Solvent-free base and method for producing the same

Technical field

The present invention relates to a solvent-free base and a method for producing the same.

Background art

Synthetic leather has been used in various fields of daily life and is becoming increasingly popular. Synthetic leather can be divided into solvent-borne synthetic leather, water-borne synthetic leather, and solvent-free synthetic leather according to production processes.

In the production process of solvent-borne synthetic leather, organic solvents, such as dimethylformamide (DMF), are required to dissolve polyurethane (Pll) resins, and then water is used to replace the DMF, so that the coating has continuous pores and thus has moisture permeability and air permeability. Solvent-borne synthetic leather uses a large amount of organic solvents, such as DMF, toluene, etc., which will cause serious ecological and environmental pollution and are detrimental to people’s health. In addition, the residual solvents in products not only cause continuous pollution, but also affect the quality of the finished leather and user experience.

In order to overcome the disadvantages of solvent-borne synthetic leather, waterborne synthetic leather has been developed, using water instead of organic solvents. However, the process for producing water-based synthetic leather consumes a significant amount of energy, and its physical properties can also be affected to some extent.

Therefore, solvent-free synthetic leather has been developed. The solvent-free process adopts the principle of reaction molding. Taking Pll as an example, the Pll raw materials are mixed, applied to a fabric, and then sent to a drying tunnel. The Pll raw materials are reacted and molded to form a Pll coating. The solvent-free process requires no solvents, and can realize rapid prototyping, low emission and low pollution. Solvent-free Pll synthetic leather is not only as good as solvent-borne synthetic leather with respect to high mechanical strength, wear resistance, aging resistance, and good elasticity, but also has the advantages of being non-toxic, pollution-free, low energy consumption, and good moisture permeability and air permeability. So, solvent-free synthetic leather has been more and more attracting the interest of people. In the prior arts, solvent-free synthetic leather is usually produced by a single manufacturer using Pll raw materials, that is, the Pll raw materials are mixed, knife coated, and sprayed on a fabric, and then sent to a drying tunnel; the Pll raw materials are reacted and molded to obtain a Pll layer. Then, an adhesive is applied to a Pll layer which is not yet completely cured, and a topcoat is applied to the adhesive layer, and cured to obtain a complete synthetic leather.

However, this approach has the following problems: 1) the manufacturer needs to provide a long drying tunnel for curing, which requires a high investment cost and a long time on modification when modifying the process; 2) for solvent-free processing, a large number of experienced workers are needed, but many small to medium size synthetic leather manufacturers do not have such knowledge; 3) for two-component Pll, a low pressure mixer is required, which greatly increases the production cost.

There is an urgent need to address these problems in the art.

Summary

It is an object of the present invention to overcome the above-mentioned disadvantages of the prior arts. Therefore, the present invention provides a solvent- free base, which comprises a substrate layer and a polyurethane layer, preferably consists of a substrate layer and a polyurethane layer. This base can be used to produce synthetic leather by downstream manufacturers. Downstream manufacturers only need to apply adhesive directly to it, and then apply a topcoat to obtain a finished synthetic leather. Thus, it saves investment costs for downstream manufacturers with respect to, for example, long drying tunnels, low pressure mixers, and training for skilled workers. In addition, compared with the solvent-borne synthetic leather and solvent-free synthetic leather in the prior art, this synthetic leather has comparable or even better peeling, flexing and other properties. In particular, this preparation process provides a better feel, as it involves directly applying a polyurethane system to the substrate layer without a step of physical squeezing. In addition, the solvent-free base of the present invention can be wound up without sticking, and is stable for storage, thus allowing for long-distance transportation or long-term storage.

In addition, the present invention also provides a solvent-free base, which is produced by a process comprising the steps of:

1a) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer,

3a) curing the components of the polyurethane system to form a polyurethane layer; or the base is produced by a process comprising the steps of:

1b) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system,

5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

Moreover, the present invention also provides a process for producing solvent-free base, which comprises the steps of: la) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer,

3a) curing the components of the polyurethane system to form a polyurethane layer; or the process comprising the steps of: lb) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system,

5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

The present invention will be described hereinbelow in more detail.

Solvent-free base of the present invention

In one embodiment of the present invention, the present invention relates to a solvent-free base, which comprises a substrate layer and a polyurethane layer, preferably consists of a substrate layer and a polyurethane layer. In the context of the present invention, “BASE” refers to an intermediate product used in the production of synthetic leather, which is formed by coating a polyurethane (Pll) layer atop a substrate layer. When using base to produce synthetic leather, an adhesive is optionally applied to the base, followed by a topcoat and curing to obtain the finished synthetic leather.

In the context of the present invention, “essentially free of organic solvents” means that the base does not contain organic solvents, for example, contains less than 500 ppm of organic solvents, more preferably less than 200 ppm, and most preferably less than 10 ppm.

In the context of the present invention, organic solvents include ethers or glycol ethers (such as diethyl ether, dibutyl ether, anisole, dioxane, tetrahydrofuran), ketones (such as acetone, butanone, cyclohexanone), esters (such as ethyl acetate), nitrogen compounds (such as dimethylformamide (DMF), pyridine, N- methylpyrrolidone, acetonitrile), sulfur compounds (such as carbon sulfide, dimethyl sulfoxide, sulfolane), nitro compounds (such as nitrobenzene), halogenated hydrocarbons (such as dichloromethane, chloroform, tetrachloromethane, trichloroethylene, tetrachloroethylene, 1,2-dichloroethane, chlorofluorocarbons), hydrocarbons (such as octane, methylcyclohexane, decalin, benzene, toluene, xylene).

In principle, the substrate layer can be any layer capable of forming an adhesion to the obtained polyurethane layer.

The thickness of the substrate layer is typically in the range of from 0.01 mm to 20 mm, preferably in the range of from 0.1 mm to 10 mm and especially in the range of from 1 mm to 5 mm.

Various kinds of substrate layers are useful for the process of the present invention, for example:

A fabric substrate layer: in this case the substrate layer can consist of one or more, identical or different, firmly interconnected plies, for example of narrowly or widely meshed wovens, knits, braids, networks (net cloths).

Batt substrate layer: sheetlike structures composed of randomly disposed fibers (examples being felts and fibrous webs), which may preferably be bound together by a binder. Batt substrate layers are usually cellulosic or textile batts consolidated with water-insoluble impregnants.

Fibrous substrate layer: articles of manufacture composed of loose, randomly disposed fibers which are consolidated by plastics being used as a binder. They are obtained for example by adhering together leather fibers (preferably obtainable from leather waste, for example from vegetable-tanned leather) with from 8 to 40% by weight of a binder.

Foil substrate layer: articles of manufacture comprising (preferably homogeneous) foils composed of metal or plastic, for example rubber, PVC, polyamides, interpolymers and the like. A foil substrate layer preferably comprises no incorporated fiber.

Leather substrate layer: it can be natural leather or synthetic leather.

One embodiment utilizes a leather substrate layer as the substrate layer. When a leather substrate layer is used, the leather in question is preferably split leather.

When a fabric substrate layer is used, the following materials will be particularly suitable to produce the fabric substrate layer: cotton, linen, polyester, polyamide and/or polyurethane.

According to the present invention, the thickness of the polyurethane layer is typically in the range of from 0.01 mm to 20 mm, preferably in the range of from 0.1 mm to 10 mm and more preferably in the range of from 0.5 mm to 5 mm.

The application of components of the polyurethane system atop the substrate layer or release layer is carried out by knife coating. The production line of a solvent-free knife coating process according to the present invention can be obtained by appropriately improving a traditional oily dry process line only with a small amount of investment. In addition, compared to a spraying process, the knife coating process hardly wastes any raw materials during the coating process. However, the spray coating process generally wastes from 15 to 30% of chemicals or even more due to different spraying process conditions. Therefore, the knife coating process saves more raw materials. After knife coating, there is no need to press the obtained base to reduce its thickness. In this way, the thickness can be maintained, achieving the goal of using fewer materials and thus saving production costs.

