Method of treating leather with amphoteric polymers

The present invention is directed to a method of treating tanned leather stock to improve its color expression characteristics. The method provides for utilizing a two-stage amphoteric polymers, which improve the color expression characteristic of the tanned leather stock while still retaining desired grain break and tensile strength. The tanned leather stock is contacted, preferably by immersion, in a float containing particles of an amphoteric polymer dispersed therein and a desired colorant. The amphoteric polymer particles comprise a first stage copolymer polymerized from at least one monomer containing an anionic functionality, such as, an acid functionality, with at least one first stage comonomer and a second stage copolymer polymerized from at least one monomer containing the cationic functionality, such as, an amine functionality, with at least one second stage comonomer.

This application claims the benefit of provisional application Ser. No. 
60/013,620 filed Mar. 11, 1996. 
The present invention is directed to treating leather and more particularly 
to a method for retanning leather to improve its color expression 
characteristic, which refers to the degree of uniformity of hue, intensity 
and saturation of color of leather as well as the degree of penetration of 
color in the leather skin provided by the colorant used during the 
coloring of leather. 
The treatment of hides and skins to form leather involves a number of 
interdependent chemical and mechanical operations. These operations may be 
divided into a sequence of wet end steps, i.e., process steps under wet 
conditions, followed by a sequence of dry steps, i.e., process steps under 
dry conditions. A typical leather making process involves the following 
sequence of wet-end steps: trimming and sorting, soaking, fleshing, 
unhairing, baiting, pickling, tanning, wringing, splitting and shaving, 
retanning, coloring, fatliquoring and setting out. These wet-end steps are 
followed by a sequence of dry steps, such as, drying, conditioning, 
staking, buffing, finishing, plating, measuring and grading. A description 
of each of these operations is provided in Leather Facts, New England 
Tanners (1972). 
The present invention is involved with the wet-end steps that take place 
after primary tanning; namely retanning and if desired, fatliquoring. The 
object of primary tanning is to convert the hide, pelt or skin to a stable 
non-spoilable material. This is accomplished by converting raw collagen 
fibers in the hide or skin into a stable product which is non-putrescible, 
or in other words will not rot. In addition, tanning improves a number of 
properties of the hide, pelt or skin, such as, for example, dimensional 
stability, abrasion resistance, resistance to chemicals and heat, improved 
flexibility and the ability to endure repeated cycles of wetting and 
drying. The principal method used to tan hides, pelts and skins is known 
as "chrome tanning". This employs a basic chromium sulfate, often referred 
to simply as "chrome", which is prepared by the reaction of a chromium 
salt, such as, sodium bichromate, with a sugar-like substance and sulfuric 
acid. The chrome penetrates into the skin and imparts a bluish-green color 
to the skin. The color change is typically used to assess the extent of 
penetration or degree of tanning. Hides, pelts and skins may also be 
tanned using vegetable extracts, for example, extracts from trees and 
shrubs, such as, quebracho, wattle, sumac, hemlock, oak and spruce. 
After primary tanning, the leather is retanned, colored and fatliquored. 
This three step operation is often considered together as one step since 
all these three operations may be carried out sequentially in the same 
retanning drum. Tanned leather stock, also referred to sometimes, as blue 
stock, retains much of the uneven fiber structure pattern in the skirt on 
the animal. Some areas of the skin possess a dense structure while other 
portions are loosely fibered and some portions may be undesirably thin and 
papery. Since the tanner desires to produce a uniform piece of leather, a 
step, known as "retanning", is employed to improve both aesthetic and 
physical properties. These properties include, for example, improvements 
to the fullness of the leather, the tightness and smoothness of the grain, 
the break, the levelness and intensity of the dye shade, better uniformity 
in temper or flexibility, better wettability and additional stability 
against water and perspiration. 
Retanning can be accomplished by using a variety of naturally derived 
materials including extracts from vegetables or plants, and synthetic 
tanning agents known as "syntans", or combinations thereof. Historically, 
extracts from trees and shrubs like quebracho, wattle, sumac, hemlock, oak 
and spruce were used as retanning agents. Over the past 50 years, many 
man-made syntans were developed and these are used extensively today. 
Naphthalene-formaldehyde and phenolic-formaldehyde syntans have been used 
as replacements for natural tannins and are strong dispersants for several 
other retanning chemicals. Cyanamide, dicyandiamide, urea, and melamine 
also react with formaldehyde to yield useful syntans. Acrylic syntans are 
acrylic based polymers that can be used as replacement or auxiliary 
syntans and sometimes as polymeric softeners depending on the types of 
monomeric species in the polymer. In some instances the hide may be 
retanned with chromium sulfate before the regular retanning step to fully 
tan any previously untanned portions and to level out the chrome 
especially in the grain for more uniform dyeing. After retanning or, if 
desired, during retanning, the hide is colored with colorants, such as, 
acid dyes, mordant dyes, direct dyes, metalized dyes, soluble sulfur dyes, 
and cationic dyes. Colorants which penetrate the leather skin or those 
that only impart color to the leather surface are typically utilized. In 
general, acidic dyes penetrate through the leather skin while basic dyes 
are used to color the leather surface. Colorants include natural pigments 
and synthetic dyes that are used to achieve the required color in both the 
cross section and the surface of crust leather before the finishing step. 
Colorants are classified both by chemistry and color. Leather during the 
wet-end process is typically treated with colorants alone or in 
combination with retanning agents. 
After retanning and coloring, the hide is then subjected to a fatliquoring 
step. Fatliquoring imparts the desired properties of strength, softness 
and temper to the leather after leather is dried. It is believed, without 
reliance thereon, that fatliquor lubricates the leather fibers so that 
after drying the fibers are capable of sliding over one another. In 
addition to regulating the pliability of the leather, fatliquoring 
contributes greatly to the tensile and tearing strength of the leather. 
Fatliquoring also affects the tightness of the break or, in other words, 
the crease pattern formed when the grain surface is bent inward; the 
object being to produce a leather which leaves no or few fine wrinkles 
when it is bent. 
Natural and synthetic materials used during the fatliquoring process are 
called fatliquors. These natural and synthetic materials are derived from 
fatty acids, fatty esters; oils from animal, vegetable, fish, petroleum 
sources; and a variety of synthetic materials, such as, lubricating 
acrylic syntans disclosed in the U.S. Pat. Nos. 5,330,537 and 5,348,807. 
