Vd. 96, No. 2
INDUSTRIAL A N D ENGINEERING CHEMISTRY
144
mlvent. In this pmceas the oil-conlaioing marsrial wan moved
TABLE 111. C&ACTEB~~TICB OF BOLVENPEXT~~CXEO dowly thro h a number of semicircular sections of the extractor hv oerforaz blades of naddle wheels in each section. in a direTUN0 01-
1.
21
3.
8.8 i.7 3.1
163.7 164.3 161.6
62.2 67.6 61.3
12v4
l3V* "'''
0.12
0.22
n.23
60; opposite to the t r a a of the solvent. Extractio~efficiencies of 997or better were obtained. 3. h e mlveneextraoted tun oils from the first experiments contained e x c w acidity and hfed to solidify hut were readered permanentlv liauid by a mild beat treatment. 4. To obtaii extricted oils of low acidity, it was found that the extraction of tun material shortly after preparation and liltration of the miscefh waa nw-w hecause the oil in tmeals~developsfree fatty acids ra idli in the resene of & ; aidersble moisture. The quality opthe tung o$ thus extracted was found to be eatisfactory, and all remained liquid at ioe-box temperature. 5. Thene oils were teated and formulated into varnishes by the National Paint, Varnish and Lacquer Aedoeiation. It waas reported that all of these oils could be Ged by the paint and varnish industry, althougb the oil from commereid p m cake was somewhat lower in quality than that expressed fmm tung nub. 6. Test m e l a were nre~aredwith these varnishes and were exposed ne& G a i n e s d ~ .' A f k 3 months of e x m no diff e k c e in durability between the varnish r o n t a i h g the solvenG extracted oil from tung seeds and a standard s p m varniah could he detected. The varnishes containion the mlventenraeted oil from tung press make appeared to be Lferior to tbe standard in durability. ~~
wan removed. This precipitate appeared to increase in quantity for 2 or 3 days, and appeared to be especially voluminous in the d from runs 5 to 8. The precipitate .was filtered off snd was found to he 0.02% of the oil in the sample from runs 5 to 8.
A preliminary examination haa failed to indicate the nature of thin mlid. The low acid value and short time of beat tast of the oil from gruund tnng seeda am noteworthy. SIJMM*BY
1. The bent preparation of tung kernels and s+ for extraction by a continuous pwas obtained by reducmg them to a medim hoe med hetween corrugated mlls Lnd w n i g this material between smooth rob. commercial tuns press Cske nesdsnorpscial I'B 2. E u - d m ~ ? ~ t i o n s of ground tung k e d and d. cornmereid tunc nrem cake. and emerimentallv nrenalpd
~~~
~
~~~~
~~~
~~~
~~~~~~~~
~~~
~~
IIT&R*TUBE U T W (1)
Freaman. A. F.. and MoKimey. R. 8., 03.Point Drw Rem., 140,No.5.6,38.46(1841).
(2) McEinna~.R.S., Ross, W.Q.. and Frseman, A. 2.277.34a mob u.IW).
F.. U. 8. Patent
(3) RMa. W.Q.. Freeman. A. F. and McKinney, R. 8.. Im. EUQ. Cm11..34,81Z13 (1942).
Urea-FormaldehydeWaterlThinned Paint EFFECTiOF CERTAIN PIGMENTS ON RESIN CURE John K . Wise LmITKD STATES GYPSUM COMPANY. CKICAGO, ILL.
--
from wld-nettiq uma-forrrmldshyde m i n e . I t i~ tial to Eboass the pigmentn and liu.?mpmperly in order that the -of the resin &dl not be inbiblted. A -ti.factory test mcthod h M been dwdopsd for the wdwtion of pigments and fillem.. In the m d w m m d pdnt pigments and extend- the phcnomsnrm of inhibition of -8 to be a d a m p m b l - r m h t h m (L &emical reaction bctwkn the accelerator and the pigment ussd.
T
HE water-thinned painta now off'ered for sale in this country may he divided into s e d classes: calcimines, dry-powder casein paints, ossein paete paints, lend reain emulsion paints (8). Calcimines am glue-bound paint@which Usuauy cantsin only a small quantity, if any, of high-rafractive-index pignente. They may he removed by washing with water (7). The .mein dry-powder paints am bound with c a i n , the powder contahhg lime or other alkali which is a mlvent for canein when rster is mixed with the powder. The carein paste paints am heavy pastes cmtahhg cssein solution with mitable pigmenta and 6Um. They am u m d y marketed at a pa%te OonsiStency which permit8 dilution of the psste with one half volume of watertopepfmthep.
