Ester in Nitrocellulose Lacquers


superior to glycerol-rosin ester (ester gum) as an additive for nitrocellulose lacquers. Its performance, in fact, compares favorably with that of mal...
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Tetrarnethvlolcvclohexanol Rosin Ester in Nitrocellulose Lacquers J

d

HAROLD WIITCQFF, M. H. BAKER, AND LOUIS CHAMPLIN, JR. General Mills Research Laboyatories, Minneapolis, Minn,

T h e rosin ester of 2,2,6,6-tetramethylolcyclohexanol, a cyclic pentahydric alcohol derived from cyclohexanone and formaldehyde, is of interest as an additive for nitrocellulose. lacquers. In this paper its performance is compared in a series of evaluations to four commercially available maleic modified rosin esters. The lacquers tested were formulated with constant amounts of resin but with quantities of plasticizers varied to provide approximately the same hardness after 1 hour at 55" C. The tests included determination of viscosity of the lacquers, and the hardness, flexibility, and abrasion resistance of the films. The films were compared alm in regard to drying times, water, alkali, acid, and solvent resistance, gloss, resistance to cold checking, yellowing, print resistance, solvent compatibility, and rate of solvent escape. It is concluded that the rosin ester of 2,2,6,6tetramethylolcyclohexanol compares very favorably with the commercial maleic modified resins and is of potential value in lacquer formulations.

T

HE cyclic, pentahydric alcohol, 2,2,6,6-tetramethyloIcyclohexanol (TMC), first prepared by Mannich and Brose (a), has been shown to provide improved drying oils when esterified with unsaturated fatty acids (3). I n the present study, the rosin eater of 2,2,6,6-tetramethylolcyclohexanol appears to be superior to glycerol-rosin ester (ester gum) as an additive for nitrocellulose lacquers. Its performance, in fact, compares favorably with that of maleic modified rosin esters. OB I

EVALUATlQN OF ROSIN ESTER

In controlled tests, made by General Mills Research Laboratories, this rosin ester produced harder nitrocellulose lacquer film than did ester gum and made possible the preparation of solutions with higher solids content. At the same time, it outperformed maleic modified resins in two ways: It provided lacquer solutions of lower viscosity, and the films from these solutions were more resistant to alkali. I t appeared logical, therefore, to test the compound rather extensively as a lacquer additive. Although 2,2,6,6tetramethylolcyclohexanol rosin ester, like ester gum, is a hard, brittle, lighbcolored solid, it melts a t much higher temperatures120" to 125' C.as compared with 68' C. for ester gum. The first tests compared the hardness, abrasion resistance, and flexibility of films from nitrocellulose lacquers formulated with the rosin ester and with ester gum. In a standard lacquer formulation including 10 parts of RS nitrocellulose 0.5 second, 8 parts of ester gum, 6.26 parts of dibutyl phthalate, 12 parts of ethyl acetate, 24 parts of butyl acetate, and 40.3 parts of toluene, replacement of the ester gum with rosin ester increased the hardness of the resulting film about 50%, as the following data show:

Lacquer Containing Ester gum TMC rosin esttr

Flexibility ( I ) Eater gur? T M C rosin ester

PREPARATION OF ROSIN ESTER

Color (rosin scale) ( I ) , N-WG Bell and ring melting point ( 1 ) . 119-123.5° Arid number. 26.7

c.

'

The flexibility and abrasion-resistance of films from the two compositions were comparable-a significant fact, because hard films often tend to be brit,tle. The following data show actual abrasion and flexibility values: Abrasion (Taher method) Laoquer Containing Ester gum TMC rosin ester

