DD254403A1 - POLYURETHANE COATING FOR THE SURFACE FINISHING OF WOVEN FABRICS, GEARS, FLEECES OR LEATHER AFTER THE REVERSE COATING PROCESS - Google Patents

Abstract

The invention relates to a polyurethane topcoat, which enables the production of synthetic leather with a particularly high surface quality by means of the reverse coating process. The goal of producing bubble-free polyurethane topcoats with good elastomeric properties to which a wide variety of carrier materials can be laminated is achieved by means of a polyurethane reactive system consisting of a solvent-free hydroxyl-containing polymer obtained by reacting a diisocyanate with a di- to trifunctional copolyether polyol with ethylene oxide endblocks and butane -1,4-diol in the equivalent ratio of 1: 0.4 to 0.6: 1.1 to 1.5 and then filling the butane-1,4-diol portion is prepared to at least 6 equivalents, a Isocyanatpraepolymer based on Diisocyanate and the above-mentioned Copolyetherpolyol in Aequivalentverhaeltnis 3: 1 to 10: 1 and a maximum of 2 wt .-% of a polydimethylsiloxane copolymer having ether side groups of molecular weight 8 000 to 12 000 as a leveling agent.

Description

Field of application of the invention

The invention relates to a polyurethane topcoat for the surface finishing of fabrics, knitted fabrics, nonwovens or leather after the reverse coating process, which allows the production of synthetic leather with a particularly high surface quality, which has good mechanical properties and is versatile processable.

Characteristic of the known state of the art

The preparation of polyurethane or polyurethane polyurea elastomers from polyisocyanates or diisocyanates, polyols and low molecular weight diols or diamines as chain extenders has long been known.

The most common way to make these polymer products is by the two-component method. In this variant, an excess of isocyanate with polyol is converted into an isocyanate prepolymer which is easy to handle for the processors.

Its conversion to polyurethane is then carried out with a second component in the following reaction step. This usually consists of chain extenders, mixtures of polyols and chain extenders or hydroxyl-containing urethane oligomers with chain extenders.

When polyester polyols are used, polymers having good mechanical properties are obtained, but with relatively poor low-temperature and hydrolysis behavior. Many polyester-based polyurethanes also show a strong tendency for hardening due to crystallization. By using polyether polyols, hydrolysis stability and low-temperature behavior are improved and the crystallization tendency is reduced. However, the mechanical properties generally deteriorate at the same time.

The processing of polyurethane systems into thin layers, as required for the surface finishing of fabrics, knitted fabrics, nonwovens or leather, places very special demands on the starting components of the polyurethane system and on the reaction regime.

Large differences in volume and viscosity between the NCO and OH components used must be avoided, since during further processing then deviations from the required mixing ratio can easily arise.

This deteriorates the reproducibility and ultimately has a negative effect on the film formation and elastomer properties. In addition, high reaction temperatures lead to very high initial rates of polyurethane formation, whereby only an incomplete course of the reaction system is obtained on the material to be coated. Thus, to achieve a uniform layer thickness, an initially slow reaction at room temperature is required. However, this is very difficult to realize because the necessary to set the required properties amount of chain extender then often does not dissolve homogeneously in the system and thus no uniform structure structure is guaranteed with high level of property of the products.

Addition of homogenizing agents results in significant changes in the properties of the prepolymers and the elastomer layers. The increase in viscosity due to admixture of the homogenizing additives in the form of large surface area inorganic materials also results in an incomplete course of the applied system with greatly varying thickness of the layers produced. At the same time, the incorporation of homogenizing agents has an extremely strong influence on the product properties in thin layers, since the usual elastomeric structures can not form undisturbed.

It has been shown that the compatibility problem is particularly noticeable in the production of thin layers and that the best properties are achieved with solvent-free reactive systems which are homogeneous at room temperature.

These systems are well suited with various technological variants for direct coatings. Thus, for example, by impregnating the textlien material with a catalyst solution, as shown in DE-OS 3042299, or by processing in limited viscosity ranges according to DE-OS 2524351 a hardening of the products can be prevented by excessive soaking. Also, by using certain combinations of catalysts according to DD-PS 235468, the viscosity curve is controlled so that too deep penetration into the material to be coated is avoided. When using the reversal process, in which the polyurethane reactive system is first applied to a polypropylene or polysiloxane coated release paper in one or more layers, then laminated with the support material and stripped off the release paper after curing, the course of the reaction mixture and the formation of uniformly thick layers throw considerable problems on. By the addition of different polysiloxanes or polyether Polysiioxan copolymers or mixtures, for. B. according to DD-PS 235469, although an improvement in the wetting of the release paper is achieved with the reactive system. Nevertheless, these thin polyurethane layers show a bubble structure due to trapped air.

