US3188224A

US3188224A - Nitrocellulose composition and process of preparation

Info

Publication number: US3188224A
Application number: US148830A
Authority: US
Inventors: Matalon Raphael
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1961-10-31
Filing date: 1961-10-31
Publication date: 1965-06-08
Anticipated expiration: 1982-06-08

Description

United States Office I LIV'UVI MY Ell 106-81 3,188,224 Patented June 8, 1965 Delaware No Drawing. Filed Oct. 31, 1961, Ser. No. 148,830 20 Claims. (Cl. 106-195) This invention relates to unique, stable, colloidal dispersions, or sols, of nitrocellulose in voltaile organic liquid compositions which are not solvents for nitrocellulose, and to methods for preparing these colloidal dispersions.

In the usual manufacture of nitrocellulose, the nitrocellulose is obtained as a water-wet mass which is dehydrated by the displacement of the water with alcohol, and the product is normally sold in the form of alcoholwet fibers or cubes. Because the bulk density of nitrocellulose in these forms is relatively low the amount of nitrocellulose that can be shipped in a container is small in relation to its actual density.

Since the majority of the ultimate uses for nitrocellulose require it to be in solution, the buyer of alcohol-wet nitrocellulose expends considerable time and labor in dissolving the nitrocellulose in the preparation of lacquers, adhesives, etc.

It is also well known that utilization of nitrocellulose in lacquers, adhesives, and other important fields of nitrocellulose application has been based from the inception of the art to the present time, on the practice of dissolving the nitrocellulose in an active nitrocellulose solvent-or solvent mixture with dilution of the composition with cheap hydrocarbon diluents, insofar as possible, in the interests of economy. Heretofore, however, the maximum amount of cheap hydrocarbon diluent which could be used in any particular instance has been limited largely by the dilution ratio of the particular nitrocellulose solvent being employed for the particular hydrocarbon to be utilized for dilution. In most applications, however, the amount of hydrocarbon diluent which can be safely used without encountering precipitation of the nitrocellulose upon evaporation of the volatile vehicle is somewhat less than the maximum amount determined by dilution ratio. In the interest of more economical formulation practice, therefore, there has been concerted effort over the years to find means whereby more of the cheap hydrocarbon diluent and less of the considerably more expensive active nitrocellulose solvent can be utilized in nitrocellulose lacquers and other nitrocellulose applications.

It is an object of the present invention to provide a process by which water-wet nitrocellulose can be simultaneously dehydrated and transformed into a flowable concentrate of nitrocellulose in a nonaqueous liquid dispersant, thus simplifying the dehydration and achieving economics for the manufacturer.

It is a further object of the invention to provide flowable nitrocellulose concentrates which permit the shipping of a greater weight of nitrocellulose in standard containers than heretofore possible, and with greater safety.

It is still another object of the invention to provide flowable nitrocellulose concentrates that are more easily handled and converted into finished products by the consumer, particularly from the standpoint of the ease with which they can be converted into solutions.

It has now been discovered in accordance with this invention how to prepare clear, homogeneous, viscous, flowable nitrocellulose compositions in organic liquid vehicles which are substantially higher in hydrocarbon content and substantially lower in active nitrocellulose solvent content than heretofore known. The unique nitrocellulose compositions which are obtained by a novel process in accordance with this invention are colloidal dispersions, or sols, of nitrocellulose in organic liquid compositions which comprise a major amount of a volatile aliphatic, cycloaliphatic or aromatic hydrocarbon or halogenated aliphatic hydrocarbon, a minor amount of active nitrocellulose solvent and further containing as an essential ingredient a polar organic compound containing a hydroxyl or keto group that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of the polar compound in water to below 0.5% by weight in an amount sufiicient to effect formation of stable sols of nitrocellulose in said organic liquid compositions. These stable colloidal dispersions are hereinafter termed nitrocellulose organosols to distinguish them from conventional orthodox nitrocellulose solutions from which they distinguish in several important respects, as will be pointed out and discussed hereinafter. The proportion of active nitrocellulose solvent to hydrocarbon diluent in the nitrocellulose organosols of this invention is substantially below the amount necessary to form conventional, orthodox nitrocellulose solutions.

Although the new nitrocellulose organosols of this invention superficially resemble orthodox nitrocellulose solutions by being clear, homogeneous, viscous, flowable compositions, they are distinguishable from orthodox nitrocellulose solutions in several important respects as follows:

(I) Unmodified with resins or plasticizers, they produce upon evaporation of the volatile liquid components clear, strongly adherent and substantially nonshrinking films on glass surfaces, whereas orthodox nitrocellulose solutions unmodified with resins or plasticizers produce films which exhibit marked shrinkage upon drying and which are nonadherent to glass.

(2) The nitrocellulose organosols of this invention exhibit marked thixotropy, with pronounced temporary reduction of viscosity when subjected to high shear. This is because these nitrocellulose organosols are colloidal swollen aggregates of nitrocellulose molecules dispersed in organic liquid systems which have only swelling action on the nitrocellulose. High shear temporarily dissociates these swollen aggregates with consequent reduction of viscosity during application of the high shear.

Orthodox nitrocellulose solutions, on the other hand, unless modified by addition of materials which impart thixotropic properties thereto, normally are not thixotropic. This is because orthodox nitrocellulose solutions use excessive active nitrocellulose solvents and are true Newtonian systems in which the nitrocellulose in substantially molecularly dissolved in the solvent.

