U.S. patent number 3,708,333 [Application Number 05/079,318] was granted by the patent office on 1973-01-02 for process for producing on impregnated waterlaid sheet and resultant product.
Invention is credited to Robert C. Carlson.
United States Patent |
3,708,333 |
Carlson |
January 2, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
PROCESS FOR PRODUCING ON IMPREGNATED WATERLAID SHEET AND RESULTANT
PRODUCT
Abstract
A leatherlike sheet material having a low apparent density (high
void volume), good internal bond strength, and a slow rate of water
pickup is provided by forming a waterlaid sheet containing leather
fiber, impregnating the waterlaid sheet with an uncured
polyurethane, polyurethane-urea, or polyurea elastomeric resin
system, and permitting the uncured resin system to cure in situ.
The uncured resin system should be mixed together and quickly
brought into contact with the waterlaid sheet, so that little, if
any, curing occurs prior to the impregnation step.
Inventors: |
Carlson; Robert C. (Saint Paul,
MN) |
Family
ID: |
22149783 |
Appl.
No.: |
05/079,318 |
Filed: |
October 8, 1970 |
Current U.S.
Class: |
428/220; 162/144;
428/904; 427/389 |
Current CPC
Class: |
D04H
1/64 (20130101); C08L 2666/26 (20130101); C08L
75/04 (20130101); D06M 15/564 (20130101); C08L
75/04 (20130101); Y10S 428/904 (20130101) |
Current International
Class: |
D06M
15/564 (20060101); D06M 15/37 (20060101); D04H
1/64 (20060101); C08L 75/00 (20060101); C08L
75/04 (20060101); B32b 027/12 (); B44d
001/32 () |
Field of
Search: |
;117/14A,142,DIG.3,161KP,DIG.7,135.5,143A,138.8UA ;162/135,144 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Gwinnell; Harry J.
Claims
What is claimed is:
1. A process for preparing an impregnated fibrous sheet
comprising:
1. forming a paper-like fibrous sheet at least 1 mm. in thickness
by depositing a mass of fibers, said fibers comprising at least
one-third by weight of leather fiber,
2. mixing together a curable liquid impregnant system
comprising
a. a polyisocyanate,
b. a compound containing a polymeric chain selected from the group
consisting of a polyester chain and a polyoxyalkylene chain, said
compound further containing at least two active hydrogen-bearing
substituents, and
c. a chain propogating agent containing at least two active
hydrogen-bearing substituents, and
d. an organic solvent,
3. impregnating said fibrous sheet uniformly throughout its
thickness with said curable liquid impregnant system less than 2
hours after said mixing,
4. substantially preventing loss of said solvent from said curable
liquid impregnant system and from said fibrous sheet at least until
said curable liquid impregnant system has cured in situ in said
fibrous sheet to a stage at which said curable liquid impregnant
system has become a substantially immobile, gel-like solid, and
5. removing said solvent by evaporation after said step (4) is
completed.
2. A process according to claim 1 wherein said impregnating is
commenced less than 10 minutes after said mixing.
3. An impregnated fibrous sheet made according to the process of
claim 1.
Description
This invention relates to leather substitute materials. An aspect
of this invention relates to insole and outsole material for shoes,
boots, and similar wearing apparel. Another aspect of this
invention relates to a waterlaid sheet of leather fibers
impregnated with a cured in situ elastomeric polyurethane (or
polyurea) composition.
For the shoe manufacturer and the consuming public, natural leather
has been and still is synonymous with high quality insofar as
footwear (particularly shoe insoles, outsoles, uppers, heels, and
the like) is concerned. Natural leather (e.g., calfskin, steerhide,
side leather, and similar epidermal or hide materials) is
considered to have a remarkable combination of properties: for
example, ease of fabrication (good stitch tear and tongue tear
resistance and easy shaping or "lasting"), good internal bond or
strength (dry peel back resistance), and good wearing properties
(resistance to compression set, abrasion resistance, flex fatigue
resistance, etc.). The consuming public associates even the
appearance, odor, and feel of leather with quality insole and
outsole material and generally overlooks the disadvantages of
leather, e.g., rapid water pickup (which may cause discomfort) and
high density.
Accordingly, for a leather substitute to be preferable to natural
leather in the high quality insole and outsole market, it would
have to mimic the advantages and characteristics of leather while
eliminating the disadvantages. The prior art approaches to making
an artificial sole material have generally involved the use of a
rubbery polymer alone or in combination with a fibrous filler or
web, the fibrous material being either synthetic (e.g., nylon,
polyester, etc.) or natural (wool, cotton, leather dust, cork,
etc.). When a rubbery polymer or elastomer per se is used, the
resulting sole material generally has very specialized uses (e.g.,
tennis shoes, work shoes, and the like) due to the lack of
leather-like characteristics. When natural or synthetic fibers (or
other fillers) are combined with an elastomer, the resulting sole
material may be more leather-like in many respects, but may also
share the disadvantages of leather. Most prior art elastomer/fiber
leather substitutes are made from a mixture of fibrous filler and
an elastomeric binder and/or by a process wherein a cloth or a
non-woven material (e.g., an air- or waterlaid web) is impregnated
and/or coated with a polymer. A good summary of the prior art is
found in U.S. Pat. No. 3,116,200 (Young et al.) issued Dec. 31,
1963. Examples of prior art techniques are found in the following
U.S. Pat. Nos. 3,255,061 (Dobbs) issued June 7, 1966; 3,102,835
(White) issued Sept. 3, 1963; 2,973,284 (Semegen) issued Feb. 28,
1961; 2,769,712 (Wilson) issued Nov. 6, 1956; 3,034,927 (Fairclough
et al.) issued May 15, 1962; 2,697,048 (Secrist) issued Dec. 14,
1954; 2,723,935 (Rodman) issued Nov. 15, 1955; 2,721,811 (Dacey et
al.) issued Oct. 25, 1955; 2,719,806 (Nottebohm) issued Oct. 4,
1955; and 3,051,612 (Bennett) issued Aug. 28, 1962. See also German
Pat. No. 1,220,384, published July 7, 1966.
