US1911937A - Leather finish - Google Patents

Description

Patented May so, 1933 UNITED STATES Lanai? PATENT OFFICE EDWARD F. ARNOLD, OF NEW BRUNSWICK, NEW JERSEY, ASSIGNOR TO' E. I. DU PON'I DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE LEATHER FINISH No Drawing.

This invention relates to coating compositions, and to a new process of treating leather. More particularly the invention relates to cellulose derivative coating compositions which when applied to a pliable base sheet, specifically leather, give a soft, pliable product having a decorative, water shedding finish of pleasing appearance.

Prior to my invention, the best method of surfacing leather was by means of the socalled water finish. This consisted in applying an emulsion of certain materials, such as casein, oils and pigments, in water to the surface of the leather, and in working it in. As is known, this process gives a soft, pliable product having a decorative finish of very attractive appearance but it necessitates a very considerable time for application and an extremely long time for drying. The lastnamed disadvantage requires the use of a very large space for the drying of the finished leather. however, the water finish has, heretofore, given better results than cellulose derivative finishes because cellulose derivative finishes, although applicable in very short periods of time and although very quick to dry, have had the disadvantage of giving a hard, unpleasant appearance to the leather, and a surface hard and horny to the touch, which upon boarding, wrinkles into large ridges, in which cracks will form, the edges of which break free from the leather.

The boarding process referred to above is carried out by folding the finished leather, grain side in, pressing upon the crease, and pulling the upper fold of the leather past the lower fold while maintaining pressure upon the crease. Asthis is done the creased line moved across the leather and produced a series of creases about I mm. apart. By folding the skin completely in one direction, and then in a direction at right angles to the first, a box grain pattern is produced. By folding the third time in a direction diagonal to the other two, a pebble effect is obtained. By boarding the fourth time in the other diagonal direction that finish is produced which is known as morocco. Folding with old type cellulose derivative finishes gave an Despite this disadvantage,

Application filed January 31, 1930. Serial No. 4253153.

unsightly appearance, while with a water finish the excellent and familiar grained leathers resulted.

Among the objects of. this invention are to produce a coating composition which, when applied to a pliable base sheet, specifically leather, will have the advantage of both old types of finish and the disadvantages of neither, and which, in addition, will render the leather washable. A further object of my invention is to produce a coating composition having excellent adhesion and low film stren th.

These objects are accomplished, generally speaking, by incorporating wax into a cellulose derivative coating composition, and in applying this composition to the surface to be protected.

In general the coating composition of my invention comprises a cellulose derivative, such as cellulose nitrate or cellulose acetate, Wax, a softener, a solvent, and a diluent.

It is possible with my invention to entirely eliminate the use of a plasticizer. By grinding the wax and pigments together and then incorporating this mixture in the film-forming ingredients the wax is made to perform the function, usually performed by the plasticizer, of incorporating the pigment into the composition. In grinding the wax and pigment, or ingrinding the wax alone for those compositions which are to contain no pi ment, excellent results are'obtained by grin ing the stated ingredients in alcohol to give a milky suspension.

A general idea of the amounts of filmforming ingredients which may be used in the solids of the coating composition after decomposition on the leather, may be obtained by reference to the following illustrative example, the proportions of which are not to be deemed limitative:

. 7 Parts Nitrocellulose 10.0 Softener .0 to 10 Wax 1.0 to 40 Pigment or dye 0.0 to 4:0

This composition, in any indicated proportion of its ingredients, is applied to a leather surface and is worked into the leather by any suitable means. It is not essential that the composition be worked into the leather, but

preferred results are obtained if this manipulation is carried out.

The following six examples give specific formulae which can be successfully used to accomplish the objects of my invention.

These examples are illustrative only and are not to be deemed in any sense limitative.

Example I Per cent High viscosity cellulose nitrate .7 Dibutyl phthalate .8 Carnauba Wax 1.7 Titanium oxide I 3.3 Ethyl acetate 15.5 Butyl acetate 10.3 Ethyl alcohol 66.7

Example 1] Per cent High viscosity cellulose nitrate 1.7 Dibutyl phthalate .8 Beeswax 1.7 Titanium oxide 3.3 Ethyl acetate 15.5 Butyl acetate 10.3 Ethyl alcohol 66.7

Example [[1 Per cent High viscosity cellulose nitrate 1.7 Dibutyl phthalate .8 (landelilla wax 1.7 Titanium oxide 3.3 Ethyl acetate 15.5 Butyl acetate 10.3 Ethyl alcohol 66.7

