U.S. patent number 3,914,501 [Application Number 05/361,149] was granted by the patent office on 1975-10-21 for porous products and processes therefor.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to Richard D. Jenkinson, Walter A. Miller.
United States Patent |
3,914,501 |
Miller , et al. |
October 21, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Porous products and processes therefor
Abstract
The invention relates to non-woven fiber structures in which the
fibers are ultra-fine, and are inter-bonded by fusion at a
plurality of points in said structure. Such fibers define open and
unfilled pores which are interconnected and extend from surface to
surface of the sheet. Such structures are produced by extruding a
blend of immiscible, thermoformable, fiber-forming polymers into a
shaped article, reducing said shaped article into a sheet
structure, heating the sheet structure to a temperature to fuse at
least a portion of the ultra-fine fibers therein, and extracting at
least a portion of the ultra-fine fibers from the sheet to render
it porous. Diverse products are produced such as synthetic leather,
apparel fabrics, and the like.
Inventors: |
Miller; Walter A. (Somerville,
NJ), Jenkinson; Richard D. (Naperville, IL) |
Assignee: |
Union Carbide Corporation (New
York, NY)
|
Family
ID: |
27001172 |
Appl.
No.: |
05/361,149 |
Filed: |
May 17, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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837302 |
Jun 27, 1969 |
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Current U.S.
Class: |
442/350; 156/155;
264/DIG.75; 428/904; 442/351; 442/411; 156/62.4; 156/62.6; 156/181;
428/151; 429/254 |
Current CPC
Class: |
D06N
3/0004 (20130101); D04H 1/541 (20130101); D04H
1/4382 (20130101); D04H 1/43838 (20200501); Y10T
428/24438 (20150115); Y10T 442/626 (20150401); D01F
6/94 (20130101); Y10T 442/625 (20150401); D01F
6/46 (20130101); Y10S 264/75 (20130101); Y10S
428/904 (20130101); Y10T 442/692 (20150401); D01F
6/56 (20130101) |
Current International
Class: |
D04H
13/00 (20060101); B32B 005/08 (); D04H
003/14 () |
Field of
Search: |
;156/62.4,62.6,155,180,181,306 ;161/157,170,DIG.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lesmes; George F.
Assistant Examiner: Robinson; Ellis P.
Attorney, Agent or Firm: Skoler; G. A.
Parent Case Text
This is a continuation, of application Ser. No. 837,302 filed June
27, 1969, now abandoned.
Claims
What is claimed is:
1. A porous sheet-like structure comprising:
A. forming shaped articles by melt extruding with drawing an
immiscible fiber forming polymer mixture, wherein at least one
polymer of said mixture is converted to an extractable fiber and at
least one other polymer of said mixture is converted to a
non-extractable fiber having a cross-sectional diameter normal to
its elongated shape of less than about five microns;
B. forming said shaped articles into an unbonded sheet;
C. heating said sheet made in (B) to a temperature whereby to
interfuse substantially all of the non-extractable fibers therein
sufficient to unite all of the fibers in the sheet;
D. extracting as a solution at least a portion of the extractable
fibers from said sheet in an amount sufficient to have said sheet
possess moisture vapor transmission; and
E. separating the solution from the sheet in an amount to produce a
porous sheet possessing moisture vapor transmission and containing
the ultrafine, thermoformable, molecularly oriented nonextractable
fibers therein, which nonextractable fibers are interbounded by
fusion at a plurality of points where such nonextractable fibers
interconnect, and said fibers define open and unfilled pores which
are interconnected and extend from surface to surface of said
sheet, and said fibers have a cross-sectional diameter normal to
their elongated shape end less than about 5 microns.
Description
This invention is directed to a novel process for making a wide
variety of novel porous nonwoven fibrous structures. Moreover,
encompassed within such a variety of nonwoven structures is
synthetic leather possessing characteristics which are remarkably
similar to natural leather.
Nonwoven fabrics can be made by a variety of methods, such as
carding, garnetting, air-laying, wet-laying, or melt spinning and
exploding mono-filaments or multi-filaments which are layed down in
a random pattern to form a mat.
These nonwoven fabrics are relatively useless until the fibers
therein are inter-bonded. This may be achieved by frictional
engagement of the fibers with one another, such as, is achieved by
needle punching or they may be inter-bonded through the use of an
adhesive.
In order to provide such nonwoven products with useful tear and
tensile strengths, it is necessary to effect a substantial amount
of inter-bonding and this results in stiffening the structure so
that it lacks the drape, hand, and other tactile properties
normally associated with woven and knitted fabrics. As a result,
these nonwoven fabrics have not significantly penetrated the
markets in which woven and knitted fabrics are employed.
In addition, there are presently in the market place a number of
substitute leather materials which are being used for making shoe
uppers, as well as gasket materials. These materials are called
"substitute leather" because they have a surface which resembles
leather and to the touch of one's finger tips, they feel like
leather, much like the leathery feel of expanded vinyl films.
However, they do not have the total tactile qualities of leather
and when such a substitute material is freely rolled in one's hand,
they possess a plastic feel.
These substitute leathers are "plastic" composites of at least two
layers. The bottom layer is typically a relatively costly nonwoven
mat of staple fibers and the other layer, typically the surface
layer, is made of a microporous film. These microporous films are
typically made from solutions or dispersions of a resin and a
liquid non-resin. When the non-resin is removed from the resin or
nonsolvent for the resin is added, the resin is coagulated, rinsed
and dried to produce a microporous film. Such coagulation is
believed to produce fused particles of the resin. The resins
presently employed are polyurethane elastomers. The surface layer
may be directly bonded to the nonwoven bottom layer by applying the
solution or dispersion of resin and non-resin to the surface of the
nonwoven layer followed by coagulation, rinsing and drying. Another
approach involves coating the solution or dispersion on a fabric
such as a woven scrim, followed by coagulation and adhesive bonding
of the underside of the coated fabric to the bottom layer. As a
rule, the non-woven mat layer is separately impregnated with a
resin to enhance bonding of the fibers therein. The nonwoven mat
may also be needled punched to increase its density and strength.
Shrinking the nonwoven mat also increases its density.
The formation of such microporous films is most difficult because
it is achieved by the deposition of a liquid resin onto a solid
surface followed by the steps of coagulation, rinsing and drying.
The resulting product, that is, the dry microporous film, can
easily contail craters, pinholes, orange peeling, variations in
thickness, streaks on the surface, and many other objectionable
characteristics unless considerable, if not extreme, care in
manufacture is employed.
There is described also other methods for forming substitute
leather products. Though these products are also laminates, their
surface layer is relatively thin and provides the aesthetic
qualities of leather. The surface layers are formed by
incorporating a soluble salt into a polymeric layer followed by
leaching the salt out to leave voids in the layer. If sufficient
salt is employed, the layer can be porous to air. However, such
layers are difficult to produce in a continuous basis to provide
uniform and consistent quality products. Invariably the surface
layer is of uneven uniformity.
Another technique mentioned in the literature involves blending two
immiscible polymers and extruding them from an orifice into fibrous
structures. Then these fibers are apparently disintegrated in water
and lapped on a screen to form a thin film. Then one of the
polymers is dissolved with a solvent, which also generally contains
a water soluble salt therein, to destroy one of the polymers to
convert it into an adhesive to bond the remaining fiber component
into a plastic sheet. None of the polymers are removed from the lap
so the resulting adhesively bonded lapped sheet contains a
substantial amount of the adhesive polymer formed by dissolution by
the solvent. By evaporation of the solvent with or without
dissolution from the lapped sheet of the soluble salt, there is
allegedly formed a porous film. The resulting film should possess a
coarse surface and to remove such coarseness, the surface must be
heat finished and this will adversely affect the film's porosity
and give it a "plastic" appearance. The film is relatively thin but
it is stated to possess the tactile qualities of leather. However,
though such allegations are magnanimous, they fail to take into
consideration that leather for footwear seldom has a thickness less
than 20 mils, a thickness beyond the apparant capabilities of this
process for producing a uniform, continuous sheet of porous
product. This thin film therefore will require lamination to
another substrate to provide the thickness and body required for a
substitute leather.
These laminated substitute leather products are susceptable to
delamination at the interface of the layers or in the proximity of
such interface, thus, severly limiting the degree of flexing to
which such product can be put. In normal flex tests used by the
leather industry, such substitute leathers generally do not compare
favorably in flex life with reasonably good quality leather. It is
believed that the layered homogeneous nature of leather is the
reason for its better flex life.
There are descriptions in the prior art of substitute leathers made
from needle punched nonwoven fiber mats. These products have very
coarse surfaces which only with great difficulty and expense can be
converted to have the appearance, physical and tactile properties
of leather. It is believed that these products represent the scheme
of an idea which resulted in the laminated structures which are in
the market place today but of themselves are not or cannot
reasonably be considered a substitute for leather.
Moreover, the needle projections in the nonwoven mat which bind the
staple fibers therein serve to create very dense points within the
mat. The non-needled sections are significantly less dense. As a
result, the product possesses an undesirable flex characteristic in
that the roll of the flex is very coarse and irregular. A
substantial amount of needling or a lot of resin binder is required
in the mat to minimize this effect. This effect is believed to be
the cause of internal failure of the nonwoven mat which typically
shows up during limited flexing of such type of mats by
conventional methods. Thus, a product made from needled nonwoven
mat does not possess homogeneity in the mat layer and has an
essentially irregular density throughout. Of course, the gross
effect of needling, so long as the needle patterns are regular,
achieves a regular and relatively uniformly dense structure.
However, in use, leather is not worn throughout its gross
structure, but at isolated points, thus, where such irregularities
exist in the substitute product, there exists locales wherein
fractures occur in the material.
