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from the fence, and the films were removed by running mercury around the edges of the panels and allowing it to amalgamate with the tin, This permitte...
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Y PHYSICAL STU'D'

TWO-COA T P

SYSTEMS D. W. ROBERTSON AND A. E. JACOBSEN Titanium Pigment Company, Inc., New York, N. Y.

HE necessity for a suitable primer or f i s t coater in connection with good house-paint performance has been generally recognized. The importance of this factor in paint performance has nevertheless been neglected, as far as actual merchandising practice in the industry is concerned. In a previous paper (2) dealing with the physical properties of single films, it was shown that the rate of paint failure was closely associated with the retention of the film's elasticity after exposure and that this property of the film also influenced the character of failure, with pa,rticular reference to checking and cracking. The technic employed in preparing and testing the films was as follows: In order to be able to test these films periodically for distensibility, flexibility, and tensile strength, it was necessary that the paints be applied to a surface which would permit their ready removal and which would not interfere with their exposure to the weather. The aints were applied to tinned copper panels by the use of a pair orshims and a straight edge used in the manner of a draw knife. For the first coat shims with a thickness of 0.003 inch (0.0076 cm.) were employed, and for the second coat shims of 0.005 inch (0.0127 cm.) were wed, so that, allowing for loss of film thickness due to evaporation of the solvent, the fist coat of paint would be between 0.002 and 0.003 inch (0.005 and 0.0076

METALTESTSTRIPS ON 45" FENCEAND ON VERTICAL FENCE T SAYVILLE, LONG ISLAND

cm.) thick, with a total thickness of approximately 0.005 inch for the two-coat system. Actual measurement of the dried films gave results in accordance with this estimate. At each test period a portion of each metal panel was taken from the fence, and the films were removed by running mercury around the edges of the panels and allowing it to amalgamate with the tin, This permitted the removal of the films without subjecting them to any unusual stress or otherwise affecting their physical condition. The films were conditioned for 24 hours at 75" F. (23.9' C.)and 50 per cent relative humidity just prior to testing. The functions of a primer in terms of its specific properties are not well defined; except for the idea that there is a direct relationship, in terms of performance, between relative hardness of undercoat and top coat, and that certain combinations are incompatible (I), a vague conception of the subject is evidenced by the great variation in thinning directions for the various coats of ready-mixed and semi-paste paints, and the great difference in the fundamental characteristics of the few special primers offered by the industry. Two objectives were in mind when the paints were selected for the series of tests described in this paper. First, it was hoped that something sufficiently fundamental might be developed to permit some generalizations in connection with the behavior of two-coat systems, and secondly,

A technic is employed which permits the removal of paint films from metal panels after various periods of exposure. By use of a two-coat system'and a physical examination of the detached films after exposure, interrelationships between the physical properties of the two films, in terms of exposure results, are shown. t ilms are tested for distensibility, flexibility, and tensile strength, and the results are tabulated with reference to failure as ordinarily observed in paint testing on panels. Results indicate the desirability of using specialized paints as undercoaters for general house painting and point to some definite formulation principles which promise improvement in results over current general practice.

-.

403

INDUSTRIAL AND ENGINEERING CHEMISTRY

404

VOL. 28, NO. 4

TABLEI. DATAON DISTENSIBILITY Pigment Resin Vol. ConConcn. tent

Primers Pigment a

%

%

30 40

2.5 5 7.5 2.5

30

7.5 2.5

5

Pigment b

Pigment c

40

7.5 2.5

30

7.5 2.5

40

.. .. ..

Commercial Self-primed White lead

5

5

5

7.5 2.5 5 7.5

... ...

...

--Top 0

2

-

20 24 30 20 20 24 18 20 18 13 15 17 20 20 22 13 18 12 23 28 18

12 15 24 10 10 6 15 15 12 12 10 14 20 18 15 10 8 10 8 .10 12

Coat 1 after Weeks of Exposure:-4 6 1 0 15 Per 8 6 4 1.5 13 12 5 1 13 8 5 1 8 8 2 0.5 10 6 3 0.5 6 4 2 1 10 14 4 1 12 15 4 1.5 8 8 3 1.5 5 5 2 2 10 8 3 1.5 9 3 1 12 10 3 3 5 . 2 2 2 4 4 3 2 4 5 4 1.5 4 7 8 1 3 4 3 1 6 4 2 2 6 3 3 2 9 5 2 2

..

