POLYURETHANE COATINGS urethane oil paint films tended to chalk earlier and somewhat more than the alkyds. After 1050 hours’ exposure no differences were noted among the four urethane oil paints tested. and all were rated equal to the alkyds in film integrity. Using the same method, a second group of three urethane oils was prepared based on refined linseed oil and pentaerythritol with 125, 115, and 1OOyQof the amount of TDI equivalent to the p01)ol. In making the two oils with the higher T D I content, 0.01 diethylethanolamine catalyst was used. Four paints were made from these three urethane oils and a long oil soybran oil alkyd. All had the same pigmentation as the paints used for the Weatherometer tests. They Tvere subjected to exterior exposure for 2 years in Minnesota. As in the previous accrlerated tests, the urethane oil paints lost gloss and began chalking at an earlier time than the alkyd. At the end of 2 years, however, the paint prepared with the highest level of T D I showed less chalking than the alkyd, although tending to check to a slightly greater degree. The urethane oil with the lowest level of TDI chalked more than the alkyd but checked less. A third series of urethane oils was prepared using refined linseed oil with
trol and sorbitol-modified coating blistered in 2 days.
results as expected-probably because of the hygroscopic nature of the sorbitol and failure of all six OH groups to react. Modification with the various polyols failed to change significantly the abrasive resistance (10- to 12-mg. loss per 1000 cycles, load 1000 grams, CS-17 wheels) of the original coating. Solvent resistance was substantially improved. T h e modified coatings - with one exception showed no failure in toluene after 2 months’ immersion. The con-
literature Cited (1) ~ ~ iM. l E.,~ s ~p journal ,~ 14, N ~ 2,. 41 (1958). (2) Metz, H. M., others, Paint Oil Chem. Rev. 121, G (April 17, 1958).
G- c* TOONE and G* s* WOOSTER National Aniline Division, Allied Chemical Corp., Buffalo, N. Y
Reactions of Isocyanates with Drying Oils tion was established and then reacting the product with tolylene diisocyanate (TDI) at 200’ F. in the presence of mineral spirits to yield a 60% solids solution. I n making products based on refined oil, the T D I used was equivalent to 10070 of the hydroxyls of the pentaerythritol. In the prebodied oil products 90% of the equivalent amount was used. When compared with linseed and soybean oil alkyds of medium oil length in clear films, the urethane oils prepared with linseed and soybean refined oils dried more rapidly than the alkyds
reaction of isocyanates with a mixture of partial esters of fatty acids was used to develop vehicles for protective coatings in Germany just prior to World War 11. The partial esters were obtained by either alcoholysis of a drying oil and polyol or by partial esterification of drying oil acids. Thwe “urethane oils” were used in wartime Germany and were reported to have outstanding properties in practical applications. Since then, however, they have received only scant attention from coatings technologists. The recent inT H E
Film Properties of Linseed Urethane Oils Pentaerythritol
Mole Ratio Polyol/Oil Equiv. TDI, yo TDI, wt. yo Dry hr. Sward hardness 1 day 7 days 14 days Impact, inch-lb. 3y0 NaOH, hr. to failure
1.2 79 19.9 2
Glycerol 1.55
8 20 24 > 28 1 l/4
terest in isocyanates in coatings has centered mainly in their use with castor oil or polyesters in two-component systems or in compositions containing free isocyanate (NCO) groups. Although both systems yield films of excellent quality, their water-sensitive nature accounts for wide variations in rate of dry (depending on the humidity of the surrounding atmosphere) and difficulties in pigmenting. ‘The urethane oils, however, contain no free NCO and are not subject to these limitations. They dry through an oxidation mechanism at the unsaturated portion of the molecule and may be pigmented and handled like alkyd resins or other vehicles familiar to the coatings industry. Using as starting materials both linseed and soybean oils which had been either alkali refined or prebodied (G-H viscosity), four urethane oils were prepared by reacting 1 mole of oil with 0.8 mole of pentaerythritol (PE) until interesterifica-
79 23.8 1 ‘/4
17 29 40 22 6
2.1 72 26.9 1
20 30 42 10 6l/2
0.9
Methyl Glucoside
81 20.1
1.0 80 21.7
1.2 74 23.0
1 ‘/2
1
1
10 25 31 12 3 ‘/i
16 30 39 6
20 33 41 4 8
S1/z
(11/2 hours for linseed urethane oil us. 23/4 hours for linseed alkyd and 23/4 hours for soybean urethane oil us. 3 3 / 4 hours for soybean oil alkyd). These urethane oils also exhibited hardness and flexibility similar to the alkyds. The urethane products based on prebodied oils dried at about the same rate as the alkyds but attained only one half the hardness of the refined oil films. Paints were prepared from the urethane oils and alkyds using rutile T i 0 2 and a talc extender pigment, and were compared for Taber abrasion, yellowing, and Weatherometer exposure. Paints based on refined linseed and soybean urethane oils were superior to the alkyds in abrasion resistance; prebodied oil products were equal to the alkyds. All the paints based on urethane oils showed higher initial yellowness values than the alkyds and yellowed somewhat more when held in darkness for 2 months. I n Weatherometer exposure, the
0 62 90 16.3 2
0.75 84 17.7
0.80 80 19.2
15/4
11‘2
10 24 31 > 28
16 30 36 > 28 3 1/2
11/2
21 33 38 20 4
glycerol, pentaerythritol, and methyl glucoside as the polyols. The proportions of poly01 and T D I were varied to yield products with viscosities in the range of D-H on the Gardner scale at 4570 solids in mineral spirits. These were compared for dry time, Sward hardness, reverse impact, and resistance to a 370 sodium hydroxide solution. Reverse impact values were determined after 21 days of air-dry, and resistance to sodium hydroxide solution was checked after a 7-day air-dry. The table shows the range of properties that may be obtained with urethane oils, depending on choice of poly01 and relative proportions of drying oil, polyol, and diisocyanate used.
GUY WILSON and J. M. STANTON Cargill, Inc., 200 Grain Exchange, Minneapolis 15, Minn. VOL. 51, NO. 11
0
NOVEMBER 1959
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