Sewing-free hot melt adhesive TPU leather and preparation method thereof

A method for preparing a sewing-free hot melt adhesive thermoplastic polyurethane (TPU) leather comprising the following steps:

• I. preparing a release paper comprising:
• (1) choosing a bottom paper layer (A1), coating a water-based polypropylene adhesive layer (A2) having a thickness of 0.8-4 μm onto the bottom paper layer (A1), then adhering a plastic layer (A3) having a thickness of 18-25 μm and formed from polyethylene terephthalate film to the adhesive layer (A2), and then curing;
• (2) adding from 3 to 5 parts by weight of sodium fatty acid methyl ester sulfonate into from 45 to 55 parts by weight of water, stirring homogeneously, then adding from 62 to 68 parts by weight of inorganic particles formed by mixing clay, barium sulfate powder and calcium carbonate powder, stirring at a high-speed rate to disperse them homogeneously, then adding from 32 to 36 parts by weight of silicone acrylic emulsion into the dispersed slurry, homogeneously mixing with a glass rod, and then adding from 2 to 4 parts by weight of dodecyl benzyl dimethyl ammonium chloride, continuing to homogeneously stir to form a transition layer coating liquid;
• (3) homogeneously coating the transition layer coating solution on the plastic layer (A3) with a scraper, heating at 80° C. for 30 seconds and curing to form a film, controlling the thickness of the film to be from 15 to 20 press-polishing the film-formed transition layer (A4) at 120° C., a linear pressure of 150 KN/m and a speed of 10 m/min;
• (4) homogeneously mixing from 58-65 parts by weight of polypropylene, from 26-34 parts by weight of poly(4-methyl-1-pentylene) and from 6 to 9 parts by weight of vinyl silicone oil, heating to a temperature of 90° C., keeping the temperature for 2 hours, adding from 1 to 2 parts by weight of 2,2′-methylene-bis-(4,6-di-tertiary-butylphenoxy)sodium phosphate and from 0.1 to 0.8 part by weight of butyl peroxybenzoate, homogeneously mixing, extruding via an extruder and coating onto the surface of the transition layer (A4) to form a release layer (A5), controlling the thickness thereof to be from 20 to 25 μm;
• II. preparing hot melt adhesive material comprising:
• (1) placing from 60 to 70 parts by weight of hydroxyl-terminated polyester diol, from 3 to 5 parts by weight of polyether polyol, from 1.5 to 1.8 parts by weight of an antioxidant and from 4 to 6 parts by weight of a tackifying agent in a reaction kettle, heating to a temperature of from 120 to 140° C., vacuum dehydrating for 1.5 to 2 h while stirring and mixing, wherein the vacuum degree is less than 0.05 MPa, then cooling to a temperature of from 70 to 75° C., wherein the hydroxyl-terminated polyester diol is prepared by polycondensing an aliphatic diol having a low molecular weight and an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid at 100-260° C., wherein the aliphatic diol of low molecular weight is selected from the group consisting of glycols, diglycols, propanediol, methyl propanediol, 1,4-butanediol, 1,6-hexanediol, 1,3-butanediol, 1,5-pentanediol, and dodecyl-hexanediol, and the hydroxyl-terminated polyester diol has a molecular weight of from 2000 to 6000;
• the polyether polyol is polytetrahydrofuranether diol;
• the antioxidant is selected from the group consisting of 2,6-tert-butyl-4-methylphenol, or tetra{β-(3,5-tert-butyl-4-hydroxylphenyl)-propionic acid}penta-erythritol ester;
• the tackifying resin is one or more selected from the group consisting of polyethylene-vinyl acetate copolymer, hydroxyl-terminated thermoplastic polyester and hydrogenated rosin resin;
• (2) adding from 15 to 20 parts by weight of diisocyanate and from 0.8 to 1.5 parts by weight of a catalyst to the reaction product in step (1) under nitrogen protection, and reacting at a temperature of from 85 to 95° C. for 1 to 1.5 h, wherein said diisocyanate is either of 4,4′-diphenylmethane diisocyanate or 1,6-hexamethylene diisocyanate;
• the catalyst is one or more selected from the group consisting of dibutyltin dilaurate, triethanolamine and dimorpholinodiethylether;
• (3) adding from 0.5 to 1.2 parts by weight of a chain extender, from 2 to 4 parts by weight of a flame retardant, from 2 to 4 parts by weight of a flexibilizer to the reaction product in step (2) under nitrogen protection, stirring and reacting at 75 to 85° C. for 45 min to 1 h, wherein the chain extender is one selected form the group consisting of 1,6-hexanediol, methylpropanediol and 1,4-butanediol;
