EP4259677A1

EP4259677A1 - Producing isocyanate-terminated, urethane group-containing prepolymers

Info

Publication number: EP4259677A1
Application number: EP21831301.3A
Authority: EP
Inventors: Christoph MALBERTZ; Stefan Hirschfeld; Dieter Mager; Oswald Wilmes
Original assignee: Covestro Deutschland AG
Current assignee: Covestro Deutschland AG
Priority date: 2020-12-09
Filing date: 2021-12-09
Publication date: 2023-10-18
Also published as: EP4011928A1; JP2023553901A; CN116529279A; WO2022122957A1; US20240052085A1

Abstract

The invention relates to a method for producing isocyanate-terminated, urethane group-containing prepolymers, comprising reacting a reaction mixture that contains a stoichiometric excess of at least one aliphatic and/or cycloaliphatic diisocyanate and a polyol composition having an OH number > 400, characterized in that the reaction mixture is mixed with a specific power input of 0.5 kW/m3 to 40 kW/m3, relative to the total volume of the reaction mixture.

Description

Production of isocyanate-terminated prepolymers containing urethane groups

The present invention relates to a process for the production of isocyanate-terminated prepolymers containing urethane groups. The invention also relates to the use of the prepolymers produced in this way for the production of polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality of >4, and a process for producing such polyisocyanates, the polyisocyanates themselves and the use of such polyisocyanates for producing elastic coatings.

Modification reactions of aliphatic diisocyanates have been known for a long time. The resulting polyisocyanates are used as crosslinking components in coating systems and adhesives. On the one hand, modification reactions in which the isocyanates react with themselves and which lead, for example, to the formation of biurets, isocyanurates, uretdiones or iminooxadiazinediones, are customary. On the other hand, the isocyanates can be reacted with polyols or polyamines to form urethane, allophanate and/or urea groups and thus oligomerized. The decisive factor is the formation of higher molecular weight adducts, which have a lower vapor pressure than the monomeric diisocyanates themselves. Unreacted diisocyanate is removed from the reaction mixture, for example by thin-layer distillation, and the polyisocyanate remains as the bottom product, which, if desired, can be diluted with solvent.

WO2019061019 describes polyisocyanates which are outstandingly suitable for producing 2-component systems for elastic coatings, in particular so-called soft-touch coatings. These polyisocyanates are characterized, inter alia, by a high isocyanate functionality, i.e. a high average number of isocyanate groups per molecule, and by a certain ratio of isocyanurate groups of the polyisocyanate to allophanate groups, with oligomers preferably also being contained in the polyisocyanate, in which Isocyanurate and allophanate groups are chemically linked, i.e. in the same molecule. Some of the isocyanurate groups can also be present in the isomeric form as iminooxadiazinediones.

Similar polyisocyanates have also been described in EP0496208A2. Here, as an example, a urethanization reaction of a (cyclo)aliphatic diisocyanate with a monofunctional alcohol is described on a laboratory scale, followed by a combined trimerization and allophanatization. The functionality of the resulting polyisocyanates is not mentioned.

However, the products made by the prior art methods can have too high haze values, making reliable use in optical extremely demanding area of coating systems and paintwork is restricted. This set of problems and possibilities for solving them are not addressed in the prior art.

The object of the invention was now to provide a process with which haze-free polyisocyanates containing urethane groups and/or allophanate and isocyanurate groups can be produced, particularly on an industrial scale, which can be used in coating systems, for example for producing elastic coatings. In the present case, non-turbidity polyisocyanates are those polyisocyanates which have a maximum turbidity of 2.0 NTU, determined by nephelometry in accordance with DIN EN ISO 7027-1:2016-11.

Surprisingly, it has now been found that the turbidity is due to unfavorable reaction conditions during the urethanization reaction.

In a first aspect, the invention relates to a process for the production of isocyanate-terminated prepolymers containing urethane groups, comprising reacting a reaction mixture containing a stoichiometric excess of at least one aliphatic and/or cycloaliphatic diisocyanate and a polyol composition with an OH number> 400, the reaction mixture having a specific power input in the range of 0.5 kW / m ³ to 40 kW / m ³ , based on the total volume of the reaction mixture, is mixed.

