August, 1930
I N D USTRI.4
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AND Eh'GINEERING CHEAVISTR Y
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Special Primers for House Paints' F. C. Schmutz, F. C. Palmer, and W. W. Kittelberger THE SEW JERSEY Zrxc COMPANY, PALMERTOS, PA
Although the painting of wood is a very old procedure, LTHOUGH the paintthan the inside. This difsome of its difficulties continue to exist. Among these, ing of wood is a very ferential is n e c e s s a r y f o r abnormal failures resulting from poor bonding of old p r o c e d u r e w i t h satisfactory results. The appaint and wood are now receiving considerable attencenturies of practical experiparatus is essentially an intion. This paper deals with an attack on the problem ence behind it, some of its tensified replica of the wet, from the viewpoint of the vehicle used and shows that deficiencies continue to exist. exterior wall conditions frevarnish in the priming coat affords much better adThe Wood Painting Conferquently associated with the hesion than vehicles now generally used. This imence ( 1 ) a t Madison, Wis., in abnormal failure of paints. provement holds regardless of the type of pigment September, 1929, focused the From 3 to 20 or more hours used in combination with the vehicle. attention of both m i n t and may be required to produce lumber men upon some of excessive blistering, as an inthese problems, especially the abnormal failures of adher- dication of decreased adherence, but 6 to 7 hours is a fairly ence which result in blistering and peeling. Hartwig (2) good average for most finishes on the '/(-inch white-pine recently emphasized the part certain construction practices boards. play in causing such failures. The differences in adherence An accelerated weathering system of the closed-tank, merupon weathering over spring- and summerwood are well cury-arc type, as developed in this laboratory (3, 4 , 5 , 6 ) mas used to evaluate the efficiency of the special primers known. The possibility of changing wood characteristics through in decreasing the influence of wood grain upon durability. a modification of milling and selection practice is so limited Since this test method tends to emphasize cracking and that very little encouragement can be offered from this angle. adherence failures due to the effects of the wood itself, any The growing necessity of more efficiently utilizing all cut improvement toward equalizing the influence of summerlumber, especially the poorer grades, may even tend to in- wood and springwood will be readily indicated. Selected crease some of the difficulties. Changes in formulation and cypress boarding was used as the test material. painting practice probably offer the greatest field for possible remedies. This paper deals with a priming system that PANEL 12: 12" has shown promising results, according to laboratory tests, for maintaining good adherence under adverse conditions, and also for decreasing the influence of wood grain upon durability. This improvement is evident regardless of the type of pigment used. PANE L li: 12'
A
hlethod of Evaluating Results
Practical observations ( 2 ) have shown that the abnormal failures of blistering or peeling are practically always associated with excessively wet conditions back of the painted surface, and that moisture, especially as vapor, ran be considered the prime moving factor in their appearance. A so-called "test house" was developed on the basis of these practical conclusions, which, in brief, may be considered a method for measuring the tendency of paint to blister from wood under very moist wall conditions. The apparatus (Figure 1) is essentially a box with removable sidewalls used as test surfaces. These map be clapboards, solid boards up to "4 inch in thickness, or any composition material, as the specific test may require. Selected inches, flat grained with white-pine boards, 12 X 12 X planed surfaces, were used for the work covered in this study. These panels were painted with the test materials on one side only, and then clamped in place with the painted side out. Brass is used for all the rigid construction of the apparatus. The bottom is mainly a shallow well holding about a half gallon of water. The temperature of the water is automatically maintained a t about 140" F. to assure a constant supply of warm vapor in back of the test suyfaces. An auxiliary heating box, using two 100-watt carbon lamps, is installed in the upper section to prevent cooling and condensation. The temperature on the outside of the whole equipment is that of the room (7C-80" F.) and much lower Received June 11, 1930. Presented under the title " A Study of Special Primers for Overcoming Some Failures oi Paints on Wood" beiore the Division of Paint and Varnish Chemistry a t the 79th 3Ceeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930.
