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Publication numberUS3573952 A
Publication typeGrant
Publication dateApr 6, 1971
Filing dateOct 21, 1968
Priority dateOct 21, 1968
Also published asDE1952762A1
Publication numberUS 3573952 A, US 3573952A, US-A-3573952, US3573952 A, US3573952A
InventorsBerger Thomas W
Original AssigneeMinnesota Mining & Mfg
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Process for imparting oil repellency to suede leather
US 3573952 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,573,952 PROCESS FOR IMPARTING OIL REPELLENCY T0 SUEDE LEATHER Thomas W. Berger, Roseville, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul,

Minn.

N0 Drawing. Filed Oct. 21, 1968, Ser. No. 769,358 Int. Cl. B44d 1/094, 1/32 US. Cl. 117-16 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel process for the application of fluorochernical materials to suede leather. In one aspect this invention relates to a novel process in which the surface of suede leather can be rendered oil and water resistant during the suede manufacturing process.

In the production of garment suede leathers the finishing operations are designed to produce a napped material which is soft to the touch and appealing to the eye. One outstanding characteristic of a fine suede leather is its ability to track, i.e. to give a lighter or darker appearance to the surface as the suede is stroked or touched. Any finishing operation which diminishes either the soft feel or the ability to track is considered to diminish the value of the finished suede product. The ordinary tanning and treating of leather includes the introduction of fat or oil in a fat liquoring step and frequently includes a treatment of the suede leather to impart stain repellency. Commonly included in the finishing of suede leathers are such water repellent materials as chromium complexes, silicone oils, and various fiuorochemicals, such as the fluorochemical chromium complexes and fluorine containing urethane resins, which provide not only water repellency but stain repellency as Well and which further permit the suede to be washed.

In the preparation of stain repellent suede leathers the material is normally fat liquored and often given further water repellent treatments by using silicones, chromium complexes and, occasionally, an emulsified urethane material. These treatments are normally conducted in a wet tanning drum. After drying the leather is bufied to provide the suede surface. The suede skins are then placed into a drum in which they are tumbled for a period of time to soften the skins and to free them of dust, short fibers, dye particles, etc. by passing air through the drum during the tumbling operation. During the bufiing and tumbling steps many untreated or lightly treated fibers on the suede surfaces are exposed, and the resulting surface readily accepts oil stains and fingermarks. To eliminate this problem it has become customary to provide a top spray treatment in which a dilute solution of a fiuorochemical in a volatile organic solvent is sprayed over the surface of the suede material, and the solvent is then evaporated. In order to obtain uniform coverage with an economically small amount of fluorochernical relatively large quantities of solvent must be applied, and solvent removal is usually conducted in an oven with ice the exhaust gases passing through a solvent recovery system. In addition to the expense of providing and maintaining such solvent recovery systems and the expense incurred by the unavoidable loss of at least some of the organic solvent, this treatment also tends to produce a suede with a somewhat harsher feel than the suede material immediately after tumbling and usually with a significant loss in the ability of the surface to track. The top spraying of suede materials from organic solvent systems is, therefore, to be avoided whenever possible. Although aqueuos solutions or suspensions of fluorochemicals have been tried as a top spray on a dry suede material after tumbling, the large quantities of water necessary to uniformly distribute the fluorochemicals results in a very wet skin. Since rapid drying of wet suede materials would cause them to harden, only slow and controlled drying is permissible, during which time mildew or spoilage can occur. At best, the resulting suede leather is unacceptable due to the relatively harsh feel. In the top spray treatment attempts to minimize the damage by decreasing the amount of organic solvent or water produces an uneven distribution of the fiuorochemical and consequently produces spotty results and a product with less than desirable soil resistance.

