Melamine-Formaldehvde Film-Forming Compositions J
T. S. HODGINS, A. G. HOVEY, S. HEWETT, W. R. BARRETT, AND C. J. MEESKE Reichhold Chemicals, Inc., Detroit, Mich
Structural formulas are suggested for the deamination products of melamine. Resinification of methylolmelamines is postulated as proceeding through either the methylene or the ether linkage. The wide range of properties of hydrocarbonsoluble melamine-aldehyde-alcohol resins can be explained by etherification as the mechanism whereby the final resins are formed from the methylolmelamines. Heat stability of melamine resins, as compared to urea resins, may be due to the absence of carbonyl groups. Acidity of the resulting etherified melamine resin is a major factor in low-temperature conversion and a function of its stability life. Etherified melamine resins have a wide range of solubility, depending upon their degree of etherification. Triaxial diagrams for the three-component system melamine-urea-alkyd resin show adherence, hardness, and flexibility areas for drying, semidrying, and nondrying alkyds. Composition-hardness curves of melamine-alkyd and urea-alkyd enamels indicate that, for a given percentage of amine resin, the melamine-alkyd approaches
maximum hardness more rapidly. Time-hardness isotherms show that, for a given composition, melamine-alkyd blends are harder than the corresponding urea-alkyd blends at any given time and temperature. Melamine-alkyd compositions are superior in color retention to the corresponding urea-alkyd enamels based on a time-hardness study a t 350' F. Chemical resistance of heat-converted melamine resins is equal to or better than that of the corresponding urea resins. The baking temperature of enamels containing melamine resin may be lowered as much as 100" F. compared to urea-alkyd or alkyd enamels and still retain equal or greater hardness. A t the same temperature melamine-alkyd enamels may be baked in less time than the corresponding urea-alkyd enamels. In general, the properties of clear melaminealkyd compositions carry over to pigmented enamels. Enamels containing as high as 75 per cent melamine and/or urea resin and 25 per cent alkyd can be used below 200' F. for special applications where flexibility is not a major factor.
NE of the most recent advances in the field of synthetic resins is the production of melamine-aldehyde condensation products (6A)resulting in a new and valuable addition to the long list of synthetics which are rapidly becoming indispensable to twentieth century life and industry.
compounds can be formed from the halogen derivatives of cyanuric acid (f2,61),from melam or by the action of titanium chloride on hexamethylene tetramine (68). Perhaps the most widely used method utilizes dicyandiamide or cyanamide as raw materials. This mechanism was described by Drechsel (20, Sf), Cldez and Cannizzaro (f6),Lemoult (67), Davis (17), Franklin (93),Chastellain (f5),and Stoil6 and Krauch (78). This tendency to form six-membered heterocyclic rings was treated to some extent by Smith, Sabetta, and Steinbach (74), and may be postulated somewhat as in Figure 1. Numerous other mechanisms have been suggested. The reaction as given in Figure 1 is usually carried out on a commercial scale in the presence of anhydrous ammonia under a pressure of 10 to 100 atmospheres at temperatures varying from 100' to 400' C. or 212' to 752' F. (22, 30, SI, 36, 38, 41, 62, 81,85). In actual practice the reaction is carried out either by batch or continuous process. Although
0
(fa),
CHEMISTRY OF MELAMINE RESINS
Melamine, the chief raw material employed in the manufacture of these resins, was discovered by Liebig in 1834 (68). It is another outstanding example of a chemical which has recently become available on a commercial scale both here (68.4) and abroad. Though melamine is the term most commonly used, it is also known in literature as 2,4,6-triamino-1,3,5triazine, as cyanuric acid amide, and as cyanuric triamide. In the years following the first preparation of melamine and ammeline from ammonium chloride and potassium thiocyanate (68), these novel compounds were formed by numerous investigators. Lemoult (67), Claus (f4,f6), and Klason (66) prepared melamine in much the same way from thiocyanates. Volhard (80) and Rathke (67) aminated melam by heating with ammonia and thus obtained melamine. Smolka and Friedreich (76, 76)and Nencki (69)prepared melamine from guanidine; Hofmann (48), Klason (66),and Lemoult (67) produced the material or its derivatives by treatment of cyanuric acid or its derivatives. However, other general methods of preparing melamine are of greater commercial importance. Melamine and similar
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FIGWRBI 1. FORMATION OF SIX-MEMBERBID HETEROCYCLIC RING 769
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 33, No. 6
general consideration, however, those suggested (Figure 3) c provide sufficient detail. /\ As a complex amine, melNH, H2N N N "2 amine exhibits the reactions cI \ I c c:I1 CI common to both primary and /\ / \? secondary amines. It reacts N TU' N H / K with numerous alkyl and aroI " ' 11 matic halogen derivatives to 'C'C /\/ \)/ \/ form many different comNH, N N pounds, substitutions taking Melani Meleni Melor1 place on both the ring and FIQURE 2. DEAMINATION PRODUCTS FROM DICYANDIAMIDE amino nitrogens. Compounds such as di-, tri-, and hexamethylmelamines (7) and mono-, di-, tri-, and hexaphenylmelamines (7) have been prepared. Compounds melamine is usually made under pressure, it may be prehave been prepared in which the amino groups have been repared a t atmospheric pressure (64). This has been found possible by employing a mono- or dialcohol amine as a complaced by alkyl, aromatic-alkyl, and aromatic compounds. bined solvent, heat buffer, and condensation catalyst. Such a compound is 2,4,6-tris-(4-aminophenyl)-1,3,5-triazine I n the processes involving the production of melamine from (Figure 4). I n a similar way mono- and diamino triazines dicyandiamide, varying quantities of other similar compounds react to form alkyl and aromatic derivatives. are formed, such as the deamination products melam, melem, Under favorable conditions melamine reacts to form more and melon (Figure 2). These products are similar to melcomplex compounds of nitrogen, perhaps most notable of amine in many ways and, like melamine, form both the esowhich is tricyanmelamine (11, 43, 60). This compound, simiand exo-substitution products. lar to melamine, readily forms complex salts with many Melamine crystallizes from hot water as white monoclinic metals such as copper, lead, silver, and potassium (11). prisms (7, 68, 70A). If carefully heated, melamine sublimes Another compound of interest is cyanuric triazide which, in the presence of colloidal palladium, can be quantitatively (21); strong heating, however, decomposes the material. I n contrast to some of its related compounds, melamine is a weak reduced to melamine (84). base (7, 23, 24). Possibly owing to this basic character, melamine exhibits a great tendency t o form stable complex compounds with organic and inorganic acids. The preparation and properties of many acid addition products have been treated by numerous authors ( 1 , 6, 21, 68, 62, 63). With certain organic polybasic and/or polyfunctional acids, melamine gives, under favorable conditions, complex resinous condensation products. Melamine also reacts with certain inorganic salts to form complex compounds of which the salts of platinum and silver FIGURE4. 