US 3536572 A
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United States Patent O 3,536,572 POROMERIC LAMINATE Walter T. Murphy, Cuyahoga Falls, and Floyd D.
Stewart, Akron, Ohio, assignors to The B. F. Goodgchkcompany, New York, N.Y., a corporation of New or No Drawing. Filed Aug. 30, 1967, Ser. No. 664,261 Int. Cl. 1532b 5/18, 5/26'; D06n 3/14 U.S. Cl. 161-84 2 Claims ABSTRACT OF THE DISCLOSURE Leather replacements comprising nonwoven textile backers faced with poromeric microporous linear polyesterurethane films have been made. When the polyesterurethane is prepared from a polyester having a zero acid number, the laminated construction has a greatly increased flex fatigue strength at 35 F. compared to similar constructions prepared with films made from polyesterurethanes based on polyesters with acid numbers from 3 to about 10.
BACKGROUND OF THE INVENTION Poromeric materials with properties of permeability to air and water vapor, but not to liquid Water, and with high abrasion resistance, easy cleanability, high tear strength and the like have recently become available. These materials, alone or adhered to substrates, are able to compete with natural leather in such diverse articles as shoe uppers, upholstery and clothing articles such as coats, jackets, dresses and skirts. The major difficulty in creating synthetic poromerics to compete with leather has been in maintaining a balance of all the desired properties that will at least equal the balance of properties exhibited by leather.
A successful laminated construction useful for shoe uppers has been developed which comprises a nonwoven textile substrate impregnated with an elastomeric polymer latex and coated with a poromeric microporous film of a linear polyesterurethane. The nonwoven textile backer, with an optional reinforcing layer of woven sheeting, is an excellent substrate material. It is porous and is found to contribute to successfully duplicating the strength, workability and vamp break properties of leather in shoe upper constructions. The microporous linear polyesterurethane top film provides a scuff resistant, easily cleanable, embossable surface that can be processed to duplicate leather surface effects and to create entirely new surface effects not heretofore possible with leather. The polyurethane film is spread on the substrate from a solution and then is precipitated in the form of a microporous layer by the action of an inert fluid which is a non solvent for the polyesterurethane, but is miscible with the actual solvent employed therewith.
Linear polyesterurethane polymers, prepared according to the teaching of U.S. Pat. 2,871,218 contain essentially no free hydroxyl or isocyanate groups. The polymers can be dissolved in a solvent such as dimethylformamide or dimethylsulfoxide and spread on a nonwoven textile substrate. When the construction of a dissolved polyesterurethane spread on the nonwoven bat is immersed in an inert fluid such as water, the polymer coagulates in the form of a microporous film. After all of the solvent and inert fluid have been extracted, the construction is a leatherlike material that can be dyed or colored to simulate natural leather and can be shaped or lasted into the form of uppers for shoes. In the form of finished shoes the material displays permeability, abrasion resistance, tear strength, cleanability and other properties.equal to or better than those of natural leather. When subjected to flex test in the Bally flexometer, a machine devised for 3,536,572 Patented Oct. 27, 1970 'ice determining the flex life of shoe upper leathers while they are flexed in a manner simulating wear conditions, at 35 F., these materials will flex about 200,000 times before the sample surface cracks. This is a completely adequate flex life for the life of leathers; but a piece of top grade calf skin leather, the material used for top quality shoes, will flex about 400,000 times and it is desired to bring the flex life of the manmade poromeric into this region.
SUMMARY OF THE INVENTION The exact relation between the acid number of the polyester employed to make the linear polyesterurethane and the flex life in the final leatherlike product is not known, but it has been discovered that if the said acid number is controlled at a level of 0 to a maximum of 0.2 the ulti mate microporous polyurethane film, mounted on a textile backer, has an enormously improved Bally flex strength at 35 F. of 800,000 or more. The Bally flexometer is a standard commercial machine manufactured by Ballys Shoe Factories, Ltd., Switzerland. A flex sample 45 mm. x 70 mm. is clamped into the machine in a folded position. The sample is continuously flexed along the crease lines of the folds. When linear polyesterurethanes are prepared from polyesters displaying acid numbers of 10, 7.5, 5, 3, 2 and 1.5, the Bally flex results at 35 F. of poromeric materials made from the polyurethanes all run in the range of 150,000 to 225,000. When the polyester acid number is controlled at essentially zero, the ultimate poromeric material has an enormously improved Bally flex strength.
DETAILED DESCRIPTION OF THE INVENTION Nonwovenfabrics are variously defined as felts, mats, webs and the like. They embody natural or artificial fibers formed into a web or bat by carding, garneting, air-laying, Water-laying and other methods known in the art. Mats weighing about 4 to 10 ounces per square yard are generally preferred. Nonwoven webs are made in a variety of thicknesses and densities, Polymeric impregnants can be applied in latex form or from solution to strengthen the web and improve its leatherlike properties. Typical binder adhesives and impregnants are synthetic latices of butadiene-styrene, butadiene-acrylonitrile, and the lower alkyl acrylates, methacrylates and copolymers thereof. The fibers employed may be wool, cooton, jute, rayon, polyamides, polyesters, polyacrylonitrile and the like. Fiber denier is preferably 1 to 3 and preferred fiber lengths are about 1 inch to about 5 inches. The nonwoven mats are often given a degree of orientation and are compacted by needle-punching on a loom that will pierce the mat up to 20,000 times per square inch with needles 1 to 10 mils in diameter.