(3) The nitrocellulose organosols of this invention can be diluted substantially with a lean mixture of such as 4:1 by volume mixture of a volatile aromatic hydrocarbonzaliphatic alcohol mixture, e.g., 4:1 toluenezbutyl alcohol, without coagulation or separation of the nitrocellulose from the diluted composition, and the thus diluted composition upon evaporation also produces clear, strongly adherent, substantially nonshrinking films on glass. Orthodox nitrocellulose solutions, on the other hand, will tolerate only limited dilution with lean mixtures such as hydrocarbomalcohol mixtures, the amount of such dilution being governed largely by the dilution ratio characteristic of the active solvents present in the nitrocellulose solution. Greater dilution results in coagulation and separation of the nitrocellulose from the solution.

The capacity of the nitrocellulose organosols of this invention for dilution with lean hydrocarbomalcohol mixtures without precipitation of the nitrocellulose, combined with the capacity for such diluted organosol compositions to form clear, adherent, nonshrinking films upon evaporation are essential characteristics of these organosol compositions, and are of great economic significance in the formulation and application of nitrocellulose coatings, adhesives, and the like.

The process in accordance with this invention for preparing the new nitrocellulose organosols comprises forming a nitrocellulose solution in an organic liquid vehicle comprising a volatile nitrocellulose solvent having a boiling point below about 65 C., and a volatile, liquid hydrocarbon selected from the group consisting of aliphatic, cycloaliphatic, and aromatic hydrocarbons, and halogenated aliphatic hydrocarbons having a boiling point substantially above about 65 C., the proportion of said volatile nitrocellulose solvent to said volatile liquid hydrocarbon being substantially in excess of the dilution ratio characteristic of said volatile nitrocellulose solvent for said volatile liquid hydrocarbon, evaporating said volatile nitrocellulose solvent from said nitrocellulose solution at a temperature up to about 65 C., and preferably at reduced pressure, until said volatile nitrocellulose solvent remaining therein is reduced to an amount between about 50% by weight, based on the weight of nitrocellulose, and a lower amount at which incipient phase separation begins, and adding at any stage of the process a polar organic compound containing a hydroxyl or keto group that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of the polar compound in water to below 0.5% by weight in an amount within the range between about 0.1 and about 125 parts per part of nitrocellulose by weight, and preferably between about 0.1 and about 0.5 part. In this process, therefore, the polar organic compound can be present in the nitrocellulose solution, or can be added during the volatile nitrocellulose solvent removal or can be added upon completion of volatile nitrocellulose solvent removal. In a preferred and economical embodiment of the process in accordance with this invention, water-wet nitrocellulose is subjected to azeotropic distillation in the presence of a volatile aromatic hydrocarbon until all water has been removed to produce an aromatic hydrocarbon-wet nitrocellulose prior to formation of the nitrocellulose solution.

Nitrocellulose organosols containing up to 50% by weight of nitrocellulose have been prepared by the above process.

Nitrocellulose organosols in accordance with this invention can also be prepared by direct high shear mixing of the ingredients of the nitrocellulose organosol composition, as for example, in a Baker-Perkins mixer.

In the preparation of the new nitrocellulose organosols, it is postulated that the polar organic compound having a hydrophobic hydrocarbon residue orients itself at the interface between the solvent swollen nitrocellulose molecules and the hydrocarbon phase by hydrogen bonding of the polar group thereof to residual hydroxyl groups in the nitrocellulose, with the hydrophobic hydrocarbon residue thereof oriented outwardly in the hydrocarbon phase. The nitrocellulose sol is thus believed to be stabilized by the hydrophobic layer of the polar additive which shields the nitrocellulose from the diluent during stripping off of active nitrocellulose solvent, or during dilution of the organosol with lean solvents, or during evaporation of the volatile vehicle in the process of film formation.

It is apparent, therefore, that the polar organic compound having a hydrophobic hydrocarbon residue is essential and must meet certain requirements to be suitable for the purposes of this invention. More specifically, the polar group of the compound must be capable of strong hydrogen bonding with residual hydroxyl groups present in the nitrocellulose and with active hydrogen atoms adjacent to the nitrate substituent groups in the nitrocellulose in order to form a stable interfacial shield between the nitrocellulose and the hydrocarbon diluent. Moreover, the hydrocarbon residue of the polar compound should have sufiicient hydrophobic capacity to promote compatibility with the hydrocarbon phase, without, however, being so strongly hydrophobic as to promote desorption of the polar compound away from the interfacial boundary of the nitrocellulose into the hydrocarbon phase. It is well known, of course, that the hydrophobic character of polar organic compounds increases with increasing length or size of the hydrocarbon residue. In general, it had been found that polar compounds having methyl, ethyl, propyl, and isopropyl hydrocarbon residues do not have sufficient hydrophobic capacity for the purposes of this invention, whereas polar compounds having heptyl, octyl and higher hydrocarbon residues have excessive hydrophobic capacity for the purposes of this invention. Thus, when the hydrocarbon residue of the polar compound is an acyclic aliphatic residue it should contain from 4 to 6 carbon atoms. On the other hand, when the hydrocarbon residue is wholly or in part cycloaliphatic, it can contain from 6 to 8 carbon atoms. In any event, the proper balance of polar and hydrophobic groupings in such compounds should be such as to give it a solubility of at least 0.5%, by weight, in water.