2,4,6-TRIS-(4-AMINOPHEXYL)-1,3,5-TRIAZ are particularly well known (16, 49, 68, 63, 86); salts of the lighter metals are also known (24). Methylolmelamines. Melamine reacts with alcohols, Resinous Products from Melamine. In the organic simple sugars such as glucose (66), and phenol (6). But of field melamine enters into many reactions which are of interest greater importance to the resin chemist is the reaction of both to the resin chemist. Hofmann (47) first found that melamine alkyl and aromatic aldehydes and ketones with melamine. produces resinous products when he was working with tetraThese condensations are so extensively used that they warphenylmelamine. To provide a background for this discusrant particular consideration. sion, i t is necessary to examine the structure of melamine more The most important of this large group of condensation .closely. products are the methylol compounds. They are produced As a clue to the chemical nature and reactions into which in good yields when melamine is reacted with neutral or melamine can enter, it might be well to consider i t by its slightly alkaline formaldehyde, or with some substance prochemical name 2,4,6-triamino-1,3,5-triazine.This material ducing formaldehyde. Of the six products possible from the probably exists in equilibrium with its is0 form (7, 24, 42) as condensation of these two compounds, the most stable and in Figure 3. Ostrogovich (63)and Barnett (6) favor other readily isolated is hexamethylolmelamine (10, 82). This formulas which they claim are more representative. For compound may be produced either by heating melamine with an excess of neutral formaldehyde to 90" C. (194" F.), or by allowing the melamine to react with neutral formaldehyde a t room temperature over a period of 15 to 18 hours. Elemental analysis indicates that the product formed in both cases is the same and contains one molecule of water of crystallization A H-N N-H per molecule of hexamethylolmelamine. Though the trimethylol compound is not so stable as the NI N ll thexamethylol compound, it has also been prepared. If one mole of melamine is reacted with three moles of neutral or slightly alkaline formaldehyde in the cold for 15 hours, the trimethylol compound is obtained. The entire separation and AND IS0 FORMS OF ~ , ~ , ~ - T R I A M I N O - purification of this material must be carried out with extreme FXGUBE 3. NORMAL rapidity and a t very low temperatures to prevent further re1,3,5-TRIAZINE "2
NH,
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June, 1941
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INDUSTRIAL AND ENGINEERING CHEMISTRY
HOCHt-N-CH20H
1
H-N-CHaOH
1‘
771
dimethylolurea but can be pictured as forming through similar mechanisms. There are two linkages which may exist bet w e e n m o l e c u l e s of methylolmelamine under t h e s e c on d i ti o n s-t h e ether linkage and the methylene linkage. In the case of methylolmelamines below h e x a m e t h y l o l melamine, which contain one or more unreplaced hydrogen atoms, t h e mechanism can be readily -N-CHZ-N-CH2I I f o r m u l a t e d as going through the methylene l i n k a g e . W i t h hexamethylolmelamine, however, it is necessary to split off formaldehyde in order to make such a linkage possible. On the other hand, the condensation may take place through the elimination of water TEROUGH (1) METHYLENBI AND (2) ETHERLINKAQES FIQURE5. RESINIFICATION and with the formation of an ether linkage as illustrated in Figure5. If produced under carefully controlled conditions, condensation action. Elemental analysis shows that under these conditions products of the structure suggested in Figure 5, result in the compound crystallizes from aqueous solution with two water-soluble resins (18, 26, 27, 82, 38,40, 63). These unmolecules of water of crystallization. Owing to its extreme modified resins find application as textile and paper coatings reactivity, the material has no definite melting point and is not and as adhesives (87). Of greater commercialimportance are stable on standing. the water-soluble melamine-formaldehyde resins which have The methylol compounds of melamine exhibit many of the been modified by the addition of such compounds as glycerol, characteristics of complex alcohols and, similar to the alcoglycols, or simple sugars. hols, they can be esterified. This is of interest to the resin In a similar way, molding compounds can be produced chemist, for here are complex polyhydric alcohols which, dif(28) by slightly modifying the conditions. The finished ferent from many of the more common alcohols, are resistant to discoloration a t high temperatures. Under favorable conproducts are characterized by high softening point, rapid ditions the methylolmelamines can be reacted with certain molding cycle, and good mechanical strength (9). These products can be further modified by the addition of fillers polybasic and/or polyfunctional acids to form complex resinsuch as wood flour and coloring matter. A slight change in ous esters. When such reactions are carried out in the presformulation enables the production of casting resins of exence of an oil or fatty acid, resins of the alkyd type are proceptional clarity and water resistance (8). duced. In order that melamine-formaldehyde resins are to be of use t o the paint and varnish industry, they must be comResins from Methylolmelamines. Although resins can patible with commonly used paint, varnish, and lacquer inbe produced from the methylolmelamines by esterification, most of the common resins now available are produced by digredients such as solvents, resins, and pigments. T o obtain rect condensation of several units. (Throughout this paper this property it is necessary to modify the structure of the condensation unit. This is usually done by causing the conwe have used “condensation” to express the initial reaction densation to take place in the presence of an alcoholicmedium mechanism for melamine resins; compare Brown, 1OA). These condensation products, like those of dimethylolurea, (9, 10, 86, 89, 82). The resulting product is a melaminemay be divided into three classes-water-soluble, hydrocarformaldehyde etherified product similar in many respects t o urea-formaldehyde etherified resins (4,60). bon-soluble, and insoluble. The water-soluble and insoluble Analogous to the case of urea-formaldehyde resins (&), condensation products may be considered as different stages of these condensation products are often further modified by the same reaction, while the hydrocarbon-soluble condensates carrying out the reaction in the presence of the ingredients of are slightly different in character. an alkyd resin and under conditions such that a complex mixed The reactions resulting in the production of these three classes of compounds are controlled by four general factorscondensate is formed. Perhaps a more common modification, vis., ratio of components, catalysts employed, time of rehowever, is that in which the melamine is mixed with some other substance capable of reacting with formaldehyde in action, and temperature. By adjusting these variables the much the same way-e. g., phenol, urea, and thiourea (89, size and complexity of the condensation unit of the iinal product can be controlled. Under similar conditions the methylol84, 40, 66, 69). The intermediate condensation products are melamines, in common with dimethylolurea (&), form threesimilar to hexamethylolmelamine, and a three-dimensional dimensional heabconvertible condensates. mixed condensation product having a certain degree of homogeneity is probably formed. Owing to the greater number of functional points, these The condensation products resulting from the above mixcondensates are somewhat more complicated than those of I
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PROPERTIES OF MELAMINE TABLE I. PHYSICAL Molecular weight Melting point (69) C. Sp. heat (8.41, oal. k t 15’ C./gram/” C. Solubility in Cold water (68) Hot water (68) Cold ethyl alcohol Hot ethyl alcohol Ether
TABLE 11.
126 347 (354 cor.) 0.352 Slightly sol. (0.29 gram) Sol. Insol. Slightly sol. Insol.
