I . E.
F.
CARLSTON and
F. G.
LUM
California Research Corp., Richmond, Calif.
Isophthalic Acid Application in Alkyd Oils Heat-bodied isophthalic alkyd oils are excellent vehicles for improved house paints and other architectural finishes
IN
WORK on the application of isophthalic acid in oil-modified alkyd resins (7), it was found that isophthalic alkyds have excellent thermal stability and good drying properties and that isophthalic acid is ideal for the production of upgraded drying oils. The term "alkyd oil" describes alkyd compositions that have bodied oil viscosities as differentiated from the considerably more viscous alkyd resins. The dividing line between alkyd oils and alkyd resins is arbitrarily taken to be a viscosity of Z - 6 on the Gardner-Holdt scale, although the change from oil properties to resin properties is a gradual one. Propepties of alkyd oils made
with isophthalic acid are compared with the properties of alkyd oils made with phthalic anhydride and maleic anhydride.
Experimental The alkyd oils were made by ordinary alkyd resin cooking procedures. The examples described show a typical alkyd o i l made from a natural oil involving alcoholysis and a n alkyd oil made from fatty acids derived from natural oil. The soybean oit and lead monoxide are charged to the kettle and heated to 200' C. in about 1 hour, with the lead monoxide added in the form of a paste
DRYINGoils and their acids are among the most important raw materials used in modern surface coatings. The oils of relatively low molecular weight polymerize in the presence of oxygen to form crosslinked molecules of much larger size. Most natural oils are slow drying and produce soft films; therefore, the improvement of natural oils to produce faster drying and harder films has been an important part of the technology of surface coatings. Many methods of upgrading natural oils have been developed: thermal polymerization of drying oils to form bodied oils; reaction of drying oils with hard resins to farm varnishes; esterification of fatty acids derived from natural oils with more highly functional alcohols, such as pentaerythritot, to give more reactive oils; and reaction of oils and fatty acids with polyhydric alcohols and polybasic acids to form alkyd resins. This report describes the alkyd method of upgrading drying oils.
Example A Ingredients Soybean oil, alkali refined Pentaerythritol, technical Lead monoxide (litharge) After alcoholysis, add isophthalic acid
Grams 900 41
0.5 82
Example B Ingredients Soybean fatty acids Pentaergthritol, technical Isophthalic acid
Grams 840 148
a2
in ail to facilitate dispersion. The pentaerythritol is added when the temperature is 200' C., and the mixture is further heated to 250' C. and held a t that temperature for 0.5 hour. The mixture is then cooled to below 200' C., and the isophthalic acid is added. Inert gas is bubbled through the oil to prevent oxidation and to help remove water, the product of reaction. Esterification of the isophthalic acid with the alcoholysis mixture is accomplished by slowly heating to 260' C. in about 2 hours and then holding at 260' C. until the acid number is 10 or less. All of the ingredients are charged to the kettle. The temperature is quickly raised to 180' C., then slowly to 260' C. over a period of 2 hours and held there
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Table 1. Composition of Alkyd Oil Rcsin Oil 5 10
95 90
10
90
15
85
20 20
80 80 75 75 90
25 25
10 20
80
IO
90 80
Viscosity Properties of Soybean Alkyd Oils
Composition of Resin Dibasic acid Polyhydric alcohol Isophthalic Pentaerythritola Isophthalic PentaerythritoP Isophthalic Isophthalic Isophthalic Isophthalic Isophthalic Isophthalic Phthalic anhydride
Pentaerythrit~l~ Pentaerythritola PentaerythritoP PentaerythritoP Glycerol Pentaerythritola Pentaer ythritola
Phthalic anhydride Maleic anhydride 20 Maleic anhydride a Pentek, Heyden Chemical Co.