-Top Xu 0 2 Cevt Elongation 0

0 0 0 0

0 0 0 0 0 0 0 0

0

0 0

0

0 0 0 0

18 25 2 10 1 1 21 26 19 10 12 1 15 19 16 11 1 14 1 17 16

Coat 2 after Weeks of Exposure:--4 6 1 0 15

4 2 4 2 5 4 2 10 3 2 7 3 5 6 3 4 3 4 4 3 3 3 2 4 2 2 5 2 3 2 3 2 3 3 6 4 0 3 3 5 4 4 2 2 3 2 2

5

Top Coat 3 15 5 3 2 1 0.5b F 15 5 10 4 3 1 1 0.5b F 21 4 15 6 4 1 1 0.5 0 23 4 40 9 6 2 3 1 0.5 0 1 2 5 10 4 2 2 0.5 1.5 0 1 5 7.5 11 5 2 2 1 1 0 1 6 Pigment b 30 2.5 15 3 3 3 1 1 F 13 5 5 17 6 6 2 1 0.5b FF 13 4 7.5 20 7 3 1 1 0.5 F 15 4 40 2.5 12 5 4 1 0.5 1 0 10 3 5 10 5 4 4 1 0.5 F 13 5 7.5 10 7 4 5 1 0.5 F 12 3 9 4 Pigment o 30 2.5 10 5 2 2 1 0.5 F 5 11 5 3 4 1.5 lb F 15 6 7.5 10 4 3 3 2 b lb FF 20 3 40 2.5 8 5 4 2 2 0.5 F 12 3 5 9 4 4 3 1.5 0.5 F 13 4 7.5 9 6 3 3 1.5 0.5 F 14 3 Comm&ial .. ... 15 5 4 2 1 1 0 12 2 Self-primed .. . 13 3 2 1 0.5 0 FF 1 2 White lead .. 17 4 3 2 1 1 0 10 2 X indicates visible failure i n the form of checks or cracks i n films before test, F a t 15 weeks, FF at 10 weeks. Top coat cracked before fracture of composite film. Pigment a

30

2.5 5 7.5 2.5

b

that by the use of a new and in many respects a unique pigment material, lead titanate (S), some contribution to the knowledge of the behavior of that material might be made. The paints described in the following paragraphs were used.

3

2 2 3 4 2 3 3 2 2 3 1 1 1 2

lb 2b 1 1 1 1 lb l b

0.5 0.5

lb

1 0.5b 1.5b 2b 1.5b 1 2b 1 0.5

1.5

Top Coat 4 1 0.5b 1 lb 2 1 lb 2 2 1 2 2 1 2 2 1 4 2 lb 4 4 1.5h 3 3b 2b 3 3 0.5 3 3 lh 3 2 16 1 2b 2b 3 2b 0.5b 2 26 1.56 3 2 2b 2 2 1.5 3 2 0.5b 1 1 0.5b 1 1 0 2 2 0.5b

2

1

5 6 6

.. ...

a

2 2 3 3 3 2

2

0.5

0.5b 0.5b

Xa

FF

F F

0.5

F

0 0

0 0

0.0 0.j 0.0 0.5

FF F F

0.2

0.5 0.0 0.5b

1b 0.5

0.Ob 0.5 0.5

0.5 0.5 0.5

0.5h

0.56 lb

0.5b 0.5 1b 0.56 1-b 0.5 0.5 0.5

1 0.5b

O.5b 0.5b 0.5b 1 0.5 0.5b 0 0

0

FF FF FF

FF FF F F FF F FF F

F FF FF FF F F FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF

The four top coats were formulated with the idea that they would produce progressively harder films, in the order 1, 3, 2 , 4.

Primers

Top Coats PIGMENT. The pigments were as follows: Top coat 1

40% basic-carbonate white lead 40% titanium-barium pigment

Top coat 2

40% titanium-barium pigment

;;g

E

Top coat 4

VEHICLE. The vehicle in the case of pigments 2 , 3, and 4 was composed of: $I: 0

Primera

;;?;;tine

29.2 basic-carbonate white lead 30.8T o leaded zinc (35%) 25 basic-carbonate white lead 25 titanium-barium pigment 25 o lead titanate 25 0 zinc oxide (American process, lead-free) 40% basic-carbonate white lead 40% titanium-barium pigment 20% zinc oxide (American process, lead-free)

Top coat 3

PIGMENT.Three principal pigment combinations were used in the special primers:

raw linseed oil polymerized linseed oil (viscosity Q) drier and thinner

The vehicle for pigment 1 was modified to contain 7.5 per cent resin. PIGMENT VOLUMECONCENTRATION. The pigment-vehicle ratio by volume ranged from 29 to 30 per cent; there was only a slight variation between the four paints.

