Base material for artificial leather

A base material for artificial leather having a water vapor absorption capacity of from 2 to 8% by weight, based on a fibre fleece impregnated with a rubber latex mixture containing a heat sensitizer, a quick-acting vulcanization accelerator and, as expanding agent, a silicone oil emulsion or an inert, emulsifiable substance which is insoluble both in the rubber and the other constituents of the latex. After the impregnation of the fibre fleece, the latex mixture is coagulated by heat, vulcanized and then dried.

This invention relates to a base material for artificial leather based on 
fiber fleeces impregnated with a rubber latex, and to a process for the 
production of this base material. The base material for artificial leather 
according to the invention has a particularly high water vapour absorption 
capacity which reaches about 70 % to 80 % of the absorption capacity of 
natural leather. 
Microporous sheet-form materials permeable to water vapour and based on 
substrates impregnated with rubber latices are known from DT-AS No. 
1,570,088. Although these products are microporous and, hence, show a 
certain permeability to water vapour, they have no absorption capacity for 
water vapour. The processs by which they are produced is unsuitable in 
practice for the production of large surfaces on a commercial scale 
because the latex mixtures used are only stable for a short period and, 
hence, are unsuitable for continuous impregnating processes. 
Accordingly, there is a need to provide a base material for artificial 
leather which, on the one hand, has a high water vapour absorption 
capacity and which, on the other hand, can be manufactured easily and 
reproducibly. The water vapour absorption capacity is particularly 
important because it is one of the most outstanding properties of natural 
leather and, hitherto, it has never been adequately reproduced in 
synthetic products. 
Accordingly, the present invention provides a base material for artificial 
leather based on a fiber fleece impregnated with a rubber latex, which is 
characterised by a water vapour absorption capacity of from 2 to 8 % by 
weight, based on the dry weight of the material, a tensile strength of 
from 30 to 250 kg/cm.sup.2 and an elongation at break of from 30 to 150 %. 
The process for producing this base material for artificial leather by 
impregnating a fiber fleece with a rubber mixture, coagulating the 
mixture, followed by vulcanisation, is distinguished by the fact that a 
fiber fleece is impregnated with a rubber latex mixture containing a heat 
sensitiser, a quick-acting vulcanisation accelerator and, as expanding 
agent, a silicone oil emulsion or an inert, emulsifiable substance which 
is insoluble both in the rubber and in the other constituents of the latex 
and, after coagulation of the latex mixture by heating it, is vulcanised, 
preferably in steam, and then dried. 
Fiber fleeces suitable for the production of the artificial leather base 
material are, in particular, fleeces consisting of natural and/or 
synthetic fibers. Polyamide, polyester, polypropylene, viscose and 
cellulose fibers are preferably used. 
Rubber latices suitable for impregnation are, in principle, any 
heat-sensitisable natural or synthetic rubber latices. Particularly 
suitable rubber latices are natural rubber latex and synthetic rubber 
latices such as, for example, carboxylated and non-carboxylated latices 
based on copolymers of butadiene/acrylonitrile, butadiene/styrene, 
chloroprene and butadiene/acrylic acid esters, and also isoprene and 
corresponding copolymers. In addition, the polymers may contain acid amide 
functions and autocrosslinking groups such as, for example, N-methylol 
acrylamide. 
Heat sensitisers which may be used in accordance with the invention are, 
for example, polyvinyl methyl ethers, polyethylene- and polypropylene 
oxide adducts and/or their co-adducts, polyalkyl and polyaryl siloxanes 
and ethylene diamine polyether adducts. 
Vulcanisation agents are, for example, dispersion mixtures consisting of 
sulphur, zinc oxide and vulcanisation accelerators. In the case of 
reactive polymers which normally crosslink in the absence of sulphur and 
vulcanisation accelerators, suitable crosslinking agents are condensation 
products of melamine, urea or phenol with formaldehyde, or metal oxides. 
It is preferred, however, to use polymers which contain no autocrosslinking 
groups. For the crosslinking of these polymers according to the present 
invention the latex is compounded with a mixture suitable for 
vulcanisation, preferably in form of a dispersion or a paste. This paste 
contains in addition to water, a dispersing agent, and known fillers like 
titanium dioxide the usual vulcanising agents like sulfur and zinc oxide 
and according to the invention a quick-acting water-soluble vulcanisation 
accelerator besides a water-insoluble vulcanisation accelerator. 
The presence of a quick-acting vulcanisation accelerator is of particular 
importance. Suitable quick-acting vulcanisation accelerators are, 
primarily, water-soluble sodium or ammonium salts of various derivaties of 
dithiocarbamic acid, optionally in combination with salts of 
mercaptobenzothiazole. 