This invention relates to the manufacture of unitized nonwoven
fibrous sheet material which can be employed in diverse areas of
use ranging from gaskets, dialytic membranes, battery separators,
to textile fabrics and synthetic leather. This invention is
particularly directed to the manufacture of a porous, fibrous sheet
which can be made to possess the tactile qualities of woven and
knitted fabrics, the drape and roll of woven and knitted fabrics,
and which can be made, on the other hand, to possess the full
tactile qualities of leather, such that it can be classed not only
a substitute for leather but a synthetic leather. Such a synthetic
leather is microporous, in that the pores therein are not visible
to the eye but under microscope are visible such as is the case of
the polished surface of leather.
This invention is directed to a sheet-like structure containing
ultra-fine, thermoformable fibers which are interbonded by fusion
at a plurality of points where such fibers contact. These fibers
define open and unfilled pores which are inter-connected and extend
from surface to surface of the sheet. The ultra-fine,
thermoformable fibers desirably have a denier of less than about
0.5, and preferably, these fibers are drawn, most preferably
molecularly oriented as well, and possess a cross-sectional
diameter normal to their elongated shape of less than about 5
microns.
The fiber characteristics in the sheet-like structure are selected
with consideration to the type of product desired. The density of
the sheet, the thickness of the sheet, the thickness and length of
the fibers, the tensile modulus and other properties, all bear on
the eventual properties of the sheet-like structure.
Tensile modulus as employed herein and in the claims is the 1 per
cent (1%) tensile modulus of the polymer employed in the
manufacture of the particular ultra-fine fiber in question
determined in accordance with ASTM D-638.
The term "major amount," as employed herein and in the claims,
means that at least fifty per cent (50%), on a weight basis, of
that material referred to as being present in such major amount.
The term "minor amount," as employed herein and in the claims,
shall mean that amount less than fifty per cent (50%), on a weight
basis, of that referred to as being present in such minor amount.
"On a weight basis" means herein and in the claims the total weight
in the sheet of the particular class of materials being referred
to, such as total weight of ultra-fine fibers, etc.
Herein and in the claims reference shall be made to
"non-extractable" or "residual ultra-fine fiber(s)" and
"extractable ultra-fine fiber(s)." An extractable ultra-fine fiber
shall mean an ultra-fine fiber which is removed from the structure
and is not present therein and non-extractable or residual
ultra-fine fiber, shall mean those fibers which are contained in
the breathable sheet-like structure of this invention.
In the manufacture of sheet-like structures of this invention, the
following process, employing the steps recited hereinafter, is
employed:
A. a shaped article is made comprising extractable and
non-extractable fibers, wherein the non-extractable fibers comprise
not more than about the volume of the extractable fibers therein,
by extrusion with drawing of an immiscible polymer mixture wherein
at least one polymer is converted to the extractable fiber and at
least one polymer is converted to the non-extractable fiber and
both polymers are thermoformable; this step is described in U.S.
Pat. No. 3,099,067, patented July 30, 1963 (assigned to the same
assignee hereof), and our copending U.S. application Ser. No.
671,238 filed Sept. 28, 1967.
B. forming the shaped article into a sheet, such as by forming a
pulp and shaping the pump into a sheet, this step is described in
U.S. Pat. No. 3,097,991, patented July 16, 1963 (assigned to the
same assignee hereof) or by weaving, air laying, cross lapping, and
the like, the shaped article into a sheet;
C. heating said sheet made in Step (B) to a temperature whereby to
fuse at least a portion of the ultra-fine fibers therein; and
D. extracting at least a portion of the extractable ultra-fine
fibers from said sheet to render the sheet porous, that is, the
sheet exhibits "moisture vapor transmission" as described
herein.
"Fusion" or "inter-fusion" as employed herein and in the claims
means that condition in which two individual fibers of the same
composition are caused to be inter-bonded through an indefinable
interface by application of heat to said fibers. Inter-bonding can
be achieved at isolated points on each of said fibers and need not
involve the totality of these said fibers though this condition is
not excluded by the definition of fusion or inter-fusion.
GENERAL DESCRIPTION OF TECHNOLOGY
Fundamentally, this invention is characterized by a porous fibrous
sheet and the process for making it in which the major amount of
the fibers in the sheet are ultra-fine, that is, they have a denier
of less than 0.5, preferably a crosssectional diameter determined
normal to the drawn length of the fiber which is less than about 5
microns. Most preferably, they have a cross-sectional diameter
ranging from as low as 0.1 micron and below about 2.5 microns. In
the preferred embodiment of the invention, a portion of the fibers
in the sheet, generally at least 5 weight per cent thereof, are
ultra-fine fibers which have a tensile modulus less than about
25,000 psi, and these fibers are bound in the sheet by being fused
together. This class of ultra-fine fibers may be present in the
sheet up to 100 per cent by weight thereof. Preferably at least 10
per cent by weight of the sheet to a 100 per cent by weight of the
sheet is made of ultra-fine fibers having a tensile modulus below
about 25,000 psi. The amount of these fibers which are present in
the sheet determine, to a great extent, the ultimate utility of the
sheet.
These ultra-fine fibers which have a tensile modulus below about
25,000 are herein called "soft ultra-fine fibers." Ultra-fine
fibers which possess a higher tensile modulus are herein called
"hard ultra-fine fibers." When the soft ultra-fine fibers are
elastomeric, and at least 50 per cent by weight of the sheet
contains such elastomeric soft ultra-fine fibers, then the sheet
has such properties that it can be employed as a synthetic leather.
When the amount of such soft elastomeric fibers is less than about
20 weight per cent of the fibrous sheet and the remaining are hard
ultrafine fibers therein, for example, having a high tensile
modulus even in excess of 100,000, such a sheet can range in
utilities from a textile fabric to a gasket material depending upon
the particular ultra-fine fibers therein. Moreover, the thinner the
sheet, the more susceptible it is for textile useage. Also, the
measurement of the cross-sectional diameter of the ultra-fine
fibers will be a significant factor in the tactility, i.e., hand
and drape properties, of the sheetlike structure. Because of the
interplay of the various components making up the sheet-like
materials in determining particular usages therefor, this invention
is definable in terms of the groups of products obtainable, thus
allowing for a more specific illustration of each of the various
factors necessary to make such products; for example, there will be
sections below which refer to the manufacture of synthetic
leathers, textile quality fabrics, and stiff, sheet-like structures
suitable for use as gaskets, battery separators, filters, and the
like. Prior to these sections are sections of general technology
common to the other sections relating to processing techniques
involved in the manufacture of the products described herein.
STARTING MATERIALS
As mentioned previously, the shaped structure of this invention is
predicated upon the manufacture of ultra-fine fibers, as
characterized in Step (A) above.
There are two types of soft polymer fiber employable in practice of
this invention, to wit, elastomeric soft ultra-fine fibers and
non-elastomeric soft ultra-fine fibers. The elastomeric soft
ultra-fine fibers are characterized as being made up of a polymer
having a tensile modulus below about 10,000 determined at
25.degree.C., which tensile modulus is preferably above 100, most
preferably above 250. It is desirable that it have a tensile
strength of at least 50 psi (pounds per square inch), preferably at
least 200 psi and most preferably at least 600 psi. The elastomeric
ultra-fine fiber, in isolated condition, is capable of at least 100
per cent extension (i.e., stretch) and at least about 50 per cent
recovery within 10 minutes when relaxed at room temperature
(25.degree.C.). In addition, the elastomeric ultra-fine fiber is
capable of at least 25 per cent elongation at room temperature. The
elastomeric polymer which is employed in making the ultrafine fiber
is thermoformable, that is, a polymer which can be shaped to an
extremely fine diameter fiber, such as below 5 microns in diameter
under pressure and heat.
Particularly illustrative of a thermoformable polymer is a
thermoplastic polymer, but the definition of thermoformable is not
restricted thereto. A polymer which is not wholly thermoplastic
because it contains some cross-linking but is capable of being
shaped into the ultra-fine fiber is encompassed by the term
thermoformable.
The non-elastomeric, soft ultra-fine fiber is also made of a
polymer which is thermoformable. It has a tensile modulus of less
than about 25,000. Its tensile modulus is generally above 5,000. As
an ultra-fine soft fiber it does not possess the rubbery quality of
the elastomeric, soft ultra-fine fiber as is shown by the fact that
it does not recover when relaxed after 100 per cent extension
within 10 minutes at room temperature. Though this fiber is soft,
it is typically considered somewhat harder and stiffer than the
limp elastomeric ultra-fine fiber. The hard ultra-fine fiber, as
employed herein and in the claims, is made from a thermoformable
polymer which has a tensile modulus in excess of about 25,000,
preferably in excess of about 50,000. Its other properties
including nonrubbery quality is the same as described above for the
soft non-elastomeric ultra-fine fiber.
Included in the definition of raw materials are other inert
ingredients which are not critical to the manufacture of porous
sheet-like structure. Such materials include, by way of example,
fillers, pigments, dyes, plasticizers, and the like. They are
called herein "inert ingredients."
Illustrative of non-elastomeric soft polymers which form the soft
non-elastomeric ultra-fine fibers are the following: low density
polyethylene, resinous polyethylene oxide, polyvinylacetate,
partially hydrolyzed polyvinylacetate, nonelastomeric copolymers of
ethylene and acrylic acid, nonelastomeric copolymers of ethylene
and alkylacrylates such as ethylacrylate, n-butyl acrylate and
2-ethylhexyl acrylate and the like, maleic acid anhydride adducts
of pyrolyzed polyethylene, polypropylene, copolymers of ethylene
and propylene, polyepsilon-caprolactone, wholly aliphatic polyester
and polycarbonate resins, and the like.