431

basic-carbonate white lead titanium-barium pigment asbestine 10 silica 33.33% basic-carbonate white lead 33.34% lead titanate 33.33% silica and silicates basic-carbonate white lead titanium-barium pigment (1

Primer b Primer c

25% silica and silicates

VEHICLE. The primer vehicle in all cases was the same, except for a variation in resin content (2.5, 5 , and 7 . 5 per cent) and had the following genera.1composition, exclusive of resin: 39.6% 14.8 9.8% 5.7'7 30.1%

raw linseed oil polymerized linseed oil pol merized tung oil oxizized linseed oil volatile matter

This particular vehicle was selected because (with 5 per cent resin) it had been extensively tested in a practical way over a period of several years in conjunction with a pigment combination similar to Primer Q and had given excellent results.

All three pignient coniliinations (a, h, and e ) wore used in the three-resin-content vmiations of the vehicles at botli 30 and 40 per cent by volume, calculated on total nonvolatile mahrial. Each primer, therefore, is designated in the following manner for identification and convenience: Primer a-302.5, a30-5, a-30-7.j, 0.40-2.5, 0-40-5, a-40-7.5, ete., makiiig a total of eighteen primers with three different pigment cornIiinations. For example, primer h-40-5 would he pigment combination b in the vehicle containing 5 per cent resin and witli 40 per cent pigment by volume, calculated on the total noijvolatilc matter in the paint. These variations in resin content and pigment volume concentration were designed to produce graduated differences in hardness. By reason of its known good performance as a prinler, xhite lead was used for comparison. There was also one comniercial primer which had been extensively used user a period of several years aud which u.as knoari tu have given goiid resiilt,s; this was also included hut will not be described. In addition to the twenty primers, each of the four top coats was applied self-primed, making a totnl of eighty-four test cornbinatims. All of these tests vere run parallel on m o d and metal n t both 45" and vertical south. Xo results are yet avnilahlr on the vertical tests, but the 45' tests on wood are begiiininx to show ,evidence of failure in some cases and will be 1)rieflr mentioned. Unless otherwise mentioned, all data. presente~l liere is in reference to films on iaetal exposed at 43' south.

Distensibility Table I siloas results obtained in the test fur perccrltage elongation. The outstanding feature is that top coat 1 priiiluced a homogeneous film with aU primers and did not crack separately from the primer in tlie course of the test as did the other top coats in many cases. This ir uniiauhtcdly corincctecl with the fact that ihis paint Iind about t.he same retained distcriribility self-primed as over the other primers, showing 2 per cent at I5 \seeks. Top coat 2 beha.ved iwll over primers a--10-2.5, 9, am1 7.5 in t,hat, it did iiot crack while the film v a s being elongateil. It is interwting to note, however, dhat even' where this top co2xi rupt,iirt?d, three primers stood thi: stress and elongated t.o 2 per cent a t 10 weeks d e spit.e the top coat cracking. Top coat 2 showed no disterisibility at 10 weeks when self-primed. At 15 weeks it sliowed l%ihle checking or top coat cracking o w all primers except three. Top c ~ a 3, t in spite of its decided hardness, as evidenced Iiy the generally low distensibilit,y figure at the l0-week period, did not crack in the course of elongat,ioii exwpt in one case; in that instance the undercoat IVRS capable of standing this strain and elongating t,o 2 per cent. Bbrcrit visible failure is noted for this top coat in the ca4c of sex-en primrs at 15 weeks, xhile, for exnmpie, risible failure wns absent in onlj'three at 15 weeks x-liere bop coat 2 \%.as involved. Top coat 4 gave tlie iioorcst ac,coiint of itnelf and was really good over only a h e l e group of three priniers, 0.40-2.5, 5,

and 7.5 at 10 weeks and had failed Over all primers at 15 weeks. This, together with results obtained over the same group of primers with top coat 2 is a rat.lier definite indication that these three primers are a t least the most versatile io the ?cries and are capable of giving relatively C;oiJd results with a. wide range of top coat types. So top coat contaiiririg zinc oxide in either fonn (leaded or lead-free) had any appreciable distensibility at 10 weeks. T I E plasticizing effect of lead titanate in top coat 3 rvas not sirffiiicientlygreat to balance the hardening effect of zinc oxide, altliough it did greatly reduce the number of visible top coat fdiirw, as comparcd irith paints 2 and 4.

