WO2014059593A1

WO2014059593A1 - Polyurethane based synthetic leathers comprising nanoparticles and having improved peel strength

Info

Publication number: WO2014059593A1
Application number: PCT/CN2012/083016
Authority: WO
Inventors: Weichao GU; Ning Kang; Bo Liu; Yunfei YAN; Chao Zhang; Hongliang Zhang
Original assignee: Dow Global Technologies Llc
Priority date: 2012-10-16
Filing date: 2012-10-16
Publication date: 2014-04-24

Abstract

Disclosed herein are methods for producing a poromeric synthetic leather having improved peel strength, the method comprising: preparing a polyurethane prepolymer, wherein the prepolymer comprises at least one isocyanate resin, and at least one polyol; preparing a first mixture comprising the polyurethane prepolymer, and at least one surfactant; preparing a second mixture comprising, the first mixture, water, and a chain extender; preparing a third mixture comprising the second mixture, at least one surfactant and a thickening agent, frothing the third mixture and thereby forming a frothed third mixture; applying the frothed third mixture to a fabric that is optionally impregnated with a polyurethane resin and thereby forming a coated fabric; optionally adjusting the thickness of the frothed third mixture on the fabric; and heating the coated fabric sufficiently to dry and cure it; wherein at least one nanoparticle is present in the polyurethane prepolymer, the first mixture, the second mixture, the third mixture, or combinations thereof. Leathers made according to such methods are also disclosed herein.

Description

POLYURETHANE BASED SYNTHETIC LEATHERS COMPRISING NANO PARTICLES AND HAVING IMPROVED PEEL STRENGTH

Background of the Invention

Currently, most polyurethane (PU) synthetic leathers are made using organic solvents, such as dimethyl formamide, methylethyl ketone (MEK) and toluene. These solvents vaporize during manufacture and post manufacturing, which leads to potential health issues for the manufacturing staff, the end users of the synthetic leather, and the environment. As a result, the European standard for the solvent PU based synthetic leather was changed to require less than 10 ppm DMF in the leather. Making such leathers is a challenge using organic solvent based methodologies. As a result, the use of solvent free or water borne PU (also known as polyurethane dispersion or PUD) has received attention, as it uses little, if any, organic solvent.

PUD is an aqueous emulsion of PU particles in water having high solid content, small particle size, and prolonged stability (up to six months or longer). When making synthetic leather using PUD, the following general method is used: 1) PUD is frothed 2) the frothed PUD is applied to a fabric, 3) the thickness of the frothed PUD is adjusted using methods known in the art, and 4) the now coated fabric is cured to form a synthetic leather having a poromeric layer. See U.S. Patent 7,306,825 for an example of this methodology.

Synthetic leather derived from PUD is similar to that made from PU and an organic solvent. It is breathable, and has good hand-feel. More importantly, the PUD synthetic leather is low in volatile organic compounds. However, while the PUD synthetic leather is acceptable, it does suffer from some disadvantages, such as poor peel strength perforaiance and high manufacturing costs. As a result, the application of PUD synthetic leather has been limited.

It would be advantageous to develop a PUD based synthetic leather that had improved peel strength performance and reduced cost of preparation.

Summary of the Invention

In one aspect, disclosed herein are methods for producing a poromeric synthetic leather having improved peel strength, the method comprising:

preparing a polyurethane prepolymer, wherein the prepolymer comprises at least one isocyanate resin, and at least one polyol; preparing a first mixture comprising the polyurethane prepolymer, and at least one surfactant;

preparing a second mixture comprising, the first mixture, water, and a chain extender;

preparing a third mixture comprising the second mixture, at least one surfactant and a thickening agent,

frothing the third mixture and thereby forming a frothed third mixture;

applying the frothed third mixture to a fabric that is optionally impregnated with a polyurethane resin and thereby forming a coated fabric;

optionally adjusting the thickness of the frothed third mixture on the fabric; and heating the coated fabric sufficiently to dry and cure it; wherein at least one nanoparticle is present in the polyurethane prepolymer, the first mixture, the second mixture, the third mixture, or combinations thereof. In another aspect, disclosed herein are poronieric, synthetic leathers comprising at least one nanoparticle that are made according to these methods.

Detailed Description

The following discussion applies to the leathers and methods described herein.

In one embodiment, the polyurethane prepolymer comprises an isocyanate resin, and the at least one nanoparticle added to the polyurethane prepolymer, the first mixture, or both. Typically, the nanoparticle is added to the first mixture and preferably, it is added before the formation of the second mixture.

The isocyanates used herein contain at least two isocyanate groups and include organic diisocyanates, which may be aromatic, aliphatic, or cyclo aliphatic, or a combination thereof. Representative examples of suitable diisocyanates include 4,4'- diisocyanatodiphenylmeihane, 2,4'-diisocyanatodiprienylmemane, isophorone diisocyanate, p-phenylene diisocyanate, 2,6 toluene diisocyanate, polyphenyl polymethylene

polyisocyanate, 1 ,3-bis(isocyanatomethyl)cyclohexane, 1 ,4-diisocyanatocyclohexane, hexamethylene diisocyanate, 1 ,5 -naphthalene diisocyanate, 3 ,3 '-dimethyl -4,4'-biphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, 2,4'-diisocyanatodicyclohexylmethane, and 2,4-toluene diisocyanate, or combinations thereof. More preferred diisocyanates are 4,4'-diisocyanatodicyclohexylmethane, 4,4'-diisocyanatodiphenyhnethane, 2,4'- diisocyanatodi-cyclohexylmethane, and 2,4'-diisocyanatodiphenylmethane. Most preferred are isophorone diisocyanate; 4,4'-diisocyanatodiphenylmethane (also known as 4,4'-MDI); and 2,4^,-diisocyanatodiphenylmethane (also known as 2,4'-MDI). The isocyanates may be purified or part of a mixture of one or more isocyanates. If an isocyanate is a solid, it may be melted and/or dissolved in a solvent before it used. .