Illustrative of elastomeric polymers which produce the soft
elastomeric ultra-fine fibers include for example, elastomeric
polyurethanes, polyamides, polyesters, polycarbonates,
polyalkylacrylates, copolymers of ethylene and ethylacrylate which
can be saponified with caustic and the like.
Suitable polyurethane elastomers are the segmented polymers of
soft, low-temperature melting hydroxyl-terminated polymers which
have been bonded through urethane linkages to stiff,
high-temperature melting urethane, polyamide, polyurea, and/or
polyester polymers which have been terminated with isocyanato or
groups reactable with polyisocyanates (such as hyroxyl, amino,
mercapto, and the like).
The more desirable polyurethanes typically possess at least one,
preferably at least two, recurring polyether radical, that is, a
polymeric moiety possessing recurring ether linkages i.e.,
--C--O--C-- wherein the carbon atoms adjacent the oxygen are
saturated, in the internal chain structure thereof, and/or at least
one, preferably at least two, recurring polyester radical, that is,
a polymeric moiety possessing recurring ester linkages, i.e.,
##SPC1##
in the internal chain structure thereof. The polyether and
polyester radicals preferably possess a molecular weight of at
least about 500 and not in excess of about 7,000. They are joined
to the remainder of the polymer by urethanyl linkages, i.e.,
##SPC2##
wherein R may be hydrogen or an organic group such as alkyl of from
1 to about 8 carbon atoms, cycloalkyl of from 5 to 8 carbon atoms,
phenyl, or benzyl. The urethanyl linkage is bonded to a carbon atom
of the organic residue of an organic diisocyanate which in turn is
joined through the nitrogen atom of an amide linkage (i.e.,
##SPC3##
to one of the active hydrogen-free (as determined by the well known
Zerewitinoff method) residue of, e.g., an organic diol, a polyamine
compound or amino to form a urea linkage (i.e., ##SPC4##
The polyether and polyester radicals as described herein and in the
claims may also contain urethanyl linkages of the type described
above in the chain thereof. Such radicals desirably have a melting
point below 150.degree.C., and preferably below 60.degree.C.
The polyester radical may be formed by the reaction of a
dicarboxylic acid with an organic diol or by the condensation
polymerization of an alpha-omega-hydroxy-carboxylic acid or an
alpha-omega-lactone. Preferably, these polyesters are hydroxyl
end-blocked in that the end groups of the polyester are hydroxyl
bonded to noncarbonyl containing carbon atoms. These polyesters are
then reacted, if they are of the desired molecular weight, with an
organic diisocyanate, most desirably in the ratio of at least 2
moles of diisocyanate to one mole of the polyester, to form a
diisocyanato end-block prepolymer. This prepolymer is then reacted
with a chain extender such as diol or dithiol chain extenders,
diamino chain extenders, or water, to form a substantially linear,
solvent-soluble polyurethane. A process for the manufacture of the
aforementioned polyurethanes are described in U.S. Pat. No.
3,097,192. Specific illustrations of chain extenders include
hydrazine, ethylene diamine, 1,3-propylene diamine, 1,4-butane
diamine, 1,6-hexamethylene diamine, 1,4-piperazine, ethylene
glycol, 1,2-propylene glycol, 1,4-butane diol, ethanol amine,
diethanolamine, urea, dimethylol urea, and the like.
Other suitable polyesters may be formed by the reaction of epsilon
caprolactone and/or alkyl-substituted epsilon caprolactone and an
active hydrogen containing initiator such as water, ethylene
glycol, ethylene diamine, diethylene glycol, dipropylene glycol, or
1,2-propylene glycol, such as described in U.S. Pat. Nos.
3,169,945; 3,186,971; and 3,427,346.
The polyesters possessing hydroxyl end groups and having a
molecular weight in excess of 500 and up to 7,000 may then be
reacted with an organic diisocyanate to produce a polyurethane
prepolymer having a molecular weight of from about 1,000 up to
about 10,000. This polyurethane may be isocyanato end-blocked for
direct reaction with the chain extender or may be hydroxyl
end-blocked and is considered a prepolymer for additional reaction
with diisocyanate, as described in U.S. Pat. No. 3,186,971.
Another polyurethane which is most suitably employed is that
described in U.S. Pat. No. 2,871,218. The polyesterpolyurethane of
this patent is made by admixing a hydroxyl end-blocked or
terminated polyester, formed by the reaction of 1,4-butane diol
with adipic acid, with diphenylmethane-p,p'-diisocyanate and
1,4-butane diol in essentially exact stoichiometric proportions.
The polyester should have a molecular weight of about 800 to 1,200
and for every mole of polyester there is employed from about 1.1 to
3.1 moles of the diisocyanate and from about 0.1 to 2.1 moles of
the butane diol. By increasing the mole amount of diisocyanate, it
is possible to increase the melting point and hardness of the
resulting polyurethane and by reducing the mole amount of
diisocyanate, it is possible to decrease the melting point and
hardness of the resulting polyurethane.
The polyethers may be characterized in essentially the same manner
as the polyester above. They fall in the same melting point ranges,
are desirably in the same molecular weight range and are hydroxyl
end-blocked or terminated. They are formed by the alkaline or acid
condensation of alkylene oxides. Such polyethers and their
utilization in polyurethanes are described in U.S. Pat. Nos.
2,813,776; 2,818,404; 2,929,800; 2,929,803; 2,929,804; 2,948,707;
3,180,853 and RE 24,691.
Suitable polycarbonate elastomers include the segmented polymers of
soft, low-temperature multihydroxyl-terminated polymers which have
been bonded through carbonate linkages to stiff, high-temperature
multicarbonate polymers.
Such polycarbonate elastomers are illustrated in the following
patents:
Canadian Pat. No. 668,153, issued Aug. 6, 1963, note particularly
Examples 2, and 3; U.S. Pat. No. 3,030,335, patented Apr. 17, 1962,
note Ex. 2 and the disclosure at column 1, lines 56 to 68,
inclusive; U.S. Pat. No. 3,161,615, patented Dec. 15, 1964, note
particularly Examples 3, 7, 10, 14, 15, 19, 20, 21, 22, 24 and 25;
U.S. Pat. No. 3,207,814, patented Sept. 21, 1965, note Examples 1,
2, 5, 7, 9, 10 and 11; and U.S. Pat. No. 3,287,442, patented Nov.
22, 1966, note Examples 9, 10, 11, 13, 16, 18, 21, 23, 29 and 30.
The method and the components involved in the manufacture of such
polycarbonte elastomers suitable for use in the practice of this
invention are disclosed in the above patents and the disclosures of
these patents are incorporated herein by refernce with respect to
their teachings of methods and reactants.
Suitable elastomeric polyesters are described in U.S. Pat. No.
2,623,031, patented Dec. 23, 1962, note Examples 1, 2, 3, 4, 5 and
6; U.S. Pat. No. 3,023,192, patented Feb. 27, 1962, note all of the
Examples therein; and U.S. Pat. No. 3,037,960, patented June 5,
1962, note all of the Examples therein. These elastomeric
polyesters are also segmented copolymers in which a soft segment is
interbonded to a hard segment by an ester linkage. The hard segment
is polyester and the soft segment may be polyester or polyether
such as described above with respect to polyurethane
elastomers.
Suitable elastomeric polyalkyl acrylates include, by way of
example, poly(ethylacrylate), copolymers of ethylacrylate and other
alkylacrylates such as n-butylacrylate, 2-ethylhexylacrylate, and
the like. Also included are copolymers of ethylene with
alkylacrylates (such as ethylacrylate) which can be saponified with
caustic such as sodium and/or potassium hydroxide, to produce
useable terpolymers of ethylene, alkylacrylate and acrylic acid.
Other copolymers of this class include copolymers of ethylene with
acrylic acid and/or other alkylacrylates such as
2-ethylhexylacrylate, and the like.
Suitable elastomeric polyamides for use in this invention are
described in U.S. Pat. Nos. 2,929,801; 3,044,987 and 3,044,989.
The hard ultra-fine fibers are obtained from thermoformable
polymers, as characterized above, such as high density
polyethylene, polypropylene, poly-1-butene, polystyrene,
polyalpha-methylstyrene, poly-alpha-chlorostyrene, copolymers of
vinyl chloride and vinyl acetate, partially hydrolyzed copolymers
of vinyl chloride and vinyl acetate, polyvinylpyrrolidone,
copolymers of N-vinylpyrrolidone and vinyl acetate, copolymers of
vinyl methyl ketone and vinyl chloride, vinyl acetate or N-vinyl
pyrrolidone, polymethylmethacrylate, polymethacrolein,
diethylacetal of polyacrolein, copolymers of styrene and
acrylonitrile, nylon (such as polyhexamethyleneadipate,
polytetramethylenesebacamide, poly-epsilon-caprolactam,
polypyrrolidone), the polyimidazolines, polyesters (such as
polyethyleneterephthalate, poly-1,4-cyclohexyleneterephthalate, and
the like), oxymethylene homopolymers and copolymers (the
formaldehyde polymers), polycarbonates such as the reaction product
of phosgene or monomeric carbonate esters with bis Phenol A
[2-bis(4-hydroxyphenyl)propane], and the like, polyarylene
polyethers such as described in U.S. Pat. No. 3,264,536, patented
Aug. 2, 1966, and the like.
