NO131250B - - Google Patents

Description

Process for the production of synthetic leather.

The invention relates to a method for the production of porous, water vapour-permeable cover layers based on polyurethanes, of the kind that are particularly used in the production of synthetic leather.

In order to produce synthetic leather, you can, as is known, start from fiber piles that are bound with polymeric, elastomeric binders, e.g. polyurethanes. Fiber pile treated in this way is able to collect water vapor and emit it again on the surface. For artificial leather used in the production of shoes, this is of great importance, as the upper leather in shoes must be able to absorb the water vapor released by the foot during transpiration and release it back to the surface. If the upper leather does not fulfill this function, the water vapor accumulates in the interior of the shoe and the moisture in the shoe will have a very unpleasant effect on the wearer.

feeling.

However, the fiber piles treated in this way are also permeable to water in liquid form, so that rainwater can penetrate into the shoe from the outside. It is therefore necessary to place a covering layer on the bonded fiber pile, also known as a substrate, which, although it is still permeable to water vapour, blocks the passage of liquid water. This cover layer should also give the shoe material a leather-like feel

appearance and a leather-like grip. Of the quality of the tire layer is

properties such as compressive strength, bending strength, cold resistance, crack resistance, etc., also largely depend on the finished material.

It is known to produce cover layers on synthetic leather

from polyurethanes. In this way, you can e.g. start from solutions of polyurethanes in dimethylformamide, transfer polyurethane by adding a non-solvent, e.g. water, into a gel and then apply the gel to the bonded fiber pile. After coagulation of polyurethane, washing out of the solvent and drying, polyurethane dental cover layers with improved water vapor permeability are obtained.

The invention relates to a method for production

of artificial leather by placing a cover layer on a substrate which consists ■ of a polyurethane-bound fibrous textile material, where a solution of polyurethane in an organic solvent forms a gel, the gel on

is applied to the substrate and transferred into a microporous layer by coagulation, washed to remove the solvent and dried, the method being characterized in that 1 to 10, preferably 2 to 4% by weight, referred to dissolved polyurethane, is added to the polyurethane starting solution,

of a silicone oil, the oil being distributed evenly in finely dispersed form in the solution at the point where the dissolved polyurethane is transferred to gel.

Polyurethanes that can be used in the method according to the invention are generally known. They are obtained e.g. by reaction of diisocyanates with hydroxyl-end group-containing polyesters or polyethers to an NCO group-containing pre-adduct, and further reaction with chain extenders, such as diamines, glycols, etc.

The solvent used above all is dimethylformamide, but other substances known from the literature can also be used,

such as dimethylsulfoxide, dimethylacetamide and their mixtures.

In the method according to the invention, the content of polyurethanes in the solution can vary within wide limits, advantageously concentrations of 15 to 40% by weight can be used. In the polyurethane solution, up to 30% calculated for polyurethane of other polymers, e.g. polyvinyl chloride. Of course, you can add other agents, such as stabilizers, pigments or dyes.

The silicone oils used according to the invention are generally known. These are polymeric compounds in which silicon atoms are partially linked over oxygen atoms and the remaining valences of silicon are saturated with hydrocarbon residues. Further details on silicone oils can be found e.g. in "Chemie-Lexicon" by Hermann Rompp, 6th edition, Frank'sche Verlagshandlung, Stuttgart.

Particularly suitable within the scope of the invention are silicone oils with a viscosity of 100 to 1000 cP.

The silicone oils used can be soluble or

insoluble in the solvent used, e.g. in dimethylformamide.

The silicone oils used in the invention are used in quantities of 1 to 10, preferably 2 to 4, parts by weight calculated on the dissolved polyurethane. The addition of oils is best done when the polyurethane has already dissolved. In particular, it must be ensured that the silicones in the solution are uniformly and finely distributed when the dissolved

polyurethane is transferred in a gel, e.g.' by adding a non-solvent._ This primarily applies when using silicone oils which are insoluble in dimethylformamide.

The processing of gels for cover layers takes place in a manner known per se. In this way, the gel is placed, e.g. with the help of a scraping knife on bound fiber fleece, coagulate, water and dry. After drying, the cover layer placed on the substrate has a thickness of 0.3-0.6 mm, preferably 0.3-0.4 mm.

The substrate is impregnated with a fiber fleece, obtained e.g. by the method of British Patent No. 1,017,023, bonded with a polyurethane solution.

It has surprisingly been shown that the workability of the polyurethane for cover layers was significantly improved by the addition of silicone oils according to the invention. One was thus able to eliminate the extensive tendency of certain polyurethanes, e.g. of those obtained by the method according to French patent No. 1,546,169, to collapse during the drying of the cover layer into a non-porous, water vapor permeable foil. The resulting cover layers are also particularly stable.

It was also not to be expected that with the method according to the invention one can proceed from polyurethane solutions with a

very high concentration. Until now, it was possible, when using e.g.

the polyurethanes in and of themselves suitable for the production of cover layers in accordance with German patent no. 1,106,959, only using solutions with a content of polyurethanes up to a maximum of J>0% without special precautions during the deposition, e.g. a particularly long storage in a humid atmosphere. By means of the addition of silicone oils according to the invention, it is possible to use without special conditions

rules with good results polyurethane solutions with a content of

over 30%, i.e. up to approx. H0% in the production of cover layers of synthetic leather. The desired cover layers are thus achieved quickly and easily.

In a particular embodiment of the method according to the invention, polyurethane solutions containing 30

to 40 wt# polyurethanes and 1 to 10 wt% silicone oils, calculated thereon. dissolved polyurethane.

