GB2124640A - Process for the production of modified polyisocyanates and the use thereof - Google Patents

Abstract

A process for the production of a modified polyisocyanate which comprises reacting an organic polyisocyanate with a sub- stoichiometric quantity of a compound containing one or more isocyanate- reactive groups as a modifying agent, a from 10 to 80%, by weight, aqueous solution of a water-soluble isocyanate-reactive group-containing compound selected from primary and secondary alcohols, carboxylic acids, ammonium carboxylates and amides being used as modifying agent is disclosed. Such modified polyisocyanates may be used in the production of polyurethane plastics by the isocyanate polyaddition process.

Description

SPECIFICATION Process for the production of modified polyisocyanates and the use thereof This invention relates to a new process for the production of modified polyisocyanates by reacting simple organic polyisocyanates with substoichiometric quantities of certian modifying agents containing isocyanate-reactive groups and to the use of the products obtained by this process as synthesis component in the production of polyurethane plastics.

The production of modified polyisocyanates by reacting simple polyisocyanates with substoichiometric quantities jof compounds containing isocyanate-reactive groups is already known in principle. Thus, US-PS No. 3,124,605 for example describes the production of polyisocyanates containing biuret groups by reacting organic polyisocyanates with water. US-PS No. 3,358,010 describes the production of polyisocyanates contaiing biuret groups by reacting organic polyisocyanates with substoichiometric quantities of a tertiary alcohol. US-PS 4,127,599 relates to the production of polyisocyanates containing biuret groups by reacting organic polyisocyanates with substoichiometric quantities of a mixture of water and organic amines. DE-OS No. 26 54 745 recommends the use of a ternary mixture of alcohols, primary amines and water as a modifying agent. The biuret-groupcontaining polyisocyanates obtainable by this known process are suitable for use as starting materials in the production of polyurethane plastics having improved mechanical properties by comparison with the use of the corresponding unmodified polyisocyanates.

Using special modifying agents described in more detail hereinafter, the process according to the invention, which is also described in more detail hereinafter, makes it possible to produce modified organic polyisocyanates which represent a further addition to the state of the ar insofar as polyurethane plastics and, more particularly, polyurethane foams produced form them are superior in their mechanical properties, particularly compression set and compression hardness, to corresponding foams based on known biuret-modified polyisocyanates.

The present invention relates to a process for the production of modified polyisocyanates by reacting organic polyisocyanates with substoichiometric quantities of compounds containing isocyanate-reactive groups as modifying agents, characterised in that 10 to 80% by weight aqueous solutions of water-soluble compounds containing isocyanate-reactive groups selected from the group comprising primary and secondary alcohols, carboxylic acids, ammonium carboxylates and amides, are used as the modifying agents.

The present invention also relates to the use of the modified polyisocyanates obtained by this process as synthesis component in the production of polyurethane plastics by the isocyanate polyaddition process.

Starting polyisocyanates suitable for use in the process according to the invention are any known aliphatic, araliphatic, cycloaliphatic and, more particularly, aromatic polyisocyanates. Examples of suitable starting polyisocyanates are hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, 2,4- and/or 2,6-diisocyanatotoluene or polyisocyanate mixtures of the diphenyl methane series of the type which may be obtained in known manner by phosgenating aniline/formaldehyde condensates. The last-mentioned aromatic polyisocyanates, particularly 2,4- and/or 2,6diisocyanatotoluene, are the preferred starting materials for the process according to the invention.

10 to 80% by weight and preferably 1 5 to 50% by weight aqueous solutions of compounds of the above-mentioned type are used as modifying agents in the process according to the invention.

Particularly preferred modifying agents are aqueous solutions of organic carboxylic acids, ammonium carboxylates and/or acid amides.