Some of these lubricating acrylic syntans produce leather that is water 
resistant, washable, dry-cleanable and having a low fogging 
characteristic. Leather during the wet-end process is typically treated 
with fatliquors alone or in combination with retanning agents. Typically 3 
to 10 weight percent of fatliquor, based on weight of wet leather stock, 
is used during the fatliquoring process. The manner in which the fatliquor 
is distributed throughout the leather affects the character of the leather 
and subsequent finishing operations. To obtain a uniform oil coating over 
a large surface of leather fibers it is necessary to dilute the fatliquor 
with an organic solvent or preferably to disperse the oil in an aqueous 
system using emulsifiers. See Leather Technician's Handbook, J. H. 
Sharphouse, Leather Producers' Association (1971) chapters 21 and 24. 
Techniques directed to improving color expression characteristic of the 
retanned leather have been tried before. Monsheimer, et al. in U.S. Pat. 
No. 4,314,800 (hereafter '800 patent) describe the use of an aqueous 
solution or dispersion of a copolymer comprising monomers of a nitrogenous 
ester of acrylic or methacrylic acid, acrylic or methacrylic acid, and a 
different ester of acrylic or methacrylic acid for compensating the 
negative effects of the outward appearance of naturally dyed, soft aniline 
leather. The copolymer described in the '800 patent has acid and 
nitrogenous groups on the same polymer backbone. The applicants have 
unexpectedly discovered that the color expression characteristic of the 
retanned leather can be significantly improved by using a polymer wherein 
the acid and he basic groups are on different polymer segments, i.e., by 
using multi-stage amphoteric polymers while still retaining desired grain 
break and tensile strength. 
The present invention is directed to a method of treating a tanned leather 
stock comprising: 
retanning said tanned leather stock with particles of an amphoteric polymer 
dispersed in an aqueous medium to produce a retanned leather stock having 
improved color expression characteristic, said and amphoteric polymer 
particles comprising: 
a first stage copolymer polymerized from at least one monomer containing an 
anionic functionality with at least one first stage comonomer, and 
a second stage copolymer polymerized from at least one monomer containing 
the cationic functionality with at least one second stage comonomer. 
The method of the present invention further comprises retanning, 
fatliquoring or waterproofing of the tanned leather stock. 
As used herein: 
"GPC weight average molecular weight" means the weight average molecular 
weight determined by gel permeation chromatography (GPC) which is 
described on page 4, Chapter I of The Characterization of Polymers 
published by Rohm and Haas Company, Philadelphia, Pa. in 1976, utilizing 
polymethyl methacrylate as the standard. The GPC weight average molecular 
weight can be estimated by calculating a theory weight average molecular 
weight. In systems containing chain transfer agents, the theory weight 
average molecular weight is simply the total weight of polymerizable 
monomer in grams divided by the total molar amount of chain transfer agent 
used during the polymerization. Estimating the molecular weight of an 
emulsion polymer system that does not contain a chain transfer agent is 
more complex. A cruder estimate can be obtained by taking the total weight 
of polymerizable monomer in grams and dividing that quantity by the 
product of the molar amount of an initiator multiplied by an efficiency 
factor (in our persulfate initiated systems, we have used a factor of 
approximately 0.5). Further information on theoretical molecular weight 
calculations can be found in Principles of Polymerization 2nd edition, by 
George Odian published by John Wiley and Sons, N.Y., N.Y. in 1981 and in 
Emulsion Polymerization edited by Irja Pirma published by Academic Press, 
N.Y., N.Y. in 1982. 
"Glass transition temperature (Tg)" is a narrow range of temperature, as 
measured by conventional differential scanning calorimetry (DSC), during 
which amorphous polymers change from relatively hard brittle glasses to 
relatively soft viscous rubbers. To measure the Tg by this method, the 
copolymer samples were dried, preheated to 120.degree. C., rapidly cooled 
to -100.degree. C., and then heated to 150.degree. C. at a rate of 
20.degree. C./minute while data was being collected. The Tg was measured 
at the midpoint of the inflection using the half-height method. 
Alternatively, the reciprocal of the glass transition temperature of a 
particular copolymer composition may typically be estimated with a high 
degree of accuracy by calculating the sum of the respective quotients 
obtained by dividing each of the weight fractions of the respective 
monomers, M.sub.1, M.sub.2, . . . M.sub.n, from which the copolymer is 
derived by the Tg value for the homopolymer derived from the respective 
monomer, according to an equation of the form: 
##EQU1## 
wherein: 
T.sub.g(copolymer) is the estimated glass transition temperature of the 
copolymer, expressed in .degree.Kelvin (.degree.K); 
w.sub.(Mi) is the weight fraction of repeat units in the copolymer derived 
from an i.sup.th monomer M.sub.i ; and 
T.sub.g(Mi) is the glass transition temperature, expressed in 
.degree.Kelvin (.degree.K), of the homopolymer of an i.sup.th monomer 
M.sub.i. 
The glass transition temperature of various homopolymers may be found, for 
example, in "Polymer Handbook", edited by J. Brandrup and E. H. Immergut, 
Interscience Publishers. 
"Tanned leather stock" means hides, such as, those from bovines; skins, 
such as, those from pig, sheep, deer and snake; and pelts from furry 
animals, such as, rabbits, mink, sable and otter, that have been subjected 
to chrome or other metal or vegetable tanning step. 
"Retanned leather stock" means tanned leather stock that has been subjected 
to retanning step. 
"Crust leather stock" means retanned leather stock that has been dried and 
staked, i.e., mechanically softened. 
"Float" means the weight of water added to the tanning drum before the 
start of retanning or other operations, such as, coloring and 
Fatliquoring. 
"Amphoteric" means having the capacity of behaving as either an acid or a 
base. 
"Amphoteric syntan" means colloidal dispersion of particles of an 
amphoteric polymer in an aqueous medium or an aqueous mixture of 
"solubilized amphoteric polymer" (defined below) with the colloidal 
dispersion of the particles of the amphoteric polymer in the aqueous 
medium. 
"Solubilized amphoteric polymer" includes "Water Soluble amphoteric 
polymer", "Water reducible amphoteric polymer" or a mixture thereof. Water 
soluble amphoteric polymer means an amphoteric polymer dissolved in water. 
Water reducible amphoteric polymer means an amphoteric polymer dissolved 
in water and water miscible solvent. Solubilized amphoteric polymer 
results in a polymer solution characterized by having the self-crowding 
constant (K) of the Mooney equation 1/ln.sub.hrel =1/BC-K/2.5! equal to 
zero. By contrast, dispersed polymer has (K) equal to 1.9. The details of 
Mooney equation are disclosed in an article entitled "Physical 
Characterization of Water Dispersed and Soluble Acrylic Polymers" by 
Brendley et al., in "Nonpolluting Coatings and Coating Processes" 
published by Plenum Press, 1973 and edited by Gordon and Prane. 
