Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2002-07-15
2003-07-29
Sergent, Rabon (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C008S09410R, C427S389000, C428S506000, C428S319300
Reexamination Certificate
active
06599629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to coated natural leather and, more particularly, to leather coated on the flesh side with polyurethanes or polyurethaneureas.
2. Description of Background Art
Coatings are generally applied to natural leathers on the grain side of the leather for aesthetic, waterproofing, or durability purposes. Although some applications of polymers to the flesh side of leather have been disclosed, the results have not been satisfactory with regard to stretch and recovery.
French Patent Number 2,129,056 discloses a method for reinforcing leather by coating the flesh side with a rigid, crosslinked polyurethane elastomer, the polymer being formed in situ on the leather. Shoes made from the coated leather are also disclosed but, because the polymer is rigid, neither the leather nor the shoes made therefrom have the desirable stretch and recovery needed for comfortable wear.
German Patent Number 1,469,530 discloses a process for impregnating an unspecified side of natural leather with a solution of an irreversibly heat-hardenable resin (e.g. polyurethane), followed by deep-drawing or vacuum-shaping and heating to a permanent form having shape stability. Leather processed in this way will not have a desirable combination of stretch and low set, because it will be hardened into a permanent form.
French Patent Number 866,856 discloses coating the flesh side of dyed leather with dilute solutions of chlorinated rubber to bind leather dust to the leather. The properties of the leather, however, are not affected by this treatment.
Romanian Patent Number 104,707 discloses the use of crosslinkable polyurethane prepolymers to coat a variety of materials, but specifics of their application to leather are not disclosed.
U.S. Pat. No. 3,027,276 discloses lightly spraying a thin, low-solids solution of a diisocyanate prepolymer onto the flesh side of dyed or pigmented suede containing free moisture to prevent crocking. In this method, curing is completed on the leather by reaction with environmentally available water. This method does not alter the mechanical properties of the treated suede.
U.S. Pat. No. 5,932,056 discloses a method of laminating a one-way stretch fabric in alignment with natural leather, but such laminates can be too thick for some uses.
French Patent Number 1,589,164 discloses reinforcing the back of thin or split skins by coating the flesh side of leather with an aqueous emulsion of thermoplastic acrylic and vinyl polymers without significant penetration of the leather. The abrasion and water resistance of the leather is improved. However, such a coating will not provide sufficient recovery to avoid permanent distortion after the coated leather is highly stretched.
A combination of high stretch (for comfort and ease of shaping), low set (for shape retention), high air permeability, and visual aesthetics of natural leather is still needed.
SUMMARY OF THE INVENTION
The coated natural leather of the present invention comprises
(a) natural leather having at least about 15% elongation prior to coating; and
(b) 5-70 wt %, based on the weight of uncoated leather, of elastomeric polyurethane, from a polyurethane solution having a viscosity of 1,000-300,000 centipoise, coated on the flesh side of the leather which is capable of absorbing the polyurethane solution, wherein the coated leather has an elongation of at least about 15%, a set of no more than about 25%, and a measure of deformation (ratio of fifth cycle set to fifth cycle elongation) at least 0.05 lower than the uncoated leather.
DETAILED DESCRIPTION OF THE INVENTION
It has now been discovered that natural leather which has been coated on the flesh side with a solution of an elastomeric polyurethane has low percent set relative to its elongation. This unexpected combination of properties means that the coated leather retains its softness and stretch (for comfort) but resists permanent deformation for good fit retention. It has also been discovered that the solution-coated leather retains surprisingly high elongation and low set after extended storage. Further, the polyurethane solution-coated leather of the invention displays highly desirable soft-leather tactile aesthetics on the (coated) flesh side. The coated leather of the invention can be made into articles such as footwear, apparel such as jackets and pants and apparel accessories such as purses, belts and gloves, upholstery, and luggage.
As used herein, “natural leather” means the tanned or partially tanned skin of any suitable animal. “Flesh side” means the inside of the leather or skin when it is still part of the animal, and “grain side” means the outside of the leather or skin when it is still part of the animal. When the leather is a split-grain leather, “split side” means the side that was within the leather or skin before it was split. By “coated on the flesh side” is meant coating the flesh side of full grain (un-split) leather or the split side of split grain leather. “Set” means the percent residual extension of a measured length of coated or uncoated leather after it has been stretched at a force of 17.5 Newtons per centimeter (N/cm, of sample width) at room temperature and allowed to relax to substantially zero force.
Elastomeric polyurethanes useful in this invention can be prepared by reacting a polymeric glycol with a diisocyanate to form a capped glycol, dissolving the capped glycol (in a suitable solvent), and then reacting the capped glycol with a difunctional chain extender having active hydrogen atoms. Such polyurethanes are termed “segmented” because they are comprised of “hard” urethane and urea segments derived from the diisocyanate and chain extender and “soft” segments derived primarily from the polymeric glycol. Suitable solvents for preparing solutions of such polymers are amide solvents such as dimethylacetamide (“DMAc”), dimethylformamide (“DMF”), and N-methylpyrrolidone, but other solvents such as dimethylsulfoxide and tetramethylurea can also be used.
Polymeric glycols used in the preparation of the elastomeric polyurethanes include polyether glycols, polyester glycols, polycarbonate glycols and copolymers thereof. Examples of such glycols include poly(ethyleneether) glycol, poly(trimethyleneether) glycol, poly(tetramethyleneether) glycol, poly(tetramethylene-co-2-methyl-tetramethyleneether) glycol, poly(ethylene-co-butylene adipate) glycol, poly(2,2-dimethyl-1,3-propylene dodecanedioate) glycol, poly(3-methyl-1,5-pentamethylene dodecanedioate) glycol, poly(pentane-1,5-carbonate) glycol, and poly(hexane-1,6-carbonate) glycol.
Useful diisocyanates include 1-isocyanato-4-[(4′-isocyanatophenyl)methyl]benzene, 1-isocyanato-2-[(4′-isocyanato-phenyl)methyl]benzene, isophorone diisocyanate, 1,6-hexanediisocyanate, and 2,4-tolylene diisocyanate, and mixtures thereof.
The chain extender can be a diol or a diamine. Useful diols include ethylene glycol, 1,3-trimethylene glycol, 1,4-butanediol, and mixtures thereof. Diol chain extenders lead to polyurethanes. Useful diamines include ethylene diamine, 1,2-propanediamine, 2-methyl-1,5-pentanediamine, 1,3-diaminopentane, 1,4-cyclohexane-diamine, 1,3-cyclohexanediamine, and mixtures thereof. In this case, the polymer produced is a polyurethaneurea. When a polyether glycol and a diamine chain extender are utilized, the polymer produced is a polyetherurethaneurea; when a polyester glycol is utilized in combination with a diamine chain extender, a polyesterurethaneurea is produced. Monofunctional amine chain terminators such as diethyl amine, butylamine, cyclohexylamine, and the like can be added to control the molecular weight of the polymer.
Additives, for example, antioxidants and lubricants, can be added in small quantities to the polyurethane coating solution, provided such additives do not detract from the benefits of the invention.
Leather from sheep, goat, cattle, calf, pig, ostrich, kangaroo, elephant, deer, lizard, crocodile, snake, and the like can be used in the present invention. The characteristic
Karayianni Eleni
Mendoza Yery A.
E. I. du Pont de Nemours and Company
Sergent Rabon
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