U.S. patent number 3,645,775 [Application Number 04/884,731] was granted by the patent office on 1972-02-29 for process for production of an artificial leather and product.
Invention is credited to Helmut Schulze, Gerhard Seibert.
United States Patent |
3,645,775 |
Schulze , et al. |
February 29, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
PROCESS FOR PRODUCTION OF AN ARTIFICIAL LEATHER AND PRODUCT
Abstract
Process of producing an artificial leather by coagulating or
hardening a polyurethane gel applied to a substrate into a
microporous layer which is permeable to water vapor, wherein a
silicone oil is added to the initial gelable solution of the
polyurethane in an organic solvent.
Inventors: |
Schulze; Helmut (Erlenbach,
DT), Seibert; Gerhard (Erlenbach, DT) |
Family
ID: |
5716407 |
Appl.
No.: |
04/884,731 |
Filed: |
December 12, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Dec 17, 1968 [DT] |
|
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P 18 15 043.1 |
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Current U.S.
Class: |
428/315.5;
428/425.5; 428/904; 521/64; 427/246; 428/446; 521/63; 524/233 |
Current CPC
Class: |
D06N
3/0065 (20130101); C08L 75/04 (20130101); C08L
75/04 (20130101); D06N 3/14 (20130101); C08L
83/00 (20130101); Y10S 428/904 (20130101); Y10T
428/31598 (20150401); Y10T 428/249978 (20150401) |
Current International
Class: |
D06N
3/14 (20060101); D06N 3/00 (20060101); D06N
3/12 (20060101); C08L 75/00 (20060101); C08L
75/04 (20060101); D06n 003/00 (); B32b
027/40 () |
Field of
Search: |
;117/135.5,161KP,161ZA,63 ;161/DIG.2 ;260/824R,858 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Katz; Murray
Assistant Examiner: Husack; Ralph
Claims
The invention is hereby claimed as follows:
1. In a process for the production of an artificial leather wherein
a solution of polyurethane is an organic solvent is gelled, the gel
is applied to a substrate and is converted into a microporous layer
by coagulation, washing to remove the solvent and drying, the
improvement which comprises:
adding to the initial polyurethane solution about 1 to 10 percent
by weight, with reference to the dissolved polyurethane, of a
silicone oil, said oil being uniformly distributed in finely
dispersed form in said solution at the point where the dissolved
polyurethane is converted into a gel.
2. A process as claimed in claim 1 wherein the amount of silicone
oil is about 2 to 4 percent by weight, with reference to the
dissolved polyurethane.
3. A process as claimed in claim 1 wherein organic solvent is
dimethyl formamide.
4. A process as claimed in claim 1 wherein said solution contains
from 30 to 40 percent by weight of polyurethane.
5. A process as claimed in claim 4 wherein the organic solvent is
dimethyl formamide.
6. A process as claimed in claim 1 wherein the silicone oil has a
viscosity of about 100 to 1,000 centipoise.
7. The artificial leather product obtained by the process of claim
1.
Description
As is well known, a synthetic or artificial leather can be produced
from a nonwoven web or fleece which has been bonded with a
polymeric elastomeric binder such as a polyurethane. Nonwoven webs
or fabrics which have been treated in this way are generally
capable of storing water vapor and then giving it off again at the
surface of the web. This is of the greatest importance for an
artificial leather which is to be used in the manufacture of shoes
because the upper leather of a shoe must absorb water vapor as
perspiration from the foot and then pass it to the outside at the
exposed surface. If the upper leather does not fulfill this
function, the water vapor accumulates inside the shoe and causes
discomfort to the wearer.
Nonwoven webs or fabrics treated in this way, however, are also
highly porous and permeable to liquid so that, for example, rain
water can enter the shoe from outside. The porous bonded web or
fleece, also termed the substrate, must therefore be provided with
a microporous covering layer which although permeable to water
vapor is impermeable to liquid water. In addition, this covering
layer must give the shoe material the appearance of a leather
surface and a leathery handle. Properties such as compression
strength, bending or flexing resistance, resistance to cold, scuff
resistance and the like of the finished material also depend
largely on the quality of this surface covering layer.
It is known to produce covering layers for an artificial leather
from polyurethanes. These layers can be produced for example from
solutions of polyurethanes in dimethylformamide or other suitable
organic solvents, the polyurethane in the solution being converted
into a gel by the addition of a nonsolvent such as water and the
gel then being coated onto the bonded nonwoven web or fabric. After
coagulation of the polyurethane, washing to remove the solvent and
drying, polyurethane surface layers with improved permeability to
water vapor are obtained. With previously known microporous
polyurethane layers, however, various mechanical or physical
properties still have not been fully developed to yield durable and
dependable artificial leather products.