The polyurethane layer can be foamed or non-foamed (i.e. , compact), preferably foamed. The polyurethane layer is completely cured.

The polyurethane layer is formed from a polyurethane system, which can be a one- component (1 K) polyurethane system or a two-component (2K) polyurethane system.

1K polyurethane system

In one embodiment of the present invention, the polyurethane system is a 1 K polyurethane system. The 1K polyurethane system may contain at least one isocyanate (NCO) terminated polyurethane prepolymer as a resin component, and be cured by the reaction of NCO groups with crystal water from fillers or moisture from the surrounding environment.

NCO terminated polyurethane prepolymers are obtained by reacting polyols or polyol mixtures with a stoichiometric excess of di- or polyisocyanates. The polyols used in the preparation of the prepolymers can be any polyols commonly used in polyurethane synthesis, such as polyester polyols, polyether polyols, or a mixture thereof, preferably polyether polyols or a mixture thereof.

The polyether polyols are obtained by known processes, for example via anionic or cationic polymerization of alkylene oxides with addition of at least one starter molecule comprising from 2 to 8, preferably from 2 to 6, and particularly preferably from 2 to 4, reactive hydrogen atoms, in the presence of catalysts. Catalysts used can comprise alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, or alkali metal alcoholates, such as sodium methoxide, sodium ethoxide, potassium ethoxide, or potassium isopropoxide, or, in the case of cationic polymerization, Lewis acids, such as antimony pentachloride, boron trifluoride etherate, or bleaching earth. Other catalysts that can be used are double-metal cyanide compounds, also known as DMC catalysts.

The alkylene oxides used preferably comprise one or more compounds having from 2 to 4 carbon atoms in the alkylene moiety, e.g. tetrahydrofuran, ethylene oxide, propylene 1 ,2-oxide, butylene 1 ,2-oxide or butylene 2,3-oxide, in each case alone or in the form of a mixture, and preferably propylene 1 ,2-oxide, ethylene oxide and/or tetrahydrofuran.

Examples of starter molecules that can be used are ethylene glycol, propylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, sugar derivatives, such as sucrose, hexitol derivatives, such as sorbitol, methylamine, ethylamine, isopropylamine, butylamine, benzylamine, aniline, toluidine, toluenediamine, naphthylamine, ethylenediamine, diethylenetriamine, 4,4’-methylenedianiline, 1 ,3- propanediamine, 1 ,6-hexanediamine, ethanolamine, diethanolamine, triethanolamine, and also other di- or polyhydric alcohols, or di- or polybasic amines.

The polyether polyols used for synthesizing polyurethane prepolymers may have an average molecular weight of from 100 to 10,000 g/mol, preferably from 500 to 8000 g/mol, and more preferably from 1000 to 5000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 20 to 70 mg KOH/g, and most preferably from 25 to 60 mg KOH/g.

The polyester polyols used are mostly produced via condensation of polyhydric alcohols having from 2 to 12 carbon atoms, e.g. ethylene glycol, diethylene glycol, butanediol, trimethylolpropane, glycerol, or pentaerythritol, with polybasic carboxylic acids having from 2 to 12 carbon atoms, e.g. succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, and the isomers of naphthalenedicarboxylic acids, or their anhydrides.

The polyester polyols used for synthesizing polyurethane prepolymers can have an average molecular weight of from 100 to 20,000 g/mol, particularly from 330 to 4,500 g/mol, and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 20 to 70 mg KOH/g, and most preferably from 25 to 60 mg KOH/g.

In one preferred embodiment of the present invention, the polyol used for synthesizing NCO terminated polyurethane prepolymer is a mixture of polyether polyols, comprising:

(i) polypropylene glycol, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 1000 to 4000 g/mol, and most preferably from 1500 to 2500 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 50 to 60 mg KOH/g; and

(ii) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 2000 to 5000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 600 to 5000 g/mol, preferably from 800 to 4000 g/mol, more preferably from 1000 to 3500 g/mol, and most preferably from 1500 to 3000 g/mol; and a hydroxyl value of from 10 to 100 mg KOH/g, preferably from 30 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 45 to 65 mg KOH/g, and which is terminated by primary hydroxyl groups.

Surprisingly, it has been found that this polyol mixture ensures reaction activity with isocyanates, good implementability of the process, as well as the good feel and physical properties, such as peeling, tearing, winding properties, of the final leather.

The raw materials used for synthesizing NCO terminated polyurethane prepolymers may include conventional chain extenders. Useful chain extenders are known in the art. Preference is given to using diols having molecular weights below 400 g/mol, in particular in the range of from 60 to 150 g/mol. Examples are ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, dipropylene glycol, tripropylene glycol, preferably ethylene glycol or 1 ,4-butanediol. The di- or polyisocyanates used include conventional aliphatic, cycloaliphatic, or aromatic di- and/or polyisocyanates, preferably aromatic di- and/or polyisocyanates.

The aliphatic di- and/or polyisocyanates can be selected from ethylene diisocyanate, 1 ,4-tetramethylene diisocyanate, 1 ,6-hexamethylene diisocyanate, 1 ,12-dodecane diisocyanate, and a mixture thereof; in particular, 1 ,6-hexamethylene diisocyanate trimer (HDT), 1 ,12-dodecane diisocyanate, and a mixture thereof.

The cycloaliphatic di- and/or polyisocyanates can be selected from cyclobutane 1 ,3-diisocyanate, cyclohexane 1 ,3-diisocyanate, cyclohexane 1 ,4-diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6-diisocyanate, hexahydrophenylene 1 ,3-diisocyanate, hexahydrophenylene 1 ,4-diisocyanate, perhydrodiphenylmethane 2,4’-diisocyanate, 4,4’-methylenedicyclohexyl diisocyanate (e.g., Desmodur ® W from Bayer AG), or a mixture thereof.

The aromatic di- and/or polyisocyanates can be selected from 4,4’- diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’- MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), and combinations thereof. In addition, the composition may include other conventional aromatic di- and/or polyisocyanates, such as toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

The di- and/or polyisocyanates may also be modified, for example through incorporation of uretdione, carbamate, isocyanurate, carbodiimide or allophanate groups. It is further possible to use blends of the various di- and/or polyisocyanates. Carbodiimide-modified di- and/or polyisocyanates are preferably used.

The polyol/di- and/or polyisocyanate ratio is generally selected such that the NCO content of the prepolymer is in the range of from 5% to 30% by weight, preferably in the range of from 7% to 20% by weight and more preferably in the range of from 7% to 15% by weight.

The preparation of NCO terminated polyurethane prepolymer can in principle be carried out in various ways known to those skilled in the art. In one advantageous embodiment, it is prepared by reacting a polyol or a polyol mixture with an excess of at least one di- or polyisocyanate, optionally followed by partial distillation to remove the unreacted di- or polyisocyanate compound. This reaction may be carried out in the presence of a catalyst (“prepolymerization catalyst”) that catalyzes the prepolymerization (“prepolymerization catalyst”), but preferably the reaction is not carried out in the presence of a prepolymerization catalyst. Suitable prepolymerization catalysts are known to those skilled in the art.

The polyurethane prepolymer has an average molecular weight of from 300 to 20,000 g/mol, preferably less than 12,000 g/mol, in particular less than 8,000 g/mol. The NCO terminated polyurethane prepolymer can have a viscosity in the range of from 1000 mPas to 30000 mPas, particularly from 1000 mPas to 10000 mPas, measured at 25°C according to DIN 53019 (2008). This is particularly advantageous, since such polyurethane prepolymers can still to be further processed well.

