This invention relates to stable foams, which are produced from highly concentrated aqueous polyurethane dispersions. It further relates to the use of such foams for producing foam-coated textile fabrics which are in turn used for producing darkening materials or decorative materials.

Foam-coated woven fabrics are known, inter alia from US A 3 713 868. This reference describes woven fabrics which have been coated with a foam which comprises acrylate. These woven fabrics have very limited utility, if any, for the hereinbelow described darkening materials and decorative materials, since their adhesion to planar glass surfaces or ceramic surfaces is either too low or too high. When the woven fabrics are pressed lightly against flat glass surfaces, for example window panes, and left in place for some time, they are in many cases impossible to remove again from the glass surface without leaving a residue. WO 01/85 863 A1 likewise describes foam-coated woven fabrics wherein the foam may comprise polyurethane, inter alia. The products mentioned therein may have an outer layer of an adhesive in order that they may bond to other materials. The preferred application for these woven fabrics is in the production of adhesive tapes which additionally possess an additional layer of adhesive applied atop the foam-coated woven fabric. The reference is silent on the concentration of the aqueous polymer dispersion from which the foam is obtained. The foam with which the woven fabric has been coated is not generated before the coating is applied, but is formed in situ on the woven fabric. The articles mentioned in this reference do not have the requisite bonding and release properties (as described below) to flat glass surfaces, and therefore have only limited utility, if any, as darkening materials for window panes.

It is an object of the present invention to provide a process for producing a stable foam, to obtain a foam for coating textile fabrics which subsequently shall be very useful as darkening materials or decorative materials.

We have found that this object is achieved by a process for producing a stable foam having a density of 150-350 g/l, which comprises foaming a stable aqueous dispersion comprising from 50% to 70% by weight of a polyurethane or of a mixture of polyurethanes. The process of the present invention produces stable foams. Stable is to be understood in this context as meaning that the foams do not collapse within 1 minute when left to stand in the air and on air access.

The foams produced by the process of the present invention have a density in the range from 150 to 350 g/l at room temperature. The density of the foam is determined by placing a certain amount of the foam into a measuring vessel having a volume scale, determining the volume of this foam and determining the weight of this amount of foam by weighing. Foams having a density in the range mentioned are obtainable by appropriately controlling the parameters on the apparatuses used as foam generators. Commercially available foam generators like those mentioned hereinbelow possess appropriate control means.

The foams are produced by the process of the present invention by foaming an aqueous dispersion. This dispersion shall comprise from 50% to 70% by weight of a polyurethane or of a mixture of polyurethanes. The polyurethane used will normally not be self-dispersing, so that the aqueous dispersion will typically further comprise one or more dispersants. Useful dispersants include known surface-active products, such as ethoxylated fatty alcohols for example. Ionic or amphoteric surfactants can frequently also be used, provided a stable aqueous dispersion results. A stable aqueous dispersion in this context is a dispersion which is free of any precipitates or phase separation after it has been stored at room temperature for 3 months. Polyurethanes useful for the process of the present invention are available on the market. However, for a polyurethane to be suitable it has to yield a stable aqueous dispersion which comprises from 50% to 70% by weight of that particular polyurethane and from this it is possible to produce a stable foam conforming to the above definition. The process of the present invention preferably utilizes polyesterpolyetherpolyurethanes, in particular aliphatic polyesterpolyetherpolyurethanes, i.e., polyurethanes without aromatic, cyclic or unsaturated units. Such polyurethanes, as well as urethane units, comprise ester units and ether units and are likewise obtainable on the market. The aqueous dispersions comprising from 50% to 70% by weight of a polyurethane or of a mixture of polyurethanes can be produced by customary methods known to one skilled in the art. For example, a polyurethane is dispersed in an initial charge of an aqueous surfactant solution, normally by employing shearing forces (stirring) and, if appropriate, at elevated temperature. Ready-produced aqueous polyurethane dispersions having a solids content in the range from 50% to 70% by weight are moreover likewise obtainable on the market. An example of a very highly suitable polyurethane dispersion is the product DICRYLAN® 7753 or DICRYLAN® PGS from Ciba Spezialitatenchemie Pfersee GmbH, Germany. There are also suitable polyurβthanes or polyurethane dispersions in the IMPRAN1L® range (Bayer AG, Germany) and also in the WITCOBOND range from Baxenden, UK. The pH of the aqueous dispersion is preferably in the range from 7.5 to 10 at 2O0C. An aqueous ammonia solution is very useful for setting the pH.