until the acid number is 10 or less, Inert gas is used during the cook as in Example A. The phthalic anhydride and maleic anhydride alkyd oils used for comparative purposes were made by the procedure of Example A. Alkyd oils of different viscosities were obtained by varying the ratio of oil to phthalic, isophthalic, or maleic ester. Many of the alkyd oils were polymerized further by heating them at oil-bodying temperatures of 285' to 305' C. until the drsired viscosities were obtained. Heat-bodied linseed oil and mixtures of heat-bodied and raw linseed oil were included in this test because of their widespread use as house paint vehicles. Preparation of Paints. T h e alkyd oils were made into paints according to the following formula (2) :
Composition of Oil Glycerol Penta
Pentaerythritola Glycerol Glycerol
Oil
260
188 81 215
9.7 1.1
1.1
35%
The pigments and oil were ground in porcelain-lined ball mills containing flint pebbles. After grinding, the driers were added, and the paints were thinned to a viscosity suitable for brushing. T h e paints were strained before use. Preparation of Test Panels. Exposure panels were prepared from fir, redwood, and 20-gage cold rolled steel. T h e steel panels were primed with a thin coat of polyvinyl butyral wash-primer, followed by one coat of zinc chromate primer ( 3 ) . Two coats of paint were applied to each panel, with one week
1052
+ 2 hours + 4 hours 2-4 + 2.5 hours Z-10 + 1.5 hours
J
W
2-2
S T
X X X
Z 2-3
X X
z- 1
X
2-4
X
G
T
V
X
+ 2 hours + 4 hours
2-2
z-1
X
+ 1.5 hours
Gelled before reaching 260' C.
X
of outdoor drying between coats. T h e total film thickness of dry paint was controlled a t 0.005 inch by a n even application of a known weight of paint, determined by weighing can and brush before and after application. T h e wood and steel panels were exposed a t test stations in Miami, Fla., Woodland, Calif., and Richmond, Calif. All the wood exposure panels included a portion painted with a control alkyd resin paint to compare alkyd oils and alkyd resins with respect to cracking of paint films on wood. A maleic modified phthalic anhydride, soybean alkyd resin of commercial manufacture (4)
was used; and the pigmentation was the same as that used for the alkyd oil paints. Results
T h e data in Table I show that isophthalic alkyd oils are more viscous than phthalic anhydride alkyd oils of the same oil content. T h e maleic anhydride alkyd oils, as expected, are considerably higher in viscosity because of the additional reactivity of the maleic double bond and the lower molecular weight of maleic acid. Thermal polymerization of the isophthalic alkyd oils a t 285' to
ExDosure Data on Alkvd Oils
(Steel panels)
Grams
Titanium dioxide, rutile Zinc oxide, fine particles Magnesium silicate, fibrous Naphthenate drier solution, 24% lead Naphthenate drier solution, 6% cobalt Naphthenate drier solution, 6% manganese Paint thinner, as required Pigment volume of paint solids,
I
X X
Y
Table II. Ingredients
Viscosity (Gardner-Holdt) After 4 hours After additional at 260' C. heating at 305' C.
Ingredients 68-month exposure test Linseed oil (75% raw, 25% 2-4) Linseed oil (50% raw, 50% 2-4) Linseed oil (100%.2-4) Soybean alkyd oil, 10% pentaerythritol phthalate Soybean alkyd oil, 10% pentaerythritol isophthalate Same alkyd oil, heat-bodied Same alkyd oil, heat-bodied Pentaerythritol soyate alkyd oil, 10% pentaerythritol isophthalate, heat-bodied Same alkyd oil, heat-bodied 56-month exposure test Commercial maleic alkyd oil, 95% soybean Soybean alkyd oil, 10% glyceryl maleate Soybean alkyd oil, 15% pentaerythritol isophthalate, heat-bodied Soybean alkyd oil, 20% pentaerythritol isophthalate, heat-bodied Commercial phthalic alkyd oil, 78% soybean
Ratings" Viscosity Mildew Checking (Gardner- ___- ~ _ _ _ Rb M" W d Rb Mc ITd Holdt) G V
6
6
8
0 0 0
1 0 0
0
8
1
0 10 10
10 10 10
10
10
0
6 0 0
2-4
8
8 4
F
8
6
H
6
Y 2-4
6 4
3 3
0 0
0 0
0 0
2-2 2-6
0 0
3 3
0 0
0 0
0
0
0
0
G
6 6
8
0
8
8
0
0
10 10
10
2-4
Z
0
4
0
0
0
0
Z-6 2-1
0 0
2 4
0
0
0 0
0
6
0
0
0
8
1
1
10
0
a Ratings. 0 = none; 2 = slight; 4 = moderate; 6 = considerable; 8 = over most of panel; 10 = over entire panel. b Richmond, Calif. 0 Miami, Fla. d Woodland, Calif.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ISOPHTHALIC A L K Y D OILS 305' C. is extremely effective in producing higher viscosities. Phthalic anhydride alkyd oils heated under the same conditions show much less viscosity increase. T h e maleic anhydride alkyd oils were not heat-bodied because the high reactivity of the maleic double bond was sufficient to produce the desired viscosities a t lower temperatures. Drying characteristics of isophthalic alkyd oils improve as the isophthalic content increases, and alkyd oils with the highest isophthalic content have drying properties typical of alkyd resins. Low viscosity soybean isophthalic alkyd oils have drying properties similar to linseed oil but with more aftertack. This aftertack is decreased by thermal polymerization of the isophthalic alkyd oil. Phthalic anhydride alkyd oils have poor drying properties; and, in contrast to isophthalic alkyd oils, heat-bodying produces darker colored oils with even poorer drying properties. Apparently, some inhibitor is formed by the decomposition of the phthalic anhydride oil during heat bodying. Comparative data on the subject have been given
L
Table 111.