Object of the invention

It is the object of the invention to produce bubble-free polyurethane topcoats with good elastomeric properties by means of reverse coating technology, which can be easily laminated on a wide variety of carrier materials.

Explanation of the essence of the invention

From the goal of the task results to provide a polyurethane active system available, which ensures the formation of bubble-free, uniform layers without further additives.

The object is achieved by means of a polyurethane reactive system whose hydroxyl-containing component A is a solvent-free Hydroxylpräpolymer by reacting a diisocyanate or diisocyanate with a di- to trifunctional Copolyetherpolyol with Ethylenoxidendblöcken or a mixture

such copolyether polyols and butane-1,4-diol in the equivalent ratio of 1: 0.4 to 0.6: 1.1 to 1.5, wherein the total content of the hydroxyl compounds based on 1 equivalent of diisocyanate is 1.7 to 1.9 equivalents , and then replenishing to at least 6 equivalents of butane-1,4-diol, the isocyanate group-containing component B is an isocyanate group-containing prepolymer prepared from a diisocyanate or diisocyanate mixture and the above dibis trifunctional copolyether polyols in an equivalent ratio of 3: 1 to 10: 1 and the leveling agent is a branched polydimethylsiloxane copolymer having ether side groups of ethylene oxide and propylene oxide in the molar mass range from 8000 to 12000, the amount of leveling agent being at most 2% by mass.

Surprisingly, only the polyurethane reactive system consisting of this particular hydroxyl and isocyanate prepolymer can be processed in the presence of the branched polyether-polysiloxane copolymer with a butane-1,4-diol amount of at least 6 equivalents to bubble-free layers having good properties. This means that only by a large amount of the polar butane-1,4-diol per equivalent of diisocyanate allows the course on the non-polar release paper with simultaneous elimination of blistering.

The production of the polyurethane topcoat by the inversion process is usually carried out so that the hydroxyl and the isocyanate group-containing component with 5 mol .-% isocyanate excess with the addition of about 2 wt .-% polyether-polysiloxane copolymer mixed, then onto a polypropylene or polysiloxane coated release paper applied at room temperature in a layer thickness up to 0.1 mm and then cured within about 2 minutes at 160 ° C.

The resulting polyurethane topcoats can be very well bonded with other layers of polyurethane or other plastic and various support materials such as fabrics, knitted fabrics, nonwovens, leather and the like for the production of artificial leather. This can also be done without laminating not yet completely cured layer.

The hydroxyl prepolymer according to the invention and the isocyanate prepolymer according to the invention are based on copolyether polyols which contain ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol or trimethylolpropane as starter substances, which are randomly polymerized in blocks of ethylene oxide and propylene oxide and which have ethylene oxide end blocks and thus a high concentration of reactive primary hydroxyl groups , The mass ratio of ethylene oxide and propylene oxide of the polyols for the hydroxyl prepolymer lies between 40:60 and 20:80 and that of the polyols of the isocyanate prepolymer between 40:60 and 10:90, the average molecular weights being 1,500 to 5,500.

Examples of suitable diisocyanates for preparing prepolymers are hexamethylene-1,6-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, diphenylmethane-4,4'-diisocyanate, toluene-2,4- and toluylene-2,6-diisocyanate and isomer mixtures from that.

The preparation of the prepolymers of the invention is set forth in detail in the embodiments.

To set the desired cure rate, up to 0.5 mass% catalyst can be added to the polyurethane reactive system. Suitable catalysts for the reactive system according to the invention are hydrolysis-stable, thermally activatable tin compounds. A very good cure can be achieved with organotin oxides, sulfides and thiolates such as bis (tributyltin) oxide, dibutyltin sulfide, dioctyltin sulfide, bis (tributyltin) sulfide, dibutyltin bis (thioglycolic acid 2-ethylhexylester), dioctyltin bis (thioglycolic acid-2 ethyl hexyl ester), octyl tin tfis (2-ethylhexyl thioglycolate), dioctyltin bis (thioethylene glycol 2-ethyl hexoate) and dibutyltin bis (thioethylene glycolollaurate).

