U.S. patent application number 12/360862 was filed with the patent office on 2009-05-21 for natural grain leather.
This patent application is currently assigned to Seton Company. Invention is credited to Hermann Winkler.
Application Number | 20090130429 12/360862 |
Document ID | / |
Family ID | 32073520 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090130429 |
Kind Code |
A1 |
Winkler; Hermann |
May 21, 2009 |
Natural Grain Leather
Abstract
A leather finishing process in which, in pertinent part, a warm
water milling step is added after the base coat is applied to
"crust" leather and cured. The warm water contains at least one dye
fixation agent including but not limited to about 0.1-2.0% by
weight of formic acid. Moreover, the base coat itself is an aqueous
base coat containing at least two polymers such as an acrylic salt
or a polyurethane salt. Between the polymeric constituents of the
base coat, the acid fixation agent, and the use of the warm water
milling step after the base coat has been applied and dried, a
surprisingly natural feel to the leather is attained without loss
of excellent adhesion, wear-resistance and other properties when
the leather is completely finished.
Inventors: |
Winkler; Hermann; (Malvern,
PA) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING, 436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Assignee: |
Seton Company
Norristown
PA
|
Family ID: |
32073520 |
Appl. No.: |
12/360862 |
Filed: |
January 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10682689 |
Oct 9, 2003 |
|
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12360862 |
|
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60418785 |
Oct 15, 2002 |
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Current U.S.
Class: |
428/323 ;
428/423.4 |
Current CPC
Class: |
C14C 11/006 20130101;
B05D 7/12 20130101; Y10T 428/31551 20150401; C09D 133/08 20130101;
C14B 3/00 20130101; Y10T 428/31558 20150401; C08L 75/04 20130101;
Y10T 428/25 20150115; C08G 18/0823 20130101; Y10T 428/4935
20150401; C09D 133/08 20130101; C08L 2666/20 20130101 |
Class at
Publication: |
428/323 ;
428/423.4 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B32B 27/40 20060101 B32B027/40 |
Claims
1. A natural grain leather comprising: a natural grain leather
sheet having a grain surface area, said grain surface area having a
plurality of hair cells therein; and said grain surface area having
a coating thereon, wherein when the natural grain leather sheet is
curved over a U-shaped half pipe, said half pipe having a diameter
of about 70 mm, said natural grain leather sheet folds into a
series of upturns that form shallow ridges, each shallow ridge
having a peak, wherein said natural grain leather has a peak to
peak distance from an adjacent shallow ridge of 1 mm or less,
wherein said leather withstands 30,000 cycles on a Toyota 5.9.2B
test, survives 3,000 cycles on a Nissan NES M0155-15.2 test and
withstands 6,000 cycles on a Mercedes DIN 53,339 test.
2. The natural grain leather according to claim 1, wherein said
coating of said grain surface area contains two polymers, wherein
said two polymers are polyurethane and acrylic.
3. The natural grain leather according to claim 2, wherein said
coating has a plurality of particles, and further wherein said
particles have a diameter of about 10 .mu.m.
4. The natural grain leather according to claim 3, wherein said
natural grain leather sheet exhibits a volatile organic hydrocarbon
content less than about 0.1 mg/kg.
5. The natural grain leather according to claim 4, wherein said
natural grain leather sheet exhibits a formaldehyde concentration
less than about 2 mg/kg.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/682,689, filed Oct. 9, 2003, which claims the benefit of
U.S. Provisional Application No. 60/418,785, filed Oct. 15, 2002,
the entire contents of all of said applications is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a new leather manufacturing process
which gives an enhanced natural feel to automotive leather without
sacrificing wear, abrasion-resistance, adhesion or other qualities
essential to satisfying rigorous automotive leather
specifications.
[0004] 2. Description of Related Art
[0005] Leather manufacturing is a technology which has developed
over many centuries using cattle, goat, kid, sheep and lamb hides,
and even horse, pig, kangaroo, deer, reptile, seal and walrus,
among others. The properties of the leather end-product vary
depending upon the type of hide as well as the method used to tan
and otherwise to treat and to finish the hide used to make it.
Leather production normally consists of three processes, namely,
the "beamhouse" processing; tanning; and finishing. The "beamhouse"
process removes dirt and unwanted constituents of the hide, such as
hair. Tanning includes the physical and chemical processes whereby
the collagen of the leather is crosslinked to stabilize the leather
into a permanent material which will not putrefy and decompose.
Finishing gives the leather the properties essential for its
ultimate use.
[0006] Leather is used in an enormous variety of applications,
including but not limited to furniture upholstery, clothing, shoes
including athletic shoes, luggage, handbag and accessories and
automotive applications, including automotive seating, and
instrument panels, door panels and other interior components. Of
all the uses of leather, virtually the most difficult durability
specifications to meet are those in the automotive industry,
because the life of the leather must be extremely long in the
automotive application while at the same time the leather must be
able to withstand excesses of physical stress, temperature extremes
and sunlight. Traditionally, therefore, automotive leather has
required intensive manufacturing treatment, usually with repeated
polymer coatings during the finishing process, in order to meet the
applicable strength and durability standards.