Example IV Per cent Low viscosity cellulose nitrate Dibutyl phthalate 2.5 Carnauba wax 5.0 Butyl acetate 30.0 Ethyl acetate 57.5

Example V Per cent Cellulose acetate .7 Dibutyl tartrate .8 (Jarnauba wax 1.7 Acetone 53.7 Alcohol 9.0 Diacetone alcohol 33.1

Example VI The compositions named above, and other compositions which I use in the practice of my invention, may be prepared by any of the methods useful in preparing cellulose derivative lacquers. Any known type of cellulose nitrate may be used whose use in plastics, films, lacquers, etc., is advantageous. The range of viscosity of cellulose nitrates which have been successfully used, is very Wide, cellulose nitrates when incorporated in a 16 oz. solution in GP ethyl acetate having viscosities between 50 centipoises and 25,000 centipoises, measured in the Stormer viscometer at 28 (3., having proved satisfactory.

In place of cellulose nitrate any suitable cellulose ester, such as cellulose acetate, may be employed, but their use will be accompanied by a variation in the amounts of the solvents and softeners employed in order to obtain the best composition. The proportions of diiferent ingredients to be used depend upon the particular ingredients used, and no general rule for the incorporation can be given beyond what is herein indicated.

The nature of the plasticizer in this composition is not important. Any cellulose ester plasticizer which is compatible with the remainder of the mixture and capable of dispersing the desired pigments can be used. Examples are dibutyl phthalate, castor oil, tricresyl phosphate and dibutyl tartrate. It is understood that these examples are illustrative and not inclusive.

A particular advantage of my invention resides in the fact that by grinding the wax and pigmenttogether the use of plasticizers can be entirely eliminated. This grinding of wax and pigment together is facilitated by the presence of a substance such as alcohol.

The pigment to be used may consist of a single pigment or dye, or of a combination of pigments, or dyes, designed to give any desired color effect. Any pigment whose use in lacquers is suitable may be used with my invention, or the pigment may be left out entirely and a clear finish be utilized. Examples of pigments which I have successfully used are zinc oxide, titanium oxide, chrome yellow or orange, iron oxide and iron blue. An example of a useful dye is nigrosine.

The use of a high ratio of inert material to binder contributes to the discontinuity of the film and can be used with advantage.

Pisang wax The waxma be of any kind, including those of vegeta 1e animal, insect, mineral or synthetic origin. The following waxes are exam les of those which are more or less suit- 5 able or use in my coating composition:

Carnauba wax Candelilla wax Montan wax 0 Beeswax Flax wax Raphia wax Cotton seed wax Condang wax Sugar cane wax Insect (Chinese) wax Psylla wax Bayberry wax Cofi'ee berry wax Palm wax Japan wax Myrtle wax Ceresin wax Ocotilla wax Ozokerite wax It is advantageous to use a wax, such as carnauba, candelilla, beeswax, Montan, having a melting point such that it does not soften under the mechanical finishing operations and smear the finish. Waxes having the higher melting points or softening points have been found to give excellent results under operating conditions. Carnauba wax appears to be particularly advantageous in this connection.

It is not generally desirable to use a'resin in my composition as most resins tend to produce a sticky film when subjected to the mechanical operation of leather finishing. However, suitable natural, or synthetic, resins, such as shellac, can be successfully used when a finish of high gloss is desired.

Any of thehquids commonly used as solvents for the cellulose derivatives may be used although it is advisable to adopt those which give the best compatibility, flow, blush resistance, etc.

It is advisable to dilute my coating compositions with a suitable quantity of alcohol or other thinner, the proportion of dilution depending upon the method of application,-

the physical characteristics of the sk'n to be finished, and the type of finish desired. In general a dilution of approximately twice the weight of the composition is satisfactory.

A coating composition of my invent'on may be applied by any of the methods known to the finishing of leather, such as by brushing, swabbing, roller coating, or spraying, although the latter method because of its ease and speed is preferred. Any known method of applying a uniform film of the coating composition to the base sheet may be employed. -If the composition is to, be applied b swabbing, a high-boiling solvent should used. In the application of a coating composition to a piece of leather, the leather may be stretched on a frame to obtain a smooth surface. The composition is then applied and forms a continuous film which will remain continuous as long as the skin is not moved or disturbed. However, when the skin is subjected to graining, or boarding, the 5 film breaks at all points where stress is applied. This is due to the fact that the film strength is so weak that when the leather carrying the finish is grained or boarded it immediately cracks or breaks, forming, instead of unsightly ridges of prior art pyroxylin coated leather, microscopic cracks similar to those produced when a water finish is subjected to the same treatment. Thus the coat ing, instead of being a continuous film completely covering the skin, presents a surface coated with discontinuous small patches of lacquer through which the ventilation so necessary to the wearers comfort can take place when the leather is being used for shoes.