The 1K polyurethane system is moisture curable. Moisture curing can be carried out using moisture from the surrounding environment or crystal water from filler. Specific procedures can be found in the description below.

The 1 K polyurethane system may include at least one catalyst suitable for catalyzing the reaction of the polyurethane prepolymer with moisture from the surrounding environment, such as moisture in the air.

The catalysts can be amine catalysts. Examples of catalysts that may be used are bis(dimethylaminopropyl)urea, bis(N,N-dimethylaminoethoxyethyl) carbamate, dimethylaminopropylurea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropylether), N,N,N-trimethyl-N-hydroxyethylbis(aminoethylether), bis(N,N-dimethyl-3- aminopropyl)amine, dimethylaminopropylamine, 3-dimethylaminopropyl-N,N- dimethylpropane-1 ,3-diamine, dimethyl-2-(2-aminoethoxyethanol) and (1,3- bis(dimethylamino)propan-2-ol), N,N-bis(3-dimethylaminopropyl)-N- isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl- N-(3-aminopropyl)-bis(aminoethylether), 3-dimethylaminoisopropyl diisopropanolamine, 2-dimorpholinyldiethylether (abbreviated as “DM DEE”, CAS: 6425-39-4), or a mixture thereof. DM DEE is preferred.

In addition to amine catalysts, other catalysts may also be used. Examples include amidines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-, and N- cyclohexylmorpholine, 2, 2-dimorpholinyldiethylether (DMDEE), N,N,N’,N’- tetramethylethylenediamine, N , N, N’, N’-tetramethylbutanediamine, N , N , N’, N’- tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-dimethylimidazole, 1- azabicyclo[3.3.0]octane, and preferably 1,4-diazabicyclo[2.2.2]octane, and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, dimethylethanolamine, and diethylethanolamine. Likewise suitable are organometallic compounds, preferably organotin compounds, such as tin(ll) salts of organic carboxylic acids, for example tin(ll) acetate, tin(ll) octanoate, tin(ll) ethylhexanoate, and tin(ll) laurate, and dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, tin ricinoleate, dibutyltin maleate, and dioctyltin diacetate, and also zinc carboxylates such as zinc ricinoleate, and also bismuth carboxylates such as bismuth(lll) neodecanoate, bismuth 2-ethylhexanoate, and bismuth octanoate, or a mixture thereof. The organometallic compounds may be used either alone or preferably in combination with strongly basic amines.

If catalysts are used, these may be used in an amount of 0.001 to 5 parts by weight, in particular 0.05 to 2 parts by weight, based on 100 parts by weight of the NCO terminated polyurethane prepolymer.

The 1 K polyurethane system may include a blowing agent.

All blowing agents known in the production of polyurethanes may in principle be used. These may comprise chemical and/or physical blowing agents. Such blowing agents are described in, for example, “Kunststoffhandbuch [Plastics Handbook], volume 7, Polyurethane [Polyurethanes]”, 3rd edition 1993, chapter 3.4.5. Chemical blowing agents are understood here as meaning compounds that form gaseous products by reaction with isocyanate. Examples of such blowing agents include not only water but also carboxylic acids. Physical blowing agents are understood here as meaning compounds that are dissolved or emulsified in the starting materials for the polyurethane production and vaporize under the conditions of polyurethane formation. Examples of these are hydrocarbons, halogenated hydrocarbons, and other compounds, for example perfluorinated alkanes such as perfluorohexane, chlorofluorohydrocarbons, and ethers, esters, ketones, acetals and/or liquid carbon dioxide.

It is preferable if water is used as sole blowing agent. Water used as blowing agent can be the same as water as curing agent, that is, moisture from the surrounding environment; or crystal water introduced from filler.

The blowing agent is preferably used in an amount that results in a polyurethane foam having a density of from 10 to 80 g/L, more preferably from 20 to 60 g/L, and particular preferably from 25 to 60 g/L.

Auxiliaries and/or additives may additionally be included in the 1 K polyurethane system. All auxiliaries and additives known in the production of polyurethanes may be used. Examples include surface-active substances, foam stabilizers, cell regulators, release agents, fillers, dyes, pigments, flame retardants, hydrolysis stabilizers, and fungistatic and bacteriostatic substances. Such substances are known and are described for example in “Kunststoffhandbuch [Plastics Handbook], volume 7, Polyurethane [Polyurethanes]”, Carl Hanser Verlag, 3rd edition 1993, chapter 3.4.

Examples of suitable surface-active substances are compounds which are used to promote homogenization of the starting materials and which are optionally also suitable for regulation of the cell structure of the foams. Examples of these include siloxane-oxyalkylene copolymers and other organopolysiloxanes, ethoxylated alkylphenols, ethoxylated fatty alcohols, paraffin oils, castor oil esters or ricinoleic esters, which are used in amounts from 0.2 to 8, preferably from 0.5 to 5 parts by weight per 100 parts by weight of the 1 K polyurethane system.

Examples of suitable flame retardants are intumescent flame retardants.

Suitable intumescent flame retardants include expandable graphite or kaolin. The expandable graphite or kaolin can have a particle size in the range of from 50 to 500 pm.

In addition, the intumescent flame retardants can also include acid sources, carbon sources, and gas sources. The acid sources include inorganic acids or compounds that can generate acids in situ during combustion, such as phosphoric acid, boric acid, sulfuric acid, or salts or esters thereof. The carbon sources are generally polyhydroxy compounds, such as starch, sucrose, dextrin, pentaerythritol, ethylene glycol, phenolic resin, and the like. The gas sources are generally nitrogen-containing compounds, such as urea, melamine, polyamide, and the like.

Moreover, the flame retardants may include other flame retardants aside from intumescent flame retardants. Examples of other flame retardants include compounds containing phosphorus and/or halogen atoms, for example tricresyl phosphate, tris(2-chloroethyl) phosphate, tris(chloropropyl) phosphate (TCPP), 2,2- bis(chloromethyl)trimethylene bis(bis(2-chloroethyl) phosphate), oligomeric organophosphorus compounds (for example Fyrol® PNX, Fyrolflex® RDP), and tris(2,3-dibromopropyl) phosphate. In addition, the flame retardants used may also comprise inorganic flame retardants, for example antimony trioxide, arsenic oxide, ammonium polyphosphate, expandable graphite, and calcium sulfate, or melamine, in order to render the polyurethane foams flame-retardant.

It has generally been found to be advantageous to use 5 to 50 parts by weight, preferably 5 to 35 parts by weight of said flame retardant, based on 100 parts by weight of the 1 K polyurethane system.

In one preferred embodiment, the 1 K polyurethane system comprises fillers. The customary fillers known in the field of polyurethane chemistry are generally suitable. Examples of suitable fillers are glass fibers, mineral fibers, natural fibers, such as flax, jute or sisal for example, glass flakes, silicates such as mica stone or mica, salts, such as calcium carbonate, chalk or gypsum. Calcium carbonate is preferred.

The filler is typically used in an amount from 0.5% to 60% by weight and preferably from 3% to 10% by weight based on the total weight of the 1 K polyurethane system.

In one preferred embodiment, the components of the 1 K polyurethane system are essentially free of solvents.

The 2K polyurethane system comprises separately packaged isocyanate component (a) and polyol component (b), which are mixed and reacted only before use.

The isocyanate component (a) is di- or polyisocyanates, which include conventional aliphatic, cycloaliphatic, or aromatic di- and/or polyisocyanates, preferably aromatic di- and/or polyisocyanates.

The aliphatic di- and/or polyisocyanates can be selected from ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, and a mixture thereof; in particular, 1 ,6-hexamethylene diisocyanate trimer (HDT), 1 ,12-dodecane diisocyanate, and a mixture thereof.