THE PROCESS
STEP A
This step involves blending two or more thermoformable polymers,
melt extrusion of the blend into the shape of a monofilament,
multi-filaments, rod, ribbon or film with drawing of the shaped
article either during extrusion or thereafter. As stated
previously, the shaped article contains at least one extractable
and one non-extractable fiber therein. These fibers are derived
from the extrusion and drawing of a blend of polymers which are
immiscible in each other, that is, they are mutually incompatible
in each other either in solid or molten state. Usually, both
polymers have molecular weights greater than 10,000. Generally
speaking, in combining mutually incompatible polymers prior to
extruding them into the shaped article, conventional methods and
apparatus are entirely suitable. If the polymers are available as
raw materials in powder, pelletized or granular form of sizes
substantially uniform and equal as between the two or more
polymers, dry blending, e.g., in a conical blender or a ribbon
blender, is quite good. However, if the particle sizes of the
individual polymers are too dissimilar, poor mixing results from
these methods. In this event, hot processing methods may be
employed. Fluxing the polymers on a two-roll mill or a Banbury
mixer at a temperature dependent on the polymers being handled
produces suitable mixtures. Another means of mixing is to dissolve
all of the starting materials in a suitable mutual solvent system
and then removing the solvent(s) by evaporation. Still another
method, practical when polymers are being used which show little
tendency to degrade at temperatures near their melting point, is
the so-called "double" extrusion in which the polymers are fluxed
by a normal melt extrusion operation, pelletized or chopped after
being extruded and dry mixed before the final extrusion into the
shaped article.
Particle and pellet size of the incompatible polymers in a dry
blended mixture effects the dimension of the fibers ultimately
obtained only when very little working of the mixture in molten
state is done prior to extrusion through an orifice or slot to form
a shaped article such as mono-filament, multi-filament, rod, ribbon
or film. If for example, a mixture of two incompatible polymers is
charged into a heated cylinder equipped with a piston to force the
molten mixture out through a small orifice with a minimum amount of
milling of the mass, the dimensions of the fibers comprising the
extruded filament can be controlled by correlating the particle
size in the dry blend mixture with the dimension of the fibers
produced, having set a fixed rate of filament attenuation (drawing
or stretch). If there is no milling prior to or during extrusion, a
proportional relationship exists between fiber diameter and
pre-extrusion particle size.
Normal operation, however, produces ultra-fine fibers such as
described above. By normal operation is meant that at some point in
the extrusion process the incompatible polymers are fluxed in a
plastic state to such an extent that initial particle size of the
starting materials is not a factor in determining the dimensions of
the fiber in the article. The amount of fluxing required is not
great -- the operation of the feeding screw in a conventional screw
type extruder being sufficient. Hot processing of a granulated
polymer mixture on a two-roll mill or Banbury mixer before
extrusion is sufficient even if a non-milling type ram or plunger
extruder is used.
Extrusion conditions, particularly temperature, will vary over a
relatively wide range. The conditions depend on the physical and
chemical properties of the extruded polymers and thus may even vary
for identical compositions according to the preference of the
skilled operator. However, the fluxed mixture of the incompatible
polymers must obtain a melt fluidity in the extruder such that
during the first drawn stage there is a smooth reduction of the
diameter as the composite mono-filament, multi-filaments, or film
issues from the orifice or slot and elongates while being hot
drawn. While the extruded mix, as it issues from the extruder
nozzle, does have a fibrous nature, attenuation (or drawing)
ensures production of ultra-fine fibers. Such drawing can be
achieved in the extruder providing the extruder is machined for
this purpose.
It is to be understood that whereas either hot drawing or cold
drawing alone may produce fine fibers in a composite shaped article
of this invention of the two or more mutually incompatible
polymers, each such operation produces unique characteristics in
the final ultra-fine fiber produced and such result may be achieved
by employing both techniques in combination. Hot drawing will, in
the main, serve to reduce the diameter in thickness of the extruded
article thereby necessarily reducing the diameter of the individual
fibers of which it is composed. After hot drawn in the melt, the
fibers in the article have little or no molecular orientation in
the longitudinal direction.
The amount of hot processing or fluxing of the two or more mutually
incompatible granulated polymers will be a factor in determining
the diameter of the ultra-fine fibers making up the composite
article at the moment it emerges from the extruder die. The
difference in diameter between the bore of the extruder and the die
orifice or slot causes a certain amount of attenuation which may
vary between extruders of for the same extruder depending on the
size die that is attached. However, once the fluxing and extruding
conditions for a given polymer mixture has been adapted, a single
determination of the fiber size produced for a given amount of hot
drawing is sufficient to establish approximately the amount draw to
produce fibers of a desired diameter. Assuming ideal
characteristics for the individual ultra-fine fibers in the shaped
article, that is, they are uniform rods, preferably having circular
cross-sectional areas, and elongate the same extent as the shaped
article is elongated, the diameter of a fiber after drawing is
equal to the diameter before drawing divided by the square root of
the ratio of the new length to the old length.
If desired, cold drawing to induce molecular orientation may be
included as an intergral part of the overall process and follow
immediately after hot drawing or may be carried out at any time,
even after storage of the shaped article.
Cold drawing is primarily for the purpose of inducing the
ultra-fine fibers' molecular orientation in a longitudinal
direction. This "stretch orientation," as it is commonly called, is
well known in the synthetic fiber art to effect improvement in
physical properties such as tensile strength and, in some
instances, resistance to a heat aging. The stretching of the shaped
article is carried out in the same fashion as it is effected in the
prior art. The degree of orientation imparted to the fiber is
dependent upon the polymer employed and the uses to which the
product will be put. Due to the relationship of the diameter to the
length of ultra-fine fiber before and after stretching, cold
drawing sufficient to induce orientation to the extent of several
hundred percent stretch or elongation does not greatly alter the
ultra-fine fiber's diameters even when hot drawing had previously
reduced it to a range of for example 0.125 microns.
It is preferred in the practice of this invention that the molten
immiscible polymer mixture be drawn at least 100 percent either
during extrusion or after extrusion to obtain a shaped article most
favorably employable in the practice of this invention. This
drawing is exhibited or evidenced by a commensurate reduction in
the diameter or thickness of the shaped article from the
corresponding diameter or thickness of the immiscible polymer
mixture from which it is obtained just before its extrusion. Such
drawing can be achieved in the extrusion opening or by pulling the
article at a great rate as it issues from the opening.
As stated previously, the shaped extruded article described above
contains therein a plurality of extremely fine (ultra-fine) fibers.
The extruded shaped article, regardless of whether it is a
mono-filament, multi-filament, film, etc., contains many such
ultra-fine fibers therein, for example, a rod having a one-inch
square cross-section can contain one million or more of such fibers
laying parallel to the drawing axis of the rod.
STEP B
As pointed out in U.S. Pat. No. 3,097,991, referred to above, the
shaped article of Step (A) can be readily converted into a paper
pulp. Though the aforementioned U.S. patent stresses the
manufacture of a shaped article in the form of a mono-filament,
multi-filaments or thin sheeting cut into strips can be handled in
the same manner to be beaten by conventional means into a pulp from
which interfelting is readily accomplished. The first step of the
process in forming a felt of the ultra-fine fibers is to make a
slush of the shaped article. In the case of a film, ribbon or rod,
they are first slit into a predetermined width and thickness then
cut in the pre-determined length and deposited in water to form the
slush.
With respect to use of mono-filaments and multi-filaments, they are
cut in pre-determined lengths in making the slush according to the
amount of beating or refining employed. It is preferred that the
cut shaped article containing the ultra-fine fibers have a length
not in excess of 12 inches, most preferably not in excess of 8
inches, and preferably not less than one-sixteenth inch when
employed in formation of a slush. The thickness and width of any
shaped article employed in making the slush should not exceed
one-half inch preferably not in excess of one-fourth inch. The
slush is nothing more than a dispersion of the cut and/or sliced
shaped article.
The slush is thereafter treated to effect mechanical fibrillation,
that is, the shaped article is mechanically attavked to effect
breakage and splitting thereof whereby the shaped article, which is
a unitary bundle of ultra-fine fibers, is fractured into smaller
bundles of said ultra-fine fibers and the individual ultra-fine
fibers. Such fibrillation causes extremely small bundles of the
ultra-fine fiber or the individual ultra-fine fibers to be loosen
from the surface of these smaller bundles as fibrils. This may be
accomplished by any conventional paper beating or refining
technique such as in a Hollander type beater, a Hydrapulper, a
Vortex beater, a Sharple pulper, a Dynopulper, a Jordan refiner, a
Bauer refiner, a Curlator refiner and the like.
The beating or refining step is important to the process of this
invention and will greatly determine some of the significant
properties of the resulting product. If beating does not reduce the
ultra-fine fiber length or the length of the bundles of ultra-fine
fibers to any great extent and the fiber length is in excess of,
e.g., one-half inch, the resulting product, that is the breathable
product of this invention, will possess superior tear strength,
though it is possible in some cases that other properties such as
degree of breathability, hand and drape may suffer. In the step of
beating or refining, one may employ a minor amount of conventional
staple fibers such as cotton, nylon, polyester, acrylic,
modacrylic, and the like, to enhance such properties as tear and
tensile strengths even though they alone do not lend themselves to
the formation of the cohesive sheet-like structure of this
process.
One may only partially beat and refine a given slush and thereafter
combine it with a slush of another composition such as cellulosic
paper pulp or the partially beaten or refined slush made of other
ultra-fine fibers, that is, a slush of a fractured shaped article
having a different composition. In this way, blends of different
fibers can be obtained in a simple manner. As will be pointed out
later, variations in the manufacture of a pulp in which there
exists different fiber lengths can be of extreme advantage in the
manufacture of certain products.
Usually, the beating and refining step reduces the length of the
shaped article to no more than about 1 inch, typically less than
one-half inch and most usually between about one thirty-second inch
and three-eighths inch. The pulp resulting from the beating and
refining step is now employable in making the felted sheet
described in Step B above. This may be accomplished in any of the
known ways by hand or by machine.
