Effect of Dehydration of Nitrocellulose on Orange Peel of Sprayed Lacquer Films CARROLL A. HOCHWALT AND PAUL E. MARLING, Thomas & Hochwalt Laboratories, Inc., Dayton, Ohio The amount of orange peel in a sprayed lacquer gree in sprayed lacquer Jilms. Various viscosities film is accelerated by the increase of water in the of nitrocellulose may be used to obtain lacquer films liquid that wets the nitrocellulose. A double dehy- that are practically free from orange peel when the dration process in which the treatment of the nitro- nitrocellulose is completely dehydrated and formucellulose with a low-boiling alcohol, followed by a lated with medium slowly evaporating liquids of higher boiling alcohol, removes more water from the proper solvent pourer. Industrial application upnitrocellulose and thereby reduces the orange peel in pears to be promising. Saving of the sanding and a sprayed lacquer film. Slowly evaporating solvents repair costs appears to more than balance the inin combination with completely dehydrated nitro- creased cost of moisture-free nitrocellulose and more cellulose reduce the orange peel to a negligible de- slowly evaporating solvents.
M
ANY commercial nitrocellulose lacquers have a tendency when sprayed to give a pimpled surface appearance generally known as “orange peel.” This
pimpled surface, in greater or less degree, appears to have been a characteristic of sprayed lacquer films since their inception. Its occurrence has been ascribed to various factors such as composition of the lacquer and faulty spraying technic. It is generally conceded that the principal demand of the public is for a perfectly smooth, glossy surface. Therefore, the characteristic slightly pimpled surface of sprayed lacquer films must be smoothed out by sanding and polishing operations. This is a very great economic loss, both in regard to the destruction of an otherwise valuable protective material and in the consumption of labor hours. The investigation covered by this paper was inspired by the belief that the prevalence of orange peel in sprayed lacquer films was a basic weakness which lay hidden in lacquer formulation. The course of the research led through a minute examinbtion of raw materials, formulation procedure, and application technic. As the data were accumulated and correlated, it gradually became evident that the presence of water in the sprayed film played a niajor role in the production of orange peel, and further efforts were concentrated upon the study of this factor. Corollary to it was the effect of medium- or low-boiling solvents on the leveling of lacquer films. Much effort has been expended in minimizing orange peel by improving spraying technic and obtaining a proper balance between solvents, plasticizers, and diluents, but practically no fundamental studies have been made of the conditions of the nitrocellulose for the purpose of eliminating this pernicious effect. This paper is devoted to a brief description of a development that accomplishes the practically complete exclusion of water from all of the elements which enter into the production of sprayed lacquer films. Of these, the removal of water from nitrocellulose was found to be the most important, since it is almost universal practice in lacquer manufacture to start with nitrocellulose that is wet with ethyl alcohol containing from 8 to 10 per cent of water. It was definitely demonstrated that nitrocellulose containing these quantities of water always produces orange peel in the lacquer film, while this defect is practically absent when the water content of the nitrocellulose is less than one per cent. Naturally this result presupposes the use of proper formulation and correct spraying technic. The method of attack (9) has been to extract the waterwet nitrocellulose with an alcohol of moderately slowly evapo-
rating quality, and to incorporate medium slowly evaporating solvents in the formulation of the lacquer. The use of this procedure has reduced the orange peel tendency of lacquer films to a point where sprayed lacquer coatings give a smooth surface without sanding.