The cycloaliphatic di- and/or polyisocyanates can be selected from cyclobutane 1,3-diisocyanate, cyclohexane 1 ,3-diisocyanate, cyclohexane 1 ,4-diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6-diisocyanate, hexahydrophenylene 1 ,3-diisocyanate, hexahydrophenylene 1,4-diisocyanate, perhydrodiphenylmethane 2,4’-diisocyanate, 4,4’-methylenedicyclohexyl diisocyanate (e.g., Desmodur ® W from Bayer AG), or a mixture thereof.

The aromatic di- and/or polyisocyanates can be selected from 4,4’- diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’- MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), and combinations thereof. In addition, the composition may include other conventional aromatic di- and/or polyisocyanates, such as toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

The di- and/or polyisocyanates may also be modified, for example through incorporation of uretdione, carbamate, isocyanurate, carbodiimide or allophanate groups. It is further possible to use blends of the various di- and/or polyisocyanates. Carbodiimide-modified di- and/or polyisocyanates are preferably used.

The polyisocyanate component (a) can also be employed in the form of polyisocyanate prepolymers. These prepolymers are known in the art. They are prepared in a conventional manner by reacting above-described polyisocyanate component (a) with hereinbelow described compounds having isocyanate-reactive hydrogen atoms - polyol component (b) to form the prepolymer. The reaction may be carried out at a temperature of about 80°C for example. The polyol/polyisocyanate ratio is generally selected such that the NCO content of the prepolymer is in the range of from 8% to 25% by weight, preferably in the range of from 10% to 24% by weight and more preferably in the range of from 13% to 23% by weight. More preferably, a prepolymer of diphenylmethane diisocyanate and polytetrahydrofuran (PTHF), in particular PTHF having a number average molecular weight in the range of from 1000 to 2500 and a hydroxyl value of from 10 to 120 mg KOH/g, preferably 30 to 70 mg KOH/g, more preferably 40 to 60 mg KOH/g, is used as isocyanate component (a). The NCO content of this prepolymer is preferably in the range of from 14% to 22% and more preferably in the range of from 16% to 20%.

The polyol component (b) can be polyester polyols, polyether polyols, or a mixture thereof, preferably polyether polyols or a mixture thereof.

The polyether polyols are obtained by known processes, for example via anionic or cationic polymerization of alkylene oxides with addition of at least one starter molecule comprising from 2 to 8, preferably from 2 to 6, and particularly preferably from 2 to 4, reactive hydrogen atoms, in the presence of catalysts. Catalysts used can comprise alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, or alkali metal alcoholates, such as sodium methoxide, sodium ethoxide, potassium ethoxide, or potassium isopropoxide, or, in the case of cationic polymerization, Lewis acids, such as antimony pentachloride, boron trifluoride etherate, or bleaching earth. Other catalysts that can be used are double-metal cyanide compounds, also known as DMC catalysts.

The alkylene oxides used preferably comprise one or more compounds having from 2 to 4 carbon atoms in the alkylene moiety, e.g. tetrahydrofuran, ethylene oxide, propylene 1 ,2-oxide, butylene 1 ,2-oxide or butylene 2,3-oxide, in each case alone or in the form of a mixture, and preferably propylene 1 ,2-oxide, ethylene oxide and/or tetrahydrofuran.

Examples of starter molecules that can be used are ethylene glycol, propylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, sugar derivatives, such as sucrose, hexitol derivatives, such as sorbitol, methylamine, ethylamine, isopropylamine, butylamine, benzylamine, aniline, toluidine, toluenediamine, naphthylamine, ethylenediamine, diethylenetriamine, 4,4’-methylenedianiline, 1 ,3- propanediamine, 1 ,6-hexanediamine, ethanolamine, diethanolamine, triethanolamine, and also other di- or polyhydric alcohols, or di- or polybasic amines.

The polyether polyols may have an average molecular weight of from 100 to 10,000 g/mol, preferably from 500 to 8000 g/mol, and more preferably from 1000 to 5000 g/mol; and a hydroxyl value of from 5 to 200 mg KOH/g, preferably from 10 to 180 mg KOH/g, more preferably from 20 to 150 mg KOH/g, and most preferably from 25 to 120 mg KOH/g.

The polyester polyols used are mostly produced via condensation of polyhydric alcohols having from 2 to 12 carbon atoms, e.g. ethylene glycol, diethylene glycol, butanediol, trimethylolpropane, glycerol, or pentaerythritol, with polybasic carboxylic acids having from 2 to 12 carbon atoms, e.g. succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, and the isomers of naphthalenedicarboxylic acids, or their anhydrides.

The polyester polyols can have an average molecular weight of from 100 to 20,000 g/mol, particularly from 330 to 4,500 g/mol, and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 20 to 70 mg KOH/g, and most preferably from 25 to 60 mg KOH/g.

In one preferred embodiment of the present invention, the polyol component (b) is a mixture of polyether polyols, comprising:

(i) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 2000 to 6000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(ii) polyether polyol terminated by primary hydroxyl groups, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 3000 to 6000 g/mol, and most preferably from 4000 to 5000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 70 mg KOH/g, more preferably from 25 to 50 mg KOH/g, and most preferably from 30 to 40 mg KOH/g;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 100 to 5000 g/mol, preferably from 400 to 4000 g/mol, more preferably from 600 to 2500 g/mol, and most preferably from 700 to 1500 g/mol; and a hydroxyl value of from 20 to 200 mg KOH/g, preferably from 50 to 160 mg KOH/g, more preferably from 80 to 140 mg KOH/g, and most preferably from 100 to 120 mg KOH/g, and which is terminated by primary hydroxyl groups.

The 2K polyurethane system may include conventional chain extenders. Useful chain extenders are known in the art. Preference is given to using diols having molecular weights below 400 g/mol, in particular in the range of from 60 to 150 g/mol. Examples are ethylene glycol, propylene glycol, diethylene glycol, 1 ,4-butanediol, dipropylene glycol, tripropylene glycol, preferably ethylene glycol or 1,4-butanediol.

The 2K polyurethane system may include at least one catalyst suitable for catalyzing the reaction of the isocyanate component (a) with the polyol component (b).

The catalysts can be amine catalysts. Examples of catalysts that may be used are bis(dimethylaminopropyl)urea, bis(N,N-dimethylaminoethoxyethyl) carbamate, dimethylaminopropylurea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropylether), N,N,N-trimethyl-N-hydroxyethylbis(aminoethylether), bis(N,N-dimethyl-3- aminopropyl)amine, dimethylaminopropylamine, 3-dimethylaminopropyl-N,N- dimethylpropane-1 ,3-diamine, dimethyl-2-(2-aminoethoxyethanol) and (1,3- bis(dimethylamino)propan-2-ol), N,N-bis(3-dimethylaminopropyl)-N- isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl- N-(3-aminopropyl)-bis(aminoethylether), 3-dimethylaminoisopropyl diisopropanolamine, 2-dimorpholinyldiethylether (abbreviated as “DM DEE”, CAS: 6425-39-4), or a mixture thereof. DM DEE is preferred.

