MOVIE FILM CLEANING SOLVENT

Abstract: This invention relates to a solvent system and process for cleaning photographic film, especially cellulose triacetate polymer movie film. The solvent system comprises n-propyl bromide and an alkyl bromide in which the alkyl group contains 4 to 7 carbon atoms.

Description: MOVIE FILM CLEANING SOLVENT Background of the Invention: This invention relates to an environmentally friendly solvent having no flash point for use in cleaning photographic film, in particular, cellulose triacetate movie film. Movie film is designed for repetitive use and, as such, must be durable and true to its original shape and size over a long period of time. Curling, cracking or peeling of the film is not tolerable. In addition, the film must be kept clean from skin oils, dust and other matter which can be deposited during film processing and handling. It is generally necessary to clean movie film several times during its life. Cleaning is conveniently done by immersing the film in a solvent which may be contemporaneously subjected to sonication. The solvent may be contained in a tank and the film is fed through the tank via film guides while it is simulta¬ neously brushed with special rollers. Alternatively, the film may be passed through solvent wetted rollers. The film is dried as it is removed from the tank and is rewound. The solvent must be capable of cleaning the film without leaving a deposit on the film and without causing any distortion or damage to the film. Heretofore, a preferred solvent has been 1,1,1- trichloroethane. However, this solvent is no longer favored as it has been banned worldwide from manufacture for solvent applications due to environmental concerns. Environmental concerns could be attenuated if an alkyl bromide solvent could be used instead of 1 , 1 , 1 -trichloroethane. This would be especially so if n-propyl bromide could be the solvent as it has good cleaning characteristics, a low boiling point and is environmentally friendly, e.g., its Ozone Depletion Potential is low as compared to 1 , 1 , 1 -trichloroethane. Also, n-propyl bromide does not possess a flash point. The low boiling point is advantageous as it insures that there will be no or very little solvent residue left on the cleaned film. The lack of a flash point contributes to safety in use. n-Propyl bromide was tried on several types of film and was found to be suitable except for films based on cellulose triacetate polymer. For this last type of film, the n-propyl bromide caused unacceptable curling. Despite this fatal infirmity, the benefits of using n-propyl bromide made it well worthwhile to investigate the problem and to search for a solution which would yield a n-propyl bromide containing solvent which did not cause film curl, but which still retained the benefits of n-propyl bromide. Another alkyl bromide was investigated. n-Butyl bromide was an effective solvent for cleaning cellulose triacetate films. It did not cause film curl or otherwise damage the film. Despite these beneficial qualities, n-butyl bromide was not considered a panacea as it does possess a flash point. The Invention: This invention relates to an environmentally friendly solvent system which does not possess a flash point and which is suitable for use in cleaning cellulose triacetate polymer based camera film. The solvent systems of this invention comprise 10 to 70 wt% n-propyl bromide product and 90 to 30 wt% alkyl bromide in which the alkyl group contains 4 to 7 carbon atoms. The weight percentages are based upon the total weight of n-propyl bromide product and alkyl bromide in the solvent system. The n-propyl bromide product used in the solvent systems of this invention can be pure n-propyl bromide or any of the commercially available products which are preferably of high purity, i.e., at least 98+ wt% n-propyl bromide. Lower purity product may be used, say 94 to 98 wt% n-propyl bromide. The main impurity in most all cases is isopropyl bromide. Isopropyl bromide is a process impurity and its presence can be reduced by distillation. Thus, for the purposes of this invention, the term "n-propyl bromide product" is to mean pure n-propyl bromide or a product which contains n-propyl bromide and up to 6 wt% normally occurring process impurities, the most prominent of which is often isopropyl bromide. The most preferred n-propyl bromide product is that which is 99+ wt% pure n-propyl bromide. The weight percentages are based upon the total weight of the n-propyl