It has now be en found that the top spray treatment of suede leathers can be replaced by the addition of a fiuorochemical capable of imparting oil repellency to leather to the water repellent suede material during the tumbling operation. Two critical conditions must be observed. First, the fiuorochemical must be applied in particulate form and the particles must be capable of being uniformly distributed over the surface fibers of the suede leather during the tumbling operation. The particles of fluorochernical material can be obtained and used as a dry powder or as the emulsified or suspended phase in an aqueous emulsion or suspension. In each instance the fluorochernical particulate material, whether as a dry powder or an emulsion or suspension, can be introduced directly into the drum during the tumbling of the suede materials. It is unexpected that the fluorochernical particulates could be made to uniformly treat the water repellent suede surfaces in a tumbling drum. It appears probable that the fiuorochemical treatment provides a substantially continuous film or fluorochemical over the suede surface. When using a small amount of fluorochemical the particle size should be as small as possible to permit adequate and uniform coverage over the entire surface during the tumbling operation. Small particle size may be provided by fine grinding of the dry fluorochemical, such as by passage through a micropulverizer. Alternatively, small particle size fiuorochemical materials are inherently provided in an aqueous emulsion or suspension. In the alternative case, under the conditions prevailing in the tumbling drum, the aqueous medium is evaporated at such a rate that the particles do not have an opportunity to coalesce and are therefore distributed uniformly over the fiber surface. By contrast, the use of a solution of fiuorochemical in an organic solvent has been found to provide very unsatisfactory and non-uniform treatment of the suede surface, apparently because the solvent is absorbed into the suede surface and carries the fluorochernical with it, thereby providing less time for the fiuorochemical to be redistributed over the suede surface during tumbling. However, since the suede materials are substantially water repellent, due to the prior treatment with fat liquor, silicones, chromium complexes, etc., the water of the emulsion or suspension does not penetrate into the surface but remains thereon until it is removed by evaporation during tumbling. As tumbling continues and the solvent is removed, the fluorochernical particulate material is distributed over the surface by the motion of the hides and the heat generated during th tumbling.

Even with fiuorochemical material of a relatively large particle size, the powdered material is readily distributed during the tumbling operation if the fiuorochemical itself has a melting point below about 200 (3., preferably below 150 C. If the fiuorochemical particulate material has a melting point below about 50 C. it is diflicult or impossible to grind the solids to an extremely fine particle size. For those materials melting below about 100 C. it is possible to mix the solid with granulated, solid carbon dioxide while it is being passed through a micropulverizer, and the material is then sufficiently brittle to permit further pulverization to occur.

In carrying out this invention in its preferred aspect, using an aqueous emulsion or suspension, the amount'of water is important. The use of excess water will produce a wet leather having poor characteristics, as mentioned earlier. Accordingly not more than about 7 weight percent of water, based on the weight of the suede leather in the drum, is applied during the tumbling operation. Preferably as little water is used as possible and, in general, between about 1.5 and 4 weight percent of water is added. The amount of the fiuorochemical particulate material added, either as a dry powder or in a suspension or emulsion, depends upon the thickness of the skins, the particular set of tanning conditions, colorants, etc., but at least about 0.05 weight percent of fiuorochemical, based on the total weight of suede material, is necessary to provide satisfactory stain resistance, and no appreciable advantage is obtained with amounts much in excess of about 1 weight percent.

Many different types of fluorochemicals useful in treating leather for oil or stain repellency have been de scribed in the literature, and any of these having suitable melting points may be used in this invention. The most useful fluorochemicals are those having a perfluoroaliphatic group containing at least three carbon atoms, preferably no more than about twenty carbon atoms, and a terminal trifiuoromethyl group. The perfluoroaliphatic chain may also contain nitrogen or oxygen atoms bonded only to carbon atoms, without significantly affecting performance. The presence of an occasional hydrogen or chlorine atom in the fluoroaliphatic group is not particularly harmful, but a perfiuoroaliphatic radical is much preferred. To obtain reasonable oil repellency the fiuorochemical compound should have at least about percent by weight of fluorine in the form of fluoroaliphatic radicals. Suitable compounds can be prepared with up to 60 weight percent or higher of fluorine, but generally those containing between about 30 and 50 percent fluorine have been found most satisfactory. The exact chemical structure of the fiuorochemical has not been found to be critical in the practice of this invention, and any of the various fluorochemicals in particulate form which otherwise meet the melting point requirements and which are of value in imparting stain repellency to leather can be used in the practice of this invention. In general, one or more polar groups, such as ester groups, amide groups, or aromatic rings, are necessary in such fiuorochemical compounds to provide a material melting in the preferred range. Extremely high molecular weight polymers generally have unacceptably high melting points, and completely non-polar materials generally have unacceptably low melting points. When a fiuorochemical polymer is used it should be substantially free of crosslinking and must be truly thermoplastic in order for it to be distributed over the suede surface during tumbling. A low percentage of crosslinking is permissible, provided the material flows readily at a temperature below about 200 C. Although no external heat is necessary during the tumbling operation, the continuous impact, twisting and folding of the suede materials during the tumbling operation apparently generates suf- 4 ficient internal heat to permit relatively uniform distribution of the fiuorochemical over the sueded surfaces.

Amide derivatives having a perfluoroaliphatic radical, including urethanes, have been found to be a particularly preferred class of fiuorochemicals for the practice of this invention. Such materials bond quite readily to the fiber, are sufficiently low melting to be readily spread into a continuous film and characteristically remain on the fiber despite extended and prolonged abrasion, such that the effect of the treatment continues during actual use of the sueded product. Unless the fiuorochemical material is modified to allow for crosslinking after application, such materials are not particularly resistant to removal by dry cleaning solvents. However, the presence of, for example, N-methylol groups or conjugated diene groups in relatively low occurrence can provide sufficient crosslinking sites to permit some crosslinking to occur after the tumbling treatment, thereby providing more substantial resistance to dry cleaning solvents and provide a more permanent treatment.