[0007] Unfortunately, the traditional addition of heavy polymer
coatings to the surface of the leather has also altered the natural
hand and feel of the leather, so that the most durable leathers for
automotive applications heretofore also had the poorest aesthetic
qualities. Ironically, these traditional, heavily coated leathers
often resembled, to the discerning touch, the very vinyl or other
leather-substitute materials for which satisfactory natural leather
replacements were sought. Reducing the number of polymer coatings
and/or the amounts of polymer applied per layer can restore natural
feel to the leather but then in turn reduces wear-resistance and
other strength properties. In view of the aesthetic reasons for
incorporating leather into automotive interiors in the first place,
rendering the leather into a seemingly polymeric product is
counterproductive. Therefore, a need remains for a leather
manufacturing method which can meet strict automotive standards and
still retain the hand and feel characteristics of "natural" leather
such as aniline and semi-aniline leather; leather types which
heretofore have not had sufficient light and stain resistance to be
used in automotive applications.
SUMMARY OF THE INVENTION
[0008] In order to meet this need, the present invention is a
leather finishing process in which, in pertinent part, a warm water
milling step is added after the base coat is applied to "crust"
leather. The warm water contains at least one acid fixation agent
such as, without limitation, formic acid, acetic acid, propionic
acid or hydrochloric acid. The base coat itself is an aqueous base
coat containing at least two polymers such as aliphatic
polyurethane and acrylic. Ordinarily, in order to obtain an aqueous
polymer, such as polyacrylic acid or, for example, a
dimethylolpropionic acid-containing polyurethane, an amine group is
admixed into the aqueous polymer solution in order to form a salt
with the carboxylic acid group on the polymer molecule. The amine
complexes with the carboxylic acid to form a carboxylic acid salt,
thus increasing the solubility of the associated polymer. In view
of the nature of the solubility of the polymers, it is believed
that upon the addition of the acid fixation agent, the carboxyl
groups are competitively reassociated with hydrogen, due to the
excess of hydrogen ions provided by the acid. It is believed,
without any intention to be bound by this theory, that this
competitive reassociation, sometimes called "salting out," causes
the polymer base coat to precipitate within the crevices of the
leather, thus fixing the polymer well within the grain. In view of
the polymeric constituents of the base coat, the use of the acid
fixation agent, and the use of the warm water milling step after
the base coat has been applied and dried, even after subsequent top
coating, a surprisingly natural feel to the leather is attained
without loss of excellent adhesion or wear-resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1-6 are scanning electron micrographs of flat and
curved surfaces of three representative samples of different
leathers at 1,000.times. magnification;
[0010] FIG. 1 is a photomicrograph of a flat surface of the present
leather ("Prestige");
[0011] FIG. 2 is a photomicrograph of a curved surface of the
present leather;
[0012] FIG. 3 is a photomicrograph of a flat surface;
[0013] FIG. 4 is a photomicrograph of a curved surface of prior art
Nappa leather;
[0014] FIG. 5 is a photomicrograph of a flat surface;
[0015] FIG. 6 is a photomicrograph of a curved surface, of prior
art Black Furniture leather;
[0016] FIGS. 7-12 are scanning electron micrographs of flat and
curved surfaces of three representative samples of different
leathers at 300.times. magnification;
[0017] FIG. 7 is a photomicrograph of a flat surface;
[0018] FIG. 8 is a photomicrograph of a curved surface, of the
present leather ("Prestige");
[0019] FIG. 9 is a photomicrograph of a flat surface;
[0020] FIG. 10 is a photomicrograph of a curved surface, of prior
art Nappa leather;
[0021] FIG. 11 is a photomicrograph of a flat surface, and FIG. 12
is a photomicrograph of a curved surface, of prior art Black
Furniture leather;
[0022] FIGS. 13-18 are scanning electron micrographs of flat and
curved surfaces of three representative samples of different
leathers at 100.times.. magnification;
[0023] FIG. 13 is a photomicrograph of a flat surface;
[0024] FIG. 14 is a photomicrograph of a curved surface, of the
present leather ("Prestige");
[0025] FIG. 15 is a photomicrograph of a flat surface;
[0026] FIG. 16 is a photomicrograph of a curved surface, of prior
art Nappa leather
[0027] FIG. 17 is a photomicrograph of a flat surface;
[0028] FIG. 18 is a photomicrograph of a curved surface, of prior
art Black Furniture leather;
[0029] FIGS. 19-24 are scanning electron micrographs of flat and
curved surfaces of three representative samples of different
leathers at 30.times. magnification;
[0030] FIG. 19 is a photomicrograph of a flat surface, and FIG. 20
is a photomicrograph of a curved surface, of the present leather
("Prestige");
[0031] FIG. 21 is a photomicrograph of a flat surface, and FIG. 22
is a photomicrograph of a curved surface, of prior art Nappa
leather;
[0032] FIG. 23 is a photomicrograph of a flat surface, and FIG. 24
is a photomicrograph of a curved surface, of prior art Black
Furniture leather;
[0033] FIGS. 25-30 are scanning electron micrographs of flat and
curved surfaces of three representative samples of different
leathers at 10.times. magnification;
[0034] FIG. 25 is a photomicrograph of a flat surface;
[0035] FIG. 26 is a photomicrograph of a curved surface of the
present leather ("Prestige");
[0036] FIG. 27 is a photomicrograph of a flat surface;
[0037] FIG. 28 is a photomicrograph of a curved surface, of prior
art Nappa leather;
[0038] FIG. 29 is a photomicrograph of a flat surface;
[0039] FIG. 30 is a photomicrograph of a curved surface, of prior
art Black Furniture leather;
[0040] FIG. 31 is a polarized light micrograph of the present
leather ("Prestige") (magnified 141.times.);