The linear polyesterurethanes employed to form the microporous top film of these leatherlike constructions are elastomers prepared according to the teachings of U.S. Pat. 2,871,218. They are made by reacting one mol of polyester having a molecular weight of about 600 to 2000 with 1.1 to 3.1 mols of a diphenyl diisocyanate in the presence of 0.1 to 2.1 mols of a glycol containing from 2 to 10 carbon atoms. The polyesters are hydroxyl termi nated condensation products of 4 to 10 carbon atoms acyclic dicarboxylic acids with a molar excess of a 2 to 10 carbon atom alkylene glycol and have an acid number less than 10 and preferably less than 3. When a mixture of a dicarboxylic acid is heated with a polyhydric alcohol such as a glycol, glycerol or a polymethylol compound, esterification takes place even in the absence of catalysts. The reaction takes long periods of 16 to 18 hours to obtain polyester with an acid number of the desired level of only 3 or less. If a catalyst such as p-toluene sulfonic acid is employed, acid number levels of 3 and as low as 2.5 can be obtained, but the products suffer from discoloration and susceptibility to hydrolysis. Recently an improved class of catalysts, tin salts containing no hydro carbon groups directly attached to the metal, became available and polyester acid number levels of 0.2 and below became attainable. The polyesterurethane may have additives such as curatives, coloring agents, plasticizers, fillers and the like incorporated therein.
EXAMPLE I PREPARATION OF REGULAR POLYESTER Poly(tetramethylene adipate) glycol is prepared as follows:
Material: Amounts, mole Adipic acid 1,4-butane-diol A 3-neck, S-liter flask is fitted with an aeration tube, an agitator, thermometer and distillation column leading to a water cooled condenser.
Esterification is conducted by heating the agitated mixture of acid and diol at atmospheric pressure to 140 C. While bubbling carbon dioxide (an inert gas) through the aeration tube. Water resulting from the esterification is distilled off as pot temperature rises from 140 C. to 200 C. Water removal continues for 27 hours.
Excess butanediol is removed by continuing the disstillation for 18 hours at pot temperature 185 C., head temperature 101 C., pressure 1-2 mm. Final weight of polyester in flask is 1089 g. The polyester is washed three times with distilled water at 70 C., then it is dried. Polyester acid No.:2.8; polyester mol. wt.=1010'.
The product is marked polyester A.
PREPARATION OF LOW ACID NO. POLYESTER Material: Amount, mols Adipic acid 12 1,4-butanedoil 24 SnCl -2H O .001
The mixture of adipic acid and butanedoil is agitated and heated to 200 C. at atmospheric temperature. Carbon dioxide is bubbled through the aeration tube. Water is distilled off for 19 hours. The stannous chloride catalyst is added and distillation continues at atmospheric pressure for 9 hours. The inert gas flow is turned off; pressure is reduced to 1 mm. and the pot is held at 205 C. for 2.5 hours to remove excess diol. The product is washed three times in distilled water an dried. Polyester acid No.=0.2; polyester mole Wt.=l192.0.
The product is marked polyester B. Although prepared by slightly different procedures, polyesters A and B have molecular weights which are considered by one skilled in the art to be similar within experimental limits.
PREPARATION OF POLYESTERURETHANES The polyesters prepared above are separately reacted with butanedoil and diisocyanate according to the teaching of Pat. 2,871,218.
Material: Amount, mols Polyester 1.0 1,4-butanediol 2.0 Diphenyl methane diisocyanate 2.9
Polyester- Polyesterurethane A urethane B Soluble in dimethylformamide Yes Yes. Intrinsic viscosity 0.83. 0.98.
4 PREPARATION OF TEXTILE BACKER A nonwoven bat, consisting of 60% polypropylene, 40% rayon, formed by carding and cross-laying technique from 1.5 denier, 1.5-inch long fibers, with a weight of 9.5 oz. per sq. yd., a thickness of 0.040 inch, a density of 0.29 g./cc., needled to a level of 2300 punches per sq. in., is dipped in a 10% aqueous solution of sodium bicarbonate, then immersed in 35% solids carboxyl-modified butadiene-acrylonitrile (70/30) copolymer latex containing 5% sodium bicarbonate on latex total solids. Next the bat is dipped into 5% calcium chloride to coagulate the latex, and in 5% acetic acid to remove the bicarbonate. The bat is dipped into a bath of 50% aqueous latex binder, a carboxyl modified acrylic latex, and drawn through squeeze rolls set at a presure necessary to remove excess solution and leave a solids pick up of 71% on the weight of fabric. The impregnated mat is dried. The treated bat is then washed in water and dried. It has a polymer pickup of 119% on weight of fabric, thickness of 0.045 inch, moisture vapor transmission (MVT) of 690 g./sq. m./24 hours, and a degree of suppleness as measured by ASTM procedure D 138855T of 71.5 p.s.i.