If desired, the pulp can be formed by other means such as by ball
milling the cut and/or stripped shaped articles with water or by
air micronizing or micropulverizing and then depositing in water
the small fractured fragments containing fibrils extending from
their surfaces to form the pulp. The sheet which is formed from any
one of these pulps can be accomplished by hand in the conventional
way by depositing the pulp onto a screen, squeezing the mass on the
screen to form a filtered cake followed by further water removal
such as by suction and then heating to remove the water to form a
felted sheet. Of course, the most desirable way is to form a felted
sheet on machinery such as a Fourdrinier paper machine. Standard
paper making techniques are employable to make a very uniform
cohesive dry-felted sheet which can be treated in accordance with
Step C described herein.
As mentioned previously, the pulp can contain ultrafine fibers from
a plurality of different shaped articles defined in Step A, each
composed of different fibers, and/or the pulp can contain as well
cellulosic paper pulp or pulp of other fibrous matter such as
cotton, nylon, polyester, acrylic and modacrylic type fibers. These
pulps can be formed in the initial stages of the paper making
process such as prior to or in the head box of a Fourdrinier
machine. The options available are numerous and are easily within
the skill of the operator.
The dry inter-felted sheet containing the ultra-fine fibers is now
ready for Step C.
Instead of pulping, forming a slush and felting, the shaped
articles can be formed into a sheet by numerous methods including,
but not limited thereto: air laying cut staple of the shaped
article (in the form of mono and multi-filaments); cross-lapping
continuous tapes, films and/or filaments of the immiscible polymers
using conventional hand or machine cross-lapping techniques to form
a scrim, web or batting; or by weaving tapes or filaments to form a
woven fabric. These sheet products are now ready for Step C.
STEP C
The dry sheet of Step B is heated to a temperature sufficient
enough to fuse at least a portion of the non-extractable ultra-fine
fibers in the sheet. The temperature employed is one which under
the pressure employed causes sufficient softening of such
non-extractable ultra-fine fibers that they are fused together to
form a cohesive bond and to interbond together all of the fibers in
the sheet. It is very desirable, but not critical to the most broad
aspects of the invention, to similarly interfuse the extractable
ultra-fine fibers in the sheet. In the usual case, the softening
point of the non-extractable ultra-fine fibers is higher than the
softening point of the extractable ultra-fine fibers, and hence,
these fibers are also fused in the heating step.
In a most significant embodiment of this invention, pressure is
applied to the surfaces of the sheets while the sheet is being
heated. In such case, it is preferred that the temperature applied
while the sheet is being pressed be at least as high as the
softening temperature of the non-extractable ultra-fine fibers
which are being fused, i.e., the softening temperature of the fiber
determined at normal temperature pressure (NTP).
It is most preferred that the temperature applied be sufficient to
fuse a major amount of the non-extractable ultrafine fibers in the
sheet.
This step of the process can be accomplished in a platen press
wherein the platens are heated to the desired temperature. It can
also be accomplished by passing the sheet of Step (B) through
heated calender or nip rolls, typically a series of such rolls, or
it can be passed around a large roll and be put under pressure on
said roll by an endless belt which circumscribes at least a portion
of such roll. The last described apparatus is illustrated by a
Rotocure, a machine which is employed for curing rubber sheets.
Suitable apparatus for effecting this heating and pressure step of
the process is described in copending application Ser. No. 379,268,
filed June 30, 1964, assigned to assignee hereof, and in U.S. Pat.
No. 2,971,218, patented Feb. 14, 1961. The sheet can be heated
dielectrically if desired.
The pressure employed is typically at least 25 pounds per square
inch of the felted sheet. As a rule, the amount of pressure is
sufficient to effect a degree of compression of the sheet,
typically at least 5 percent compression in thickness of the sheet.
This compression is permanent in that when pressure is relieved and
the sheet is cooled to room temperature, it does not expand to its
original thickness. If the ultra-fine fibers in the sheet are
stretch oriented, then there is usually a small amount of shrinkage
occurring during the heat fusion and pressure step. Such shrinkage
may be noted in reductions in the width or length of the sheet or
in its thickness or in all three dimensions simultaneously.
STEP D
It is this step of the process in which microporosity or
breathability is achieved. The fused sheet is transported from the
compression step, in the preferred case, to a bath of a liquid
which is a solvent for the extractable ultra-fine fiber in the
fused sheet but which is essentially a non-solvent for the
non-extractable ultra-fine fiber in the sheet. The choice of
solvent is important in the manufacture of the desired product and
for processing efficiency. The solvent should be readily active in
dissolving the extractable ultra-fine fiber and most preferably
should be a total non-solvent for the non-extractable ultra-fine
fibers. If conventional staple fibers have been incorporated in the
fused sheet, it is preferred that the solvent be a non-solvent for
such staple fibers. It is preferred in the practice of this
invention that essentially all of the extractable ultra-fine fibers
be removed from the fused sheet such that the sheet is essentially
free of such fibers. It is particularly desirable to preclude the
formation of resinous nonfibrous-like materials inside the porous
structure and hence, any fiber which is dissolved should be
essentially totally removed from the fused sheet. It is in this
fashion that there can be obtained a sheet having the most
desirable porosity and/or breathability. Also, it is this factor
which achieves a uniformly porous sheet.
The extraction step simply involves the immersion of the fused
sheet into the bath of solvent. The bath should be essentially free
of any liquid therein which is a solvent for the non-extractable
fibers. The bath may contain an amount of liquid which is a
non-solvent for any of the extractable ultrafine fibers in the
fused sheet for the purpose of controlling the rate of dissolution
of the extractable fibers. Other techniques similar to immersion
can be employed such as spraying the sheet with a solvent until
extraction is achieved. The wet sheet is then removed from the
extraction step and dried at as low a temperature as is needed to
remove essentially all traces of the solvent within the alloted
processing time. Most desirably, this temperature is below the
softening temperature of the non-extractable ultra-fine fibers in
the sheet.
The solvent employed is typically present in an amount greater, on
a volume basis, than the amount of extractable fiber in the sheet.
Most desirably, a substantially excess of solvent is employed and
multiple baths involving sequential extraction are generally used
to insure maximum extraction of the extractable fiber. The
resulting leached sheet, after drying, has the desired properties
of porosity, hand, drape, tactility, and the like.
If desired, the fused sheet prior to or as part of the treatment of
Step (D) may be heat embossed with a calendar embossing roll to
impart designs in one or both of the surfaces of the sheet. This
embossing step may take place after the extraction step and if it
does, it should be recognized that some of the surface pores of the
sheet will be compressed and reduced in size thereby reducing the
rate of breathability of the sheet.
In addition, one or both of the surfaces of the resulting sheet may
be buffed or scoured to effect surface characteristics for
particular uses without adversely affecting the porosity of the
sheet.
SYNTHETIC LEATHER
One of the most significant characteristics of leather is that it
does not readily pass liquids but allows moisture vapor to pass
through it. This latter quality is characterized as "moisture vapor
transmission." These are important properties for a shoe upper
material.
The synthetic leather of this invention possesses each of these
qualities. In addition, the synthetic leather of this invention can
exhibit the flexing, hand, and drape properties of leather.
The term "moisture vapor transmission" is meant herein and in the
claims as that weight of moisture determined in grams per square
meter per hour which passes through the sheet when evaluated under
the following conditions:
a circular disc of the sheet having a known area is sealed with wax
at its edge on the top of a cup containing an excess quantity of
desiccant (such as calcium chloride). The cup is placed under
constant temperature and humidity of 70.degree.F. (dry bulb
temperature) and 65 percent relative humidity for 16 hours, after
which time the cup with the film is weighed;
after the first weighing, the cup is left in the same atmosphere
for an additional hour and is weighed again, and this procedure of
weighing is repeated until such time as a static or constant
"moisture vapor transmission" determined in grams per square meter
per hour, is obtained. The final figure represents the "moisture
vapor transmission" (referred to hereinafter as "MVT"). The MVT of
good quality, finished calfskin typically runs from about 15 to
about 60 and higher, though usually the MVT is from about 20 to
about 25. The most widely promoted leather substitute today is
"Corfam," sold by E. I. du Pont de Nemours and Company, which is
described as a poromeric material. Samples of it have been found to
possess MVT's ranging from as low as 15 and as high as about 35 to
40, depending upon the type of embossment and surface finish.
In addition to MVT requirements, synthetic leather should possess a
flex life, drape, body, hand, tactility, workability, tear strength
and tensile strength comparable to natural leather. Many of the
above characteristics are the subjective evaluation of an expert in
the characteristics of leather. The synthetic leather of this
invention satisfies such subjective standards and possesses
advantages over those products in the market place with respect to
physical properties which can be evaluated in accordance with
standard tests.
A most significant quality of the synthetic leather of this
invention is that it is an extremely homogeneous material, that is,
it can be made of essentially single composition and is not a
nonwoven laminate. At best, the synthetic leather of this invention
does not require any backing fabric because of its extremely good
physical properties but in certain circumstances it may be
desirable to bond it to a backing fabric, such as a woven or bonded
nonwoven fabric for the purpose of giving the synthetic leather
added dimensional stability.
The surface of this synthetic leather is most uniform due to the
nature of the process employed and in many cases it will not be
necessary to finish the surfaces of the synthetic leather with a
lacquer or latex coating which is common practice with leather
substitutes presently in the marketplace. The surface of the
synthetic leather can be embossed to give the product a leather
grain appearance, e.g., the appearance of alligator hide, calfskin,
and snakeskins. The surface may be brushed in the conventional
manner to give a suede effect if such is desired.