Examples of suitable modifying agents are aqueous solutions of alcohols having a molecular weight in the range from 32 to 400, such as methanol, ethanol, cyclohexanol, isopropanol, phenol, ethylene glycol, propylene glycol and oligomeric glycols, glycerol, trimethylol propane, pentaerythritol, sorbitol, xylitol, formose, fructose, glucose, sucrose, dextrose and other sugars and sugar alcohols; aqueous solutions of amides having a molecular weight in the range from 45 to 200, such as urea, melamine, dicyanodiamide, formamide, acetamide, biuret, acrylamide, dicyanodiamide, cyanamide, maleic amide, oxamide; aqueous solutions of water-soluble carboxylic acids having a molecular weight in the range from 46 to 200 and containing aliphatically or aromatically bound carboxyl groups, such as formic acid, acetic acid, phthalic acid, trimellitic acid, maleic acid, itaconic acid, adipic acid, oxalic acid, citric acid, glycolic acid, acrylic acid or methacrylic acid, and aqueous solutions of ammonium salts of the carboxylic acids mentioned by way of example with ammonia, hydrazine or amines having a molecular weight in the range from 31 to 200, such as methylamine, ethylamine, ethylene diamine, propylene diamine, hexamethylene diamine, diethylene triamine, diethylene tetramine, tetraethylene pentamine, ethanolamine, diethanolamine, cyclohexyl amine or aniline.

Aqueous solutions of salts of carboxylic acids and amines of the type mentioned by way of example are particularly suitable.

It is of course also possible to use aqueous solutions of mixtures of the compounds containing isocyanate-reactive groups which were mentioned by way of example earlier on. In principle, it is also possible to use aqueous solutions of other compounds containing isocyanate-reactive groups, such as sulfonic acids, sulfonamides, polysaccharides, peptides or proteins.

In the process according to the invention, the modifying agents are used in quantities corresponding to an equivalent ratio of isocyanate groups of the polyisocyanate to be modified to isocyanate-reactive groups, including the water used as solvent, of from 1:0.01 to 1:0.4 and preferably from 1:0.05 to 1:0.3.

In the process according to the invention, the modifying agent and the polyisocyanate are reacted with vigorous stirring, optionally in the presence of catalysts accelerating the isocyanate addition reaction, such as for example tertiary amines, such as N,N-dimethyl benzylamine or bis (dimethylaminoethyl)-ether, in catalytically active quantities and/or-for more effective homogenisation of the initially two-phase reaction mixture - in the presence of emulsifiers such as, for example, the addition products of ethylene oxide with substituted phenols, such as nonyl phenol, known as emulsifiers in quantities of from 0.01 to 5% by weight, based on the mixture as a whole. Where tertiary amines are used as catalysts, it is best to deactivate the end product after its production by the addition of a stabiliser, such as benzoyl chloride for example.

The process according to the invention is carried out at a temperature in the range from 20 to 2000 C, preferably at a temperature in the range from 50 to 1 800C and, more particularly, at a temperature in the range from 80 to 1 500 C, temperatures in the range from 90 to 1 200C being particularly suitable.

It is particularly advisable to carry out the modifying reaction according to the invention with vigorous mixing of the reactants and with mechanical size-reduction of the reaction products initially accumulating which form a dispersion in excess starting polyisocyanate. Technically the easiest way of doing this is to carry out the mixing process and the size-reduction process at the same time in the reaction zone. However, it is also possible to carry out the first stage, i.e. the modifying reaction, in such a way that an unstable dispersion of the modified products in excess polyisocyanate is initially obtained and, for example in the event of continuous working, is subjected after its production to the sizereduction process with a high local energy density, for example until an opaque solution is obtained.

Suitable mixing units, particularly for size-reduction of the primary dispersions, are for example ultrasonic size-reducing machines or machines in which the streams of material are projected against one another or against baffles at high speed through nozzles. However, machines of the type in which the dispersion to be size-reduced is projected through grids or slots with high acceleration and an intense shear effect are particularly suitable. This result is achieved for example using machines operating on the rotor-stator principle which force the material for example through perforated plates lying on top of one another and moving in opposite directions, through rotating slotted cylinders separated by a narrow gap or through contra-rotating toothed rings. Machines of this type are available on the market and are known for example as mixing sirens.In addition to machines of this type, it is also possible in principle to use size-reducing machines operating on other principles, for example on the principle of the ball mill, the bead mill, the impact mill or the friction mill. Machines operating on the rotor-stator principle are preferably used because their technically advantageous construction is particularly suitable for continuous operation or rather continuous circulation.

Machines of this type are marketed for example under the names of Supraton, Condux or Ultraturrax. Particularly suitable mixing units of this type enable liquid materials to be mixed for an output in the region of the mixing head of 15 to 250 watts/cc.