bromide product. The other constituent in the solvent system is alkyl bromide in which the alkyl group contains 4 to 7 carbon atoms. Exemplary alkyl groups are: n-butyl, isobutyl, n-pentyl, sec- butyl, 2-methylbutyl, 3-methylbutyl, n-hexyl, 2,3-dimethylbutyl, n-heptyl and the like. Preferred alkyl groups are the n-alkyl groups. It is preferred that the alkyl bromide be a primary bromide; however, secondary and tertiary bromides are also suitable. Also preferred are those alkyl bromides having a boiling point within 35 centigrade degrees of the boiling point of n- propyl bromide. The most preferred alkyl bromide is 1 -bromobutane, i.e., n-butyl bromide. For the purposes of this invention, the term "alkyl bromide" is meant to cover both a single alkyl bromide compound and a mixture of two or more of such single alkyl bromide compounds. The respective amounts of n-propyl bromide product and alkyl bromide is, as before noted, about 10 to about 70 wt% n-propyl bromide product and about 90 to about 30 wt% alkyl bromide. Preferably, the n-propyl bromide product is present in an amount of about 10 to about 50 wt% with the alkyl bromide being present in an amount of about 90 to about 50 wt%. Especially preferred are mixes containing from about 10 to 25 wt% n-propyl bromide product and from about 90 to about 75 wt% alkyl bromide. The weight percents are based on the total amount of n-propyl bromide product and alkyl bromide present in the solvent system. The highly preferred mix of n-propyl bromide product and n-butyl bromide is unique in that it represents a balance between two solvents having different qualities. The n-propyl bromide product is considered a strong solvent while the n-butyl bromide is considered a weaker solvent. In combination with n-propyl bromide product, n-butyl bromide seems to attenuate the former's solvent strength. It is believed that it is the strong solvency of the n- propyl bromide product which makes it, when used alone, prone to cause curling of the cellulose triacetate polymer film. Another difference is found in their respective flash points. The n- propyl bromide product does not possess a flash point. On the other hand, n-butyl bromide does possess a flash point. It is intriguing that it takes very little n-propyl bromide product to obtain a mix with n-butyl bromide that does not possess a flash point. It has been demonstrated that not much more than 5 wt% n-propyl bromide product will yield a mix with n-butyl bromide having no flash point. Mixtures containing between about 10 and about 70 wt% n-propyl bromide product and from about 90 to about 30 wt% n-butyl bromide product have good film cleaning (no curl) features and no flash point. Preferred mixes contain from about 10 to about 25 wt% n-propyl bromide product and from about 90 to about 75 wt% n-butyl bromide. Most highly preferred is a solvent system containing a mix of from about 10 to about 20 wt% n-propyl bromide product and from about 90 to about 80 wt% n-butyl bromide. All weight percents are based on the total weight of the n-propyl bromide product and n-butyl bromide. The n-propyl bromide product and alkyl bromides are highly miscible one with the other and, thus, the two can be conventionally mixed together with no particular requirements needed. Since, in most film cleaning applications, the solvent is used at a temperature below about 60° C, the n-propyl bromide product/alkyl bromide mixture need not be stabilized against decomposition should it come into contact with a metal such as magnesium, titanium, steel or aluminum. These metals, at higher temperatures, can act as catalysts which dehydro- brominate alkyl bromides. The dehydrobromination product is HBr, which can, in turn, attack metal and leave it corroded. Should the solvent system be expected to encounter temperatures over about 60° C and be in the presence of any of the before-mentioned metals, it may be necessary to include any of the conventional stabilizers used to stabilize halogenated alkane solvents, the only caveat being that the stabilizer not adversely affect the film to be cleaned. The stabilizer may be a singular stabilizer or a combination of stabilizers. The stabilizers can be nitroalkanes, ethers, amines or any combination thereof. When used, the nitroalkanes will be present in an amount of from about 0.1 to about 0.5 wt%. Use of the ethers will usually entail using from about 2.5 to about 4 wt % ether. Finally, when used, the amines are present in an amount of from about 