In a preferred embodiment of the process according to the present invention, the aqueous dispersion further comprises one or more of the following components A to C: A is an aqueous solution comprising from 40% to 70% by weight and preferably from 45% to 65% by weight of an etherified tetra-, penta- or hexamethylolmelamine, B is an aqueous composition comprising from 10% to 25% by weight of the stearate of an alkali metal or of ammonium and from 70% to 90% by weight of water, C is an aqueous dispersion comprising from 20% to 40% by weight of a copolymer of (meth)acrylic acid and a (meth)acrylic ester having from 2 to 6 carbon atoms in the alcohol component, the dispersion preferably comprising said components A, B and C in the following amounts (per 1000 parts by weight of polyurethane): from 20 to 50 parts by weight of A from 50 to 200 parts by weight of B from 3 to 20 parts by weight of C. Component A is preferably an aqueous solution comprising from 45% to 65% by weight of a methanol- or ethanol-etherified pentamethylol-melamine. It provides better adhesion of the coating to woven fabrics and increases the durability of the effects. Component B acts as a stabilizer and as a foam generator. Component C acts as a thickener.

Useful components A, B and C include products obtainable on the market, for example the products LYOFIX® CHN or LYOFIX® MLF new (component A)1 DICRYLAN®-STABILISATOR FLN (component B) and DICRYLAN®-VERDICKER HV 30 or DICRYLAN®-VERDICKER R (component C) from Ciba Spezialitatenchemie Pfersee GmbH, Germany. The dispersions used for foam generation may further comprise dyes or pigments.

Stable foams can be produced from the aqueous dispersions mentioned by generally known processes in known apparatuses. Foaming by mixing with air is suitable for example. Foaming can be carried out in commercial foam generators of the kind available from Hansa, for example "Hansa Industrie-Mixer Top-Mix-K" or from Stork, Netherlands, for example FP III (Foam Processor). - A - Thβ foams produced by the process of the present invention are very useful for foam coating of textile fabrics. These fabrics may be wovens, knits or nonwovens. Preferably, they are wovens. The fabrics may comprise natural or synthetic polymers and preferably consist of polyester, polypropylene, polyacrylonitrile, cellulose, polyamide or of mixtures thereof. They are particularly suitable for producing darkening materials or decorative materials of the hereinbelow described kind for planar surfaces. These darkening or decorative materials are self-adhesive to planar glass surfaces on the foam coated side; that is, they do not require any additional layer of adhesive.

Darkening materials for the purposes of the present invention are foam coated textile fabrics which reduce the amount of light passing through a completely or partially transparent material having an essentially planar surface after the textile fabric has been applied to this material. Such complete or partially transparent materials to which the foam-coated textile fabrics are applied for the purpose of darkening can be, for example, plastic films or Plexiglas. Planar glass panes, for example panes of window glass, as used in buildings or automobiles are particularly suitable. The degree to which the amount of light passing through is reduced can be such that the material obtained, for example a glass pane to which the foam-coated textile fabric has been applied, is virtually opaque to visible light. In this case, the darkening materials will be black-out materials. Or a certain amount of light may still pass through. The darkening materials are dim-out materials. In any case, however, the amount of light passing through is distinctly reduced. Whether the articles obtained are black-out materials or dim-out materials can be controlled via the identity and amount of foam applied to the textile fabric and via the identity and thickness of this fabric itself. It is also possible to apply a plurality of layers of the stable foam to the textile fabric in successive operations, for example in order that a desired higher layer thickness may be achieved.

The textile fabrics to which foams produced by the process of the present invention have been applied are very useful as darkening materials or decorative materials for essentially planar surfaces. These materials are applied to the planar surface by employing a light pressure; normally, light hand pressure will be sufficient. They find utility inter alia as a darkening material in the form of light or glare protection, in particular for glass surfaces such as window glass or automotive glass panes, or as a decorative material, for example for tiles in kitchens or bathrooms or on the surface of furniture. In the case of decorative materials, a dye or pigment can be added to the foams produced by the process of the present invention. It is also possible for the textile fabric which is to be coated to have been printed or dyed. The textile fabrics which have been coated with the foam and subsequently dried as described can also be efficiently applied to floors composed of a very wide variety of materials, and possess good adhesion thereto. One way of taking advantage of this fact is in the form of nonslip puzzle pieces which are laid by children on floors. Further possible uses will now be described for foams according to the present invention or to be precise for textile fabrics coated with foams produced according to the present invention. - Coasters for drinking vessels that do not slip on tables having a glass surface - Covering for a portion of television screen, for example to hide unwanted advertising texts. - Tablecloths: the underside of the tablecloth may bear the foam coating and the upper side a paste coating with a fluoropolymer for the purpose of achieving oil and water repellency - Painting paper for children: the reverse/underside can be a coating of foam according to the present invention to achieve good adhesion to a table top and the upper side may be a paste coating by means of polyacrylate. Such painting papers can be written on by means of different implements such as ballpoint pens or crayons. - Screen savers composed of foam-coated woven fabric, for laptops for example - Nonslip inserts for drawers - Antifrost protection for exterior car mirrors - Nonslip grips for tennis rackets, golf clubs, squash rackets and also for tools such as hammers, axes