TOLERANCES O F UREA MELAMINE REBINSO
PERCENTAGE SOLVBNT
BP-138 Urea
B-3500 Melamine
Alcohols Ethyl Butyl Amyl Hexyl Octyl Diaoetone
1000 1000 1000 1000 1000 1000
I000 1000 1000 1000 1000 1000
Esters Ethyl acetate Butyl acetate Amyl acetate Butyl lactate
1000 1000 1000 1000
1000 1000 1000 1000
BP-138 B-3500 Urea Melamine Petroleum hydrocarbons Mineral spirits V. M. P. naphtha Hi-Flash n m h tha Gasoline Kerosene Aromatic hydrocarbons Toluene Benzene Xvlsne __“
a Tolerance measured on 1O-cc. sample of resin solution. All samples reported 1000% have over 100 cc. solvent/10 cc. sample.
tures are so complex and so little understood that there is little point in suggesting a
Miscellaneous Acetone Turpentine Cellosolve Carbon tetrachloride
I 50
1
AND
300
350
250
300
350 250 300
400 300 350
1000 1000
1000 1000
inno -..
1000 850
I000 950 1000
1000
lo00
temperatures above 500” F. as evidenced by color retention. Urea-formaldehyde condensations which have a high percentage of carbonyl oxygen are, on the other hand, decomposed by temperatures above 350’ F. This stability of melamine resin a t elevated temperatures, as compared to ureaformaldehyde resins, may be due in part t o the absence of the carbonyl group. By a careful choice of catalysts, reaction media, time, and temperature, the properties of the organophilic melamine resins may be varied between wide limits. Resins can be made having a low degree of etherification and subsequent low tolerance for hydrocarbon solvents, or they can be made with a high degree of etherification and infinite compatibility with hydrocarbon solvents such as mineral spirits. Various resins with properties in between the two extremes can be prepared. PHYSICAL PROPERTIES OF MELAMINE RESINS Since melamine-formaldehyde-butanol condensation products may be prepared with varying degrees of etherification and consequent wide range of physical properties, any endeavor to define the physical properties of melamine resins must be limited to the description of a specific product with a definite amount of monohydric alcohol “tied in”.
moo
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I
ture. Turning our attention to the LL P simpler hydrocarbon-soluble meli * 20, 2 3 4 amine-f o r m a1d eA C I 0 NUMBER hyde-alcohol conFIQURE 6. EFFECTO F HEAT O N d e n s a t i o n prodHYDROCARBON-SOLUBLE RESINS ucts, we find them to have the same skeletal structure as the water-soluble condensation products. The alcohol serves the double purpose of, imparting solvent compatibility and limiting the size of the condensation unit by blocking some of the reactive points. This is accomplished through the formation of ethers by the condensation of alcohol with free methylol groups. The tendency to form ethers by the reaction between amino groups, formaldehyde, and alcohols (preferably butyl and higher) was discussed by Robinson and Robinson (YO) and McLeod and Robinson (69). This tendency is also shown by nitrogen atoms which are part of a six-membered ring, provided a free hydrogen is attached (61). Thus, even if melamine exists in its is0 form. the reaction may follow a similar course. Resins of increased complexity can be readily made by substituting complex or polyhydric alcohols for part or all of the monohydric alcohol. This introduces the added resinforming possibility of ether bridges linking the molecules together as shown in Figure 5. These hydrocarbon-soluble condensation products can be readily converted by heat or catalysts or both (Figure 6) to hard, water-white, extremely resistant films; the heat or catalyst functions to release the etherified alcohol and thus makes possible the formation of larger condensation units. One of the most striking advantages of these condensation products is that, in addition to their hardness, they are extremely heat resistant and remain stable on exposure to
Solvent Tolerances. From this point of view the data of Table I1 show the solvent tolerances of two resins-BP-138, a pure urea-formaldehyde-butanol resin, and B-3500, a pure melamine-formaldehyde-butanol resin. For practical purposes these two resins may be regarded as having the same degree of etherification; as the data indicate, the melamine resin solution tolerates more petroleum hydrocarbons than the corresponding urea resin. The tolerance of these two resins for other solvents is in most cases sufficiently great to be regarded as infinite. These qualities may be varied, and it seems likely that melamine resins can be “custom-made” to any reasonable specifications set up by the paint and enamel formulator. However, B-3500 appears to be the best possible compromise in so far as a single all-round melamine resin for use of the enamel manufacturer is concerned. TABLE 111. PHYSICAL AND CHEMICAL PROPERTIES OF RESINS Resin No. % nonvolatile
ColorC Acid No. Viscosit a t
B-1323 50 toluene
B-1308 50 toluene
...
...
48.5
44.8
ZL-2
4.3
2 ~ - 2
13.5
B-1307 50 xylene
... 43.2 1-2~ 5.6
B-1313 BP-138 50 20 buhydrotanol, naphtha 20 tolueue 18
...
43.2 2~ 4.2
cbidrless 5.0
B-3500 35 butanol, 15 xylene 24 cbidrless < 1.0
L N-0 N-0 U-VV T-U u-w 0.975 1.025 1.025 0.994 0.990 NonSemiMelNondr&g &rig Drying Ureaaminedrying formalalkyd, alkyd, alkyd formalalkyd, shord dehvde. dehyde, short medium short oil oil oil oil butanol- butanollengthe lengthd lengthe lengths modified modified a Kjeldahl method. b Kappelmeier (66) method. 0 Hellige-Klett. d Gardner-Holdt method. 8 0?1 lengths of alkyd resins are generally described as short (less than 40% oil), medium (40-50’%), and long (greater than 50%). 25O C?d
Sp, gr. a t Z O O C Type of resin
0.999
Physical Characteristics. The properties of B-3500 and the other resins used in this work are recorded in Table 111. This melamine resin is compatible with nondrying, semidrying, and drying alkyd resins, regardless of their oil length, and also with urea-formaldehyde-butanol resins in all proportions. B-3500 will tolerate the usual amounts of chemical plasticizers, such as the phthalates, but has only limited oil compatibility. However, it d l tolerate sufficient castor oil for plasticizing uses.
June, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
Procedures. The methods employed in the measurement of film properties of aints and other surface coatings are arbitrary in many cases, anfthe tests may vary from one plant to another. The results obtained are influenced by many variables. The method of film production (spraying, casting, brushing, etc.), the thickness of the film, the method of baking, and the conditioning of the finish after baking all have their effects upon the accuracy of the data obtained. Since in modern industrial practice the control of these procedures is not completely standardized, certain routine test methods were adopted for this work. The data reported in this paper were taken on films cast at a setting of 6 on the Dow microfilm caster (19), and the dry films had a thickness of approximately 0.0015 inch. They were airdried for 30 minutes prior t o being placed in a Freas mechanical convection oven, 18 X 18 X 18 inches. It was controlled t o 1 2 " F., as recorded by a Micromax recording thermometer. Upon removal from the oven, the panels were permitted to cool and remain at room temperature approximately 15 hours before testing. HARDNESS specimenswere cast on plate glass panels,l2 X 18 X l / 4 inch in size, with five films t o a panel. The films were processed as described above, and the hardness was measured on a Sward hardness rocker (79). The rocker was adjusted so that it swung fifty times (+1) on clean plate glass. Measurements were made at room temperature in a location free from air currents. FLEXIBILITY specimens were cast on tin panels ranging from 0.013 to 0.014 inch thick, as previously described. Flexibility was reported as passing (P) or failing (F), dependin upon whether or not the tin anel upon which the 6lm was bake2 could be bent 180' over a '[-inch mandrel without impairing the film. If the 61m cracked, it was designated as failing. ADHERENCE.Panels were prepared as for the flexibility test, and the cross-cut adherence test (26)was used to evaluate the resin films. A series of l/le-inch parallel cuts were made with a razor blade, and another series were made perpendicular to the first. The films were rated as failing or pmsing, depending upon whether or not the squares came off during the cutting operation. This test was not entirely satisfactory for evaluating the films because compositions containing any alk d whatsoever were found to be passing. It is believed that a test is satisfactory for pigmented films but is not sufficientlysevere for clear film evaluation.