In practice, it is extremely difficult to both imitate and improve
upon the properties of natural leather with fiber/polymer
materials. For example, in selecting the fiber-to-polymer ratio, it
is necessary to avoid using too much polymer in order to avoid
unduly accentuating the rubbery properties of the polymer at the
expense of the leather-like properties provided primarily by the
fiber. If too much fiber is used, the internal strength of the
resulting leather substitute will tend to be strikingly inferior to
natural leather. This is particularly true when leather fiber is
included in the fiber/polymer material. In Raymond et al., U.S.
Pat. NO. 3,436,303, issued Apr. 1, 1969, the patentees teach that a
sample containing 60 percent fiber and 40 percent polymer "was a
loose fibrous porous material." Furthermore, it can be quite
difficult to maintain uniformity of the fiber-to-polymer ratio
throughout the structure.
In optimizing prior art fiber/polymer sheet materials, it is almost
always desirable to provide low apparent density (high void
volume); however, this desideratum must be balanced against the
likelihood of rapid liquid water pickup and poor internal strength
or high compression set. This is particularly true when the fiber
is leather fiber. Since leather has an affinity for water, the rate
of water pickup would be expected to be rapid when leather fiber is
used in a fiber/polymer material. High void volume (low apparent
density) can also speed up the rate of water pickup, because
sponge-like structures (e.g., those of U.S. Pat. No. 2,977,330
(Brower), issued Mar. 28, 1961) have a large capacity for
water.
Furthermore, a high void volume is difficult to maintain; it tends
to be markedly decreased by processes, materials, or treatments
which improve internal bond strength. (Low density waterlaid sheets
require, as a rule, reinforcing, heating, and/or pressing, while
air-laid sheets containing a substantial amount of leather fiber
are generally too flimsy to be made into insole or outsole
materials.) Other problems are also created by such treatments or
processes. Reinforcing or binding a leather fiber sheet with
solution polymers generally calls for a relatively low molecular
weight, linear polymer system for high solubility of the polymer
and low viscosity of the solution. Another drawback is that
migration of the polymer impregnant tends to occur while the
solvent is evaporating, resulting in a nonuniform fiber/polymer
ratio. The use of emulsified polymer systems is complicated by the
nonuniform penetration of larger emulsoid particles (above 0.1
micron) and the salt content and pH characteristics of leather
fibers. As with solution systems, polymer migration can occur
during drying.
Void volume is particularly likely to be sacrificed when pressing
and/or large amounts of binder are used to achieve a good internal
bond. Large amounts of saturant tend to fill up voids, and pressing
reduces the number and/or size of the voids. To illustrate: a
typical fiber/polymer sheet containing a substantial amount of
leather fiber has a true density (density at 0 percent void volume)
of at least 1.1 g/cc and generally greater than 1.2 g/cc. If a void
volume of at least 20 percent could be achieved and maintained, the
sheet could have an apparent density lower than 0.9 g/cc, a
significant improvement over natural leather and many types of
synthetic outsole materials. (However, the danger of more rapid
water pickup must always be borne in mind.) But pressed sheets
often have <20 percent voids.
Despite all the aforementioned difficulties, leather fiber has
striking aesthetic and economic advantages for use as a filler or
fibrous component in a shoe sole material; for this reason a
leather-fiber/polymer sheet with low apparent density, low
compression set, slow water pickup, good internal strength, etc.,
is still being sought by industry.
Accordingly, this invention contemplates providing a sheet material
from natural leather fiber and a rubbery binder wherein: pressing
or other densification of the sheet and the amount of rubbery
binder in the sheet are kept to a minimum, thereby maintaining a
high void volume; both desirable leather-like properties and the
amount of leather fiber in the sheet are maximized, thereby taking
full advantage of the aesthetic appeal and properties of leather;
the rate of water pickup of the sheet is made as slow as possible,
so that upon brief immersions in liquid water, only a minor amount
of the voids will take up liquid water; the internal bond of the
sheet is maximized; the permanent compression set of the sheet is
minimized; and the method of making the sheet is designed such that
strict control over all of the aforementioned properties is
possible. This invention also contemplates a substantially uniform
impregnation of a waterlaid sheet with a rubbery binder which can
be non-linear and/or relatively high in molecular weight.
Briefly, this invention involves:
1. Forming a waterlaid sheet (or batt or fiber cake) from an
aqueous slurry of fibrous material, at least one-third, preferably
at least two-thirds, of this material being leather fiber,
2. Mixing together a free isocyanate-containing material and an
active hydrogen-containing material, (wherein "active hydrogen" is
defined according to the Zerwitinoff test, J. Amer. Chem. Soc. 49,
3181 (1927) ), with or without suitable solvents, catalysts, or the
like, and
3. Impregnating the aforementioned dry waterlaid sheet with the
mixture of starting materials described previously before these
starting materials have interacted to any great extent. It is
possible to combine the mixing and impregnating steps (Steps (2)
and (3) ), provided the resulting impregnation is both complete and
uniform. However, to achieve the outstanding quality control which
is an important feature of this invention, it is not desirable to
impregnate the pre-formed waterlaid sheet with either unmixed
starting materials (i.e., with seriatim impregnation steps) or with
starting materials that have been in admixture for a period of time
sufficient to allow total curing or even a substantial amount of
curing prior to impregnation.