Although these produci~have been widely accepted and have
made considerable inroada into the flst oil paint market, they
have always been subject to the criticism of lower washability than the flat oil paints. They have, in turn, a nmher of pinta of mpsriority over flst oil painta (S,8):
1. Greater ease of application. 2. Lower cost of a plication. These painta may he applied with a 7-inch brush, the usual maximum brush size with oilpainteis4inches. 3. Elimination of fire b a r d from Bammable solvents. 4. Freedomfromodor. 6. Greater drying spead. These painta 818 dry to the toucl and ma be recoated in 1 4 hours. 6. &uction of a uniform flat t surface. There is nc tendency for atreaks to appear whicL%ve a greater sheen than themainbodyofthepaintedmufm. 7. Hiding is s e e d with fewer coats. 8. There is a0 d t v to seal uorsus Wrfaoea before the paint is applied. 9. Freedom, for practical puposea, fmm any tendency to aftmydlow.
wh-
Whhin the last few years resin emulsion painta have appeand on the markst. They have a wet abwion Rsiataocs (4) 8 q d to that of many commarcialtlat adl oil paints, and hsva thua
INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1944
been able to overcome the most serious criticism directed a t the water-thinned paints. They are usually made by emulsifying an alkyd resin in an aqueous emulsifying medium, generally a protein solution (8, 6 ) . To this emulsion are added suitable pigments and fillers. This product, like the casein paste paints, is marketed as a paste designed to be reduced with one half volume of waterifor application. Some disadvantages were found, however, in the early resin emulsion paints along with the advantage of high washability. The early emulsions were not too stable; it must be recognized, of course, that a paint brush is an excellent device for breakingemulsions, by furnishing a large amount of hydrophobic surface combined with gentle mechanical agitation. During application a small proportion of the emulsion broke and deposited the resinous binder on the bristles of the brush. As the resin accumulated, the brush became stiffer and stiffer, and finally was too stiff to use until it had been cleaned with an organic solvent. This problem of emulsion stability received a good deal of attention from the manufacturers of these products, and the emulsion paints available today are practically free from this difficulty. Alkyd resins, excellent as they are in color retention, are never completely free from afteryellowing when used in emulsion paints, even when they are prepared from nonyellowing oils such as soybean. They are, however, generally superior t o the flat wall oil paints in this respect and only slightly inferior to the casein paints. REQUIREMENTS FOR AN IDEAL BINDER
The binder should be soluble in water, in order to do away with the necessity of emulsifying it. It should dry to an insoluble film. It should be light in color and free from tendency to afteryellow. It must be a binder; that is, it must be capable of holding pigment and filler particles to form a serviceable a m . It should be available a t a price which falls within the general range of casein prices, in order that it be able to compete with these products on a price basis. This specification could just as well have been written to describe cold-setting urea-formaldehyde resins, which fill the requirements in every particular (1). They are soluble in water, dry to an insoluble fi.m, are light in color and free from afteryellowing, are capable of binding pigments and fillers, and are available a t a competitive cost. A paint was prepared from a commercial urea-formaldehyde resin solution and standard paint pigments and fillers (paint 1, Table I). The paint was accelerated with ammonium chloride and applied to a gypsum wallboard surface. After a drying period of 7 days a washability test was made, and it was found that the film was completely removed in one stroke. Tests were made in which the clear resin was applied to the wallboard surface. A sample accelerated with 3.5% ammonium sulfate cured completely in 4 days; one accelerated with 2.5% ammonium sulfate cured in 6 days. A sample accelerated with 2% ammonium chloride cured completely in 5 days.
TABLE I. PAINT FORMULAS
ii
Paint number Spray-dried urea-formaldehyde resin Aqueous urea-formaldehyde resinsoln. (70% solids) Mica Double-strength lithopone 1 Talo
1
2
..
50 2.1:1
Water Drying period, days Washability, strokes Pigment vol./binder vol.
3
4
5
. . . . . . . . . . 400 600 15 35 .20.. .. 20.. .. 20.. 350 . . . 175 . . ... . .... . ... 200 .. .. .... 330 100 .. ...... .. .. 46:4 .. *. .. 4e:4 200 125 9 7 1 350 1.08 0.56
2:s
19 7 200 1.0
4i:4 2.8 15 12 7 60 56 1.0 1.0
2:8
6
7
14
14
.. . ... ... . . . .. ** ..