Flexibility Test The same films tested for distensibility were also tested for fiexiirility by bending over rods of varying diameter. Bods I l l # , I/*, I/*, and 5,'iB inch (0.16, 0.32, 0.48, 0.64, a i d 0.8 em.) w r c used in this test, and all filins were tested by lmxliiig in botli directions -that is, t,op coat. up and revtmed with priming coat, up. This, in effect, constitutes a separate elongation test for tlie two coats (if paint. ltesrilts are sbomn in Table IT. Tlie mnndrels or rods Irere nuinhered 1 to R in order of iricrensiiig diuniotcr ('iiG t.o E / , $ inch), and the results in Table I1are i:xpressed in tlie forrri of a common fraction, tlie numr:rat.or indicating the smallest ruandrel size over vhich the filrn could be bent witlrout cracking, with the top coat out, and the ilcriaininat.or showing the same thing for tlie primer or underribat \vlicn t,lic film was reversed. 3landrel size niag also lie translated int,o percentage elongat,im of oiiier film in this t,est. Rased on t,lie assumption that tlie neut,rnl pliirrc of film movement is cquidistunt from the upper isid Iomr surfaces of the two-coat composite film and allowing 0.005 in& as the added cffcctive diameter of the ma,ndrel, the p e r c e n t a g e elongatim for each size xould bc as foilom:

Top coat 1 sbowerl perfect perforinance in this test, indicating that the period of test has not yet extended to t h a t p o i n t where real differences in primers with this top coat can be shown, as well as the relative good behavior of this top coat. Top coat 2 cracked over eight of the primers and over itself at 10 weeks and over seventeen primers and itself at 15 xeeks, licfore the film was siibject,ed t o tlie test. In the case of this top coat

...

(7':~) TOPCo~~Cnacnrh-o IX'-I-B:XSILE ~ ~ F A ~ ; AND T WE L o ~ ~ i h ~ TF:sI.s iox Top roat 4 over primer n - 3 0 7 . 5

(C'enlw) TOP COATCRACKING OYER Pamns~; C ~ ~ c nI)o s NOTEXTEKD TXROUIJIT 1"IMF:R

TOYcoat 2 over primer e-80-7.6 ( X 9)

(Bollom) Top COAT4 e-30.5

O V ~ RPRIMER

I h a k s are in t o p ?oat unly ( X

1'/1)

INDUSTRIAL AND ENGINEERING CHEMISTRY

406

VOL. 28, NO. 4

self-primed, the film broke completely in the test over the largest mandrel at 10 weeks. Top coat 3 gave a better performance than 2 in that i t showed cracking over only two of the primers and itself at 10 weeks and over thirteen a t 15 weeks. Top coat 3 continued to give a perfect record over primers a-40-2.5, 5, and 7.5, t h e commercial primer, and white lead. This result is a rather definite indication of the value of those particular primers. Top coat 4 was again the poorest as evidenced by the high ratio of mandrel size required as between the test with t o p coat out and the same film reversed and also the fact that i t showed visible failure over fifteen 'primers and itself at 10 weeks and over all primers at 15 weeks.

Tensile Strength The tensile strength of all films was also measured periodi1 2

50

3

4

5

6

7

9

8

1

0

1

3

2

I

4

/

d 45 g 40

g 35

1::

a 20

8

SW-PRMQ)

I l5

;

10

w

1

Two-coat b a t m u Xwabors 2 and 4 too brittle to test bepnd ten reeks. 2 3 1 5 6 7 8 9 io 1 2 3