The uncured impregnant can undergo an exothermic in situ cure in
the waterlaid sheet at ambient temperatures, e.g., 20.degree. C. or
higher. For maximum control over internal bond strength, uniformity
of impregnation, and water pickup, substantially all of the curing
(chain propagation -- including chain extension, branching, and
crosslinking) should be in situ, i.e., after impregnation, rather
than during the mixing step, and the uncured impregnant should
contain at least about 20 wt. percent solvent. If the starting
materials of the impregnant are dissolved in a solvent, removal of
the solvent from the waterlaid sheet can be accomplished by drying
at room temperature or, preferably, at suitable elevated
temperatures. Solvent removal should not be begun until the in situ
cure is substantially completed. After the in situ cure of the
impregnant is complete, pressing of the resulting sheet material is
generally not necessary and is not preferred.
The term "waterlaid sheet", as shown by the previously cited prior
art (e.g., U.S. Pat. Nos. 2,769,712 and 3,436,303), has a
well-recognized meaning in the art. The term denotes a paper-like
sheet having a small thickness (relative to the area) and
comprising solids which have been deposited from an aqueous slurry
or the like onto a foraminous surface, e.g., onto the screen of a
handsheet mold or Fourdrinier machine.
Leather-like sheet materials made according to this invention have
a substantially uniform fiber/polymer ratio throughout their
thickness. The thickness, for outsole materials or heels can be up
to 2 or 3 cm or more; typically, 6 or 9 Iron (0.32 or 0.48 cm)
sheets make good sole materials. Lamination can be used to increase
the thickness still further, and splitting can be used to reduce
the thickness to, for example, a millimeter. The process of this
invention is inherently capable of producing, without lamination,
sheets about 0.5 -1.0 cm in thickness. In this context, the term
"substantially uniform" means that, in the innermost regions or
core areas of the impregnated and cured sheet produced by this
invention (which will normally be 0.5-1 cm thick), the
fiber/polymer ratio is substantially the same as that of the areas
or regions near (within a millimeter of) the exposed surfaces of
the sheet, differences or variations in this ratio between such
core and near-surface regions being substantially less than 20
percent and preferably less than 10 percent. (It may be desirable
to have a higher fiber/polymer ratio at one or more surfaces of the
sheet to provide a leather-like skin.) The apparent density of
sheets made according to this invention can be less than 1.0 g/cc,
and apparent densities as low as 0.3 g/cc have been achieved in
practice. To provide a noticeable advantage over natural leather,
the apparent density should be well below 1.4 g/cc, and preferably
below 1.2 g/cc. An internal bond strength (dry peel back)
substantially greater than 10 pounds per lineal inch (1,800 g. per
lineal cm) can be obtained according to the teachings of this
invention. The theoretical void volume of sheets of this invention
can be as high as 80 percent, but preferably is less than 75
percent. For low apparent density, the void volume should be at
least 20 percent. Of the total apparent volume of a sheet made
according to this invention, about 15 to about 35 percent will be
closed, or substantially closed, cells. As a general rule, roughly
one-half to two-thirds of the total void volume will be closed
cells having elastomeric walls--certainly more than 15 or 20
percent of the total void volume will be closed cells--but the
desirable properties of sheets made according to this invention are
apparently not entirely dependent upon water repellent and internal
bonding effects caused by such closed cells. A substantial portion
of the void volume of sheets of this invention, e.g., more than
one-third, can be open or intercommunicating cells without
adversely affecting the desired properties. The permanent
compression set (ASTM test B-2213-63T) of the cured sheet is less
than about 25 percent and is preferably less than 15 percent. The
fiber/polymer ratio (by weight) of the cured sheets ranges from
0.4:1 to 1.7:1, preferably about 1:1, and the particular
fiber-to-polymer ratio for a particular sheet will have the
substantial uniformity described previously. (Expressed in terms of
polymer-to-fiber ratio, this range is 0.6:1-2.5:1, and preferably
about 1:1.) The flex fatigue resistance or "flex life" of sheets of
this invention is determined by cutting a hole in a sample sheet
and flexing it on a "Ross Rubber Flexing Machine" (Emerson
Apparatus Co., Melrose, Mass.). Samples are conditioned at 50
percent relative humidity and 23.degree. C. before the "Ross" flex
test. The flex life of preferred sheets of this invention is in
excess of 30,000 cycles.
A particularly advantageous feature of cured sheets made according
to this invention is the slow water pickup rate. The expression
"water pickup rate," as used herein, means the percent of water
absorbed at room temperature by an initially dry sample in a given
increment of time. The percent of water absorbed can be expressed
as either weight percent (based on the weight of a dry sample) or
volume percent (based on the apparent volume of a dry sample). For
ease of calculation, all measurements are in grams and cubic
centimeters, and the density of water at room temperature is
assumed to be exactly one gram per cc. If W.sub.1 is the weight of
the dry sample and W.sub.2 is the weight of the sample after
immersion in a room temperature water bath, the weight percent
water absorption will be given by:
100 .times. (W.sub.2 - W.sub.1)/W.sub.1.
The volume percent absorption is obtained by multiplying the above
expression by the apparent density, assuming the density of water
is 1.00 g/cc.
In determining the water pickup rate, 30 minutes is a particularly
meaningful time increment, insofar as insole and outsole material
is concerned. For a 30-minute immersion, representative water
pickup rates of sheets made according to preferred embodiments of
this invention are less than 10 wt. percent and are generally less
than 5 wt. percent, even though such sheets have a void volume
greater than 20 percent and contain a significant amount of leather
fiber. The 2-hour rate is less than 20 wt. percent and generally
less than 10 wt. percent for these preferred materials.
Surprisingly, the 24-hour rate is still less than three-fourths
(and can be less than half) of the theoretical absorptive capacity
of the sheet. This slow penetration of water can readily be
appreciated by comparing the rate of pickup in volume percent with
the theoretical void volume of the sheet. As a practical matter,
this means that an outsole made from a sheet of this invention
could be in contact with a wet pavement or wet ground for long
periods of time without picking up a significant amount of water.