In a second aspect, the present invention relates to a process for preparing polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality >4, comprising the steps

(1) Production of an isocyanate-terminated prepolymer containing urethane groups,

(2) Reaction of the prepolymer obtained in step (1) in the presence of a catalyst with the formation of isocyanurate and allophanate groups to form a polyisocyanate,

(3) distillative removal of monomeric diisocyanate from the polyisocyanate obtained in step (2), where steps (1) and (2) can be carried out in the order mentioned in succession, partially simultaneously or simultaneously, characterized in that the preparation of the isocyanate-terminated, urethane group-containing prepolymer in step (1) by reacting a reaction mixture containing a stoichiometric excess of at least one aliphatic and/or cycloaliphatic diisocyanate and a polyol composition with an OH number > 400, characterized in that the reaction mixture with a specific power input in the range of 0 5 kW/m ³ to 40 kW/m ³ , based on the total volume of the reaction mixture. In a third aspect, the present invention relates to a polyisocyanate containing isocyanurate and allophanate groups with an average isocyanate functionality >4 and a turbidity measured by nephelometry according to DIN EN ISO 7027-1:2016-11 of at most 2.0 NTU, preferably at most 1.0 NTU and more preferably at most 0.5 NTU.

According to the invention, the expressions “comprising” or “containing” preferably mean “consisting essentially of” and particularly preferably “consisting of”.

In the present case, the mean OH functionality is to be understood as meaning the average number of OH groups per molecule. It can be calculated by dividing the total number of all OH groups of the polyols that make up the polyol composition by the number of molecules in the polyol composition.

Analogously, the mean isocyanate functionality is to be understood as the average number of NCO groups per molecule. In the present case, it is determined using the following formula:

Mn(GPC) F(GPC) =>

100x42

%NCO(Titr.)

Here, the NCO content is given in wt Tetrahydrofuran determined as eluent.

"At least one" as used herein refers to 1 or more, for example 2, 3, 4, 5, 6, 7, 8, 9 or more. In connection with components of the compounds described herein, this information does not refer to the absolute amount of molecules, but to the type of component, "at least one aliphatic and / or cycloaliphatic diisocyanate" therefore means, for example, that only one type of diisocyanate or several different Types of diisocyanates, without specifying the amount of each compound, may be included.

Numerical values given herein without decimal places refer to the full stated value with one decimal place. For example, "99%" means "99.0%".

Numerical ranges given in the format "in/from x to y" are inclusive of the stated values. When multiple preferred numeric ranges are given in this format, it is It goes without saying that all areas that result from the combination of the various endpoints are also recorded.

In the context of the present invention, the reaction of the reaction mixture is a urethanization reaction. This does not completely rule out any side reactions that may take place to a small extent.

As used herein, the term “stoichiometric excess” refers to the total amounts of the at least one aliphatic and/or cycloaliphatic diisocyanate and the polyol composition added at the end.

Suitable aliphatic or cycloaliphatic diisocyanates for the process according to the invention are selected, for example, from the group consisting of 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), 2-methyl-1,5-diisocyanatopentane , 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- and 1, 4-diisocyanatocyclohexane, 2,4- and 2,6-diisocyanato-l-methylcyclohexane, 1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, l-isocyanato-3,3,5-trimethyl- 5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4,4'-diisocyanatodicyclohexylmethane, 2,4'-diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, bis(isocyanatomethyl)norbomane and any mixtures thereof.

The aliphatic or cycloaliphatic diisocyanate is preferably selected from the group consisting of 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), l-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI ), 4,4'-diisocyanatodicyclohexylmethane and any mixtures thereof.

More preferably, the aliphatic or cycloaliphatic diisocyanate is a linear aliphatic diisocyanate selected from the group consisting of 1,5-diisocyanatopentane (PDI) and 1,6-diisocyanatohexane (HDI).

Instead of a single diisocyanate, a mixture of different diisocyanates can also be used in the process according to the invention. However, preference is given to using a single type of diisocyanate.

Suitable polyol compositions for the process according to the invention are those with an OH number >400. The alcohols present can optionally contain further functional groups which are, however, unreactive towards isocyanates, such as, for example, ether groups. The average OH functionality of the polyol composition is preferably >2 and <8, particularly preferred The average OH functionality of the polyol composition is >2 and <6, the average OH functionality of the polyol composition being very particularly preferably >3 and <5.