The general object of the present invention is to provide an
initial gellable polyurethane composition and an improvement in the
conventional process of providing a microporous surfacing of
artificial leathers based on polyurethane whereby a number of
important properties are enhanced in a relatively simple and
economical manner. Specific objects and advantages of the invention
are set forth in greater detail in the following disclosure.
It has now been found, in accordance with the invention, that an
artificial leather with improved properties can be produced
particularly advantageously by the application of a polyurethane
layer to a substrate, if there is used a gellable solution of
polyurethane in an organic solvent which contains about 1 to 10
percent and preferably 2 to 4 percent by weight of a silicone oil,
based on the weight of the dissolved polyurethane. The organic
solvent is preferably dimethylformamide.
Polyurethanes used in the process according to the invention are
generally known. They may be obtained, for example, by reacting
diisocyanates with polyethers or polyesters which contain terminal
hydroxy groups to produce an NCO-containing prepolymer which may
then undergo further reactions with chain lengthening agents such
as diamines or glycols. A complete description of such
polyurethanes and their preparation is set forth in numerous
patents and other literature sources, e.g., U.S. Pats. No.
2,871,218 and No. 3,190,766, and standard references such as
"Polyurethanes" by Dombrow, Rheinhold Publ. Corp. (1957), or
"polyurethanes: Chemistry and Technology" by Saunders and Frisch,
Interscience Publishers of John Wiley & Sons (1962). The
polyurethane film-forming or coating material should be one which
consists predominately of the polyurethane, preferably 65 percent
by weight or more, and may contain one or more other film-forming
thermoplastic organic polymers of the many polymers and copolymers
known to be compatible with a polyurethane gel, preferably other
elastomeric polymers. For example, it is known that polyvinyl
chloride and various copolymers of vinyl chloride, e.g., with vinyl
acetate or maleic acid anhydride, can be incorporated in minor
amounts into the polyurethane film-forming composition. Other
polymers include butadiene/acrylonitrile or
butadiene/acrylonitrile/styrene interpolymers and also chlorinated
rubber or nitrocellulose. These other polymers replace only a
portion of the polyurethane in the composition, usually not more
than 5 or 10 percent by weight thereof, and the total weight of
such polymer mixtures is considered the weight of the polyurethane
for purposes of the present invention.
The organic solvent normally used is dimethyl formamide but other
well-known solvents for polyurethane are also suitable, for example
dimethyl sulphoxide, dimethylacetamide and mixtures of such
solvents. The quantity of the polyurethane in the solution may vary
within wide limits in the process according to the invention. In
general, concentrations of the polyurethane in the solvent of 15 to
40 percent by weight are found to be suitable. The polyurethane
solution may also contain up to 30 percent by weight, based on the
polyurethane, of other polymers such as polyvinyl chloride. Other
additives such as stabilizers, pigments or dyes may of course also
be included.
Silicone oils which may be used within the scope of the invention
are generally known liquid substances. They are polymeric
organosilicon compounds in which silicon atoms are linked together
via oxygen atoms and the remaining valencies of the silicon atoms
are saturated with hydrocarbon radicals. The preferred silicone
oils have a predominately linear structure with recurring units of
the formula
sometimes expressed as --(SiR.sub.2 --O)--, in which the side
groups R represent a hydrocarbon radical of one to 12 carbon atoms,
preferably one to six carbon atoms, such as lower alkyl, e.g.,
methyl, or aryl, e.g., phenyl. Further details about silicone oils
may be found in such references as "Chemical Encyclopaedia" by
Hermann Rompp, 6th Edition, Frank'sche Verlagshandlung, Stuttgart,
Germany. See also "Silicic Science" by Hauser, D. VanNostrand Co.,
Inc. (1955), Chapter XIII, pages 146-154. Commercially available
silicone oils are generally quite similar in their chemical
structure, corresponding to the above noted formula of the
individual recurring unit in the polymer, although minor
modifications can be made without affecting the essential
properties of these silicone oils. Their viscosity is primarily
determined by the chain length of the linear polyorgano-siloxane
structure, although there may occasionally occur a cross-linking of
individual chains by a silicon-oxygen-silicon linkage. Such minor
variations of the well-known silicone oils are to be included
within the scope of the invention.
Silicone oils which have a viscosity of 100 to 1,000 centipoise
(cP) are found to be particularly suitable for purposes of the
invention.
The silicone oils may be soluble or insoluble in the organic
solvent such as dimethylformamide employed in the preparation of
the polyurethane gel.
