Full-grained milled napa leather and process for the production thereof

#1. Field of the Invention

#The invention relates to a full-grained milled napa leather which is provided on its grain side with a dressing formed of a solidified plastics dispersion, optionally a finish coat being applied to the dressing. Furthermore, the invention relates to a process for the production of such a milled napa leather.

#The term “full-grained milled napa leather” is understood as meaning a full-grained leather which acquires its softness in combination with the formation of the napa surface structure with the characteristic “pebbled grain” by mechanical treatment, in particular by prolonged milling. The formation of the pebbled grain may be round or flat, large or small and may also be differently formed within a leather hide of a hide cut. In the area where the leather hide has a higher density and is stiffer, the pebbled grain is formed only slightly, if at all.

#The drawing shows a section through the leather according to the invention, on a greatly enlarged scale.

#Referring now to the sole figure of the drawing in detail, there is shown the natural grain 1 of a full-grained untreated cowhide leather 2. The leather is provided, after a milling process lasting several hours, with a dressing 3 which is formed from a solidified plastics dispersion and has a thickness of from 0.02 mm to 0.07 mm, preferably from 0.05 mm to 0.07 mm. The plastics dispersion forming the dressing 3 predominantly comprises a pigment-containing polyurethane dispersion, to which high molecular weight polysiloxane in the form of a dispersion, emulsion and expediently hollow microspheres having a polyvinylidene chloride copolymer shell, an antifoam and a dulling agent have been added.

#A chrome-tanned hard black cattle leather hide (crust) dried on a vacuum dryer and having a full-grained, even and smooth grain side and a thickness of about 1.2 mm was drummed for 6 hours. As a result, the leather became very soft and also had a softness of more than 5.5, measured in a softness tester BLC ST300 according to IUP36 at a ring diameter of 25 mm, in the harder zones. The full-grained, unpretreated grain side of the leather showed slight areas of damage on its surface. The small indentations attributable to cracks on the back or the like were rough and better visible after drumming, as were the hair pores.

#The drumming resulted not only in the formation of the pebbled grain but also in the characteristic surface structure of the leather being visible again, and the previously smooth surface had a microscopic roughness. The grain side was “opened” after the drumming.