The polyol composition preferably contains one or more mono- and/or polyols selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, 2-pentanol, 3-pentanol , neopentyl alcohol, isomers of methyl butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,

Ethylene Glycol Monopropyl Ether, Ethylene Glycol Monobutyl Ether, Propylene Glycol Monomethyl Ether, Propylene Glycol Monoethyl Ether, Propylene Glycol Monopropyl Ether, Propylene Glyol Monobutyl Ether, Furfuryl Alcohol, Trimethylolpropane, Pentaerythritol, Ethylene Glycol, 1,2-Butanediol, 1,3-Butanediol, 1,4-Butanediol, 2,3-Butanediol, Diethylene Glycol, 1,2- Propanediol, 1,3-propanediol, glycerol and polyols which are obtainable by alkoxylation, preferably by ethoxylation or propoxylation of these polyols, particularly preferably by ethoxylation of these polyols. The polyol composition particularly preferably contains at least one polyol selected from the group consisting of trimethylolpropane, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, diethylene glycol and glycerol. The polyol composition very particularly preferably contains at least one polyol selected from the group consisting of trimethylolpropane, 1,3-butanediol, 1,4-butanediol and diethylene glycol.

In a preferred embodiment, these mono- or polyols make up at least 95%, preferably at least 99%, and more preferably at least 99.9% by weight of the polyol composition. The polyol composition preferably does not contain any solvents which are unreactive towards isocyanate.

In a particularly preferred embodiment of the invention, the polyol composition consists of trimethylolpropane.

The process according to the invention is preferably suitable for reactions for the production of isocyanate-terminated prepolymers on an industrial scale. On an industrial scale, a batch size of 10 kg to 100,000 kg per batch, preferably 100 kg to 50,000 kg per batch, particularly preferably 500 kg to 30,000 kg per batch, and very particularly preferably 1000 kg to 25,000 kg per batch, is to be understood here Batch size relates to the total mass of the starting materials in the reaction mixture.

Since the metering and conveying of solids on an industrial scale is generally difficult and therefore undesirable, it is advantageous to melt solid polyol compositions, such as, for example, trimethylolpropane, which is particularly preferably to be used, before adding them to the reactor. This eliminates the need to handle solids. Accordingly, in In another preferred embodiment of the invention, the polyol composition is added to the isocyanate in liquid form.

The urethanization reaction can generally be carried out in any reactor which the person skilled in the art deems suitable.

A stirred tank, for example, is suitable as a reactor. It is preferably a rotationally symmetrical stirred tank with a vertical main axis. The stirred tank can have different diameters along this main axis, but is preferably essentially cylindrical. Bottom and lid can be designed as a dished bottom or flat. For temperature control, the stirred tank can be provided with heat-exchanger tubes, welded-on half-tube profiles and/or a double jacket, with the heat-exchanger tubes being able to be embodied both on the inside and on the outside. It is preferably a reinforced stirred tank, ie a stirred tank which has baffles, preferably baffles attached to the tank wall. Alternatively or additionally, a substream of the reaction mixture can be removed from the reactor and temperature-controlled via an externally arranged heat exchanger before it is fed back into the reactor in order in this way to control the temperature in the reactor. Connections for inlets and outlets can be present at any point on the wall, lid and base of the stirred tank.

To carry out the urethanization reaction, it is advantageous first to charge the reactor with diisocyanate and to heat it to a temperature in the range from 60° C. to 140° C., preferably in the range from 70° C. to 130° C. and particularly preferably in the range from 80° C to heat up to 120 °C. The urethanization reaction preferably takes place at a reaction temperature in this range. The polyol composition is then added while mixing the contents of the reactor. In the case of a polyol composition which is solid at room temperature, it is advantageous, as already mentioned above, to add this in the form of a melt in order to keep the demands on the apparatus and auxiliary units low.

In order to fulfill the essential feature of the invention that the reaction mixture is mixed with a specific power input in the range from 0.5 kW/m ³ to 40 kW/m ³ , based on the total volume of the reaction mixture, the mixing can be done in different ways. For example, it is possible to remove a partial flow from the reactor and to feed it back into the reactor via a mixing device. The mixing device can be, for example, a rotor-stator mixer, a mixing nozzle, a static mixer, a stirred tank or a pump, for example a centrifugal pump. The mixing and thus the power input preferably takes place directly in the reaction vessel with the aid of an agitator. The agitator is preferably an agitator mounted on a rotating axis, preferably an axially conveying stirrer which, depending on the H/D ratio (H=height of the liquid level in the reactor and D=internal diameter of the reactor), can be designed in one or more stages. The higher the ratio, the more stirring levels are recommended.