In addition to amine catalysts, other catalysts may also be used. Examples include amidines such as 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-, and N- cyclohexylmorpholine, 2, 2-dimorpholinyldiethylether (DMDEE), N,N,N’,N’- tetramethylethylenediamine, N , N, N’, N’-tetramethylbutanediamine, N , N , N’, N’- tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1,2-dimethylimidazole, 1- azabicyclo[3.3.0]octane, and preferably 1,4-diazabicyclo[2.2.2]octane, and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, dimethylethanolamine, and diethylethanolamine. Likewise suitable are organometallic compounds, preferably organotin compounds, such as tin(ll) salts of organic carboxylic acids, for example tin(ll) acetate, tin(ll) octanoate, tin(ll) ethylhexanoate, and tin(ll) laurate, and dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, tin ricinoleate, dibutyltin maleate, and dioctyltin diacetate, and also zinc carboxylates such as zinc ricinoleate, and also bismuth carboxylates such as bismuth(lll) neodecanoate, bismuth 2-ethylhexanoate, and bismuth octanoate, or a mixture thereof. The organometallic compounds may be used either alone or preferably in combination with strongly basic amines.

If catalysts are used, these may be used in an amount of 0.001 to 5 parts by weight, in particular 0.05 to 2 parts by weight, based on 100 parts by weight of the isocyanate component (a) and polyol component (b).

The 2K polyurethane system may include a blowing agent.

All blowing agents known in the production of polyurethanes may in principle be used. These may comprise chemical and/or physical blowing agents. Such blowing agents are described in, for example, “Kunststoffhandbuch [Plastics Handbook], volume 7, Polyurethane [Polyurethanes]”, 3rd edition 1993, chapter 3.4.5. Chemical blowing agents are understood here as meaning compounds that form gaseous products by reaction with isocyanate. Examples of such blowing agents include not only water but also carboxylic acids. Physical blowing agents are understood here as meaning compounds that are dissolved or emulsified in the starting materials for the polyurethane production and vaporize under the conditions of polyurethane formation. Examples of these are hydrocarbons, halogenated hydrocarbons, and other compounds, for example perfluorinated alkanes such as perfluorohexane, chlorofluorohydrocarbons, and ethers, esters, ketones, acetals and/or liquid carbon dioxide.

It is preferable if water is used as sole blowing agent. The moisture from the surrounding environment; or crystal water introduced from filler; or water directly added to the reaction system after mixing the isocyanate component (a) and polyol component (b) can be used as blowing agent.

The blowing agent is preferably used in an amount that results in a polyurethane foam having a density of from 10 to 80 g/L, more preferably from 20 to 60 g/L, and particular preferably from 25 to 60 g/L.

Auxiliaries and/or additives may additionally be included in the 2K polyurethane system. All auxiliaries and additives known in the production of polyurethanes may be used. Examples include surface-active substances, foam stabilizers, cell regulators, release agents, fillers, dyes, pigments, flame retardants, hydrolysis stabilizers, and fungistatic and bacteriostatic substances. Such substances are known and are described for example in “Kunststoffhandbuch [Plastics Handbook], volume 7, Polyurethane [Polyurethanes]”, Carl Hanser Verlag, 3rd edition 1993, chapter 3.4.

Examples of suitable surface-active substances are compounds which are used to promote homogenization of the starting materials and which are optionally also suitable for regulation of the cell structure of the foams. Examples of these include siloxane-oxyalkylene copolymers and other organopolysiloxanes, ethoxylated alkylphenols, ethoxylated fatty alcohols, paraffin oils, castor oil esters or ricinoleic esters, which are used in amounts from 0.2 to 8, preferably from 0.5 to 5 parts by weight per 100 parts by weight of the 1 K polyurethane system.

Examples of suitable flame retardants are intumescent flame retardants.

Suitable intumescent flame retardants include expandable graphite or kaolin. The expandable graphite or kaolin can have a particle size in the range of from 50 to 500 pm.

In addition, the intumescent flame retardants can also include acid sources, carbon sources, and gas sources. The acid sources include inorganic acids or compounds that can generate acids in situ during combustion, such as phosphoric acid, boric acid, sulfuric acid, or salts or esters thereof. The carbon sources are generally polyhydroxy compounds, such as starch, sucrose, dextrin, pentaerythritol, ethylene glycol, phenolic resin, and the like. The gas sources are generally nitrogen-containing compounds, such as urea, melamine, polyamide, and the like. Moreover, the flame retardants may include other flame retardants aside from intumescent flame retardants. Examples of other flame retardants include compounds containing phosphorus and/or halogen atoms, for example tricresyl phosphate, tris(2-chloroethyl) phosphate, tris(chloropropyl) phosphate (TCPP), 2,2- bis(chloromethyl)trimethylene bis(bis(2-chloroethyl) phosphate), oligomeric organophosphorus compounds (for example Fyrol® PNX, Fyrolflex® RDP), and tris(2,3-dibromopropyl) phosphate. In addition, the flame retardants used may also comprise inorganic flame retardants, for example antimony trioxide, arsenic oxide, ammonium polyphosphate, expandable graphite, and calcium sulfate, or melamine, in order to render the polyurethane foams flame-retardant.

It has generally been found to be advantageous to use 5 to 50 parts by weight, preferably 5 to 35 parts by weight of said flame retardant, based on 100 parts by weight of the 2K polyurethane system.

In one preferred embodiment, the 2K polyurethane system comprises fillers. The customary fillers known in the field of polyurethane chemistry are generally suitable. Examples of suitable fillers are glass fibers, mineral fibers, natural fibers, such as flax, jute or sisal for example, glass flakes, silicates such as mica stone or mica, salts, such as calcium carbonate, chalk or gypsum. Calcium carbonate is preferred.

The filler is typically used in an amount from 0.5% to 60% by weight and preferably from 3% to 10% by weight based on the total weight of the 2K polyurethane system.

In one preferred embodiment, the 2K polyurethane system is essentially free of solvents.

In another aspect, the present invention also provides a solvent-free base, which is produced by a process comprising the steps of: la) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer, 3a) curing the components of the polyurethane system to form a polyurethane layer; or the base is produced by a process comprising the steps of: lb) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system, 5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

The specific process steps will be described hereinbelow in detail.

Process for producing solvent-free base of the present invention

In another aspect, the present invention also provides a process for producing solvent-free base, which comprises the steps of (hereinafter also referred to as process 1): la) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer,

3a) curing the components of the polyurethane system to form a polyurethane layer; or the process comprising the steps of (sometimes hereinafter also referred to as process 2): lb) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system,

5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

In the context of the present invention, examples of useful release layers are layers, for example in the form of foils, composed of metal, plastic, leather and/or textile materials. Useful release layers are commercially available, for example, Favini B100 purchased from Favini.

In the process of the present invention, the application of components of the polyurethane system atop the substrate layer or release layer is carried out by knife coating, spraying, and brushing, preferably by knife coating or spraying. After application, there is no need to press the obtained base to reduce its thickness. The production line of a solvent-free knife coating process according to the present invention can be obtained by appropriately improving a traditional oily dry process line only with a small amount of investment. In addition, compared to a spraying process, the knife coating process hardly wastes any raw materials during the coating process. However, the spray coating process generally wastes from 15 to 30% of chemicals or even more due to different spraying process conditions. Therefore, the knife coating process saves more raw materials. After knife coating, there is no need to press the obtained base to reduce its thickness. In this way, the thickness can be maintained, achieving the goal of using fewer materials and thus saving production costs.

In steps 3a) and 5b) of the process of the present invention, the components of the polyurethane system are cured to form a polyurethane layer. This curing can be accelerated by increasing the temperature (such as in an oven, preferably in a drying tunnel).

In process 1 ,

(1) For the 1 K polyurethane system, curing can be carried out at a temperature of from 40 to 100°C, preferably from 45 to 90°C, and at a humidity of from 45 to 95%, preferably 50-90%; the curing time can be from 1.5 to 40 minutes, preferably 5 to 30 minutes;

(2) For the 2K polyurethane system, curing can be carried out at a temperature of from 80 to 180°C, preferably from 90 to 140°C; the curing time can be from 1 to 30 minutes, preferably from 5 to 15 minutes.