"Polymer particle size" means the diameter of the amphoteric polymer 
particles measured by using a Brookhaven Model BI-90 Particle Sizer 
supplied by Brookhaven Instruments Corporation, Holtsville, N.Y., which 
employs a quasi-elastic light scattering technique to measure the size of 
the polymer particles. The intensity of the scattering is a function of 
particle size. The diameter based on an intensity weighted average is 
used. This technique is described in Chapter 3, pages 48-61, entitled Uses 
and Abuses of Photon Correlation Spectroscopy in Particle Sizing by Weiner 
et al. in 1987 edition of American Chemical Society Symposium series. 
"Amphoteric polymer solids" means amphoteric polymer in its dry state. 
The term "(meth)acrylate" includes acrylate and methacrylate. 
The first step of the method of the present invention includes contacting a 
tanned leather stock with particles of an amphoteric polymer dispersed in 
an aqueous medium to produce retanned leather stock having improved color 
expression characteristic. Preferably the tanned leather stock is 
immersed, more preferably in a tumbler drum which contains float 
maintained in range of 25.degree. C. to 60.degree. C., preferably in the 
range of 25.degree. C. to 45.degree. C., for 15 minutes to 3 hours, 
preferably for 30 minutes to an hour. The float contains the aqueous 
medium containing the dispersion of the amphoteric polymer particles. 
Tumbling of the tanned leather stock in the tumbler drum containing the 
particles of the amphoteric polymer dispersed in an aqueous medium is 
preferred. 
The amphoteric polymer in the form of particles of the amphoteric polymer 
dispersed in the aqueous medium is preferred, wherein the particle size of 
the dispersed polymer particles varies in the range of from 20 to 1000 
nanometers, preferably in the range of from 50 to 500 nanometers, more 
preferably in the range of from 70 to 150 nanometers. The aqueous 
evaporable medium includes water or water having dissolved therein a water 
miscible organic solvent, such as, methanol, ethanol and glycol ethers. 
Water is preferred. 
The aqueous evaporable medium includes in the range of from 15 percent to 
75 percent, preferably in the range of from 30 percent to about 50 percent 
of the particles of the amphoteric polymer, all in weight percentages 
based on amphoteric syntans. 
The amount of amphoteric polymer added to the float varies from 0.25 parts 
by weight (pbw) to 10 pbw, preferably 0.5 pbw to 5.0 pbw, of the 
amphoteric polymer per 100 pbw of the wet tanned leather stock. 
The amphoteric polymer includes multi-stage polymer particles having two or 
more stages of various geometric structures, such as, for example, 
exterior/interior regions, core/sheath particles, core/shell particles 
with shell phases incompletely encapsulating the core, core/shell 
particles with a multiplicity of cores and interpenetrating network 
particles. A first stage of the amphoteric polymer is a copolymer, 
emulsion polymerized from at least one monomer containing an anionic 
functionality with at least one first stage comonomer and a second stage 
copolymer emulsion polymerized from at least one monomer containing the 
cationic functionality with at least one second stage comonomer. 
The particles of the amphoteric polymer include in the range of from 90 
percent to 10 percent, preferably in the range of from 65 percent to 35 
percent, of the first stage copolymer and in the range of from 10 percent 
to 90 percent, preferably in the range of from 35 percent to 65 percent, 
of the second stage copolymer, all percentages being in weight percent 
based on the total weight of the amphoteric polymer solids. 
The copolymer of the first stage has a T.sub.g in the range of from 
-40.degree. C. to 140.degree. C., preferably, in the range of from 
-30.degree. C. to 120.degree. C. and, more preferably, in the range of 
from -20.degree. C. to 100.degree. C. The copolymer of the first stage has 
a weight average molecular weight, as determined by gel permeation 
chromatography using a sample of the copolymer, in the range of from 5,000 
to 3,000,000, preferably in the range of from 7,500 to 1,000,000 and more 
preferably in the range of from 10,000 to 100,000. 
The monomer of the first stage containing the anionic functionality of the 
copolymer of the first stage include one or more of the monoethylenically 
unsaturated carboxylic acid monomers which include, for example, acrylic 
acid, methacrylic acid, iraconic acid, crotonoic acid, aconitic acid, 
atropic acid, maleic acid, maleic anhydride, fumaric acid, vinyl benzoic 
acid, half-esters of ethylenically unsaturated dicarboxylic acids, 
half-amides of ethylenically unsaturated dicarboxylic acids and various 
mixtures thereof. Other suitable monomer of the first stage containing the 
anionic functionality include one or more monomethyl itaconate, monomethyl 
fumarate, monobutyl fumarate, acrylamido propane sulfonate, sodium vinyl 
sulfonate and phosphoethyl(meth)acrylate. The monomer of the first stage 
containing the monoethylenically unsaturated carboxylic acid are preferred 
and acrylic acid, methacrylic acid and mixtures thereof are more 
preferred. 
The first stage comonomer include one or more copolymerizable 
monoethylenically unsaturated monomers, that is, a monomer having a single 
ethylenically unsaturated site per molecule. Such monomers include 
olefins, (C.sub.1 -C.sub.20) alkyl or hydroxy alkyl (meth)acrylate 
monomers, vinyl aromatic monomers, vinyl esters, neutral monomers, 
crosslinkable monomers and various mixtures thereof. 
Suitable alkyl or hydroxy alkyl (meth)acrylate monomers include (C.sub.1 
-C.sub.20)alkyl (meth)acrylate monomers. As used herein the terminology 
"C.sub.1 -C.sub.20)alkyl" denotes an alkyl substituent group having from 1 
to 20 carbon atoms per group. Suitable (C.sub.1 -C.sub.20)alkyl 
(meth)acrylate monomers include, for example, acrylic and methacrylic 
ester monomers including methyl (meth)acrylate, ethyl (meth)acrylate, 
butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, 
lauryl (meth)acrylate, cetyl (meth)acrylate, eicosyl (meth)acrylate, 
isobornyl (meth)acrylate, isodecyl (meth)acrylate, oleyl (meth)acrylate, 
palmityl (meth)acrylate, stearyl (meth)acrylate, hydroxyethyl 
(meth)acrylate, and hydroxypropyl (meth)acrylate, or various mixtures 
thereof. 