The use of more concentrated polyurethane solutions for the production of cover layers is very advantageous already for the reason that less solvent needs to be recovered. The tire layers produced according to the invention are very well washable. out before they are dried, and there are no residues that later disturb and which e.g. can cause the cover layer to collapse or the material to become discoloured. In addition, with higher concentrations, cover layers with better properties are obtained.

When greater polyurethane concentrations are used, cover layers with a higher density are obtained and a material with better mechanical properties is produced, the increase in crack resistance being particularly important.

The method according to the invention also enables

a production of colored cover layers in which the dye is very uniformly distributed. The formation of spots often observed in the cover layers produced using known methods no longer occurs. This makes the treatment of cover layers much easier.

The cover layers also have a particularly uniform pore structure

and a high compressive strength.. One also achieves an improvement in the bending strength. In particular, an improvement is achieved in the mechanical properties in the cold, primarily in the bending strength.

The cover layers produced in this way can be grained and provided with one or more covers, e.g. with a polyurethane-containing base layer and a nitrocellulose-containing final coating. The coatings to be applied only reach a thickness of a few microns. It is admittedly known to use silicones in polyurethane-containing preparations for synthetic leather, however, one does not thereby achieve the advantages that one gets from the invention.

On the contrary, it is extremely surprising that the application

of silicone oils in the production of covering layers several hundred microns thick for artificial leather leads to such greatly improved properties.

The invention is explained in more detail using the following examples:

Example ,1^

To 300 g of a polyurethane solution obtained in

according to example 3 of French patent no. 1,546,169, 5 g of a commercial silicone oil ("TEGO NV") are added and then 100 g of a mixture of equal parts by weight of water and dimethylformamide. A gel is formed in this way, which is centrifuged and, with the help of a scraping knife, placed on a substrate that was made from a fiber pile,

made of viscose-polyamide, <p>g copolyamide fibers according to British Patent No. I.OI7.O23, and bonded with a polymeric, elastomeric binder, which

e.g. polyester urethane. After coagulation in a saline solution, wash with water until the solvent is removed and dry at 0

50 - 60°C. A product with a stable, micro-

porous cover layer.

Bending number of the product at -20°C is over 100,000,

without the use of silicone oils, however, they are only at approx.

40,000. In the Bally flexibility meter, at a temperature of -5°C, bending numbers of over 36O.OOO are achieved, with a cover layer without silicone addition only approx. 180,000.

Example 2.

In accordance with the method of French patent no.

1,546,169, a 30% polyurethane solution is prepared from poly-butadiene adipate, molecular weight 1000, and diphenylmethane-4,4'-diisocyanate in a molar ratio of 2:3, and chain extension with diethanolamine and ethylenediamine

min in molar ratio 0.15 : 0.70. To 300, g of this solution to-

while stirring, 3.7 g of a commercial silicone oil ("FF 400") and then 100 g of a mixture of equal parts by weight of water and dimethylformamide are added. The resulting gel is centrifuged and

brought with the help of a scraping knife on a surface as in

walking example. After coagulation in a saline solution, wash with water and dry at 50 - 60°C. Stable, microporous cover layers with good bending and flexion values at -5 and -20°C are obtained.

The water vapor permeability determined according to DIN 53.333 amounts to

750 g/m<2> d.

If silicone oil is not added to polyurethane,

the cover layer collapses during drying into a non-porous water vapor permeable foil.

Example 3.

Of polyethylene adipate (molecular weight 2000), diphenylmethane-

4,4'-diisocyanate and ethylene glycol are prepared in a molar ratio of 1:

4.3 : 3.3 in a known manner a 35% polyurethane solution in dimethyl

formamide. To 207 g of this solution, 20.5 g of water, 22.5 g of dimethylformamide, 1.0 g of a commercial metal complex dye consisting of a mixture of equal parts of savinyl dyes brown GLS and yellow RLS and 2.2 g of a commercial silicone oil "Getren 4". The solution becomes homo-

genized, upon cooling to room temperature converted to a gel and directly applied to a water vapor-permeable substrate according to example 1 in a layer thickness of 0.8 mm. The polyurethane layer is stored for 6 minutes at room temperature and 60% relative humidity,

then coagulated in water at 20°C and washed. The polyurethane cover layer, dried at 100°C, is very smooth and completely uniformly coloured. Bend-

number of the product at -20°C is higher than 300,000. In flexo

the meter at -5°C and +20°C, the sample still shows no damage after 1,000,000 bends. If using the same method, but without the addition of silicone oil, a polyurethane cover layer is produced, then

is this sample, in contrast to the one described here, non-uniform on

the surface, i.e. that it exhibits a large number of irregularities and color spots. In the Bally flexometer, this sample already has broken parts after 190,000 bends, after 80,000 bends at -20°C

is the sample already broken.

Claims (3)

1. Method for the production of artificial leather by placing a covering layer on a substrate consisting of a polyurethane-bonded fibrous textile material, where a solution of polyurethane in a organic solvent gel is formed, the gel is applied to the substrate and transferred in a microporous layer by coagulation, washed to remove the solvent and dried, characterized in that 1 to 10, preferably, is added to the polyurethane starting solution 2 to 4 wt/5, referred to dissolved polyurethane, of a silicone oil, as the oil is evenly distributed in finely dispersed form in the solution at the point where the dissolved polyurethane is transferred to gel. 2. Method according to claim 1, characterized in that polyurethane solutions with a content of 30 to 40% by weight of polyurethanes are used. 3. Method according to claim 1, characterized in that silicone oils with a viscosity of 100 to 1000 cP are used.