In process 2,

(1) For the 1 K polyurethane system, the pre-curing can be carried out at a temperature of from 40 to 100°C, preferably from 45 to 80°C, and at a humidity of from 40 to 95%, preferably from 50 to 90%; the pre-curing time is in the range of from 1 to 25 minutes, preferably from 1.5 to 10 minutes. The post-curing can be carried out at a temperature of from 35 to 100°C, preferably from 45 to 80°C, and at a humidity of from 45 to 95%, preferably from 50 to 90%; the post-curing time can be from 1 to 40 minutes, preferably from 5 to 30 minutes.

(2) For the 2K polyurethane system, the pre-curing can be carried out at a temperature of from 40 to 150°C, preferably from 60 to 120°C; the pre-curing time is in the range of from 0.5 to 30 minutes, preferably from 1 to 10 minutes. The postcuring can be carried out at a temperature of from 60 to 180°C, preferably from 90 to 140°C; the post-curing time can be from 2 to 30 minutes, preferably from 5 to 15 minutes.

In step 6b) of process 2 of the present invention, the release layer is separated from the polyurethane layer. This separation can be performed by the methods commonly known in the art. For example, the release layer is peeled off from the polyurethane layer.

The process 1 of the present invention can also include step 1a’) before step 1a) providing a substrate layer, that is, providing a release layer.

In process 2 of the present invention, pre-curing and post-curing steps are used, which has the following advantages: pre-curing and post-curing can be directly used on traditional oily dry production lines, and the pre-curing and post-curing processes of the basecoat are not affected by the topcoat. When using water-borne topcoat, the acidic groups of water-borne polyurethanes and insufficient drying of water both can affect the pre-curing and post-curing of 2K Pll. Therefore, this makes the knife coating process easier to implement.

The process of the present invention can be operated in a continuous manner or in batches. It is preferred to operate in a continuous manner.

In the context of the present invention, “continuous” is to be understood as meaning that the release layer and/or the substrate layer are present in the form of a strip which is continuously advanced and treated according to the process of the present invention. The strip is generally from 10 to 500 meters and preferably from 20 to 200 meters in length.

In one continuous process of the present invention, the release layer forms a quasi release strip. The release layer is preferably unwound off a reel at the start of the process, the release layer removed from the polyurethane layer in the process of the present invention may preferably be wound up again on a reel. This wound-up release layer may be reused in the process of the present invention; that is, it is reusable. The wound-up release layer is preferably reused from 2 to 5 times.

In one continuous process of the present invention, the substrate layer forms a quasi substrate strip. The substrate layer is preferably unwound off a reel at the start of the process.

This continuous process of the present invention provides a polyurethane layer — bonded to the substrate layer — as a product which is likewise in the form of a strip. The product obtained is preferably wound up on a reel.

Specific embodiments of the present invention are as follows:

1. A solvent-free base comprising a substrate layer and a polyurethane layer, preferably consisting of a substrate layer and a polyurethane layer.

2. The base according to embodiment 1, wherein the polyurethane layer is formed by a 1 K polyurethane system or a 2K polyurethane system. 3. The base according to embodiment 2, wherein the 1K polyurethane system contains at least one isocyanate terminated polyurethane prepolymer as a resin component, and is cured by the reaction of NCO groups with crystal water from fillers or moisture from the surrounding environment.

4. The base according to embodiment 3, wherein the isocyanate terminated polyurethane prepolymers are obtained by reacting polyols or polyol mixtures with a stoichiometric excess of di- or polyisocyanates.

5. The base according to embodiment 4, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polypropylene glycol, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 1000 to 4000 g/mol, and most preferably from 1500 to 2500 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 50 to 60 mg KOH/g; and

(ii) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 2000 to 5000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 600 to 5000 g/mol, preferably from 800 to 4000 g/mol, more preferably from 1000 to 3500 g/mol, and most preferably from 1500 to 3000 g/mol; and a hydroxyl value of from 10 to 100 mg KOH/g, preferably from 30 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 45 to 65 mg KOH/g, and which is terminated by primary hydroxyl groups.

6. The base according to embodiment 4 or 5, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’-diphenylmethanediisocyanate (4,4’-MDI), 2,2’- diphenylmethanediisocyanate (2,2’-MDI), 2,4’-diphenylmethanediisocyanate (2,4’- MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

7. The base according to embodiment 2, wherein the 2K polyurethane system comprises separately packaged isocyanate component (a) and polyol component (b). 8. The base according to embodiment 7, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 2000 to 6000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(ii) polyether polyol terminated by primary hydroxyl groups, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 3000 to 6000 g/mol, and most preferably from 4000 to 5000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 70 mg KOH/g, more preferably from 25 to 50 mg KOH/g, and most preferably from 30 to 40 mg KOH/g;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 100 to 5000 g/mol, preferably from 400 to 4000 g/mol, more preferably from 600 to 2500 g/mol, and most preferably from 700 to 1500 g/mol; and a hydroxyl value of from 20 to 200 mg KOH/g, preferably from 50 to 160 mg KOH/g, more preferably from 80 to 140 mg KOH/g, and most preferably from 100 to 120 mg KOH/g, and which is terminated by primary hydroxyl groups.

9. The base according to embodiment 7 or 8, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’-diphenylmethanediisocyanate (4,4’-MDI), 2,2’- diphenylmethanediisocyanate (2,2’-MDI), 2,4’-diphenylmethanediisocyanate (2,4’- MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

10. The base according to any one of embodiments 1 to 8, wherein the polyurethane layer is foamed or non-foamed, preferably foamed.

11 . The base according to any one of embodiments 1 to 10, wherein the polyurethane layer is completely cured.

12. A solvent-free base, which is produced by a process comprising the steps of:

1a) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer, 3a) curing the components of the polyurethane system to form a polyurethane layer; or which is produced by a process comprising the steps of:

1b) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system,

5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

13. The base according to embodiment 12, wherein the polyurethane layer is formed by a 1 K polyurethane system or a 2K polyurethane system.

14. The base according to embodiment 13, wherein the 1K polyurethane system contains at least one isocyanate terminated polyurethane prepolymer as a resin component, and is cured by the reaction of NCO groups with crystal water from fillers or moisture from the surrounding environment.

15. The base according to embodiment 14, wherein the isocyanate terminated polyurethane prepolymers are obtained by reacting polyols or polyol mixtures with a stoichiometric excess of di- or polyisocyanates.

16. The base according to embodiment 15, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polypropylene glycol, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 1000 to 4000 g/mol, and most preferably from 1500 to 2500 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 50 to 60 mg KOH/g; and

(ii) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 2000 to 5000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter; (iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 600 to 5000 g/mol, preferably from 800 to 4000 g/mol, more preferably from 1000 to 3500 g/mol, and most preferably from 1500 to 3000 g/mol; and a hydroxyl value of from 10 to 100 mg KOH/g, preferably from 30 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 45 to 65 mg KOH/g, and which is terminated by primary hydroxyl groups.

17. The base according to embodiment 15 or 16, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’-diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’-MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

18. The base according to embodiment 13, wherein the 2K polyurethane system comprises separately packaged isocyanate component (a) and polyol component (b).

19. The base according to embodiment 18, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 2000 to 6000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(ii) polyether polyol terminated by primary hydroxyl groups, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 3000 to 6000 g/mol, and most preferably from 4000 to 5000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 70 mg KOH/g, more preferably from 25 to 50 mg KOH/g, and most preferably from 30 to 40 mg KOH/g;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 100 to 5000 g/mol, preferably from 400 to 4000 g/mol, more preferably from 600 to 2500 g/mol, and most preferably from 700 to 1500 g/mol; and a hydroxyl value of from 20 to 200 mg KOH/g, preferably from 50 to 160 mg KOH/g, more preferably from 80 to 140 mg KOH/g, and most preferably from 100 to 120 mg KOH/g, and which is terminated by primary hydroxyl groups.