The silicone oil selected for purposes of the invention is added in
a quantity of from about 1 to 10 and preferably about 2 to 4
percent by weight, based on the dissolved polyurethane. Addition of
the silicone oil is best carried out when the polyurethane is
already dissolved in the organic solvent. Care should be taken to
ensure that the silicone oil is uniformly distributed in finely
divided or finely dispersed form in the solution at the point where
the dissolved polyurethane is converted into a gel, e.g., by the
addition of a suitable non-solvent such as water. This uniform
distribution is particularly applicable when using a silicone oil
which is insoluble in the dimethylformamide or other solvent.
Working up the gel to produce a microporous covering layer or film
coating is carried out in known manner. The gel can be applied to a
porous nonwoven web or fleece, for example with the aid of a doctor
blade, and is then coagulated, washed and dried. After drying, the
microporous covering layer on the substrate preferably has a
thickness of about 0.3 to 0.6 mm. and especially 0.3 to 0.4 mm.
The substrate itself is bonded with a polyurethane solution or any
suitable elastomer solution by impregnating the nonwoven web or
fabric and hardening the elastomeric binder in a conventional
manner. A suitable nonwoven web can be obtained for example by the
process according to British Pat. specification No. 1,017,023. Many
techniques are known for the manufacture of nonwoven webs and their
bonding into a flexible, porous substrate capable of providing the
body or primary layer of an artificial leather, and the present
invention is not limited to the use of any particular
substrate.
It has been found, surprisingly, that the addition of a silicone
oil according to the invention substantially improves the
microporous covering or surface layers. Thus, it is possible by
means of the silicone oil to substantially eliminate the tendency
of certain polyurethanes, e.g., as obtained by the process
according to French Pat. No. 1,546,169, to disintegrate when drying
the covering layer so as to yield a film or surface layer which is
nonporous and impermeable to water vapor. In addition, the covering
layers obtained according to the invention are extremely
stable.
Another advantage which was not expected is the fact that the
process according to the invention permits the use of initial
polyurethane solutions which contain a very high concentration of
the polyurethane. By comparison, when using polyurethanes as
disclosed in German Pat. specification No. 1,106,959, which in
themselves are quite suitable for the production of microporous
covering layers, it was not possible to work with solutions
containing more than 30 percent of the polyurethane without taking
special precautions during the gelling or precipitation step, e.g.,
a very long storage in a moist atmosphere. When a silicone oil has
been added according to the present invention, a polyurethane
solution having a concentration of over 30 percent, e.g., up to
about 40 percent, can be used successfully without the necessity of
taking any special precautions. The required microporous covering
layers can therefore be rapidly obtained in a simple and effective
manner.
Polyurethane solutions which contain 30 to 40 percent by weight of
the polyurethane and about 1 to 10 percent by weight, based on the
dissolved polyurethane, of a silicone oil therefore represent a
preferred embodiment of the invention, these solutions being gelled
and subsequently coagulated, washed and dried to yield the desired
microporous layer.
The use of these more highly concentrated polyurethane solutions
for the production of a microporous polyurethane layer is
particularly advantageous because less solvent needs to be
recovered. The microporous layers produced according to the
invention can be easily washed out very thoroughly before they are
dried and no residues remain which could subsequently cause
difficulties, such as collapse of the microporous or fine cellular
structure of the covering layer or discoloration of the
polyurethane. Furthermore, covering layers with improved physical
or mechanical properties are obtained when higher concentrations of
the initial solution are used.
By using higher polyurethane concentrations, covering layers of
higher density are obtained. A material with better surfacing
properties is obtained, and in particular the scratch or scuff
resistance is substantially increased.
The process according to the invention moreover makes it possible
to produce colored surface coatings or layers in which a dye or
pigment is very uniformly distributed. The patchiness frequently
observed in the covering layers produced by previously known
processes no longer occur. This greatly facilitates the finishing
and final appearance of the coating or layer as an artificial
leather.
The covering layers produced according to the invention are also
notable for a very uniform pore structure and increased compressive
strength. The bending resistance is also improved. Low-temperature
mechanical properties, particularly the response to bending, are
likewise superior in comparison to previous products.
Microporous covering layers produced according to the invention may
be grained and provided with one or more coatings, e.g., an
undercoat containing a polyurethane and a top lacquer containing
nitrocellulose. The surface coatings which are applied when
finishing the covering layer of the invention have a total
thickness of only a few microns.
Although it is already known to use silicones in
polyurethane-containing dressings or finishing agents for synthetic
leather, the use of silicones in this limited way does not achieve
the advantages of this invention. Moreover, it is extremely
surprising that the use of silicone oils in the production of a
microporous covering layer which is several hundred microns in
thickness results in an artificial leather which has many improved
properties.