Suitable vinyl ester monomers include, for example, vinyl acetate, vinyl 
propionate, vinyl neononanoate, vinyl neodecanoate, 
vinyl-2-ethylhexanoate, vinyl pivalate, vinyl versatate or a mixture 
thereof. Suitable vinyl monomers include, for example, vinyl halide, 
preferably vinyl chloride, vinylidene halide, preferably vinylidene 
chloride, or various mixtures thereof. 
Suitable vinyl aromatic monomers include, for example, one or more 
polymerizable vinyl aromatic compounds and mixtures thereof and also 
include styrene, alkyl-substituted styrenes, such as, 
.alpha.-methylstyrene, .alpha.-ethylstyrene, p-methylstyrene and vinyl 
xylene, halogenated styrenes, such as, chlorostyrene, bromostyrene and 
dichlorostyrene, other styrenes having one or more nonreactive 
substituents on the benzene nucleus, vinyl naphthalene or various mixtures 
thereof. 
Suitable neutral monomers include, for example, one or more monomers, such 
as, acrylonitrile, acrylamide, alkyl substituted acrylamide monomers or 
mixtures thereof. 
Suitable crosslinkable monomers include allyl (meth)acrylate; acrylic and 
methacrylic esters of diols, triols, such as, ethylene di(meth)acrylate, 
1,3-butylene di(methacrylate), 1,6-hexane di(meth)acrylate, 
trimethylolpropane triacrylate; divinyl benzene; dicyclopentadienyl 
(meth)acrylate; butadiene monomers; glycidyl (meth)acrylate; 
acetoacetoxyetlyl (meth)acrylate; acrolein, methacrolein; isocyanoatoethyl 
methacrylate, dimethyl meta-isopropenyl benzyl isocyanate or various 
mixtures thereof. 
The first stage comonomer is preferably a monoethylenically unsaturated 
monomer selected from the group consisting of methyl methacrylate, butyl 
acrylate, butyl methacrylate, ethyl acrylate, ethylhexyl acrylate, 
styrene, methyl styrene and various mixtures thereof. 
Even more preferred first stage comonomer is at least one or more of the 
following monomeric mixtures: 
1) butyl acrylate and methyl methacrylate, 
2) butyl methacrylate and methyl methacrylate, 
3) butyl acrylate and styrene, 
4) 2-ethylhexyl acrylate with methyl methacrylate, or 
5) 2-ethylhexyl acrylate with styrene. 
The most preferred monoethylenically unsaturated monomer is a mixture of 
styrene and 2-ethylhexyl acrylate. 
The copolymer of the first stage includes in the range of from 0.5 percent 
to 20.0 percent, preferably in the range of from 5 percent to 15 percent, 
of the monomer containing the anionic functionality and in the range of 
from 99.5 percent to 80.0 percent, preferably in the range of from 95 
percent to 85 percent, of the first stage comonomer, all percentages being 
in weight percent based on the total weight of the amphoteric polymer 
solids. 
The copolymer of the second stage has a T.sub.g in the range of from 
-40.degree. C. to 140.degree. C., preferably, in the range of from 
-30.degree. C. to 120.degree. C. and, more preferably, in the range of 
from -20.degree. C. to 100.degree. C. The copolymer of the second stage 
has a weight average molecular weight, as determined by aqueous gel 
permeation chromatography using a hydrolyzed sample of the copolymer, in 
the range of from 5,000 to 3,000,000, preferably in the range of from 
7,500 to 1,000,000 and more preferably in the range of from 10,000 to 
100,000. 
The monomer of the second stage containing the cationic functionality 
includes one or more of monomers containing an amine functionality, such 
as, for example, tert-buytlaminoethyl acrylate, dimethylaminoneopentyl 
(meth)acrylate, diethylaminopropyl (meth)acrylamide, 
dimethylamino-2,2'-dimethylpropyl (meth)acrylamide, amino-substituted 
olefins, such as, p-diethylaminoethyl styrene; basic nitrogen-containing 
heterocycles that carry a polymerizable ethylenically unsaturated 
substituent, such as, for example, vinyl pyridine, N-vinyl pyrrolidone and 
2-vinyl-5-ethyl pyridine; esters of amino alcohols with ethylenically 
unsaturated carboxylic acids, such as, for example, N, 
N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, N, 
N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl methacrylate and 
N-tert-butylaminoethyl acrylate; monoamides of diamines of ethylenically 
unsaturated carboxylic acids, such as, for example, N, 
N-dimethylaminopropyl acrylamide and N, N-dimethylaminopropyl 
methacrylamide and the quaternary ammonium salts of the above, such as 
those derived from methyl chloride, or dimethyl sulfate. 
The second stage comonomer is selected from one or more monomers from the 
list of monomers described earlier with respect to the first stage 
comonomer. If desired, it is contemplated that one of ordinary skill in 
the art may utilze the same first stage comonomer as the second stage 
comonomer during polymerization of the second stage copolymer. 
The copolymer of the second stage includes in the range of from 0.5 percent 
to 20.0 percent, preferably in the range of from 5 percent to 15 percent, 
of the monomer containing the cationic functionality and in the range of 
from 99.5 percent to 80.0 percent, preferably in the range of from 95 
percent to 85 percent, of the second stage comonomer, all percentages 
being in weight percent based on the total weight of the amphoteric 
polymer solids. 
The polymerization techniques used for preparing the amphoteric polymer of 
the present invention are well known in the art. The amphoteric polymer 
may be prepared by emulsion polymerization. Either thermal or redox 
initiation processes may be used. 
The multi-stage polymer particles of the amphoteric polymer are prepared by 
conventional emulsion polymerization process in which at least two stages 
differing in composition are formed in a sequential fashion. Such a 
process usually results in the formation of at least two polymer 
compositions. Each of the stages of the multi-stage polymer particles may 
contain the same chain transfer agents, surfactants, as those disclosed 
below. The emulsion polymerization techniques used for preparing such 
multi-stage polymer particles are well known in the art and are disclosed, 
for example, in the U.S. Pat. Nos. 4,325,856, 4,654,397, 4,814,373 and 
4,916,171. 
The polymerization process is typically initiated by conventional free 
radical initiators, such as, for example, hydrogen peroxide, t-butyl 
hydroperoxide, ammonium and alkali persulfates, typically at a level of 
0.05 percent to 3.0 percent by weight, all weight percentages based on the 
weight of total monomer. Redox systems using the same initiators coupled 
with a suitable reductant such as, for example, sodium bisulfite, sodium 
hydrosulfite and ascorbic acid, may be used at similar levels. 