Quick-acting water-soluble vulcanisation accelerators are for example the 
alkaline metal, alkaline earth metal, and ammonium salts of dimethyl, 
diethyl, diisopropyl and dibutyl dithiocarbamic acid. 
Water-insoluble vulcanisation accelerators are for example the zinc salts 
of the above-mentioned dithiocarbamic acids, mercaptobenzothiazole and its 
zinc salts, thiurame and its derivatives. 
A suitable dispersing agent is for example the condensation product of 
naphthalene sulfonic acid and formaldehyde. 
The vulcanisation paste according to the present invention is composed as 
follows: 
0.5 to 10.0 parts by weight of zinc oxide, preferably about 5.0 parts by 
weight. 
0.2 to 10.0 parts by weight sulfur, preferably about 2.0 parts by weight. 
0.2 to 3.0 parts by weight of water-soluble accelerator, preferably about 
1.0 parts by weight 
0.2 to 3.0 parts by weight of a water-insoluble accelerator, preferably 
about 1.0 parts by weight 
2.0 to 15.0 parts by weight titanium dioxide, preferably about 5.0 parts by 
weight 
0.1 to 5.0 parts by weight a dispersing agent, preferably about 1.0 parts 
by weight 
10.0 to 50.0 parts by weight water, preferably about 25.0 parts by weight. 
The amount of vulcanisation paste to be applied may vary over a wide range. 
Usually 10 to 100 parts by weight, preferably 30 to 50 parts by weight, 
and most preferably 40 parts by weight of the vulcanisation paste are 
applied on 100 parts by weight of rubber (based on the weight of dry 
substance). 
The vulcanisation paste is prepared by adding the rest of the components to 
the water and the dispersing agent or to an according solution of the 
dispersing agent in water, respectively. The mixture and its ingredients 
are then intensively mixed and triturated for 12 to 72 hours, preferably 
for 24 hours, for example in a roller mill. In this way a vulcanisation 
paste is obtained which is ready for use and contains its ingredients in a 
finely divided form. 
Insoluble and inert substances suitable for use as expanding agents in 
accordance with the invention are: 
(1) long-chain aliphatic or alicyclic isocyanates, 
(2) condensates of N-methylolated melamine, urea or cyclic ureas with 
long-chain fatty acids or their amides, long-chain alcohols and long-chain 
amines, 
(3) perfluorinated long-chain aliphatic compounds, 
(4) polyvinyl methyl ethers, 
(5) mixtures of epoxide resins with polyether siloxane, 
(6) mixtures of polyethylene with polyether siloxane, 
(7) mixtures of the products mentioned in 1) to 6). 
Examples of products of this kind are stearyl isocyanate; the condensate of 
hexamethylolated melamine with behenic acid; perfluorinated stearic acid; 
polyvinyl methyl ethers having a molecular weight in the range of from 
30,000 to 70,000 and mixtures of low molecular weight polyethylene with 
polyether siloxane. 
Silicone oils which are particularly suitable for use as expanding agents 
are silicone oils having a viscosity of from 50 to 100 0cP which are used 
in the form of aqueous emulsions having a solids content of, preferably, 
from 10 to 50 % and which preferably contain non-ionic emulsifiers. 
In general, the rubber latex mixture contains from 100 to 300 parts by 
weight, preferably about 220 parts by weight, of water; 100 parts by 
weight of rubber; from 0.5 to 5 parts by weight, preferably about 1.0 part 
by weight, of heat sensitisers; from 3 to 10 parts by weight, preferably 
about 7.0 parts by weight, of vulcanisation agent; from 1 to 4 parts by 
weight, preferably about 2.0 parts by weight of vulcanisation accelerator; 
and from 0.5 to 10 parts by weight, preferably about 5.0 parts by weight, 
of expanding agent. 
The fiber fleece is impregnated with this mixture in the usual way, a 
quantity of from 50 to 200 %, based on the fibers, generally being used. 
The fleece thus obtained is then heated to a temperature of from 25.degree. 
to 80.degree. C. Since the latex mixture contains a heat sensitiser, it is 
stable below this temperature, but coagulates very quickly above a 
predetermined critical temperature. After coagulation, the impregnated 
fiber fleece has to be immediately vulcanised. It is important to carry 
out vulcanisation as quickly as possible. For this reason, vulcanisation 
is preferably carried out with steam at temperatures in the range from 
100.degree. to 200.degree. C. Vulcanisation generally lasts from 5 to 60 
minutes. The vulcanised, impregnated fiber fleece may then be dried in the 
usual way, for example in vacuo, at 100.degree. to 170.degree. C. 
An artificial leather base material whose outstanding property is its water 
vapour absorption capacity is obtained in this way. It may be provided 
with a surface layer in known manner, for example by applying a thin 
microporous polyurethane layer. It may then be finished, again in the 
usual way, to give a particularly high-quality artificial leather whose 
properties substantially correspond to those of natural leather.