100 W. BULBS
PLAN
IMME:RSIO
HE INSULATED BASIN
EL E V A T ION Figure 1-Laboratory
T e s t House
Application of Varnish to Wood
The failure of exterior spar-varnish applications by peeling and blistering is quite rare. Brittle materials may fail by chipping and scaling, but this is essentially a breakdown within the film itself and should not be confused with failures resulting from a decrease in adherence. A good grade of spar varnish continues to display excellent adherence upon
weathering and deteriorates gradually fronr the outer surface inward. E'. L. Brownc, in his discussion at the Wood Painting Conference of some of t.he future lines of attack in the problem of paint adherence ( I ) , suggested that some cues may he taken from the research that has been done to date upon the subject of adherence as applied to wood glues. He not.ed that in a well-glued wood joint the actual penetration
that the physical chauges resulting from tlie hydrolysis reactions far overcame any superior adherence the varnish may have originally induced. Further deteruiinatious were made to assure that this iriiprorement did not apply only to one type of house paint. Five representatiye types of exterior paints (Figure 4) were tested, using for prirners the spar and synthetic-resin varnishes already mentioned. The finishing system again was one coat of varnish primer and two coats of paint of secondand third-coat corrsistencies. Three-coat finishes using tho regular paint primer were run for comparison purposes. (Figure 4-A) To facilitate cornparison of the results, the exposure tirnes on the test, home for the regular three-coat finishes were varied to produce approximately the same degree of blistering on all. In tbe tests of the different paints over the special primers, tile same exposiire times were t,hen allotted as was allowed for the regular threecoat finishes of the respective paints. Colunins 13 and C, Figure 4, indicate that the improvmient, indiii:ed by the .iwnish primers holds for all the paints.
(Magnified 40 X ) R a w linseed oil
Spar varnish Dark mess ierrresent oIl-61led wood cells Figure I-Campararive Penetration over White Pine
of the glue into the wood is very little, possibly not more than a two-cell layer. On the other hand, there is a very firm mechanical bonding wit.h the wood surface. Likewise, in the application of a spar varnish to a wood surface penetrat,ion plays oiily a v e r y ininor part. The ~:omparative peiietrat.ion OII white pine of three-coat applications of raw linseed oil and spar varnish is shown in Figure 2. Spar varnish in general dries inueh uiore rapidly t,han the iisiial l~ousepaints, and wheii ini:orporated as part of the vehicle of these paints imparts its speedier drying nction to such paints (Table I).
one
coat Of raw iinrrcd
Oil
and drier
One coat 01 heat-hodied !inseed oil m d drier
T i m e s of liouaa Paints with and without Spar Varnish 'rrMsAi 80" I.'., M*TBAZ',1,9" 45% R.H.B flours Minulrs Spar varnish 1 20 Tltanium piemen-zinc oxide-inert p d n f 7 50 Lithopone-zinc oxide-inert paint 7 50% b y ivo. 1 60% ivo.2 a 1 a mC/, by volnme o l Nu. 1 and 50% of KO. 3 35 The varnish WTF a aood errde commercial material. The anintr were or Proper printing cons h These dezerminatioos were made upon the Sanderson dryinn filnr meter.
Table I - D r y i n s
Varnish in Priming System
I'FCREASI'FG B ~ ~ r ~ n ~ s c r -view I n of the excellent adherence of variiisii to vood, the possibility of using it as R primer for tlic usual house paints is worthy of consideration. The blistcring tendency of siicli a finishing system lins been eraloatcd hy mwns of tlre test house, using one coat of varnisli as primer followed by two coats of house paint in secoiid and third coat consistencies. T h e e types of varnishes were tested: ( I ) a coinincrcial oleoresinous spar varnish; (2) a quick drying, synthetic-resin ribaterial; and (3) a lirried rosin varnish of low oil content. Since raw and kettlebodied linsced oils are used extensively iii tlie usonl paint priiners, a finishing systcm using one coat, of these materials as priiners and two coats of exterior paint was also tested. The tests (Figure 3) show that N varnish primer rlistinct!y reediices blisterina, provided a \ater-resistant material is ilsed. According to auxiliary t.ests, tlre liincd rosin rarnisli used lrad very poor water-resistant properties, indicating
o n e coat of Ey"fllrtir varnish
1!4 actlili
resin
size,
Two coats of same house paint applied over primer
Figure 3-Comparative
Bli8tering over Clear Oil and Varnish Primers
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t
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
007 basic earbaorfe ofwhite lead M%imc oxide 10% inert
SO%
zinc dust ‘20% zinc oxide
Aluminum powder ( 2 Ibu. per sd1. vehicle)
86% iron oxide 15% zinc oxide
100% red lead
( K aci”a1 sire) P B l l l i S VSXiCLBS
Raw or heat-bodied linseed oil, drier, and turpentine
100% spar varnish
50% (byvol.) uoualoil vehieie, 50% spar varnish
Two coats of same house paint applied over primer (Compare the middle column with B, F i ~ u r e4) Fisure 5-Gomgarative Blisterin8 over Colored end Metattie Type Primers