In characterizing synthetic leather of this invention, the major
amount of the fused ultra-fine fibers in the sheet are elastomeric
soft ultra-fine fibers and the remaining ultra-fine fibers in said
sheet may be hard or soft ultra-fine fibers. Preferably, at least
60 percent by weight of the porous sheet comprises the elastomeric
soft ultra-fine fibers and most preferably at least 75 percent by
weight of the porous sheet is made of said ultra-fine fibers. In a
significantly preferred embodiment of this invention, hard
ultra-fine fibers are not present in the sheet in amounts by weight
thereof greater than 10 percent. The most favorable product
obtainable for most uses is a sheet in which 100 percent of the
ultra-fine fibers therein are soft ultra-fine fibers. In accordance
with this most favorable embodiment, the porous sheet may contain
up to 25 percent weight percent thereof of soft ultra-fine fibers
other than the elastomeric ultra-fine fibers. It is most preferred
that all of the ultra-fine fibers in the sheet are elastomeric,
soft ultra-fine fibers.
In the manufacture of such a sheet, Step (A) is achieved by forming
a shaped article in which the amount by volume of the elastomeric
soft ultra-fine fibers therein is not significantly greater than
the amount by volume of either non-elastomeric soft or hard
ultra-fine fibers therein. Preferably, the amount by volume of
these elastomeric ultra-fine fibers in the shaped article is not
greater than the amount by volume of the non-elastomeric soft or
hard ultra-fine fibers in the article. The amount by volume of the
elastomeric soft ultra-fine fibers may be as little as 20 percent
(20%) of the amount by volume of the non-elastomeric hard or soft
ultra-fine fibers in the article. In the most desirable embodiment,
the amount by volume of the elastomeric soft ultra-fine fibers in
the article ranges from 40 percent to 98 percent of the amount by
volume of the non-elastomeric hard or soft ultra-fine fibers
therein.
The sheet is made in accordance with the procedures in Steps (A) to
(D). In the practice of Step (C) it is most desirable that the
temperature employed to effect fusion is at least equal to the
softening temperature of the elastomeric, soft ultra-fine fibers in
the sheet, and it is most desirable that the non-elastomeric hard
or soft ultra-fine fibers employed have softening points which are
lower than the softening points of the elastomeric, soft ultra-fine
fibers. It is also preferred in the practice of Step (C) that
pressure be applied to the surfaces of the sheet during the fusion
step sufficient to effect some reduction in the thickness of the
sheet being treated.
The use of a large concentration of elastomeric ultra-fine fibers
in the sheet is important and significant to the manufacture of
good synthetic leather. Non-elastomeric ultra-fine fibers, when
present in the sheet in too large a quantity, adversely affect the
aforementioned subjective tests which are so important in the
characterization of a good quality product.
In this respect, synthetic leather is a distinctive embodiment of
this invention, and it is important to appreciate that it typically
possesses a thickness greater than the usual fabric, in most cases
having a thickness greater than 10 mils, preferably greater than 20
mils and in most cases does not exceed 100 mils. Because of this
considerable thickness, the body characteristics of the product
become paramount in the evaluation of the product, and it has been
found that the presence of large quantities of elastomeric
ultra-fine fibers greatly contributes to this characteristic.
NONWOVEN FABRICS
The products of this category are distinctive from synthetic
leather in many respects. Nonwoven fabrics do not require the
employment of elastomeric soft ultra-fine fibers, though they may
be employed if desired. Moreover, the sheet which is treated in
Steps (C) and (D) need not contain only ultra-fine fibers as is
usually the case with synthetic leather. Thus the sheet may also
contain therein conventional staple fibers. Moreover, though the
ultimate sheet from Step (D) is porous, it need not be microporous,
as is the case with synthetic leather. Though it is usual to employ
a pulp in the case of synthetic leather in Step (B) wherein the
ultra-fine fibers are beaten to a generally uniform length, it can
be most beneficial to employ a pulp in the manufacture of nonwoven
fabrics wherein the lengths of the ultra-fine fibers in the pulp
vary greatly, indeed, ranging from as low as one thirty-second of
an inch to 1 inch or more in length in any given pulp.
Whereas a synthetic leather, in most cases, should be free of
boardiness, some nonwoven fabrics may possess boardiness because
such characteristics is desired in a certain marketplace, and in
some instances a soft limp nonwoven fabric, which would be wholly
unsatisfactory for synthetic leather purposes, will be useful for a
given fabric market.
In characterizing nonwoven fabrics one must give consideration to
the qualities of hand and feel. They are important subjective
standards in this field. There is a hazy demarcation between a soft
and a stiff hand. This difference is a product of the modulus of
the polymers employed in making the ultra-fine fibers, the
cross-sectional diameter of the ultra-fine fibers, the apparent
density of the porous sheet and the shape of the ultra-fine fibers
in the structure. Thus, in a nonporous, fully densified structure
wherein no shape identity of ultra-fine fibers is apparent or
characterized, the soft hand of the sheet falls off when the
polymer employed in making the ultra-fine fibers has a tensile
modulus above about 10,000. By reducing the density of the sheet,
as is accomplished in Step (D), a softer hand is achievable even
when the tensile modulus of the polymer employed in making the
ultra-fine fiber is as high as 50,000. If the sheet is thin, the
tensile modulus needed for a soft hand can be greater than 50,000,
even as high as 500,000. The more porous, or less dense, is the
sheet, the higher the tensile modulus of the polymer making up the
ultra-fine fiber can be in order to obtain a product with a soft
hand. So it can be seen that many significant variables are
available in the manufacture of nonwoven fabrics in accordance with
this invention. This is a great advantage because the more
variables available to the technician, the greater is his ability
to provide a product having the exact qualities desired by the
customer.
In the manufacture of nonwoven fabrics, it is desired that the
sheet contain not more than 40 percent by weight thereof of staple
fibers, preferably not more than 25 percent. The use of staple
fibers greatly increases the tear and tensile strengths of the
sheet, but it does affect the sheet's hand. An alternative
approach, and greatly favored here, is to employ two pulps in Step
(B), each pulp made from a shaped article as characterized in Step
(A) but where one pulp contains fiber lengths not greater than
about one half inch and another pulp having greater fiber lengths,
typically not greater than about 1 inch. These pulps can be blended
in various proportions depending on the type of products desired.
The term fiber lengths with respect to pulps refers to the average
length of the fibers in the pulp. Thus, ultra-fine fibers of
varying lengths can be employed to either improve or reduce the
tear and tensile strengths of the ultimate sheet. As the density of
the sheet increases, so does the tensile and tear strengths, but
there also occurs a falling off in drape and hand unless one
insures that the tensile modulus of the fibers in the sheet as
defined above, is below about 50,000, preferably below 25,000 and
most preferably below 10,000. Higher density sheets made of such
fibers of low tensile modulus will not differ significantly in
hand.
Another significant factor in the manufacture of nonwoven sheets is
that Step (C), where fusion is effected, may be practiced without
application of pressure to the surfaces of the sheet. In some
cases, particularly where textured effects are desired, it will be
most important not to apply pressure to the surfaces of the sheet
during the fusion step.
As noted previously, one does not have to rely upon pulping to
create the sheet from which the desired fabric is made. For
example, the shaped article, preferably in the form of filament(s),
slit film, ribbon or tape strips, can be woven into a fabric from
which fusion and extraction, as characterized above, there is
produced a porous fabric. In addition, mono- or multi-filaments of
immiscible polymers can be cut into staple fibers which can be air
layed into a non-woven sheet from which fusion and extraction there
is produced a porous fabric. Alternatively, mono-oriented films of
immiscible polymers may be cross-lapped by well known procedures,
such as on a mandrel or on a carding cross-lapper, to produce a
sheet which upon fusion and extraction produces the porous fabric.
Another technique involves needle punching with barbed needles any
of the above sheets or one or more of the aforedefined films
superimposed on another to cause blending of bundles of fibrils,
followed by fusion and extraction to produce a desirable porous
sheet.
The term "nonwoven fabrics," as employed herein, is not intended to
be exclusive of synthetic leather since the latter is often used in
areas normally regarded the domain of fabrics. However, this term
is intended to mean a nonwoven cloth-like textile fabric suitable
for use in areas normally regarded suitable for woven or knitted
fabrics.
Moreover, though one may weave or knit a sheet from the
aforedefined shaped articles, the final fused and extracted sheet
is not to be regarded as woven or knitted, as the case may be.
Fusion serves the purpose of destroying the woven or knit structure
and the dominant binding force of the fused sheet becomes cohesion
between the melt compatible fibrils. On extraction of the
extractable fibrils (ultra-fine fibers), the resulting porous sheet
shows little, it any, of the woven or knit structure.
STIFF STRUCTURES
The stiff and boardy structures can be made by selection of a hard
non-extractable fiber alone or in admixture with soft
non-extractable fibers or by producing a relatively dense structure
(possessing low MVT) from any fiber. The above procedures are
employable. The density can be controlled by, e.g., either reducing
the amount of extractable fiber in the sheet or the amount of
extractable fiber taken from the sheet. Alternatively, essentially
all of the extractable fiber can be removed from the sheet and
density is controlled by the amount of such fiber in the sheet
prior to extraction or by subsequently hot compressing the porous
sheet to permanently reduce its density.
These products have good structural stability and can be used as
battery separators, insulation medium, building material, gaskets,
and the like.
In order to further characterize this invention, reference is made
to the examples which follow. These examples serve the sole purpose
of further illustrating this invention and they are not intended
for the purpose of restricting the scope of this invention.
EXAMPLE 1
This example describes four thermoplastic polyurethane elastomers
employed in other examples.