[0041] FIG. 32 is a polarized light micrograph of prior art Nappa
leather (magnified 141.times.);
[0042] FIG. 33 is a polarized light micrograph of prior art Black
Furniture leather (magnified 141.times.);
[0043] FIG. 34 is a bar graph that illustrates break evaluation
data for the leather of the present invention ("Prestige") as well
as prior art Nappa and Furniture leathers, utilizing acoustic
emission (AE) technology to determine the AE energy/count
ratio;
[0044] FIG. 35 is a bar graph that illustrates tensile strength
evaluation data of the leather of the present invention
("Prestige") as well as prior art Nappa and Furniture leathers,
utilizing AE technology to determine the tensile strength of the
three leathers;
[0045] FIG. 36 is a bar graph that illustrates initial strain
energy data of the leather of the present invention ("Prestige") as
well as prior art Nappa and Furniture leathers, utilizing AE
technology to determine the softness of the three leathers, as well
as their resistance to small deformations; and
[0046] FIG. 37 is a bar graph that illustrates toughness indices of
the leather of the present invention ("Prestige") as well as prior
art Nappa and Furniture leathers, utilizing AE technology to
determine the strength, robustness and stiffness of the three
leathers.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The essential method step of the present invention inheres,
in pertinent part, within the finishing step of the leather
manufacturing process. All manner of tanning and retanning leather
processes of all types are therefore suitable to adaptation and
improvement by the methods disclosed herein. For example, the
present finishing process may be practiced on chrome-tanned and
non-chrome-tanned leathers alike, or on any type of hide as long as
it is a natural collagen-containing animal skin. In order to
establish context, the following brief summary of basic leather
manufacturing is provided below.
[0048] The "beamhouse" process is generally the first step in the
tanning process and includes soaking freshly skinned or cured hides
in order to prevent their putrefaction prior to further processing.
The curing step tends to remove moisture from the hides, causing
them to become hard and difficult to work with. As a result, the
first wet process which is used after curing is the simple soaking
and rehydrating of cured hides, followed by soaking in salts and
other rehydrating agents. After soaking, the hides may be fleshed
to remove the excess tissue and to remove muscles or fat adhering
to the hide. Hides are then dehaired to ensure that the grain is
clean and that the hair follicles are free of hair roots, by using
liming processes, scraping, or both. When liming is used, it is
followed by deliming. If the hides have not previously been
fleshed, they may be fleshed after liming.
[0049] Bating is then performed, in which the hides are treated
with proteolytic enzymes to purify the material prior to tanning.
Bating loosens the hide structure and removes unwanted proteins,
thus imparting a softness, stretch and flexibility to the leather.
Bating and deliming may be performed together in a combined
deliming-bating solution. Bating is followed by "pickling," or
soaking in acid(s) and salt(s) in order to bring the hides to the
desired pH for tanning.
[0050] The second phase, the "tanning" phase, involves the use of
chromium-containing tanning agents, vegetable-based tanning agents,
or other tanning agents. The purpose of the tanning agents is to
crosslink the collagen in the hides. Chrome tanning is performed
using a one-bath process that is based on the reaction between the
hide and a trivalent chromium salt, usually a basic chromium
sulfate. Vegetable tanning agents are similarly applied to the
hides by soaking the hides, sometimes for several days, in aqueous
solutions of tanning agents extracted from plant material parts
such as fruits, pods, and roots. Typically, what is referred to as
tanning also includes a "retanning" step, prior to finishing,
comprising neutralization, retanning, dyeing, fat-liquoring,
toggling and milling. More particularly, hides are neutralized,
tanned again, often in a different tanning agent than was
originally used, in order to impart the desired properties, colored
with water-soluble dyes and treated by applying "fat-liquoring"
agents, literally oil materials intended to replace the natural
oils in the hides that were lost in all the previous processing.
Toggling refers to clamping the hides onto screens, followed by
oven drying the hides while they are stretched on the screens.
Milling is then performed, that is, the retanned and toggled hides
are tumbled in drums to soften them.
[0051] The first and second phases of leather production are well
known in the art and do not form a central part of the present
invention. At this point in the leather production process, the
hides are referred to as "crust" leather, that is, leather which
has been tanned and retanned but not yet finished. Crust leather
will not putrefy and has extraordinary natural feel, but is not
suitable for many, if any, applications because it is very soft,
will not pass present automotive specifications, and readily
absorbs any oil or dirt with which it comes in contact and which
thereafter is impossible to remove.
[0052] Finishing of the crust leather according to the invention
generally involves the steps of base coating, optional clear top
coating, and milling in warm water, followed by toggling, further
milling, staking, and application of one or more top coats followed
by additional milling and staking. Of these finishing steps, the
steps essential to the present invention are the base coat
composition and its application, and the warm water milling acid
fixation step. The base coat to be used to coat the crust leather,
for the purpose of the present invention, is an aqueous composition
containing both polyurethane and acrylic. Any aqueous solutions or
dispersions of polyurethane and acrylic coating compositions may be
combined in order to practice the present invention.
