Thermally Stable Nitrocellulose Emulsions, Solutions and Coatings

 _ US005254161A Umted States Patent [19] an Patent Number: 5,254,161 DeVido et al. [45] Date of Patent: Oct. 19, 1993 [54] THERMALLY STABLE NITROCELLULOSE [75] [73] [21] [22] [51] [52] [58] [56] EMULSIONS, SOLUTIONS AND COATINGS Inventors: John P. DeVido, Kennett Square, Pa.; Ernest C. Linsay, Hockessin; Daniel M. Zavisza, Newark, both of Del. Assignee: Aqualon Company, Wilmington, Del. App]. No.: 781,839 Filed: Oct. 24, 1991 Int. Cl.5 .......................................... .. GED 101/18 U.S. Cl. .................................. .. 106/170; 106/176; 106/195; 106/198 Field of Search .............. .. 106/170, 176, 195, 198 References Cited U.S. PATENT DOCUMENTS 4,022,724 5/1977 Kreuder et al. .................... .. 260/16 4,515,633 5/1985 Cnlz, Jr. ........... .. . 106/18.28 4,590,019 5/1986 Luhmann et al. 264/3.4 4,657,590 4/1987 Gamblin . . . . . . . . . . . . . . . . . . .. 106/22 4,814,015 3/1989 Quinlan ..... .. 106/189 4,900,621 2/1990 Kohn ............. .. 428/333 4,902,301 2/ 1990 Rogers et al. .... .. 23/302 4,937,281 6/1990 Tang .............. .. 524/517 4,954,619 9/1990 Lang et al. ........ .. 536/20 FOREIGN PATENT DOCUMENTS 0353477 2/1990 European Pat. Off. . 76076 9/ 1970 German Democratic Rep. .................................. .. 106/189 OTHER PUBLICATIONS “Nitrocellulose”, Hercules Powder Co., 1944, No. 500—256—4M—9.46. Hawley, Condensed Chemical Dictionary, Van Nostrand Reinhold Co., N.Y., 1973, PD. 285, 455-456. Primary Examiner—David Brunsman Attorney, Agent, or Finn——James K. Luchs; David Edwards [57] ABSTRACT Emulsions, solutions and coatings comprising nitrocel- lulose are stabilized against yellowing on thermal aging when treated with boric acid or borax or hydrogen peroxide or 0.1 to 0.5% by weight of a chlorinated hydantoin such as 1,3-dichloro 5,5-dirnethylhydantoin (DCH). Boric acid or borax may be added as aqueous solutions during nitrocellulose manufacture. Combined treatments and/or additions of boric acid and DCH give optimum stabilization against yellowing. 13 Claims, No Drawings 7 5,254,161 1 THERMALLY STABLE NITROCELLULOSE EMULSIONS, SOLUTIONS AND COATINGS FIELD OF THE INVENTION This invention relates to nitrocellulose products used in the form of emulsions and solutions for coatings. In particular the invention relates to nitrocellulose emul- sions and solutions for coatings which exhibit reduced yellowing. BACKGROUND OF THE INVENTION Nitrocellulose was once widely used for automotive finishes. Henry Ford had said “Give them any color they want as long as it’s black.” This was significant since a black nitrocellulose car finish did not show yel- lowing on aging. It was this problem with yellowing which led to the phase out of nitrocellulose for auto finishes as consumers demanded more than basic black. Yellowing continues to be a problem in nitrocellulose uses for furniture lacquers and clear nail polish. Technological advances continued even though ni- trocellulose yellowing was not addressed. The develop- ment of an improved nitrocellulose manufacturing pro- cess is described in U.S. Pat. No. 4,590,019. A water based nitrocellulose spray paint is described in Euro- pean Patent Application 0 353 477 Al. U.S. Pat. No. 4,900,621 discloses pinhole-free nitrocellulose coatings. U.S. Pat. No. 4,954,619 discloses an improved film forming nitrocellulose nail polish. U.S. Pat. No. 4,022,724 discloses the use of bis- hydroxyphenyl-3-alkanes for prevention of yellowing. It would appear from U.S. Pat. No. 4,937,281 that a need existed for non-yellowing clear acrylate coatings similar to the unresolved problem with nitrocellulose yellowing. Thus, an unsatisfied need existed prior to the present invention to prevent yellowing when nitrocellulose was manufactured and used in the form of solution, emulsion or coating. SUMMARY OF THE INVENTION It is an object of the invention to provide a nitrocellu- lose composition in the form of a coating solution or emulsion, characterized in that the composition exhibits reduced yellowing during aging wherein the composi- tion comprises an effective amount of hydrogen perox- ide or boric acid or an alkali metal salt of boric_acid and/or a chlorinated hydantoin having the following structure: O=0 wherein X can be C1 or Br, where R1 and R2 can be hydrogen or methyl groups. The preferred compound (l,3-dichloro-5,5-dimethyl- hydantoin) has the structure: 10 l5 20 25 30 35 45 55 65 2 ii Cl \ c N’ \N—Cl I Me-C [ / \ Me C ll 0 A preferred nitrocellulose composition for furniture lacquer or clear nail polish coating comprises at least one of: (a) boric acid or borax; and (b) l,3—dichloro-5,5-dimethylhydantoin (DCH); wherein a coating composition or a coating containing one or both of these exhibits lower yellowing on ther- mal aging. It is a further object of the invention to provide a manufacturing process for improving the thermal stabil- ity of a nitrocellulose composition comprising the steps: (1) producing an unstabilized nitrocellulose in an aque- ous medium; (2) mixing the nitrocellulose in an aqueous medium containing dissolved boric acid or borax (Na2B203.lO H20) for a time sufficient for the nitrocellulose to absorb a stabilizing amount of boric acid or borax; and (3) recovering a stabilized nitrocellulose product suit- able for preparing a furniture lacquer or clear finger nail polish. Combined treatments and/or additions of borax and DCH are preferred for optimum benefit against yellow- mg. DETAILED DESCRIPTION OF THE INVENTION U.S. Pat. No. 4,937,281 describes the use of ultravio- let stabilizers to prevent yellowing in acrylate coatings. While it would appear that such technique might simi- larly apply to nitrocellulose yellowing, it was in fact discovered that thermal stability was the major problem requiring a solution. Finding such a solution was the advance in the state of the art provided by the inven- tion. It was indeed a surprising and unexpected result to find how simply and effectively both classes of addi- tives worked, and further that boric acid and borax could be incorporated during the nitrocellulose manu- facturing process. This advance is further significant in view of the length of time that this yellowing problem had existed without clues to any solution prior to the present invention. It has been discovered that activity for prevention of yellowing can vary as structural changes are made to the hydantoin,’ for example Most Active 0 ll Cl c \ / \ 1“ ‘.“‘°' Me—C C / \\ 0 Me Less Active 5,254,161 3 -continued 0 II c \ / \ N N—Br I I Me—C C / \\ 0 Cl Me While l,3-dichloro-5,5-dimethylhydantoin (DCH) is preferred, other suitable compounds include N- chlorosuccinimide. Effective amounts of additions are -from 0.2 to 5.0% by weight based on the weight of the nitrocellulose. Preferred amounts are from 0.4 to 2.0% by weight. While hydrogen peroxide solutions and boric acid and borax (Na; B2 03 . l0 H20) are preferred as water soluble additions, other alkali metal salts such as potas- sium borate and lithium borate could be employed. Effective amounts of additions are from 0.1 to 5.0% by weight based on the weight of nitrocellulose. Preferred amounts are from 0.8 to 1.0% by weight. Stabilized nitrocellulose can be produced by a novel manufacturing process wherein water soluble boric acid and/or borax can be added during a washing step con- current with nitrocellulose manufacture. A preferred process involves the steps: (1) producing a fibrous form of unstabilized nitrocellu- lose in an aqueous medium; (2) mixing the nitrocellulose with a solution of boric acid during a washing step and allowing the nitrocel- lulose to equilibrate at 40° C. for at least 30 minutes; and (3) decanting the now stabilized nitrocellulose to pro- duce a product slurry suitable for further treatment and formulation to prepare a lacquer or a clear finger- nail polish. During step (2) approximately 1 liter of a 0.5% by weight boric acid solution is used to treat 450 g of solid nitrocellulose. While elevated temperature might in- crease the rate of adsorption of the boric acid onto the nitrocellulose, this is not a recommended technique due to potential exotherrnal excursions which have been known to occur during nitrocellulose manufacturing processes. The invention which has applicability for industrial, home and personal use coatings is illustrated by the following examples. EXAMPLE l An aqueous nitrocellulose/acrylate emulsion was prepared according to the techniques described in U.S. Pat. Nos. 3,953,386 and 4,011,388 except that sodium hydroxide was used in place of sodium bicarbonate. With and without additions according to the invention, control and experimental formulations were drawn down onto white glass plates to prepare test coatings. These coatings were aged at 150° F. (66° C.), and yel- lowing was followed by periodically measuring Yel- lowness Index (Y I). Table 1 contains comparative re- sults of the testing. TABLE 1 150° F. 150° F. Addition % Addition Yl Initial Yl 24 Hrs. Y] 48 Hrs. Control — 6.66 22.43 26.86 DCH 0.2 2.43 10.46 12.27 Boiic Acid 0.5 4.92 3.02 10.09 l0 15 20 25 30 3.5 40 45 50 55 65 4 TABLE l-continued 150' F. 150' F. Addition % Addition Yl Initial YI 24 Hrs. Yl 48 Hrs. DCH + Borax 0.2 + 0.5 3.90 6.05 8.09 As shown, the best protection against