption. The individual oils examined are those which are used in S-W 450 ffnderepater and may not be representative of the action of other oils. Also in each case there is present the same volume of volatile thinners as are ` present in Rex 450. Table 5 Effect of Oils in 450 Ondercoater Type of Pigmentation Vehicle Combined Vehicle Rex 450 Total Oil Gals; per 100 Abs. Gals. 47.5 25.1 Gals. in Film 22-2 Gals. Pig ment 25.7 P.V.C. in Paint 35.256 P.V.C. in _ Film 53.7% 56 Oil Absorbed - ss% . \ (2) 47.5 27.4 19.9 25.7 35.2J6 56.356 : 58% . (785)* 47.5 26.5 20.8 25.7 35.2% 55.256 ; 56% (2) 4556 (2281) 5556 47.5 3.2 24.1 25.7 35.256 51.656 49% (2281) (Calc.)** 47.3 19.9 27.4 5i7 35.256 46.3% 42% (2) 50.5 9.8 20.5 25.7 33.856. 55.556 59.2% (785) 50.3 29.7 20.6 25.7 33.856 55.556 59.0% *Slightly heat bodied Linseed Oil. **Strongly bodied Tung and Perilla Oil. 0007-SWP-000006693 ! The performance of 'the Paw Linseed Oil (2) and slightly heat "bodied KV;-'_ , ` i-ti1-''" i'jss^ed - Oil (785) is almost identicals . . Hie bodied Tuag 0.11 (22P1 b/ calculation shows considerably less absorption into the wood then either, of tie preceding oils and can be used to change to some degree the ratio of "bound" to "free" oil. 4|| list. The last two results shewn on this table were obtained on another board and with the use of l/l6 more oil. It is to be noted that the oil retained in the paint films is similar to that shown by (2) and (785) in the upper portion of the table, giving the same Pigment Volume in the film. Absorption of Oil From Finish Coat Into Priming Coat. Experience has shown that some oil in the Finish Coat migrates into the Unoercoat, or through it into the wood below, leaving flat spots, especially if the undercoat and finish coat represent a self-primed system. The following table indicates that a relatively small amount of oil leaves the Finish Coat, providing that the spreading rate of the priming coat' is held down to e point giving an adequate build or thickness of film, thus preventing the oil from passing through the Primer into the wood. The Pigment Volume Concentration of SKP White and 450 Undercoaterin the films are almost Identical (see Table 1) and the Dcvoe type not greatly different, hence material differences in oil absorption from the Finish Coat would not be ejected. Table 4 Absorption of Oil From Finish Coat by Priming Coats Total Gals. Gals. Gals. Orig. P.V.C. Top Coat Oil/lOQ Gals. Abs. Left ? Abs. P.V.C. Film SEP - Outside White Rex 471 450 Undercoat Rex 471 MW 401 (Devoe Type) Rex 471 66.5 66.5 66.5 4.25 3.86 4.25 61.25 6.456 62.64 5.8? 61.25 6.4? 28.4? 28.4? 28.4? 29.7? 29.6? 29.7? 0 0 0 7 -S W P -0 0 0 0 0 6 6 9 4 -7- The last two columns show the change in the Finish Coat as. applied and after absorption into the Primer. This absorption obviously lowers the Figment > Volume Concentration in the priming. coats hs follows* griming_Cpat - S!S> - White 450 Undercoat Ml 401 (Devoe type) Before 5556 5456 59$ Mtsz 4756 50$ 54$ She dried prime coats were very low in "sheen*1 but after the Finish Coat had been applied and removed the 450 Uaderco&ter and Qevoe type had a medium end unifora oil gloss, the SWF White a low, not uniform gloss. Conclusions. Rrom the results obtained in this investigation there are good grounds for believing that from a physical performance viewpoint, we are in a well balanced condition and any changes should be of a minor nature. Also there'are grounds for believing the 450 Undercoater is in a better balanced condition as to performance than the leading competitive Primers on the market. CDH-FW/AR 0007-SWP-000006695