And this effect can be achieved without the use of waterproofing
additives.
It is difficult to explain this slow water pickup phenomenon in
view of the high void volume (which can include a substantial
number of open or intercommunicating cells) and high leather fiber
content of the sheets of this invention. Although this invention is
not bound by any theory, it is theorized that what appears to be
open or interconnected cells in air pycnometer tests of the cured
sheets are actually quite resistant to absorption of liquid water.
This resistance to water is, however, not characteristic of similar
porous materials, e.g., the sheet material described in the
aforementioned Raymond et al. U.S. Pat. No. 3,436,303. It is
further theorized that all, or nearly all, of the leather fibers in
the sheet are coated with polymer and thus rendered
hydrophobic.
Nor can it be explained precisely how the cell structure of this
invention is obtained. It is theorized that the uncured impregnant
wets out the leather fibers and cures on the surface of the fibers.
The formation of closed cells may thus be a partially chemical and
partially physical phenomenon. Direct bonding between active
hydrogen-bearing substituents present in the leather particles or
fibers and free isocyanate containing molecules is believed to
occur.
As pointed out previously, at least one-third and preferably
two-thirds, by weight, of the fiber used in practicing this
invention should be leather fiber of paper-making length (less than
about 15 mm and preferably less than 5 mm). The natural leather
fibrous material can be chrome or vegetable tanned and can be dyed
and/or pigmented. The leather fiber can be slurried with a
discontinuous (e.g., chopped staple) synthetic fiber such as
polyamide, regenerated cellulose or cellulose acetate (e.g.,
rayon), polyolefin (e.g., polyethylene or polypropylene), polyester
(e.g., polyethylene terephthalate and acetal copolymers), etc.
Naturally occurring staple fibers such as wool and cotton (or other
natural cellulosic fibers) can also be used. Such natural or
synthetic staple fiber is preferably one to six denier and
preferably shorter than 15 mm. in length. To maximize the aesthetic
and desirable physical properties of natural leather, the amount of
natural or synthetic fiber other than leather should be kept to
less than 10 wt. percent and preferably less than 5 wt. percent of
the total fiber content of the sheet. Surprisingly, these lower
synthetic fiber content materials have a slower water pickup rate.
Needless to say, it is within the scope of this invention to add
modifying ingredients other than the aforementioned fibers, e.g.,
mineral fillers or fibers such as glass or asbestos. It is
permissible, but not necessary, to add chemical agents, dyes or
pigments to the aqueous slurry prior to the formation of the
waterlaid sheet of fiber, provided that these agents, e.g., anionic
surfactants and the like, do not contain either "active hydrogen"
(as defined by the Zerwitinoff test) or free isocyanate. It is both
unnecessary and undesirable to add elastomeric binder materials or
other thermoplastic resins, polyisocyanates, or prepolymers to the
aqueous fibrous slurry prior to the formation of the waterlaid
sheet.
Elastomeric binder-forming materials used in the practice of this
invention are not introduced into the sheet until after formation
and drying of the fibrous waterlaid sheet is complete. The
preferred binder material, after curing, comprises a polyurethane
(including polyurethane-polyurea) or polyurea elastomer containing
--NH--R--NH--CO-- and --X--Z.sup.1 --X--CO-- units, and preferably
--X--Z.sup.2 --X--CO-- units, in the polymer chain, wherein R is a
divalent aliphatic, aralkylene, or aromatic group such as an
alkylene radical of four to 10 carbon atoms or a monocyclic or
polycyclic aromatic or aralkyl nucleus such as benzene, toluene,
xylene, diphenylmethane, naphthalene, etc.; X is O, S, NH,
N-aliphatic, or the like; Z.sup.1 is a polyoxyalkylene or polyester
chain; and Z.sup.2 is a divalent aliphatic, cycloaliphatic, or
aromatic radical. Although these units are shown as divalent
structures, it should be understood that, if a crosslinked,
crosslinkable, "branched-chain" polyurethane is desired, the
"Z.sup.1 ", "Z.sup.2 " or "R" groups can have one or more
additional substituents. The Z.sup.2 radical is derived from a
compound having the formula Z.sup.2 (XH).sub.m, wherein Z.sup.2 and
X are as defined previously, m is 1-5, preferably 2 or 3, and H is
an "active hydrogen" as defined previously; Z.sup.2 (XH).sub.m can
be piperazine and the like. In the preferred polymers, X is oxygen
or NH. If the Z.sup.1 chains in the molecule are not the same,
i.e., the polymer contains more than one kind of polyoxyalkylene
and/or polyester chain, at least one Z.sup.1 chain preferably has a
molecular weight of at least about 400 but less than about
5,000.
When Z.sup.1 is a polyester chain, the polyester units are
preferably of the repeating formula --O--A.sup.1 --O--CO--A.sup.2
--CO--, wherein A.sup.1 and A.sup.2 are divalent aliphatic groups
such as alkylene radicals. These polyester units can be derived
from the interaction of a bifunctional initiator with one or more
lactones, for example, as described in U.S. Pat. No. 2,933,477, or
by an esterification or ester-interchange reaction involving a
dicarboxylic acid or anhydride or ester thereof with an alkylene
polyol, preferably an alkylene glycol.
When polyesters are prepared from dicarboxylic acids, anhydrides,
or esters, and alkylene glycols, the preferred acid, anhydride, or
ester, can be selected from a wide variety of polybasic (preferably
dibasic) acids. It is preferred to use the dibasic fatty acids,
i.e., HOOC-- CH.sub.2 .sub.n --COOH, wherein n is a small integer,
e.g., 1-8. Particularly suitable dibasic acids are malonic,
succinic, and adipic. Examples of useful alkylene glycols are
ethylene glycol; 1,3-propane-diol; 1,4-butane diol, and the
like.