[0053] In the preferred embodiment, the base coat contains about
60% of an aqueous acrylic composition containing, in pertinent
part, about 20% acrylic and about 0.4% propanol (such as
isopropanol), admixed with about 2% polyurethane in aqueous
dispersion together with 10% silica duller by weight, about 22%
silica drier by weight, and about 2-3% pigment by weight. Exemplary
commercially available compositions which may be admixed include,
without limitation, aqueous acrylic AB 810 (Quaker Color division
of McAdoo & Allen, Inc., Quakertown, Pa.), aliphatic
polyurethane dispersion JK-233 (Quaker Color), BS 287 silica duller
(Quaker Color), BS 457 silica drier (Quaker Color), together with
pigments known in the art. The polyurethane should be present in
the base coat in the amount of about 1-10% by weight, preferably
about 2-4% by weight, most preferably about 2% by weight; the
acrylic should be present in the composition in the amount of about
10-40% by weight, more preferably about 15-30% by weight and most
preferably about 20% by weight. Additional ingredients may be added
according to the skill in the art, but as long as the polyurethane
and the acrylic are present in the base coat, in the above amounts,
the base coat may be used in the practice of the present
invention.
[0054] After base coating, warm water milling is conducted by
loading the hides into drums and immersing and tumbling them in
warm water containing at least one acid fixation agent such as,
without limitation, formic acid, acetic acid, propionic acid or
hydrochloric acid. The hides are immersed in 150-300% by weight 45
degrees C. water and tumbled for about 1 hour. The water
temperature may be varied from 30-55 degrees C., more preferably
35-50 degrees C., most preferably 45 degrees C. It should be
appreciated that inserting a warm water tumbling step into a
leather manufacturing process, immediately following base coating,
is not only not customary but may be tantamount to heresy in the
leather manufacturing world. For one thing, leather manufacturers
often separate their wet-treatment facilities from their coating
facilities for environmental and other regulatory reasons, because
wet-process leather tanning is not allowed in all industrial areas.
Moreover, the traditional wisdom of leather processing has assumed
that all wet-processing should take place during the preparation of
the crust leather, and that the focus of the finishing phase should
be on the coating of the leather, not the further saturation of the
hides with excesses of water. Hides thus warm water tumbled are
subsequently toggled, milled, staked, top coated, milled and
softened according to means known in the art. (Staking may be
accomplished using a "Vibrasoft" machine, which is a specialized
machine in which plates are equipped with multiple engaging
"fingers" (protrusions), which push and pull at the leather surface
to stretch it without perforating the hide.) Milling during
finishing often involves dry-tumbling the hides to soften them.
Toggling, milling and staking are well known in the leather making
arts.
[0055] Ordinarily, in order to obtain an aqueous polymer, such as
polyacrylic acid or, for example, a dimethylolpropionic
acid-containing polyurethane, an amine group is admixed into the
aqueous polymer solution in order to form a salt with the
carboxylic acid group on the polymer molecule. The amine complexes
with the carboxylic acid to form a carboxylic acid salt, thus
increasing the solubility of the associated polymer. In view of the
nature of the solubility of the polymers, it is believed that upon
the addition of the acid fixation agent, the carboxyl groups are
competitively reassociated with hydrogen, due to the excess of
hydrogen ions provided by the acid. It is believed, without any
intention to be bound by this theory, that this competitive
reassociation, sometimes called "salting out," causes the polymer
base coat to precipitate within the crevices of the leather, thus
fixing the polymer well within the grain.
[0056] After the base coat application and warm milling step is
completed, the crust leather is dried and optionally further
applied with a small amount of clear top coat prior to warm water
milling. The amount of the base coat to be applied to the crust
leather may range up to the amount of base coat typically applied
to Nappa leathers of the prior art, or may be reduced to
approximately half the amount of base coat compared to the amounts
traditionally applied to Nappa leather. For example, a typical
Nappa leather according to the prior art can have applied to the
crust leather 3.0-4.0 grams per square foot of base coating
composition, whereas in the practice of the present invention the
base coat may be applied in amounts as little as 1.0-2.0 grams per
square foot or less, preferably 1.5-1.7 grams per square foot, as
well as greater amounts. This reduction in the amount of base coat
undoubtedly contributes to the natural characteristics of the
ultimate leather product prepared using the inventive finishing
steps.
[0057] In view of the polymeric constituents of the base coat, the
use of the acid fixation agent, and the use of the warm water
milling step after the base coat has been applied and dried, even
after subsequent top coating a surprisingly natural feel to the
leather is attained without loss of excellent adhesion or
wear-resistance. In theory, although there is no intention to be
bound by the theory, it is believed that the combination of at
least two polymers in the aqueous base coating composition, namely,
polyurethane and acrylic, creates an effective yet migratable
coating on the crust leather, particularly in view of the salting
out precipitation effect. The coating thus formed is believed to be
able to migrate, during warm water milling, to descend into the
lowermost crevices of the grain of the leather, in order to expose
somewhat the grain and hair cell features which would otherwise be
covered more thickly with base coat. Regardless of the mechanism by
which the invention operates, however, empirically the combination
of the base coat, the acid fixation and the warm water milling
gives leather with improved natural feel while simultaneously
creating leather capable of passing all major automotive
wear-resistance and other tests. Data objectively corroborating
various features which correlate with the improved natural feel are
presented hereinafter.
