EP1678332B1 - Method for coating leather with dispersed synthetic resin - Google Patents

Description

The invention relates to a method for the removal of imperfections in the grain layer of a full-grain leather, in particular cowhide, wherein at the defects this eliminating plastic compound is applied. Furthermore, the invention relates to a full-grain leather, in particular cowhide, in which the imperfections are eliminated in the grain layer.

The scar layer of full-grain leathers, especially cowhide, often has, for example, caused by tears, barbed wire injuries, insect bites or the like., Defects, which are present only at individual sites, a maximum of 10% of the dermis, but still this dermis make it inferior. Such leathers are therefore converted by filling the defects and then grinding the grain layer to so-called corrected grain leather, but have a lower value and can only be marketed at a considerable discount.

EP 1 300 474 A1 discloses a process for coating the grain layer of a full grain cowhide comprising a plastic dispersion comprising polyurethane and / or polyacrylate containing isobutane filled hollow microspheres of diameter less than 45 μm or compact particles from which such hollow microspheres are formed in situ by applying heat; is applied to the leather, wherein the solidified plastic dispersion is pressed under pressure and / or heat application at an embossing temperature below 120 OC by means of an embossing roller with finely textured surface corresponding to the nappa grain structure in the leather and the resulting full grain Napparindsleder on which said plastic dispersion was applied and thus was pressed into the flaws.

It is already known to fill in defects that do not pass through the grain layer with a plastic putty, to allow them to dry and then to abrade the grain layer, removing the entire uppermost grain layer.
It has also been proposed to remove imperfections in the scar layer highly viscous, aqueous plastic putties that are foamed or contain hollow microspheres to apply over the entire surface of the surface of the scar layer, to let dry and then sand these putties, which is also the topmost layer of scar removed , Both methods have the disadvantage that the aqueous Kunststoffspachtelmassen contain a maximum of 80% solids content and therefore shrink these masses when withdrawing the water, so fall into the flaws and detach from the edge thereof, with the risk that they are at a bending stress of the leather fall out of the flaws.

It is also known to apply a so-called foaming foam with high viscosity, by means of rollers over the entire surface of the surface of the grain layer and thereby to press into the defective recesses. Such foams inevitably contain a foaming agent as well as foam stabilizers, by which the water resistance of the solidified foams is reduced. A solidified foam layer also results in full-grain leathers to lower adhesion of such a layer in the sequence applied plastic coating, because the whipped foam often splits or peels off the leather.

It has also been proposed to provide full-grain or slightly scuffed leather on the grain side with a plastic layer, which is formed from an aqueous, compact containing plastic dispersion, which is acted upon by their solidification with a hot embossing roll or embossing plate. The compact particles expand and the plastic layer foams into the negative honeycomb structure on the surface of the hot embossing roll or embossing plate. Then the leather is milled and provided with a dressing. This foamed plastic layer must have such a thickness that it fills the negative Walknappastruktur on the surface of the roll or plate, so that a leather treated in this way can no longer be called genuine leather, because the Walknappaeffekt is achieved by embossing.

The object of the present invention is to provide a method by means of which defects in the grain layer of a full-grain leather, in particular cowhide, can be eliminated so that the existing damage to the grain layer is no longer noticeable, without, however, the disadvantages of the known processes occur, with subsequent very thin finishes can be applied, so that such a leather can be referred to as genuine leather.

In particular, to be effected with the method according to the invention, the defects in the grain layer, which are usually formed by depressions to fill so that the filler does not fall out even when occurring during use of the leather continuous bending stress, further that the filler does not after their solidification Shrinks that it is waterproof and that it mainly remedies only the imperfections and not or only with a very small thickness covers the entire surface of the scar layer.

To solve this problem, the invention proposes that an aqueous, optionally slightly foamed, plastic dispersion containing the smallest compact particles, pressed into the flaws and then the leather is dried, whereupon the grain layer is subjected to a pressure and heat treatment, whereby from the compact particles in the solidified plastic dispersion at least partially hollow microspheres are formed. The fact that in the process according to the invention no pasty filler, but rather an aqueous plastic dispersion is used to fill the defects, the adhesion to the flaws is substantially improved, expand by the pressure and heat treatment, the compact particles to form the hollow microspheres and thereby creates an overpressure , So that by this at the defects the resulting after drying plastic compound firmly with the surface of the defects and in particular with the edges of the voids forming depressions and withstands any bending stress. The hollow microspheres in optionally at the not with defects provided surface of the grain layer existing, formed from the solidified plastic dispersion plastic mass are destroyed by the pressure and heat treatment, at least for the most part or can not form, so at these points a maximum of a plastic layer is formed whose thickness is not measurable in the rule, to each Case is thinner than 60 microns.

