US2550638A - Bleaching and filling leather with amino carboxylic acid-methylol melamine resin - Google Patents

Description

Patented Apr. 24, 1951 BLEACHHNG AND FILLING LEATHER- WITH AMINO CARBOXYLIC ACID-METHYLOL T/IELAIVHNE RESIN William 0. Dawson, Stamford, Conn, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing.

Application August 25, 1945,

Serial No. 612,710

4 Claims. 1

This invention relates to a method of finishing leather by impregnating it with a novel class of finishing agent having bleachin and filling properties. More particularly, the invention relates to the treatment of vegetable, mineral or resin-tanned leather with water-soluble or waterdispersible finishing compositions containing condensation products of methylol melamines with aminocarboxylic acids.

In my Patent No. 2,316,741 dated April 13, 1043, I have shown that methylol melamines are excellent tanning and finishing agents for hides, skins, and leather. I have now discovered that water-dispersible products having good bleaching and filling properties for leather are obtained when methylol melamines are condensed with aminocarboxylic acid salts. These condensation products form stable aqueous solutions which can be shipped to and stored by the customer without deterioration, and which can be added directly to leather finishing processes.

Although the present invention is not limited to condensation products of definite structure, I have found that certain well-defined com-pounds are obtained by condensing monomeric or partially polymerized methylol melamines containing 1 or more free methylol groups with watersoluble salts of aminocarboxylic acids of the aromatic and aliphatic series; such as the alanines, glycocoll, beta-aminebutyric acid and other amino fatty acids, as Well as anthranilic acid, para-aminobenzoic acid, and other aminocarboxylic acids of the aromatic series. Thecondensation reaction which takes place is illustrated by the following equation wherein the symbol M represents a methylol melamine, either in the monomeric or in a partially polymerized condition, R is the residue of an aminocarboxylic acid of the aromatic or all-- phatic series and is therefore an aryl or alkylene radical, and X is a salt-forming radical such as sodium, ammonium, ethanolamine and the like.

Although compounds of definite composition can be obtained by condensing equiinolecular quantities of a methylol melamine and a salt of an aminocarboxylic acid, as indicated by the above equation, the invention is not limited to compounds of definite composition. on the contrary, I find that stable solutions possessing bleaching and filling properties for leather are obtained when considerably less than the theoretical quantities of aminocarboxylic acid are employed. Thus, for example, I have obtained bleaching and filling compositions of good stability by reacting anywhere from 1 to 2 mols of a methylol melamine with 1 mol of an aminocarboxylic acid, and in some cases the ratio may even be as high as 2.1:1. This permits an important saving in the cost of the bleaching and filling compositions of the invention, since the aminocarboxylic acid is usually more expensive than the methylol melamine.

The condensation products used in practicing the process or" the present invention are preferably obtained by adding an aqueous solution or dispersion of the methylol melamine to a water solution of a water-soluble saltof the aminocarboxylic acid followed by heating the mixture at temperatures of about 30 to 100 C., or up to the boiling point of the solution. The reaction product is obtained as a clear, aqueous solution which can be diluted with water to the concentration desired for the tanning or bleaching of leather.

When a composition of improved stufiing or filling properties is desired it is usually preferable to heat the clear solution of the condensation product at a pH of about 5-7 to promote further polymerization, so that a solution of increased viscosity is obtained. By polymerizing the condensation product in this manner its filling properties are considerably improved. For greater stability on storage an alkali such as borax or sodium hydroxide is preferably added in amounts suflicient to raise the pH to about 9-11 after polymerizing to the desired degree.

The methylol melamine-aminocarboxylic acid condensation products may be applied to the leather by any suitable process; however, I prefer to apply them in a tanning drum by the methods described in my earlier patent referred to above. The condensation products are preferably applied to the leather as an aqueous solution containing 110% of the condensation product, although for special purposes stronger solutions may be employed. Finishing processes requiring complete penetration of the condensation product are usually carried out at relatively high dilutions of th condensation product and for considerably longer periods of time than are bleaching processes in which the principal object is to obtain a lightening of the color of the leather. After the leather has been impregnated with the condensation product to the desired de gree it is usually washed with water and may be fatliquored by an suitable procedure, such as by an aqueous emulsion of neatsfoot oil.