Polar organic compounds having a hydrophobic hydrocarbon residue which meet the requirements of this invention have been found to include primary straight chain aliphatic alcohols having from 4 to 6 carbon atoms in the alkyl group, such as butyl, amyl and hexyl alcohols; monoalkyl ethers of ethylene glycol and diethylene glycol having 4 to 6 carbon atoms in the alkyl groups, such as the monobutyl, monoamyl and monohexyl ethers of ethylene glycol and diethylene glycol; alkyl esters of hydroxycarboxylic acids having 4 to 6 carbon atoms in the alkyl groups, such as butyl, amyl and hexyl lactates, dibutyl, diamyl and dihexyl tartrates, tributyl, triamyl and trihexylcitrates, and the like; cycloaliphatic alcohols and ketones having 6 to 8 carbons in the hydrocarbon residue, such as cyclohexanol, methyl cyclohexanol, ethyl cyclohexanol, and cyclohexanone, methyl cyclohexanone, ethyl cyclohexanone; also camphor and benzyl alcohol; and mixtures of any such compounds.

The most preferred polar organic compound having a hydrocarbon residue for the purposes of this invention is n-butanol. Other preferred polar organic compounds include cyclohexanol, dibutyltartrate, and the monobutyl ether of ethylene glycol. Less preferred polar organic compounds include amyl and hexyl alcohols and other polar organic compounds containing amyl or hexyl radicals, since the greater hydrophobicity of these compounds requires their use in larger amounts to accomplish the purposes of this invention. For example, the following table shows the amount of each of several ditferent polar organic compounds which it was found necessary to add to a solvent-stripped concentrate obtained by solvent stripping a nitrocellulose solution containing Parts by weight Nitrocellulose 21 Ethyl alcohol 9 Acetone 70 Toluene to the first sign of haziness in order to prepare nitrocellulose organosols exhibiting satisfactory clear, adherent, nonshrinking film formation characteristics:

The polar compound having a hydrocarbon residue is present in the compositions of this invention in an amount sufiicient to efiect formation of stable sols of nitrocellulose in the organic liquid compositions employed, and this is generally within the range between about 0.1 and about 1.25 parts per part of nitrocellulose by weight, preferably between about 0.1 and about 0.5.

The polar compound need not be present in the original nitrocellulose solution before stripping otf the volatile nitrocellulose solvent in order to effect formation and stabilization of the nitrocellulose organosol upon stripping the volatile solvent from the solution. However, the presence of the polar compound during stripping is preferred. Since a small amount of moderately volatile polar compound such as butanol is evaporated from the solution during stripping of the volatile nitrocellulose solvent therefrom, it is desirable to add such moderately volatile polar compound to the solution in an amount in excess over the amount necessary or desired in the final nitrocellulose organosol, the excess being added to compensate for the amount evaporated during stripping.

Stripping of the volatile nitrocellulose solvent from the nitrocellulose solution may be carried out at any convenient temperature up to about 65 C. Temperatures appreciably above about 65 C. tend to promote degradation of the nitrocellulose. It is desirable to employ temperatures near or above the boiling point of the volatile nitrocellulose solvent in order to promote rapid stripping of the solvent. For the same reason, it is desirable, but not necessary, to strip the solvent under sub-atmospheric pressure. Stripping is continued until the amount of volatile nitrocellulose solvent remaining in the composition is below about 50% by weight, based on the weight of nitrocellulose. If desired, stripping may be carried to the point where incipient phase separaion in the organosol composition is noticed as evidenced by formation of haze. Stn'pping beyond this point is undesirable, since it leads to pronounced phase separation and nonhomogeneity in the organosol composition. Since the weight and composition of the starting nitrocellulose solution are known, it is possible to follow the course of the stripping operation by collecting and analyzing the stripped volatiles. The composition of the stripped volatiles may be quickly estimated by diluting with a large volume of water and measuring the volume of the insoluble fraction in a graduated cylinder. Additional information on composition can be obtained by chromatographic analysis. Because of the difiiculty in completely condensing the stripped highly volatile nitrocellulose solvent, the analytical information in the subsequent examples, if anything, err on the side of showing more volatile nitrocellulose solvent in the stripped concentrates than is actually present.

Substantially all of the commercial types and grades of nitrocellulose are suitable for the purposes of this invention having nitrogen contents from about 10.9% to about 13.5% nitrogen, and viscosity characteristics from centipoise type to 1000 second type. One-half /2) second type nitrocellulose having 12% nitrogen content has been employed in the examples, since this is widely used in the formulation of lacquers and other protective coatings, adhesives, inks, and the like.

This invention requires the use of a volatile nitrocellulose solvent having a boiling point below about 65 C. in order to facilitate removal thereof by means of solvent stripping. Acetone is the preferred solvent because of its active solvent action on nitrocellulose and ease of removal by stripping. However, any solvent for nitrocellulose which has a boiling point below about 65 C. is suitable, and includes by way of example, methyl alcohol, methyl formate, ether-alcohol mixtures, and the like.

Any volatile liquid hydrocarbon compound having a boiling point substantially above 65 C. is suitable for the purposes of this invention, including by way of example, straight and branched chain aliphatic hydrocarbons such as heptane, isooctane, decane, decene, petroleum spirits, and the like; cycloaliphatic hydrocarbons such as cyclohexane, methyl cyclohexane, ethyl cyclohexane, and the like; aromatic hydrocarbons such as benzene, toluene, xylene, and the like; various halogenated aliphatic hydrocarbons such as ethylene dichloride, perchlooroethylene, tetrachloroethane, tribromoethylene, and the like; and mixtures thereof. The boiling point requirement is to insure retaining as much as possible of the hydrocarbon compound in the organosol compositions through the solvent stripping step. Toluene is preferred, since it is widely used in lacquer and protective coating applications because of its desirable evaporation characteristics, solvency for numerous resins and plasticizers, and other well known characteristics.