EXAMPLE 1 
A needle-punched and subsequently shrunk random fiber fleece, consisting of 
60% by weight of polyamide fibers (approximately 40 mm staple length and 
1.5 den) and 40% by weight of polyester fibers (approximately 40 mm staple 
length, 1.5 den), is impregnated with an excess of a latex mixture having 
the composition specified below, so that 100 g of solids are taken up from 
the latex mixture per 100 g of fiber material. The impregnated fleece is 
then quickly heated to 500.degree. C, as a result of which the latex 
mixture gels. After vulcanisation with steam for 30 minutes at 105.degree. 
C, the fleece is dried in hot air. The fleece is then split so that the 
end product has the layer thickness indicated in Table 1. A microporous 
base material for artificial leather is obtained. The fleece has a water 
vapour absorption capacity of 4.4 % (as determined by the method described 
below). 
The latex mixture used has the following composition: 
210.0 parts by weight of a 47 % latex of a copolymer of 85 % by weight of 
butadiene and 15 % by weight of acrylonitrile (= 100 parts by weight of 
dry substance) 
10.0 parts by weight of a 50 % by weight silicone oil emulsion (100 - 100 
cP) in a 2% aqueous solution of the condensation product of 1 mol of 
benzyl phenyl phenol and 20 mols of ethylene oxide, 
1.0 part by weight of a polyether siloxane, 
8.0 parts by weight of benzyl phenyl phenol, 
75.0 parts by weight of water, 
41.0 parts by weight of a vulcanisation paste of 2 parts by weight of 
colloidal sulphur, 5 parts by weight of zinc oxide, 1 part by weight of 
zinc diethyl dithiocarbamate, 5 parts by weight of titanium dioxide, 1 
part by weight of sodium diisopropyl dithiocarbamate and 27 parts by 
weight of a 5 % aqueous solution of a condensation product of naphthalene 
sulphonic acid with formaldehyde. 
The coagulation point of this latex mixture is approximately 40.degree. C. 
Comparison Test 1 
This test is carried out in exactly the same way, except that neither the 
silicone oil emulsion nor the sodium diisopropyl dithiocarbamate (very 
quick accelerator) is added. In addition, vulcanisation is carried out in 
hot air at a temperature of from 110.degree. to 130.degree. C and not in a 
steam atmosphere. The material thus obtained has a water vapour absorption 
capacity of 0.6 %. 
The results are summarised in Table 1. The corresponding values for skiver 
are also shown for comparison. 
EXAMPLES 2 to 4 
A random fiber fleece consisting of 60% by weight of polyamide fibers 
(approximately 40 mm staple length, 1.5 den) and 40% by weight of 
polyester fibers (approximately 40 mm staple length, 1.5 den), is 
impregnated with an excess of a latex mixture having the composition 
specified below, so that 100 g of solids are taken up from the latex 
mixture per 100 g of fiber material. The impregnated fleece is then 
quickly heated to 50.degree. C, as a result of which the latex mixture 
gels. After vulcanisation with steam for 30 minutes at 105.degree. C, the 
fleece is dried in hot air. The fleece is then split so that the end 
product has the layer thickness indicated in Table 2. A microporous base 
material for artificial leather is obtained. The fleeces have a water 
vapour absorption capacity of from 4 to 5 % (as determined by the method 
described below; cf. Table 3). 
The latex mixture used has the following composition: 
210.0 parts by weight of a 47 % latex of a copolymer of 60.0% by weight of 
butadiene and 36 % by weight of acrylonitrile and 4.0 % by weight of 
methacrylic acid (= 100 parts by weight of dry substance), 
(a) 15 parts by weight of stearyl isocyanate, 33 % emulsion, or 
(b) 15 parts by weight of a mixture of polyether siloxane with 
polyethylene, 33 % emulsion, or 
(c) 30 parts by weight of the condensation product of methylolated melamine 
with behenic acid, 16.5 % emulsion, or 
(d) 30 parts by weight of polyvinyl methyl ether, molecular weight 
approximately 50,000, 16.5 % emulsion, 
1.0 part by weight of a polyether siloxane, 
2.0 parts by weight of benzyl phenyl phenol, 
75.0 parts by weight of water, 
41.0 parts by weight of a vulcanisation paste of 2 parts by weight of 
colloidal sulphur, 5 parts by weight of zinc oxide, 1 part by weight of 
zinc diethyl dithiocarbamate, 5 parts by weight of titanium dioxide, 1 
part by weight of sodium diisopropyl dithiocarbamate and 27 parts by 
weight of a 5 % solution of a condensation product of naphthalene 
sulphonic acid with formaldehyde. 
The coagulation point of this latex mixture is approximately 40.degree. C. 