The invention is further illustrated by the following examples.
EXAMPLE 1
5 grams of a commercial silicone oil (TEGO NV, available from Th.
Goldschmidt AG, Essen, Germany) are added to 300 grams of a
polyurethane solution which was prepared according to Example 3 of
French Pat. specification No. 1,546,169, and 100 grams of a mixture
of equal parts by weight of water and dimethylformamide are then
added. A gel is thus formed which is centrifuged and then applied
with a doctor blade to a substrate which has been produced from a
nonwoven web according to British Pat. Specification No. 1,017,023.
After coagulation with an aqueous solution of sodium chloride, the
material is washed free from solvent with water and dried at
50.degree. to 60.degree. C. A product which has a stable
microporous surface or covering layer is obtained.
The resistance of the product to bending stresses at -20.degree. C.
is above 100,000 but is only about 40,000 when no silicone oil is
used. Flexing numbers of over 360,000 are obtained in a Bally
Flexometer at a temperature of -5.degree. C., whereas the same
covering layer without the addition of silicone exhibits a flexing
number of only about 180,000.
EXAMPLE 2
A 30 percent polyurethane solution in dimethyl formamide is
initially prepared, wherein the polyurethane is obtained from a
polybutylene adipate having a molecular weight of 1,000 and
diphenylmethane-4,4'-diisocyanate in the molar ratio of 2:3 while
providing a chain lengthening with diethanolamine and ethylene
diamine in the molar ratio 0.15:0.70. This preparation corresponds
to that disclosed in French Pat. specification No. 1,546,169. 3.7
grams of a commercial silicone oil (FF 400, available from Dow
Corning Corp., Midland, Michigan, U.S.A.) followed by 100 grams of
a mixture of equal parts by weight of water and dimethylformamide
are then added to 300 grams of the initial 30 percent polyurethane
solution with stirring. The gel which forms from the water addition
is centrifuged off to remove excess liquid and is then applied to a
substrate with a doctor blade as is customary for the production of
synthetic leather. After coagulation in an aqueous solution of
sodium chloride, the material is washed with water and dried at
50.degree. to 60.degree. C. Stable, microporous covering layers
which have good bending and flexing numbers at -5.degree. and
-20.degree. C. are obtained. The permeability to water vapor
determined according to DIN 53 333 (German Industrial Standards) is
750 g./m..sup.2 d.
If no silicone oil is added to the polyurethane, the covering layer
collapses on drying to give a film or layer which is nonporous and
impermeable to water vapor.
EXAMPLE 3
A 35 percent polyurethane solution in dimethylformamide is prepared
in known manner from polyethylene adipate (molecular weight 2,000),
diphenylmethane-4,4'-diisocyanate and ethylene glycol in the molar
ratio of 1:4.3 : 3.3. 20.5 grams of water, 22.5 grams of
dimethylformamide, 1.0 grams of a commercial metal complex dye
consisting of equal parts of Savinyl dyes Brown GLS and Yellow RLS
(Sandoz AG, Basle, Switzerland) and 2.2 grams of a commercial
silicone oil (Getren 4, available from Th. Goldschmidt AG, Essen,
Germany) are added successively to 207 grams of this polyurethane
solution at 50.degree. C. with stirring. The solution is
homogenized, converted into a gel by cooling it to room
temperature, and directly applied to a substrate which is permeable
to water vapor to provide a surface layer having a thickness of 0.8
mm. The polyurethane layer is stored for 6 minutes at room
temperature and 60 percent relative humidity and then coagulated in
water at 20.degree. C. and washed. When the polyurethane surface
layer has been dried at 100.degree. C., it is very smooth and of
completely uniform color. The bending numbers of the product at
-20.degree. C. are higher than 300,000; in the flexometer at
-5.degree. C. and +20.degree. C., the sample shows no damage after
1,000,000 flexes. If, however, a polyurethane surface layer is
produced by the same process but without the addition of silicone
oil, the resulting sample by contrast is uneven on its surface,
i.e., it has a large number of pits and color patches. In the Bally
flexometer, this sample is damaged after only 190,000 flexures, and
it is broken after only 80,000 bendings at -20.degree. C.
The silicone oils used in the preceding examples have the following
characteristics:
Tego nv:
organopolysiloxane emulsion used as a release material.
Viscosity: 2,100 cP
Ff400:
water-soluble polydimethylsiloxane, containing polyglycol side
chains. Used as fiber finish.
Viscosity: 490 cP
Getren 4:
Water-soluble organopolysiloxane, a release material for the rubber
and plastic industry. Used for special release problems.
Viscosity: 1,300 cP
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