PREPARATION OF EXPERIMENTAL FILMS Obviously, correct spraying technic is an important factor in the production of uniform lacquer films, and, in the preparation of the comparison coatings required by this investigation, all the spraying was performed by one operator. Every effort was made to standardize all of the spraying conditions including the following: Distance of spra nozzle from coated surface Horizontal speec! of nozzle Pressure of air line and tank Atmos heric humidity Age o?lac uer Viscosity lacquer
08
In spite of this care, in making one series of fifty panels in this work, only forty were rated as satisfactory, the remaining ten being from fair to poor. All experimental lacquer films were sprayed from pigmented lacquers of automobile type, formulated, and aeplied under carefully standardized conditions, so that accurate comparisons could be made. Standard pigment pastes were made up and blended with the various nitrocellulose solutions. These mixtures were reduced with a uniform thinner to obtain a viscosity of approximately 100 seconds by Saybolt Universal standard at 25” C., and to yield a spraying lacquer having a solid content of about 12 per cent. Three double coats were sprayed on oilprimed and oil-surfaced steel panels. The general composition of the base lacquers compared in this series of tests is as follows: LACQUER
REDUCING THINNER
INQREDIENT INQREDIENT P e r cent b y weight sec. 30% wet nitrocellulose Rosin ester Dibutyl phthalate Blown castor oil Chrome yellow pigment Amyl acetate (Pentacetate) Amyl alcohol (Pentasol) Petroleum n a p h t h s (Troluoil) Toluene Xylene Total
17 5 2 4
12 25 5 13 14
3 100.0
.. .. ..
40 12 24 24
100.0
Water-wet nitrocellulose was washed with a number of different U uids on a suction Biichner funnel untjl the specific gravity the wash liquid was the same as that of the original. In general, 300 grams of the water-wet nitrocellulose were ex-
190
09f
February, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
tracted with 600 cc. of liquid in succeeding washing and suctiondrying operations. The final roduct was made to contain 70 per cent by weight of nitrocehose, the remainder being the wetting liquid. In several instances there was added a washin operation with a second liquid, in which the same thorougf extraction procedure was used. The water content of the nitrocellulose wet with amyl alcohol (Pentasol) was determined by using 50 grams of the wet nitrocellulose and 200 cc. of carbon tetrachloride in a 500-cc. Erlenmeyer flask. The liquids were distilled by heating in a water bath and condensing the volatile portion. A graduated moisture tube was inserted between the flask and condenser, and the amount of water was read directly upon the graduations (1). The moisture was removed from the air supply for the spray gun by passing the air through a cylinder of anhydrous calcium chloride.
EFFECTOF DEHYDRATIONS Table I shows the effects on orange peel of the dehydration of samples of second viscosity, water-wet nitrocellulose by means of four different alcohols, one acetate, and two hydrocarbons, Anhydrous ethyl alcohol was found to be impractical as a dehydrating agent, as it is a solvent for water-wet nitrocellulose and gelatinizes the fiber. With increasing water contents of the mixture, however, nitrocellulose becomes insoluble, so that it is possible to extract it satisfactorily with a solution containing up to 92 per cent ethyl alcohol and 8 per cent water. In commercial operations a soft fluffy fiber is obtained by the use of a 90 to 10 mixture of ethyl alcohol and water. The butyl, amyl (Pentasol), and propyl alcohols all gave satisfactory washed fiber. Amyl acetate (Pentacetate) was not satisfactory because it is a partial solvent for water-wet nitrocellulose and forms an emulsion d f i cult to break. The hydrocarbons did not dehydrate the nitrocellulose to any extent and were unsatisfactory for this purpose, The nitrocellulose washed with amyl alcohol, containing only 1.5 per cent water based on the 30 per cent of the liquid wetting the nitrocellulose, gave the least evidence of orange peel, and that washed with 90 per cent ethyl alcohol-10 per cent water showed the most pronounced orange peel of this series. OF TABLEI. EFFECT
SINGLE DEHYDRATION
WATER
CONTENT OF LIQUID
DEHYDRATING LIQCID
ORANQE P E E L R A T I N Q OP
CONDITION OF WETTINQ WASHED THE NITRONITROCELLULOSE CELLULOSD % ._
SPRAYED FILM"
*.