To produce the rosin ester, freshly broken WW gum rosin (450 grams), 2,2,6,6-tetramethylolcyclohexanol(86 grams), and zinc oxide (1.0 gram) were placed in a 1-liter, 3-necked flssk provided with a ra id agitator, a gas inlet tube for flooding with inert gas, a con&nser for removing the water of reaction, and a take-off for applying vacuum a t the end of the condenser, when needed. The ap aratus was flushed several times with oxygenfree nitrogen, anathe reaction mixture was then heated to 240" C . over a period of 2 hours. Thereafter, the temperature was raised in 1 hour to 285" C. and was maintained there fur 5 hours more, vacuum being applied during the last 2 hours. Vigorous agitation was maintained throughout. The product was cooled to 150" C . and was poured into a container. It demonstrated the following properties:

Sward Rocker Hardness ( I ) 24 hours 72 hours air-dry air-dry 21 32 34 46

Lost in 300 Cyclea, Mg. 72 hours 24 hours

at 5 5 O C.

12.1 13.9

at 5 j 0

C.

23.4 23.5

Passed 1 i a Inch Mandrel 7 days 24 hours air-dry sir-dry Yes Yes Yes Yes

In determining film abrasion, a Taber abrasion tester, equipped with CS-10 stones and carrying 1OOO-grain weights on each of its arms was used. In this devlce, films are cast on plates and weighed. They are then placed on a turntable, sub'ected to the abrasive action of the stones for 300 cycles, and reweighed. Abrasion resistance is reflected by the milligrams of film which have worn away. Flexibility was determined by bending tin plates, coated with films 0.003inch thick, over a, 1/8.inch mandrel. If the film did not loosen, check, or otherwise fail, it was said to have "passed." In addition to showing the hardness, abrasion resistance, and flexibility of nitrocellulose lacquer films containing 2,2,6,6-tetramethylolcyclohexanol, tests also demonstrated that the amount of the rosin ester in a standard formulation can be doubled with1920

INDUSTRIAL AND ENGINEERING CHEMISTRY

September 1950

1921

Figure 1. Rate of Solvent Escape from Nitrocellulose Lacquer Solutions

The following quantities of dibutyl phthalate were necessary to provide the requisite hardness:

out sacrificingflexibility to produce compositions with high solids content. Available information indicates that this is not possible with ester gum. To obtain data on this subject, standard nitrocellulose lacquer solutions were prepared with 16 parts of the rosin ester rather than the usual 8 parts. The viscosity of all the lacquer solutions, like that of the standard %part rosin ester formulation, was A-2 on the Gardner-Holdt scale a t 25' C. The hardness, abrasion resistance, and flexibility of films from the various formulations are shown in Table I. Perhaps even more startling than the superiority of 2,2,6,6tetramethylolcyclohexanol rosin ester over ester gum in nitrocellulose lacquers is its favorable performance in comparison with the maleated rosin esters. In General Mills's experiments, it waa tested against four commercial maleated pentaerythritol or glycerol esters of rosin that are widely used in lacquer formulations, To make the tests strictly comparable, the plasticizer concentration of all formulations was adjusted so that their 0.0015-inch films had equal hardness after 1 hour a t 55' C. All the constituents except the plasticizer were constant in the standard formulations tested: RS nitrooelluloee 0.5 880. (?5% alcohol present) Resin Dibutyl phthalate Toluene Butyl acetate Ethyl acetate

Lacquer Containing TMC rosin ester Resin 1 Resin 2 Resin 3 Resin 4

Parts of Butyl Phthalate

VISCOSITIES. Viscosities of the lacquer solutions, as determined by the Gardner-Holdt method ( I ) , are indicated in Table 11. Obviously, these viscosities vary with the molecular weight of the resin used. Because the rosin ester is not polymeric, it produces compositions with lower viscosities than do the maleic modified resins, whose molecular weights are higher than those of ordinary esters.

TABLE 11.