0.1 to about 0.5 wt%. All weight percents are based on the total weight of n-propyl product, alkyl bromide, acid acceptor, if used, and stabilizer. Some art recognized nitroalkanes are nitromethane. nitroethane, 1-nitropropane, 2- nitropropane and nitrobenzene. Preferred is nitromethane. They are usable either singularly or in a mixture of two or more. The ethers include 1 ,2-dimethyoxyethane, 1 ,4-dioxane, 1 ,3-dioxolane, diethyl ether, diisopropyl ether, dibutyl ether, trioxane, alkyl cellosolves in which the alkyl group has 1 to 10 carbon atoms, such as methyl cellosolve, ethyl cellosolve and isopropyl cellosolve, acetal, acetone dimethyl acetal, 2,2-dimethoxypropane, diethoxymethane, acetaldehyde dimethyl acetal, dimethoxymethane, γ-butyrolactone, methyl t-butyl ether, tetrahydrofuran and N- methylpyrrole. They are usable either singularly or in the form of a mixture of two or more. The amines include hexylamine, octylamine, 2-ethylhexylamine, dodecylamine, ethylbutylamine, hexylmethylamine, butyloctylamine, dibutylamine, octadecylmethylamine, triethylamine, tributylamine, diethyloctylamine, tetradecyldimethylamine, diisobutylamine, diisopropylamine, pentylamine, N-methylmorpholine, isopropylamine, cyclohexylamine, butylamine, isobutylamine, dipropylamine, 2,2,2,6-tetramethylpiperidine, N,N-di-allyl-p- phenylenediamine, diallylamine, aniline, ethylenediamine, propylenediamine, diethylene- triamine, tetraethylenepentamine, benzylamine, dibenzylamine, diphenylamine and diethyl- hydroxylamine. They are usable either singularly or in the form of a mixture of two or more. The total amount of stabilizer used can be the conventional amount, e.g., from above 0.1 wt% to 5 wt%, with the weight percent being based upon the total weight of n-propyl product, alkyl bromide, acid acceptor, if any, and stabilizer used. It is conventional in the film cleaning art to use an acid acceptor when the solvent system is based upon halogenated hydrocarbons which are susceptible to hydrolysis. The introduction of water into the solvent system can occur during transportation, storage or use. Suitable acid acceptors include epoxides and alcohols. For example, 1,2-butylene oxide, 2,3- butylene oxide, propylene oxide, epichlorohydrin, cyclohexane oxide, isopropanol, secondary butanol, butanol, propanol and the like. Despite the art's expected need for an acid acceptor, it has been found that the solvent systems of this invention are not especially susceptible to hydrolysis. Thus, in many cases no acid acceptor is needed or only a very low amount of acid acceptor is used. Further, if the end-user adds neutralizers to the solvent system as part of his operating practice, then the amount of acceptor needed, if any, may only be that amount which is required to thwart the effects of hydrolysis which occurs during transportation or storage. In any event, the amount of acid acceptor needed is that amount which is sufficient in the face of the amount of hydrolysis expected. When the acid acceptor is 1 ,2-epoxy butane, amounts within the range of from about 0.05 to about 0.5 wt%, and preferably between 0.10 and 0.15 wt%, are suitable for most situations. When the acid acceptor is secondary butanol, it is preferred that from about 0.2 to 1.0 wt%, and most preferably from about 0.4 to about 0.6 wt%, be used. A general range for all acid acceptors is from about 0.05 to 1.0 wt%. Higher loadings are possible, say up to about 5 wt%, and may be requested by some customers due to their custom, even though such high loadings are not needed. Such requests can be accommodated as the solvents systems of this invention can tolerate such loadings quite easily. With regard to the acid acceptors, all amounts are based upon the total weight of n- propyl product, alkyl bromide, acid acceptor and stabilizer, if used. The solvent system of this invention is used conventionally and could be seen as a suitable replacement for 1 , 1 , 1 -trichloroethane. The solvent system is kept at a bath temperature within the range of from about 20 to about 45° C. The residency time for the film in the bath is conventional, say 0.1 to 5 seconds. The film drying can be accomplished by blowing dry air onto the wet film. The air temperature is conveniently from ambient to 65° C. The drying period lasts until the film is dry, say from 0.1 to 5 seconds. The cellulose triacetate polymer based camera films discussed herein are available from Eastman Kodak Company, e.g., Kodak's Color Negative Film 5296. These