773
UREA
MELAMINE
ALKYD
FIGURE7. TRIAXIAL DIAGRAM FOR THREE-COMPONENT SYSTEM
percentages of urea, melamine, and alkyd resins. Twentyone blends were made with each of four different types of alkyds. This number was considered representative of the infinite number of possible combinations in a three-component system. I n Figure 7 the compositions chosen are numbered from 1 to 21, and such a system was followed throughout this section of the paper. Composition 1 contains 100 per cent urea resin; No. 16, 100 melamine resin; No. 21, 100 alkyd resin, etc. For instance, compositions 13 contain 40 per cent Three-Component Systems. Since melamine resins are alkyd, 40 melamine, and 20 urea resin; the data given in compatible with alkyd and urea resins, three-component Table IV for compounds 13-A, B, C, or D refer to the propersystems of melamine-urea and various alkyd resins were made ties of a clear enamel of the composition 40 alkyd, 40 melup so that the effect of the melamine resin upon film properamine, and 20 urea resin. Letters A to D designate the alkyd ties could be measured. A typical triaxial diagram, as used employed. for lacquer formulation (@), was set up for this work. The hardness line on Figure 7 divides the surface of the Three-component blends were prepared containing varying triaxial diigram into two areas. The area to the right of the line contains the compositions which have Sward hardness values of 25 per cent or less; the compositions harder than 25 per cent are located to the left of the line. The flexibility and adherence lines also bound areas of compositions possessing satisfactory properties. To the right of each of these lines lie the compounds passing the flexibility and adherence tests described under "Procedures". Consequently, in order that an enamel should be satisfactory from the standpoint of hardness and flexibility, the two limiting qualitieg, it must lie in the area to the left of the hardness curve and to the right of the flexibility and adherence curves (the cross-hatched section of Figure 7). The data obtained for the three-component systems are shown in Figure 8 and Table IV. The areas in Figure 8 seem to show only general tendencies; namely, it is imperative to use at least 55 to 80 per cent alkyd in clear enamels if flexibility and hardness h e to be obtained. For this reason blends containing 60 per cent alkyd were used BATTERY OR MANUFACTURING UNITS FOR MELAMINE-FORMALDEHYDE REISINS
SUCK
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INDUSTRIAL AND ENGINEERING CHEMISTRY
FLEXIBILITY, AND ADHERENCE OF UREA TABLE IV. HARDNESS, AND MELAMINERESINS USED WITH ALKYDS Compn. NO.
UreaFormaldehyde BP-138
MelamineFormaldehyde B-3500 Alkyd
Hardness Sward (30 Min., 250' F.)
F1,exibilitya
Adherence"
for the time-temperature data recorded later. The data indicate that, as the 100 per cent melamine resin composition is approached, the f3ms are hardest; this is true regardless of the time or temperature of the bake. Evidence points to the conclusion that, as the compositions approach 100 per cent alkvd. the lowest hardness values are obtained. Melamine resfn imparts greater hardness to a given composition than does the same amount of urea resin; conversely, a smaller amount of melamine resin produces a hardness equal to that obtained by a greater amount of urea resin. ~~
I-A 2-A 3-A 4-A 5-A 6-A 7-A 8-A 9-A 10-A 11-A 12-A 13-A 14-A 15-A 16-A 17-A 18-A 19-A 20-A 21-A
100 80 80 60 60 60 40 40 40 40 20 20 20 20 20 0 0 0 0 0 0
1-B 2-B 3-B 4-B 5-B 6-B 7-B
100 80 80 60 60 60 40 40 40 40 20 20 20 20 20 0 0 0
8-B
9-B 10-B 11-B 12-B 13-B 14-B 15-B 16-B 17-B 18-B 19-B 20-B 21-B
I-c
2-c 3-c 4-c 5-c 6-C 7-c 8 4 9-c 10-c 11-c 12-c 13-C 144 154 16-C 17-C 18-c 19-c 20-c 21-c
Alkyd Resin B-1308 0 0 40 20 0 40 0 20 42 40 0 40 20 20 36 0 40 35 60 0 45 40 20 45 20 40 38 0 60 24 80 0 53 60 20 51 40 40 47 20 60 38 0 80 10
F F
F F
F F
F
F
P P F F
F F
P P
F F F F F P F F P P F F P P P
P
F
F
P
0 0
100 80 80 60 60
6-D 7-D 8-D 9-D 10-D 11-D 12-D 13-D 14-D 15-D 16-D 17-D 18-D 19-D 20-D 21-D
60 40 40 40 40 20 20
20 20 20 0 0 0 0 0 0
Alkyd Resin B-1313 0 C 40 0 40 20 0 20 44 40 0 40 20 20 46 0 40 36 60 0 45 ~. 40 20 39 42 40 20 26 0 60 53 50 45 31 10 50 51 31 24 21 6
P
P P
F
F F P F P
F F F F F F P P F F F P P F F F P P
0 0 0
P
P P
F
P
F P P P F P P P F P P P P P
F
F
F F F F F
P
F
F F
P F F F P
P F F F
F
P
P
P denoted aomposition passed the test; F. failed in the test.
FIGURE 8. HARDNESS, FLEXIBILITY, AND ADHERENCE DATAFOR THE THREE-COMPONENT SYSTEM
F P P
P
F
0
P
F P F
0 0 Alkyd Resin B-1307 0 C 40 20 0 40 0 20 35 40 0 40 20 20 30 0 40 34 60 0 45 40 20 34 20 40 34 0 60 35 80 0 53 60 20 37 40 40 39 20 60 33 0 so 18
P
F
0
100 80 80 60 60 60 40 40 40 40 20 20 20 20 20
F F P F
F
F F P
1-D 2-D 3-D 4-D
5-D
Alkyd Resin B-1323 0 0 40 20 0 40 0 20 40 40 0 40 20 20 46 0 40 40 60 0 45 20 42 40 20 40 40 0 60 40 80 0 46 60 20 42 40 40 40 20 60 32 0 80 24 100 0 50 80 20 52 GO 40 52 40 60 45 20 80 28 0 100 0
F F
If identical compositions of urea-alkyd and melaminealkyd blends are compared, the superiority of the melamine resin is readily shown (Table V). These data are significant in that they are in the range of compositions customarily used; i. e., all the enamels contain a t least 60 per cent alkyd with the remainder of the composition being melamine or urea. The melamine is superior in each instance. Composition ws. Hardness. The data given in Table I V were also plotted on rectangular coordinate graphs. The curves show the superiority of melamine-alkyd resin compositions in a more striking manner than is possible on the triaxial diagrams. Figure 9 indicates that, when melaminealkyd mixtures are baked for hour a t 250' F., they give harder h s than urea-alkyd blends, regardless of the ratio of amine resin t o alkyd. This tendency exists regardless of the type of alkyd used. Although curves are not shown for other times and temperatures, the same tendency prevailed whatever the baking temperature used, and the time influenced the results only t o the extent that it is desirable to allow a sufficient period for the amine resins to be converted. It is possible t o obtain a given hardness with a smaller percentage of melamine resin than urea resin; this is illustrated
P P
F P P P F
P P P P
F P P P P P
TABLEV.
