TECHNICAL FIELD OF THE INVENTION

The present invention relates to novel, improved processes for tanning hides and to equally novel and improved leathers made by using those processes.

DEFINITIONS

Wet Blue Hide — A hide which has been cured, freed of excess hair and flesh, in some cases treated to remove fatty substances from the pores of the hides, and given a prime tan.

Float — The aqueous liquid in which a hide is processed in a tanning vat. Except in washing and rinsing steps, chemicals are added to the float to change characteristics of the hide and/or to impart additional characteristics to the hide.

BACKGROUND OF THE INVENTION

"Tanning" is a process for treating animal hides which employs metal saltε or substances found in plantε and called tannin or a combination of metal salts and tannin. Tannin and metal tanning salts cause changes in the skins which make the skins resistant to decomposition; flexible; and very strong, which greatly improves their wear resistance. The tanned hides are called leather.

Tanning processes have been employed for many centuries to dress and preserve animal hides or

skins. The treated skins are widely used for foot¬ wear, clothing, upholstery, sports equipment, sad¬ dlery, and many other items.

In conventional tanning processes, freshly split animal hides or skins are initially cured — typically by salting and/or drying — to prevent decay. These skins are treated to remove loose flesh and excess hair, typically by soaking them in a water bath containing enzymes and sometimes other chemical additives. The pretreated skins, commonly referred to as pelts, are bated by soaking them in an appropriate solution formulated to soften the pelts, to further remove excess proteins, and to improve color. In some cases, fatty substances are also leached out by additional soaking in solvent and/or detergent based solutions. The pelts are then chemically treated in vats with selected tanning agents of vegetable or mineral origin for conversion into leather. The leather is frequently treated with oils or fats or other lubricating agents to obtain soft and supple characteristics; and this is followed by appropriate dyeing, drying, and finishing steps.

The cleaning of such conventionally produced leathers can be difficult or impossible because leathers made by conventional tanning processes do not stay soft and compliant when wetted with water or water-based solutions of the type used for washing traditional woven fabrics. Instead, when wetted, leather products exhibit a tendency to become stiff and/or brittle as they dry with cracks or splits often occurring. Moreover, permanent discoloration and/or stains can occur when a conventional leather is wetted with water. As a result, cleaning techniques for

leather have generally been limited to relatively costly dry cleaning processes employing organic solvents.

Attempts have been made to permit at least some contact of leathers with water without signifi¬ cant adverse consequences. For example, there are specially treated suede leathers somewhat capable of withstanding occasional spot cleaning with water-based solutions with only minimal change to surface charac- teristics or color. Other leathers have been treated during post-tanning processes with specialized oil formulations to enhance their resistance to water penetration and damage. However, even these leather products are not capable of withstanding repeated washing in water in the manner used for cleaning traditional woven fabrics.

U.S. patent No. 4,999,024 discloses a novel tanning process capable of producing leathers which, in contrast to even those made by the specialized treatment of conventionally tanned leathers, can be washed in water without cracking, drying out, or otherwise deteriorating. Instead, the leathers made by the patented process are soft, supple, and compli¬ ant and retain these characteriεtics, even after repeated washing.

The process disclosed in the '024 patent employs a preliminary step in which hides are impreg¬ nated with a grease/oil lubricating solution. the impregnated skins are then preserved by tanning to produce a soft and supple leather. Residual lubricat¬ ing solution in the pores of the leather keeps the leather supple even after repeated washing in water.

Optimum results are obtained by starting with relatively thick skins having a well developed pore structure. The skins are typically split and cured by salting and/or drying. These skins are subjected to a preliminary cleaning step including tumbling in a bath of cold water. The tumbled skins are placed in a water-based bath containing a grease/oil lubricating solution designed to penetrate and impregnate the pores of the skins. The skins are tumbled in the lubricating solution at an elevated temperature, causing the pore structure of the skin to swell and absorb substantial quantities of the lubri¬ cating solution. Optimum results are obtained by first tumbling the skins in the heated bath and then allowing the skins to stand in the bath for at least several hours.

The thus-treated skins are removed from the lubricating solution bath, drained, and bated by tumbling them in a mild acid salt solution. Appropri- ate enzymes are normally added to the bating medium to assist in softening the skins and in removing excess proteins.

The bated skins are rinsed and tanned, preferably with a sequence of mineral and vegetable tanning agents. The result iε leathers having a substantially closed pore structure with the absorbed lubricating solution trapped in the pores.

After the last (typically vegetable) tanning step, the skins are tumbled again in a water-based grease/oil lubricating solution containing additional lubricating agents to ensure that the leather is εoft and supple. The resultant leather is drained and then finished in a conventional manner.