• the flame retardant comprises from 30 wt. % to 70 wt. % of polypropylene having a melt index of from 0.5 to 15.0 g/10 min, from 5 wt. % to 25 wt. % of polyethylene having a melt index of 0.01 to 2.0 g/10 min, from 20 wt. % to 40 wt. % of at least an inorganic filler selected from powdery talc, kaolinite, sericite, silicon dioxide and diatomite, and from 5 wt. % to 35 wt. % of organic halide of decabromodiphenyl ether;
• the flexibilizer is selected from polyolefin flexibilizer;
• (4) discharging under the protection condition of feeding nitrogen, aging, cooling to form hot melt adhesive material;
• III. preparing TPU material comprising:
• (1) placing from 60 to 70 parts by weight of polymer polyol into a reaction kettle, and heating to a temperature of from 80 to 90° C., wherein the polymer polyol is polytetrahydrofuranether diol having a molecular weight of 1000 and/or polybutylene terephthalate polyol having a molecular weight of 3000, then adding from 0.2 to 0.8 part by weight of an antioxidant, from 0.1 to 0.5 part by weight of di-(2,2,6,6-tetramethyl-4-piperidyl) sebacate light stabilizer, from 0.2 to 0.6 part by weight of benzotriazole ultraviolet light absorber, from 0.4 to 0.8 part by weight of montan wax and/or erucamide wax lubricant, from 3 to 5 parts by weight of carbodiimide-hydrolytic resistant agent, sufficiently stirring to obtain a polymer polyol mixed solution, wherein the antioxidant is at least one selected from the group consisting of β-(4-hydroxyl-3,5-di-t-butylphenyl)-propionic acid N-octadecanol ester, tetra{β-(3,5-di-butyl-4-hydroxylphenyl)propionic acid}-pentaerythritol ester and di-[(2,4-di-t-butyl-phenyl) phosphorous acid] pentaerythritol ester;
• (2) adding from 30 to 35 parts by weight of 1,4-cyclohexane diisocyanate having a temperature of from 55 to 65° C. into the polymer polyol mixed solution, stirring and mixing to obtain a primary reaction mixture;
• (3) keeping the temperature of said reaction mixture, adding from 4 to 9 parts by weight of 1,4-butanediol chain extender and from 0.05 to 0.2 part by weight of a titanium catalyst or a bismuth catalyst, controlling the temperature to be from 150 to 210° C. and the pressure to be from 4 to 8 MPa, and reacting for about 1 h;
• (4) when the reaction melt reaches to a temperature between 180 to 210° C., adding from 1 to 3 parts by weight of an organic halide flame retardant having an average particle size of less than or equal to 4 μm and formed by mixing decabromodiphenyl ethane with trace calcined silicon dioxide, from 1 to 2 parts by weight of a wear-resistant agent consisting of aromatic silicone oil, from 1 to 3 parts by weight of a matting agent consisting of calcium filler and from 0.5 to 1.2 part by weight of an antistatic agent consisting of metal powder or conductive carbon black, dehydrating, drying and aging after reaction to obtain thermoplastic polyurethane elastomer material;
• IV. joint-preparing sewing-free hot melt adhesive TPU leather comprising:
• (1) providing the release paper, hot melt adhesive material and TPU material prepared by the aforesaid steps and spreading out the release paper in relevant devices;
• (2) extruding the hot melt adhesive material prepared in step II via an extruder into sizing material, feeding the sizing material into an extruder at 150° C. and melting into a pasty form, extruding via the extruder die head and flow casting to the release paper, pressing via the counter roller, cooling and reeling to form a hot melt adhesive film;
• (3) extruding the TPU material prepared in step III into TPU film, placing the hot melt adhesive film onto two feeding racks respectively, feeding the hot melt adhesive film and TPU film simultaneously into an upper and lower counter pressure rollers which are thermostatic for counter pressing, wherein the counter pressure rollers have a temperature of more than 160° C., so as to make the hot melt adhesive having a low melting point instantaneously bond to the TPU film into an integral unit in the counter pressing of the upper and lower counter pressure rollers, and then be cooled and formed onto the sewing-free hot melt adhesive TPU leather.