The specific power input due to the mixing is in the range from 0.5 kW/m ³ to 40 kW/m ³ , preferably in the range from 0.7 kW/m ³ to 10 kW/m ³ and particularly preferably in the range of 1 kW / m ³ to 5 kW / m ³ , based in each case on the total volume of the reaction mixture. When using specific power inputs below the range according to the invention, it was observed that insoluble solid particles form, which lead to turbidity of the reaction mixture and the products produced therefrom. On the one hand, higher specific power inputs bring no further advantage and, precisely on an industrial scale, due to the viscosity of the reaction mixture, lead to the occurrence of high forces for which the corresponding apparatuses would have to be designed. The problem of turbidity occurs particularly severely when the dynamic viscosity of the polyol composition at the reaction temperature is at least 4 times, preferably at least 6 times, particularly preferably at least 8 times, that of the diisocyanate.

The stoichiometric excess is preferably chosen so that the equivalent ratio of the at least one aliphatic and/or cycloaliphatic diisocyanate present overall to the polyol composition is in the range from 4:1 to 200:1, preferably in the range from 5:1 to 50:1.

Another object of the invention is the use of the isocyanate-terminated prepolymer containing urethane groups produced by the process according to the invention for the production of polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality >4. The use of specific power inputs from 0.5 kW/m ³ to 40 kW/m ³ , preferably in the range from 0.7 kW/m ³ to 10 kW/m ³ and particularly preferably in the range from 1 kW/m ³ to 5 kW/m ³ , based in each case on the total volume of the reaction mixture, for urethanization reactions in a batch size of 10 kg to 100,000 kg per batch, preferably 100 kg to 50,000 kg per batch, particularly preferably 500 kg to 30,000 kg per batch and very particularly preferably 1000 kg to 25000 kg per batch, the batch size being based on the total mass of the starting materials in the urethanization reaction, is a further subject of the invention.

A further subject of the invention is a process for the preparation of polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality >4, comprising the steps

(1) Preparation of an isocyanate-terminated urethane group-containing prepolymer (2) Reaction of the prepolymer obtained in step (1) in the presence of a catalyst with the formation of isocyanurate and allophanate groups to form a polyisocyanate

(3) Separation of monomeric diisocyanate from the polyisocyanate obtained in step (2), wherein steps (1) and (2) can be carried out in the order mentioned in succession, partially simultaneously or simultaneously, characterized in that the preparation of the isocyanate-terminated, urethane-group-containing Prepolymer takes place in step (1) as described above.

Suitable catalysts for the reaction in step (2) are, for example, the catalysts mentioned in WO2019061019A1 on page 11, line 13 to page 13, line 11. They are added either as such or dissolved in a suitable organic solvent to accelerate the formation of the isocyanurate and allophanate groups. Preferred catalyst solvents are those which have isocyanate-reactive groups and can accordingly be incorporated into the polymer. These are, for example, monohydric or polyhydric alcohols such as methanol, ethanol, «-propanol, isopropanol, «-butanol, «-hexanol, 2-ethyl-1-hexanol, ethylene glycol, propylene glycol, isomers of butanediol, 2-ethyl-1,3 -hexanediol, glycerin, ether alcohols such as l-methoxy-2-propanol, 3-ethyl-3-hydroxymethyloxetane,

tetrahydrofiirtyryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,

Diethylene glycol monobutyl ether, diethylene glycol, dipropylene glycol, polyethylene glycols, polypropylene glycols, mixed polyethylene-Zpolypropylene glycols and their monoalkyl ethers, ester alcohols such as ethylene glycol monoacetate, propylene glycol monolaurate, glycerol diacetate, glycerol monobutyrate or 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, unsaturated alcohols such as allyl alcohol, 1,1 -dimethylallyl alcohol or oleyl alcohol, araliphatic alcohols such as benzyl alcohol or monosubstituted amides such as N-methylformamide, N-methylacetamide, cyanoacetamide or 2-pyrrolidinone or mixtures of such solvents.

