the sugar. There was thus a loss of 21.8 per cent of fluorine. Table IV shows that a portion of this loss took place before t h e solutions boiled, or below 107" C. The maximumerror in the fluorine determinations is *8 per cent. Although the losses found between consecutive samples were usually less than this, the facts that in every case but one a loss was indicated, that in this one exception the difference between the values found was practically negligible, and that the over-all losses are a t least twice the maximum experimental error, preclude the possibility t h a t the losses are not real and indicate that both sucrose and dextrose readily expel fluoride ion from hot solutions. The fact that t h e loss is very little above 135" C. may possibly have a n explanation in that equilibria may be set u p with the basic fluoride remaining, or complex fluorine compounds may be formed which remove fluoride ion from the attack of the sugar but retain fluorine in the sirup. TABLEIv. EFFECTS O F BOILING O N SODIUM FLUORIDE IN SUCROSE SOLUTIONS Sampling Temp.
F
T. 5.
c.
Mg.
Gams Sodium Fluoridea
O
VOL. 28, NO. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
1268
108 X F;T.
S. Loss %
Sodium Fluorideb
Sodium Fluoride and Dextrose C 0.432 (calcd.) Start 107 6:06 l2:7 0,398 7:s 135 6.29 17.3 0.364 15.7 155 6.94 19.6 0.354 18.1 176 7.33 21.1 0.347 19.7 a 0.200 gram pure NaF, 227 grams sucrose, 90 cc. water. The sirup darkened at about 160' C. b 0.400 gram pure NaF, 227 grams sucrose, 90 cc. water. The sirup darkened at about 160' C. C 0.200 gram pure NaF 227 rams commercial anhydrous cerelose (92.4%*,), 100 cc. water. Thl nirup ckarkened at 158' C.
, Acknowledgment T h e author is indebted t o S.Byall of the Carbohydrate Research Division, Bureau of Chemistry and Soils, for the analyses of the two candies given in Table I, to R. U. Bonnar of the Food Division, Food and Drug Administration, for the fluorine analysis of the candy containing sodium fluoride. D. Dahle of the Food Division made the fluorine analyses on the experiments from which the data in Table IV were obtained, by a method developed and to be published by him.
Literature Cited (1) Ambler and Byall, ISD. Eso. CHEW,Anal. Ed., 4, 379 (1932). ( 2 ) I b i d . , 7, 168 (1935). (3) Ambler, Snider, and Byall, Ibid., 3, 339 (1931). (4) Browne and Gamble, Facts About Sugar, 17, 552 (1923). (5) Hiigglund et ai., Svensk Kern. Tid., 41, 8, 55 (1929) ; Ber., 62, 84, 437, 2046 (1929); 63, 1387 (1930); 68, 822 (1935); F i n s k a Kemistsamfundets M e d d . , 39, 49 (1930). (6) Marusawa, Naito. and Uchida, Mem. R v o j u n CoZZ. Eng., 1, 351 (1929) (7) Mohr, A n n , 97, 335 (1856) (8) Pucherna, 2.Zuckerznd. EechosZouak. Rep., 5 5 , 144 (1930-31). (9) 2240 (Feb 28, 19321, .. . . Saillard. Czrc. hebdo. fabr. sucre, SUPPI. 2244 (March 27, 1932). I
RECEIVED September 3, 1936. Contribution 133 from the Carbohydrate Research Division, Bureau of Chemistry and Soils.
Permeability of c
U
A
'
l
Lacquer f-ilms to Moisture ROBERT I. WRAY AND A. R. VAN VORST A l u m i n u m Company of America, New Kensington, Pa.
Clear lacquer films of a variety of commercial compositions show considerable variation in permeability to moisture. In general, the lacquer films increase in moisture resistance with age; this behavior makes the time of testing the films after their preparation an important factor in interpreting the data. The permeability of the films has also been determined in contact with liquid water; the behavior in this test is not entirely consistent. Baking appears to increase the moisture resistance of some of the films, especially after aging.
R
ESULTS of the investigation of the permeability of oil and varnish-base paint films to moisture were published in previous papers (1, 6 ) . Data on the permeability of clear lacquer films are presented in this paper. Gettens and Bigelow (d), the Hercules Powder Company (S), and Wing (4) have already reported some work in this field; these investigations determined only the initial permeability of the lacquer films. The effect of aging of the films, discussed in the present paper, is also important. In general, the permeability was found to decrease Kith the age of the films, in some cases in a striking manner. This fact is an important consideration in comparing and interpreting tests on lacquer films. The measurements are of practical interest because the use of clear lacquer coatings with good resistance to moisture penetration is necessary for many applications. It is also important, as a rule, that the lacquers maintain good flexibility as well as moisture resistance, even when exposed indoors for extended periods.