My invention is not to be confused with the cation. It is, furthermore, to be noticed that my composition differs distinctly from prior art compositions in that it does not contain any more plasticizer than the small amount which serves to properly grind and incorporate the pigments in the composition. Indeed, the use of a considerable amount of plasticizer is deleterious in that it requires the use of increased amounts of wax and pigment to give my composition its desired fragility. 'In fact as has been above indicated the plasticizer may be eliminated.

Although the principal use of my new coating composition is in finishing leather to obtain a soft, pliable product having a decorative, water shedding finish, my coating composition is also suitable to the production of artificial leather in which art it can be used either by applying it to a fabric or other suitable base to produce a leather, or by application as a finishing material to artificial leathing or paper articles, (such as containers and wallpaper), linoleum, wood, and other surfaces. An instance of its utility is the fact that ink which has been dropped on wallpaper treated with my coating composition can be washed off without the slightest injury to the paper or the finish.

Among the advantages of my invention over water finishes are case and speed of application, rapid drying (which removes the necessity for large storage places), and relative freedom from smutting when wet. Among the advantages of my invention over previous cellulose derivatives are the lower cost which results from the practical elimination of expensive plasticizers, its good adhesion, and its beautiful appearance and feel. Other advantages will be apparent to those skilled in the art.

As many apparently widely different embodiments of this invention may be madewithout departing from the spiritand scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable base sheet carrying a substantially uniform surface film thereon including a cellulose derivative and a wax, said film having its continuity broken up by a plurality of substantially microscopic cracks.

2. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable base sheet carrying a substantially uniform surface film thereon including cellulose nitrate and a wax, said film having its continuity broken up by a plurality of substantially microscopic cracks.

3. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including a cellulose derivative and a wax, said film having its continuity broken up by a plurality of substantially microscopic cracks.

4. A soft, pliable product having a decorative, Water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including cellulose nitrate and a Wax, said film having its continuity broken up by a plurality of substantially microscopic cracks.

5. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including cellulose nitrate and a wax selected from thegroup consisting of carnauba, candelilla, beeswax and Montan waxes, said film having its continuity broken up by a plurality of substantially microscopic cracks.

6. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including cellulose nitrate and carnauba wax, said film having its continuity broken up by a plurality of substantially microscopic cracks.

7. A soft, pliable product having a decorative, water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including cellulose nitrate, a wax, and coloring matter, said film having its continuity broken .up by a plurality of substan tially microscopic cracks.

8. A soft, pliable product having. a decorative, water shedding finish, said product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon including cellulose nitrate, a wax, a plasticizer and a pigment, said film having its continuity broken up by a plurality of substantially microscopic cracks.

9. A soft, pliable product comprising a pliable leather base sheet carrying a substantially uniform surface film thereon having its continuity broken up by a plurality of substantially microscopic cracks, said film being obtained by coating a composition including cellulose nitrate, carnauba wax, dibutyl phthalate, a pigment, ethyl acetate, butyl acetate, and ethyl alcohol on said leather base sheet, and then subjecting said base sheet to mechanical action whereby the continuity of the coated film is broken up by a plurality of substantially microscopic cracks.

10. Method of preparing a soft, pliable sheet having a decorative, water shedding finish which comprises uniformly applying a composition including a cellulose derivative and a wax to a pliable base sheet, and then subjecting the sheet to mechanical action whereby the continuity of the film formed by said composition is broken up by a plurality of substantially microscopic cracks.

11. Method of preparing a soft, pliable leather sheet having a decorative, water shedding finish which comprises uniformly applying a composition including a cellulose derivative and a wax to a pliable leather base sheet, and then subjecting the sheet to mechanical action whereby the continuity of the film formed by said composition is broken up by a plurality of substantially microscopic cracks.

12. Method of preparing a soft, pliable leather sheet having a decorative, water shedding finish which comprises uniformly applying a composition including cellulose nitrate and a wax to a pliable leather base sheet, and then subjecting the sheet to mechanical action whereby the continuity of the film formed by said composition is broken up by a plurality of substantially microscopic cracks.

In testimony whereof, I aflix my signature.

EDWARD F. ARNOLD.