[0058] Finished leather can be subjected to various analytical and
experimental methodologies in order to determine qualitative and
quantitative characteristics of different leather samples. Such
characteristics can vary substantially depending on the leather
finishing techniques employed. Analytical techniques used in the
industry include, without limitation, international wear evaluation
that consists of the following tests: Wyzenbeek wear-high wear;
taber abrasion; Veslic dry, wet and sweat colorfastness; Gakushin
friction; traverse abrasion; pilling wear; and Honda abrasion;
softness evaluation including G.M. pliability, BLC, frank
stiffness, relative stiffness, Ford stiffness, bending, and Renault
softness; long term Xenon evaluation which includes light
resistance as quantified by change in color properties as measured
by delta L, delta E, delta a, delta b, percent shrinkage, and gloss
changes; wet heat cycle test; water vapor permeability test; and
Nissan slide friction test. Experimental methodologies that are
used to quantify typical leather characteristics include, without
limitation, acoustic emission analysis and microscopic analysis.
Scanning and transmission electron miscroscopy, as well as
polarized light microscopy, can be used to study how various
surface treatments affect the break (wrinkle) pattern observed on
the leather surfaces when leather samples are placed in a U-shaped
"half pipe" jig typically having a diameter of 70 mm and attached
thereto with backing tape or adhesive. Using such microscopic
techniques, the relationship of the degree of the break pattern to
surface and cross-section morphology can be examined. It is well
known in the art that the nature and severity of the break pattern
defines the acceptability of the leather product for a particular
application, such as automotive leather. Specifically, scanning
electron microscopy can be used to characterize the surface
morphology of leather samples, transmission electron microscopy can
be used on thin sections of leather samples to resolve structural
features, and polarized light microscopy can be used to examine the
cross-sections of thick sections of leather samples.
[0059] The present finishing method may be used in any other
leather manufacturing process, for grain leather, embossed leather,
or corrected leather, particularly those hides destined for
automotive use. The leathers may be chrome-tanned or
non-chrome-tanned, may be natural in color or include dyes and
pigments, and may be retanned, fat-liquored or top coated with any
materials known in the art. The central feature of the invention is
the combination of the particular base coating step with the warm
water milling step which follows the application of the base coat,
and this central feature may be transplanted into numerous other
leather processes, especially for the automotive industry.
[0060] Although the invention has been described above, the
following Examples are illustrative.
EXAMPLE 1
[0061] Cattle hides were collected and treated from hair removal
through tanning and retanning, toggling and drying to create crust
leather. A base coat in the amount of 1.5-1.7 grams per square foot
was applied to the surface of the crust leather and allowed to dry
at about 75-100 degrees C. A thin layer of clear top coat was
applied immediately over the base coat and likewise allowed to dry
at about 75-100 degrees C. The hides were then loaded into a drum
with 150% by weight 45 degree C. water and tumbled for an hour. The
hides were then subsequently gently squeezed dry without rolling,
toggled, milled for 8 hours without added water, staked, sprayed
with top coat, allowed to dry, and treated with final staking and
milling treatments to soften them. The resulting leather had a much
softer, warmer hand and feel than traditional Nappa leather,
displayed excellent "break" in the leather, and yet satisfied major
automotive leather specifications in test results described
below.
[0062] The leather finished according to the above, treated with a
single top coat, was subjected to abrasion testing using dry white
felt, wet white felt and artificial-perspiration soaked white felt
repeatedly drawn across the leather. In order to achieve a 5 on a
scale of 15, the felt had to remain free of any pigment from the
leather. In tests involving multiple repetitions of abrasion by
each felt, with repetition numbers exceeding the repetitions
necessary for commercial automotive quality control, the leather
described above consistently scored a "5."
[0063] The same leather hides were tested according to standard
automotive testing procedures which test adhesion, flexometer and
abrasion as measured in Newtons (N). While only 3 N was necessary
to meet the adhesion test, the hides exhibited 9.63 N. The minimum
grade of 4 N on the flexometer 20.000 test was necessary to meet
automotive standards, and the hides exceeded this standard with 5
N.
[0064] The same leather hides were tested according to certain
additional, international test standards. The Toyota test method
5.9.2B was used to subject the hides to 10,000 cycles per each five
minutes of 1.8 KGF tension and 2.8 weight, but the leather was able
to withstand 30,000 cycles. Likewise, the Nissan NES M0155-15.2
test (taber abrasion, CS10 wheel, 1,000 grams, 1,000 cycles) was
used to test the hides, which survived 3,000 cycles. While the
Mercedes test DIN 53,339 requires Veslic rub, dry, 2,000 cycles,
the leather hides described above were able to withstand 6,000
cycles. All of these test results are surprising in view of the
soft, natural hand and feel of the leather; in the past, leather
subjected to tests such as these have been heavily coated and
heavily compromised as to aesthetics.