NITROCELLULOSE LACQUER SOLUTIOVE

VISCOSITIES OF

(TMC id. maleated resins) Lacquer Containing 'PMC rosin ester Resin 1 Resin 2 Resin 3 Resin 4

Parts 14

Viscosity a t 25" C. (Gardner) A C C B-C

C

16 Varied

40.3

HARDNESS.Although the plasticizer content of all the Iacquers waa adjusted to equalize the hardness of 0.0015-iich films after 1 hour a t 55" C., the hardness in Sward ABRASIONRESISTANCE, AND FLEXIBILITY OF NITROCELLULOSE TABLE I. HARDNESS, units of the films was tested after 21 LACQUER FILMS CONTAINING 16 PARTS OF TMC ROSINESTER hours and after 7 days a t room temSward Rocker Lost in 3 0 0 4 ole Flexibilit Pssaed Hardness Abrasion, d g . I/dnch %andre1 perature. Results are recorded in Table 24 hours 72 hours 24 hours 72 hours 24 hours 24 hours 7 days Plasticizer Parts air-dry air-dry a t 550 C. a t 550 c. a t 55* C. air-dry airdry 111, which shows clearly that the hardTricresyl phoaphate 6.9 36 63 20.3 23.2 Yes Yes No ness of the film containing the rosin Tricreayl hosphate 10.0 .. 37 15.7 Yes Yes ester compares favorably with that of Dibutyl pithalate 6.9 48 64 24.6 26:s Yea No lacquers prepared from the other resins. 24 12

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INDUSTRIAL A N D ENGINEERING CHEMISTRY

1922

Figure 2.

Vol. 42, No. 9

Rate of Butyl Acetate Escape from Resin Solutions

previously, again using two 1000-gram weights and u CSlO TABLE111. HARDNESS OF SITROCELLULOSE LACQVERFILMS stone. After being aged for i days a t room temperature, the (0.0015-inch films. T > I C rosin ester v 8 . maleated resins) films were subjected to 300 abrasive revolutions and their loss of Sward Rocker Hardness weight was recorded. As Table V illustrates, the lacquers made 7 days with rosin ester performed on a par with those including the 1 hoiir a t 24 hoiirn a t a t rooin Lacqiier Containing 5 3 O C. room teinyi. temp. maleic modified resins. T M C rosin ester 24 26 38 DRYING TIME. Drying times of the nitrocellulose lacquer solu22 24 44 Resin 1 22 26 40 Resin 2 tions were determined by casting 0.0015-inch films on glass and 22 24 38 Resin 3 noting the time required for them t o rench the “lint-free” and the 24 28 36 Resin 4 “tack-free-to-foil” stages. The lint-free stage was defined as the point a t which cotton linters no longer adhered to the films; the tack-free-to-foil stage was determined as the point a t which OF SITROCELLTLOSE LACQCER FILMS the film had no adhesion whatever for aluminum foil. Results TABLE IV. FLEXIBILITY (0.00 18-Inch) of the drying tests are shown in Table VI. ‘ / d n c h Mandrel WATER,ALKALI, ACID, A K D SOLVENT RESISTANCE.JVater 1 hoiir a t 24 hours a t 7 Days at and alkali resistance of the lacquers were determined by coating Laeriiier Containing . 53’ C. room temp. Room Temp. T l I C rosin ester

Passed

Passed

Rcain 1

Passed

Passed

Resin 2

Passed

Passed

Reiin 3

Passed

Passed

Resin 4

Passed

Passed

Checked on 3/15 inch mandrel Failed $/a inch mandrel Failed a/g inch mandrel Checked o n 8/16 inch mandrel Checked on a/s inch mandrel

The film containing resin 1 is harder after i days than films with the other maleic modified rosin esters, probably because it includes more highly functional reagents and because less plasticizer was used initially. FLEXIBILITY. Flexibility was tested by bending lacquerroated tin plates over a mandrel as described above. Results of these tests are shown by Table IV, in which the term “checked” means incomplete failure of the film, probably because of good adhesion, and the term “failed” indicates that the film actually flaked and disintegrated. ABRASION RESISTANCE.Resistance of the lacquers to abrasion was nieasured with the Taber abrasion tester described

TABLE V.