Chain transfer agents may be used in an amount effective to provide the 
desired GPC weight average molecular weight. For the purposes of 
regulating molecular weight of the amphoteric polymer being formed, 
suitable chain transfer agents include well known halo-organic compounds, 
such as, carbon tetrabromide and dibromodichloromethane; sulfur-containing 
compounds, such as, alkylthiols including ethanethiol, butanethiol, 
tert-butyl and ethyl mercaptoacetate, as well as aromatic thiols; or 
various other organic compounds having hydrogen atoms which are readily 
abstracted by free radicals during polymerization. Additional suitable 
chain transfer agents or ingredients include but are not limited to butyl 
mercaptopropionate; isooctylmercapto propionate; bromoform; 
bromotrichloromethane; carbon tetrachloride; alkyl mercaptans, such as, 
1-dodecanthiol, tertiary-dodecyl mercaptan, octyl mercaptan, tetradecyl 
mercaptan, and hexadecyl mercaptan; alkyl thioglycolates, such as, butyl 
thioglycolate, isooctyl thioglycoate, and dodecyl thioglycolate; 
thioesters; or combinations thereof. Mercaptans are preferred. 
When a dispersion of amphoteric polymer particles is utilized, the polymer 
particle size is controlled by the amount of conventional surfactants 
added during the emulsion polymerization process. Conventional surfactants 
include anionic, nonionic emulsifiers or their combination. Typical 
anionic emulsifiers include the salts of fatty rosin and naphthenic acids, 
condensation products of naphthalene sulfonic acid and formaldehyde of low 
molecular weight, carboxylic polymers and copolymers of the appropriate 
hydrophile-lipophile balance, alkali or ammonium alkyl sulfates, alkyl 
sulfonic acids, alkyl phosphonic acids, fatty acids, and oxyethylated 
alkyl phenol sulfates and phosphates. Typical nonionic emulsifiers include 
alkylphenol ethoxylates, polyvinyl alcohols, polyoxyethylenated alkyl 
alcohols, amine polyglycol condensates, modified polyethoxy adducts, long 
chain carboxylic acid esters, modified terminated alkylaryl ether, and 
alkylpolyether alcohols. Typical ranges for surfactants are between 0.1 to 
6 percent by weight based on total weight of total monomer. 
Preferably, the first stage copolymer of the amphoteric polymer is emulsion 
polymerized in the aqueous medium by copolymerizing at least one monomer 
containing the anionic functionality, such as, the acid functionality, 
with at least one first stage comonomer. Once the copolymerization is 
completed, the pH of said aqueous medium is sufficiently raised to avoid 
coagulation of the amphoteric polymer particles in the presence of an 
cationic functionality by adding a base, such as, ammonia, alkali metal 
hydroxide, morpholine and lower alkyl amine, to the aqueous medium. The pH 
of the aqueous medium is typically raised to be in the range of from 6 to 
12, preferably in the range of from 8 to 11. 
Following the addition of base, the second stage copolymer of the 
amphoteric polymer is emulsion polymerized in the aqueous medium by 
copolymerizing at least one monomer containing the cationic functionality, 
such as, the amine functionality, with at least one second stage 
comonomer. 
The aqueous medium containing the amphoteric syntan is added to the float, 
which may contains one or more colorants, for imparting the desired color 
to the tanned leather stock. If desired, one or more colorants may be 
added to the float after the addition of the aqueous medium containing the 
amphoteric syntan to the float. Typically one or more colorants in the 
range of from 0.5 percent to 7.5 percent per 100 percent of the weight of 
wet tanned stock are added to the float during the retanning step or, if 
desired, added as a coloring separate step after the retanning step. The 
amount of colorant added depends upon the desired result, i.e., if 
coloring of the leather surface is desired, preferably colorants in the 
range of from 0.5 percent to 4.0 percent per 100 percent of the weight of 
wet tanned stock are added to the float. Higher amounts may be needed if 
penetration of colorant in the leather skin is desired. Some of the 
typical dyes used in coloring leather include anionic dyes, such as, those 
supplied by Sandoz Chemical Corporation, Charlotte, N.C., include Derma 
Blue R 67, Derma Green BS, Derma Grey LL. Some of the anionic metal 
complex dyes supplied by Sandoz Chemical Corporation, Charlotte, N.C., 
include Sandoderm Yellow R, Sandoderm Brown G. 
If desired, the float further contains one or more fatliquors, such as, 
those described earlier, for improving the strength and temper of the 
retanned leather stock. If desired, the fatliquoring step may be combined 
with the retanning step or coloring step.

PREATION OF SYNTANS 
EXAMPLE 1 
Comparative Example 1 was a solubilized polymer commercially available as 
Relugan.RTM., RE--Anionic acrylic syntan and supplied by BASF Corporation, 
Rensselaer, N.Y. 12144. 
EXAMPLE 2 
Comparative Example 2 was a solubilized amphoteric polymer commercially 
available as Magnopal.RTM., III--Amphoteric acrylic syntan and supplied by 
Stockhausen, Greensboro, N.C. 27406 
EXAMPLE 3 
Comparative Example 3 was a solubilized copolymer was prepared in the 
following manner: 
At the start of preparation, 1250 g of deionized water (DI water) was added 
to a 3 liter, round bottom, four necked flask, equipped with an agitator, 
a condenser, a thermocouple to monitor the temperature, inlet ports for 
nitrogen gas, a monomer feed line and an initiator feed line. The 
headspace of the flask was swept with nitrogen and then the contents were 
heated to 85.degree. C. In a separate vessel, a monomer mix was prepared 
front 300 g of acrylic acid (AA) and 200 g of methacrylic acid (MAA) to 
provide a 60/40 proportion by weight. A portion of the monomer mix (50 g) 
was added to the flask, followed by 2 g of ammonium persulfate dissolved 
in 10 g of deionized water. After 20 minutes, feeds of the remaining 
monomer mix and a solution of 5 g of ammonium persulfate dissolved in 60 g 
of deionized water were begun and continued at a constant rate for a 
period of two hours while the reaction temperature was maintained at 
90.degree. C. When the feeds were completed, the feed lines were rinsed 
with 35 g of deionized water and the reaction mixture was maintained at 
90.degree. C. for another hour. The reaction mixture was then cooled and 
poured into a jar. The resulting clear, pale yellow solution polymer was 
found to have a 27.7 weight percent solids content, a pH of 2.2 and a 
viscosity of 815 cps (measured by Brookfield viscometer with No. 2 spindle 
rotated at 30 rpm). 
EXAMPLE 4 
Comparative Example 4 was a one-stage amine and acid containing amphoteric 
copolymer dispersion prepared according to Example 1 from U.S. Pat. No. 