According to a preferred embodiment of the invention, the plastic dispersion is pressed into the flaws by means of a, preferably opposing, optionally having a finely structured surface, so that a squeegee-like application of the plastic dispersion takes place in a very low strength outside of the flaws.

The pressure and heat treatment according to the invention by a heated to a temperature of at least 100 ° C, preferably between 120 ° C and 180 ° C, the grain layer contacting pressure roller causes, through which the at least partially solidified plastic dispersion is pressed firmly into the flaws and while the compact particles expand to form the hollow microspheres in the solidified plastic dispersion.

The surface of the pressure roller can be smooth. However, the pressure roller preferably has a finely structured surface, as can be achieved, for example, by sandblasting, as a result of which the surface of the plastic mass filling the defects also acquires such a structure.

It is particularly advantageous if compact particles with a size of less than 10 .mu.m, preferably less than 7 .mu.m, in an amount between 15 g and 60 g, based on 1 kg of a 40% plastic dispersion, are used, and from a thermoplastic Plastic, and contain a liquid propellant. In this case, a complete filling of the depressions forming the voids with the plastic composition formed from the plastic dispersion and an intimate connection thereof with the surface of the wells is ensured.

Suitably, compact particles are used which expand at a temperature below 120 ° C, preferably below 80 ° C. At such temperatures, a pronounced spatial structure does not form on the undamaged surface of the scar layer due to any plastic dispersion applied there after its solidification.

In a solidified plastic dispersion located in areas next to the imperfections, troublesome hollow microspheres can be eliminated or their formation can be prevented altogether, according to the invention, a mixture of water and solvent, for example 90 parts of water, on the solidified plastic dispersion and 10 parts of solvent, in particular ethyl acetate applied, preferably sprayed, and then a pressure and heat treatment takes place. The then in a moist state microbubbles then collapse in the presence of a small amount of solvent already at temperatures below 65 ° C and at a pressure less than 0.5 kg / cm or they are not formed at all.

In order to match the appearance of the plastic body filling the imperfections to those of the scar layer, suitably pigmented compact particles are used whose color corresponds to that of the grain layer and / or the plastic dispersion.

A full-grain leather, in particular cowhide, which partially has defects on its grain layer, which are corrected by a Kunststoffüllmasse, according to the invention is characterized in that the Kunststoffüllmasse consists of a solidified, aqueous, formed of compact particles by heat micro hollow balls containing plastic dispersion, which when applied in the flaws is pressed.

Preferably, the formation of the hollow microspheres in the area adjacent the surface of the grain layer is stronger than in the area more remote from this surface, which has the advantage that after solidification the solidified plastic dispersion containing microspheres does not expand beyond the surface of the grain layer.

The sole drawing shows in a greatly enlarged scale a full-grain leather, whose existing in the grain layer defects were corrected by the method according to the invention.

A leather 1, of which only the uppermost region is shown in the drawing, has a grain layer 2 which has defects 3 caused by injuries of the grain layer, which are formed by depressions in the grain layer 2. These depressions can penetrate the entire thickness of the scar layer, but also be present only superficially on the scar layer 2. In order to eliminate the defects 3 formed by these recesses, these recesses are filled by an aqueous dispersion of any plastics or plastic mixtures, which in the liquid state, but good sticks after their solidification, and then has an elongation at break of more than 300%. This plastic dispersion contains compact particles of a thermoplastic copolymer, from which hollow microspheres are formed by supplying heat