The experiments to be described were carried out in a dry mill or drum somewhat smaller than is usually employed in actual commercial practice. The dry mill consisted of a wooden drum, approximately 8 feet in diameter and 4 feet long, supported on hollow gudgeons through which a finely divided spray of the aqueous emulsions could be introduced. The solid fiuorochemical particulate materials were added by placing in the drum an open paper bag containing the desired amount of the fluorochemical powder. The working load of the drum consisting of about 90 pounds of essentially dry suede leather (dry leather normally contains about 15 percent by weight moisture), equivalent to approzimately 550 square feet of sueded side material. The drum was rotated at about 15 /2 revolutions per minute. The fiuorochemicals were added in an amount of about 0.25 grams per square foot of the sueded surface, either dry or dispersed in an appropriate liquid medium.

The materials were prepared by standard processes. As an example, the emulsion of Run II was prepared by charging 18.5 parts of solid urethane (prepared in accordance with the method of Example 3 of U.S. 3,398,- 182) to a 25 gallon glass lined stirred jacketed reactor, along with 42 parts of ethyl acetate, 0.75 part of a polyoxyethylene sorbitan monooleate non-ionic emulsifier and 0.75 part of a complex organic phosphate ester anionic emulsifier. The charge was heated with agitation to 60 C. 63 parts of water containing 0.4 part of an alkylarylsulfonate anionic surfactant, preheated to 60 C., was slowly added with stirring. The suspension so formed was passed through a homogenizer until a stable creamy emulsion was formed. The emulsion was then returned to the reactor, further diluted with parts of water, heated to 65 C., and ethyl acetate volatilized by a mild reduction of pressure, care being taken to avoid foaming. Heating was continued up to 85 C., at which point the ethyl acetate was substantially removed. The pH of the emulsion was adjusted to 8 with 20 percent ammonium hydroxide. Before addition to the tumbling drum the emulsion was further diluted with Water to a 9 percent solids content. The particular emulsifiers used in preparing aqueous emulsions of the fluorochemicals are not critical and depend upon the particular fiuorochemical being emulsified. In some cases, excellent results have been obtained with the non-ionic emulsifier alone, and in other cases a combination of a non-ionic emulsifier and a cationic surfactant, such as C F SO NH'C H N(CH Cl has proven effective as stabilizer. Generally from 2 to 12 percent by weight of emulsifier is used, on the basis of the fiuorochemical particulate material. Polymeric latices were prepared generally as indicated in U.S. 3,062,765, and diluted to the appropriate concentration. Powdered solids were prepared by drying solutions or latices at about 25-50 C. under vacuum. The resulting solids were reduced by passage through a micropulverizer to produce a powder with a particle size distribution from about 100 to less than 2 microns, with a major fraction of the particles between 20 and 50 microns.

was then used to provide a fine powder and another part of this emulsion was dried to provide a solid which was dissolved in xylene hexafluoride. The polymeric particles TABLE I Properties of treated suede Melting point, Oil Spray Abrasio n Run Chemical 0. Form rating rating resistan ce II I [CaFnS O2N(CH3)CH2CH2OCHNH]2[(C0H4)2CH2] 195 Powder 65 80 55 II II..." [CaF S O2N C2H5 OH CHzOCN hweHaCHfl 105-115 9% aqueous emulsion 70 85 55 II III. [CKF S OzN(C2H CHzCH2OCNH12ICaHaCH 105-115 Powder 70 80 60 H IV-- [C F S O2N(CH )CHzCHNH]a[CsH4CH2CeH3CH2CsH4] 125 ....-do 55 90 50 II II V.-. [CsF S O2N(OH3)CHZOH2CN ]2[CflH4CH2C6H3CH2C0H-1NHCC18H37] 85 9% aqueous 011111181011- 75 80 50 ll ll VI---- [053F175 O2N(CH3) CH2CH2CNH]2[C6H4CH2C6H3CH2CBHJNHCCISHQY] 85 5%cigllglcog 1n 0 0 a 3. VII. C1Fi5CO2H.Cr(OH) C12 (Werner Complex) 0 80 0 VIII CgFgSO K 0 70 0 ll IX CBF17CO2N(CH3) CHZCHZOCCH=CII2 Homopolymer 95-100 do 0 80 0 H X.--" C8F11C O2N(CH CHzCHzO C CH CH2 Homopolymer 95-100 9% aqueous emulsion 50 80 50 ll XI. C F C OzN(CH CH2CH2O C CH= CH2 Homopolymer 95-100 5% solution in 0 80 0 CeHK FaM' II XII Copolymer of 05F 11G OzN CH3) CHzC H20 0 CH C H2 and butyl 80-100 9% aqueous emulsion. 50 80 50 acrylate (90:10 mol ratio). XIIL Control-no top coat 0 80 0 OIL REPELLENCY \RATING SCALE Oil repellency Percent n-heptane in mineral rating oil-heptane mixture (by vol.) 100 50 60 10 5O O 0 (No holdout to mineral oil) The abrasion resistance of the test samples is measured by repeating the Oil Repellency Test after the suede surface has been stroked ten times in one direction with a brass wire brush. This provides an indication of the durability of the treatment during normal garment or shoe manufacturing processes, and subsequent wear.