All of the methods and leathers disclosed herein comprise at least one nanoparticle. In one embodiment, the nanoparticle is present in the polyurethane prepolymer, the first mixture, or both. Nanoparticles are particles with dimensions between 1 and 100 nanometers and are known in the art. As used herein, nanoparticles include mixtures of various particle sizes, which are typically in the 10-90 nm range. Examples of nanoparticles include CaC0₃, Ti0₂ and Si0₂. If desired, the surface of the nanoparticle may be modified with a compound in order to change the nanoparticles characteristics. For example, CaC0₃ may be made less hydrophilic by surface treatment with one or more fatty acids, acrylic acids, resin acids, stearic acid, boric acid esters, etc. When making CaC0₃ less hydrophilic, it is important to use a surface treating molecule that has a hydrophobic tail. Nanoparticles of CaC0₃ that have been surface modified with stearic acid have been used to increase the stiffness and toughness of polypropylene (see CM. Chan, J.S. Wu, J.X. Li, Y.K. Cheung, Polymer, 43 (2002), pp. 2981-2992.) and are preferred in at least one embodiment. If desired mixtures of different nanoparticles may be used. In one embodiment, the

nanoparticle is CaC0₃ (surface modified with stearic acid), Ti0₂, Si0₂, or a combination thereof. A preferred nanoparticle (when used alone or in combination with other nanoparticles) is CaC0₃ (surface modified with stearic acid).

Typically, the nanoparticles are present in 0.1 to 10%, based on the solid content of the PUD. More preferably, the nanoparticles comprise 0.3 to 7% of the solid content of the PUD.

And while the nanoparticles may be added to the prepolymer, the first mixture, the second mixture, the third mixture of combinations thereof, it is preferred to add the nanoparticles to the prepolymer and/or the first mixture.

The term "surfactants," as used herein, refers to any compound that reduces surface tension when dissolved in water or water solutions that reduces interfacial tension between two liquids, or between a liquid and a solid and/or acts to stabilize the bubbles in the poromeric layer. Surfactants useful for preparing a stable dispersion in the practice of the present invention may be cationic surfactants, anionic surfactants, zwitterionic, or a non- ionic surfactants. Examples of anionic surfactants include, but are not limited to, sulfonates, carboxylates, and phosphates. Examples of cationic surfactants include, but are not limited to, quaternary amines. Examples of non-ionic surfactants include, but are not limited to, block copolymers containing ethylene oxide and silicone surfactants, such as ethoxylated alcohol, ethoxylated fatty acid, sorbitan derivative, lanolin derivative, ethoxylated nonyl phenol or alkoxylated polysiloxane. Furthermore, the surfactants can be either external surfactants or internal surfactants. External surfactants are surfactants which do not become chemically reacted into the polymer during dispersion preparation. Examples of external surfactants useful herein include, but are not limited to, salts of dodecyl benzene sulfonic acid, and lauryl sulfonic acid salt. Internal surfactants are surfactants which do become chemically reacted into the polymer during dispersion preparation. Examples of an internal surfactant useful herein include, but are not limited to, 2,2-dimethylol propionic acid

(DMPA) and its salts, quaternized ammonium salts, and hydrophilic species, such

polyethylene oxide polyols. It should be understood that the surfactants that are most useful in the first mixture are not necessarily those that are most useful in the third mixture. In one embodiment, the surfactant(s) in the first mixture differ from the surfactant(s) in the third mixture.

Specific examples of surf actants include, for example, DABCO™ DC 193 (supplied by Air Products), which has Polydimethylsiloxane (PDMS) backbone and polyethylene oxide-co-propylene oxide (PEO-PPO) random copolymer grafts; TEGOSTAB™ B8488 (supplied by Evonik), which has a polydimethylsiloxane (PDMS) backbone and

polyethylene oxide-co-propylene oxide (PEO-PPO) random copolymer grafts with viscosity of 1000 cPs, insoluble in water; TEGOSTAB™ B8526 (supplied by Evonik), which has a polydimethylsiloxane (PDMS) backbone and polyethylene oxide-co-propylene oxide (PEO- PPO) random copolymer grafts with viscosity of 3000 cPs, insoluble in water;

TEGOSTAB™ B8535 (supplied by Evonik), which has a Polydimethylsiloxane (PDMS) backbone and polyethylene oxide-co-propylene oxide (PEO-PPO) random copolymer grafts with viscosity of 1200 cPs, Cloud point of 59C; and VORASURF™ 504 (supplied by The Dow Chemical Company), which is a polyethylene oxide-co-butylene oxide triblock organic surfactant with equivalent weight of 3400 and nominal viscosity of 3300 cPs at 25C, ammonium stearate, disodium octadecyl sulfosuccinimate, cocamidopropyl betaine, sodium dodecylbenzene sulfonate (RHODACAL DS-4, supplied by Rhodia), triethanolamine dodecylbenzene sulfonate, and sodium alpha olefin sulfonate. If desired, mixtures comprising more than one surfactant may be used.

Preferred surfactants in the first mixture are external surfactants. It is preferred that all surfactants in the first mixture be external surfactants. In one embodiment, preferred · external surfactants in the first mixture are sulfonate or sulfonic acid based. More specifically, preferred surfactants in the first mixture include sodium dodecylbenzene sulfonate, triethanol amine dodecylbenzene sulfonate, and sodium alpha olefin sulfonate. One especially preferred surfactant in the first mixture is sodium dodecylbenzene sulfonate.

Preferred surfactants in the third mixture help to stabilize the bubbles in the frothed, third mixture. Preferred surfactants in the third mixture comprise at least one of ammonium stearate, disodium octadecyl sulfosuccinimate and cocamidopropyl betaine. More preferably, the surfactant in the third mixture comprise at least two or even more preferably, all three of the aforementioned surfactants.

Chain extenders are always used when making the synthetic leathers disclosed herein. Chain extenders are bifuncational or polyfuncational, low molecular weight

(typically weighing from 18 up to 500 g mol) compounds that contain at least two active hydrogen containing groups. Any chain extender known to be useful to those of ordinary skill in the art of preparing polyurethanes can be used in the leathers and methods disclosed herein. Examples of chain extenders include diols, polyols, diamines, polyamines, hydrazides, acid hydrazides, and water. Of these, amine containing chain extenders and water are preferred. Furthermore, one or a combination of chain extenders may be used. For example, the chain extender may be mixed with or otherwise contain water.