4,314,800. The copolymer was polymerized from a monomeric mixture 
containing 77.9 percent butyl acrylate (BA)/9.4 percent methtyl 
methacrylate (MMA)/10 dimethyl aminoethyl methacrylate (DMAEMA)/2.7 MAA, 
all by weight percentages based on polymer solids. 
EXAMPLE 5 
Comparative Example 5 was a two-stage amine after acid, amphoteric 
copolymer prepared according to Example 1 from U.S. Pat. No. 3,404,114. 
The copolymer was polymerized from a first stage monomeric mixture 
containing 32.5 percent ethyl acrylate (EA), 15.3 MAA, 0.5 percent AA and 
1.0 percent MAA and a second stage monomeric mixture containing 32.5 
percent EA, 15.3 percent MMA and 2.9 percent (tertiary-butyl aminoethyl 
methacrylate) t-BAEMA, all by weight percentages based on polymer solids. 
EXAMPLE 6 
At the start of the preparation, 255 g of deionized water and 3.6 g of 
Alipal.RTM. CO-436 anionic surfactant, ammonium salt of sulfated 
polyethoxynonylphenol @ 58 percent concentration were added to a 3 liter, 
round bottom, 4 neck glass flask, equipped with an agitator, a condenser, 
a thermocouple to monitor the temperature and inlet ports for nitrogen 
gas, and for adding reagents. The headspace was swept with nitrogen and 
the contents of the flask were heated to 85.degree. C. In a separate 
vessel, a first monomer pre-emulsion was prepared from 255 g deionized 
water, 3.9 g of Alipal.RTM. CO-436 anionic surfactant, 150 g styrene, 175 
g of 2-ethylhexyl acrylate (2-EHA), 35 g methacrylic acid and 1.1 g butyl 
mercaptopropionic acid. A heel charge of 20 g of the monomer pre-emulsion, 
0.75 g of ammonium persulfate dissolved in 7.5 g of deionized water and 
1.4 g of sodium carbonate dissolved in 15 g of deionized water was added 
to the reaction flask. After 10 minutes, the remainder of the first 
monomer pre-emulsion and 0.35 g of ammonium persulfate dissolved in 45 g 
of deionized water were added continuously to the flask over 1.5 hours 
while maintaining the reaction temperature at 85.degree. C. A total of 45 
g of deionized water was used to rinse the feed lines to the flask. The 
reaction mixture was maintained for another 30 minutes at 85.degree. C. 
and then cooled to 60.degree. C. while a second monomer pre-emulsion was 
prepared from 214 g of deionized water, 3.8 g of Alipal.RTM. CO-436 
anionic surfactant, 140 g styrene (Sty), 175 g 2-ethylhexyl acrylate, 35 g 
dimethylaminopropyl methacrylamide (DMAPMA) and 1.1 g butyl 
mercaptopropionic acid. The pH of the reaction was adjusted from 5.0 to 
10.8 with 80 g of 28 percent ammonium hydroxide and a solution of 0.014 g 
iron sulfate heptahydrate and 0.014 g of the tetrasodium salt of 
ethylenediamine tetraacetic acid in 10.7 g deionized water was then added 
to the reaction mixture. The second pre-emulsion, 1.9 g of tert-butyl 
hydroperoxide dissolved in 50 g of deionized water and 1.1 g of sodium 
formaldehydesulfoxylate dissolved in 50 g of deionized water were added 
continuously to the reaction mixture over 1.5 hours at 60.degree. C., 
followed by an additional 3.0 g of tert-butyl hydroperoxide dissolved in 
45 g deionized water and 2.0 g sodium formaldehydesulfoxylate dissolved in 
52.5 g deionized water. The dispersion was then cooled to room temperature 
and 15 g of nonionic surfactant (Triton.RTM., X-405, octylphenoxy 
polyethoxy ethanol, HLB: 17.9, 70% concentration) in 15 g of deionized 
water was added. The resulting two-stage amine after acid amphoteric 
polymer was produced from a first stage copolymer containing 25 percent 
2-EHA, 20 percent Sty/5 MAA and from a second stage copolymer containing 
25 2-EHA/20 Sty/5 DMAPMA, all in weight percentages based on polymers 
solids. The amphoteric polymer of Example 6 was found to have a 37.3 
weight percent solids content, a pH of 10.6 and a Brookfield viscosity of 
36 cps (measured with a spindle No. 1 turning at 60 rpm). 
EXAMPLE 7 
At the start of the preparation, 340 g of deionized water and 10.2 g of 
Alipal.RTM. CO-436 anionic surfactant, ammonium salt of sulfate 
polyethoxynonylphenol @ 58 percent concentration were added to a 2 liter, 
round bottom, 4 neck glass flask, equipped with an agitator, a condenser, 
a thermocouple to monitor the temperature and inlet ports for nitrogen 
gas, and for adding reagents. The headspace was swept with nitrogen and 
the contents of the flask were heated to 85.degree. C. In a separate 
vessel, a monomer pre-emulsion was prepared from 110 g deionized water, 
10.2 g of Alipal.RTM. CO-436 anionic surfactant, 163.2 g styrene, 139.8 g 
butyl acrylate, 139.8 g butyl methacrylate 35 g methacrylic acid and 1.1 g 
butyl mercaptopropionic acid. A heel charge of 20 g of the monomer 
pre-emulsion, 0.75 g of ammonium persulfate dissolved in 7.5 g of 
deionized water and 1.4 g sodium carbonate dissolved in 15 g of deionized 
water was added to the reaction flask. After 10 minutes, the remainder of 
the first monomer pre-emulsion and 0.35 g of ammonium persulfate dissolved 
in 45 g of deionized water were added continuously to the flask over 1.5 
hours while the reaction temperature was maintained at 85.degree. C. A 
total of 45 g of deionized water was used to rinse the feed lines to the 
flask. The reaction mixture was held for additional 30 minutes at 
85.degree. C. and then cooled before adding 0.01 g of iron sulfate 
heptahydrate, 1.6 g of tert-butyl hydroperoxide and 1.1 g sodium 
formaldehydesulfoxylate in a total of 156 g of deionized water. After 
cooling to room temperature, the pH of the reaction mixture was adjusted 
to 6.0 with 28 percent aqueous ammonium hydroxide. The resulting one-stage 
acid containing emulsion copolymer produced from a monomeric mixture 
containing 30 percent BA, 35 percent Sty, 30 percent BMA and 5 percent 
MAA, all in weight percentages based on polymers solids, was found to have 
a 42.0 weight percent solids content, a pH of 6.0. 