The textile fabrics coated with the foams are self-adhesive on many materials such as glass panes for example in that all that is needed for them to adhere firmly is a light pressure to press them into place. But they are also easily removable again from the planar surface by peeling them off, and no residues are left on the surface. Thus, these foam-coated textile fabrics can be used not just once but many times. Compared with conventional window-pane darkening materials, which consist of slatted blinds for example, the foam-coated textile fabrics of the present invention have one or more of the following advantages: a) they are less costly to make b) they require no installation, which can be fairly costly in the case of slats c) they are also suitable for inclined, i.e., non-vertical, surfaces, where slats, whose effect is gravity dependent, fail.

To obtain the identified properties for the foam-coated textile fabrics, namely not only good ■ adhesion to planar glass surfaces but also residueless detachability by peeling, a plurality of conditions have to be fulfilled:

1. The aqueous dispersions from which foam is produced by the process of the present invention have to comprise polyurethanes in a concentration from 50% to 70% by weight, and they have to be stable. It follows from these conditions that not all polyurethanes are suitable for the process of the present invention. Whether a certain polyurethane is suitable for producing such dispersions can be ascertained by only few trials.

2. The foams produced by the process of the present invention have to be stable, as explained above.

It is further very beneficial when the following conditions are maintained in addition:

3. The thickness of the coating which results after application of a hereinbelow more closely defined foam to a certain textile fabric and subsequent drying and curing, as described hereinbelow, should possess a value of at least 0.2 mm and preferably in the range from 0.2 mm to 3 mm.

4. The thickness of the coating identified under 3. should not decrease by more than 10% after the coated textile fabric has been exposed to a mechanical load of 5 kg for 5 minutes.

Whether a certain aqueous polyurethane dispersion is capable of meeting conditions 3 and 4 can be tested as follows:

A stable aqueous dispersion comprising 55% by weight of the polyurethane to be investigated and about 5% of suitable nonionic dispersants is produced. To this dispersion are added, per 1000 parts by weight of dispersion, 30 parts by weight of component A, 100 parts by weight of component B, 10 parts by weight of component C of the above-described kind. The pH of the composition obtained should be about 9.5 and can, if appropriate, be adjusted by addition of aqueous ammonia solution. The composition obtained is foamed up to form a stable foam having a density of about 200 g/l. The foam is subsequently applied to a woven polyester fabric having a basic weight of about 180 g/m2. This is followed by drying at 80°C/5 minutes essentially without application of an elevated mechanical pressure, and also by curing at 15O0C for 5 minutes. Subsequently, the layer thickness is determined. This determination is performed by placing the coated sample of fabric between two small, thin planar platelets of glass and determining the thickness of the sum total of glass platelets and fabric sample using a Frank thickness meter. No mechanical pressure is exerted on the fabric in this measurement other than the low weight of the upper glass platelet. The assembly formed from the two glass platelets and the interposed fabric sample is then subjected for 5 minutes to the load of the 5 kg weight placed on top. After the weight has been removed and a 1 minute recovery has been allowed, the thickness is remeasured by the method described above. The percentage decrease in layer thickness can be calculated from the thickness values before and after loading.

Polyurethane dispersions which do not meet condition 3 and/or condition 4 are less suitable and in some cases even unsuitable for the process of the present invention.

It has been determined that, to obtain the positive properties of the darkening or decorative materials, coating has to take place by foam application. Coating in another form, for example by means of customary paste coating, does not lead to the above-described advantages of these materials, even when the same polyurethanes are used for the paste coating.