The mixtures of volatile nitrocellulose solvent and volatile liquid hydrocarbon employed to prepare the nitrocellulose solution obviously must be active solvent mixtures for the nitrocellulose. This means, therefore, that the proportion or ratio of volatile nitrocellulose solvent to volatile liquid hydrocarbon in such mixtures must be substantially in excess over the dilution ratio characteristic of the volatile nitrocellulose solvent for the volatile liquid hydrocarbon. The amount of such volatile nitrocellulose solvent-volatile liquid hydrocarbon mixture employed is at least sutficient to form a fluid, stirrable nitrocellulose solution, and is generally within the range from about 3 to about 10 parts by weight of the mixture for each part by weight of nitrocellulose, depending somewhat on the viscosity characteristic of the nitrocellulose, and the desired percentage of nitrocellulose in thefinal nitrocellulose organosol produced. It is a relatively simple matter to select the composition and amount of such volatile nitrocellulose solvent-volatile liquid hydrocarbon mixture for preparing the nitrocellulose solution, which after stripping will produce a nitrocellulose organosol having the desired nitrocellulose content.

It has been found that the nitrocellulose organosols of this invention are readily adapted to conventional lacquer and protective coating applications, since, in addition to their unique capacity for tolerating dilution with hydrocarbon-alcohol mixtures, they can be readily modified with a wide range of conventional resins, plasticizers, softening agents, pigments and fillers, and similar modifying agents for nitrocellulose coating compositions. Moreover, if desired, they can be thinned with conventional nitrocellulose solvents. These nitrocellulose organosols, prior to thinning with hydrocarbon-alcohol mixtures are stable with respect to phase separation indefinitely, and can therefore be stored and shipped as desired. After thinning and modifying with suitable resins, plasticizers and the like, the thinned compositions can be applied by any of the conventional methods of application, such as spraying, brushing, dipping, roller coating, and the like.

The general nature of the invention having been set forth, the following examples illustrate some specific embodiments of the invention. It is to be understood, however, that the invention is in no way limited to the examples, since this invention may be practiced by the use of various modifications and changes within the scope of the invention as described herein.

Example I (A) A nitrocellulose solution was prepared with 30 parts by weight of ethyl alcohol-wet 36 second nitrocellulose of 12% nitrogen content and containing approximately 30% by weight of denatured ethyl alcohol, 70 parts by weight of acetone, and parts by weight of toluene. This solution while being stirred was solvent stripped in a vacuum vessel at approximately 60 C. under a vacuum of approximately 100 mm. of mercury until 100 parts by weight of volatiles had been stripped from the solution. The stripped volatiles were collected in two Dry Ice cooled traps, combined, and subjected to chromatographic analysis, which indicated the combined volatiles to contain approximately 6 parts by weight of Nitrocellulose 21 Denatured ethyl alcohol 3 Toluene 65.5 Acetone This stripped concentrate prepared in the absence of a polar organic compound showed very pronounced phase separation and dried to a chalky film. However, upon the addition of 9 parts by weight of cyclohexanol, a clear, homogeneous, viscous liquid resulted which dried without shrinking to a clear, adherent film on glass. It also exhibited thixotropy.

(B) The procedure of A was repeated, except that the original nitrocellulose solution contained 9 parts by weight of cyclohexanol. The stripped concentrate was a clear, homogeneous, viscous fluid which dried to a clear, continuous, adherent film on glass. The stripped concentrate was calculated to contain Parts by weight Nitrocellulose 21.0 Denatured ethyl alcohol 3.0 Cyclohexanol 9.0 Toluene 65.5 Acetone 10.0

This stripped concentrate exhibited thixotropy.

To 10 grams of the above stripped concentrate was added cc. of a diluent composed of Cc. Toluene 43 Butyl acetate 4 Acetone 4 Ethyl alcohol 1 Parts by weight 40 10 the resulting diluted organosol composition was clear, homogeneous and fluid, and upon evaporation produced a clear, adherent, nonshrinking film on glass.

Toluene n-Butanol Example 2 A nitrocellulose solution was prepared with 90 parts by weight of butanol-wet /2 second nitrocellulose of 12% nitrogen content and containing approximately 30% by weight of n-butanol, 210 parts by weight of acetone, 120 parts by weight of toluene, and 6 parts by weight of dibutyltartrate. This solution while being stirred was solvent stripped in a vacuum vessel at approximately 60 C. under a vacuum of approximately 100 mm. of mercury until approximately 275 parts by weight of volatiles had been stripped from the solution. Based on chromatographic analysis of the stripped volatiles, the resulting stripped concentrate, amounting to approximately 151 parts by weight was calculated by difference to contain:

Percent by weight This concentrate was clear, homogeneous flowable nitrocellulose organosol which exhibited thixotropy and which upon evaporation produced a clear, adherent, nonshrinking film on glaSS.

To 10 grams of the above concentrate was added 13 cc. of a diluent consisting of Cc. Toluene 40 n-Butanol 10 The resulting diluted composition was a clear, homogeneous flowable nitrocellulose organosol exhibit thixotropy which upon evaporation produced a clear, adherent, nonshrinking film on glass.