Examples of chain extenders include water, piperazine, 2-mefhylpiperazine; 2,5- dimefhylpiperazine; 1 ,2-diaminopropane; 1 , 3-diaminopropane; 1 ,4-diaminobutane; 1 ,6- diaminohexane, isophorone diamine, mixtures of isomers of 2,2,4- and 2,4,4-trimethyl hexamethylene diamine, 2-methyl pentamethylene diamine, diethylene triamine, dipropylenetriamine, triethylenetetramine, 1,3- and 1,4-xylylene diamine, a,a,a',a'- tetramethyl-1,3- and -1,4-xylylene diamine and 4,4'-dicyclohexylmethanediamine_} 3,3'- dimethyl-4,4'-dicyclohexylmethanediainine, 1 ,2-cyclohexanediamine; 1 ,4- cyclohexanediamine, dimethyl ethylene diamine, hydrazine or adipic acid dihydrazide ethylene glycol; ethylene oxide; propylene oxide; aminoethylethanolamine (AEEA);

aminopropylethanolamine, aminohexylethanol mine; aminoethylpropanolamine, aminopropylpropanolamine, aminohexylpropanolamine; cyclohexane dimethanol; hydroquinone bis(2-hydroxyethyl)ether (also known as HQEE); ethanol amine;

diet anolamine; piperazine, JEFF AMINE D-230 (a polyetlier with two amino terminating groups, having a molecular weight of approximately 230 that is sold by the Huntsman Co.) , methyldiethanolamine; phenyldiethanolamine; diethyltoluenedi amine,

dimethyltliiotoluenediamine and trimethylolpropane. Particularly preferred chain extenders include water, AEEA, piperazine and 1,4-diaminobutane. The typical ratio of the NCO in the prepolymer to the diamine chain extender is 8: 1.

In one embodiment, two chain extenders are used. In such a situation, the first chain extender is water, and the second chain extender may be a diamine or polyamine based compound. Preferred diamines for use in this embodiment include piperazine and 1 ,4- diaminobutane, with 1,4-diaminobutane being the most preferred. When two chain extenders are used, they may be added simultaneously to the mixture, or sequentially.

The methods and leathers disclosed herein utilize at least two polyols, wherein the polyols are polyether polyols, polyester polyols, aromatic polyols, or combinations thereof. Polyols include one or more other polyether or polyesters polyols of the kind typically employed in processes to make polyurethanes. Other compounds having at least two isocyanate reactive hydrogen atoms may also be present, for example polythioether polyols, polyester amides and polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, amine terminated polyoxyalkylene polyethers, and preferably, polyester polyols, polyoxyalkylene polyether polyols, and graft dispersion polyols. Mixtures of two or more of the aforesaid materials may also be employed. In one preferred embodiment, the mixture of at least two polyols comprises at least one polyether polyol, and at least one polyester polyol.

It was unexpectedly found that using a mixture of two different polyols affords synthetic leathers having improved embossing characteristics.

The term "polyester polyol" as used herein includes any minor amounts of unreacted polyol remaining after the preparation of the polyester polyol and/or unesterified polyol (for example, glycol) added after the preparation of the polyester polyol. Suitable polyester polyols can be produced, for example, from aliphatic organic dicarboxylic acids with 2 to 12 carbons, preferably aliphatic dicarboxylic acids with 4 to 6 carbons, and multivalent alcohols, preferably diols, with 2 to 12 carbons. Examples of aliphatic dicarboxylic acids include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The corresponding dicarboxylic acid derivatives may also be used such as dicarboxylic acid mono-or di-esters of alcohols with 1 to 4 carbons, or dicarboxylic acid anhydrides. Examples of divalent and multivalent alcohols, especially diols, include ethanediol, diefhylene glycol, glycerine and trimethylolpropanes or mixtures of at least two of these diols. Polyester polyols derived from vegetable oils (natural oil polyols or NOPs) may also be used.

Useful aromatic polyols include aromatic polyether polyol or an aromatic polyester polyol or combinations of the two. Particularly desirably aromatic polyester polyol is an aromatic dicarboxylic acid with 8 to 24 carbons. While the aromatic polyester polyols can be prepared from substantially pure aromatic dicarboxylic acids, more complex ingredients are advantageously used, such as the side stream, waste or scrap residues from the manufacture of phthalic acid, terephthalic acid, dimethyl terephthalate, and polyethylene terephfhalate. Other residues are dimethyl terephthalate (DMT) process residues, which are waste or scrap residues from the manufacture of DMT. The present applicants have observed that for certain applications it is particularly advantageous for reasons of foam performance and processing to have present in the polyol composition both the "Novolac" polyol and an additional aromatic polyol which can be an aromatic polyether or aromatic polyester polyol.

Polyether polyols are compounds that have an ether backbone and further comprise at least two OH groups. Polyether polyols are commonly made by reacting monomelic compounds (either alone or in combination), such as glycerine (a triol), pentaerythritol (a tetraol), ethylene glycol (a diol), diethylene glycol (a diol of the formula:

HOCH₂CH₂OCH₂CH₂OH), and/or sucrose with ethylene oxide, propylene oxide and/or butylene oxide in the presence of an initiator and/or a catalyst. Suitable initiators include aliphatic and aromatic amines, such as monoethanolamine, vicinal toluenediamines, ethylenediamines, and propylenediamine. Useful catalysts include strong bases, such as NaOH, or KOH, and double metal cyanide catalysts, such as zinc hex cyano cobalt- 1- butanol complex. Common polyether polyols include polyethylene glycol (PEG), polypropylene glycol, and poly(tetramethlene ether)glycol. Preferred polyether polyols are comprised of monohydroxyl polyethylene oxide units. In a preferred embodiment, at least one of the polyols used herein is a polyether polyol having an average molecular weight of 400 to 1500 g/mol. Some preferred polyols include VORANOL 9287 A (a 2000 molecular weight, 12 percent ethylene oxide capped diol stabilized with alkyldiphenylamine, a product of The Dow Chemical Company); CARBOWAX Polyethylene Glycol (PEG) 1000 (CAS # 25322- 68-3, a 1000 molecular weight, polyethylene glycol monomethyl ether, >= 99.0 %, a product of The Dow Chemical Company); Bester 48 (a polyester polyol having a molecular weight of approximately 1,000, it is an ethylene glycol/butane diol/adipic acid (EG/BD/AA) type polyol that is a product of The Dow Chemical Company); Bester 104 (a DEG/IPA/AA based polyester polyol, i.e., a diethylene glycol/isopropyl alcohol/adipic acid based polyester polyol ); PEG 400 (a 400 molecular weight, polyether polyol based on ethylene oxide that is a product of the Sinopharm Chemical Reagent Corporation, Shanghai, China); PPG 425 (a propylene oxide based polyether polyol have a molecular weight of 425 that is a product of The Dow Chemical Company); and DEG (diethylene glycol, which is sold by Sigma).