The reaction in step (2) is preferably carried out under an inert gas atmosphere at a temperature in the range from 0.degree. C. to 150.degree. C., preferably in the range between 20.degree. C. and 130.degree. C. and particularly preferably between 40.degree. C. and 120.degree. While the urethanization reaction to form the prepolymer in step (1) generally proceeds spontaneously under these conditions, the reaction to form isocyanurate and allophanate groups essentially takes place only after addition of a corresponding catalyst.

After the desired degree of conversion has been reached, the conversion is stopped. This can be done, for example, by cooling the reaction mixture. Stopping preferably takes place by adding a catalyst poison and optionally subsequently heating the reaction mixture to a temperature above 80.degree. Suitable catalyst poisons (stoppers) are known to those skilled in the art. These are, for example, hydrochloric acid, phosphoric acid, phosphonic acid, carboxylic acid chlorides such as acetyl chloride, benzoyl chloride or isophthaloyl dichloride, sulfonic acids or sulfonic esters such as methanesulfonic esters, p-toluenesulfonic acid, trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, dodecylbenzenesulfonic acid, methyl p-toluenesulfonate, ethyl p-toluenesulfonate, mono- or dialkyl phosphates such as tridecyl phosphate, dibutyl phosphate, dioctyl phosphate, or silylated acids such as methanesulfonic acid trimethylsilyl ester, trifluoromethanesulfonic acid trimethylsilyl ester,

tris(trimethylsilyl)phosphate or diethyl(trimethylsilyl)phosphate.

The amount of catalyst poison required to stop the reaction depends essentially on the amount of catalyst used. In principle, an equivalent amount of stopper is required, but since part of the catalyst is usually deactivated in some other way, a smaller amount of stopper may also be sufficient.

The catalyst poison can also be added as such or in solution, suitable solvents being, for example, the catalyst solvents listed above. In addition to these solvents, the starting isocyanates can also be used as solvents for the catalyst poisons.

After the reaction has ended, monomeric diisocyanate is separated from the reaction product. This preferably takes place by distillation, for example at a pressure below 5 mbar, preferably below 1 mbar and particularly preferably below 0.5 mbar and for example at a temperature in the range from 100 to 200° C., preferably in the range from 120 to 180° C. The residual content of monomeric diisocyanate after the distillation is preferably <0.50% by weight, particularly preferably <0.3% by weight and particularly preferably <0.2% by weight.

Polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality >4 and which can be obtained or produced using the process according to the invention are another subject of the invention.

The polyisocyanates according to the invention containing isocyanurate and allophanate groups have a turbidity measured by nephelometry in accordance with DIN EN ISO 7027-1:2016-11 of at most 2.0 NTU, preferably at most 1.0 NTU and particularly preferably at most 0.5 NTU, with the Polyisocyanate has a residual monomer content according to DIN EN ISO 10283:2007-11 of preferably <0.50% by weight, particularly preferably <0.3% by weight and very particularly preferably <0.2% by weight. The NCO content of these polyisocyanates is preferably 15% by weight to 25% by weight, measured by titration in accordance with DIN EN ISO 11909:2007-05. It is also preferred that the residual content of monomeric diisocyanate is <0.50% by weight, particularly preferably <0.3% by weight and particularly preferably <0.2% by weight, measured according to DIN EN ISO 10283:2007-11 by gas chromatography using an internal standard.

If necessary, a solvent can also be used to lower the viscosity of the isocyanurate- and allophanate-group-containing polyisocyanate of the present invention. Suitable solvents include those known as paint solvents, such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, 1-methoxy-2-propyl acetate, 3-methoxy-w-butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone , cyclohexanone, toluene, xylene, chlorobenzene, benzine, solvent naphtha, carbonic acid esters such as dimethyl carbonate, diethyl carbonate, 1,2-ethylene carbonate, 1,2-propylene carbonate, lactones such as ß-propiolactone, γ-butyrolactone, s-caprolactone or s-methylcaprolactone , but also solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate,

diethylene glycol monobutyl ether acetate, N-methylpyrrolidone or N-methylcaprolactam. Any mixtures of the solvents exemplified above can also be used.

The polyisocyanates according to the invention containing isocyanurate and allophanate groups are particularly suitable for use in a two-component system, which is another subject of the invention.