U.S. patent No. 4,999,024 is hereby incorpo¬ rated by reference in and made a part of this specifi¬ cation.

SUMMARY OF THE INVENTION

There have now been invented and disclosed herein certain new and novel tanning processes which have advantages over even that state-of-the-art process disclosed in the '024 patent. In particular, the herein disclosed tanning processes are capable of producing leathers which are washable and dryable even in common household appliances and, in addition, are waterproof, nonflammable, and extremely colorfast. Another important advantage of these novel processes is that the volume of toxic discharges generated in tanning hides is significantly reduced.

The novel tanning process disclosed herein, like that disclosed in the '024 patent, starts with pretreated hides — i.e., with hides which have been cured, freed of flesh and excess hair, and treated by chrome tanning or an equivalent process. These prime tanned hides are referred to in the industry as pelts or wet blue hides. In the practice of the present invention, the wet blue hides are washed and rinsed in lukewarm water to remove chemicals with which the hides have previously been treated. Next are buffering and character building steps which equalize the pH at the surface and in the interior of the leather and build wanted characteriεticε such as suppleness into the hides.

Retanning of the hides is continued by treating them with additional character builders to enhance and impart additional desirable characteris¬ tics to the hides. The hides are then washed and refloated at a mildly elevated temperature to substi¬ tute a softening agent for fat removed from the pores of the hides in a previous process step or steps. In a typical application of the present invention the refloat step is followed by treatment in a water-based solution (a term employed herein to include disper¬ sions, colloidal suspensions, etc. as well as true solutions) of additional softening agents to optimize the feel which the leather will have and a dyeing step to impart the wanted color to the leather. Next are steps which fix the previously added chemical or additives in place in the leather and refloatation with a hydrophobic waterproofing agent. These steps are followed by buffering for pH equalization and increase of the pH to an appropriate level. Then, the hides are washed, rinsed, and treated with an additive selected to impart a pleasing silky feel to the leather into which the hides are being converted. This step is followed by treatment with a hydrophobic silicone to promote waterproofability and washability; a second fixing step; and a final rinse of the pro¬ cessed hides.

All of the just-deεcribed steps need not be employed in every application of the invention. Those steps that are considered essential and thus always employed are those of: treating the hide with a pH equalizer and a character builder selected to develop characteristics wanted in the leather; treating the hide with a softening agent to soften the hide and

thereby improve the feel of the leather into which the hide is converted; treating the hide with an organic hydrophobe to impart water repellency; and treating the hide with a cationic topping oil in an amount effective to impart a pleasant tactile character.

The important objects, features, and advan¬ tages of the invention will be apparent to the reader from the foregoing, the appended claimε, and the ensuing detailed deεcription and discussion of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The novel, improved process disclosed herein can be applied to a variety of types and grades of animal hides or skins such as cattle, pig, sheep, deer and elk, goat, reptile, fish, etc. It is preferred that the skins have a relatively well developed grain or pore structure to optimize absorption of various agents with which the skins are treated. Relatively aged skins are normally preferred for this same reason. For best results, only skins of approximately uniform density and thickness are processed in the same batch.

As mentioned above, the selected hides are normally split; treated to remove excess flesh materi¬ al and hair; and cured, typically by drying and/or salting them to at least minimize preprocessing decay. The thus pretanned skins are cleaned to remove foreign material and chemicalε employed in pretanning by waεhing them in cold water for a selected time period, typically on the order of about one-half to one hour. This washing step can be repeated aε necessary with intervening draining and rinsing of the hides. The preliminary washing step or steps, as well as the subsequent process stepε deεcribed below, are carried out in traditional tanning vats having driven paddles for tumbling the skins in the tanning vat and agitat¬ ing the variouε treating solutionε.

The next step of equalizing the interior and exterior pH's of the hides and retanning the hides to build character is carried out by floating the hideε in a solution containing a buffering agent and a tanning agent, preferably one of vegetable origin such

as chestnut powder. This step is carried out in the tanning vat at a temperature of 80 to 110°F for a period of 25 to 45 minutes. pH equalization and retanning is followed by a step which continues the retanning of the hides being processed to build into the hides characteris¬ tics such as suppleness wanted in the leather being produced. The active ingredients in the retanning solution are added to the solution in which the hides are processed in the preceding steps, and the tempera¬ ture is kept the same. The retanning agents may be a combination of TERGOTAN EFB and TERGOTAN MC, both products supplied by Sandoz Chemicals Corporation.

The chemical family of TERGOTAN EFB, which is also employed to some extent as a filler, iε amino acidε; and this liquid product contains sodium εaltε of protein hydrolysates; formaldehyde; and a mixture of hydrocarbons, ethers, and ketoneε. TERGOTAN MC-N iε alεo a liquid and haε a proprietary formulation. It is dilutable in water and contains acrylic poly¬ mers.