PREPARATION OF SUBSTRATE LAMINATE It is optional in the practice of this invention to employ a thin woven reinforcing layer of cotton sheeting between the nonwoven textile bat and the microporous polyesterurethane top surface film. If a sheeting is employed, a recommended one is a cotton sheeting, count x95, Weight 3 /2 oz. per sq. yd., thickness .009 inch.
An adhesive cement is made by dissolving 50 parts of the linear polyesterurethane described above in 100 parts of dimethylformamide. The cotton sheeting is dipped in this adhesive cement, then adhered to the nonwoven backer mat by passing the laminate between steel rolls set .005 inch less than the original thickness of the two textile layers.
PREPARATION OF MICROPOROUS FILM ON LAMINATE Material Amount Polyesterurethane A or B 100 Dimethylformamide 229.5 Pyrogenic silica 12.5 Dimethylformamide 70.5 Water 21.0 Glycerol 2.0 Octadecyl-trimethyl ammonium chloride 2.5 Water 17.4
Spreading cement solutions of polyesterurethanes A and B are prepared to the recipe above. Separate solutions are made. The polyesterurethane is first dissolved in 229.5 parts dimethylformamide. The pyrogenic silica is dispersed in water and the balance of the dimethylformamide in an Eppenbach. homogenizer and added to the polyesterurethane solution at 65 C. The octadecyl-trimethyl ammonium chloride and glycerol are then added with stirring at 65 C. The cloud point (temperature at which the true solution of polyurethane in solvent changes to a colloidal dispersion as water is added is 55 C.
Viscosities, run in a Brookfield viscometer model RVT with a number 5 spindle at 2.5 r.p.m., at 65 C. are: A- 127,000 centipoises; B132,000 centipoises.
These values are approximately equal within limits of experimental error and again show that the two batches are almost identical with the exception that B has been made with a polyesterurethane based on a very low acid number polyester.
The nonwoven bat/woven cotton sheeting laminate is dipped in a water bath and run through squeeze rolls to leave a 40% pickup of water by weight of the textiles. The polyesterurethane solution is spread at 65 C. onto this wet substrate to a wet thickness of 35 mils. The assembly is cooled in air for 5 minutes, then immersed in water at 30 C. until the dimethylformamide is removed.
Test A B Bally flexometer, flexes at 35 F 274,000 855, 000 MVT, gJsq. rn./24 hrs 665 683 Density, g./ec 0. 59 0. 58
The greater than threefold increase in Bally flex strength at 35 F. and the same or slightly higher MVT of structure B over structure A (the densities of the two being essentially the same) is completely unexpected as a result of making only one change in the method of making B as compared to Athat change being the use of polyester of essentially zero acid number in the preparation of the linear polyesterurethane employed as the microporous top film and the adhesive in forming the laminate porormeric material.
What is claimed is:
1. A laminate structure useful as an artificial leather, comprising a nonwoven fiber backer bonded to a reinforcing woven sheeting center layer and adhered thereto a microporous linear polyesterurethane coating, said polyesterurethane having been prepared by the reaction of one mol of polyester having a molecular weight of 600 to 2000 with about 1.1 to 3.1 mols of a diphenyl diisocyanate in the presence of about 0.1 to 2.1 mols of a glycol containing from about 4 to carbon atoms, said polyester being a hydroxyl-terminated condensation product of 4 to 10 carbon atoms acyclic dicarboxylic acid with a molar excess of a 2 to 10 carbon atom alkylene glycol, wherein said polyester has a maximum acid number of 0.2, said polyesterurethane has essentially no free hydroxyl or isocyanate groups, said laminate structure being characterized by a Bally flex fatigue strength at F. of about 855,000 flexes compared to a Bally flex strength at 35 F. of about 275,000 flexes or less of a laminate structure of the same composition except that therein the said polyester has an acid number of 3.8 or more, and to calf leather which has a Bally flex strength at 35 F. of about 400,000 flexes.
2. The laminate structure coating of claim 1 wherein said polyester is a poly(tetramethylene adipate) glycol, said diphenyl diisocyanate is diphenyl methane diisocyamate and said glycol is butanediol-1,4.
References Cited UNITED STATES PATENTS 3,214,290 10/1965 Larner et al. 1l7l35.5 2,956,961 10/1960 Kibler et al. 161190 XR 3,047,517 7/1962 Wherley 2602.5 3,284,274 11/1966 Hulslander et a1. 15677 XR 3,399,102 8/1968 Matsushita et a1 16164 ROBERT F. BURNETT, Primary Examiner W. A. POWELL, Assistant Examiner US. Cl. X.R.
117-l35.5, 156-280; l6ll56, 159,