It is possible to modify the stiffness of the polymer by
introducing in the polyurethane-forming reaction various
chain-extending, chain-branching, or chain-terminating agents,
e.g., arylene diamine chain extenders. A particular advantage of
this invention is the freedom of using tri or higher functionality
materials to achieve crosslinking in the resultant finished sheet
material. Preferred chain-branching agents are the triols and
triamines commonly used in the polyurethane art. Chain propagation
can be carried out in any suitable manner know in the art, e.g.,
the "one shot" procedure, which generally involves the use of a
catalyst, or the chain-extension of a suitable prepolymer.
Prepolymers are preferred. The preferred components are: an
aromatic diisocyanate, an "active hydrogen" component comprising a
polyoxyalkylene glycol and an aromatic diamine, and, optionally,
one or more compounds having 3-5 active hydrogen-bearing
substituents (e.g., a triol), and a suitable catalyst, e.g., an
organo-metallic compound such as stannous octoate, mercuric
acetate, phenyl mercuric acetate, or the like. Polyoxyalkylene
diamines can be substituted for the polyoxyalkylene glycol with
good results. An advantage of this substitution is that the
resulting polyurea can be more degradation resistant. Water and/or
carboxyl containing compounds can be included in the "active
hydrogen" component, but due to the formation of carbon dioxide,
such inclusion is ordinarily not preferred.
The molecular weight, cross-link density (if any), amount of
aromatic content (if any), amount of urea and/or urethane linkages,
etc., of the polyurethane or polyurea binder material must be
selected such that the binder is elastomeric in nature. By
"elastomeric" is meant the ability of an article, e.g., a cast film
consisting of the polymer, to be elongated substantially more than
100 percent of its length and to return with force to substantially
the original length. Elastomeric polymers suitable for use in this
invention have a molecular weight greater than 10,000 and form
films with the following physical properties: (tested free of
fillers and the like at 23.degree. C. and 50 percent relative
humidity) a tensile strength of at least 300 (21.1 Kg/cm.sup.2)
psi, preferably at least 750 psi (52.8 Kg/cm.sup.2), a stress at
100 percent elongation of at least 50 psi (3.5 Kg/cm.sup.2),
preferably at least 150 psi (10.5 Kg/cm.sup.2), and an elongation
at break of at least 300 percent, preferably at least 500 percent.
To avoid undue stiffness, the stress at 100 percent elongation
should not exceed 1,000 psi (70 Kg/cm.sup.2). To avoid undue
rubberiness, the elongation at break should not exceed 1,500
percent.
As pointed out previously, the elastomeric binder materials of this
invention are preferably formed by mixing the starting materials in
the presence of a volatile organic liquid solvent or vehicle (i.e.,
a solvent for the uncured starting materials, not necessarily the
fully cured polymer) and a suitable catalyst to form a low
viscosity "saturant" system with which the waterlaid sheet is
saturated. The starting materials interact primarily while in situ,
i.e., in the sheet. When a suitable catalyst is included in the
saturant mixture, curing of the mixture can be completed at ambient
temperatures near room temperature, e.g., 20.degree.-25.degree. C.
Since the curing reaction is exothermic, the use of ordinary
ambient temperatures is preferred; however, ambient temperatures up
to 65.degree. C. can be used. If the starting materials are of
sufficiently low viscosity, the use of a solvent can be avoided.
However, some solvent (ordinarily at least 20 wt. percent) is
preferably always used in order to control the final polymer/fiber
ratio. Suitable solvents include esters such as ethyl acetate and
butyl acetate, ethers such as tetrahydrofuran and dioxane, ketones
such as acetone and methylisobutylketone (but, with ketones,
Schiff's base reactions must be considered), sulfones, hydrocarbons
(particularly aromatic hydrocarbons such as toluene) sulfoxides,
chlorinated hydrocarbons, and mixtures of one or more of these.
Organic liquids can, if desired, be selected from the above list
with a view toward low toxicity and/or miscibility with water.
After the in situ cure is substantially complete, the organic
liquid solvent can be evaporated or drawn off from the cured,
impregnated sheet at ambient temperatures near room temperature or
at elevated temperatures, e.g., up to 70.degree. C., and at
atmospheric or subatmospheric pressure. The aromatic hydrocarbons
(benzene, toluene, xylene, etc.) are particularly suitable for
removal from the cured sheet. A possible explanation for this might
be because they have little, if any, affinity for the fully cured
polymer.
Prior to impregnation with the elastomeric binder-forming
impregnant, a waterlaid sheet of fiber is made according to
standard papermaking techniques using a Fourdrinier screen or a
hand sheet mold. This waterlaid sheet is substantially
self-supporting and has sufficient strength after drying to permit
further processing. The sheet is saturated with the impregnant by
any suitable method including immersion in, floating upon, or
spraying with the impregnant. The preferred method (hereinafter
referred to as "float saturation") is to float the sheet upon a
bath of the impregnating agent. As pointed out previously, the
starting materials which make up the impregnant are preferably
premixed prior to the impregnation step. The time lapse between
mixing up the impregnant and commencing the saturation of the
waterlaid sheet should not be unduly long, however. With some
systems, a lapse of up to 2 hours is not too detrimental, but the
lapse should preferably be as short as possible, e.g., less than 10
minutes, preferably less than 5 minutes. The time lapse can be
reduced to zero by spraying the waterlaid sheet with two
sprayheads, one dispensing an "active hydrogen"-containing
component and the other dispensing the free isocyanate component.
The two sprays intermingle in the interstices of the sheet, thus
combining the impregnating and mixing steps of this invention.
Although the preceding description has been directed primarily
toward using the impregnated waterlaid sheet of this invention as
insole or outsole material, heels, and other elements of footwear,
other uses will occur to the skilled technician. Among these uses
are pads for abrasive-surfaced discs, backup layers for
dye-cutting, gaskets, furniture, conveyor belts, and any other use
where a tough, leather-like sheet or laminate is needed.
