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INDUSTRIAL AND ENGINEERING CHEMISTRY
would be used per pound of fertilizer. The increased throughput due to greater ease of operation reduced this t o 4.04.5 cubic feet of air per pound of material. Experience has shown in the full-scale cooler that the relative humidity of the air in the dryer is usually 65 per cent until the air temperature reaches 100-110" F., and then gradually decreases to 40 or 50 per cent a t 130" F. Table I1 contains data typical of the cooler operation for summer and winter conditions. In summer, with the cooler operated beyond estimated capacity, 72 per cent of the heat was removed by vaporizing water. If it had been feasible
Vol. 33, No. 4
to increase the air volume while maintaining the same material throughput, then a lower material temperature would have been reached, and a larger percentage of the heat would have been transferred to the air.
Li terature Cited (1) Hardesty and Ross, IND. ENG.CHEM.,29, 1283 (1937). (2) Saokett, U. 9. Patents 2,028,413 (1936); 2,174,896 2,174,897 (1937). (3) Smith, I b i d . , 2,188,798 (1940).
(1936);
PRESENTED before the Division of Fertilizer Chemistry a t the 100th Meeting of the American Chemical Society, Detroit, Mioh.
Urea-Formaldehyde Film-Forming Compositions' Air-Drying Films by Acid Catalysis T. S. HODGINS AND A. G. HOVEY Reichhold Chemicals, Inc., Detroit, Mich.
HE hardening effect of facturers of refrigerators, autoUrea-formaldehyde film-forming compoacidic catalysts on hydromobiles, bicycles, toys, and other sitions, hitherto used in high-baking important industrial articles, phylic urea-formaldehyde enamel vehicles, are now made to air-dry particularly when used with the condensation products was early by special acidic accelerators which are nondrying and semidrying alkyd recognized (W,21). It has often soluble in organic solvents, including resins. The new resins make been stated in the literature that possible not only greater harda pH below 7.0 tends to promote hydrocarbons. These accelerators consist ness without sacrifice in color, instability of an aqueous ureaprincipally of inorganic acid esters of alcobut also many new types of enformaldehyde solution and to hols; the latter contain at least 4 carbon amel such as the polychromatic cause gelation (22,24). Calcium atoms in length i n the alcoholic radical, finish described by Hicks ( 3 ) . chloride as a catalyst for heat which imparts solubility in organic solTo obtain conversion a t lower hardening aqueous urea-formaltemperatures than the presdehyde plywood adhesives was vents, and yet since the acid components ent industrial baking schedules, described by Ludwig (16) and are only partially esterified, a low pH of there appear t o be two prinby others. The authors (6, 7) the vehicle system may be maintained cipal lines of attack-the use of and others (19, 87, 28) have which renders gelation possible in a relaacidic catalysts and modification elaborated upon the effect of low tively short time. By the use of these by melamine (2,4,6-triaminop H by the introduction of acidic (18) l,3,5-triazine). Pollak materials, but until recently this acidic accelerators, not only can baking and Ripper (23) early described work has been mostly confined schedules be shortened and the baking the uses of small quantities of to the aqueous type of ureatemperatures lowered, but also air-drying melamine in urea-formaldehyde formaldehyde condensationproditself can be effected. condensation products. Reucts. Ludwig (16) and others cent discoveries (IO, 26) have (go), in preparing urea-formalshown that melamine modificadehyde-butanol resins, used a tion of urea-formaldehyde-butanol resins not only gives better volatile organic acid (formic) 'as the catalyst during the heat resistance, but also promotes faster setting and lower processing, but made certain that it was removed by volabaking schedules. The use of acidic accelerators with ureatilization before the final product was packaged in an effort formaldehydc-butanol rcsins may be considered as more to improve stability of the resin solution; thus, any catalytic desirable than their use with melamine-modified urea-formaction was stopped. aldehyde resins in lowering the baking temperature and in I n the past three years the butanol-etherified urea-formaleffecting air-drying, because of the stability characteristics. dehyde resins have achieved vast industrial acceptance Where cost and package stability are not major factors, it is (1, 4, 6, 11, 12, 17, 35). These resins have been widely probable that some combination of both lines of attack may adopted as part of the vehicle of baking enamels by manuproduce the ultimate results. 1 For previous papers in this series, see literature citations 4, 6, and 11
T
April, 1941
513
INDUSTRIAL AND ENGINEERING CHEMISTRY
phoric anhydride, and the organic portion consists of organic radicals derived from alcohols. The general equation may be written as follows:
#=O
dI +
P=O
HOR HOR
OH
OR
OH
Thus, these accelerators, which may be either mono- or diphosphoric esters of alcohols, are generic to the basic reaction of Pz06 ROH, the nature of the alcohol determining the nature of the catalyst, the solubility of the catalyst, and the operativengss of the resulting catalyst for the type of resin with which it is to be used (i. e., whether the resin is a hydrophobic or hydrophylic product). The use of acidic catalysts of this type is entirely different from the use of neutral esters of phosphoric acid-for example, tributyl phosphate-because only the monoLABORATORY PEBBLE MILLPREPARATION OF BASESFOR ENAMELS or the dialkyl phosphates have capacity for causing sufficient acidity of the system to produce the desired extent of hardening. The use of completely neutralized alkyl phosphates thus This paper deals with the development of hydrocarbonhas no catalytic hardening action but acts in the