EXAMPLE 2
[0065] A quantity of hides were treated in exactly the same way,
from hair removal to finishing, except that a warm water milling
step was added after the base coat was applied to some of the hides
and the remaining hides were base coated without a subsequent water
milling step. The base coat enumerated in Example 1 was used in the
amount of 3.0-3.5 grams per square foot of hide on all the hides;
roughly double the amount of base coat as used in Example 1.
Notwithstanding the additional amount of base coat, the hides that
were warm water tumbled displayed significantly improved hand,
feel, break (as judged in the half pipe test), softness and
apparent warmth as compared to the hides that were not warm water
milled. The hides which had been warm water milled subsequent to
base coating also had a more pronounced visual appearance of
leather grain and hair cells compared to the hides which had not
been warm water milled.
EXAMPLE 3
[0066] Finished hides of four chrome-tanned prior art leathers
("Vision," "New Frontier," "Classique," "Salon"), as well as a
chrome-tanned leather of the present invention ("Prestige"), were
subjected to volatile organic hydrocarbon (VOC) analysis in order
to determine the total VOC content (mg/kg) of the leathers, using
the Toyota Tedlar Bag Method. Of the five finished hides tested,
"Prestige" had the lowest VOC content of 0.05 mg/kg. The other four
prior art leathers had substantially higher VOC contents, ranging
from 0.6 mg/kg up to 2.6 mg/kg.
EXAMPLE 4
[0067] Finished hides of four chrome-tanned prior art leathers
("Vision," "New Frontier," "Classique," "Salon"), as well as a
chrome-tanned leather of the present invention ("Prestige"), were
subjected to formaldehyde analysis using the Toyota Tedlar Bag, IUC
19 Photometric, and IUC 19 HPLC test methods in order to determine
the formaldehyde concentration (mg/kg) in the leathers. Using the
Toyota Tedlar Bag method, "Prestige" leather exhibited no
formaldehyde concentration; "Salon," "Classique," and "New
Frontier" had 0.01 mg/kg formaldehyde concentration; and "Vision"
had 0.05 mg/kg formaldehyde concentration. Using the IUC 19
Photometric method, "Prestige," "Salon," "Classique" and "New
Frontier" had less than 0.1 mg/kg formaldehyde concentration.
Finally, using the IUC 19 HPLC method, "Prestige" had the lowest
formaldehyde concentration of 1 mg/kg. The other four prior art
finished hides had formaldehyde concentrations ranging from 2.5
mg/kg ("Salon") up to 20 mg/kg ("Vision").
EXPERIMENT 1
Microscopy Analysis
1. Materials and Methods
[0068] A. Scanning Electron Microscopy (SEM)
[0069] SEM was used to examine samples of leather ("Prestige")
prepared according to Example 1, as well as samples of prior art
Nappa and Black Furniture leathers. SEM uses a highly focused
electron beam (less than 10 nm diameter) which can be scanned in a
raster on the sample surface. The intensity of secondary electrons
produced at each point is used to form a picture of the sample.
Magnification factors from 10.times. to 100,000.times. can be
obtained. The depth of field is inherently quite large which allows
the micrographs to be in focus at all points across a rough
surface. In addition, SEM does not suffer from light reflecting off
at odd angles and being lost from view, a problem encountered with
light microscopy.
[0070] Leather samples were submitted as approximately 9
inch.times.9 inch sheets. The sheets were initially examined using
a Bausch and Lomb StereoZoom stereoscope. A small one-inch square
piece was sectioned from each sample for scanning electron
micrograph examination. An adhesive-backed paper was applied to the
backside of the leather products. Each leather sample was then
prepared in two ways. A section was applied flat onto an aluminum
mount using a carbon double-sided adhesive tape. A second section
was affixed with backing tape into a U-shaped half-pipe with a
constructive 70 mm diameter. This device simulates the concave
curvature used in break pattern testing. The samples were gold
coated using an SPI Supplies Sputter Coater Module System to ensure
electrical conductivity in the SEM. The analysis was conducted
using a scanning electron microscope manufactured by JEOL (USA),
Inc. of Peabody, Mass. Representative scanning electron micrographs
were obtained on two representative areas in series form at the
magnifications of 10.times., 30.times., 100.times., 300.times., and
1,000.times. using 0 degree tilt and 25 KeV. Images were captured
digitally directly from the scanning electron microscope using the
Spectrum Mono software package.
[0071] B. Polarized Light Microscopy (PLM)
[0072] PLM was used to examine samples of present leather
("Prestige"), as well as samples of prior art Nappa and Black
Furniture leathers. PLM is a method for determining the unique
optical crystallographic properties of various crystal phases in a
sample. PLM is an invaluable tool in the identification of
crystalline materials and, when used in conjunction with dispersion
staining, is typically used in the identification of minerals such
as asbestos. The combination of PLM with dispersion staining makes
it possible to systematically identify transparent substances by
their dispersion colors in known refractive index media. The
technique can be used to examine thick sections of polymers in
order to determine their crystalline and spherilitic structure,
surface (skin) effects, and inconsistencies in morphology which can
be caused by the lack of homogeneity in the polymers. PLM
methodology can be used to examine materials prepared under similar
conditions and to obtain information on sections with regard to
their gross similarities or differences.