In the step juεt described and employed to continue the retanning of the hides, the hides are tumbled in the retanning solution for 25 to 40 and typically 30 minutes.

After the continued retanning step, the hides are washed in water until clean, which typically takes 10-15 minutes, at a temperature in the range of 90 to 110"F and typically 100 ^β F. Once the wash and rinse water has been drained from the tanning vat, the hides are floated with a solution containing a softening agent. The softening agent replaces fat removed from the pores of

the hides in previous process steps and impartments supplenesε and other pleasing tactile characteristics to the hides. DERMALIX C (Sandoz Chemicals Corpora¬ tion) is a preferred softening agent because of its compatibility with the treatment agents employed to make the hides washable and waterproof.

DERMALIX C is a paste with a proprietary formulation, and it belongs in the chemical family of alkyl phosphate ester amine salts. This product contains ethylene and diethylene glycols, petroleum distillateε, and glycol etherε.

This step in which a softening agent is introduced into the pores of the hides being treated is carried out at a modestly elevated temperature — 122 to 140 ^* F and typically 130'F — to promote pene¬ tration of the softening agent into the pores of the hides. The hides are floated in the softening agent solution for a period of 30 to 45 and typically 30 minutes. Particularly for garments, softer leathers are preferred. Theεe can be readily produced by adding a εecond softening agent such as L-80 (Salem Oil & Grease Co.) to the solution with which the hides are floated in the softening step. This product iε an amber oily liquid with a pleaεant aromatic odor.

In a typical application of the invention, the hideε are dyed while they are being floated with the solution containing the softening agent(s) with this step being omitted if a leather of natural color is wanted. A variety of leather dyes and the tech¬ niques for utilizing them are well-known and commer¬ cially available, and appropriate ones of these can be readily selected by those skilled in the arts to which

this specification is addressed. The dye is added to the float solution containing the softening agent in a concentration dependent upon the dye being employed but typically on the order of two percent. A penetration aid may be added to the float solution during the 30-minute (or other duration) dye cycle to ensure that the dye penetrates through the pore structures of the hides. One appropriate pene¬ tration aid is concentrated ammonium hydroxide. This compound can be employed in a concentration of 0.5 to 2.5 percent with a 2 percent concentration being typical.

Subsequently added to the float solution in the tanning vat in a representative application of the invention are a fixing agent or a combination of fixing agents. The fixing agent permanently estab¬ lishes in the pores of the hides being treated chemi¬ cals introduced into those pores in previous process stepε εuch aε softening agents, other character builderε, and dyeε. Preferred for typical applica¬ tions is a combination of fixing agents with different fixation mechanisms — typically acid fixation and metal salt fixation. The three fixation agents are added separately to the float. Formic acid is a representative acid fixa¬ tion compound. That compound is typically employed in a concentration of 0.5 to 2.5 and typically 2 percent. Preferred mineral fixing agents are BYSANTAN DLE (BASF Corporation) and CHROMITAN FM (BASF Corporation) . The first-identified fixing agent is a proprietary liquid product containing formic acid, methanol, phenol, and ammonium sulfate, and CHROMITAN FM contains chromium hydroxide sulfate and sodium formate. The float is

continued for 30 to 60 (typically 60) minutes after the first fixing agent such as BYSANTAN DLE is added, for 10 to 15 (typically 15) minutes after the second fixing constituent such as the acid fixation agent formic acid is added, and for 15 to 30 (typically 30) minutes after the third fixing constituent such as the chrome salt fixation agent CHROMITAN FM is added. The formic acid is divided into three equal moieties. These moieties are added at equal — 5-10 (typically 10) minute — intervals to the float. The float solution can be kept at the same temperature over the course of the just-described character building (softening) , dyeing, and fixing steps.

Once these εtepε are completed, the tanning vat is drained, and the hides are washed and rinsed in clean room temperature water to remove excess procesε chemicalε with the water being drained from the tanning vat after each εtep. The hideε are tumbled in the wash and rinse waters for 5 to 10 and typically 5 minutes until clean.

The clean hideε are waterproofed by intro¬ ducing a waterproofing agent into, and permanently fixing it in, the pore structure of the hide being proceεεed. Preferred is a hydrophobic composition capable of imparting water buoyancy to the hides as well aε waterproofing them. One preferred product is OMBROPHOB M, a proprietary liquid product supplied by Sandoz Chemicalε Corporation. It contains a metal¬ lized organic compound with the formula C ₁₄ H ₂₀ Cl ₄ Cr ₂ O ₃ , hydrochloric acid, and acetone. In this step of the tanning procesε, the float is maintained at room temperature for a period of 50 to 70 (typically 60) minutes.