yellowing on thermal aging involved the DCH and boric acid combi- nation. EXAMPLE 2 A solvent nitrocellulose lacquer was prepared using the following formulations: Nitrocellulose i see. (IPA wet) 750 g Ethanol 2B 107 g Butnnol 172 g Xylene 770 g Methyletliylketone (MEK) 259 g Butyl acetate 548 g Exxate ® 600 (Exxon Chemicals) 51 g Dried costings were thermally aged by first being tested for 44 hours at 1500' F. followed by 47 hours at l800° F. Results are shown in Table 2. TABLE 2 Y1 After Addition Initial YI Therm. Aging Control 2.69 8.09 DCH 1.32 5.58 As shown, DCH gives superior protection under thermal aging. EXAMPLE 3 Example 1 was repeated except that either borax or hydrogen peroxide was substituted for boric acid. Simi- lar results were obtained, but hydrogen peroxide gave slightly less yellowing protection than DCH. EXAMPLE 4 Example 1 was repeated except that the water wet nitrocellulose was manufactured with different viscos- ity, which varied from 1 sec. to 5 sec. Equivalent pre- vention of yellowing was obtained with DCH, borax or boric acid and combinations thereof. Slightly poorer protection was provided when hydrogen peroxide was used in from 1% to 5% by weight based on the weight of nitrocellulose. EXAMPLE 5 Example 1 was repeated except that a bromo- chlorohydantoin was substituted for DCH. This was less effective at equivalent addition levels to DCH, but it was suitable for providing significant protection from thermal aging yellowing for either an emulsion or a coating. COMPARATIVE EXAMPLE 6 Materials tested in the same manner as DCH which proved to be ineffective against yellowing on thermal aging were: N-bromosucciriimide, N-bromoacetamide, trichloro- melamine, trichloroisocyanuric and, N-bromophthali- mide, azobisisobutyronitrile, benzophenone, dicumyl- peroxide, mixture of para and meta isomers of alpha, i254J6l 5 alpha’-bis(t-butylperoxy)diisopropylbenezene, peroxide, and t-butylhydroperoxide. EXAMPLE 7 Example 3 was repeated except that benzoyl peroxide MEK was substitited for hydrogen peroxide. Similar reduced . yellowing was observed. What is claimed is: 1. A nitrocellulose composition in the form of a coat- ing, solution or emulsion, characterized in that the com- position exhibits reduced yellowing during aging wherein the composition comprises nitrocellulose and an effective amount of one or more of borax or a chlori- nated hydantoin having the following structure: 0 II C X-l'|~I/ ‘1'~1—c1 R1‘-C C I ll R2 0 wherein X can be C1 or Br, and where R1 and R2 can be hydrogen or methyl groups. 2. The nitrocellulose composition of claim 1 where the composition includes the chlorinated hydantoin that is 1,3-dichloro-5,5-dimethylhydantoin (DCH) with the structure: added in an amount of 0.2 to 5.0% by weight based on the weight of nitrocellulose. l0 15 20 25 30 35 45 50 55 65 6 3. The composition of claim 2, further characterized in that the composition contains 0.4 to 2.0 weight per- cent DCH based on the weight of nitrocellulose. 4. The composition of claim 1 where boric acid or borax are added to an aqueous nitrocellulose system. 5. The composition of claim 1, further characterized in that the composition contains 0.01 to 0.50 weight percent boric acid or borax based on the weight of nitrocellulose. . 6. A process for improving the thermal stability of a nitrocellulose composition comprising the steps (1) producing an unstabilized nitrocellulose in an aqueous medium, (2) mixing the nitrocellulose in an aqueous medium containing dissolved boric acid or borax for a time sufficient for the nitrocellulose to adsorb a stabiliz- ing amount of boric acid or borax for at least 30 minutes at 40° C., (3) recovering a stabilized nitrocellulose product suitable for preparing a coating composition. 7. A nitrocellulose protective or decorative coating comprising nitrocellulose and an organic solvent, char- acterized in that the nitrocellulose is stabilized against yellowing on thermal aging with DCH or borax or hydrogen peroxide. 8. The coating of claim 7 where the nitrocellulose is contained in a nitrocellulose lacquer. 9. The coating of claim 8 containing from 1 to 5% by weight hydrogen peroxide based on the weight of nitro- cellulose. 10. The coating of claim 7 where the nitrocellulose is contained in a nitrocellulose/acrylate or nitrocellulose lacquer emulsion. 11. The coating of claim 7 where the nitrocellulose is contained in a nail polish composition. 12. The coating of claim 7 containing from 0.8 to 1.0% by weight borax or boric acid based on the weight of nitrocellulose. 13. The coating of claim 7 containing from 0.4 to 2.0% by weight DCH based on the weight of nitrocellu- lose. 1 3 I 3 t