EXAMPLE 8 
Comparative Example 8 was a one-stage acid containing emulsion polymer with 
composition 30 BA/35 MMA/30 BMA/5 MAA, prepared by the method of Example 
7, except that the monomer pre-emulsion was prepared from 110 g deionized 
water, 10.2 g of Alipal.RTM. CO-436 anionic surfactant, 163.2 g methyl 
methacrylate, 139.8 g butyl acrylate, 139.8 g butyl methacrylate 35 g 
methacrylic acid and 1.1 g butyl mercaptopropionic acid. The resulting 
anionic emulsion polymer was found to have a 42.2 weight percent solids 
content, a pH of 6.0. 
EXAMPLE 9 
Example 9 was a two-stage amine after acid amphoteric polymer with 
composition (15 BA/17.5 MMA/15 BMA/2,5 MAA-first stage coplymer)/(10 
BA/17.5 MMA/12.5 BMA/10 DMAEMA-second stage copolymer), prepared by the 
method of Example 6, except that the monomers in the first pre-emulsion 
were 105 g butyl acrylate, 122.5 g methyl methacrylate, 105 g butyl 
methacrylate and 17.5 g methacrylic acid, the monomers in the second 
pre-emulsion were 70 g butyl acrylate, 122,5 g methyl methacrylate, 87.5 g 
butyl methacrylate and 70 g dimethylaminoethyl methacrylate, and the first 
pre-emulsion was added to the reactor over 3 hours and the second 
pre-emulsion was added to the reactor over 30 minutes. In addition, the 
nonionic surfactant was omitted. The resulting two-stage amine after acid 
amphoteric polymer produced from a first stage monomeric mixture 
containing 15 percent BA, 17.5 percent MMA, 15 percent BMA and 2.5 MAA and 
from a second stage monomeric mixture containing 10 BA, 17.5 percent MMA, 
12.5 percent BMA and 10 percent DMAEMA, all in weight percentages based on 
polymers solids, was found to have a 42.8 weight percent solids content. 
EXAMPLE 10 
Example 10 was a two-stage amine after acid amphoteric polymer with 
composition (15 BA/17.5 Sty/15 BMA/2.5 MAA-first stage copolymer)/(10 
BA/17.5 Sty/12.5 BMA/10 DMAEMA-second stage copolymer), prepared by the 
method of Example 6, except that the monomers in the first pre-emulsion 
were 105 g butyl acrylate, 122.5 g styrene, 105 g butyl methacrylate and 
17.5 g methacrylic acid, the monomers in the second pre-emulsion were 70 g 
butyl acrylate, 122.5 g styrene, 87.5 g butyl methacrylate and 70 g 
dimethylaminoethyl methacrylate, and the first pre-emulsion was added to 
the reactor over 3 hours and the second pre-emulsion was added to the 
reactor over 30 minutes. In addition, the nonionic surfactant was omitted 
from this sample. The resulting two-stage amine after acid amphoteric 
copolymer produced from a first stage monomeric mixture containing 15 
percent BA, 17.5 percent Sty, 15 percent BMA and 2.5 MAA and from a second 
stage monomeric mixture containing 10 BA, 17.5 percent Sty, 12.5 percent 
BMA and 10 percent DMAEMA, all in weight percentages based on polymers 
solids, was found to have a 41.8 wt % solids content. 
Treatment of Leather 
All retanned leathers were prepared from either lightweight (thickness 
varying from 1.0 to 1.4 mm) or heavyweight (thickness varying from 1.9 to 
2.3 mm) shaved wet-blue, chrome tanned bovine leather. The retanning step 
was conducted in matched tanning drums manufactured by Dose Maschinenbau 
Gmbh, which were specifically designed for wet-end leather procedures. 
These heated, rotating, stainless steel drums had a volume of about 396 
liters. 
All the weights used during the retanning or any subsequent steps, such as, 
coloring and fatliquoring steps, were based on the relative weight of the 
wet blue stock (chrome tanned leather) in a tanning drum. For example, a 
100 percent float was a weight equal to the weight of the wet blue stock. 
A 200 percent float would be equal to the addition of twice the amount of 
water to stock weight. The term "offer" means the amount weight of dry 
(also known as solid additives or copolymer solids), added to the float. 
Evaluation of Treated Leather 
The evaluation the retanned leather examples included physical 
measurements, aesthetic handle evaluations, and qualitative color 
evaluations. The retanned leather examples were grouped into sets of six 
to four examples to reflect experimental controls on retan process, raw 
materials, or blue stock. The treated leather examples prepared by the 
retan processes were subject to physical testing for 
Tongue Tear: The crust leather's strength was measured by a tensile 
strength tester similar to that used for conducting the Standard Test 
Method for Tearing Strength, Tongue Tear of Leather, ASTM D4704-93. The 
sole exception was that the leather sample did not have a 4.76 mm hole 
located on the long axis 25.4 mm from one end. The Tongue Tear test 
involved cutting the test specimen and then pulling the two tongues apart. 
The Tear Strength was reported in Newtons. The tongue tear strength for a 
piece of upholstery leather, such as, the light weight leather, used in 
the Examples 1 to 6, was measured against a scale in which a value of 20 
Newtons is considered to be acceptable and and a value of 30 Newtons is 
considered to be excellent. 
In addition to the quantitative evaluation of thickness ratio, temper, 
water resistance, and strength, we qualitatively observed and evaluated 
aesthetic properties of the treated leather by methods familiar to those 
skilled in the art. The rating of the grain break pattern seen when 
evaluating crust leather has both an objective and an end use component. 
Objectively, finer and tighter grain is better, but what is very good for 
a heavyweight, stand-up boot may not be acceptable for a fine piece of 
lightweight leather. The attributes of color as described in Color 
Matching With Dyes On Leather, Joseph A. Casnocha, a Sandoz, Ltd. 
publication, have three recognized components: hue, lightness, and 
saturation. Dyeing results are rated qualitatively, but are expected to 
relate to getting a vivid, true color with minimum dye used during the 
coloring step. 
Grain Break is evaluated by visual inspection (observation) of the treated 
leather as it is hand flexed or bent. The break is rated on a scale of 
excellent, good, fair and poor. A grain break rating better than poor but 
less than fair (fair to poor) is considered acceptable for heavy leather 
stock. 
Dyeing Result is evaluated by visual inspection of the treated leather with 
the emphasis on the hue (relative to the expected "true color") and the 
vividness (lack of grayness, whiteness, or bleaching). The color is rated 
on a scale of very good, good, fair, and poor. 