551

4

# l

/

501

451

TOP COATS OVER WTE WAD P B u e e Two-Coat S y a h

601 40 12

35 30

cally. Some composite results are shown in Figure 1. Two interesting features are connected with these results : (1) There was a general increase in tensile strength of t h e paints which continued for some time after exposure. (2) This increase continued for the whole period of test in the case of the paints over the special primers but started to fall off rapidly in from 4 to 6 weeks in the case of all self-primed paints, except toR coat 1, again indicating that top coat 1 is suitable for use as a first coater or primer and that on the basis of these tests, none of the other paints is suitable for priming use. Top coat 3 (self-primed) showed a slight secondary increase in tensile strength between 10 and 15 weeks, while top coats 2 and 4 were too brittle to test after 10 weeks. A series of identical exposures on wood have, in general, shown the same relative results, in so far as they show anything, but they have not progressed in their failure to a sufficient degree to warrant a report on their condition except in a few isolated instances. For example, the four top coats were applied on wood over an aluminum primer, and top coats 2, 3, and 4 all show slight cracking over this primer, whereas over other primers all of these paints are showing absent checking and cracking in one or more cases. An example is primer b-30-5, showing perfect results with all top coats. This behavior indicates that primers selected for test are a t least as good as those which are in common usealuminum, white lead, and one commercial primer of known good performance. The primers were exposed as single coats on a vertical fence and tested for elongation a t 11 weeks. The results of these tests are a general confirmation of the flexibility results in Table 11. Pigment a a t 30 per cent pigment volume concentration averaged 2 per cent elongation (2.5, 5, and 7.5 per cent resin); a-40, 1 per cent elongation; b-30, 8 per cent elongation; b-40, 3.6 per cent elongation; e-30, 10.5per cent elongation; e-40, 4 per cent elongation; white lead, 1.5 per cent elongation; and the commercial primer, 2 per cent elongation. These figures are considered significant in relation to results shown in Tables I and 11. This test could not be made a t 45O, in direct comparison with the two-coat series, for the reason that failure of a single film of ordinary paint is too rapid ,at 45" to permit consistent testing by this method.

Conclusions

25 20

TOP COATS OVER COtUERCIy PRDLFIL Two-coat system

15 10 2

3

4

5

6

7

8

9

Weeks Erposurs

FIGURE 1

10

1

2

3

4

The tests have not yet progressed over a sufficient length of time to generalize with respect to primers except in a very broad way, but a few conclusions are warranted: 1. Assuming that top-coat paints 1to 4 represent the range in elastic properties of first-grade ready-mixed paints as formulated today, it may also be assumed that only top coat 1 is suitable for self-priming, in that better results with all other paints are possible by the use of a specialized paint for first-coat use. 2. The group of primers a-40-2.5, 5, and 7.5 will give superior

APRIL, 1936

INDUSTRIAL AND ENGINEERING CHEMISTRY

407

TABLE 11. DATAON FLEXIBILITY Pi ment Primers Pigment a

$01. Concn.

Resin Content

%

%

30

2.5 5 7.5 2.5 5 7.5 2.5 5 7.5 2.5 5 7.5 2.5 5 7.5 2.5 5 7.5

40 Pigment b

30 40

Pigment c

30

40 Commercial Self-primed White lead

. .. ...

Pigment a

30 40

Pigment b

30 40

Pigment c

30

... ...

... 2.5 5 7.5 2.5 5 7.5

-Top

Coat 1 after Weeks of Exposure:44 6 10 15

0

2

1/1 1/1 1/1 1/1

... ... .. . . .

;$; ::: lil .. . ;$; ::: 1/1 .. ;$; ::: 1/1 ... ;$; ::: 1/1 .. . ;$; :::

1/1 1/1 1/1 1/1

:$; 1/1 1/1

1/1 1/1 1/1 1/1

Xb

$;1/1 ; 00" :$; 8

;$; ;1/1 $; ;1/1 $; 1/1 0 1/1 1/1 0 ;$1/1 ; ;$;$; ; ;$;$; ; ;G 8 1/1 0 0 ;1/1 ;; 1/1 1/1 8; 0 1/1 1/1 1/1 0 ;$; :;; ;$; :0 1/1 1/1 1/1 1/1 ;$; ;$: ;$; ;$; : 1/1 .. 1/1 1/1 1/1 1/1 0 3; ::: ;$; ;$; ;$: $;; 00 ,

,

1/1

1/1

1/1 1/1 1/1

1/1 1/1 1/1

1/1

;$; % ;$; $;1/1 ; ;1/1 $;

Top Coat 3 1/1 2/1

$:;

.. ..