The polyols used in the methods and leathers described herein typically weigh less than 5,000 g mol. More preferably, the polyols weigh less than 4,000 g/mol, with polyols having a molecular weight of less than 3,000 g/mol being even more preferred. Still more preferably, each polyol has an average molecular weight of less than 2000 g/mol.

The use of a strong base catalyst to make a polyether polyol often causes the polyether polyol to be too basic, which has a detrimental effect on the aforementioned prepolymer. Consequently, it is often necessary to treat the polyether polyol with a scavenger compound, which reacts with the residual base and makes the prepolymer more acidic. Suitable scavenger compounds include benzoyl chloride, and 85% phosphoric acid, with benzoyl chloride being preferred. Typically, adding aqueous acids introduces excess water into the prepolymer, which will react with the isocyanate and adversely impact the resulting leather. The inventors typically use a scavenger compound to adjust the net controlled polymerization rate of the mixture to be lower than -10. ASTM D 6437 - 05 corresponds to the CPR procedure.

In one embodiment, the methods and leathers utilize two polyols, wherein one polyol is a polyester polyol and the other is a polyether polyol. Alternatively, the two polyols are both polyether polyols.

In another embodiment, the methods and leathers utilize three polyols, wherein one polyol is a polyester polyol and the other two are polyether polyols. Alternatively, 1) two polyols are polyester polyols, while one polyol is a polyether polyol; 2) all three polyols are polyether polyols; or 3) all three polyols are polyester polyols.

In still another embodiment, the methods and leathers utilize four or more polyols. In such cases any combination of polyols may be used. Preferably, the polyurethane prepolymer contains less than five polyols.

In the methods and leathers disclosed herein, the weight ratio of the polyols to the isocyanate resin in the prepolymer is typically 1 :1 to 4:1. Preferably, the weight ratio is 1 :1 to 3 : 1. More preferably, the weight ratio is 2: 1 to 3: 1.

The weight ratio of the surfactant to the combined weight of the polyols and the isocyanate(s) is 1 :5 to 0.01 :5. More preferably this ratio is 0.3 :5 to 0.1 :5.

The weight ratio of water to the combined weights of the polyols, the isocyanate(s), surfactants and chain extender(s) is 25:75 to 99:1. More preferably, the ratio is 40:60 to 60:40.

In one embodiment, the polyurethane prepolymer is made by combining a liquid isocyanate resin and at least two liquid polyols. If necessary, solid isocyanate may be melted to form the liquid isocyanate resin.

In another embodiment, the polyurethane prepolymer is made by melting the isocyanate resin, heating the at least one polyol and then combining the melted isocyanate resin and the heated at least one polyol. Preferably, the melted isocyanate is combined with a mixture comprising at least two polyols, wherein the polyol mixture is heated to 50-90 °C before it is combined with the melted isocyanate. More preferably, the polyol mixture is heated to a temperature that is at least 60 °C; still more preferably, it is heated to at least 70 °C, with 80 ^DC being particularly preferred. If all reagents are liquids or if a solid reagent is soluble in the other liquid reagents, then the preheating of the polyol mixture is optional.

The methods require drying or otherwise treating curing the coated fabric (i.e., the optionally impregnated fabric that is coated with the frothed mixture) so that the synthetic leather forms. Any method known in the art, such as using UV light and/or heat may be used. Generally, heating takes place as quickly as practicable to fix the desired cell structure. The curing temperature may be any temperature suitable so long as the desired cell structure is retained and none of the components of the synthetic leather are decomposed. The heating time is desirably as short as practicable. Typical heating times range between seconds up to 1 hour. Any suitable heating method or heating energy source may be used such as a convection oven, heating plates, infrared oven, microwave heating or combination thereof. Suitable drying conditions include subjecting the froth coated fabric to 1) a constant temperature until dry, 2) a temperature gradient wherein the temperature changes over time, or 3) a multistep drying regime where the temperature is held for a set amount of time and then changed to a different temperature, which is then held for a set amount of time (3, 4, 5, or more drying steps may also be used). The drying times for each step may be the same or different. Typical drying times are from a few seconds up to one hour. Typical drying temperatures are in the range of at least 50 °C and no more than 250 °C. Preferably the temperature is at least about 75° C, more preferably at least about 90° C. In one embodiment, the temperature is 90-190 °C. and most preferably at most 170° C. One preferred example of a suitable drying protocol is to subject the froth covered, optionally impregnated fabric to a temperature of 95-105 °C for 4-10 minutes and then to a

temperature of 165-175 °C for 3-10 minutes. During the drying process, the water evaporates and the polyolefm sets (which may include melting of at least some of the material coated onto the fabric) and thereby forms the final coating. The drying process should not cause decomposition of any of the synthetic leather components.

Typically, the drying is performed in an oven at atmospheric pressure, but it can be performed at pressures above or below atmospheric pressure.

The synthetic leathers and methods described herein utilize a PUD mixture that may further comprise additional additives as is known in the art. Examples of suitable additives include Ν,Ν-dimethylethanolamine, fillers (such as wood fibers, Si0₂, Ti0₂, magnesium oxide, aluminium oxide, Talc, and/or glass beads), a thickener, a flame retardant, a pigment, a flowing additive, hand feel additive, antioxidant, anti-UV additive, antistatic agent, antimicrobial agent, or combinations thereof. Wood fibers also include wood flour. In one embodiment, the leathers and methods require the presence of at least one of the aforementioned additives.