In the following nonlimiting Examples, all parts are by weight
unless otherwise specified. Weight percent and apparent volume
percent pickup are determined as described previously. Theoretical
percent void volume is determined by 100 .times. (1.27 -- apparent
density)/1.27, since 1.27, on the average, is the true density of
the solid material (leather and polyurethane) in the sheets made
according to these Examples.
EXAMPLE 1
A dyed pigmented leather fiber sheet was prepared as follows:
Chrome tanned leather fibers (Lorum Fiber Co. Y-020-015 chrome
tanned leather fibers) were beat up with water using a "Vally"
paper beater (Vally Iron Works). A 6.3 wt. percent total solids
leather fiber slurry was obtained having an S.R. (Schopper-Riegler)
freeness of 19.5.degree.. One hundred thirty-eight grams of leather
solids (2,190 grams of slurry) was diluted to 15-liters in a
5-gallon (17.9 liters) pail with cold tap water. The diluted slurry
was added to a 12 .times. 12 inch (30.5 .times. 30.5 cm) Williams
Apparatus Co. handsheet mold. The slurry was drained catching the
fibers on the wire. The resulting waterlaid sheet was then removed
and dried in a 150.degree. F. (66.degree. C.) forced air oven.
The two-part polyurethane impregnant system was as follows:
Two hundred parts of a Part "A" (composed of 712 parts of a 2,000
molecular weight polyoxypropylene glycol, 43.2 parts of
methylenebisorthochloroaniline, 4.3 parts phenylmercuric acetate,
32.0 parts of an amorphous silica filler with particle size of
approximately 0.1 micron (available under the trademark "Cab-O-Sil"
from Cabot Corp.), 3.0 parts of a mull of 80% PbO.sub.2 (by wt.) in
a 2,000 molecular weight polyoxypropylene glycol, 2.40 parts of
calcium octoate and 3.2 parts of 2,6-ditertiary butyl paracresol),
and
Sixty parts of a Part "B" prepolymer (composed of 30.6 parts of a
400 molecular weight polyoxypropylene diol and 8.7 parts of a 435
molecular weight polyoxypropylene triol reacted with 60.7 parts of
80/20 [by wt.] isomer mixture of 2,41/2,6-toluenediisocyanate at
66.degree. C. for approximately 4 hours).
Parts "A" and "B" were mixed with 482 parts toluene and poured into
a 81/2 .times. 12 inch (21.5 .times. 30.5 cm) glass tray
immediately after mixing. Within a minute after this pouring step,
a 6 .times. 12 inch (15.25 .times. 30.5 cm) piece of the above
described dried, waterlaid sheet of leather fiber was submerged in
this bath and saturated. After about an hour an immobile gel
formed. The impregnated sheet was removed, the excess polymer
scraped from its surface, followed by drying at 150.degree. F.
(66.degree. C.). The dried sheet looked very much like leather.
The finished sheet had the following properties:
Polymer-to-fiber ratio: 0.91:1 Apparent density 0.56 g/cc
Theoretical void volume 56 % Dry peel back resistance (peel back
rate = 1 ft/min or 30.48 cm/min.) 13 lb./inch (2300 g/cm)
Water pickup rate: (at room temperature, 22.degree. C.):
time Immersed Wt. % Vol. %
__________________________________________________________________________
30 minutes 3.4% 1.9% 2 hours 7.1% 4.0% 24 hours 34.7% 19.4%
__________________________________________________________________________
Thus, after 24 hours, less than half of the theoretical void volume
had taken up water.
Similar results can be obtained by maintaining the impregnating
conditions of this Example and using the "float saturation"
technique, wherein the sheet is floated on the surface of the
higher-density, uncured impregnant liquid.
EXAMPLE 2
In this Example, the effect of varying the amount of saturant
solids was investigated.
Several dyed pigmented leather fiber sheets were prepared by
beating up chrome tanned leather fibers (Lorum Fiber Co.
Y--020--015 chrome tanned leather fibers) in water with a paper
beater. The leather fiber slurry was refined until it had a S.R.
freeness of 19.degree.. Then 7.5 lb. (3,420 g.) of these solids
were diluted, in a chest, with water wash to obtain a 3 percent
slurry. Enough of this was added to a 20 .times. 20 inch (50.8
.times. 50.8 cm) handsheet mold so as to have about 1,000 grams of
solids per sheet of material. The water was drained from the
handsheet mold filtering out the fibers on a wire grid. Each
waterlaid sheet was rubber dammed by placing a thin sheet of latex
film over the still-wet waterlaid sheets and removing the air from
below so as to further remove water. The sheets were dried at
200.degree. F. (93.degree. C.) for 8 hours. The dried waterlaid
sheets were all approximately 0.4 inch (1.0 cm) thick, having an
apparent density of approximately 0.3 g/cm.sup.3.
Example 2(A): 35 wt. percent Solids Saturant
The saturant was: 158 parts of a Part "A" (composed of 3,560 parts
of a 2,000 average molecular weight polyoxypropylene glycol and 216
parts methylenebisorthochloroaniline) mixed with 50.4 parts of the
same Part "B" described in Example 1, 388 parts toluene, and 3.12
parts of a 30 wt. percent solution, in aqueous ammonia, of
phenylmercuric acetate catalyst ("Metasol 30," trademark of Metal
Salts Corp., Hawthrone, N.J.). An 8 .times. 8 inch (20.3 .times.
20.3 cm) piece of the above described dried waterlaid sheet was
then float saturated as described in Example 1; the sheet was
allowed to gel; and the excess polymer was scraped from its
surface, followed by drying at 150.degree. F. (66.degree. C.).