ABRASIONRESISTAKCE OF KITROCELLCLOSE LACQUER FILMS

(Taber abraser, CS-10 stone, 1000-gram weights T M C rosin ester ua. nialeated resins) Loss of Weight Lacquer Containing after 300 Revolutions, Gram 0.0354 T M C rosin ester 0.0291 Resin 1 0.0288 Resin 2 0.0523 Resin 3 0.0444 Resin 4

O F SITROCELLULOSE L.4CQUERFILMS TABLE VI. DRYISGTIMES

(O.OOl3-inch, on glass-TXIC rosin eater u s . maleated mains) Drying Time, Min. Lacquer Containing Lint-free Tack-free-to-foil TBlC rosin ester 4.0 10-20 10.0 10-20 Resin 1 4.8 10 Resin 2 4.0 10-20 Resin 3 4.5 10-20 Resin 4

5.pt.mber

1950

INDUSTRIAL AND ENGINEERING CHEMISTRY

1923

Figure 3. Rate of Amy1 Acetate Escape from Resin Solutions jected to a series of the following c~.rlcs: 1 hour a t 49' C., 1 hour at -29' C., and 0,5 hour at room temperature. After ( T h l C rosin ester u8. maleated reoins) each complete cycle of these three temLacquer HOAc and HCI Benzene peratures, the films were examined and Containing Watar Reaistance 5% NaOH Resistance Resistance Resistance the results were tabulated (Table VIII). 12-16 Disspl,,ed T M C rosin 21 hours sl. blushing, no 24 hours,. not blushed No effect eater increde after 72 hours. but disintegrated in nun. Because flowed films had thick edges Completely recovered severs1 small spots. in 24 hours N o recover for these that raused premature checking, brushed films served in this test, which covered spots, cause ofprocably pinholes bfin film single and double coats of lacquer on Resin 1 Orange peel increased 3 hours, blushed, 7.5 N o effect Dissolved after 72 hours. Rehours disintegrated. immediately both wood and steel as well as a single covered 24 hours No recovery coat of lacquer over a commercial sealer Resin 2 Orange peel increased 24 hours, disintegrated. No effect Blushed o.5-o.,5 after 72 hours. ReNo recovery hour on yood. covered 24 hours Resin 3 Orange peel increased 24 houre, disintegrated. HOAc, blushed Dissolved YELLOWING. Yellowing was deterafter 72 hours. ReN o recovery after 24 houro 3-5 min. mined by flowing nitrocellulose films "21, no effect oovered 24 hours Resin 4 Orange peel increased 24 hours, disintegrated. No effect Dissolved onto glass, drying them for 48 hours, after 72 hours. ReNo recovery 3-5 min. subjecting them to a 3.5-ampere ultracovered 24 hours violet light at a distance of 1 foot for 8 hours, and then comparing their rolor wit,h that of similar films which had test tubes, allowing the resulting films to dry a t room temperaremained in the dark during the testing period. Although ture for 72 hours, and then immersing the tubes in water a t room those made with 2,2,6,6-tetramethylolcyclohexanolrosin ester temperature and in 5% sodium hydroxide. Acid and solvent yellowed the most (see Table IX), all the rosin-conresistance tests were made by placing drops of benzene, hydrochloric acid, and acetic acid on films which had been dried on glass plates at TABLE VIII. RESISTANCE OF NITROCELLULOSE LACQUER FILMSTO room temperature for 72 hours; the drops of TEMPERATURE CHANGES liquid were covered with watch glasses to minimize ( T M C rosin ester u.s. maleated rerrins) evaporation. From the results shown in Table Cold Check Cycle VII, it is obvious that the rosin ester produced Lacquer Single Double 6ingle Double 6ingle coat Solution coat coat coat coat over lacquer nitrocellulose lacquer with exceptionally good Containing on steel on steel on wood on wood sealer on wood alkali resistance. Checked on Passed 18 Checked on Checked on c~~~~~~~~~~ G ~ ~ ~1 the 1 ~ nitrocellulose ~ . T M C rosin Passed 24 ester cycles 13th cycle cycles 15th rycle 2nd cycle Paesed 24 Checked on Paseed 18 Checked on Checked on lacquer films showed excellent gloss, with no Resin 1 cycles 21st cycle cycles 15th cycle 3rd cycle detectable differences among those made from Resin 2 Passed 24 Checked on Passed 18 Checked on Checked on cycles 13th cycle cycles 15th cycle 2nd cycle different resins. Resin 3 Passed 24 Checked on Passed 18 Passed 18 Checked on cycleu 12th cycle cycles cycles 4th cycle COLDCHECKCYCLES, To test the resistance Resin Passed 24 Checked on Passed 18 Checked on Cherlied on of the lacquer films to changes in temperature, cycles 13th cycle cycles 15th cycle 2nd cycle coated stcd plates and wooden panels were sub-