HARDNESS OF VARIOUSCOMPOSITIONS
compn. No. IO-A 19-A 16-A 20-A 10-c 194 15-C 20-c 10-D 19-D 15-D 20-D
Amine Resin Urea Melamine 40 40 20
..
BQ
..
20
..
40
.. ..
20
..
io
.. 40
.. 20 .. 40
..
20
Alkyd Resin Sward Hardness B-1323 B-1307 B-1313 (30 min.. 250' F.) 60 40 60 45 80 24 80 28 Bb 35 60 39 80 18 80 20 24 60
.. ..
..
.. .. ..
.. ..
....
.. ......
60
80
80
26
10 21
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I
I
I
I
MELAMINE
\-
50-
-
I 0 IO0
PO 80
40 00
60 40
80
20
0 100
I
I
40AMINE S O 60ALKlD40 COMPOSITION
20
a0
FIQURE 9. HARDNE~S OF %SIN
in Figure 9. Indications are that hardness increases in direct proportion to the amine-resin content until a maximum value is attained which is determined by the alkyd used. For example, with nondrying alkyd B-1323,compositions containing 50 per cent amine resins are very near the maximum hardness attainable under these conditions; in the case of semidrying alkyd B-1307 the composition must contain about 70 per cent amine resin to provide a similar hardness. For drying alkyd B-1313 a t least 80 per cent of the melamine or urea resin is needed for maximum hardness.
Time-Hardness Isotherms. The three-component work illustrated that at least 60 per cent alkyd is required in clear vehicles if they are to pass the tests set up. Hence, for the following curves and data the vehicles employed contained 60 per cent alkyd, the remainder being melamine resin, urea resin, or blends of the two. 60
/ /
/
+ I
I1
BAKING TIME
IN
I 80 20
0 100
I
1
I
I
20
40 00
SO 40
80 20
e0
IO0 0
COMPOSITIONS
Figure 11 presents evidence that melamine-alkyd enamels are more heat stable than urea-alkyd enamels of the same amine-alkyd ratio. The appreciable drop in hardness of the urea-alkyd blend must be due to the decomposition of the urea component in the blend, for the alkyd does not break down under identical conditions when used with the melamine resin. This drop in hardness may not necessarily be due to a softening of the film but rather an impairing of the surface by the formation of minute pinholes. These "pores" may be formed by the volatilization of the urea resin decomposition products. Evidence of this decomposition is further substantiated in that the urea-alkyd films, baked for long periods at 350" F. (up to 2 hours), are much darker than the melamine-alkyd films.
Chemical Resistance. Simple t q t s were performed in an attempt to compare qualitatively the resistance of melaminealkyd and urea-alkyd films to various chemicals and water. Immersion tests were made to determine the resistance of melamine and urea resins to concentrated hydrochloric acid, dilute potassium hydroxide, and water, all a t room temperature. In each test melamine resin proved superior to urea resin, whether alone or in combination with alkyds.
MINUTES
FIGURE10. TIME-HARDNESS ISOTHERMS BAKED AT 350. F.
Figure 10 gives time-hardness isotherms; the compositions were identical and submitted to representative baking schedules. The curves indicate that a t a given time the hardness of the melamine-alkyd or urea-alkyd clears are dependent upon the temperature of the bake. They show that for each time and temperature melamine-alkyd blends (40-60) are harder than the corresponding compositions with ureaalkyd blends. The curves give visual evidence that prolonged baking at the higher temperatures does not always improve hardness proportionately. I n fact, the bakes a t 350' F. for prolonged periods seemed to cause a loss of hardness in the urea-alkyd blends. These figures emphasize the fact that for every composition of alkyd with melamine or urea resin there is an optimum baking time and temperature, and that these conditions can be accurately ascertained.
A - BO 40
ALKYD MELAMINE
8 - 30 40
ALKYD UREA
PO
-
M o
0
TIME
IN
MINUTES
FIQURE11. HEATSTABILITY OF RESINS
Similar results were obtained on automotive steel panels coated with each of the resins and then placed in a cabinet saturated with water vapor (at 100" C.) for 90 hours. The steel panel showed only a slight tendency to rust under the pure melamine resin film, and when the melamine resin was combined with alkyd resin, the rusting was negligiblie.
INDUSTRIAL AND ENGINEERING CHEMISTRY
776 + . m a
Vol. 33, No. 6
Spot tests were made to measure the grease resistance of the films, oleic acid being used as the grease; the melamine resin was found t o equal the nearly perfect inertness of the urea resin film. In so far as resistance to attack by chemicals, melamine resins appear t o have a t least as good chemical resistance as the urea resins.
Properties of Melamine Resins in Enamels The use of melamine resins in enamels WELL discussed by Sanderson (72, 73) and briefly by Stager (77)'but throughout this paper the emphasis has been upon one single concentrated melamine-formaldehydebutanol resin rather than upon many hybrid b l e n d s of u r e a a n d alkyds. The exceptional properties t h a t t h e melamine resin gives to clear films are also imparted to pigmented films. If one concentrated melamine resin can be introduced into enamel t o make it "highpowered" in an analogous way to the addition of t e t r a e t h y l l e a d t o gasoline, the simplicity of control is very great. By the introduction of this concentrated melamine-f ormaldehydebutanol resin, there are five advantages: The baking schedule may be lowered almost 100' F. and still obtain the hardness formerly secured only with high bakes using a l k y d or alkyd- urea-formaldehyde resin enamels alone. The baking schedule may be speeded up if the same t e m p e r a t u r e is maintained. From the standpoint of economy more alkyds can be used with melamine resins than with urea resins and still obtain the same hardness. The heat resistance of m e l a m i n e r e s i n s is su erior to urea formaldeKyde resins; discoloration occurs at 450" F. t o
I
l50'F.