The two-component system according to the invention contains a component A) comprising at least one NCO-reactive compound, and a component B) comprising at least one polyisocyanate according to the invention containing isocyanurate and allophanate groups. The at least one NCO-reactive compound is preferably a polyol, particularly preferably at least one polyol with a hydroxyl functionality of between >2 and <5. In addition, other polyols and additives, such as defoamers, matting agents, catalysts, stabilizers, antioxidants, biocides, fillers, paint pigments, inorganic or organic pigments, flow control agents, light stabilizers, dispersants, thickeners, adhesives, inhibitors, catalysts, emulsifiers and / or others Excipients may be included, these optional compounds in component A) and / or in component B) may be included.

If necessary, a solvent can also be used to reduce the viscosity of the polyol or the mixed two-component system. Suitable solvents are, for example, those known as paint solvents, such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, 1-methoxy-2-propyl acetate, 3-methoxy-w-butyl acetate. Acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, chlorobenzene, benzine, solvent naphtha, carbonic acid esters such as dimethyl carbonate, diethyl carbonate, 1,2-ethylene carbonate, 1,2-propylene carbonate, lactones such as ß- Propiolactone, y-butyrolactone, s-caprolactone or s-methylcaprolactone, but also solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, N-methylpyrrolidone, N-methylcaprolactam or water.

The two-component system according to the invention can preferably be used to coat substrates. Therefore, a further object of the present invention is a coating obtainable or produced by reacting the two-component system according to the invention or by reacting the polyisocyanate according to the invention containing isocyanurate and allophanate groups with a component which is reactive towards isocyanate groups, the respective reaction taking place under the action of heat and/or actinic radiation and/or in the presence of one or more catalysts. Preferably the coating is an elastic coating.

For this purpose, the two-component coating system is preferably applied to the optionally pretreated, for example primed, substrate and cured, for example by heating. The composite of a substrate and the coating according to the invention, preferably the elastic coating according to the invention, is a further subject of the present invention.

examples

All percentages are by weight unless otherwise noted.

The NCO content was determined titrimetrically according to DIN EN ISO 11909:2007-05.

The residual monomer content was measured according to DIN EN ISO 10283:2007-11 by gas chromatography using an internal standard.

The turbidity was determined by nephelometry according to DIN EN ISO 7027-1:2016-11.

Comparative example 1

1500 kg of hexamethylene diisocyanate (HDI) were initially taken under a nitrogen atmosphere and heated to 105° C. in a 3 m ³ stirred reactor equipped with a multistage pulsed countercurrent stirrer (MIG stirrer). At this temperature, 150 kg of a melt of trimethylolpropane were added with stirring. The specific power input was 0.25 kW/m ³ based on the total volume of the reaction mixture. About 2 hours after the addition was complete, the urethanization reaction was complete and the reactor temperature was lowered to 95°C. A sample of the prepolymer obtained was taken and subjected to visual inspection. This resulted in a clearly visible turbidity due to suspended matter. The trimerization and allophanatization reaction was then started by adding a 0.5% trimethylbenzylammonium hydroxide solution in 2-ethylhexanol. Upon reaching 36% NCO, the reaction was terminated by adding a stopper solution (10% dibutyl phosphate in HDI) in a weight ratio of 100 parts catalyst solution to 3 parts stopper solution. The mixture was stirred at 95° C. for a further 30 minutes and then the remaining monomeric HDI was separated off in a short-path evaporator at 140° C. and 0.1 mbar. The product obtained directly from the process had a turbidity of 2.6 NTU, an NCO content of 19.5% and a residual monomer content of 0.09%. Dilution with butyl acetate to a polyisocyanate content of 80% by weight in the diluted product also failed to detect any reduction in turbidity.

example 1

Comparative example 1 was repeated, with the difference that the stirrer speed was increased, so that a specific power input of 2.2 kW/m ³ , based on the total volume of the reaction mixture, was used. The product obtained directly from the process had a turbidity of 0.29 NTU, an NCO content of 19.3% and a residual monomer content of 0.17%. No greater turbidity was found for the product diluted with butyl acetate to a polyisocyanate content of 80% by weight either. example 2

Example 1 was repeated, with the difference that the stirrer speed was reduced, so that a specific power input of 0.8 kW/m ³ , based on the total volume of the reaction mixture, was used. The product obtained directly from the process had a turbidity of 0.45 NTU, an NCO content of 19.5% and a residual monomer content of 0.20%. No greater turbidity was found for the product diluted with butyl acetate to a polyisocyanate content of 80% by weight either.