Examination of Runs IX, X and XI in the table illustrates the procedures of this invention. The same material is used in these three runs and was initially prepared in the form of an emulsion. Some of this emulsion in the aqueous emulsion had an average particle size of less than two microns. When, as in Run X, the emulsion was sprayed onto suede leather while it was rotating and tumbling in the drum, the water apparently evaporated and very fine particles remained on the surface. This particular polymer has been found to flow readily at a temperature of 100 C. Under the conditions of strong mechanical agitation and continuous tumbling contact of the suede surfaces the particles evidently are able to flow and form a substantially continuous film sufiicient to impart oil repellency which is retained even after severe abrasion. When the same polymer was dissolved in solvent and applied to the material, very poor oil repellency results were obtained, apparently because the solution was readily absorbed into the leather.

The distinction between emulsion and solution treatment is indicated in Runs V and VI, where the polyurethane material provides excellent oil resistance when applied from an emulsion but no perceptible improvement when applied from solution.

Even with relatively large particle size, powdered materials having a melting point below about 200 C. provide excellent treatment, as shown in Runs I, III and IV, whereas higher melting materials provide little or no effective treatment, as shown in Runs VII and VIII.

It would be possible to use an extremely low boiling solvent, such as dichlorodifluoromethane, as the dispers ing medium for the fluorochemical, and the rapid evaporation of such solvents should provide a finely dispersed fluorochemical particulate on the sueded surface. However, such solvent systems would be obviously difficult to control and would have the same problems of high cost and air pollution inherent in the solution methods presently in use.

What is claimed is:

1. A process for imparting oil repellency to the surface of suede leather which comprises adding to said suede leather during the dry tumbling thereof a fluorochemical in particulate form as a dry powder or as suspended or emulsified particles in water, the amount of added water not exceeding about 7 weight percent of the total suede leather weight, said fiuorochemical being capable of imparting oil repellency to leather and having a melting point below 200 C., and tumbling said leather until said fluorochemical is uniformly distributed over the suede surface.

2. The process of claim 1 in which said particulate form is a dry powder.

3. The process of claim 1 in which said particulate form is suspended particles of an aqueous suspension.

4. The process of claim 1 in which said particulate form is emulsion particles of an aqueous emulsion.

5. The process of claim 1 in which said fluorochemical has a melting point between 50 C. and 150 C.

6. The process of claim 1 in which said fiuorochemical is present in an amount of at least 0.05 percent of the weight of said suede leather.

References Cited UNITED STATES PATENTS WILLIAM D. MARTIN, Primary Examiner R. M. SPEER, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,573 952 Dated April 6 1971 Inventor(s) Thomas W. Berger It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 5 and 6, TABLE I, items: IX, X, XI and XII,

I "C F CO should be C F SO Columns 5 and 6, TABLE I, item XII, "(90=l0 mol ratio)" should be -(90:1O mol ratio)-- Signed and sealed this 21st day of September 1971.

(SEAL) Attest:

EDWA Q J ROBERT GOTTSCHALK Attesting Offlcer Acting Commissioner of P211 FORM POJOSO (10-69] LJSCOMM-DC cos

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5714082 *Jun 2, 1995Feb 3, 1998Minnesota Mining And Manufacturing CompanyAqueous anti-soiling composition
US6479612Jun 19, 2000Nov 12, 2002E. I. Du Pont De Nemours And CompanyFluorochemical water and oil repellents
US7160480 *Feb 22, 2005Jan 9, 2007E. I. Du Pont De Nemours And CompanyLeather treated with fluorochemicals
Classifications
U.S. Classification427/184, 427/242
International ClassificationC14C11/00
Cooperative ClassificationC14C11/00
European ClassificationC14C11/00