Objection limy be offered to the use of a clear priniing coat because of the complete loss in biding. Mixing some of the paint with the varnish would partially overcome this objection. Tests were run to determine the efficiency of a system wherein the paint, thinned in the usua1 way for priming new wood, is further reduced 50 per cent (by volume) with varnish. The same spar and synthetic-resin varnishes were used and the regular second- and third-coat paints applied over the primer. According to columns U and E, Figure 4, the results continue t o be favorable, but not quite so good 8s those obtained with the straight varnishes. A 50-50 mixture of unreduced third-coat paint and varnish also produces excellent results, possibly better than when the paint was first thinned to priming-coat consistency. Because of their rcacti6ty inaiiy varnishes cannot be mixed with house paints without thickening within a short time. The paint and varnish mixes used in these experiments could be made up and stored satisfactorily for at least a month. However, from the practical viewpoint the safest gerwal recommendation would be to mix the special primers shortly before application. It must also be borne in mind that all “so-called” varnish inaterials will not produce the desired results; for exainple, as previousl?* indi-
cated, a high degree of water resistance is one characteristic that is required. Since the varnish type of primers showed such promising results with representative house paints, the experimental work was expanded to include some of the colored and m e tallic type pigments (Figure 5 ) that have been suggest.ed and sometimes used for wood priming. Three distinct lines of primer iormulation were followed: (1) The pigments in raw and kettle-bodied linseed oil yehides. (2) The pigments in a 100 pcr cent spar-varnish vehicle. the same as previously used. (3) Fifty per cent by volumc of primer, as prepared under (l), and 50 per cent varnish.
Two finishing coats of the s a n e white house paint were used in every case. All panels were exposed for the same length of time on the tcst house. As indicated in Figure 5, none of the pigments wit11 the straight oil vehicles showed any particular eflieiency in blistering resistance, hut even tended to peel more than the regdar paint primer. On the whole, the varnish vehicle improved the adherence d i e tinctly, while the 50-50 mixture was intermediate. The results were on a par with those obtained with the regalar
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1930
(% actual sire)
(Actual size)
859
1%
aCL"I1
size)
P , , , Leaded zinc oxide Repeat tert with previous paint zinc oxide Lithopone High zinc sulfide lithopone Inert Inert Primer for lower h d f d each section-Respective paints, priming-coat consirtency Primer for top half of each nection-50%
Figure 6-Decreasing
(by vol.) of spar vzroinh and 50% oi respective paints. priming-coat consistency
the Influence of Wood upon Durability by Means of Varnish in the Primel
house paint using a clear varnish primer and a 50-50 mix. The important part the vehicle plays in the adherence of primers of this type is very evident.
DECREASING INFLUENCE OF Woon GRUNUPON DURARILZTY -Accelerated weathering durability determinations were run upon the finishing system using as primer the 50-50 paint and varnish mixture, followed by two coats of the same white house paint. The exposure waa under a cycle simulat ing the weather conditions a t Palmerton, Pa., which is probably representative for a large portion of the United States. As shown in Figure 6, the reduction in the slitting and cracking was very marked where the special primer was used. To verify further the importance of varnish in the primer, accelerated tests were run upon an aluminum-pigmented urimer. wine a commercial bodied oil and volatile thinner iype of vehizc in the one case, and a 100 per cent spar varnish vehicle in the other. (Figure 7)
Conclusion
PRIMERS
Aluminum powder in bodied .Iluminum powder in spar-varnish Oil vehicle vehicle T w o coat3 of same white house paint applied over both primen Figure 7
The results as presented in this.paper indicate that a consideration of the problem of paint adherence on wood from the viewpoint of changes in primer formulation or painting practice is worth while. A continuation of the work may point to other vellicle components for accomplishing the desired improvements, hut the results with the proper varnish primers, while of a preliminary nature, are definite and clear cut. They indicate that in many cases where excellent adherence or reduced influeuce of wood on the failure of a
INDUSTRIAL AiYD ENGINEERING CHEMISTRY
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paint has been obtained these superior qualities may have been due largely to the type of vehicle used. Literature Cited ( 1 ) Browne, Proc., Wood Painting Conference, Madison, Wis., September
13 and 14, 1929.
Vol. 22, No. 8
(2) Hartwig, Am. Paint Varnish Xffrs. Assocn., Circ. 866 (August, 1929). (3) Nelson, Proc. A m . SOL. Testing M a t e r i a l s , 22, Pt. 11, 485 (1922). (4) Nelson and Schmutz, Ibid., 24, Pt. 11, 923 (1924). ( 5 ) Nelson and Schmutz, I N D . ENC. CHEM.,18, 1222 (1926). (6) Nelson, Schmutz, and Gamble, Pror. 4 m. SOL. T e s t i n g M a l e r i a l s , 26, Pt. 11, 565 (1926).