Claims

patent claims

1. A process for producing isocyanate-terminated prepolymers containing urethane groups, comprising reacting a reaction mixture containing a stoichiometric excess of at least one aliphatic and/or cycloaliphatic diisocyanate and a polyol composition with an OH number >400, the reaction mixture having a specific power input in the range from 0 5 kW/m ³ to 40 kW/m ³ , based on the total volume of the reaction mixture.

2. The method according to claim 1, characterized in that the at least one aliphatic and / or cycloaliphatic diisocyanate is selected from the group consisting of 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 2-methyl-l ,5-diisocyanatopentane, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- and 1,4-diisocyanatocyclohexane, 2,4- and 2,6-diisocyanato-l-methylcyclohexane, 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, l-isocyanato-3,3,5-trimethyl- 5-isocyanatomethylcyclohexane, 4,4'-diisocyanatodicyclohexylmethane, 2,4'-diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, bis(isocyanatomethyl)norbomane and any mixtures thereof.

3. The method according to claim 1 or 2, characterized in that the polyol composition has an average OH functionality >2 and <8, preferably >2 and <6 and particularly preferably >3 and <5.

4. The method according to any one of claims 1 to 3, characterized in that the polyol composition contains at least one polyol selected from the group consisting of trimethylolpropane, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1, 4-butanediol, diethylene glycol and glycerol and preferably at least one polyol selected from the group consisting of trimethylolpropane, 1,3-butanediol, 1,4-butanediol and diethylene glycol.

5. The method according to any one of claims 1 to 4, characterized in that the reaction in a batch size of 10 kg to 100,000 kg per batch, preferably 100 kg to 50,000 kg per batch, particularly preferably 500 kg to 30,000 kg per batch and very particularly preferably 1000 kg to 25000 kg per batch is carried out, the batch size being based on the total mass of the starting materials in the reaction mixture.

6. The method according to any one of claims 1 to 5, characterized in that the reaction is carried out in a stirred tank and the specific power input takes place by mixing with an agitator, preferably by mixing with an axially conveying stirrer.

7. The method according to any one of claims 1 to 6, characterized in that the stoichiometric excess is selected such that an equivalent ratio of the total of at least one aliphatic and/or cycloaliphatic diisocyanate present to the polyol composition is in the range from 4: 1 to 200: 1 , preferably in the range 5:1 to 50:1.

8. The method according to any one of claims 1 to 7, characterized in that the reaction of the reaction mixture at a reaction temperature in the range of 60 to 140 ° C, preferably in the range of 70 ° C to 130 ° C and particularly preferably in the range of 80 ° C to 120 °C.

9. Use of an isocyanate-terminated, urethane-group-containing prepolymer produced according to one of Claims 1 to 8 for the production of polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality of >4.

10. Process for the preparation of polyisocyanates containing isocyanurate and allophanate groups and having an average isocyanate functionality >4, comprising the steps

(3) distillative removal of monomeric diisocyanate from the polyisocyanate obtained in step (2), where steps (1) and (2) can be carried out in the order mentioned in succession, partially simultaneously or simultaneously, characterized in that the preparation of the isocyanate-terminated, urethane group-containing prepolymer in step (1) according to any one of claims 1 to 8 takes place.

11. Polyisocyanate containing isocyanurate and allophanate groups with an average isocyanate functionality >4 and a turbidity measured by nephelometry in accordance with DIN EN ISO 7027-1:2016-11 of at most 2.0 NTU, preferably at most 1.0 NTU and particularly preferably at most 0, 5 NTU, the polyisocyanate having a residual monomer content according to DIN EN ISO 10283:2007-11 of preferably <0.50% by weight, particularly preferably <0.3% by weight and very particularly preferably <0.2% by weight. %.

12. Use of a polyisocyanate produced according to claim 10 in a two-component system.

13. Two-component system containing a component A) comprising at least one NCO-reactive compound, and a component B) comprising at least one polyisocyanate according to claim 11. - 16 - Coating obtainable or produced by reacting a two-component system according to claim 13 or by reacting a polyisocyanate containing isocyanurate and allophanate groups according to claim 11 with an isocyanate-reactive component, the respective reaction under the action of heat and/or actinic radiation and/or in the presence of one or more catalysts. Composite of a substrate and a coating according to claim 14.