Effect of Age on Permeability of Films A series of tests was made to determine the relative moisture resistance of several types of commercial lacquers : The lacquer films were applled to amalgamated tin plate panels bv minninz. as Dreviouslv described (6). After the films were dried for various periods,'they were stripped from the panels and cemented to shallow Petri dishes containing activated alumina. After weighing, they were placed in a cabinet maintained at 95 per cent humidity and 80" F. (26.7' C.). The dishes, with films attached, were weighed every 24 hours to determine the amount of moisture passing through the films and absorbed by the activated alumina. In applying the different lacquers, they were reduced to a uniform viscosity (where possible) of 0.85 poise. Two of the lacquers tested had viscosities lower than this when received and
NOVEMBER. 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
year, since some of them had become too brittle. I n practically all cases, increased moisture impedance was accompanied by a loss in flexibility. Of the lacquers tested, those containing alkyd resin and chlorinated diphenyl resin offered the highest resistance to the passage of moisture.
TABLEI. MOISTUREIMPEDANCE OF CLEARLACQUER FILMSAFTER LABORATORY STORAGE Lacquers Xitrocellulose lacquer taining alkyd resin
1269
No. of Film -Moisture Impedance" after:Coats Thickness 48 hours 1 week 2 weeks 1 month 1 year Mm. b 4.5 5.5 0.007 4.3 4.5 con1 46 6.5 10 0,013 5.7 7.0 2 16 77 8,6 9.5 10 0.019 3 3.6 5.1 30 3.9 1 0.009 4.0 con8.9 71, 7.5 8.0 2 0.017 7.6 di-
Effect of Liquid Water
Nitrocellulose lacquer taining chlorinated Dhenvl resin Vinyl resin lacquer (in solvent)
The one- and three-coat films of the various 12 12 15 11 3 0.020 lacquers, after dryingfor a month, were also tested 2.8 3.2 3.2 3.4 b 0.016 1 5.7 6.3 5.5 8.2 b 0.025 2 with liquid water on one side of the film, instead 5.8 7.5 7.9 11 c 0.045 3 of a moisture-saturated atmosphere. The film Nitrocellulose lacquer con1 0.011 0.5 0.4 0.4 0.5 0.5 taining vinyl resin 2 0.026 0.6 0.8 0.7 0.7 1;s was cemented t o the Petri dish containing acti3 0.043 0.8 0.8 0.8 0.9 vated alumina (as before), and a ring of wax was Nitrocellulose lacquer con1 0,012 1.8 2.8 2.7 3.1 taining phenolic resin 2 0.025 4.2 5.9 +:5 9.1 5.4 fastened t o the top edge so that a layer of mater 3 0.043 5.3 8.1 10.9 22 about inch (3.2 mm.) deep could be held on Moisture impedance - area of film in sq. om. X hours. top of the film during the test. At the same time mg. of moisture penetration , calculated for a film thickness the effect of the water on the various lacquer films of 0.012 mm. per coat. During tests, the films were subjected to an atmosph ere of 95 per oent humidity at 26 7' C. was observed. Only one lacquer (nitrocellulose b Film too brittle t o remove intact for measurement. Film not available for measurement. lacquer containing phenolic resin) showed any visible effect of the water on the film itself. A three-coat film of this lacquer exhibited marked hence could be given no further thinning. An attempt t o produce whitening but regained its original appearance when the water different film thicknesses by varying the solvent content of the was removed and the film allowed to dry. The results of the lacquers proved unsuccessful because of the difficulties enimpedance measurements of the films in contact with liquid countered in obtaining a smoot,h uniform film; the lacquers set water are shown in Table 11. Generally, three coats of lacquer too quickly to flow out evenly when the solids content was too high. Variations in film thickness were secured, however, by appeared less resistant to moisture penetration by contact applying additional coats. There was a slight tendency for sucwith liquid r a t e r than when exposed to a saturated atmosceeding coats of lacquer to soften the undercoats, but by applyphere; the reverse was true of the singlecoat films. ing the coatings as rapidly as possible, this tendency was minimized. 1