[0073] PLM was performed on the leather samples using a Vickers M41
PhotoPlan Light Microscope marketed by Vickers' Instruments of
Malden, Mass. Sections of the leather samples were cut and mounted
in a 1.550 Refractive Index Liquid and a glass coverslip was added.
The sections were examined using brightfield light and
representative images were taken at 141.times..
[0074] Dimensional measurements made on all of the micrograph
images are accurate to within 10% of their stated values.
2. Results
[0075] A. SEM
[0076] Flat surfaces of the present leather ("Prestige") (FIGS. 1,
7, 13, 19, 25) were found to exhibit a fairly uniform surface
structure with a number of "pits" believed to correspond to hair
cells or pores. Higher magnifications revealed a coated surface
that contained a high concentration of particles, approximately 10
.mu.m in size. Curved surfaces of Prestige leather (FIGS. 2, 8, 14,
20, 26) revealed similar structures, with the addition of a series
of shallow ridges. The peak to peak distance between adjacent
shallow ridges were 1 mm or less.
[0077] Flat surfaces of prior art Nappa leather (FIGS. 3, 9, 15,
21, 27) revealed a smooth surface with little evidence of hair
cells or pores. A number of ridge-like features were observed on
the surface. Higher magnifications revealed a higher concentration
of coating particles than what was observed with Prestige leather.
Curved surfaces of Nappa leather (FIGS. 4, 10, 16, 22, 28) revealed
significantly larger ridges than those observed on the Prestige
leather. The peak to peak distance between the ridges ranged from 1
mm to several millimeters.
[0078] Flat surfaces of prior art Black Furniture leather (5, 11,
17, 23, 29) more closely resembled Prestige leather than Nappa
leather because of the presence of hair cells or pores. The pores
observed in the leather, however, appeared less distinct and more
coated with particles than those observed in the Prestige leather.
The surface of the Black Furniture leather also appeared smoother
than Prestige leather, which was likely due to the smaller size of
the coating particles found on the Black Furniture leather. Curved
surfaces of Black Furniture leather (FIGS. 6, 12, 18, 24, 30)
revealed sharp channels and ridges, as well as flat islands. Some
deeper channels with an almost crack-like appearance were also
observed. The peak to peak distance between the ridges ranged from
1 mm to 2 mm.
[0079] B. PLM
[0080] The leather of the present invention ("Prestige") (FIG. 31)
revealed a coating layer on the thick sections. The leather
substrate, or skin (Area A), the coatings on the surface (Area B),
and the epoxy layer (Area E) can all be observed clearly. The
coatings appeared to fill in deep pore regions and extend down well
below the surface. The coatings, however, did not appear to totally
fill the pores. The coating thickness was approximately 30-40
.mu.m.
[0081] Cross sections of prior art Nappa leather (FIG. 32) revealed
a coating layer of approximately 90 .mu.m, which was two to three
times thicker than what was observed on the Prestige leather. The
coating layer appeared continuous with no apparent breaks, and pore
areas were generally not infiltrated by the coating material,
although there was evidence of some penetration of the coating into
the surface of the leather.
[0082] Prior art Black Furniture leather (FIG. 33) revealed a thin
coating layer approximately 20 .mu.m in thickness. The coating
layer was generally uniform with some areas, typically around the
pores, having a thinner coating than other areas. The coating did
not fill the pores although it did extend into some of the
underlying voids.
3. Discussion
[0083] Microscopic analysis indicates that the nature and extent of
the coating was at least partially responsible for the observed
break patterns, which suggests a complex mechanism for the
formation of the observed break patterns in the three types of
leather examined. The leather of the present invention ("Prestige")
revealed a relatively thin coating layer with unfilled pores which
allowed the surface of the leather to fold along lines from pore to
pore, thus minimizing the uplifting of the ridge areas and
producing a desirable break pattern.
[0084] Prior art Nappa leather revealed a heavy coating layer that
almost completely filled the few pores that were present and
appeared to form some of the surface ridge features. This resulted
in leather with no pore features that could "absorb" the folding of
the leather. Bending the leather created large, wide ridges, and
revealed that the thick coating layer was more restrictive than the
present leather, characteristics that become apparent only when the
leather is affixed with backing tape to a substrate.
[0085] In prior art Black Furniture leather, pores were observed;
however, either they were not as deep as the pores observed with
the present leather or they may have been partially filled with
coating material. An embossing feature on the surface of the
leather was also observed, which resulted in the formation of a
number of deep channels. When the leather was curved, it appeared
to create folds along the channels that had a greater spacing and a
bigger break pattern than what was observed in either the present
("Prestige") or Nappa leathers.
4. Conclusions
[0086] The leather of the present invention ("Prestige") revealed
numerous hair cells or pore structures that appeared to be
responsible for minimizing the height of ridge formation during
break testing. Prior art Nappa leather was observed to have a thick
coating with little or no exposed pore structures. Curving the
Nappa leather resulted in the formation of large, unacceptable
ridges. Prior art Black Furniture leather revealed a number of
pores, however they were not deep or were partially filled with
coating. Embossing of the Black Furniture leather created deep
channels. Curving the Black Furniture leather created folds along
the channels that had greater spacing, larger ridges, and a bigger
break pattern than what was observed in the either the present
("Prestige") or Nappa leathers, with the present leather having the
smallest peak to peak ridge distance of 1 mm or less.