The invention will be further illustrated by Example 1 To 37.5 grams of glycine add grams of so dium hydroxide and 230 grams of water. To the clear solution add 126 grarns of melamine and 284 grams of 37% aqueous formaldehyde. Heat at 50-55 C. until a clear solution is obtained. Dilute hydrochloric acid is added, if necessary, to adjust the pH to 6.0-7.6. The mixture is heated until the desired viscosity is obtained. Alkali is then added to adjust the pH to 9.011.0 and water then added to dilute the solution to 20% solids. This solution is stable during shipment and storage and is an excellent bleaching agent for chrome tanned leather.

Example 2 A solution of sodium p-aminobenzoate is prepared by' dissolving 68.5 grams of p-aminobenzoic acid and 100 grams of a 20 sodium hydroxide solution in 185 grams of water. 126 grams of melamine and 284 grams of 37% aqueous formalin are then added and the mixture is heated with agitation at 50-55 C. until a clear solution is obtained. The pH is then adjusted to 6.0 and 1 heating is continued until the desired viscosity is obtained. When a filling and bleaching agent for chrome tanned leather is desired the viscosity is usually carried to a higher degree than when the compound is to be used for tanning. Sufficient alkali is then preferably added to raise the pH of the finished solution to 9-11 after which it is diluted to 20% solids.

Erample 3 50 grams of 20% sodium hydroxide solution and 44.5 grams of beta-alanine are dissolved in 200 grams of water to a clear solution.

A trimethylol melamine solution is prepared by dissolving 126 grams of melamine in 284 grams of 37% aqueous formaldehyde solution, neutralized with sodium hydroxide to a pH of 7-3, at a temperature of G0-70 C., followed by cooling.

The two solutions are mixed and heated at 50-55 C. until no turbidity remains, after which the pH may be adjusted to 6 and heating con-- tinued if a solution of higher viscosity is desired. Increased storage stability is obtained by adding sufiicient borax or caustic soda to raise the pH to 9-10, after which the product may be diluted with water to any desired concentration for use.

Example 4 pounds of chrome tanned kipskins (six skins) were suspended in water at F. and 2% of sodium acetate, based on the dry weight of the skins, was added. After drumming 20 minutes, draining, and again drumming 5 minutes with fresh water and draining, the leather was suspended in water in a tanning drum at F. and 10% of the solution of Example 1 (20% solids) was added. The drum was then rotated for 1 hour, after which the leather was drained, washed with water fatliquored and pigmented and horsed up over night. The next morning the leather was set out and dried. In this cordition it was full and tight and considerably lighter and of better color than regular chrome tanned leather.

What I claim is:

1. A method of bleaching and filling leather which comprises impregnating the leather with an aqueous solution of the polymerized condensation product of 1 mol of an aminocarboxylic acid with 1-2.5 mols of a methylol melamine.

2. A method according to claim 1 in which the aminocarboxylic acid is an aliphatic amino'carboxylic acid.

3. A method according to claim 2 in which the aliphatic aminocarboxylic acid is glycocoll.

4. A method of bleaching and filling leather which comprises impregnating the leather with an aqueous solution of the polymerized condensation product of one mol of an aromatic aminocarboxylic acid with 1 to 2.5 mols of a methylol melamine.

- WILLIAM O. DAWSON.

REFERENCES CITED The following references are of record in the

Claims (1)

1. A METHOD OF BLEACHING AND FILLING LEATHER WHICH COMPRISES IMPREGNATING THE LEATHER WITH AN AQUEOUS SOLUTION OF THE POLYMERIZED CONDENSATION PRODUCT OF 1 MOL OF AN AMINOCARBOXYLIC ACID WITH 1-2.5 MOLS OF A METHYLOL MELAMINE.