With machines of this type, it is best to adopt the following procedure for example: A vessel is filled with the polyisocyanate to approximately 50% by volume, after which the stirrer head of a size-reducing machine operating on the rotor-stator principle (for example Ultraturrax, type T 45, generator, Type T 45 G 4) is introduced into the vessel and the polyisocyanate stirred at a moderate speed. The modifying agent is then introduced over a period of 5 to 10 minutes with vigorous stirring. After a few minutes, a deposit is formed and the viscosity increases. The rotational speed of the Ultraturrax is then increased and, in case serious thickening occurs, the stirrer head is charged with the stream of material.After about 20 minutes, the viscosity begins to decrease and, after about 25 to 45 minutes, a stable, thinly liquid and finely particulate dispersion is obtained, its isocyanate number remaining substantially constant. If the Ultraturrax is left rotating at a high speed, a more or less opaque to clear solution is generally formed after 35 to 75 minutes.

The modification reaction according to the invention may optionally be carried out in an inert gas atmosphere or in the absence of air in order to rule out undesirable influences of atmospheric oxygen and moisture. In addition to CO2, nitrogen or argon for example may be used for this purpose.

In the course of the reaction, the temperature rises not only on account of the exothermic chemical reaction, but also under the effect of the mechanical energy applied, so that in many cases the reaction mixture does not have to be externally heated to reach the above-mentioned reaction temperatures. In some cases, the temperature rises to such an extent that the reaction may even have to be cooled. Carbon dioxide formed during the reaction may be let off during the mixing of the reaction components.

The reaction conditions of the process according to the invention are generally maintained until the reaction mixture has a constant isocyanate content, i.e. until two samples taken at a brief interval of about 5 to 10 minutes show no difference in their isocyanate content. In general, the reaction according to the invention is over after at most 1 20 minutes and, in many cases, less than 20 minutes.

During the modifying reaction according to the invention, in which a coarse, highly viscous dispersion is often formed during the first stage of the reaction, the modification mixture not only becomes more finely dispersed during the following or simultaneous size-reduction phase of the second stage of the reaction, but also thinly liquid again despite the increase in the particle surfaces attributable to the size-reduction process and, as the size-reduction process continues, subsequently changes from a stable, relatively thinly liquid finely particulate dispersion having a stable isocyanate content as defined above into a more or less clear solution which also has a stable isocyanate content.

The products obtained by the process according to the invention are eminently suitable for use as a synthesis component in the production of polyurethane plastics by the isocyanate polyaddition process. The products obtained by the process according to the invention are particularly suitable for the production of polyurethane foams having improved mechanical properties. In this case, the products obtained by the process according to the invention are used instead of or together with the usual polyisocyanate(s) in the processes known per se.

In the following Examples, all the percentages and parts quoted represent percentages and parts by weight unless otherwise indicated.

EXAMPLE 1 2000 parts of technical diisocyanatotoluene consisting of approximately 80% of 2,4- and 20% of 2,6-isomer are vigorously stirred in a cylindrical vessel equipped with a mixing unit operating on the rotor-stator principle (Turrax type T 45/G 4), which in the region of the mixing head develops a maximum stirring power of 25 watts/cc, the stirrer rotating at less than 50% of its maximum speed. At the same time, a mixture of 30 parts of water, 30 parts of methanol, 0.1 part of N,N-dimethyl benzylamine and 5 parts of a non-ionic emulsifier (a standard commercial ethylene oxide/nonyl phenol adduct) is run in over a period of 5 minutes. The rotational speed of the stirrer is then increased to 80% of its maximum speed.After about 1 5 minutes, the temperature of the reaction mixture has risen from 250C to 1050C and is kept constant by cooling.

Samples are then continuously taken: Total mixing time: % Isocyanate: Nature of dispersion: 15 minutes 29.3 coarse, thick 20 minutes 35.0 settled out, thinly liquid 30 minutes 38.5 stable, thinly liquid 35 minutes 38.7 stable, thinly liquid 40 minutes 38.7 opaque solution, thinly liquid 50 minutes 38.8 almost clear solution, thinly liquid EXAMPLE 2 The procedure is as in Example 1, except that, instead of the stirrer used in that Example, a gate paddle stirrer rotating at approximately 300 r.p.m. is initially used for stirring the reactants. Only after the modifying agent has been added is the gate paddle stirrer replaced by the mixing unit described in Example 1. The reaction mixture is then stirred for 25 minutes at 1 80CC at 80% of the maximum rotational speed, a stable opaque product solution having an isocyanate content of 38.8% being obtained.