The aforementioned fillers, when present, account for 0.1 -50 % by weight of the composition (excluding the fabric). More preferably, when present, the fillings account for 0.1 - 40 % by weight of the composition. Still more preferably, the fillers account for 0.1 - 30 % by weight of the composition.

The non-filler additives, i.e., the aforementioned additives, not including the fillers, typically account for 0.01-20 % by weight of the composition. More preferably, the non- filler additives account for 0.1-10 % by weight of the composition. Still more preferably, the non-filler additives account for 1-5 % by weight of the composition. Flowing additives, hand feel additives, antioxidants, anti-UV additives, antistatic agents, and antimicrobial agents are typically comprise less than 5% by weight of the composition. The additives may be added to the polyester polyol modified PUD, to the mixture comprising the polyester polyol modified PUD or combinations thereof.

In one embodiment, the first mixture, the second mixture, or both further comprise at least one of Si0₂ or Ti0₂.

Examples of pigments, include Ti0₂, carbon black and other, known pigments.

Pigments are well known in the art and typically present in less than 10% by weight, based on the dried leather.

Examples of flame retardants that may be used in the leathers and methods disclosed herein include those typically used to give enhanced flame retardant properties to a typical latex foam. Such flame retardants include phosphonate esters, phosphate esters, halogenated phosphate esters or a combination thereof. Representative examples of phosphonate esters include dimethylphosphonate (DMMP) and diethyl ethylphosphonate (DEEP).

Representative examples of phosphates esters include triethyl phosphate and tricresyl phosphate. When used the phosphonate or phosphate ester flame retardants are present in the final foam at a level of from 0.5 to 10 percent by weight of the final foam.

Representative examples of halogenated phosphate esters include 2-chloroethanol phosphate (C6Hi₂CI₂0₄P); l-chloro-2-propanol phosphate [tris(l-chloro-2-propyl) phosphate] (C₉H_lgCl₃0₄P) (TCPP); l,3-Dichloro-2-Propanol Phosphate (C₉Hi5Cl₆0₄P) also called tris(l₅3-dichloro-2-propyl) phosphate; tri(2-chloroethyl) phosphate; tri (2,2- dichloroisopropyl) phosphate; tri (2,3-dibromopropyl) phosphate; tri(l,3- dichloropropyl)phosphate; tetrakis(2-chloroethyl)ethylene diphosphate; bis(2-chloroethyl) 2-chloroethylphosphonate; diphosphates [2-chloroethyl diphosphate]; tetrakis(2-chloro ethyl) ethylenediphosphate; tris-(2-chloroethyl)-phosphate, tris-(2-chloropropyl)phosphate, tris- (2,3-dibromopropyl)-phosphate, tris(l,3-dichloropropyl)phosphate tetrakis (2-chloroethyl- ethylene diphosphate and tetrakis(2-chloroethyl) ethyl eneoxyethylenediphosphate. When used as a flame retardant, the halogenated phosphate ester will comprise 0.5 to 10 percent by weight of the final foam.

Dehydratable flame retardants, such as alkali silicates, zeolites or other hydrated phosphates, borosilicates or borates, alumina hydroxides, cyanuric acid derivatives, powdered melamine, graphites, mica, vermiculites, perlites, aluminohydrocalcite, liydromagnesite, thaumasite and wennlandite. A1₂0₃H₂0, and Alumina trihydrate, may also be used.

The dehydratable flame retardant is generally added to the polyurethane dispersion in an amount of from 5 to 120 parts per 100 parts dispersion solids of the final Compound. Preferably the flame retardant is added in an amount from 20 to 100 parts per 100 parts dispersion solids of the final Compound. More preferably the flame retardant is added in an amount from 50 to 80 parts per 100 parts dispersion solids of the final Compound.

Examples of hand feel additives include organic silicon compounds. When present, the amount of hand feel additive is 0.1% to about 10% by weight of the total weight of the dispersion. Preferably the amount of hand feel additive is between about 0.5% to about 5% by weight. In another embodiment, it is less than 3 % by weight.

Antioxidants are known in the art and include polymeric hindered phenol resins. In an embodiment according to any of the preceding aspects and/or embodiment(s), the synthetic leathers and methods described herein further comprise at least one additive that is Si0₂, wood fibers, Ti0₂, or combinations thereof.

In another embodiment of any of the previously described aspects and/or embodiments, the mixture further comprises at least one additive that is a flame retardant, a pigment, a flowing additive, hand feel additive, antioxidant, anti-UV additive, or combinations thereof. Typically, these additives comprise 0.01 to 10% by weight of the solid content. More preferably, these additives comprise 0.1 -8% by weight (still more preferably, 2-5%) of the solid content.

The leathers disclosed herein typically are comprised of 0.1-99% PUD based on the weight of the pre-dried mixture. Preferably, the leathers are comprised of 60-99% PUD based on the weight of the pre-dried mixture. Still more preferably, the leathers are comprised of 70-95% PUD based on the weight of the pre-dried mixture.

In the leathers and methods of making the leathers disclosed herein, the PUD has a solid content of at least 25% by weight. In one embodiment, the PUD has a solid content that is 25-65 % by weight. More preferably the solid content of the PUD is at least 30% or more preferably at least 3 % by weight. More preferably still, the solid content is at least 40% or 45%.

In another embodiment, the methods for producing synthetic leathers comprise the following: the polyurethane prepolymer comprises a liquid isocyanate resin and two polyols; the second mixture is made by 1) combining the prepolymer with a mixture comprising a surfactant, wherein said mixture is made by combining at least one surfactant and at least one nanoparticle, and then 2) adding water and the chain extender;

preparing the third mixture comprises combining the second mixture, a thickening agent and at least three surfactants;

frothing the third mixture;

applying the frothed third mixture to an optionally impregnated fabric and thereby forming a coated fabric;

adjusting the thickness of the frothed third mixture on the coated fabric; and heating the coated fabric sufficiently to dry and cure it; wherein

the synthetic leather is a poromeric leather having improved peel strength.

In a preferred embodiment of any of the previously disclosed methods, the liquid isocyanate resin comprises 4,4'-methylenediphenyl diisocyanate and the two polyols in the first mixture are propyleneglycol-propylene oxide-ethyl ene oxide polymer (CAS # 53637- 25-5) and a polyethylene glycol monomethyl ether based polyol.