Comparison Test 2 
This test is carried out in exactly the same way, except that neither the 
inert substances which are insoluble both in the rubber and in the other 
constituents of the latex nor the sodium diisopropyl dithiocarbamate (very 
quick accelerator) are added. In addition, vulcanisation is not carried 
out in a steam atmosphere, but in hot air at a temperature in the range of 
from 100.degree. to 130.degree. C. The material thus obtained has a water 
vapour absorption capacity of 0.6%. 
The results are summarised in Table 2 and 3. The corresponding values for 
skiver are also shown for comparison. 
Table 1 
__________________________________________________________________________ 
Tear 
Layer prop- 
Stitch Extension 
thick- 
Tensile 
Elong- 
agation 
tear re- 
Repeated 
(2) Water-vapour take- 
ness strength 
ation at 
tance 
sistance 
flexural 
Pre- up (3) 
(mm) kp/cm.sup.2 
break % 
kp/cm 
kp/cm strength 
sure after 
after 
after 
according 
(DIN (DIN (DIN 
(DIN (1) atms 4 hrs 
8 
24 hrs 
Direction 
40 IUPA 
53328) 
53328) 
53329) 
53329) 
IUP 20 
gauge 
I % 
II % 
% % % 
__________________________________________________________________________ 
Com- 
parison 
longit- 
1.0 78 90 44 69 &lt; 3.6 25 11.5 
0.6 
0.6 
0.6 
Test udinal 
trans- 
1.0 97 110 39 64 
verse 
Example 
longit- 
0.9 58 90 27 62 &lt; 3.2 25 10.3 
4.4 
4.5 
4.6 
udinal 
trans- 
0.9 106 70 35 61 
verse 
Skiver longit- 
1.5 198 50 48 140 &gt; -- -- -- 5.3 
5.9 
6.9 
udinal 
trans- 
1.5 203 50 52 130 
verse 
__________________________________________________________________________ 
.sup.(1) Bally-Flexometer, flexing (dry) 200,000 times (IUP 20) 
.sup.(2) Extension, Bally-Tensometer (IUP 13) I = linear extension II = 
permanent extension 
.sup.(3) By the method described below. 
&lt;means damaged 
&gt;means undamaged 
Table 2 
__________________________________________________________________________ 
Layer Tear* 
Stitch* Extension (2) 
thick- 
Tensile* 
Elong-* 
prop- 
tear re- (IUP 13) 
ness strength 
ation at 
agation 
sistance 
Flexural* 
Pre- 
(mm) kp/cm.sup.2 
break % 
resis- 
kp/cm 
strength 
ssure 
according 
(DIN (DIN tance 
(DIN (1) atms 
Direction 
to IUP4 
53328) 
53328) 
kp/cm.sup.2 
53329) 
IUP 20 
gauge 
I % 
II % 
__________________________________________________________________________ 
Comparison 
Test longit- 
1.0 78 90 44 69 &lt; 3.6 25 11.5 
udinal 
trans- 
1.0 97 110 39 64 
verse 
Example 
longit- 
1.1 58 90 27 62 3.2 25 10.3 
udinal 
trans- 
1.1 106 70 35 61 &lt; 
verse 
Skiver longit- 
1.4 198 50 48 140 -- -- -- 
udinal 
trans- 
1.4 203 50 52 130 &gt; 
verse 
__________________________________________________________________________ 
(1) Bally-Flexometer, flexing (dry) 200,000 times (IUP 20) &lt;means damage 
&gt;means undamaged 
(2) Extension, Bally-Tensometer (IUP 13) I = linear extenion II = 
permanent extension 
*These values are substantially identical for the artificial leather 
materials obtained with expanding agents a) to d). 
Table 3 
______________________________________ 
Water vapour uptake*) 
after 4 after 8 after 24 
hours % hours % hours % 
______________________________________ 
Comparison test 
0.6 0.6 0.6 
Skiver 5.3 6.2 6.9 
Example a) 1.4 2.1 3.9 
Example b) 1.7 2.2 4.4 
Example c) 1.5 2.7 4.4 
Example d) 1.7 2.2 4.8 
______________________________________ 
*)by the method described below 
The water vapour absorption capacity was determined as follows: 
The test specimens (measuring 50 .times. 20 mm) were prepared for 24 hours 
at 20.degree. C in a conditioned room with a relative air humidity of 65 
%. Thereafter they were accurately weighed (to 0.0001 g) and then 
introduced into a conditioned room with a relative air humidity of 86 % at 
20.degree. C. After storage for 4, 8 and 24 hours, they were reweighed and 
the increase in weight determined to an accuracy of 0.0001 g. 
The result of measurement is the percentage increase in weight based on the 
weight obtained after conditioning. The results quoted are averages of 
three individual results.