Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-10-04
2004-05-11
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S305500, C428S314800, C428S318600, C428S319300, C428S403000, C428S423400, C428S423300, C428S473000
Reexamination Certificate
active
06733877
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of leather processing. More specifically, the invention relates to a full grain napa cowhide, one side of which is provided with a finish that partially comprises a foam structure formed from a stabilized polyurethane dispersion containing hollow microspheres. The invention furthermore relates to a method for fabricating such leather.
Such leathers are already known. German patent DE 24 45 605 C3 and the corresponding U.S. Pat. No. 4,016,326 (Schäfer), for example, disclose a leather for producing shoes, cushion covers, or the like, which is provided with a porous elastomer coating that contains microspheres whose shell consists of polyvinylidene chloride copolymerisate or polyvinyl chloride copolymerisate and contains an interior gas. The surface of the coating that is averted from the leather can be additionally provided with a finish.
U.S. Pat. No. 4,751,116 (Schäfer et al.) discloses the application of a coating consisting of two layers on the fibrous surface of split leather. The layer facing the surface of the split leather is formed by a stabilized polyurethane dispersion containing hollow microspheres. The surface of the coating that is averted from the split leather can be additionally provided with a finish.
U.S. Pat. No. 4,923,732 (Schäfer) likewise describes a split leather which is provided with a coating of two layers on its fibrous side. The layer facing the split leather includes hollow microspheres.
In the automotive industry and in the fabrication of high-quality upholstered furniture, as well as for shoe upper material, full grain cowhide is used, which has the necessary characteristics and which can have only a very thin finish in order to be classified as real full grain cowhide. The leather must exhibit the requisite elasticity and have a softness grade of at least 4, preferably better than 4.5, so that on one hand it can be formed into the required shape, and on the other hand, it guarantees a pleasant sitting sensation and a pleasant reaction to touch.
The softness grade is measured with a softness tester BLC ST300 according to IUP36 given a ring diameter of 25 mm. Such softness is achieved by extra long milling (fulling) of the leather skins. But in the process loose grains emerge on large parts of the leather skin equaling between 25% and 40% of the overall surface of the skin, for instance in the stomach region. This area is unsuitable for processing the leather for high-quality auto interiors such as seats or for upholstered furniture or high-quality shoes; therefore, a large amount of expensive leather skin is wasted by extended milling. Another disadvantage of using the known leathers which are provided with a finish is that they are insufficiently breathable, if at all.
It has therefore been proposed that a plastic material that has been foamed by stirring in air be applied on the grain side of the leather and covered after being stabilized by a varnish layer which undergoes embossing in order to form a grainy surface. But the foam material is pressed together in the region of the grain valleys, so that the softness and elasticity which is produced by the foam is lost there. The foam layer thus has different thicknesses; namely, it has a lower thickness on the peaks of the grains, which are more heavily worn with use, which is disadvantageous for later utilization. Besides this, with this known configuration the danger exists that the grain structure may be lost when the leather is stretched over edges or curves or the like owing to the pliability of the foam layer, above all under the influence of heat.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a full grain napa cowhide leather and an associated production method which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which further improve a fully grained napa cowhide such that it has the characteristics required in the automotive and upholstery industries and above all has no notable grain pipeyness after the required milling and does not lose its grain stability even with expansion, and which has the required permeability to water vapor. In particular, the inventive leather should be breathable, wearproof even with respect to its color, lightproof, hydrolysis resistant, and scratchproof. The leather must also be fogless and have low perspiration, so that when it is utilized for auto furnishings the inside of the windshield does not steam up. Also, above all, no toxic gases must be released. The surface of the leather must also be resistant to certain chemicals as well as water, and the leather surface which is provided with the graining should not change disadvantageously when applied over base materials, for instance when the leather is stretched around curves or edges.
With the foregoing and other objects in view there is provided, in accordance with the invention, a dressed leather product, comprising:
full grain cowhide having a grain side;
a finish provided on the grain side, the finish including:
a first layer with a thickness of between 0.015 mm and 0.04 mm applied on the grain side of the cowhide and formed of a stabilized dispersion of at least one material selected from the group consisting of polyurethane and polyacrylate and having a primary proportion of hollow microspheres with a diameter of less than 45 &mgr;m forming closed cells and a proportion of at least 10% by volume-of open cells; the first layer having an embossed top surface; and
a second layer disposed on the first layer and formed from a cross-linked polyurethane-based varnish application containing a dulling agent;
and wherein the leather product undergoes a milling treatment.
In accordance with an added feature of the invention, the first layer is a pigmented layer, the microspheres have a diameter of substantially between 15 &mgr;m and 35 &mgr;m, and the second layer is a multi-coating layer.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing a full grain napa cowhide. The method comprises:
providing cowhide material having a grain side;
providing a first dispersion based on at least one material selected from the group consisting of polyurethane and polyacrylate, the dispersion containing at least one of hollow microspheres with a diameter between 15 &mgr;m and 45 &mgr;m and compact particles from which the microspheres are formed in situ by heat addition, the microspheres having a thin shell of polyvinylidene chloride and polyacrylnitrile containing a heavy gas;
applying the first dispersion on the grain side of the cowhide, and thereby selecting a quantity of the dispersion such that, after the dispersion is stabilized by dehydration, a first layer with a thickness between 0.015 mm and 0.04 mm is formed, the first layer comprising primarily closed cells formed by the microspheres and at least 10% open cells by volume;
embossing the stabilized first layer with one of pressure and heat processing;
applying a cross-linkable polyurethane dispersion on the first layer to form a second layer; and
subjecting the leather to a milling treatment.
The term full grain napa cowhide refers to a leather which acquires its softness by extended milling, during which the milled napa surface structure with the characteristic “milling grain” develops. This type of leather can only be produced inadequately by known techniques if at all.
According to the invention, the object is achieved in that the finish consists of a first, preferably pigmented layer with a thickness between 0.015 mm and 0.04 mm on the grain side of the full grain napa cowhide—which consists of a stabilized dispersion containing polyurethane and/or polyacrylate and comprising primarily hollow microspheres with a diameter of less than 45 &mgr;m (preferably between 15 &mgr;m and 35 &mgr;m) forming closed cells but also a portion of at least 10% by volume of open cells, and comprising an embossing on its top surface—
Locher Ralph E.
Thomas Alexander S.
LandOfFree
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