Example 3 Sixty (60) parts by weight of water-wet /2 second nitrocellulose having 12% nitrogen content and containing approximately 30% by weight of water were immersed in 258 parts by weight of xylene and subjected to azeotropic distillation under a vacuum of approximately mm. of mercury until 206 parts by weight of volatiles had been removed and analysis of the stripped volatiles showed that all water in the nitrocellulose had been removed. To the xylene-nitrocellulose mixture remaining, consisting of Parts by weight Nitrocellulose 42 Xylene 70 Percent by weight Nitrocellulose 40.4 Cyclohexanol 19.2 Acetone 14.7 Xylene 25.7

This concentrate was a clear, homogenous flowable nitrocellulose organosol exhibiting thixotropy, which upon evaporation produced a clear, adherent, nonshrinking film on glass.

To 10 grams of the above concentrate was added 13 cc. of a diluent consisting of Toluene 40 n-Butanol 10 The resulting diluted organosol composition exhibiting thixotropy was clear, homogeneous and fluid, and upon evaporation produced a clear, adherent, nonshrinking film on glass.

Example 4 A nitrocellulose solution was prepared with 30 parts by weight of ethyl alcohol-wet /2 second nitrocellulose having 12% nitrogen content and containing approximately 30% by weight of ethyl alcohol, 70 parts by weight of acetone, 10 parts by weight of the mono-n-butyl ether of ethylene glycol, and 40 parts by weight of toluene. This solution while being stirred was solvent stripped in a vacuum vessel at approximately 60 C. under a vacuum of approximately 100 mm. of mercury until approximately 91 parts by weight of volatiles had been stripped from the solution. Based upon chromatographic analysis of the stripped volatiles, the resulting stripped concentrate was calculated to contain Percent by weight Nitrocellulose 35.5 Mono-n-butyl ether of ethylene glycol 16.9 Acetone 11.3 Ethyl alcohol 5.1 Toluene 31.2

Toluene 40 n-Butanol 10 The resulting diluted organosol composition exhibiting thixotropy was clear, homogeneous and fluid, and upon evaporation produced a clear, adherent, nonshrinking film on glass.

Example Substantially the same procedure as set forth in Example 3 was followed, employing toluene instead of xylene to azeotropically strip water from the water-wet nitrocellulose. To the toluene-nitrocellulose mixture remaining after stripping off the water, and consisting of 42 parts by weight nitrocellulose and 70 parts by weight toluene was added 20 parts by weight cyclohexanol and 140 parts by weight acetone to form a nitrocellulose solution. This solution was then stripped of volatiles by the same procedure set forth in Example 3 until the final weight of the stripped concentrate was 90 parts by weight, containing 46.7% by weight of nitrocellulose.

This stripped concentrate was a clear, homogeneous, very viscous fiowable nitrocellulose organosol exhibiting thixotropy which upon evaporation produced a clear, adherent, nonshrinking film on glass.

To grams of the above concentrate was added 13 cc. of diluent consisting of Cc. Toluene 40 n-Butanol 10 A nitrocellulose solution was prepared with 90 parts by weight of isopropyl alcohol-wet /2 second nitrocellulose having 12% nitrogen content and containing approximately 30% by weight of isopropyl alcohol, 210 parts by weight of acetone, 132 parts by weight of perchloroethylene, and 20 parts by weight of dibutyltartrate. This solution while being stirred was solvent stripped in a vacuum vessel at approximately 60 C. under a vacuum of approximately 100 mm. of mercury until 352 parts by weight of volatiles had been stripped from the solution, and the stripped concentrate remaining weighed 100 parts by weight. Based on analysis of the stripped volatiles, the composition of the stripped concentrate was calculated by difierence to contain Percent by weight Nitrocellulose 35.6 Di-n-butyltartrate 1 1.3 Perchloroethylene 30.0 Acetone 12.0 Isopropanol 11.1

Cc. Toluene 40 n-Butanol 10 The resulting diluted organosol composition exhibiting thixotropy was clear, homogenous and fluid, and upon evaporation produced a clear, adherent, nonshrinking film on glass.

Following substantially the procedure set forth above, clear, homogeneous flowable nitrocellulose organosols were propared with heptane, and with isooctane, in place of perchloroethylene. The heptane-containing and isooctane-containing organosols each exhibited thixotropy and each formed clear, adherent, nonshrinking films on glass upon evaporation, and each, when diluted with a diluent consisting of 40 cc. toluene and 10 cc. n-butanol, as set forth for the perchloroethylene-containing organosol, as set forth above, was a clear, homogeneous flowable fluid exhibiting thixotropy which upon evaporation produced clear, adherent, nonshrinking films on glass.

Example 7 A nitrocellulose solution was prepared with 30 parts by weight of ethyl alcohol-wet /2 second nitrocellulose having 12% nitrogen content and containing approximately 30% by weight of ethyl alcohol, 70 parts by weight of acetone, parts by weight of toluene, and 10 parts by weight of cyclohexanol. This solution while being stirred was solvent stripped in a vacuum vessel at approximately 60 C. under a vacuum of approximately 100 mm. of mercury until the first incipient sign of phase separation (faint cloudiness) was noticed. At this point approximately 116 parts by weight of volatiles had been stripped from the solution, and stripping was discontinued. Approximately 1 cc. of ethyl alcohol added to the stripped concentrate caused disappearance of the cloudiness. Based upon chromatographic analysis of the stripped volatiles, the composition of the stripped concentrate was calculated by difference to contain Parts by weight Nitrocellulose 21.0 Cyclohexanol 9.7 Acetone 10.0 Ethyl alcohol 2.9 Toluene 41.1

This stripped concentrate was a clear, homogeneous viscous nitrocellulose organosol exhibiting thixotropy, which dried to a clear, adherent, nonshrinkiing film on glass.