"
(I
0
Most of the lacquers tested produced clear, smooth, transparent films. One lacquer, consisting of a solution of vinyl resin in solvent, gave a film which was somewhat cloudy, and hence the films formed with it were slightly opaque. Another vinyl lacquer, containing vinyl acetate and nitrocellulose, gave a clear, tough film which stretched easily. It was quite flexible but not elastic, since it did not resume its original shape after stretching, and was difficult t o handle. The first films were tested after drying for 48 hours. The films of some of the lacquers had to be handled carefully to prevent tearing. One lacquer containing phenolic resin showed a tendency to break as it was being stripped from the panel. After drying for 2 weeks or more, most of the lacquers had improved in their handling characteristics. T h e results of the tests on the various lacquers, after airdrying for various periods, are given in Table I. Considering the difficulties encountered in preparing and handling the films, the results are fairly consistent. I n general, the moisture impedance tends to increase as the films age, showing a marked increase, in most cases, after aging for one year. It was not possible to remove all of the films for test after a
TABLE11. MOISTUREIMPEDANCE OF CLEARLACQUER FILMS AFTER ONE-MONTH LABORATORY STORAGE' Lacquers Nitrocellulose lacquer containing alkyd resin
No. of Film Moisture Coats Thickness Impedanceb 1
h'itrocellulose lacquer containing chlorinated diohenvl .~ resin Vinyl resin lacquer (in solvent)
3 1 3 1 3
Nitrocellulose lacquer containing vinyl resin
1
3
Mm. 0.007 0.019 0.009 0.020 0.016 0.045 0.011 0.043 0.012 0.043 . . ~
7.3 11 6.3 15 E
8.3 0.4 1.0 2.7
Nitrocellulose lacquer containing phenolic 1 resin 3 11 ..~ . ~a During testa, the upper surface of all films was in contact with liquid water a t room temperature. b Calculated for a film thickness of 0.012 mm. per coat. c Film too brittle to remove intact for measurement. ~
Effect of Baking
The moisture impedance of single coats of all the lacquers, after force-drying for 5 and 10 minutes a t 225' F. (107.2' C.), was also determined (Table 111). I n only two cases (vinyl resin lacquer and nitrocellulose lacquer containing alkyd resin) did force-drying for this length of time prove beneficial initially. After aging one year, the baked films in most instances gave higher impedance values than the air-dried films, TABLE
111. MOISTUREIMPEDANCE OF O N E COAT O F AFTER BAKINGAT 107.2" c.. L.4CQCER FILMS
CLEAR
Impedanceb Moisture
Nitrocellnlose alkyd resin
Lacnuer lacquer
containing
Time Film of Thickness Baking Initial Mm. Min. 0.007 3 2 2
c
4.0 4.3 5.S e 15 7.2 c 30 7.0 e Sitrocellulose lacquer containing 5 3.2 c chlorinated diphenyl resin 10 3.8 36 Vinyl resin lacquer (in solvent) 5 5.9 38 10 4.7 41 Nitrocellulose lacquer containing 5 0.4 c vinyl resin 10 0.4 2.6 Nitrocellulose lacquer containing 5 1.0 c phenolic resin 10 0.9 2.9 a Subjected t o an atmosphere of 95 per cent humidity a t 26.7O C. b Calculated for film thickness of 0.012 mm. per coat. C
0.0066 0.0066 0.0065 0.0065 0.0094 0.0097 0.0178 0.0175 0.0114 0.0109 0.0118 0.0122
After awe
1 year
5
10
Films not available for measurement.
Literature Cited ( 1 ) E d w a r d s , J. D., a n d Wray,
R. I., ISD. ENQ. C m x , 28, 549
(1936).
R. J., a n d Bigelow, E l i z a b e t h , Tech. Studies Field Fine ATtP, 2, 16-25 (1933). (3) H e r c u l e s P o w d e r C o . , " M o i s t u r e P e r m e a b i l i t y of V a r i o u s Prot e c t i v e C o a t i n g s , " 1933. (4) W i n g , H. J., IND. ENGI. CHEM., 28, 786 (1936). (5) W r a y , R. I., a n d V a n V o r s t , A. R., Ibid.,25, 842 (1933). (2) G e t t e n s ,
RECEIVED September 14, 1936. Presented before the Division of Paint and Varnish Chemistry a t the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936.