46:4
2:s *
’7
60 1.0
.. .. .. .. .. ..
46:4 2.8
“‘7 80 1.0
145
It was apparent, therefore, that the pigments and fillers were the ingredients of the composition which inhibited the cure of the resin. The work done on various commercial paint pigments and fillers furnishes the data on which this paper is based. In the first place, the curing requirements for the resin in a, paint of this type are not especially severe. It is not necessary that the resin cure in a matter of minutes or even a few hours, as is so often the case in other industrial applications of these resins. As a matter of fact, it is preferable that the resin cure slowly (say in a day or two) in order that the painter be able to remove readily any drops of paint spilled around the room, or marks on the woodwork, etc. In practice, a few such spots are always found, and it is much more desirable for the painter to be able to remove them with clear water than for him to have to scour them off. Some accelerated method of test was required to eliminate the necessity of waiting for several days to find out whether a particular pigment or filler would inhibit the cure of the resin. Since the cure of urea-formaldehyde resins is catalyzed by acids and acidic reagents and therefore depends on the pH of the solution (I), it seemed likely that the pigments and extenders were inhibiting the cure of the resin simply by preventing the accelerator from reducing the pH t o curing range. TITRATION OF PIGMENTS
The pigment or filler was suspended in a solution of the resin and titrated electrometrically with a 10% solution of ammonium chloride. The pH meaaurements were made either with antimony or glass electrodes. From practical considerations it wag felt that 501, of ammonium chloride, based on the pigment, was about the maximum that could be considered. It was necessary, therefore, that this amount of ammonium chloride bring the pH of the solution below about 5. Although in ordinary commercial applications of urea-formaldehyde resins the pH of the accelerated resin solution often reaches 2 or 3, a pH of about 5 was considered more desirable for the slower cure desired in a product of this type. The standard titration sample was: aqueous urea-formaldehyde resin solution (70% solids), 20 grams; pigment or filler, 20 grams; water, 50 ml. The resin solution was diluted with a small amount of water, and the pigment and the balance of the water were added gradually, keeping the mix to a paste consistency until the pigment was incorporated and well dispersed. The rest of the water was then added. The suspension was titrated immediately with 10% ammonium chloride solution. Figure 1 shows the titration curves of several fillers. The control curve is simply the resin solution with no added fillers. The pH falls to about 4.5 with 5% of ammonium chloride. The ideal pigment or filler would be one which did not change this curve at all; so far none have been found. Talc and whiting (ground limestone) both show a considerable interfering effect. The curve for talc is not a straight line; it seems that the buffering action of the talc increases somewhat as the pH is reduced. A t 5% ammonium chloride neither whiting nor talc has reached pH 6.25. Diatomaceous earth givcs a curve which reaches 4.95 a t 5y0 ammonium 8 8 chloride. The behavior of the two clay samples is interesting. In the first sample the curve has a p ,. 64.4 proximately tbe same slope as the control curve, 400 2o although the curve is displaced to the right. Clay ..... 2 shows a constant pH (additions of ammonium 200 ‘ ‘40 chloride havc no effect). Since this pH is well below 5, it is obvious that a filler of this type would be 534 1&:8 useful primarily in powder paints and could evcn ..... replace some of the accelerator. 5011 235 i... 0:3 The curve for barytes (Figure 2) is helpful in 7 7 that it furnishes data for establishing whethcr the behavior of these materials on titration is a 1.12 300 0.94 40 function of their chemical composition or whether
...
.....
INDUSTRIAL AND ENGINEERING CHEMISTRY
146
P
fig.4. .5
fig. /.