0
1
,-I
iOC
I
o
20
40 60 80 BAKING TIME IN MINUTES
io0
120
FIGURE 12. TIME-TEMPERAT~E RELATIONS OF WHITEENAMELS
the same degree as or t o a lesser degree than it does with ureaformaldehyde resins at 300" F. The chemical resistance appears t o be at least equal to the urea-formaldehyde resins and, in some cases, slightly superior. The introduction of the concentrated melamine resins into alkyd enamels fits in with both the new, modern types of baking and with the older, more conservative, and possibly safer methods of baking. As demonstrated by the pioneer work of the Ford Motor Company and also by Bennett and Haynes (8),infrared enamel baking has made considerable progress in the past two years. The urea-formaldehydealkyd enamels have been especially well adapted to this new type of baking and here the use of melamine resins enables a choice of either shorter baking schedules a t the same temperature, a lower temperature a t the same length of time, or the use of more alkyds with melamine instead of less alkyds and more urea. The great heat resistance of the melamine resins offers possibilities in the field of flash baking where enamels go through an oven a t temperatures of 500-800° F. for very short periods of time. On the other hand, the quick convertibility of melaminealkyd enamels a t low baking temperatures is a boon to the owners of the older steam-coil ovens, for new, modern, hard, and resistant enamels may be baked in these safe and efficient ovens.
White Enamels. A series of white enamels was made from varying proportions of melamine (B-3500), urea (BP-138), and a nondrying alkyd (B-1323) resin, using a low oil absorption type of titanium dioxide pigment. The pigment was first prewet (71) 30 minutes with toluene and then ground 72 hours in a pebble mill with the alkyd. This paste was "let down" with various amounts of alkyd, urea, and melamine resins to form a series of enamels with a pigment-binder ratio of 1.0 to 1.0 (Table VI). Three series of enamels were prepared, the pigment-binder ratios including 1.0 to 0.8, 1.0 to 1.0, and 1.0 to 1.2; for brevity only the 1.0 to 1.0 series is reported.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1941
777
TABLEVII. HARDNESS AND GLOSSOB COLOREID ENAMEL FORMULATION Enamel No. A 1 2 3
Name of Pigment C. P. chrome yeb low dark
B1 2 3 C 1
Formulation. Parts by Weight Solid resin Solventsa BP-138 B-3500 Toluene Xylene Butanol .. 60 20 l6 4 .. 44 16 20 40 18 7 ..
Pigment 100 100 100
B-1323
C. P. c h r o m e orange dark
67 67 67
loo
C. P. para toner dark
22 22 22
100 80
D1 2 3
Toluidine dark
27 27 27
loo 80 80
20
E 1
Permanent green toner
25 25 25
100 80 80
20
C. P . nitrate green light
67 67 07
100 80 80
Phosphotungstic acid blue toner
25 25 25
100 80 80
2 3
2 3
F1 2
toner
3
G1 2 3
loo 80 80
80 80
80
..
..
20
.. .. 20 ..
..
..
.. .. .. 2o .. io
..
.. ..
60
44 40
lo lo 13
4 7
60 44 40
36 35 38
4 7
20
50 44 40
38 38 41
4 7
60
20
40 44
14 14 17
4 7
20
60 44 40
32 32 36
4 7
50 44 40
11 11 14
4 7
20
.. ..
20
.... .. ..
.. .. .. ..
2o
Pigment/ Binder Ratio 1.0/1.0 1.0/1.5
30 Min. at 250" F . Sward hardness Gloss 0 1 12 2 16 2 0 10, 22
1 2
2
1.0/4.5
0 8 22
2
1.0/3.7
0 13 15
2 3 1
1.0/4.0
0 18 18
3 2
1.0/1.6
0 18 20
1 3 2
1.0/4.0
0 8 18
a
3 1
1
1
2
All compositions reduced 30% with xylene to adjust to proper spraying viscosity.
Each enamel was adjusted to satisfactory spraying viscosity by the addition of 20 per cent by volume of toluene and sprayed on bare cold-rolled automotive steel panels. The panels were air-dried 15 minutes before baking in order to obtain the best possible gloss. Hardness was determined by the Sward hardness rocker (79), and gloss by visual comparison on an arbitrary scale from 1 to 6. These data are given in Table VI and Figure 12. The change in hardness with baking time is shown for six different compositions a t three temperatures. At 150" F. no satisfactory degree of hardness is attained even after 2 hours. Enamels 5 and 6 (containing melamine) are hardest a t this low temperature. At 250" F., the thermosetting amine resins are converted a t the end of 30 minutes, and the hardness increases very little with time.
A C I D NUMBER O F MELAMINE RESIN
OF ACIDITY ON FIGURE13. EFFECT THE HARDNESS OF WHITEENAMELS
Enamel 3, containing 20 per cent melamine resin, has twice the hardness of enamel 2, containing 20 per cent urea resin; equal hardness is attained in approximately half the time. An increase in amine resin content of 20 per cent (enamels 4, 5, and 6) increases the hardness about 10 per cent, but in the case of 40 per cent urea (enamel 4), the hardness is little greater than that of 20 per cent melamine (enamel 3). The straight nondrying alkyd enamel (enamel 1) is still soft a t this temperature. At 350' F. only 15 minutes are needed to convert the resins, but there is a slight further increase in hardness with time due to the slow conversion of the nondrying alkyd component at that temperature which does not occur a t the lower baking schedules. Also, enamel 3, containing 20 per cent melamine,
reaches the same hardness after 30 minutes a t 250" F. that i t attains after 30 minutes a t 350" F.; this means that it is completely converted a t the lower temperature. At 350" F. enamels 4 and 5 (containing urea) reach greater hardness than enamel 6 (containing only melamine) which is no harder than i t was a t 250" F. However, a t high temperatures the melamine resins show superiority in color retention. This makes them a more or less essential ingredient in enamels that are to be baked in infrared ovens where they are subjected to temperatures over 400" F. for short periods (4, 8). The difference in color stability of urea and melamine resins is demonstrated by baking enamels for 30 minutes a t 450" F. (Table VI). Those containing urea are the worst and those with melamine are the best. The nonoxidizing alkyd (B1323) used is very stable and has an optimum color retention for an alkyd resin. The rate of conversion of urea and melamine resins is increased greatly with the degree of acidity. Figure 12 shows the effect on hardness of white enamels with change of the acid number of melamine resin used in the enamel. The pigment-binder ratio is 1.0 to 1.2, and the binder is 50 per cent melamine with 50 per cent alkyd resin. Figure 12 indicates that, as the acid number increases, the rate of conversion is accelerated. The use of acidic accelerators, such as those previously described (&), in urea-alkyd combinations to produce air drying and very fast low-temperature baking enamels does not now seem advisable for melamine-alkyd combinations because of the extremely fast rate of conversion to the gel state and consequent lack of package stability. The only way this could be accomplished a t the present stage of develop ment in industrial enamels would be to incorporate the accelerators only a short time before application. High acid numbers also seem to result in loss of gloss in white enamels. As in the study of urea-alkyd enamels described by Hodgins, Hovey, and Ryan (46), highly acid pigments should be avoided on account of the stability of the enamel. Also, highly alkaline pigments should be avoided for the same reason, since the melamine resin is accelerated by extreme alkalinity.