Polyurethane A
To a 2,000 milliliter reaction flask equipped with heating mantle,
stirrer thermometer, ebulater and vacuum inlet tube is charged 730
grams (0.75 equivalent) of polycaprolactone diol (hereinafter
called "polyol"). The polyol has a molecular weight of 2,000 and is
formed by the reaction of epsiloncaprolactone with diethylene
glycol. The polyol is heated to 100.degree.C. and is allowed to
degas at 100.degree.C. for 1 hour under about 0.1 inch mercury to
remove moisture and dissolved gasses. A portion of
bis(4-isocyanatophenyl) methane (565 grams) is similarly melted and
degassed at 50.degree.C. The temperature of the polyol is raised to
149.degree.C. Vacuum is broken and the heated and degassed polyol
is poured into a heated (177.degree.C.) steel cylinder mold. To the
polyol is added 169 grams (3.75 equivalents) of 1,4-butane diol
with stirring, followed by 565 grams of the
bis(4-isocyanatophenyl)methane. The mixture is stirred for 1 minute
after the addition of the bis(4-isocyanatophenyl)-methane and cured
in an air-oven at 177.degree.C. for 1 hour. The resulting
thermoformable polyurethane elastomer is granulated.
Polyurethane B
This elastomer is prepared by the same procedure as polyurethane A,
except that the equivalent ratio of
bis(4-isocyanatophenyl)methane/polyol/1,4-butane diol is 5:1:4
instead of 6:1:5. Weights and equivalents used are as follows:
Weight (Grams) Equivalents ______________________________________
Polyol 730 0.75 1,4-butane diol 135.3 3.00
bis(4-isocyanatophenyl)methane 471.6 3.75
______________________________________
Polyurethanes A and B, produced as described above have the
following physical properties.
TABLE 1 ______________________________________ A B
______________________________________ Hardness Shore D 50 45 100%
Modulus, psi 2350 1225 300% Modulus, psi 4850 3250 Tensile
Strength, psi 4950 5400 Ultimate Elongation, % 305 360 C Tear psi
730 640 B Compression Set, % 51 55 Zwick Resilience, % 37 47
______________________________________
Polyurethane C
This polyurethane is an elastomer which is believed to be produced
by the reaction of a hydroxyl end-blocked polyethyleneadipate
(molecular weight above 700 and believed to be below 2,000) with
bis(4-isocyanatophenyl)methane and 1,4-butane diol. This
polyurethane is called "ESTANE 5701 resin" produced by B. F.
Goodrich Chemical Company, a division of the B. F. Goodrich
Company, 3135 Euclid Avenue, Cleveland, Ohio 44115. It has the
following physical properties:
Value ASTM No. ______________________________________ Specific
Gravity 1.20 D12-27 Hardness, Durometer A 88 D-676 Durometer C 60
Tensile Strength (psi) (min) 5800 D-412 Modulus at 300% Elongation
(psi) 1300 Elongation (%) (min) 500 Graves Tear (lbs/in) (approx.)
350 D-624 Low-Temperature Brittleness <-80 D-746 Point
(.degree.F) Gehman Low Temperature Freeze -24 D-1053 Point
(.degree.F) Taber Abrasion (mg loss) (CS17 wheel, 1000 gms, weight,
5 D1044-49T 5000 cycles) Processing Stock Temperature (.degree.F)
340 ______________________________________
Polyurethane D
This polyurethane is an elastomer which is believed to be produced
by the reaction of a hydroxyl end block polyethyleneadipate
(molecular weight above 700 and believed to be below 2,000) with
bis(4-isocyanatophenyl)methane and 1,4-butane diol. This
polyurethane is called "ESTANE 5740 .times. 070 resin" produced by
B. F. Goodrich Chemical Company, a division of the B. F. Goodrich
Company, 3135 Euclid Avenue, Cleveland, Ohio 44115. It has the
following physical properties:
Value ASTM No. ______________________________________ Specific
Gravity 1.20 D12-27 Hardness, Durometer A 95 D-676 Durometer C 70
Durometer D 48 Tensile Strength (psi) (min) 5800 D-412 Modulus at
300% Elongation (psi) 3500 Elongation (%) (min) 450 Grave Tear
(lbs/in) 700 D-624 Low-Temperature Brittleness Point (.degree.F)
<-100 D-746 Gehman Low Temperature Freeze Point (.degree.F) -1
D-1053 Compression Set - Method A* 22 Hours at 158.degree.F. 11
D-395-55 Taber Abrasion (mg loss) (CS 17 wheel, 1000 gms. weight,
5000 cycles 3 D1044-49T Processing Stock Temperature (.degree.F)
350-380 ______________________________________ *Method A uses
constant compression stress at constant test temperature.
EXAMPLE 2
A mixture weighing 4,000 grams is made up by combining 1,200 grams
of Polyurethane D, 400 grams of film and fiber grade polypropylene
resin (melt index of 2-4; density of 0.88) and 2,400 grams of
atactic crystal clear polystyrene having a molecular weight of
50,000. The resins are each in approximately 1/8 inch dice form and
the mixture is effected by tumble blending the three resins
together. The mixture is melted in a 11/4 inch single screw
extruder at 180.degree.C. The extruded strand is diced into 1/8
inch pellets. The 1/8 inch pellets are mixed and again melted and
then extruded through the same extruder into an approximately 1/16
inch diameter strand which is drawn by a Godet from the extruder at
the rate of 10 feet per minute. This strand is then passed into a
glycerine stretching bath, maintained at 125.degree.C. and the
strand is there stretched by drawing it out of the bath at 110 feet
per minute. This imparts a molecular orientation to the strand that
may be expressed as (110-10)/10 .times. 100% = 1,000% stretch
oriented. The strand is cut to staple lengths of from one-half inch
to 6 inches and is next fed to a Noble and Wood Cycle Beater with a
blade clearance setting of 5 mils. The cut strands are beaten to
produce a thoroughly digested pulp of the mixed polymer
mono-filaments.
The pulp is then processed into 12 inches .times. 12 inches hand
sheets using a Noble and Wood Laboratory Paper Hand Sheet
Apparatus. The felt or paper is 200 mils thick.
The felt is dried in an air-oven at 70.degree.C. After drying the
felt is pressed at 165.degree.C. and 100 psi in a platen press to
produce a full density molded sheet of 120 mils thick. The sheet is
then placed in a beaker containing toluene to extract the
polystyrene. The sheet after extraction is dried and is a
semi-finished leather like product. The sheet is approximately
four-tenths of its full density, has porosity comparable to
leather, showing a MVT of 15, and mechanical properties similar to
leather. It has excellent flex life and abrasion resistance.
Furthermore it has the "break" and "hand" of leather.
EXAMPLE 3
The process of Example 2 is repeated except that the mix weighs
2,000 grams and is formed by combining 1,000 grams of Polyurethane
D with 1,000 grams of atactic, crystal clear polystyrene. The 1/8
inch melt mixed pellets are extruded into an approximately 1/16
inch diameter strand and drawn by a Godet at 10 feet per minute.
The strand is passed into the glycerine stretching bath at
125.degree.C. and is drawn out of the bath at 250 feet per minute.
The molecular orientation imparted may be expressed as (250-25)/25
.times. 100% = 900% stretch orientation. The strand is arbitrarily
cut to staple lengths of from about one-quarter inch to about 4
inches and is next fed to a Noble and Wood Cycle Beater with a
blade clearance setting of 7 mils. The strand is beaten to produce
a pulp of the mixed polymer monofilament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 100 mils thick.
The felt is dried in an air-oven at 65.degree.C. After drying the
felt is pressed at 170.degree.C. and 300 psi in a platen press to
produce a full density molded sheet of 60 mils in thickness. The
sheet is then placed in a beaker containing toluene to extract the
polystyrene. The sheet after extraction is dried and is the
semi-finished leather like product. The sheet is approximately
one-half of its full density, has porosity comparable to calf skin,
showing an MVT of 18, and mechanical properties similar to leather.
It has excellent flex life and abrasion resistance. Furthermore it
has the "break" and "hand" of leather.
EXAMPLE 4
Example 1 is repeated except that the mix weighs 2,000 grams
achieved by combining 1,000 grams of the polystyrene of Example 3,
800 grams of Polyurethane D and 200 grams of film and fiber grade
polypropylene having a melt index of 2-4 and a density of 0.88. The
blended pellets are melt mixed using a 11/4 inch single screw
extruder heated to 200.degree.C. The extruded strand is diced into
1/8 inch pellets. The 1/8 inch pellets are melt extruded into
approximately 1/32 inch diameter strand and drawn by the Godet at
10 feet per minute. The strand is then passed into a hot stretching
bath at 130.degree.C. and is drawn out of the bath at 100 feet per
minute. This imparted on orientation expressed as 900% stretch. The
strand is abritrarily cut to staple lengths of about 1 inch to
about 3 inches and is next fed to a Noble and Wood Cycle Beater
with a blade clearance setting of 6 mils. The strand is beaten to
produce a pulp of the mixed polymer mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 50 mils thick.
The pressed felt is dried in an air-oven at 50.degree.C. After
drying the felt is pressed at 170.degree.C. and 50 psi to produce a
full density molded sheet having a thickness of 25 mils. The sheet
is then placed in a beaker containing toluene to extract the
polystyrene. The sheet after extraction is dried and is the
semi-finished leather like product. The sheet is approximately
one-half of its full density, has porosity comparable to calf skin,
showing an MVT of 30, and mechanical properties similar to leather.
It has excellent flex life and abrasion resistance. Furthermore it
has the "break" and "hand" of leather.
EXAMPLE 5
Example 4 is repeated except that the 2,000 grams mixture contains
600 grams of Polyurethane D, 156 grams of Polyurethane C, 244 grams
of the polypropylene and 1,000 grams of the polystyrene. The four
resins are in approximately 1/8 inch diced form and tumble blended.