Gelatinized Not sprayed 10 4 Soft and fluffy 2-3 2 Soft a n d fluffy 3 2 Soft and fluffy 2 1.5 S o f t and fluffy Not sprayed Emulsified 5 Poor dehydration 5 Poor dehydration Toluene 5 Orange peel rating: 1, no orange peel. 2, trace orange peel; 3, slight orange peel; 4, considerable orange peel; b a d orange peel.
hols, one acetate, and two hydrocarbons. Absolute alcohol gelatinized the nitrocelluIose as in the first series, and the other alcohols behaved in a manner similar to that of the singly dehydrated series. Toluene appears to be promising, since it reduced the water content of the 30 per cent liquid of the wet nitrocellulose from 10 to 2.4 per cent, and the sprayed lacquer gave an orange peel rating of 2. Double dehydration improved the orange peel ratings of practically all of the lacquers over those shown by single dehydration. In the series of experiments shown in Table 111, the nitrocellulose portions were dried by blowing with moisture-free air and the wetting liquids were immediately added. The lacquer produced by nitrocellulose wet with anhydrous ethyl alcohol gave a rating of 2 to 3, while the nitrocellulose wet with 90 per cent ethyl alcohol gave a rating of 4. Dry nitrocellulose wet with straight amyl alcohol gave a product with zero water content and yielded a sprayed film with practically no orange peel effect. It was also shown that the addition of 1 and 3 per cent of water to the amyl alcohol proportionally raised the orange peel rating of the resultant lacquers. In the absence of water in the nitrocellulose and a formulation of medium slowly evaporating solvents, it has been observed that the substitution of rapidly evaporating alcohols or acetates in the base lacquer increases the orange peel, and the advantages gained by complete dehydration and moderately slowly evaporating liquids may thus be completely destroyed by too rapid setting of the lacquer films. OF DEHYDRATION BY AIR BLOWIXQ TABLE 111. EFFECT L I Q U I D 3 A D D E D TO
AIR-BLOWN
NITROCELLULOSE
%
LIQUID
WATER
%
%
..
..
Not sprayed 4 2 3 1-2 Not sprayed
2:4
2-3
10 1 1 1
5
Table I1 shows the results of double dehydration of '/2 second viscosity nitrocellulose on the orange peel effect of lacquers made from materials so treated. Portions of waterwet nitrocellulose were first extracted with 90 per cw$ ethyl alcohol and then further dehydrated ,with each of four alco-
SECONDARY DEHYDRATINQ L I Q U I D S
sec. nitrocellulose wet with amyl alcohol (Pentasol) sec. nitrocellulose wet with amyl alcohol (Pentasol) 5 t o 6 sec. nitrocellulose wet with amyl alcohol (Pentasol) i/z
NITRO-
Gelatinized Soft and fluffy Soft and fluffy Soft and fluffy Soft and fluffy Emulsified Poor dehydration Soft and fluffy
0 1.0 3.0
2-3 4 2 1-2 2-3 3
CONTESTO F ORANGEPEEL LIQUID WETTINQ RATINQ O F THE NITROCELLULOSESPRAYED FILMS A.
SECONDARY DEHYDRATINQ
0
TABLEIV. EFFECTOF COMMERCIAL DEHYDRATION
5,
O F L I Q V I D ORANQE PEEL WETTINO R A T I N Q OF CONDITION OF WASHED THE SPRAYED NITROCELLULOSE CELLULOSE F I L m
0 10.0
Table N - A shows some orange peel results obtained from lacquers produced from nitrocellulose doubly dehydrated on a commercial scale. The water-wet nitrocellulose was first extracted with 90 to 92 per cent by weight of ethyl alcohol, and then further dehydrated with amyl alcohol. The l/1 second viscosity nitrocellulose with a water content of one per cent based on the 30 per cent wetting liquid gave the least orange peel, and those with and 5 to 6 second viscosities yielded very satisfactory sprayed films.
..
WATER CONTENT
WATERCONTENT OF ORANQE PEEL LIQUID WETTINQ RATINQO F THE NITROCELLULOSESPRAYED FILMS
Anhydrous ethyl alcohol 90% ethyl alcohol Butyl alcohol 100% amyl alcohol (Pentasol) 99% amyl alcohol (Pentasol) 97% amyl alcohol (Pentasol)
....
TABLE11. EFFECTOF DOUBLEDEHYDRATION
191
B.