Colored Enamels. A series of colored enamels was prepared with a few representative pigments, using the prewet method of preparation (71)in porcelain pebble mills in much
778
INDUSTRIAL AND ENGINEERING CHEMISTRY
the same manner as in the white enamels. For simplicity the choice of vehicles was limited to three: (a) 100 per cent nondrying alkyd B-1323, (b) 20 per cent BP-140 urea resin, 80 per cent B-1323 alkyd, and (c) 20 per cent B-3500 melamine resin, 80 per cent B-1323 alkyd. The pigment-binder ratio could not be kept constant for all colors on account of differences in oil adsorption, but the ratio was kept constant for all the enamels prepared from the same pigment (Table VII). After a 72-hour grind the enamels were thinned t o spraying viscosity with xylene. Each enamel was sprayed on unprimed, cold-rolled, automotive steel panels and baked for 30 minutes at 250” F. I n this baking schedule, commonly used in industry, the full hardening effect of melamine resin may be best utilized as compared to urea-alkyd resin combinations or to alkyds alone, Figure 9 shows that on clear films a maximum hardness a t 250” F. is obtained with melamine resin and an alkyd such as B-1323. Table VI1 indicates that in all cases the enamels containing melamine-alkyd resins as the vehicle have equal hardness to or, in all cases but one, greater hardness than the urea-alkyd combination. With this particular nondrying alkyd used alone as the vehicle, there is no comparison since this type of resin does not convert on the specific baking schedule followed. I n all cases the gloss of the melamine-alkyd enamels is at least equal to, and usually better than, that of the urea-alkyd combinations. I n the case where the two easily dispersible pigments-i. e., para toner and toluidine tonerare employed, the gloss is better than that of the alkyd enamel alone. From Tables VI and VI1 as suggested starting points on white and colored enamels, the enamel formulator can probably prepare finishes with a concentrated melamine resin of a new high standard of color retention under heat and of maximum hardness in the shortest possible time. Enamels for refrigerators, stoves, metal cabinets, and automobiles are a few of the mass production items for which efficiency engineers are always seeking greater speed on the assembly lines. Wooden furniture is another high-speed industry which should be benefited by the rapid hardening of light colored, glossy enamels which can be converted a t lower temperatures and shorter schedules through the incorporation of some melamine resin in the vehicle. Specialties in paper and leather, which cannot withstand higher baking temperatures, may also be eventually benefited from the low-temperature convertibility. New, cheap, molded plastic articles which have dark colored binders, such as phenolic resin and/or lignocellulose, offer new possibilities for coating materials. For hard, resistant, white or pastel enamels they require much larger proportions of melamine resin to alkyd than have been considered in the enamels proposed in this paper. I n such cases where maximum hardness and resistance are required in the shortest possible time so that decomposition of the cellulose or bleeding of the dark binder into the enamel will not take place, the ratio of amine resin to alkyd may approach unusually high proportions. A ratio of amine to alkyd resin as high as 3 to 1 is possible since adhesion requirements are not so severe owing to anchorage to the cellulose fibers; as a result of the rigidity of the plastic article, flexibility is not a major problem.
Acknowledgment The authors wish to express thanks to H. Reichhold for his kind permission to publish this article and to the Research Department of Reichhold Chemicals, Inc., for cooperation and assistance.
Vol. 33, No. 6
Literature Cited Andreasch, Monatsh., 48, 145 (1927). Anonymous, Brit. Plastics, June, 1939, 27-8. Ibid., Dec., 1939, 326. Anonymous, Product Eng., 11, 307-10 (1940). Arndt, Ann., 384, 322-52 (1911). (6) Barnett, J . Phys. Chem., 34, 1497-504 (1930). (6A) Barsky, News E d . (Am. Chem. Soe.), 18, 759 (1940). (7) Beilstein, Handbuch der organischen Chemie, Vol. 26, pp. 2457, Berlin, Julius Springer, 1918. (8) Bennett and Haynes, Chem. & Met. Eng., 47, 106 (1940). (9) Bloxam, Brit. Patent 466,096 (March 10, 1937). (10) Ibid., 468,677 (Feb. 7, 1936). (1OA)Brown, P a i n t , Oil Chem. Rev., 99, No. 4, 14 (1937). (11) Burdick, J . Am. Chem. SOC.,47, 1485 (1925). (12) Carpmael, Brit. Patent 496,690 (Dec. 5, 1938). (13) Chastellain, H e h . Chim. Acta, 18, 1287 (1935). (14) Claus, Ann., 179, 120 (1875). (15) Claus. Ber.. 9. 1915 (1876). CIBex’and Canniaaaro, Ann., 78, 229 (1851). Davis, J. Am. Chem. SOC.,43, 2230-3 (1921). Deutsche Hydrierwerke Aktiengesellschaft, Brit. Patent 502,720 (March 29, 1939). Dow Chemical Co., Ethocel Handbook, p. 8 (1940). Drechsel, J . prakt. Chem., [2] 11, 302 (1875). Ibid., [2] 13, 330 (1876). Fisch, U. S. Patent 2,164,705 (July4, 1939). Franklin, J. Am. Chem. Soc., 44, 504 (1922). Franklin, “Nitrogen System of Compounds”, A. C. S. Monograph 68, p. 101, New York, Reinhold Publishing Corp., 1935. Gardner, “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors”, p. 125, Washington, D. C., Inst. of Paint and Varnish Research, 1939. Gesellschaft far chemische Industrie in Basel. Brit. Patent 480,316 (March 17, 1938). Ibid., 480,339 (March 17, 1938). Ibid., 482,345 (April 21, 1938) ; French Patent 826,631 (April 6, 1938). Gesellschaft fur chemische Industrie in Basel, French Patent 811,804 (April 23, 1937). Ibid., 814,761 (June 29, 1937). Gesellschaft fur chemische Industrie in Basel, Swiss Patent 189,406 (May 18, 1937). Ibid., 197,486 (Aug. 1, 1938). Ibid., 197,487 (Aug. 1, 1938). Ibid., 197,489 (Aug. 1, 1938). Ibid., 197,490 (Aug. 1, 1938). Ibid., 199,784 (Nov. 16, 1938); 200,244 (Dec. 16, 1938); 200,664 (Jan. 2, 1939). Ibid., 201,007 (Jan. 16, 1939). Ibid., 202,245 (April 1, 1939). Ibid., 202,548 (April 17, 1939). Ibid., 203,436 (June 1, 1939). Groves, Brit. Patent 502,148 (Sept. 1, 1938). Hartley, Dobbie, and Lauder, J . Chem. SOC.,79, 848 (1901). Hoard, J . Am. Chem. SOC.,60, 1194-8 (1938). Hodgins and Hovey, IND.ENQ. CHEM.,30, 1022 (1938). Tbfd., 33, 512-15 (1941). Hodgins, Hovey, and Ryan, Ibid., 32, 334-5 (1940). Hofmann, A. W., Ber., 7, 1746 (1874). [bid., 18, 2765 (1885). Hofmann, H . E., and Reid, E. W., IND.ENO. CHEW.,20, 431 (1928). Hovey, Hodgins, and Bevan, Brit. Patent 521,380 (May 20, 1940). I. G. Farbenindustrie A.