20. The base according to embodiment 18 or 19, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’-diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’-MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

21. The base according to any one of embodiments 12 to 20, wherein the polyurethane layer is foamed or non-foamed, preferably foamed.

22. The base according to any one of embodiments 12 to 21 , wherein the polyurethane layer is completely cured.

23. A process for producing a solvent-free base, comprising the steps of: la) providing a substrate layer,

2a) applying components of the polyurethane system atop the substrate layer,

3a) curing the components of the polyurethane system to form a polyurethane layer; or the process comprising the steps of: lb) providing a release layer,

2b) applying components of the polyurethane system atop the release layer,

3b) pre-curing the components of the polyurethane system,

4b) applying a substrate layer atop the pre-cured components of the polyurethane system,

5b) post-curing the components of the polyurethane system to form a polyurethane layer,

6b) separating the release layer from the polyurethane layer.

24. The process according to embodiment 23, wherein the polyurethane layer is formed by a 1 K polyurethane system or a 2K polyurethane system.

25. The process according to embodiment 24, wherein the 1 K polyurethane system contains at least one isocyanate terminated polyurethane prepolymer as a resin component, and is cured by the reaction of NCO groups with crystal water from fillers or moisture from the surrounding environment.

26. The process according to embodiment 25, wherein the isocyanate terminated polyurethane prepolymers are obtained by reacting polyols or polyol mixtures with a stoichiometric excess of di- or polyisocyanates.

27. The process according to embodiment 26, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polypropylene glycol, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 1000 to 4000 g/mol, and most preferably from 1500 to 2500 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 50 to 60 mg KOH/g; and

(ii) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 6000 g/mol, more preferably from 2000 to 5000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 600 to 5000 g/mol, preferably from 800 to 4000 g/mol, more preferably from 1000 to 3500 g/mol, and most preferably from 1500 to 3000 g/mol; and a hydroxyl value of from 10 to 100 mg KOH/g, preferably from 30 to 80 mg KOH/g, more preferably from 40 to 70 mg KOH/g, and most preferably from 45 to 65 mg KOH/g, and which is terminated by primary hydroxyl groups.

28. The process according to embodiment 26 or 27, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’- diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’- MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

29. The process according to embodiment 24, wherein the 2K polyurethane system comprises separately packaged isocyanate component (a) and polyol component (b).

30. The process according to embodiment 29, wherein the polyols are polyether polyols, polyester polyols, polycarbonate polyols or a mixture thereof, preferably polyether polyols or a mixture thereof, more preferably mixtures of the following polyether polyols:

(i) polyethylene oxide, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 2000 to 6000 g/mol, and most preferably from 3000 to 4000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 60 mg KOH/g, more preferably from 15 to 50 mg KOH/g, and most preferably from 25 to 35 mg KOH/g, and which is prepared using propylene glycol as a starter; (ii) polyether polyol terminated by primary hydroxyl groups, which has an average molecular weight of from 100 to 10,000 g/mol, preferably from 1000 to 8000 g/mol, more preferably from 3000 to 6000 g/mol, and most preferably from 4000 to 5000 g/mol; and a hydroxyl value of from 5 to 100 mg KOH/g, preferably from 10 to 70 mg KOH/g, more preferably from 25 to 50 mg KOH/g, and most preferably from 30 to 40 mg KOH/g;

(iii) polytetrahydrofuran (PTHF), which has an average molecular weight of from 100 to 5000 g/mol, preferably from 400 to 4000 g/mol, more preferably from 600 to 2500 g/mol, and most preferably from 700 to 1500 g/mol; and a hydroxyl value of from 20 to 200 mg KOH/g, preferably from 50 to 160 mg KOH/g, more preferably from 80 to 140 mg KOH/g, and most preferably from 100 to 120 mg KOH/g, and which is terminated by primary hydroxyl groups.

31. The process according to embodiment 29 or 30, wherein the di- or polyisocyanates are aliphatic, cycloaliphatic, or aromatic di- or polyisocyanates, preferably aromatic di- or polyisocyanates, more preferably 4,4’- diphenylmethanediisocyanate (4,4’-MDI), 2,2’-diphenylmethanediisocyanate (2,2’- MDI), 2,4’-diphenylmethanediisocyanate (2,4’-MDI), toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), or a mixture thereof.

32. The process according to any one of embodiments 23 to 31 , wherein the polyurethane layer is foamed or non-foamed, preferably foamed.

33. The process according to any one of embodiments 23 to 32, wherein the polyurethane layer is completely cured.

34. The process according to any one of embodiments 23 to 33, wherein steps 2a) and 2b) are carried out by brushing, knife coating, spraying, preferably by knife coating or spraying.

35. A solvent-free base obtained by the process according to any one of embodiments 23 to 34.

Brief description of the drawings

Figure 1 shows a schematic diagram of one embodiment of applying the 1K Pll system using process 1 of the present invention;

Figure 2 shows a schematic diagram of one embodiment of applying the 2K Pll system using process 1 of the present invention;

Figure 3 shows a schematic diagram of one embodiment of applying the 1K Pll system using process 2 of the present invention; Figure 4 shows a schematic diagram of one embodiment of applying the 2K Pll system using process 2 of the present invention.

The reference numerals in each of the figures are assigned the following meanings:

1 substrate layer

2 coater

3 oven

3’ pre-curing oven

3” post-curing oven

4 Pll base

5 release layer

Preferred embodiments of the process according to the present invention will now be more particularly described with reference to Figures 1 to 4.

Figure 1 shows a schematic diagram of one embodiment of applying the 1 K Pll system using process 1 according to the present invention. As shown in Figure 1 , the substrate layer 1 and the release layer 5 are wound up on different reels, respectively. When coating, the substrate layer 1 and the release layer 5 are unwound off the reels, respectively, making the substrate layer 1 atop the release layer 5. The 1 K Pll system is applied to the substrate layer 1 atop the release layer 5 by the coater 2, and then sent to the oven 3 for curing. The release layer 5 is then separated to obtain Pll base 4, and the obtained Pll base 4 can be wound up on a reel.

Figure 2 shows a schematic diagram of one embodiment of applying the 2K Pll system using process 1 according to the present invention. As shown in Figure 1 , the substrate layer 1 and the release layer 5 are wound up on different reels, respectively. When coating, the substrate layer 1 and the release layer 5 are unwound off the reels, respectively, making the substrate layer 1 atop the release layer 5. The 2K Pll system is applied to the substrate layer 1 atop the release layer 5 by the coater 2, and then sent to the oven 3 for curing. Thereafter, the release layer 5 is then separated to obtain Pll base 4, and the obtained Pll base 4 can be wound up on a reel. Among these, before applying the 2K Pll to the substrate layer 1 by the coater 2, a low pressure mixer (not shown) is used to mix components (a) and (b). The low pressure mixer used can be GJJF coater from Zhejiang Haifeng Automation Equipment Co. Ltd.

Figure 3 shows a schematic diagram of one embodiment of applying the 1 K Pll system using process 2 according to the present invention. As shown in Figure 3, the release layer 5 is wound up on a reel. When coating, the release layer 5 is unwound off the reel. The 1 K Pll system is applied to the release layer 5 by the coater 2, and then sent to the pre-curing oven 3’, in which it is pre-cured. Then the substrate layer 1 is unwound off the reel, layered on the polyurethane layer which is not yet completely cured, then sent to the post-curing oven 3”, in which it is post-cured. The obtained Pll base 4 is peeled off the release layer 5, and the obtained Pll base 4 and the release layer 5 can be wound up on reels, respectively.