Depending on the particular application, the reactive system and additives such as pigments, dyes, aging stabilizers u.a. be added.

embodiments example 1

Preparation of the Hydroxyl Prepolymer

In a 2.5-liter three-necked flask, 1.0 equivalent of a polyether diol having an OH number of 43.1 mg KOH / g, containing diethylene glycol as a starter on which is polymerized a randomly constructed from ethylene and propylene oxide-based strain and the an ethylene oxide endblock (total ethylene oxide = 30% by mass) and 2.5 equivalents of butane-1,4-diol. With stirring, the addition of 2 equivalents of toluene diisocyanate (2.4- / 2.6-lsomerengemisch in the ratio 80:20). After 70 minutes reaction time at 8O ⁰ C for an additional 11.5 equivalents are butane-1,4-diol was added. It is stirred for 30 minutes at this temperature and after cooling the catalyst - 0.3Ma .-% dioctyltin bis (thioglycolic acid 2-ethyl-hexyl ester) - added. The resulting prepolymer has an OH number of 349.2 mg KOH / g and a viscosity of 3000mPas.

Example 2

Preparation of the isocyanate prepolymer

There are added 0.6 equivalents of a polyether having OH number 34.8 with 4.5 equivalents of diphenylmethane-4,4'-diisocyanate and stirred at 80 ° C for one hour. The polyether consists of glycerol as a starter on which propylene oxide is grafted. The chains have an ethylene oxide endblock and the total ethylene oxide content is 13 mass%. Thereafter, the addition of 0.6 equivalents of a polyether diol having an OH number of 48.5 mg KOH / g, which contains dipropylene glycol as a starter, to which a randomly from ethylene and Prokopylenoxid constructed stem and a Ethylenoxidendblock is grafted. The total amount of ethylene oxide is 25Ma .-%. The reaction mixture is then stirred for a further 3.5 hours at 80.degree. _: ,

The NCO equivalent of this product is 690.0 g / equivalent and the viscosity is 8100 mPas.

Example 3

Artificial leather production

From the hydroxyl prepolymer of Example 1 and the isocyanate prepolymer of Example 2, with 5 mol .-% isocyanate excess with the addition of 2Ma .-% of the inventive course by branched polyether-polysiloxane copolymer having a molecular weight of 10000 and an ethylene-propylene oxide ratio of 50:50 Ma. -% - Using a laboratory coating system on polysiloxane-coated release paper polyurethane films produced in a layer thickness of 0.05 mm, the curing at 12O ⁰ C in 120 seconds. After applying a second layer of the same composition and thickness and after 50 seconds pre-reaction at 12O ⁰ C is laminated with roughened or not roughened cotton fabric. Thereafter, the further curing takes place within 60 seconds at 120 ° C and after cooling the separation from the release paper.

This results in composites with uniformly trained, bubble-free surface without wetting error, which have the following property profile:

Bending test (Bally test)

150000 load cycles without damage at 2O ⁰ C,

100,000 load changes without damage at -2O ⁰ C.

Layer separation strength 28-31 N / cm.

The polyurethane foils (thickness 0.05 mm) show the following mechanical properties:

Tensile strength: 15.0MPa

Elongation at break: 510% κ

Tear strength: 168 N / cm.

The cited polyurethane system is processed in the same way on polypropylene coated release paper into layers of 0.12 mm, which are laminated after 50 seconds pre-reaction at 120 ⁰ C with roughened cotton fabric. Subsequently, the final curing takes place as already stated.

Products with a defect-free surface structure were also obtained, which survive the fatigue bending test without damage at the indicated temperatures of 150000 cycles

 The delamination resistance is 30 N / cm

 The film used for composite production (thickness 0.12 mm) has the following mechanical properties:

Tensile strength: 14.5 MPa

Elongation at break: 480%

Tear strength: 150 N / cm.

Claims (1)

Claim: Polyurethane topcoat for the surface finishing of woven, nonwoven or nonwoven fabrics by the reverse coating process based on a solvent-free polyurethane component A, an isocyanate group-containing component B, leveling agents, catalysts and optionally further additives such as pigments, dyes or aging stabilizers characterized in that the hydroxyl-containing component A of the polyurethane reactive system is a solvent-free hydroxyl prepolymer obtained by reacting a diisocyanate or diisocyanate mixture with a di- to trifunctional Copolyetherpolyol with Ethylenoxidendblöcken or a mixture of such Copolyetherpolyole and butane-1,4-diol in the equivalent ratio of 1: 0.4 to 0.6: 1.1 to 1.5, wherein the total content of the hydroxyl compounds ^ relative to 1 equivalent of diisocyanates, 7 to 1.9 equivalents, and then filling to mi At least 6 equivalents of butane-1,4-diol is produced, the isocyanate group-containing component B is an isocyanate group-containing prepolymer prepared. from a diisocyanate or diisocyanate mixture and the above di- to trifunctional copolyether polyols in an equivalent ratio of 3: 1 to 10: 1, and the leveling agent is a branched polydimethylsiloxane copolymer having ether side groups of ethylene and propylene oxide in the molecular weight range of 8,000 to 12,000, wherein the amount of leveling agent is at most 2% by mass.