-G., Ibid., 414,105 (July 26, 1934). I. G. Farbenindustrie A.-G., French Patent 817,895 (Sept. 13, 1937). I. G . Farbenindustrie A.-G., Swiss Patent 203,956 (July I, 1939). Jayne, U. S. Patent 2,180,298 (Nov. 14, 1939). Kappelmeier, Farben-Ztg., 40, 1141 (1935). mason, J. prakt. Chem., 33, 290 (1886). Lemoult. Ann. chim. vhvs.. 171 16.. 410 (1899). . . (58) Liebig, Ann., 10, 48 (1834). ENQ.CHEM.,32, 1181 (1940). (58A) McClellan, IND. (59) McLeod and Robinson, J . Chem. SOC.,119, 1470 (1921). (60) Madelung and Kern, Ann., 427, 26 (1922). (61) Mason and Block, J . Am. C h m . Soc., 62, 1443 (1940). (62) Nencki, J. p a k t . Chem., 17, 235 (1878). (63) Ostrogovich, Gazz. chim. ital., 65, 566 (1935). (64) Padoa, Ibid., 50, 312-17 (1920). (65) Pollak, Austrian Patent 101,283 (Aug. 2, 1922); Brit. Patent 201,906 (Sept. 4, 1924): German Patent 448,201 (Sept. 3, 1927). (1) (2) (3) (4) (5)
June, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
(66) Radlberger, Oesterr.-ungar. 2. Zuckerind. Landw., 42, 236-9 (1915). (67) Rathke, Ber., 23, 1675 (1890). (68) Rathsburg, Zbid., 54,3183 (1921). (69) Ripper, U. 6.Patent 2,056,142(Sept. 29, 1936). (70) Robinson and Robinson, J . Chem. SOC.,123, 532 (1923). (70A) Rochow, Stafford, Davis, and Miller, IND. ENG. CHEIM.,32, 1187 (1940). (71) Ryan, U. 8.Patent 2,211,912(Aug.20,1940). (72) Sanderson, Paint, Oil, Chem. Em.,102,No. 8, 7-9 (1940). (73) Ibid., 102,No. 12, 12 (1940). 23, 1124 (74) . . Smith, Sabetta, and Steinbach, IND.ENO. CHEIM., (1931). (75) Smoika and Friedreich, Monatsh., 10,86 (1889).
779
(76) Ibid., 11, 179-220 (1890). (77) St&ger, Sohweiz. Arch. angew. Wias. Tech., 5, No. 8, 221-6 11939). (78) St& and Erauch, Ber.,46,2337 (1913). (79) Sward, Natl. Paint, Varnish Lacquer Assoc., Sci. Sect., Circ. . . 510 (1936). Volhard, J . p u k t . Chem., [2]9,29 (1874). Widmer and Fisch, U. 8. Patent 2,170,491(Aug 22, 1939). Ibid., 2,197,357(April 16, 1940). Widmer. Fisch, and Jakl. Ibid., 2,161,940(June 13, 1,939). Wienhaus and Ziehl. Ber..65. 1461 (1932). . . Zirnmermann, Zbid.,’7, 289 (1874).
.
P R E S ~ N before T ~ D the Dividon of Paint and Varnish Chemistry a t the 100th Meeting of the American Chemiosl Society, Detroit, Mioh.
Molecular Volume of Saturated
Hvdrocarbons Recently Aranda (2,3) and S. S. KURTZ, JR., AND M. R. LIPKIN TUDIES of the composiKomshilov (22, 28) have pubtion of the high-moSun Oil Company, Marcus Hook, Penna. lished linear equations for the lecular-weight fractions of paraffin homologous series. petroleum (17,31, 88, 41, 4.2, Calingaert (6) and Huggins The molecular volume of saturated hydro@, 64) make it clear that, in (20) independently developed spite of the extensive work of carbons can be calculated with considerable more precise equations which Mikeska (33), still more data accuracy, using the equation: involve a third term, both for are needed for pure compounds V = 16.28 ni 4-13.15 n2 4-9.7 n3 31.2 normal paraffins and certain of Qf high molecular weight, esthe isomers. pecially compounds containing This equation is used to calculate graphs of The present work continues several rings and side chains. density vs. molecular weight for paraffins the study of molecular volume Molecular volume has long of high-molecular-weight comand various classes of naphthenes. There been known as an approxipounds, taking into consideramately additive property (2, is a large difference in density between tion rings containing from 3 to 8, 9, 28-86,29,37,61) ; therenaphthenes of equal molecular weight and 8 carbon atoms of both the confore it seemed possible that equal number of rings per molecule, dedensed and noncondensed information concerning the pending on the number of carbon atoms in types. density of high-molecularBy “condensed” naphthenes weight compounds could be the ring. It is suggested that this differwe mean compounds having obtained if a sufficiently relience can be used to determine the average structure analogous to decaable system of calculating number of carbon atoms per ring. hvdronavhthalene-i. e.. commolecular volumes of such A means of calculating the degree of pounds i n which no carbon compounds could be decyclization in hydrocyclorubber and reatom forms part of more than veloped. two ring structures. Few data The early work on molecular lated compounds is also proposed. are available on naphthenes volume by Kopp (24, 26) and in which one or more carbon L e Bas (29), which was reatoms are common to three-ring structures, and there is little -viewed by Cohen (9),was complicated by the fact that they evidence (27,41, 4.2) that such compounds exist in petroleum. .compared molecular volumes a t the boiling point rather than Therefore, we feel justified in omitting, for the present a t least, .at a oonstant temperature. In spite of this difficulty Le Bas consideration of naphthenes of this more highly condensed (29,page 7 and Chapter 11) recognized the fact that moilecular volume is well adapted to the study of ring structure. type. Richards (87)was interested in molecular volumes but was Molecular Volume of CH2 Group in Paraffins and ’harnnered by a lack of reliable data. Davis and McAllister in Side Chains of Naphthenic Compounds (11) published a chart (similar to our Figure 1) showing a Graphs of molecular volume 8s. number of carbon atoms linear relation between molecular volume and molecular were prepared for paraffins and naphthenes with five and six .weight for paraffins and mono-, di-, and tricyclic naphthenes carbon atoms in the rings. The data used were mainly those in whi& the rings were of the six-carbon (cyclohexane) type. of Ward and Kurtz (60). Where necessary, these were supEach ring structure has its characteristic line on the chart. plemented by data of Mikeska @), Kreulen (26),Eaton ( l a ) , This chart did not, however, take into consideration the fact and Egloff (14). The graph for paraffins and the cyclothat ring structures containing more or less than six carbon hexane, decahydronaphthalene, and higher carbon ring naphatoms Rer ring might be present. The Davis and McAllister thenes is shown in Figure 1. The corresponding graph for ,chart has never been widely used even though it is fairly the five-carbon ring naphthenes is similar except that the accurs,te CerS).
S
+