Gases Produced b y the Decomposition of Nitrocellulose and Cellulose Acetate Photographic Films' John C. Olsen, Austin S . Brunjes, and Victor J. Sabetta T H E POLYTECHAIC INSTITUTEBROOKLYN, N. Y.
H E great loss of life resulting from the Cleveland hospital fire, reported to be due to the poisonous gases given off by the decomposition of the x-ray films, indicated the desirability of undertaking a thorough investigation of the nature and quantity of the gases given off by the decomposition of such films. As the investigation also included the explosive limits of the gases evolved when mixed with known amounts of air, it should be possible to establish rules for safe storage of cellulose films. It was anticipated that the character of the gases would be influenced by the presence or absence of air. For this reason the decomposition was effected in the entire absence of oxygen and in the presence of sufficient air to give a reasonable excess of oxygen.
T
Decomposition Procedure
The apparatus employed consisted of a 140-cc. Lunge nitrometer. Weighed amounts of the samples being investigated were placed in small flasks and decomposition effected by heating the flask by means of a Bunsen burner. For the experiments in which absence of oxygen was desired, a 20cc. flask filled with nitrogen was employed. The nitrocellulose films decomposed very rapidly when heated to the decomposition temperature (about 154' C.), leaving a small oily or carbonaceous residue. This was further heated with the Bunsen burner in order to obtain decomposition as nearly complete as possible under such conditions as would prevail during the decomposition of large quantities of the material when high temperatures prevailed. After the flask had cooled to room temperature, the volume of the gas, as well as the temperature and pressure, was read. From these data the volumes of the gases a t standard conditions given off per gram of material could be calculated. On cooling the gases evolved from the acetate films and newspaper, a small amount (1 or 2 cc.) of condensate was obtained. It consisted of water and p-poligneous matter. A small amount of the soluble gases such as nitrogen peroxide and carbon dioxide was no doubt absorbed, but the error from this source could not be very large. The condensate from the nitro films was so small as to be negligible. Varying per'centages of air were then added to the gas and the mixture passed into a Hempel explosion pipet and ignited with an electric spark. I n this way the minimum amoust of air, as well as of gas, which would form an explosive mixture a t atmospheric pressure was determined. The method described for decomposition of the films in nitrogen proved satisfactory for both nitrocellulose and 1 Received March 3, 1930. Presented before the Division of Cellulose Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ca., April 7 to 11, 1930.
cellulose acetate films. The behavior of the two types of films under these conditions differed considerably. The nitrocellulose films decomposed rapidly, leaving some residue. The cellulose acetate films melted a t low temperatures and decomposed gradually on being heated, leaving finally a considerable carbonaceous residue. A large quantity of distillate was obtained consisting of water, pyroligneous acid, and tarry matter. As the gases were allowed to cool before being measured or analyzed, the composition found is somewhat different from the composition of the hot gases, which would contain considerable amounts of the condensate in the vapor state. The decomposition of the films in the presence of excess air was carried out without difficulty in the case of the nitrocellulose product. A weighed quantity of the film was introduced into a 250-cc. flask, which was then connected to the nitrometer. As the decomposition of this product is very rapid, the heating was conducted so that a portion only of the sample was decomposed, after which on further heating the remainder decomposed. Under these conditions the first portion of the gas in the flask mixed with the air would be ignited in the flask by the heat developed by the decomposition of the second portion of the sample. I n some cases explosions occurred in the flask which were so violent as to cause loss of the sample. Undoubtedly under these or similar conditions a more or less violent explosion would undoubtedly result when larger quantities of the nitro film were decomposed. It was found impossible to produce an explosion in the Hempel pipet of any mixture of air and the gases obtained by decomposition of the nitrocellulose films in nitrogen. As the nitrogen would dilute the gas and reduce its explosibility, the experiment was repeated with gas produced by decompositions of the film in a flask filled with the gas produced by a previous decomposition. It was also found impossible to explode this gas. This behavior of the gas is undoubtedly due to the presence of the large volume of nitric oxide. When this gas was removed the residue exploded easily. When the cellulose nitrate film was heated in a test tube, it was not difficult to obtain ignition of the gases issuing from the mouth of the test tube. The temperature of the gas produced in this manner was high enough to produce ignition on contact of the gases with the air. It is evident that a t high temperatures these gases will burn in the air and that the temperature is high enough to produce ignition. Undoubtedly explosions would also be produced in this manner. The failure of the attempts to obtain an explosive mixture of these gases a t ordinary temperatures is undoubtedly due