The blended pellets are melt mixed in the extruder at 175.degree.C.
and the extruded strand is diced and re-extruded into an
approximately 1/32 inch diameter strand which is drawn by the Godet
at 20 feet per minute. The strand is then passed into a glycerine
stretching bath at 125.degree.C. and then drawn out of the bath at
220 feet per minute. There is obtained a molecular orientation
expressed as 1,000% stretch. The strand is cut and next fed to a
Noble and Wood Cycle Beater with a blade clearance setting of 7
mils. The strand is beaten to produce a pulp of the mixed polymer
mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 35 mils thick.
The pressed felt is dried in an air-oven at 25.degree.C. After
drying the felt is pressed at 170.degree.C. and 100 psi to produce
a full density molded sheet having a thickness of 18 mils. The
sheet is then placed in toluene to extract the polystyrene. The
sheet after extraction is dried. The sheet is approximately
one-half of its full density, has porosity comparable to glove
leather or a closely woven fabric, and mechanical properties
similar to leather. It has excellent flex life and abrasion
resistance. Furthermore it has the "break" and "hand" of leather as
well as the suppleness of a soft woven fabric.
EXAMPLE 6
The process of Example 5 is repeated except that the 2,000 grams
mixture is made by combining 1,000 grams of the polystyrene and
1,000 grams of Polyurethane A. The two resins are both in powder
form and tumble blended. The blend is melted using a 11/4 inch
single screw extruder at 195.degree.C. and then the extruded strand
is diced as before. The resulting pellets are again extruded in
approximately 1/32 inch diameter strand and drawn at 19 feet per
minute. The strand is then passed into a glycerine stretching bath
at 125.degree.C. and drawn out of the bath at 90 feet per minute,
thus, imparting a molecular orientation expressed as 370% stretch.
The strand is cut and next is fed to a Noble and Wood Cycle Beater
with a blade clearance setting of 6 mils. The strand is beaten to
produce a pulp of the mixed polymer mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 17 mils thick.
The pressed felt is dried in an air-oven at 75.degree.C. After
drying the felt is pressed at 190.degree.C. and 50 psi in a platen
press to produce a full density molded sheet having a thickness of
7.2 mils. The sheet is then placed in toluene to extract the
polystyrene. The sheet after extraction is dried. The sheet is
approximately one-half of its full density, has substantial
porosity, showing an MVT of 51, and mechanical properties between
that of glove leather and a supple woven fabric. It has excellent
flex life and abrasion resistance. Furthermore it has the "break"
and tactility of leather.
EXAMPLE 7
A 1000 grams mixture is made by combining 500 grams of the
polystyrene of Example 2 and 500 grams of Polyurethane B. The two
resins are in approximately 1/8 inch diced form and tumble blended.
The blended pellets are mixed in the melt in a 11/4 inch single
screw extruder at 220.degree.C. The extruded strand is diced into
1/8 inch pellets and the pellets are mixed and again extruded but
this time into a strand having a diameter of 1/32 inch. The strand
is drawn from the extruder by a Godet at 20 feet per minute. The
strand is then passed into a glycerine stretching bath at
130.degree.C. and is drawn out of the bath at 100 feet per minute,
to impart a molecular orientation expressed as 400% stretch. The
strand is cut to lengths of one-quarter inch to about 6 inches and
next fed to a Noble and Wood Cycle Beater with a blade clearance
setting of 6 mils. The strand is beaten to produce a pulp of the
mixed polymer mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 123 mils thick.
The pressed felt is dried in an air-oven at 75.degree.C. After
drying the felt is pressed at 190.degree.C. and 50 psi to produce a
full density molded sheet having a thickness of 62 mils. The sheet
is then placed in toluene to extract the polystyrene. The sheet
after extraction is dried and is the semi-finished leather like
product. The sheet is approximately one-half of its full density,
has porosity comparable to leather and mechanical properties
similar to leather. It has excellent flex life and abrasion
resistance. Furthermore it has the "break" and "hand" of
leather.
EXAMPLE 8
The process of Example 3 is repeated except that the 2,000 grams
mixture contains 1,000 grams of the polystyrene, 333 grams of the
polypropylene of Example 4 and 666 grams of Polyurethane D. The
strand of the re-extruded pellets is approximately 1/32 inch
diameter and drawn by the Godet at 20 feet per minute. The strand
is passed into the glycerine stretching bath and drawn out of the
bath a 250 feet per minute to impart a molecular orientation
expressed as 1,150% stretch. The strand is cut and next is fed to a
Noble and Wood Cycle Beater with a blade clearance setting of 8
mils. The strand is beaten to produce a pulp of the mixed polymer
mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 200 mils thick.
The pressed felt is dried in an air-oven at 55.degree.C. After
drying the felt is pressed at 165.degree.C. and 150 psi to produce
a full density molded sheet having a thickness of 125 mils. The
sheet is then placed in toluene to extract the polystyrene. The
sheet after extraction is dried and is the semi-finished leather
like product. The sheet is approximately one-half of its full
density, has porosity comparable to leather and mechanical
properties similar to leather. It has excellent flex life and
abrasion resistance. Furthermore it has the "break" and "hand" of
leather.
EXAMPLE 9
The process of Example 8 is repeated except that the 2,000 grams
mixture is made by combining 756 grams of Polyurethane D, 244 grams
of the polypropylene and 1,000 grams of the polystyrene. The strand
upon extrusion has a 1/64 inch diameter and is drawn by the Godet
at 30 feet per minute; then it is passed into the glycerine
stretching bath at 130.degree.C. and drawn out of the bath at 330
feet per minute to impart a molecular orientation expressed as
1,000% stretch. The cut strand is next fed to a Noble and Wood
Cycle Beater with a blade clearance setting of 5 mils. The strand
is beaten to produce a pulp of the mixed polymer mono-filament.
The pulp is processed into 12 inches .times. 12 inches hand sheets
using a Noble and Wood Laboratory Paper Hand Sheet Apparatus. The
felt or paper is 150 mils thick.
The pressed felt is dried in an air-oven at 60.degree.C. After
drying the felt is pressed at 170.degree.C. and 50 psi to produce a
full density molded sheet. The sheet is then placed in toluene to
extract the polystyrene. The sheet after extraction is dried and is
the semi-finished leather like product. The sheet is approximately
one-half of its full density, has porosity comparable to leather
and mechanical properties similar to leather. It has excellent flex
life and abrasion resistance. Furthermore it has the "break" and
"hand" of leather.
EXAMPLE 10
The process of Example 9 is repeated except that the 2,000 grams
mixture contains 1,000 grams of polyvinylacetate, 667 grams of
Polyurethane D and 333 grams of the polypropylene. The melt mixing
in the single screw extruder is at 170.degree.C. and the extruded
strand has a diameter of 1/32 inch and is drawn by the Godet at 25
feet per minute. The glycerine stretching bath is at a temperature
of 120.degree.C. and the strand is drawn out of the bath at a rate
of 250 feet per minute, thus, imparting a molecular orientation
expressed as 900% stretch. Using the procedures of the previous
examples, an excellent synthetic leather is produced from a felt of
this fiber using toluene to extract the polyvinylacetate fiber
therein.
EXAMPLE 11
Example 6 is repeated except that the 1/8 inch melt mix pellets are
extruded through a multi-orifice die to produce a 20 filament,
continuous filament yarn wherein each filament has a denier of 0.5
and is stretch oriented.
The yarn is woven into a 120 .times. 120 pick fabric and a 12
inches .times. 12 inches swatch is pressed at 190.degree.C. in a
platen press at 50 psi to produce a full density molded sheet
having a thickness of about 2 mils. The sheet is then extracted
with toluene to remove the polystyrene using the procedure of
Example 6 to produce a soft, highly porous sheet which has good
strength and considerable elasticity.
EXAMPLE 12
Repeating Example 6, except that the felt is made 123 mils thick
and hot pressed at 190.degree.C. to a full density sheet of 60 mils
thickness. The following are comparative properties characterizing
this porous sheet:
5% Bally Thick- Den- Elonga- Tangent Flexo- Satra ness sity Tensile
tion Modulus Tear MVT meter Flex
__________________________________________________________________________
mils gm/cc psi % psi lb/in. gm/M.sup.2 /hr.sup.1 cycles cycles
Synthetic leather of Example 12 60 0.530 817 93 2,450 216 18.sup.2
>1.6MM >8MM Corfam (Dupont) 62 0.500 1,200 36 2,350 125 19
100M Aztran (Sold by B. F. Goodrich Company) 60 0.580 1,380 23
2,100 183 17 50M 1MM Calf Skin perpendicular to Backbone 50 0.630
2,700 44 2,300 216 28 >1.6MM >8MM Calf Skin parallel to
Backbone 50 0.630 3,800 48 4,000 347 28 >1.6MM >8MM
__________________________________________________________________________
.sup.1 75% relative humidity at 82.degree.F.? .sup.2 Unfinished,
not surface coated "1.6MM" and "8MM" mean 1.6 million and 8
million, respectively. "100M" and "50M" mean 100 thousand and 50
thousand, respectively.
EXAMPLE 13
The procedure of Example 2 is repeated by combining equal parts by
weight of the polypropylene and polystyrene without adding
Polyurethane D. The pulp of polypropylene and polystyrene polymer
fibers is processed into a 12 inches .times. 12 inches hand sheet,
15 mils thick. After hot pressing and extraction with toluene,
followed by drying, there is obtained a 5 mil thick porous nonwoven
sheet of polypropylene fibers. The sheet is broadly and finds
usefulness as a battery separator and as a gasket.
EXAMPLE 14
The procedure of Example 13 is repeated with equal parts by weight
of the same polypropylene and polycaprolactam having a molecular
weight of 40,000. There is obtained a 2 mil thick porous nylon
sheet from extraction with hot toluene of hot pressed 10 mil thick
felt. The nonwoven has good hand and drape and can be used in
making outerwear.
* * * * *