0

2

Coat 2 after Weeks of Exposure:@4 6 10 15 Xb

1/1 ;(; ;$; : . :. $;1/1 : $; 2/1 1/1 33//; ;$; .: : $:1/1 ; 211 1/1 3/1

4/1

0 0

1/1 1/1 1/1 1/1

4/1 5/2

2;;

FF F F

,

1/1 1/1

,

... ... ... . ..

1/1 1/1

311

:(;

2/1 2/1

3/1

3/1T 411 4/1

g;

$;1/1 ; ::: $; $; $:; $;: . . . 2/1 3/1 4/1 4/1 ;$; .... . . 2/1 2/1 ;$; ;$; ;$f ... ...

1/1 1/1

;$;

,

:$; :$::$;T

g$iT

1/1

3/1

4/1T

4/1

5/1

1/1

'I1

,.

1/1

FF F F F

0

FF FF FF FF FF F F FF F FF F

Top Coat 4 3/1

225: $!;

F

F 0

5 2.5 5 7.5 2.5 5 7.5 2.5 5 7.5

;$; ;$;

1/1

;$:'1/1 2/1 2/1 3/1 F 1/1 1/1 ;$; $;; i;; gF ;$: 1/1 ;$; 2/1 3/2 FF 1/1 ;$; 1/1 $:! ;$2" F 1/1 $:;

40 1/1 Commercial 1/1 Self-primed White lead * Numeralsindicate smallest mandrelsise over which films will bend; 1 s/,,inch, 2 I / ~ , 3 of film.(both coats).in t h e test, b X indicates visible.failure i n the form of checks or cracks i n films before test, F a t 15 weeks,

..

--Top

... ... ...

$;;

-

average results as compared with any of the paints self-primed or in comparison with other primers included in the test. 3. In comparing a pigment volume concentration of 30 and 40 per cent, the results are conclusively in favor of the higher pigment concentration. 4. There is unmistakable evidence that primers may be either too hard or too soft, as indicated by some of the self-primed paints which were obviously too hard. Pigment a at 30 per cent can be assumed to be more flexible than the same pigment combination at 40 per cent pigment volume concentration, and was not as good in performance. Pigments b and c, where by the use of lead titanate the primer's elasticity was further increased, gave results which were not so good as in the a-40 series. 5. The percentage distensibility of a primer film need not be great but should be maintained over a long period of time to give best results. With this viewpoint, based on evidence to date which is admittedly incomplete, it is thought that lead titanate offers the best possibility of achieving this result, but that the formulation of primers with this pigment will have to be decidedly modified, in comparison with any of those included in this series of tests. Where the primers were separately tested for distensibility, the a-40 series averaged 1per cent elongation a t 11 weeks and showed best results in the tests involving their use as undercoats, whereas the primers containing lead titanate were about four to ten times more elastic. 6. Where both top coat and primer had good flexibility, it is noticeable that no break in the film was visible. It is therefore permissible to conclude that top-coat formulations should be generally revised to give increased flexibility with age. This amounts to a converse statement to the effect that primers must be formulated to sacrifice some desirable properties in order to meet the conditions which are brought about through the necessity for adapting them to use with inferior top coats. In other words, a satisfactory primer from a commercial viewpoint must be compatible with paints that are generally sold, even those which are not considered good.

1/1

1/1

$:

$;;

$:;

2/1

3/1

://:$: $5/2 :

alia,

4

i,14,

5

-

s/~~.

FF FF FF FF FF FF

T indicates complete rupture

FF a t 10 weeks.

7 . These results definitely point to the necessity for special primers or first coaters in order to obtain best results in exterior painting and justify the current tendency among paint manufacturers to offer special primers with their house-paint line, to be used both on new and repaint work.

These tests will be continued to the point of ultimate failure of the several paints and a further report of results' offered at that time.

Acknowledgment Acknowledgment is made to C. E. Reynolds for,his careful work in preparing the panels and in making the tests.

Literature Cited (1) Browne, F.L.,Forest Products Lab. Bull., July, 1935. (2) Jaoobsen, A. E., Oficial Digest Fed. Paint & Varnish Production Clubs, NO.146,215-28 (1935). (3) Robertson, D.W.,IND.ENQ.CHEM.,28,216 (1936). RECEIVEDNovember 11, 1935. Presented before the Division of Paint and Varnish Chemistry a t the 13th Regional Midwest Meeting of the American Chemical Society, Louisville, Ky.,'October 31 to November 2, 1935.