Example 2(B): 45 wt. percent Solids Saturant
Another sheet was prepared by the procedure of Example 2(A) and
with the same materials except that the following saturant
formulation was used:
204 parts of Part "A"
65.5 parts of Part "B"
330 parts of toluene
2.47 parts of the catalyst solution of Example 2(A).
Example 2(C): 55 wt. percent Solids Saturant
Another sheet was prepared using the same procedure and materials
as in Example 2(A) except the following saturant formulation was
used:
250 parts of Part "A"
80 parts of Part "B"
270 parts of toluene
1.82 parts of the catalyst solution of Example 2(A)
Example 2(D): 65 wt. percent Solids Saturant
Again still another sheet was prepared using the same procedure and
materials as Example 2(A) except the following saturant formulation
was used:
295 parts of Part "A"
94.6 parts of Part "B"
210 parts of toluene
1.17 parts of the catalyst solution of Example 2(A)
Example 2(E): 70 wt. percent Solids Saturant
Finally a fifth sheet was prepared using the same procedure and
materials as in Example 2(A) except the following saturant
formulation was used:
318 parts of Part "A"
101 parts of Part "B"
179 parts of toluene
0.84 part of the catalyst solution of Example 2(A).
The above five sheets were evaluated with the following results
tabulated:
TABLE I
Formulation and Properties
180.degree. Dry Peel Back measured Wt. % Theo- on 1" (2.54 cm)
Solids Polymer retical Apparent wide sample Fiber Void Density at
12" (30.48 cm) Ex. Saturant Ratio Volume g/cc per min.
__________________________________________________________________________
2(A) 35 0.80/1 54% 0.58 10 lb./in (1800 g/cm) 2(B) 45 0.91/1 47%
0.67 11 lb./in. (2000 g/cm) 2(C) 55 1.06/1 36% 0.81 12 lb./in.
(2100 g/cm) 2(D) 65 1.44/1 28% 0.92 16 lb./in (2800 g/cm) 2(E) 70
1.55/1 31% 0.87 20 lb./in. (3600 g/cm)
__________________________________________________________________________
TABLE II
WATER PICKUP
Wt. % H.sub.2 O pick-up after 30 min. submer Approx. Volume %
Example sion at 20-25.degree. C. pickup, 30 min., 20-25.degree. C.
__________________________________________________________________________
2(B) 3.1% 2.0% 2(C) 1.9% 1.5% 2(D) 0.8% 0.7%
__________________________________________________________________________
example 3
in this example, up to 50 percent by weight of the leather fiber
was replaced by a cellulosic fiber.
Example 3(A): 100 percent Leather, 0 percent Rayon
A dry waterlaid sheet was prepared from dyed, pigmented leather
fiber by the same procedure as in Example 2. The saturant system
was 200 parts of the Part "A" of Example 1 mixed with 60 parts of
the Part "B" of Example 1 and 482 parts toluene. The above sheet
was "float saturated" followed by placing in a press with warm
plattens heated to a temperature in the range of
50.degree.-60.degree. C., between release liners, under very
moderate pressure (only enough to hold the sheet perfectly flat).
During this time gellation occurs, after which the sheet is removed
and dried at 150.degree. F. (66.degree. C.).
Example 3(B): 75 wt. percent Leather/25 wt. percent Rayon
A dyed, pigmented 75 percent leather/25 percent rayon fiber dry
waterlaid sheet was prepared by the same process as in Example 2
except that 25 percent of the leather was replaced with one-quarter
inch (0.63 cm) long .times. 2 denier rayon fiber. This sheet was
then float saturated, pressed, and dried as in Example 3(A).
Example 3(C): 50 wt. percent Leather/50 wt. percent Rayon
A dyed, pigmented 50 percent leather/50 percent rayon fiber dry
waterlaid sheet was prepared by the same process as in Example 2
except that 50 percent of the leather was replaced with one-quarter
inch (0.63 cm) long by 2 denier rayon fibers. This sheet was then
float saturated, pressed and dried as in Examples 3(A) and
3(B).
The following tabulated data are the results of the evaluation of
Examples 3(A) - 3(C).
TABLE III
Example 3(A) 3(B) 3(C)
__________________________________________________________________________
Polymer to Fiber Ratio 0.81/1 1.17/1 1.10/1 Density, g/cm.sup.3
0.57 0.55 0.47 180.degree. Dry Peel Back 7 lb/in. 13 lb/in. 8
lb/in. (1200 g/cm) (2300 g/cm) (1400 g/cm) Flex Cycles to Failure
>50,000 50,000 7,500 ("Ross" Flex Test)* >50,000 41,000
19,000 % Compression Set** 17% 14% 16% Wt. % of Fiber Leather 100
75 50 Wt. % of Fiber Rayon 0 25 50
__________________________________________________________________________
table iv
theoretical Void Volume vs. Water Pickup
Theoretical 30-Minutes 2 Hours 24 Hours Void H.sub.2 O Pickup
H.sub.2 O Pickup H.sub.2 O Pickup Ex. Wt.%luVol. % Wt.% Vol.% Wt.%
Vol.%
__________________________________________________________________________
3(A) 55% 3.4 1.9 7.1 4.0 34.7 19.8 3(B) 57% 2.5 1.4 5.8 3.2 20.0
11.0 3(C) 63% 13 6.1 26 12 53 25
__________________________________________________________________________
in every case the 24-hour water pickup, by volume, was less than
half of the theoretical void volume. However, the sheets with 75
wt. percent or more of leather fiber were more water resistant and
had better flex life and internal strength.
EXAMPLE 4
This example illustrates the uniformity of the polymer-to-fiber
ratio throughout the impregnated waterlaid sheet.
A dry waterlaid sheet was prepared from dyed, pigmented leather
fiber as in Example 2. An 8 .times. 12 inch (20.3 .times. 30.4 cm)
piece of this dry sheet was "float saturated" and dried at
66.degree. C. as described in Example 1.