TABLE VII. WATER,ALKALI,ACID,AND SOLVENT RESIST.4NCE LACQUER FILMS

O F ~ITROCELLVLOSE

1924

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

Figure 4.

Vol. 42, No. 9

Rate of Ethyl Acetate Escape from Resin Solutions

taining lacquers yellowed intensely. It was noted, however, that the presence of maleic anhydride tended to decrease the yellowing. PRINTRESISTANCE ( 1 ) . The print resistance of 0.003-inch nitrocellulose lacquer films, dried at room temperature for 72 and 96 hours and a t 55’ C. for 6 hours, was determined in the following manner: A single thickness of cheesecloth was spread over the film and subjected to the pressure of a metal block weighing 3 pounds per square inch; the films were observed

Figure 5.

after 8 to 12 hours, and the amount of print was rated on a scale of 1 to 10, the smaller number indicating “complete print” and the larger number “no print.” Although the results, recorded in Table X, reveal that commercial resins 1 and 4 produce the most print-resistant lacquers, they also show that the rosin ester film was virtually printresistant after 96 hours at room temperature. SOLVENTCOMPATIBILITY. In General Mills’s tests, all the resins proved to be compatible with isopropyl alcohol, butyl

Rate of Toluene Escape from Resin Solutions

September 19SO

INDUSTRIAL AND ENGINEERING CHEMISTRY

1925

XI. RATEOF SOLVENTESCAPEFROM NITROCELLULOSE TABLE IX. YELLOWING OF NITROCELLULOSE LACQUERFILMS TABLE ON GLASSUNDER ULTRAVIOLET LIQHT ( T M C rosin ester V I . mealeated resins. All films yellowed intensely) Amount of Yellowing Lacquer Containing Least

LACQUER SOLUTIONS

( T M C rosin ester u8. maleated resins) Time of g Escape Maximrim of Bolvent, Escape Solution 3 Hours Hours’ T M C rosin ester 90.22 95 Resin 1 02.87 95 Resin 2 90.44 168 Resin 3 91.41 144 Resin 4 91.21 144

+I

Moat

TABLE x. PRINT RESISTANCEOF o.oo3-INCH ~ITROCEIALULOSE INCH LACQUER FILMS TO WEIGHT OF 3 POUNDSPER SQUARE (1 = Complete print, 10 = no print. T h I C rosin ester ua. maleated resins) Dearee of Print 72 hours a t 96 hours a t Lac qurr Containing room temp. room temp. Th4C rosin ester Reain 1 Resin 2 Reuin 3 Reain 4