To 10 grams of the above stripped concentrate was added 15 cc. of a diluent consisting of The resulting diluted organosol composition was clear, homogeneous and fluid, and upon evaporation produced a. clear, adherent, nonshrinking film on glass.

Following substantially the same procedure set forth above, clear, homogeneous, viscous nitrocellulose organosol compositions exhibiting thixotropy were prepared with cyclohexanone, camphor, monobutyl ether of ethylene glycol, monobutyl ether of diethylene glycol, and benzyl alcohol in place of cyclohexanol, and these organosols showed substantially the same dilution characteristics and film-forming characteristics as set forth above for the nitrocellulose organosol containing cyclohexanol.

By contrast, however, when cyclohexanol was replaced by acetone, diacetone alcohol, Cellosolve acetate (ethoxyethylacetate) butyl acetate, 2-ethylhexylacetate, dibutylphthalate, butyl Cellosolve acetate (butoxyethylacetate), monoethyl ether of diethylene glycol, monoethyl ether of ethylene glycol, methyl isobutyl carbinol, or cetyl alcohol, satisfactory nitrocellulose organosols in accordance with this invention were not obtained.

This example clearly demonstrates that it is not the capacity of the polar compound to function as nitrocellulose solvents which determines suitability for the purposes of this invention, since esters such as butyl acetate, ethoxyethyl acetate, 2-ethyl hexyl acetate, and butoxyethyl acetate, known to be good solvents for nitrocellulose, nevertheless failed to produce nitrocellulose organosols having the characteristics of this invention. On the other hand, cyclohexanol, butanol, benzyl alcohol, amyl alcohol, and hexyl alcohol, recognized as having no solvency for nitrocellulose, have clearly been demonstrated by the examples to produce satisfactory nitrocellulose organosols in accordance with this invention. The evidence is clear, therefore, that it is the capacity of polar organic compounds to form an interfacial protective layer between solvent-swollen nitrocellulose molecules and the diluent phase by hydrogen bonding between the hydroxy or keto groups of the polar organic compound and the nitrocellulose molecules which determines suitability for the purposes of this invention, and not the capacity of the polar organic compound to function as a nitrocellulose solvent.

Example 8 A nitrocellulose solution was prepared with 29.4 parts by weight of n-butanol-wet second nitrocellulose having 12% nitrogen content and containing 28.5% by weight of n-butanol, 4.6 parts by weight of additional n-butanol, 40 parts by weight of toluene, and 70 parts by weight of acetone. This solution while being stirred was solvent stripped in a vacuum vessel under a vacuum of 18 to 20 inches of mercury while gradually raising the temperature of the solution from room temperature to approximately 54 C. until 88 parts by weight of volatiles had been stripped from the solution. Based on chromatographic analysis of the stripped volatiles, the resulting stripped concentrate was calculated by diflerence to contain Percent by weight Nitrocellulose 37.3 n-Butanol 19.0 Acetone 11.1 Toluene 32.6

This concentrate was a clear, homogeneous fiowable nitrocellulose organosol exhibiting thixotropy, which upon evaporation produced a clear, adherent, nonshrinking film on glass.

To grams of the above concentrate was added 13 cc. of a diluent consisting of Ce. Toluene 40 n-Butanol 10 The resulting diluted organosol composition exhibiting thixotropy was clear, homogeneous and fluid, and produced upon evaporation a clear, adherent, nonshrinking film on glass.

Example 9 A stable nitrocellulose organosol composition was prepared by charging a Baker-Perkins mixer with the following ingredients and then mixing until the resulting composition was homogeneous:

Parts by weight of V2 second nitrocellulose of 12% nitrogen content and containing 30% by weight of denatured ethyl alcohol 115.3 Parts by weight of cyclohexanol 38.4 Parts by weight of acetone 23.2 Parts by weight of toluene 44.9

Ce. Toluene 40 n-Butanol 10 The resulting diluted organosol composition was clear, homogeneous and flowable, and upon evaporation produced a clear, adherent, nonshrinking film on glass.

From the foregoing description, it is apparent that the present invention provides new and unique nitrocellulose compositions having important advantages over previously known compositions, and also provides methods for their manufacture. An important characteristic and advantage of these new compositions is their capacity to be successfully thinned with hydrocarbon-alcohol mixtures, so that the thinned mixtures can contain as high as 70- 75% of hydrocarbon diluent. For the lacquer formulator this makes possible a substantial reduction in the cost of making lacquers and other protective coatings with nitrocellulose. Moreover, since the new compositions of this invention are viscous, flowable, colloidal dispersions of nitrocellulose in organic liquid vehicles, there are further economies for the formulator in that he does not require means for dissolving the usual dehydrated fibrous or cubed nitrocellulose. Mixing time in formulating finished lacquers and coating compositions is therefore markedly reduced, since it is only necessary to add the required thinner, resin solution, plasticizer, etc., and blend by stirring for a few minutes.

For the nitrocellulose manufacturer, this invention provides a new and economical form for supplying nitrocellulose to the trade, since a greater weight of nitrocellulose as nitrocellulose organosol containing on the order of to by weight of nitrocellulose can be shipped in a standard container than is possible with conventional dehydrated fibrous or cubed nitrocellulose. There are also manufacturing economies in the present invention in processing water-wet nitrocellulose into a form suitable for use by the nitrocellulose forrnulator.