In another preferred embodiment of any of the previously disclosed methods, in the second mixture, the surfactant is sodium dodecylbenzene sulfonate, the chain extender is amino ethyl ethanol amine, and the nanoparticle is CaC0₃ that was surface modified in order to increase its hydrophobicity, Si0₂, or Ti0₂. One preferred surface modifier for the CaC0₃ is stearic acid.

In still another preferred embodiment of any of the previously disclosed methods, in the third mixture, the at least three surfactants comprise ammonium stearate, disodium octadecyl sulfosuccinimate and cocamidopropyl betaine; and wherein the synthetic, poromeric leather has a peel strength that is at least 25% higher than a corresponding synthetic, poromeric leather that does not contain a nanoparticle.

In one embodiment of any of the aforementioned methods, the solid content of the second mixture is 25-65 % by weight.

And as previously mentioned, disclosed herein are synthetic leathers made according to the any and all of the previously disclosed methods.

In an embodiment according to any of the preceding aspects and/or embodiment(s), the synthetic leathers and methods described herein utilize a fabric, which is coated with the mixture comprising PUD and optionally, latex. Many different fabrics that are known in the art may be used. The fabric may be woven or nonwoven. The fabric may be made by any suitable method such as those known in the art. The fabric may be prepared from any suitable fibrous material, such as, but not limited to, synthetic fibrous materials and natural or semi synthetic fibrous materials and mixtures or blends thereof. Examples of synthetic fibrous materials include polyesters, polyamides, acrylics, polyolefins, polyvinyl chlorides, polyvinylidene chlorides, polyvinyl alcohols and blends or mixtures thereof. Examples of natural semi-synthetic fibrous materials include cotton, wool and hemp. One preferred fabric is needled cotton and polyester fiber hybrid woven fabric having short fibers (less than 1 mm) on the surface.

Another preferred fabric is needled cotton and polyester fiber hybrid woven fabric having long (greater than 3 mm) fibers on the surface.

Acceptable resins include isocyanate containing resins, such as polyisocyanates (which contain at least two isocyanate groups) were discussed above.

The impregnation of the fabric may be conducted by any suitable method known in the art. Examples include dipping, spraying or doctor blading. After impregnating, the impregnated textile may have excess resin removed to leave the desired amount of dispersion within the textile. Typically, this may be accomplished by passing the

impregnated textile through rubber rollers.

Generally, the impregnated fabric is impregnated with a resin in an organic solvent

(which makes a solution) or water (which makes a dispersion). Typical solvents include dimethylfomiamide (DMF), methylethyl ketone (MEK) and toluene, although other solvents will afford acceptable results. Generally, the organic solvent used to impregnate the fabric will contain 0.5-50% by weight of resin. More preferably, the organic solvent will contain 5-30% by weight of resin. Still more preferably, 15-25% by weight of resin.

If the fabric is impregnated with a resin in an organic solvent, then typical solvents include dimethylfonnainide (DMF), methylethyl ketone (MEK) and toluene, although other solvents will afford acceptable results. Generally, the organic solvent used to impregnate the fabric will contain 0.5-50% by weight of resin. More preferably, the organic solvent will contain 5-30% by weight of resin. Still more preferably, 15-25% by weight of resin.

The frothed mixture may be applied to the fabric using any suitable method known in the art. Examples include using a Labcoater type LTE-S (Werner Mathic AG). Likewise, the thickness of the froth on the fabric can be adjusted using methods known in the art. Examples include using a doctor blade assembly.

The methods require drying or otherwise treating/curing the coated fabric (i.e., the optionally impregnated fabric that is coated with the frothed mixture) so that the synthetic leather forms. Suitable drying conditions include subjecting the froth coated fabric to 1) a constant temperature until dry, 2) a temperature gradient wherein the temperature changes over time, or 3) a multistep drying regime where the temperature is held for a set amount of time and then changed to a different temperature, which is then held for a set amount of time (3, 4, 5, or more drying steps may also be used). The drying times for each step may be the same or different. Typical drying times are from a few seconds up to one hour. One example of a suitable drying protocol is to subject the froth covered, optionally impregnated fabric to a temperature that is at least 80 °C and no more than 250 °C. More preferably, the optionally impregnated fabric is heated to a temperature of 80-105 °C for 4-10 minutes and then to a temperature of 165-175 °C for 3-10 minutes. During the drying process, the water evaporates and the polyolefin sets (which may include melting of at least some of the material coated onto the fabric) and thereby forms the final coating. The drying process should not cause decomposition of any of the synthetic leather components.

In one embodiment, the polyester polyol modified PUD, the filler or fillers, and the other additives comprise 0.1-99.9% by weight of the total composition. More preferably, they comprise 60-99.9% by weight of the total composition. Still more preferably, 70-99.9 % by weight of the total composition.

Impregnating the fabric will afford synthetic leather having improved peel strength relative to synthetic leathers that were made from fabrics that were not impregnated.

In one embodiment, the solid content of the second mixture is 15-75 % by weight. More preferably, it is 25-45 % by weight.

At least one thickener is added to the PUD before it is frothed. Thickeners are well known in the art and any thickener may be used in the leathers and methods disclosed herein. The thickener may be non-associative or associative. It may be a cellulose ether derivative, natural gum alkali swellable emulsion, a clay, an acid derivative, an acid copolymer, a urethane associate thickener (UAT), a polyether urea polyurethane (PEUPU), a polyether polyurethane (PEPU) or a hydrophobically modified ethoxylated urethane (HEUR). One preferred thickener is based on an acrylic acid copolymer, with ethylene acrylic acid copolymer (which is sold by The Dow Chemical Company as ACUSOL 81 OA) being particularly preferred. Preferably, the thickener does not cause the PUD containing mixture to become unstable. If desired, a combination of thickeners may be used.