camera films are used in movie cameras. As the following examples illustrate, the film curling tendencies of n-propyl bromide is obviated by the presence of an alkyl bromide in the solvent system. This is a surprising result since both of these compounds are low molecular weight bromides and have several similar physical characteristics. However, their combination yields a high quality solvent which does not cause film curling while still retaining an environmentally friendly quality. EXAMPLES A solvent system bath at room temperature was prepared in a vessel. Into the bath was immersed processed Eastman Kodak Company Color Negative Film 5296. The film was a cellulose triacetate polymer based film. The immersion lasted for 10 minutes. The film was removed and dried at room temperature. The dried film was then examined for curling, cracking and peeling. The following Table gives the results obtained for several runs. TABLE I Solvent System Curling Cracking Peeling Discoloration* 1,1,1-TCA none none none none 99 wt% NPB slight curl none none none 90/10 wt% NPB/NBB slight curl none none none 80/20 wt% NPB/NBB slight curl none none none 66/33 wt% NPB/NBB none none none none 50/50 wt% NPB/NBB none none none none 33.3/66.6 wt% NPB/NBB none none none none Solvent System Curling Cracking Peeling Discoloration* 15/85 wt% NPB/NBB none none none none 15/85 wt% NPB/NBB 5 none none none none * - discoloration of the solvent system TCA - trichloroethane NPB - n-propyl bromide NBB- n-butyl bromide s - stabilized with 0.15 wt% 1,2-epoxy butane (wt% based on total weight of solvent system) None of the solvent systems listed in Table I have flash points by the Tag Closed Cup (TCC) method (ASTM-D56). Solvents having no flash points by the TCC method are not regulated by the Department of Transportation as flammable liquids.

Claims: CLAIMS 1. A solvent system comprised of from about 10 to about 70 wt% of a n-propyl bromide product and from about 90 to about 30 wt% alkyl bromide in which the alkyl group contains 4 to 7 carbon atoms. 2. The solvent system of claim 1 wherein the n-propyl bromide product is present in an amount of from 10 to about 25 wt% and wherein the alkyl bromide is present in an amount of from about 90 to about 75 wt%. 3. The solvent system of claim 1 wherein the n-propyl bromide product is present in an amount of from 10 to about 20 wt% and wherein the alkyl bromide is present in an amount of from about 90 to about 80 wt%. 4. The solvent system of claim 2 wherein the alkyl bromide is n-butyl bromide. 5. The solvent system of claim 1 wherein the alkyl bromide is n-butyl bromide and wherein the n-propyl bromide product is present in an amount of from about 10 about 25 wt% and wherein the n-butyl bromide is present in an amount of from about 90 to about 75 wt%. 6. The solvent system of claim 1 in which the solvent system contains 0 to 1 wt% acid acceptor. 7. A process for cleaning photographic film, which process comprises: contacting the film in a solvent system comprised of from about 10 to about 70 wt% of a n-propyl bromide product and from about 90 to about 30 wt% alkyl bromide in which the alkyl group contains 4 to 7 carbon atoms; removing the film from contact with the solvent system; and drying the removed film. 8. The process of claim 7 wherein the n-propyl bromide product is present in an amount of from 10 to about 25 wt% and wherein the alkyl bromide is present in an amount of from about 90 to about 75 wt%. 9. The process of claim 7 wherein the n-propyl bromide product is present in an amount of from 10 to about 20 wt% and wherein the alkyl bromide is present in an amount of from about 90 to about 80 wt%. 10. The process of claim 9 wherein the alky bromide is n-butyl bromide. 1 1. The process of claim 7 wherein the alkyl bromide is n-butyl bromide and wherein the n-propyl bromide product is present in an amount of from about 10 about 25 wt% and wherein the n-butyl bromide is present in an amount of from about 90 to about 75 wt%. 12. The process of claim 7 wherein the solvent system contains from 0 to 1 wt% acid acceptor.

Inventors: AZARNIA FARAH D, LEE BURNELL, LIIMATTA ERIC W, SHUBKIN RONALD L, AZARNIA, FARAH, D., LEE, BURNELL, LIIMATTA, ERIC, W., SHUBKIN, RONALD, L.
Applicants: ALBEMARLE CORP, AZARNIA FARAH D, LEE BURNELL, LIIMATTA ERIC W, SHUBKIN RONALD L, ALBEMARLE CORPORATION, AZARNIA, FARAH, D., LEE, BURNELL, LIIMATTA, ERIC, W., SHUBKIN, RONALD, L.
Application year: 1997
Main classification: G03C11
IPC codes: C11D7, G03C11