I claim:

1. As a new composition, a colloidal dispersion of nitrocellulose in an organic liquid composition containing from about 20% to about 50% by weight of nitrocellulose, said organic liquid composition consisting essentially of (a) a major amount of a volatile hydrocarbon compound selected from the group consisting of aliphatic, cycloaliphatic and aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and mixtures thereof, having a boiling point above C.,

(b) a minor amount, at least about 20% and not exceeding about 50% by weight, based on nitrocellulose weight, of a volatile nitrocellulose solvent having a boiling point below about 65 C., the ratio of said hydrocarbon to said volatile nitrocellulose solvent being at least about 1.5 and not more than about 6.6 by weight,

(c) and containing as an essential ingredient a polar organic compound having a polar group selected from the class consisting of hydroxyl and keto groups that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of said polar organic compound in water to below 0.5% by weight in an amount from about 0.1 to about 1.25 parts per part by weight of nitrocellulose, and suflicient to effect formation of a stable sol of said nitrocellulose in said organic liquid composition,

said colloidal dispersion of nitrocellulose being characterized by (1) being a clear, homogeneous, flowable, thixotropic material,

(2) the capacity to tolerate dilution without separation of the nitrocellulose when 10 grams of said colloidal dispersion are diluted with 15 cc. of a 4:1 by volume mixture of a volatile hydrocarbon:aliphatic alcohol mixture,

(3) and the capacity to produce clear, adherent, non- 13 shrinking films on glass and also when diluted as described in (2) above.

2. A composition in accordance with claim 1 in which the polar organic compound is butanol.

3. A composition in accordance with claim 1 in which the polar organic compound is dibutyltartrate.

4. A composition in accordance with claim 1 in which the polar organic compound is cyclohexanol.

5. A composition in accordance with claim 1 in which the polar organic compound is the mono-n-butyl ether of ethylene glycol.

6. A composition in accordance with claim 1 in which the volatile hydrocarbon compound is an aromatic hydrocarbon.

7. A composition in accordance with claim 1 in which the volatile hydrocarbon compound is an aliphatic hydrocarbon.

8. A composition in accordance with claim 1 in which the volatile hydrocarbon compound is a halogenated aliphatic hydrocarbon.

9. A composition in accordance with claim 1 in which the volatile nitrocellulose solvent is acetone.

10. A process for preparing stable colloidal dispersions of nitrocellulose comprising (1) forming a nitrocellulose solution in an organic liquid vehicle consisting essentially of (a) a volatile nitrocellulose solvent having a boiling point below about 65 C. and (b) a volatile liquid hydrocarbon compound selected from the group consisting of aliphatic, cycloaliphatic, and aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and mixtures thereof, having a boiling point above about 65 C., the proportion of said volatile nitrocellulose solvent to said volatile liquid hydrocarbon compound being substantially in excess of the dilution ratio characteristic of said volatile nitrocellulose solvent for said volatile liquid hydrocarbon,

(2) evaporating said volatile nitrocellulose solvent from said nitrocellulose solution at a temperature up to about 65 C. until said volatile nitrocellulose solvent remaining therein is reduced to an amount between about 50% by weight, based on the weight of nitrocellulose, and a lower amount at which incipient phase separation begins and the ratio of said hydrocarbon to said volatile nitrocellulose solvent is at least about 1.5 and not more than about 6.6 by weight,

(3) and adding at any stage of the process a polar organic compound containing a polar group selected from the class consisting of hydroxyl and keto groups that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of said polar organic compound in water to below 0.5% by weight in an amount from about 0.1 to about 1.25 parts per part by weight of nitrocellulose.

11. A process in accordance with claim in which the polar organic compound is butanol.

12. A process in accordance with claim 10 in which the polar organic compound is dibutyltartrate.

13. A process in accordance with claim 10 in which the polar organic compound is cyclohexanol.

14. A process in accordance with claim 10 in which the polar organic compound is the mono-n-butyl ether of ethylene glycol.

15. A process in accordance with claim 10 in which the volatile nitrocellulose solvent is acetone and the volatile liquid hydrocarbon is toluene.

16. A process in accordance with claim 10 in which step (2) of the process is carried out under subatmospheric pressures.

17. A process in accordance with claim 10 in which step (3) of the process is carried out by incorporating the polar organic compound in the nitrocellulose solution before performing step (2) of the process.

18. A process in accordance with claim 10 in which step (3) of the process is carried out by incorporating the polar organic compound into the nitrocellulose composition after performing step (2) of the process.

19. A process for preparing stable colloidal dispersions of nitrocellulose comprising (1) subjecting water-wet nitrocellulose to azeotropic distillation in the presence of a volatile aromatic hydrocarbon until all water is removed to produce an aromatic hydrocarbon-wet nitrocellulose,

(2) forming a nitrocellulose solution from the aromatic hydrocarbon-wet nitrocellulose in an organic liquid vehicle consisting essentially of (a) a volatile nitrocellulose solvent having a boiling point below about 65 C. and (b) a volatile liquid hydrocarbon compound selected from the group consisting of aliphatic, cycloaliphatic, and aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and mixtures thereof, having a boiling point above 65 C., the proportion of said volatile nitrocellulose solvent to said volatile liquid hydrocarbon compound being substantially in excess of the dilution ratio characteristic of said volatile nitrocellulose solvent for said volatile liquid hydrocarbon,

(3) evaporating said volatile nitrocellulose solvent from said nitrocellulose solution at a temperature up to about 65 C. until said volatile nitrocellulose solvent remaining therein is reduced to an amount between about 50% by weight, based on nitrocellulose weight, and a lower amount at which incipient phase separation begins and the ratio of said hydrocarbon to said volatile nitrocellulose solvent is at least about 1.5 and not more than about 6.6 by weight,

, (4) and adding at any stage of the process, after step (1) above, a polar organic compound containing a polar group selected from the class consisting of hydroxyl and keto groups that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of said polar organic compound in water to below 0.5 by weight in an amount from about 0.1 to about 1.25 parts per part of nitrocellulose by weight.