Examples of thickeners include those that do not cause the dispersion to become unstable. More preferably, the rheological modifier is a water soluble thickener that is not ionized. Examples of useful thickeners include methyl cellulose ethers, alkali swellable thickeners (e.g., sodium or ammonium neutralized acrylic acid polymers), hydrophobically modified alkali swellable thickeners (e.g., hydrophobically modified acrylic acid

copolymers) and associative thickeners (e.g., hydrophobically modified ethyl ene-oxide- based uretliane block copolymers). Preferably the rheological modifier is a methylcellulose ether. The amount of thickener may be any useful amount. Typically the amount of thickener is at least about 0.1% to about 10% by weight of the total weight of the dispersion. Preferably the amount of thickener is between about 0.5% to about 7% by weight.

Experimental Procedures and Data

Table 1. Raw material information for PUD/NPs hybrids and fabrics

Component Grade name Characteristic Supplier

2000 MW, 12% EO

Polyol VORANOL 9287A Dow

Capped, PO diol.

CARBOWAX™ MW=1000,Polyethylene

Polyol Methoxy polyethylene glycol monomethyl ether Dow

Glycol 1000 >= 99.0 %

4,4' -Methyl enediphenyl

Isocyanate Isonate 125 M Dow

diisocyanate =98%

Sodium dodecylbenzene

surfactant Rhodacal DS-4 Rhodacal

sulfonate(23% solid)

Chain Amino Ethyl Ethanol Amino Ethyl Ethanol

TCI

Extender Amine Amine

Nanoparticle CaC0₃ (70 nm, surface Shanghai

SPT

(NP) modified by stearic acid) HuaMing

Fabric Needled cotton and Solvent PU impregnated

polyester fiber hybrid Hongdeli woven fabric Note: The fabric was impregnated with 18% PU DMF solution, which was made by Hongdeli. Comparative Example; Syntegra 3000 PUD control sample.

Prepolymer: PU prepolymer is prepared by charging 180 g Isonate 125 M into a three-neck flask, which was heated at 45° C for melt solid MDI to liquid. 408 g Voranal 9287A, 12 g MPEG 1000 is preraixed and warmed at 55° C for lh before added to flask. Increase the temperature to 80 °C, keep 80 °C for 4-5 h to reach the target NCO% of 7.1 % (NCO:OH=3.43).

PU dispersion: 524.2 g prepolymer was placed in a plastic jar. The jar was clamped and a Cowles blade was inserted into prepolymer such that the blade is just covered by prepolymer. 71.74 g DS-4 mixture was charged into prepolymer, following this procedure, the mixture was stirred with Cowles blade at 3000 rpm, and cold DI water (5 °C) is added into the mixture slowly as the water-in-oil was converted into an oil-in- water dispersion. A solution of 92.29 g chain extender (10% AEEA in water) is slowly fed into the dispersion with random stirring. The solid content of final dispersion PUD Syntegra 3000 is 55%.

Synthetic leather'. A poromeric layer of the synthetic leather was made using frothing PUD. The frothing PUD dispersion had a solids content of 50-55 percent by weight with ammonium stearate (STANFAX 320, Para-chem), disodium octadecyl sulfosuccinimate (STANFAX 318, Para-chem), cocamidopropyl betaine (STANFAX 590, Para-chem) and acrylic acid copolymer thickener (ACUSOL 81 OA, Dow). The thickened PUD viscosity was controlled to 17000cp to 28000cp. The detailed PUD fomiulations appear in Table 3.

To make a synthetic leather having a poromeric layer, the fabric was attached to pin frame. The frothing PUD was frothed using a Model 2MT1A foam machine (E.T. OAKES Corp.) run at lOOOrpm. The wet froth density was about 0.50-0.85g/cm3. The froth was applied to fixed fabric using a Labcoater type LTE-S (Werner MAthic AG). The doctor knife was positioned at 1.8-2.5mm between the roller and knife (including resin and fabric). The frothed dispersion was dispersed and the doctor bladed to foam a coating of frothed PUD on the fabric. The coated fabric was then placed in an oven at 100°C for 6-10min, which was then heated to 170°C in about 5min to form the synthetic leather having a poromeric layer. Table 2. PUD poromeric fonnulation

Inventive Example.

The PUDs in inventive examples had similar process with comparative example, the fonnulation differences are summarized in Table 3. The difference between new PUDs and Syntegra 3000 is just replacing some amount of prepolymer with nanoparticles.

Table 3 Formulation of PUDs

% (20% of the NCO groups (based on the number of moles) react with the diamine chain extender, AEEA, while the other 80% react with water). Example 1 : Sample 1 based on PUD 1

Prepolymer: PU prepolymer is prepared by charging 180 g Isonate 125 M into a three-neck flask, which was heated at 45 °C for melt solid MDI to liquid. 408 g Voranal 9287A and 12 g MPEG 1000 is premixed and warmed at 55 °C for 1 h before added to flask. Increase the temperature to 80 °C, keep 80 °C for 4-5 h to reach the target NCO%=7.1%.

PU/NPs dispersion: mix 2 g nano CaC0₃ into 71.74 g DS-4 surfactant with stir at 3000 rpm for 5 min to get fine mixture. 522.2 g prepolymer was placed in a plastic jar. The jar was clamped and a Cowles blade was inserted into prepolymer such that the blade is just covered by prepolymer. DS-4/nano CaC03 mixture was charged into prepolymer, following this procedure, the mixture was stirred with Cowles blade at 3000 rpm, and cold DI water (5 °C) is added into the mixture slowly as the water-in-oil was converted into an oil-in- water dispersion. A solution of 93 g chain extender (10% AEEA in water) is slowly fed into the dispersion with random stirring. The solid content of final dispersion is 55%, with NPs content of 0.36% in solid.

The peel strength improved PUD porometic layer had the similar process with control sample. The different amount of thickener is just for adjusting viscosity of the resins. The materials are summarized in Table 4. Table 4 New poromeric layer formulations

Control sampe Sample 1 Sample 2

Materials Weight / g Weight / g Weight / g

Syntegra 3000 1000 - -

Nanoparticle

(CaC0₃, present - 2 35.9

in the PUD)

PUD 1 - 1500

PUD 2 - - 2000

Stanfax 320 40 60.6 80.0

Stanfax 590 11.3 17.1 22.6

Stanfax 318 13.1 19.6 26.2

Acusol 81 OA 60 80 100 Viscosity / cp 17900 18700 17000

Example 2: Sample 2 based on PUD 2

Prepolymer: PU prepolymer is prepared by charging 180 g ISONATE 125 M into a three-neck flask, which was heated at 45° C for melt solid MDI to liquid. 408 g Voranal 9287A and 12 g MPEG 1000 is premixed and warmed at 55 °C for Ih before added to flask. Increase the temperature to 80 °C and maintain at 80 °C for 4-5 hours in order to reach the target NCO%.