EXPERIMENT 2
Acoustic Emission Technology
[0087] The analysis herein was conducted in association with the
Eastern Regional Research Center of the United States Department of
Agriculture. Acoustic emission (AE) technology is an experimental
method capable of characterizing the physical/mechanical properties
of leather and provides a nondestructive way to monitor the quality
of leather without damaging the leather in the process. AE
technology was used to measure the flexing endurance of the leather
coatings of the leather of the present invention ("Prestige"), as
well as prior art Nappa and Black Furniture leathers. In effect,
this technique is able to "listen" and analyze sounds emitted by
leather as it is being stretched. The particular parameters
evaluated were break pattern, tensile strength, initial strain
energy, and toughness.
[0088] 1. Break Evaluation
[0089] To evaluate break patterns, each leather sample was bent
into a 16 cm half pipe jig and affixed thereto with backing tape. A
special sensor moved across the surface at a constant weight and
speed. Fibers of the leather were compressed, causing the sides of
each fiber to rub against one another, thus emitting acoustic
signals. When the leather was bent, this compressed the grain,
which, because of its attachment to the half-pipe jig with backing
tape, produced tension in the underlying corium layer. Gaps or
"looseness" between the grain and corium layers gave off more AE
energy per count because the grain was not firmly attached to the
corium and therefore rubbed against the corium as the sensor moved
along the surface of the leather. (The looser the connection
between the grain and corium layers, the poorer the break pattern,
which results in a higher energy per count ratio).
[0090] The leather of the present invention ("Prestige"), as well
as prior art Nappa and Black Furniture leathers, were subjected to
AE break evaluation. Of the three leathers tested, the present
leather had the lowest AE energy/count ratio of 1.6 or less. Black
Furniture leather had an intermediate AE energy/count ratio of 1.7,
and Nappa leather had the highest AE energy/count ratio of 2.0
(FIG. 12). Thus, when secured with backing tape to a substrate, of
the three leathers that were tested, the present leather
("Prestige") exhibited the best break pattern. This indicates that
the grain and corium layers of the present leather were the most
intact, whereas the gaps between the grain and corium layers of
Black Furniture leather were more pronounced. Nappa leather had the
poorest break pattern, indicating that this leather contained the
most gaps and "looseness" between its grain and corium layers.
[0091] 2. Tensile Strength
[0092] Tensile strength is one of the most important qualities of
leather. Ordinarily, it is measured by stretching a leather sample
until it breaks and recording the degree of force needed for
breakage. This operation is both time consuming and destructive.
Using AE technology, leather needs only to be stretched a small
amount in order to determine its tensile strength.
[0093] There is a cumulative correlation between the tensile
strength of leather and initial AE energy. Thus, AE technology was
used to determine the tensile strength of the leather of the
present invention ("Prestige"), as well as prior art Nappa and
Black Furniture leathers. The present leather and Black Furniture
leather exhibited comparable tensile strength that was
approximately 30% higher than what was observed in Nappa leather
(FIG. 13). Thus, according to this analysis, Nappa leather was
weaker and more prone to breakage than either the present leather
or Black Furniture leather.
[0094] 3. Initial Strain Energy
[0095] Initial strain energy indicates the softness of the leather
and its resistance to small deformations. Initial strain energy is
defined as the energy needed to stretch leather to a 10% strain
level (area under the stress/strain curve from 0-10% strain). The
higher the initial strain energy, the stiffer the leather. Initial
strain energy testing is used to characterize the softness of
leather taking into account the non-viscoelasticity of leather.
[0096] The leather of the present invention ("Prestige"), as well
as prior art Nappa and Black Furniture leathers, were subjected to
AE initial strain evaluation. The present leather had the lowest
initial strain energy, prior art Black Furniture leather had an
intermediate value, and prior art Nappa leather had the highest
initial strain energy (FIG. 14). The results demonstrated that the
present leather was approximately 50% softer than prior art Black
Furniture leather and approximately 25% softer than Nappa leather.
The results also indicated that the present leather exhibited the
greatest resistance to small leather deformations when compared to
either the Nappa or Black Furniture leathers.
[0097] 4. Toughness Index (TI)
[0098] The degree of toughness exhibited by leather correlates with
the strength, robustness and softness of the leather. Furthermore,
leather having a stiffer grain correlates with poor strength. It is
well known in the art that poor strength and a stiff grain results
in a poor break pattern.
[0099] The degree of toughness of the leather of the present
invention ("Prestige"), as well as prior art Nappa and Black
Furniture leathers, was evaluated by determining their respective
toughness indices. The present leather and Black Furniture leather
exhibited similar toughness indices that was approximately 45%
higher than Nappa leather (FIG. 15). Thus, when Nappa leather is
bent when affixed with backing tape to a substrate, its usual good
break formation is altered, and it exhibits the least strength,
robustness, and softness of the three leathers, which correlates
with an undesirable break pattern.
[0100] Although the invention has been described with particularity
above, with reference to particular compositions, methods and
materials, the invention is to be limited only insofar as is set
forth in the accompanying claims.
* * * * *