/
I
f
3 4 7
/o
%" /
Vol. 36, No. 2
C
944.7
/O
0
7itmtmn of Ti'tan/um Diox/& p/gmnt.S
20
T t r o t i o n of fil/ers
/
fig 5.€ f f e d
/O
of WeoK Acid Whh M
20
7iz3, f?/g///rCnf
it is a surface phenomenon. Barytes was selected because of its insolubility and extreme chemical inertness. Barytes has a marked inhibiting effect on the action of the accelerator, which is evidence that, this effect is a surface phenomenon. Finely ground silica and diatomaceous earth 2 nearly reach pH 5 a t 5% ammonium chloride; this is also true of pyrophyllite. Mica seems to be unsatisfactory; the curve for mica, however (Figure 3), shows a reduced buffering action as the pH is reduced. The curve for pyrophyllite is similar in shape to that of mica. Silica gives a curve which follows a straight-line path until about pH 5.1; at this point there is an abrupt buffering effect. Figure 4 shows the results with several pure titanium dioxide pigments. Two of them have a slope of nearly zero, like the sample of clay shown in the first curve. Xone of the others are judied satisfactory for use with urea resins. Figure 5 represents a commercial, pure titanium dioxide pigment which is unsatisfactory. This pigment was washed with dilute hydrochloric acid and rinsed with distilled water until the filtrate was no longer acid to methyl red. The sample was dried in an oven, and the dried sample titrated. Not only the locus but also the slope of the curve has been radically changed. Figure 6 represents several single-strength lithopones (on barium sulfate). Sample 2 is almost satisfactory for use. The shape and slope of the curve for sample 3, although dissimilar, show that this pigment reaches about the same pH a t 57, am-
February, 1944
-
-. '.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
% "!C/ 2.0
147
monium chloride. It is likely, however, that the stability of a paste paint would be less when pigment 3 is used. In a powder type paint this would not be a factor. Figures 7 and 8 give the curves for several double-strength lithopones. Of these, 2, 3, and 5 are most nearly satisfactory although none of them quite reaches pH 5 a t 5% ammonium chloride. The curve for 5 indicates that here, too, there might be a stability problem in paste paints. A number of these titrations were selected et random for check determinations. The method waa found reproducible to 0.05 pH unit. These titration results were checked by preparing paints using these pigments and fillers. The detailed formulas are shown in Table I. The paints were applied to gypsum wallboard panels and tested on that surface. (It should be recognized that the particular surfaces used will also play a part in the cure of these paints; it is likely, for example, that considerable difficulties would be encountered over highly alkaline surfaces such as fresh plaster or concrete.) The test panels were allowed to dry for a few days a t room temperature and were tested for washability. The washability measurements were made by wetting the painted panel with water at 70-80' F. and allowing the panel to stand for 30 seconds. The film was then rubbed gently with wet No. 1 steel wool until the paint had been removed from the panel over one third to one half the test area. The number of strokes required for this removal was recorded as the washability of the film. For comparison, top-quality resin emulsion paints show 50 to 100strokes by this method after the films have dried for 7 days. Although this method of measuring washability is less precise than the wet abrasion test method described in Federal Specification TTP88 (4), it has the advantage of being more readily adaptable to quick testing where an approximate result is sufficient. It serves satisfactorily in determining whether the resin has cured. As Table I shows, both paste and powder paints were prepared; when suitable pigments were used, either type seemed to cure satisfactorily. Paint 1 shows the result when unsuitable pigments and fillers are used. This paint gave,a Washability of one stroke. It was noted in the discuasion of the titration results that several of the pigments and fillers of low initial pH would create a stability problem in paste paints. This can be overcome, at least in part, by the inclusion of some volatile alkali. However, the problem of stability is outside of the scope of this paper. The results show that proper selection of pigments and fillers is essential to secure a film of high washability. However, when suitable pigments are used, films of extremely high washability are formed. The validity of the test method is thus confirmed, although it is believed that it is possible to relax somewhat the 5 pH requirement. For satisfactory cure in service a pH of about 5.2 seems sufficient. ACKNOWLEDGMENT
The author wishes to acknowledge the cooperation of R. J. Magill, who charted the data. LITERATURE CITED
(1) Ellis,C., "Chemistry of Synthetic Resins", Vol. I, Chap. 26-30 It 935). \ - - - - I .
(2) Ellis, C., U. 9. Patent 2,086,903(1937). (3) Elm, A. C., and Werthan, S., Oficial Digest Federation Paint & Varnish Produdion Clubs, 223,35 (1943).
(4) Federal Standard Stock Catalog, Spec. TTP88 (1940). (6) Frick, F., U. S. Patents 2,178,474-5 (1939). (0) Sutermeister, E.,and Browne, F. L., "Casein and Its Industrial Applications", p. 315 (1939) (7) Ibid., p. 325. (8) Ibid., p. 327. P R E I S E I ~before T ~ D the Division of Paint, Vamiah, and Plastics Chemistry CHEMICAL Socrarr~,Pittsburgh. Pa. at the 106th Meeting of the AMEIRICAN