Retan Procedure for Examples 1 to 6 
1. Shaved wet blue, chrome-tanned, 1.0 to 1.4 mm (light weight stock) 
bovine stock was tumbled for 15 minutes with 200 percent float maintained 
at 40.degree. C. After 15 minutes, the water was drained from the tanning 
drum, supplied by Dose Maschinenbau Gmbh. 
2. Sodium formate at 0.5 weight percent based on the blue stock weight was 
added to 200 percent fresh float maintained at 40.degree. C. The stock was 
neutralized for 75 minutes and the pH of the float was adjusted to 5.25 
with sodium bicarbonate. After 75 minutes, the float was drained from the 
tanning drum. 
3. The neutralized stock was then washed in the tanning drum for another 15 
minutes with 200 weight percent fresh float at 40.degree.C. for 15 
minutes, and after 15 minutes the water was drained. 
4. The stock was retanned for 60 minutes with 200 percent float at 
40.degree. C. with a 5 weight percent solids of syntan offers of Examples 
1 through 6, described above. The stock was then dyed with 0.75 weight 
percent of Derma Havana R.RTM. dye (product as supplied by Sandoz 
Chemicals Corporation, Charlotte, N.C. 28205) for 30 minutes. The dye 
containing stock was then "fixed" or acidified with 10 percent of formic 
acid by adjusting pH to less than 4.0. After 120 minutes, the retan float 
was drained. 
5. The fixed, retanned stock was washed in the tanning drum for 15 minutes 
with 200 percent float maintained at 40.degree. C. After 15 minutes the 
water was drained. 
6. The retanned stock was fatliquored for 60 minutes with 200 percent float 
at 40.degree. C. containing 4 weight percent (product as sold by supplier) 
based on the blue stock weight of Morite.RTM. G82 a blend of 67 percent 
natural and 33 percent synthetic fatliquors with 2.5 percent combined 
SO.sub.3 (sulfonate content) from Whittemore-Wright Co.)! and then fixed 
with 10 percent formic acid to pH less than 3.5. 
8. The fatliquored and retanned stock was hauled, horsed overnight, set out 
by hand, vacuum dried for 1 minute at 70.degree. C., aired off overnight 
at room temperature, and then staked before evaluation. 
The test results for leather retanned with Examples 7 through 10 are 
tabulated below in Table 1. 
TABLE 1 
______________________________________ 
Example Coloring Results 
Tongue Tear (Newtons) 
______________________________________ 
1 5th best brown hue, 
22.8 
bleached to pastel-fair 
color 
2 4th best brown hue, 
16.8 
slightly bleached tan- 
good color 
3 6th best brown hue, 
22.4 
bleached whitish-poor 
color 
4 3rd best brown hue, less 
19.0 
vivid-good color 
5 2nd best brown hue, 
20.1 
vivid-very good color 
6 The best brown hue, 
22.4 
vivid-very good color 
______________________________________ 
Examples 1 through 6 exhibited excellent grain break and firm temper. Table 
1, illustrates inventors unexpected discovery of utilizing a two-stage 
amphoteric polymers (Examples 5 and 6) which impart best color expression 
characteristic while still retaining other critical properties, such as, 
tensile strength (tongue tear) and grain break relative to the comparative 
Examples 1 through 4. 
Retan Procedure for Examples 7 to 10 
1. Shaved wet blue, chrome-tanned, 1.9 to 2.3 mm (heavy weight stock) thick 
bovine stock was tumbled in the tanning drum for 15 minutes with 200 
percent float maintained at 40.degree. C. After 15 minutes, the water was 
drained from the tanning drum, supplied by Dose Maschinenbau Gmbh. 
2. The stock was neutralized for 120 minutes in 200 percent fresh float 
maintained at 40.degree. C. with 1 percent sodium acetate and 0.5 percent 
solids of Leukotan.RTM. 1028 acrylic polymer was supplied by Rohm and Haas 
Company, Philadelphia, Pa. The pH of the float was adjusted to 5.5 with 
sodium bicarbonate. After 120 minutes, the float was drained. 
3. The neutralized stock was washed in the tanning drum for 15 minutes with 
200 percent fresh float maintained at 50.degree. C. for 15 minutes. After 
15 minutes the water was drained. 
4. The stock was retanned for 120 minutes with 125 percent float maintained 
at 60.degree. C. The float contained 4 percent solids of Lubritan.RTM. WP 
acrylic polymer supplied by Rohm and Haas Company, Philadelphia, Pa. as a 
primary acrylic polymeric lubricating syntan-and waterproofing agent and 4 
percent solids of syntan offer of Examples 7 through 10 described earlier 
as an auxiliary retan agent, 0.5 percent Vitrolan.RTM. Orange dye, 
(supplied by Sandoz Chemicals Corporation, Charlotte, N.C. 28205). The 
stock was fixed with 10 percent formic acid to pH of less than 4.0. After 
120 minutes the float was drained. 
5. The fixed stock was washed in the tanning drum for 15 minutes with 200 
percent float maintained at 35.degree. C. After 15 minutes, the water was 
drained. 
6. The stock was retanned for 60 minutes with 200 percent float maintained 
at 35.degree. C. with 5 weight percent (product as sold by supplier) based 
on the blue stock weight of Wayne Tan.RTM. 150 chromium sulfate supplied 
at 33 percent basicity. Wayne Tan.RTM. 150 chromium sulfate is supplied by 
Wayne Chemical Corporation, Milwaukee, Wis. After 60 minutes, the chrome 
float was drained. 
7. The stock was washed twice for 15 minutes with 200 percent float 
maintained at 35.degree. C. After each 15 minute wash cycle the water was 
drained. 
8. The retanned stock was hauled, horsed overnight, set out by hand, vacuum 
dried for 2 minutes at 70.degree. C., aired off overnight at room 
temperature, and staked before evaluation. 
The test results for leather retanned with Examples 1 through 6 are 
tabulated below in Table 2: 
TABLE 2 
______________________________________ 
Example Coloring Results 
Grain Break Rating 
______________________________________ 
7 3rd best orange hue, off 
Good-the best grain break 
shade-fair color 
8 4th best orange hue, 
Fair to good-3rd best 
pastel brown-poor color 
grain break 
9 2nd best orange hue, 
Fair to poor-4th best 
vivid-good color 
grain break, 
10 The best orange hue, 
Fair to good-2nd best 
vivid-good color 
grain break 
______________________________________ 
Table 2, illustrates inventors unexpected discovery of utilizing a 
two-stage amphoteric polymers (Examples 9 and 10) which impart best color 
expression characteristic while still retaining acceptable grain break 
relative to the comparative Examples 7 and 8.