153.2 parts of the Part "A" described in Example 2
46.8 parts of the Part "B" described in Example 2
200 parts of toluene
1.45 parts 30 wt. % solution of phenylmercuric acetate (see Example
2(A) ).
The resultant sheet was then split into 11 layers, each as near as
possible to 30 mils (0.076 cm) thick, numbered 1-11 from top to
bottom.
Assuming the leather fiber to have a constant percent ash (run at
1,000.degree. C.), ash values were run on each of the 11 layers to
show uniform polymer distribution. The following results were
obtained: (Nos. 2-10 were similar in appearance and density.)
TABLE V
Layer No. Wt. % Ash
__________________________________________________________________________
Top: 1 3.21 2 2.67 3 2.70 4 2.73 5 2.84 6 2.90 7 2.75 8 2.77 9 2.72
10 2.64 Bottom: 11 2.59
__________________________________________________________________________
As is apparent from this data, a very uniform polymer distribution
is achieved.
EXAMPLE 5
A waterlaid sheet from dyed, pigmented leather fiber was prepared
as in Example 2. A sheet was then made with the following saturant
formulation:
128.5 g. of a Part "A" (comprised of 750 parts of a 1,000 molecular
weight hydroxyl terminated poly(epsilon-caprolactone), 66.5 parts
of methylene bis orthochloroaniline, both of which are dissolved in
toluene at 55.5 percent solids) was mixed with 243.9 parts of a
Part "B" (a prepolymer prepared by reacting 1,000 parts of a 1,000
molecular weight, hydroxyl terminated poly(epsilon-caprolactone)
with 348 parts 80/20 mixture 2,4-/2,6-isomers of toluene
diisocyanate in toluene at 52.9 percent solids for 4 hours at
75.degree. C.), 27.6 parts of toluene and 0.75 g. of a 30 wt.
percent solution of phenylmercuric acetate (see Example 2(A) ). An
8 .times. 8 inch (20.3 .times. 20.3 cm.) piece of the
above-described waterlaid sheet was float saturated as described in
Example 1. The excess gel was removed followed by drying at
150.degree. F. (66.degree. C.), as in Example 1.
The resultant sheet was rigid in comparison to those described in
previous examples.
It was found to have an apparent density of 0.63 g./cc. The water
pickup, by weight, was 3.6 percent after 30 minutes submersion.
EXAMPLE 6
A leather fiber waterlaid sheet was prepared by the same procedure
as in Example 2 except that enough crimped one-quarter inch (0.64
cm) .times. 2 denier nylon fibers were added to fiber slurry to
equal 3 percent of the total leather fiber weight. The following
saturant formulation was used:
153.2 parts of a Part "A" (same as used in Example 2) mixed with
468 parts of a Part "B" (same as used in Example 2) and 200 parts
of toluene. To this mixture 1.45 parts of a 30 wt. percent solution
of phenylmercuric acetate catalyst (see Example 2(a) ) was added
and stirred in. The resulting saturant mixture was then added to a
glass tray and a 20.3 .times. 20.3 cm piece of the above waterlaid
sheet was float saturated as described in Example 1. The saturant
was allowed to gel without the loss of solvent. The excess gel was
scraped from the surface of the sheet followed by drying at
66.degree. C.
The resultant sheet had the following properties:
Polymer-to-fiber ratio: 0.93:1 Apparent density: (40% theo. void
vol.) 0.76 g/cc 180.degree. dry peel back: 16 lbs/in (2800 g/cm)
H.sub.2 O pickup after 30 minutes submersion: 3.4 wt. %
EXAMPLE 7
A polyether urea Part "B" was prepared diluting 1,000 parts of a
2,000 molecular weight polyoxypropylene diamine with 1,000 parts of
toluene. One hundred seventy-four parts of (80/20 [wt.] mixture
2,4-/2,6-isomers) toluene diisocyanate was diluted with 174 parts
toluene also. The polyether diamine solution was then added to the
toluene diisocyanate solution with agitation. The mixture was
allowed to exotherm and then cool to room temperature.
A Part "A" was prepared by dissolving 100 parts of
methylene-bis-orthochloroaniline in 200 parts of
dimethylformamide.
60.0 parts of the above Part "A" was mixed with 388.0 parts of the
above Part "B." To this mixture, 0.75 part of a 30 wt. per cent
solution of phenylmercuric acetate (see Example 2(A) ) was added
and stirred in. This saturant mixture was added to a tray in which
an 8 .times. 7 inch (20.3 .times. 17.8 cm) piece of a waterlaid
sheet of leather fiber (as prepared in Example 2) was float
saturated as in Example 6. The saturant mixture was allowed to gel
without the loss of solvent. The excess gel was removed and the
sheet was dried at 66.degree. C., as in Example 6. The resultant
sheet had the following properties as measured by procedures
described in Example 2:
Apparent density: (46% theo. void vol.) 0.69 g/cm.sup.3 Water
pickup after 30 minutes submersion: 3.4 wt. % 180.degree. dry peel
back: 10 lbs/in (1800 g/cm.)
As will be apparent to the skilled technician from a review of the
preceding Examples, elastomeric binders containing polyoxypropylene
chains (see the "Z.sup.1 " term, defined previously) have the
advantage of providing a relatively flexible impregnated and cured
sheet wherein the leather content has somehow been made at least
partially hydrophobic. Similar advantages, at slightly greater
cost, can be obtained with other polyoxyalkylene ("Z.sup.1 ")
chains wherein the alkylene portion of the oxyalkylene units
contains at least three carbon atoms, e.g., poly(oxy-1,2-butylene),
poly(oxy-1,4-butylene), etc. Oxyethylene units are not preferred,
due to their relatively high hydrophilicity.
* * * * *