The textile fabrics to which the foams are applied can be fabrics composed of natural, semisynthetic or synthetic fibers or yarns. Useful natural fibers and yarns include in particular cotton fibers or yarns, useful semisynthetic fibers and yarns include in particular fibers and yarns composed of regenerated cellulose and useful synthetic fibers or yarns include in particular fibers or yarns composed of polyester or nylon. Similarly, textile fabrics comprising blends of such fibers are very useful in the process of the present invention. Wovens, knits or nonwovens are very useful as textile fabrics.

The foam can be applied to the textile fabric by known methods and by means of known apparatuses. Preferably, the stable foam is applied to a textile fabric by coating, the fabric is subsequently dried at a temperature in the range from 70 to 130°C essentially without application of any mechanical pressure and then cured at a temperature in the range from 1300C to 18O0C during a time from 30 seconds to 300 seconds essentially without application of any mechanical pressure. By "coating the textile fabric" is meant that at least one coat or layer of the stable foam is applied. However, it is also possible to apply a plurality of coats or layers of the same stable foam in succession, for example in order to achieve a higher layer thickness.

One way to apply the foam to the textile fabric consists in applying it by means of a knife-over- roll coater using a knife suitable for foam application, such as a shoe knife or a round knife, and a clear gap of 0.2 to 2 mm. Another way is to use a rotary screen having a suitable mesh number. The amount of foam applied to the textile fabric is preferably determined such that, following the curing described hereinbelow, the resulting solids add-on on the textile is in the range from 20 to 300 g/m2. The amount used in an individual case depends inter alia on the identity of the polyurethane and the properties desired for the article (for example black-out or dim-out). After foam application, the textile fabric is dried, preferably at a temperature in the range from 7O0C to 1300C to a residual moisture content of 5-10%, based on the amount of water present in the foam used. The textile fabrics during and after drying and during curing (described hereinbelow) should not be exposed to essentially any mechanical pressure, i.e., should not be pressed. After drying, it is advisable to subject the textile fabrics to a curing operation, i.e., a treatment at a higher temperature still. This curing is preferably carried out at a temperature in the range from 130 to 1800C for a period in the range from 30 to 300 seconds. After curing, the foam-coated textile fabrics can be further processed to form the desired final articles, for example cut to size as self-adhesive darkening materials.

The invention will now be illustrated by operative examples.

Example 1;

Production of a stable form and its use

The starting material used was an aqueous dispersion comprising an aliphatic- polyester- polyetherpolyurethane and dispersants. The polyurethane and dispersants together constituted about 60% by weight of this dispersion. The following components were added in succession to 1000 parts by weight of this dispersion by stirring: 30 parts by weight of LYOFIX® CHN 100 parts by weight of DICRYLAN®-STABILISATOR FLN 20 parts by weight of 25% aqueous ammonia solution and 10 parts by weight of a 1 :1 mixture of DICRYLAN®-VERDICKER HV 30 and water.

The dispersion obtained had a pH of about 9.5 at 2O0C. The dispersion thus obtained served as foam compound and was converted by means of an FP III foam generator from Stork, Netherlands, into a stable foam having a density of about 200 g/l by mixing with air. The foam thus produced was applied by means of a knife-over-roll coater equipped with a shoe knife, clear gap 0.9 mm, to a plain woven polyester fabric having a basic weight of 180 g/m2. This was followed by drying at 90°C/5 minutes and subsequent curing at 150°C/5 minutes. The textile fabric thus obtained had a post-cure solids add-on of 100 g/m2. The layer thickness on the textile was 0.3 mm. The above-described loading with 5 kg caused the layer thickness to decrease by less than 5%. The coated textile fabric thus obtained was cut into rectangular pieces 2 m x 0.4 m in size. These were applied to window glass by being lightly pressed into place by hand. They were self-adhesive and firmly adhered to the glass surface and were residuelessly removable even 3 months later by peeling off by hand. Similar results were obtained on Plexiglas in place of glass. After the textile fabric had been detached from the glass and stored for a few days, it could be reapplied to glass without any deterioration occurring in the bonding properties. This was true even when the textile fabric had been subjected to a domestic laundering operation at 4O0C prior to renewed attachment. In lieu of uniform application, it is possible to cut the textile fabric into certain patterned shapes such as easter or Christmas motifs and be applied to glass in that form.

Example 2

Example 1 was repeated except that the ready-produced textile fabric was not applied to glass but as a decorative material to ceramic tiles. Again there was good adhesion and the possibility of residueless detachment and reuse similarly to Example 1.