alcohol, ethyl acetate, butyl acetate, amyl acetate, acetone, methyl ethyl ketone, diacetone alcohol, methyl isobutyl ketone, Cellosolve, butyl Cellosolve, Cellosolve acetate, and Trol-u-oil. Compatibility was established by titrating 10 ml. of a 60% solution of each lacquer resin with a minimum of 4 ml. of solvent. RATEOF SOLVENT ESCAPE.The following procedure was used to determine the rate at which various solvents escaped from lacquer compositions containing the test resins and from solutions of the resins themselves: One gram of each nitrocellulose lacquer solution and 5 grams of a 50% solution of each resin were weighed into %inch paint can covers. These covers were kept at constant temperature and humidity (SO’ F., 50% relative humidity) and were weighed a t 10-minute intervals for the first hour, at 20-minute intervals for the second and third hours, at 60-minute intervals for the next 5 hours, and at 24-hour intervals until they reached constant wight. Some of the results are indicated graphically on Figures 1 through 5. A summary of the rates a t which solvents escaped from the lacquer solutions is included in Table XI, which shows that lacquer containing the rosin ester did not lose as much solvent as did the other compositions, but did lose its maximum amount of solvent rapidly. Results of tests on the resins in various solvents, listed in Table XII, show that the rosin ester lost amyl acetate and ethyl acetate a t a slower rate than did the other resins.

Maximum Escape of Solvent, % 93.34 96.04 94.42 94.97 94.63

~-

FROM TMC ROSIN TABLE XII. RATEOF ESCAPEOF SOLVENTS ESTER,MALEATED RESINS,AND ESTERGUM

Resin T M C rosin enter

Solvent

Time of % Escape of Maximum Solvent after Escape 1 Hour, 40 Min. Hour;

Maximum Encape of Solvent, yo

Butyl acetate Amyl acetate Ethyl acetate Toluene

50.41 37.82 50.95 60.64

527 67 1 67 1 503

85.19 82.77 81.99 84.56

Reain 1

Butyl acetate Amyl acetate Ethyl acetate Toluene

67.79 41.03 63.48 70.34

480 480 480 312

92.28 89.08 85.57 91.54

Reain 2

Butyl acetate Amyl acetate Ethyl acetate Toluene

55.22 40.47 58.01 59.97

600 624

86.03 79.68 84.24 85.67

Resin 3

Butyl acetate Amyl acetate Ethyl acetate Toluene

59.34 45.16 60.15 62.39

552 528 528

87.13 83.52 84.61 86.29

Resin 4

Butyl aoetate Amyl acetate Ethyl acetate Toluene

54.36 41.46 53.45 60 * 88

480 528 528 360

84.37 80.25 81.18 85.28

Eater gum

Butyl acetate Amyl acetate Ethyl acetate Toluene

70.08 43.93 65.01 71.86

288 288 312 192

86.41 85.71 80.82 85.65

600

600

600

much as it has many unexplored possibilities, it should be a fruitful source of study for the lacquer manufacturer. General Mills Research Laboratories, therefore, are now producing 2,2,6,6tetramethylolcyclohexanol on a pilot plant basis and are making samples available for evaluation. ACKNOWLEDGMENT

The authors gratefully acknowledge the technical assistance of Marjorie Iwen Buckley.

CONCLUSION

Together, then, General Mills’s tests indicate that 2,2,6,6tetramethylolcyclohexanol, formed by the reaction of cyclohesanone with formaldehyde, is a promising new compound for the protective coating industry. Because the rosin ester of 2,2,6,6-tetramethylolcyclohexanoi is highly compatible with nitrocellulose in the presence of plasticizers, is superior to ester gum in many lacquer compositions, and, in controlled tests, has at least equaled maleated resins in over-all performance, it appears to be a potentially valuable lacquer additive. Inas-

%

LITERATURE C m E D

Gardner, H. A,, and Sward, G. G., “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors,” 11th ed., Bethesda, Md., Henry A. Gardner Laboratory, 1960. (2) Mannioh, C., and Brow, W., Bar., 56, 833 (1923). (3) Wittcoff, H., J. Am. Oil Chemists’ Soc., 26, 167 (1949). (1)

RECEIVEDMaroh 1, 1950. Presented before the Division of Paint, Varnish, and Plssties Chemistry at the 117th Meeting of the AUEIUUAN CHBMICAL BOCIETY. Detroit, Mich. Paper 107, Journal Series, Reararch Laboratories, General Mills, Inc.