Idealized Isophthalic Alkyd Oils 0bser ved
No. of
Idealized Isophthalic Alkyd Oil Molecules'
(GardnerHoldt) Oil Viscosity Content, at 5-10 % Acid No.
Fatty Acids per Molecule
Molecular Weight
4
1370
86
K
5
1690
88
P
6
2010
90
T
6
2190
82
W
8
2810
86
Y
10
3610
83
z-I
-
-
(0.
Table 11 describes the condition of several alkyd oil and linseed oil paints on steel panels exposed for 68 months to outdoor weathering. I t includes a group of alkyd oil paints that were placed on exposure one year later than the others. Isophthalic alkyd oils have good resistance to checking, except for the low viscosity, unbodied alkyd oil (Table 11). T h e best mildew resistance was obtained from high viscosity isophthalic alkyd oils produced either by thermal polymerization or by using increased amounts ofisophthalic ester. T h e paints made from mixtures of raw and bodied linseed oil, loo'% bodied linseed oil, and alkyd oils of phthalic and maleic anhydrides were in poor condition because of extensive film checking and mildew staining. T h e Miami station, like the Richmond station, produces considerable mildew attack of paint films. Woodland is in a n interior valley of California where the climate is relatively dry. T h e results on the fir and redwood panels after 68 months of exposure were similar to those shown in Table I1 for the steel panels. T h e control alkyd paint cracked on some of the fir panels, but not on the redwood panels. T h e oil and alkyd oil paints did not crack on any of the wood panels. These exposure tests show that isophthalic alkyd oils are superior to linseed oil, phthalic anhydride alkyd oils, and maleic anhydride alkyd oils with respect to film checking and mildew resistance, .and that the alkyd oils have
a
F = fatty acid, soybean; Gi = glyoerol; P = pentaerythritol.
superior cracking resistance on wood, compared to a conventional alkyd resin.
Discussion T h e upgrading of natural drying oils by increasing the molecular weight and the number of fatty acid groups per molecule, as in alkyd formulation, improves drying properties and film durability. This permits the use of oils of lower unsaturation, such as soybean: instead of linseed oil. Soybean oil alkyd resins have excellent drying properties, even though the soybean oil itself is poor. T h e use of soybean oil in an alkyd has also become popular for other reasons. T h e lower unsaturation of the soybean fatty acids gives rouqher, more flexible films which show less yellowing than those from linseed fatty acids. T h e principles discussed above may be applied also to alkyd oils. Table 111 shows several idealized examples of isophthalic alkyd oil molecules to illustrate the broad range of composition possible. T h e viscosity data were obrained from alkyd oils made with a slight excess of polyhydric alcohol, having the average compositions shown.
Isolation of the pure compounds was not attempted. I t is apparent from these structures that highly cross-linked films can result when alkyd oils are air dried. Soybean oil and soybean fatty acids were used in this work; however, other oils and fatty acids can be substituted. For example, linseed and safflower oils provide faster thermal polymerization rates and greater drying capacity, while distilled tall oil fatty acids are attractive because of their low cost. Alkyd oils with widely different properties can be obtained from combinations of the many different oils and fatty acids that are available.
Literature Cited (1) Lum, F. G., Carbon, E. F., IND.END. CHEM.44, 1595 (1952) (2) U. S. Department of Navy, Navy Spec. 52P28 (March 15, 1945). (3) Zbid., 52P18 (June 1, 1945). (4) Zbid., 52R13a (Aug. 15, 1945). RECEIVED for review June 11, 1956 ACCEPTED December 13, 1956 Division of Paint, Plastics, and Printing Ink Chemistry, 128th Meeting ACS, Minneapolis, Minn., September 1955. VOL. 49, NO. 6
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