20. A process for preparing stable colloidal dispersions of nitrocellulose comprising subjecting to high shear mixing a mixture of about 20% to about 50% by weight of nitrocellulose and the balance an organic liquid composition consisting essentially of (a) a major amount of a volatile hydrocarbon compound selected from the group consisting of aliphatic, cycloaliphatic and aromatic hydrocarbons, halogenated aliphatic hydrocarbons, and mixtures thereof, having a boiling point above 65 C.

(b) a minor amount, at least about 20% and not exceeding about 50% by weight, based on nitrocellulose weight, of a volatile nitrocellulose solvent having a boiling point below about 65 C., the ratio of said hydrocarbon to said volatile nitrocellulose solvent being at least about 1.5 and not more than about 6.6 by weight, and

(c) a. polar organic compound having a polar group selected from the class consisting of hydroxyl and keto groups that is capable of hydrogen bonding with nitrocellulose molecules and at least one hydrocarbon residue of more than 3 carbon atoms but less than the number of carbon atoms which reduce the solubility of said polar organic compound in water to below 0.5% by weight in an amount from about 0.1 to about 1.25 parts per part by weight of nitrocellulose, and sufiicient to efiect formation of a stable sol of said nitrocellulose in said organic liquid composition, said colloidal dispersion of nitrocellulose being characterized by (1) being a clear, homogeneous, flowable, thixotropic material,

(2) the capacity to tolerate dilution without separation of the nitrocellulose when 10 grams of said colloidal dispersion are diluted with 15 cc. of a 4:1 by volume mixture of a volatile hydrocarbonzaliphatic alcohol mixture,

(3) and the capacity to produce clear, adherent, nonshrinking films on glass and also when diluted as described in (2) above.

1 6 References Cited by the Examiner UNITED STATES PATENTS 12/40 Donlan 106-191 11/55 Johnson 106198 4/56 Voris 106-470 11/57 Sloan l06-17O 7/58 Voris 106-170 FOREIGN PATENTS 8/34 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner. 15 MORRIS LIEBMAN, Examiner.

Claims

1. AS A NEW COMPOSITION, A COLLODIAL DISPERSION OF NITROCELLULOSE IN AN ORGANIC LIQUID COMPOSITION CONTAINING FROM ABOUT 20% TO ABOUT 50% BY WEIGHT OF NITROCELLULOSE, SAID ORGANIC LIQUID COMPOSITION CONSISTING ESSENTIALLY OF (A) A MAJOR AMOUNT OF A VOLATILE HYDROCARBON COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC, CYCLOALIPHATIC AND AROMATIC HYDROCARBONS, HALOGENATED ALIPHATIC HYDROCARBONS, AND MIXTURES THEREOF, HAVING A BOILING POINT ABOVE 65*C., (B) A MINOR AMOUNT, AT LEAST ABOUT 20% AND NOT EXCEEDING ABOUT 50% BY WEIGHT, BASED ON NITROCELLULOSE WEIGHT, OF A VOLATILE NITROCELLULOSE SOLVENT HAVING A BOILING POINT BELOW ABOUT 65*C., THE RATIO OF SAID HYDROCARBON TO SAID VOLATILE NITROCELLULOSE SOLVENT BEING AT LEAST ABOUT 1.5 AND NOT MORE THAN ABOUT 6.6 BY WEIGHT, (C) AND CONTAINING AS AN ESSENTIAL INGREDIENT A POLAR ORGANIC COMPOUND HAVING A POLAR GROUP SELECTED FROM THE CLASS CONSISTING OF HYDROXYL AND KETO GROUPS THAT IS CAPABLE OF HYDROGEN BONDING WITH NITROCELLULOSE MOLECULES AND AT LEAST ONE HYDROCARBON RESIDUE OF MORE THAN 3 CARBON ATOMS BUT LESS THAN THE NUMBER OF CARBON ATOMS WHICH REDUCE THE SOLUBILITY OF SAID POLAR ORGANIC COMPOUND IN WATER TO BELOW 0.5% BY WEIGHT IN AN AMOUNT FROM ABOUT 0.1 TO ABOUT 1.25 PARTS PER PART BY WEIGHT OF NITROCELLULOSE, AND SUFFICIENT TO EFFECT FORMATION OF A STABLE SOL OF SAID NITROCELLULOSE IN SAID ORGANIC LIQUID COMPOSITION, SAID COLLOIDAL DISPERSION OF NITROCELLULOSE BEING CHARACTERIZED BY (1) BEING A CLEAR, HOMOGENEOUS, FLOWABLE, THIXOTROPIC MATERIAL, (2) THE CAPACITY TO TOLERATE DILUTION WITHOUT SEPARATION OF THE NITROCELLULOSE WHEN 10 GRAMS OF SAID COLLOIDAL DISPERSION ARE DILUTED WITH 15 CC. OF A 4:1 BY VOLUME MIXTURE OF A VOLATILE HYDROCARBON:ALIPHATIC ALCOHOL MIXTURE, (3) AND THE CAPACITY TO PRODUCE CLEAR, ADHERENT, NONSHRINKING FILMS ON GLASS AND ALSO WHEN DILUTED AS DESCRIBING IN (2) ABOVE.