After the waterproofing step, a pH equaliz¬ ing agent such as the above-discussed sodium formate is added to the solution in the tanning vat to again ensure that the pH of the hides being process is uniform throughout the structure of the hides and to raise the pH of the hides which is very low (e.g., ca. 2.8-3.0) after treatment with a chrome salt fixation agent such as the above-discussed CHROMITAN FM. The sodium formate is typically employed in a somewhat lower concentration (0.7 percent as opposed to one percent in the pH equalization and elevation step) . The hides are floated at room temperature until the selected pH (typically 3.5) is reached — typically 25 minutes after the pH equalization and adjusting agent iε added to the solution in the tanning vat.

Next, the hides are washed and rinsed in warm water until clean.

In the next stage of the procesε, the clean hideε are treated sequentially in the same float with: a character building agent selected to impart a smooth, silky, even εlick feel; a second waterproofing agent; and a fixative selected to permanently retain procesεing agents added to the hides since the previ¬ ous fixation step in the pore structure of the hides. The character builders preferred at this step of the process are cationic topping oils. Representative, if not preferred, is CATALIX GS (Sandoz Chemicals Corpo¬ ration) . This paste-type product is a proprietary mixture in the fatty-acid amine condensation product family of chemicalε, and it contains acetic acid.

The hides are tumbled in the CATALIX GS- containing εolution for 25 to 35 and typically 30 minutes at a mildly elevated (100 to 115 and typically

110°F) temperature. Then, the process agent selected to further waterproof the hides and improve their washability is added to the solution in the tanning vat. Hydrophobic silicones can be used to advantage to impart washability and water repellency to the hides at this stage. A representative and often preferred product of this character is DENSODRIN S (BASF Corporation) . This proprietary product is a creamy paste which is soluble in water. After the washability/waterproofing agent is added to the float in the tanning vat, tumbling of the hides in the procesε solution is continued for a period of 15 to 30 and typically 15 minutes; and the formic acid or other fixing agent is then added. Formic acid, if selected, is effective at a lower concentration than in the earlier proceεε stage employing that compound as a fixative (0.5 as opposed to 2 percent) and iε added to the float in three equal moietieε, typically at 5-10 minute intervalε. Tum- bling of the hideε in the tanning vat iε continued for a period of 15 to 30 and typically 15 minutes after the fixative is added to the float solution.

The process is completed by draining the float solution from the tanning vat; washing the hides in room temperature water until clean to remove excess chemicals; and drying the clean hides.

As will be apparent to the reader by this juncture, hides are procesεed in accord with the principles of the present invention in a succeεsion of aqueous floats which, except for washes and rinses, contain one or more active ingredients specifically selected to impart particular characteristics to the hides being processed. Exemplary productε containing

each of these ingredients and the concentrations in which they are used appear in Table 1 below. The balance of each solution is water.

TABLE 1

Concentra¬ tion^)

Active Representative Typically

Principle Product(s) Range(ε) Preferred

Buffer Sodium Formate 0.5-1 1

Character Chestnut Powder 4-6 6

Builder TERGOTAN EFB 4-10 6

TERGOTAN MC-N 2-8 4

Softening DERMALIX C 4-8 6

Agent L-80 1-5 5

Fixing Agent BYSANTAN DLE 0.25-0.5 0.3

CHROMITAN FM 2-3 3

Formic Acid 0.5-2.5 2 and 0.5 and 0.5 to 1

Waterproofing OMBROPHOB M 6-12 10

Agent

Character CATALIX GS 1-5 2

Builder

Washability DENSODRIN S 2-4 3

Imparting/

Waterproofing

Agent

All percentages identified in Table 1 and elsewhere in thiε specification are weight percentag¬ es.

One of the important advantages of the present invention, discussed above, is that the process effluents have a εignificantly lower concen-

tration of toxic chemicals. This was confirmed by an independent testing laboratory which reported that the effluents are burdened with substantially lower amounts of organic carbon, oil, and grease and that the quality of the effluents is furthermore superior because no phenols are present.

The following Material Safety Data Sheets are hereby incorporated by reference in this specifi¬ cation. Product Product Number

TERGOTAN EFB 284002

TERGOTAN MC-N 262493

DERMALIX C 240352

L-80 N.A. BYSANTAN DLE 510211

CHROMITAN FM 595072

OMBROPHOB M 238072

CATALIX GS 233612

DENSODRIN S 512618 Many changes may of course be made in the process as described above without exceeding the scope of the present invention. For example, the optional step of dyeing the hides may be carried out after, not before, the stage in which a softening agent is introduced and fixed in the pores of the hides being treated. The invention may also be embodied in many other formε without departing from the spirit or esεential characteriεtics of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of

equivalency of the claims are therefore intended to be embraced therein.