PU/NPs dispersion: mix 35.9 g nano CaC0₃ into 71.74 g DS-4 surfactant with stir at 000 rpm for 5 min. to get fine mixture. 488.3 g prepolymer was placed in a plastic jar. The jar was clamped and a Cowles blade was inserted into prepolymer such that the blade is just covered by prepolymer. DS-4/nano CaC0 mixture was charged into prepolymer, following this procedure, the mixture was stirred with Cowles blade at 3000 rpm, and cold DI water (5 °C) is added into the mixture slowly as the water-in-oil was converted into an oil-in- water dispersion. A solution of 84.8 g chain extender (10% AEEA in water) is slowly fed into the dispersion with random stirring. The solid content of final dispersion is 55%, with NPs content of 6.5% in solid.

The peel strength improved PUD porometic layer had the similar process with control sample. The different amount of thickener is just for adjusting viscosity of the resins.

Peel strength test:

Peel strength tests were conducted according to GB/T 8949-2008 Chinese Standard. The synthetic leather was cut into two 15cmxl2cm leather sheets. These two leather sheets were glued together by suitable adhesive leaving about 5cm (in the length direction) trips where no adhesive was applied. The two pieces were allowed to press by 5 g steel plate, dry and cured over 24 hours. The bonded sheet was cut along the length direction into 4 pieces of samples with 15cm> 3cm. These 4 samples were tested by Instron machine with speed of 200cm min.

PUD Viscosity measurement Bulk viscosities of the thickened PUD before f othing were measured using a Brookfield viscometer with a 20rpm #6 spindle.

Results of Leather peel strength:

Table 6 Peel strength of the poromeric layer samples

Table 6 summarized the peel strength of different samples. The peel strength was increased from 45N/(3cm) (control sample) to 90N/(3cm) (sample 1) when we add 0.36% nano CaC0₃ in PUD. When the nano CaC0₃ loading increased from 0.36% to 6.5%, the peel strength of Sample 2 was slightly decreased relative to Sample 1, but was still much better than the control sample.

Claims

WHAT IS CLAIMED IS:

1. Methods for producing a poromeric synthetic leather having improved peel strength, the method comprising:

preparing a polyurethane prepolymer, wherein the prepolymer comprises at least one isocyanate resin, and at least one polyol;

preparing a first mixture comprising the polyurethane prepolymer, and at least one surfactant;

frothing the third mixture and thereby forming a frothed third mixture;

optionally adjusting the thickness of the frothed third mixture on the fabric; and heating the coated fabric sufficiently to dry and cure it; wherein at least one nanoparticle is present in the polyurethane prepolymer, the first mixture, the second mixture, the third mixture, or combinations thereof.

2. Methods according to claim 1 , wherein the polyurethane prepolymer comprises an isocyanate resin, and wherein the at least one nanoparticle is added to the polyurethane prepolymer, the first mixture, or both.

3. Methods according to claims 1 or 2, wherein the polyurethane prepolymer comprises

4,4'-methylenediphenyl diisocyanate.

4. Methods according to claims 1 - 3, wherein the nanoparticle is present in the first mixture.

5. Methods according to any one of claims 1-4, wherein at least one surfactant in the first mixture is an external surfactant.

6. Methods according to any one of claims 1-5, wherein the chain extender comprises water, at least one diamine, or a combination thereof.

7. Methods according to any one of claims 1-6, wherein the nanoparticle comprises CaC0₃, Ti0₂, Si0₂, or a combination thereof.

8. Methods according to any one of claims 1-7, wherein the prepolymer comprises at least two polyols.

9. Methods according to claims 1-8, wherein at least one polyol is a polyether polyol.

10. Methods according to claims 1-9, wherein preparing the prepolymer comprises melting the isocyanate resin, heating the at least one polyol and then combining the heated isocyanate resin and the heated at least one polyol.

11. Methods according to claims 1-10, wherein the/drying is conducted at a temperature that is at least 80 °C and no more than 250 °C.

12. Methods according to any one of claims 1-11, wherein the first mixture, the second mixture, or both further comprise at least one of Si0₂ or Ti0₂.

13. Methods according to any one of claims 1-12, wherein the polyurethane in water has a solid content of 25-65 % by weight.

14. Methods according to claims 1-13, wherein the isocyanate resin is melted before being combined with at least one polyol.

15. Methods for producing synthetic leather according to any one of claims 1-14, wherein:

the polyurethane prepolymer comprises a liquid isocyanate resin and two polyols; the second mixture is made by 1 ) combining the prepolymer with a mixture comprising a surfactant, wherein said mixture is made by combining at least one surfactant and at least one nanoparticle, and then 2) adding water and the chain extender;

frothing the third mixture;

the synthetic leather is a poromeric leather having improved peel strength.

16. Methods according to claims 1-15, wherein the liquid isocyanate resin comprises 4,4'-methyoenediphenyl diisocyanate and the two polyols in the first mixture are propyleneglycol-propylene oxide-ethylene oxide polymer (CAS # 53637-25-5) and a polyethylene glycol monomethyl ether based polyol.

17. Methods according to claims 1-16, wherein in the second mixture, the surfactant is sodium dodecylbenzene sulfonate, the chain extender is amino ethyl ethanol amine, and the nanoparticle is CaC0 that was surface modified in order to increase its hydrophobicity, Si0_2; or Ti0₂.

18. Methods according to claim 1-17, wherein in the third mixture, the at least three surfactants comprise ammonium stearate, disodium octadecyl sulfosuccinimate and cocamidopropyl betaine; and wherein the synthetic, poromeric leather has a peel strength that is at least 25% higher than a corresponding synthetic, poromeric leather that does not contain a nanoparticle.

1 . Synthetic leathers made according to the methods of any one of claims 1-1 .