Figure 4 shows a schematic diagram of one embodiment of applying the 2K Pll system using process 2 according to the present invention. As shown in Figure 4, the release layer 5 is wound up on a reel. When coating, the release layer 5 is unwound off the reel. The 2K Pll system is applied to the release layer 5 by the coater 2, and then sent to the pre-curing oven 3’, in which it is pre-cured. Then the substrate layer 1 is unwound off the reel, layered on the polyurethane layer which is not yet completely cured, then sent to the post-curing oven 3”, in which it is post-cured. The obtained Pll base 4 is peeled off the release layer 5, and the obtained Pll base 4 and the release layer 5 can be wound up on reels, respectively. Among these, before applying the 2K Pll to the release layer 5 by the coater 2, a low pressure mixer (not shown) is used to mix components a and b. The low pressure mixer used can be GJJF coater from Zhejiang Haifeng Automation Equipment Co. Ltd.

The present invention is further illustrated by the following example without limiting the scope of it.

Examples

Materials:

Polyol #1: polypropylene glycol, molecular weight 1500-2500 g/mol, OH value 50-60 mg KOH/g;

Polyol #2: prepared by using ethylene oxide as repeating units and propylene glycol as a starter, with ethylene oxide terminated with primary hydroxyl groups, molecular weight 3000-4000 g/mol, OH value 25-35 mg KOH/g;

Polyol #3: polyether polyol terminated with primary hydroxyl groups, molecular weight 4000-5000 g/mol, OH value 30-40 mg KOH/g;

Polyol #4: polyether polyol polymerized with tetrahydrofuran terminated by primary hydroxyl groups, molecular weight 1800-2200 g/mol, OH value 50-60 mg KOH/g;

Polyol #5: polyether polyol polymerized with tetrahydrofuran terminated by primary hydroxyl groups, molecular weight 800-1200 g/mol, OH value 100-120 mg KOH/g;

Chain extender #1: 1 ,4-butanediol Chain extender #2: ethylene glycol

Isocyanate #1 : Lupranat Ml available from BASF;

Isocyanate #2: isocyanate prepolymer, NCO content -12.8%, based on Lupranat MS and polytetrahydrofuran with an OH value of 56 mg KOH/g;

Lupranat MP 102: available from BASF;

Catalyst #1 : 2,2-dimorpholinyldiethylether (DMDEE, CAS No. 6425-39-4);

Catalyst #2: Additive CX 93600 available from BASF;

Catalyst #3: neodecanoic acid, zinc salt;

Catalyst #4: triethylenediamine (33%) and dipropylene glycol (67%);

Release layer: Favini B100 available from Favini.

Haptex CC 6945/90 C-CH is a water-borne PUD produced by BASF with a solid content of 34.5%.

Permutex PP-39-611 is a black pigment produced by Stahl with a solid content of 20.0%.

Permutex RM 4456 is a Stahl thickener produced by Stahl with a solid content of 28.0%.

Astacin Hardener Cl is an isocyanate type water-borne crosslinking agent produced by BASF with an isocyanate group content of about 12%.

Astacin Hardener CA is a polycarbodiimide type water-borne crosslinking agent produced by BASF.

Byk348 is a BYK type wetting agent produced by BYK with a solid content of 100%.

JF-S-AY8050 is available from Zhejiang Huafon Synthetic Resin Co., Ltd.

JF-A-5035 is available from Zhejiang Huafon Synthetic Resin Co., Ltd..

High F shoe material base is available from Fujian Boyi New Materials Co., Ltd.

Paliogen Black L 0086 is available from BASF.

0.65 mercerized velvet (Adi cloth) is available from Haining Anyu Textile Co., Ltd. with a fabric composition of 100% polyester yarn.

Example 1 : Preparation of 1 K PU base using process 1 : direct coating on a fabric

As shown in Figure 1 , the polyurethane prepolymer having the raw material composition shown in Table 1 is coated onto a fabric of 0.65 mercerized velvet (Adi cloth) with a knife coater, with a thickness gap being configured as 250 pm, and then cured in an oven for 15 minutes at a temperature of 70°C and at a humidity controlled to be 80%. Thereafter, the obtained Pll base is separated from the release layer.

Table 1 The raw material composition of the 1K polyurethane prepolymer

Example 2: Preparation of 2K Pll base using process 1: direct coating on a fabric

As shown in Figure 2, the 2K polyurethane system shown in Table 2 is coated onto a fabric of 0.65 mercerized velvet (Adi cloth) with a knife coater with a thickness of 350 pm, and then cured in an oven for 10 minutes at a temperature of 100°C. Thereafter, the obtained Pll base is separated from the release layer.

Table 2 The formulation of the 2K polyurethane system (parts by weight)

Example 3: Preparation of 1 K Pll base using process 2: coating on a release layer

As shown in Figure 3, the polyurethane prepolymer shown in Table 1 is coated onto a release layer with a knife coater with a thickness of 250 pm, and pre-cured in a pre- curing oven 3’ for 5 minutes at a temperature of 80°C and at a humidity controlled to be 80%. Thereafter, a fabric is attached, and then cured in a post-curing oven 3” for 15 minutes at a temperature of 90°C and at a humidity controlled to be 80%. Subsequently, the obtained Pll base is separated from the release layer.

Example 4: Preparation of 2K Pll base using process 2: coating on a release layer

As shown in Figure 4, the 2K polyurethane system shown in Table 2 is coated onto a release layer with a knife coater with a thickness of 350 pm, and pre-cured in a precuring oven 3’ for 5 minutes at a temperature of 100°C. Thereafter, a fabric is attached, and then cured in a post-curing oven 3” for 10 minutes at a temperature of 120°C. Subsequently, the obtained Pll base is separated from the release layer.

Example 5: Preparation of 2K Pll base using process 2: spraying on a release layerThe 2K polyurethane system shown in Table 3 is sprayed onto a release layer with Hennecke high pressure machine with a thickness of 350 pm, and cured in a pre-curing oven 3’ for 5 minutes at a temperature of 100°C. Thereafter, a fabric is attached, and then cured in a post-curing oven 3” for 10 minutes at a temperature of 120°C. Subsequently, the obtained Pll base is separated from the release layer.

Table 3 The spray formulation of the 2K polyurethane system (parts by weight)

Performance evaluation

Table 4 The knife coating formulation of water-borne topcoat #1 formulation (parts by weight)

Table 5 The knife coating formulation of oily topcoat #2 formulation (parts by weight)

Table 6 The knife coating formulation of bonding layer #2 formulation (parts by weight)

The ingredients are mixed in sequence according to the knife coating formulation of water-borne topcoat formulation in Table 4 or the knife coating formulation of oily topcoat formulation in Table 5, then knife coated on the release layer (release paper Favini B100) with a thickness of 100 pm, subsequently dried in the oven at 80°C for 2 minutes, dried in the oven at 120°C for 2 minutes. Next, the knife coating formulation of the bonding layer formulation in Table 6 is applied at 100 pm, then dried in the oven at 90°C for 6 minutes, attached to different bases, rolled with a pressure roller, dried again in the oven at 120°C for 10 minutes, and separated from the release layer to obtain the final synthetic leather product. Table 7 The properties of synthetic leather based on solvent-free base

Compared with the prior art, the process of producing dry veneer using solvent-free base is similar to the process of producing dry veneer using traditional oily base. The existing production line can even switch directly from oily base process to solvent- free base process. From Table 7, it can also be seen that the releasing and flexing properties are similar, wherein the leather sample prepared with 2K Pll base has better properties. Since the base layer is essentially free of solvents, the final finished leather has lower solvent residue. The bonding layer can also be selected from two- component polyurethane glue, aqueous polyurethane dispersion, and the like, ultimately resulting in synthetic leather that is essentially free of organic solvents.