Butyl Amyl Amyl Amyl
1.0
1-2
1.0
2
2.6
2-3
I / & SEC. NITROCELLULOSE. S I N G L E DEHYDRATION LIQUIDS
alcohol alcohol (Pentasol) alcohol Pentasol) alcohol {Pentasol)
2.0 1.4 2.0 3.4
2-3 1-2 2 2-3
Table IV-B shows the results of varying contents of water in second viscosity nitrocellulose wet with amyl alcohol to the extent of 30 per cent. As the water content of the nitrocellulose increases, the degree of orange peel becomes greater. The industrial application of these principles appears to be promising. Several lacquer manufacturers have prepared formulations that include the practice of the principles of this research. These lacquer formulations have been prepared in black, several shades of blue, and several shades of
INDUSTRIAL AND ENGINEERING CHEMISTRY
192
gray. These formulations are typical of the one used in this experimental research. In general these formulations consist of the following ingredients:
higher gloss than the regular production work. The saving in sanding has been estimated to be more than equal to any increase in the cost of the lacquer containing the moisturefree nitrocellulose and higher evaporating solvents.
REDUCINQ LACQUER THINNER INORWDIENT INOREDIENT Parts by weight 20-25
Pentasol Toluene Petroleum naphtha Xylene
,..
6-6.5 3-3.2 4-5.0 7-12.0
...
20-30.0 5-10.0
35-40
10-15 10-15 5-10
,..
... 15-20 20-25 20-25
...
Several automobile manufacturers have used these formulations on their production line. In one instance forty cars ,were sprayed and finished without sanding. The results obtained were satisfactory and in accord with the laboratory spray tests, and in many cases the iilm was smoother and had
VoI. 27, No. 2
ACKNOWLEDGMENT
The authors are indebted to The Sharples Solvents Corporation of Philadelphia, which financed this work, for permission to publish this paper. LITERATURE CITED (1) Hercules Powder Company, method obtained by private communication. (2) Hochwalt and Marling, U. S. Patent 1,961,120 (May 29, 1934). R~CEIVE September D 21, 1934. Presented before the Diviaion of Paint and Varnish Chemiatry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14. 1934.
Effect of Continued Heating on Asphalts ALFREDW. SIKES'AND CALVINH. COREY,~ Western Electric Company, Chicago, Ill. Continued heating, at the temperature and under ihe conditions of the experiments reported here, appreciably affects many properties of certain asphalts and asphaltic materials. Of the materials and the characteristics studied, it was found that aiscosiiy and penetration changed most rapidly for the first few days or weeks of heating, whereas flash points were least affected, even after many weeks. The softening points changed regularly but markedly throughout the kst. A general decrease in acidity, which finally reached a constant figure, after a n initial increase in the case of the two asphalts was noted in each of the rnaferials examined. It is realized that the results here reported may not be duplicated with different materials or under other conditions of heating.
T
HE authors recently became interested in
ascertaining the extent of the changes to be expected in some of the general physical and chemical properties of asphalts and asphaltic compounds resulting from heating such materials for varying periods of time a t elevated temperatures. From theoretical considerations it would seem probable that many of the characteristics of a given asphalt would change considerably under such conditions of heating, and experience based on general observation has borne out this supposition. A fairly comprehensive review of the literature, however, has revealed few data in standard reference works or in the periodical literature for the past twenty-five years concerning the extent of the progressive changes i n t h e p r o p e r t i e s of 1 Present address, Engineering Division, Publio Works Administration, Washington, D. C. 1 Prewnt address, Univenity of Michigan, Ann Arbor, Mich.
asphalts which are brought about by continued heating a t definite temperatures. Abraham (1) has tabulated a summary of the chemical changes that occur upon subjecting bitumens and pyrobitumens to increasing temperatures. He does not, however, give any data concerning the time of heating involved or the magnitude of progressive changes resulting in various properties due to continued heating a t definite temperatures. Some work was reported in 1917 by Hixon and Hands (3) concerning changes in certain chemical and physical properties resulting from heating various asphalts a t temperatures up to 300' C. (572" F.), but the time of heating in each case was limited to 5 hours, which is too short a period to use as a basis for predicting changes that might occur in similar materials after days or weeks of heating a t any given temperature. Spiel-
I20
100
M
10
40
20
0
0
IN PROPERTIES OF AN ASPHALTOF 91 O F. SOFTENING FIQURE 1. CFIANQES POINT ON C O ~ N U EHEATINQ D AT 340 O F.