The application of the aqueous plastic dispersion to the surface 4 of the grain layer 2 takes place by means of a finely structured applicator roll on its surface, by means of which the aqueous plastic dispersion is spread as in the wells with a doctor blade. Subsequently, the leather is dried with the applied plastic dispersion and it is subjected to the surface 4 of the grain layer 2 by means of a heated to a temperature between 120 ° C and 180 ° C pressure roller of a pressure and heat treatment. The compact particles expand, so that a small hollow microspheres 5 containing plastic mass is formed in the wells, which is firmly pressed by the pressure exerted in the wells and intimately connects with the boundary of the wells. By choosing a suitable pressure, but especially by choosing a suitable temperature of the pressure roller and the residence time of the same on the surface 4, it is achieved that form the hollow microspheres in the main, only in the surface 4 adjacent to the area of the depressions 3 forming depressions whereas less training occurs in the lower regions or the compact particles do not expand at all. Thus, for example, given a residence time of the pressure roller of about 1 second and a roller temperature of about 145 ° C., hollow microspheres only up to a depth of 0.12 mm. Nevertheless, however, the wells are completely filled by the solidified plastic dispersion. At a temperature of the pressure roller of more than 170 ° C, the residence time is halved, and then in those areas where no defects 3 are present, the formation of the hollow microspheres due to the heat is prevented.

Likewise, in a next to the wells on the surface 4 applied plastic dispersion by the applied pressure, the formation of the hollow microspheres prevented at all or already resulting hollow microspheres are compressed so that there, if any, only a non-interfering plastic coating hardly measurable strength is formed by which the scar layer of the leather is not affected.

For example, in a plastic coating present in these areas hollow microspheres can be further eliminated by spraying a mixture of about 90 parts of water and 10 parts of solvent, for example, ethyl acetate, and then subjected to pressure and heat treatment these areas. In this wet state then the hollow microspheres collapse even at temperatures below 65 ° C at a pressure of less than 0.5 kg / cm ² , so that occur in this procedure, the hollow microspheres or are not formed at all.

Claims (16)

1. A process for eliminating defects (3) in a grain layer (2) of a full-grain leather (1), a plastics compound being applied to the defects (3), wherein an aqueous, optionally lightly foamed, plastics dispersion which comprises very small compact particles is pressed into the defects (3) and the leather (1) is then dried, whereupon the grain layer (2) is subjected to a pressure and heat treatment, with the result that hollow microspheres (5) are at least partly formed from the compact particles in the solidified plastics dispersion, wherein compact particles having a size of less than 10 µm are used in an amount of from 15 g to 60 g, based on 1 kg of a 40% strength plastics dispersion, and where the pressure and temperature treatment is effected using a pressure roll which is heated to a temperature of at least 100°C and makes contact with the grain layer (2).
2. The process according to claim 1, wherein the leather is cattle leather.
3. The process according to claim 1 or 2, wherein the plastics dispersion is pressed into the defects (3) by means of an application roll optionally having a finely structured surface.
4. The process according to any of claims 1 to 3, wherein the application roll is a counterrotating application roll.
5. The process according to any of claims 1 to 4, wherein the pressure roll is heated to a temperature from 120°C to 180°C.
6. The process according to any of claims 1 to 5, wherein the pressure roll has a finely structured surface.
7. The process according to any of claims 1 to 6, wherein compact particles comprising a thermoplastic, which comprise a liquid blowing agent, are used.
8. The process according to any of claims 1 to 7, wherein compact particles which expand at a temperature below 120°C are used.
9. The process according to any of claims 1 to 8, wherein a mixture of water and a solvent is applied to the solidified plastics dispersion and a pressure and heat treatment is then effected.
10. The process according to any of claims 1 to 9, wherein a mixture of water and a solvent is sprayed onto the solidified plastics dispersion and a pressure and heat treatment is then effected.
11. The process according to either of claims 9 and 10, wherein the solvent is ethyl acetate.
12. The process according to either of claims 9 and 11, wherein the mixture comprises 90 parts of water and 10 parts of solvent.
13. The process according to any of claims 1 to 12, wherein pigmented compact particles whose color corresponds to that of the grain layer and/or of the plastics dispersion are used.
14. A full-grain leather, which has on parts of its grain layer, defects which are corrected by means of a plastics filling compound, wherein the plastics filling compound consists of a solidified, aqueous plastics dispersion which comprises hollow microspheres (5) formed from compact particles by supplying heat and is pressed into the defects on application, where compact particles having a size of less than 10 µm are used in an amount of from 15 g to 60 g, based on 1 kg of a 40% strength plastics dispersion.
15. The full-grain leather according to claim 14, which is cattle leather.
16. The full-grain leather according to claim 14 or 15, wherein the formation of the hollow microspheres (5) in the region adjacent to the surface (4) of the grain layer is greater than in the region further away from this surface (4).

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