reverse soluble acidic catalysts which have made possible not only manner-i. e., as a plasticizer. Catalysts of this type are low baking enamels, but also air-drying urea-formaldehydeusually viscous, light-colored, acidic liquids readily miscible alkyd resin enamels. A prediction of the future usefulness with urea-formaldehyde-butanol and alkyd resins. They of the air-drying urea-alkyd enamels was given (II), and during the past year considerable development work has been produce marked effects upon .films of such products. These carried out with the result that at least one air-drying ureacatalysts are also of great value in hardening urea-phenolformaldehyde etherified resin (8) has made its appearance on formaldehyde resins (9, 13) and may be used with melamineformaldehyde-butanol resins where package stability is not the market. The use of air-drying enamels was described a major factor. by Knauss (14). Considerable industrial interest has been shown in this new type of urea-formaldehyde resin used as an air-drying or forced-drying (55-60' C.) enamel vehicle in Properties of Resin Solutions upon Addition of combination with alkyd resins. Such enamels, of course, Accelerators may be used on new fields of application where baking temI n previous papers (11,11),the general formulation of white peratures are not permissible, such as wood furniture, and and colored urea-formaldehyde-alkyd resin enamels was disyet where the hardening effect of urea-formaldehyde resins on cussed in detail. I n general, the principles involving enamel alkyd enamels is still desirable. formulation using accelerated urea-formaldehyde resin solutions remain substantially the same; but the effect of the Theory and Development of Oil-Soluble Acidic accelerators in relatively small quantities cuts down the Accelerators baking time from schedules such as 1 hour a t 260-300" F. (127-149' C.) to forced air-drying a t temperatures around I n general, the acidic accelerators for conversion of urea130-140' F. (54-60' C.); and when sufficient accelerators are formaldehyde-monohydric alcohol films should be either an used, the product may be made to air-dry a t room temperaacid or an acid-forming substance which has sufficient proporture. Table I shows the hardening effect, as measured by tions of hydrocarbon structure so that the catalyst is comSward hardness, of various amounts of accelerators upon pletely soluble in aliphatic solvents of low solvent power urea-formaldehyde-monohydric alcohol resin solutions when without precipitation-e. g., mineral spirits. They should cast on glass a t film thicknesses of 0.004 inch (0.1016 mm.) not contain water on account of the possibility of causing and allowed to air-dry. Table I1 summarizes the physical pitting in enamels-e. g., hydrochloric acid (I7)-and should and chemical data on the resins employed in the experiments. not be reactive with pigments with consequent livering or As in the case of the baking enamels, the air-drying urealoss of drying (9, IS). formaldehyde resin solutions are almost always used in One of the most suitable substances for forming acceleracombination with alkyd resin solutions because of the imtors is phosphoric anhydride. Acid esters may be formed with provement in adhesion, flexibility, etc. As previously pointed alcohols or other hydroxyl-containing substances which have out ( I I ) , alkyd resins are ideal resin plasticizers for use with sufficient hydrocarbon structure to keep the acid esters soluble urea-formaldehyde resins in the baking enamels and are in the commonly used enamel ingredients. These catalysts likewise extremely useful with the air-drying urea-formalare partly organic and partly inorganic. The inorganic dehyde-monohydric alcohol resins. Table I11 summarizes portion consists of radicals obtained from the use of phos-
+
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INDUSTRIAL AND ENGINEERING CHEMISTRY
EFFECT OF ACCELERATOR TABLE I. HARDENISG Composition BP-196 B-1307
BP-170
... ... ... ...
100 100 100 100 10 1 100 100 100
BP-198 0 1 2 3 4 5 4 10 2 5 4 10
... ...
... ...
...
...
...
...
...
100 100
...
... ...
100
100
... ...
,..
100 100
100 100
Sward Hardness of Films Cast a t 0.004 In. 4 hr. 24 hr. Soft 20 44 48 48 75 50 75 50 SO 52 82 30 44 36 65 30 42 36 44 36 44 52 66
TABLE 11. Resin
yo Non-
NO.
volatile
% Solvents
B-3440 BP-138
60 60
BP-196
60
BP-170
60
BP-254 B-1307 B-1323 BP-198 BP-231
50 50 50 80 80
40 butanol 20 butanol-20 toluene 2 0 butanol-20 ethanol 20 butanol-20 ethanol 50 butanol 50 xylene 50 toluene 20 toluene 20 mineral spiritsd
a E
% Phthalic AnhyColor drideb (Hellige)
P?h
18.0
0
0
Colorless
18.0
0
0
18.0
0
0
17.5
0 0
0
Colorless Colorless 2L-2 1L-2
0
0 40.0
0 43.2 48.5 0
0
10.7
0
0 0
0
tent than when the resin is uncatalyxed. Since resin BP-254 has a much greater tolerance for mineral spirits than BP-138 (Table 11), it may be assumed that there is more combined butanol per mole of urea. Furthermore, the higher etherified resin BP-254 loses considerably more weight than the lower etherified BP-138 resin; this indicates that weight loss is largely due to the butanol but not necessarily t o the exclusion of the loss of formaldehyde and water. There are cases where it will be desirable t o add the accelerator after the finished enamel has been made-that is, after addition of pigment, plasticizer, resin, and other ingredients-and included just before application. Of course few parallels exist in the case of the present paint application. However, one of these is the addition of aluminum powder to
VEHICLE AND ACCELERATOR PROPERTIES
% Nitrogena
...
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Co. Mineral Acid Viscosityc Sp. Gr. Spiritsd per No. a t 25' C. a t 20' C. 10-G. Sample
Type of Kesiu
5
T-U
1,030
20-25
Urea-formaldehyde
Colorless
5
T-U
1.025
20-25
Urea-formaldehyde
Colorless
5
L-1\Z
1,035
15-20
Urea-formaldehyde
H
1. O O 0.975
20-25 300-400