If the modifying agent reacts completely with the isocyanate, the end product may theoretically be expected to have an isocyanate content of 39%.

EXAMPLES 3 TO 26 The procedure for the Examples set out in the following Table is the same as in Example 1 using the Turrax machine throughout the entire reaction time, the reaction temperature being kept at 105 to 11 00C after a reaction time of 20 minutes. 2000 parts of the same technical tolylene diisocyanate as in Example 1 are used. A solution of 0.05 part of bis-dimethylaminoethyl ether and 0.05 part of N,Ndimethyl benzylamine in 30 parts of water and 30 parts of the Zerewitinoff-active compounds mentioned in the following are added as modifying agents over a period of about 3 minutes.

Example Compound Reaction -NCO No. added time % Remarks mins.

3 methanol 30 39.8 thinly liquid, stable dispersion 4 methanol 50 38.9 thinly liquid, stable solution 5 ethylene glycol 55 35.8 opaque solution 6 0.15% of methyl cellulose in aqueous solution 45 38.2 solution 7 glycerol 30 38.2 thinly liquid, stable dispersion 8 glycerol 60 37.4 clear solution 9 same as for 6, but twice the quantity 45 35.6 yellowish clear solution 10 trimethylol propane 60 42.0 stable dispersion, thinly liquid 11 sucrose 60 44.6 thinly liquid dispersion 12 urea , 60 39.2 opaque solution 13 formamide 60 43.6 yellowish fine dispersion 14 fructose 60 41.5 stable thinly liquid dispersion 15 dicyanodiamide 60 44.9 stable fine dispersion 16 acrylamide 60 38.9 stable dispersion 17 maleic acid 60 41.8 yellow fine dispersion 1 8 acetic acid 60 42.0 stable fine dispersion 19 ammonium acetate 60 38.0 stable fine dispersion 20 ammonium formate 60 40.5 stable fine dispersion 21 ammonium carbonate 60 39.9 stable fine dispersion 22 ethanolamine 60 39.7 opaque solution 23 diethyanolamine, urea (1::1) 60 39.0 opaque solution 24 acetic acid (50 parts) 60 37.0 stable fine dispersion 25 same as for 13, but without activator 60 42.9 stable fine dispersion 26 same as for 19, but without activator 60 38.1 stable fine dispersion The end products obtained may be stabilised by the addition of 0.1 to 0.3 part of benzoyl chloride.

In the present case, 0.1 part of benzoyl chloride was added to the products of examples 3, 5, 13 and 16.

Both the stabilised samples and also the unstabilised samples remained thinly liquid and easy to handle during storage for 2 months at room temperature.

EXAMPLE 27 A mixture (referred to as component A in Examples 28 to 32 below) consisting of 100.00 parts of a trimethylol-propane-started polyoxyethylene-oxypropylene)-triol having an OHnumber of 35 3.00 parts of water 2.00 parts of diethanolamine 0.50 part of a chlorine-containing polysiloxane stabiliser 0.30 part of a 33% solution of tnethylene diamine in dipropylene glycol 0.10 part of dimethylaminoethyl ether 0.15 part of tin dioctoate is intensively mixed with 54.7 parts of the modification product of Example 5 and the resulting mixture reacted in an open vessel. An open-cell, non-shrinking foam is formed, its mechanical properties being shown in Table II.

EXAMPLES 28 TO 32 The procedure is as in Example 27. The A-component is reacted with the quantity indicated below of the corresponding modified isocyanate according to Examples 8, 10, 12, 1 3 and 1 9 (Table I).

TABLE I Example No. 28 29 30 31 32 Reacted with the A-component Parts by weight 52.1 46.4 49.7 44.7 46.6 Modified isocyanate according to Example No. 8 10 12 13 19 Open-cell, non-shrinking elastic foams are obtained in Examples 27 to 32, their mechanical properties being set out in Table II.

TABLE II Example No. 27 28 29 30 31 32 Modification product used (Example No.) 7 10 14 16 17 21 Gross density (kg/m3) 33 38 43 43 45 41 Tensile strength (KPa) 100 125 80 130 140 130 Breai;ing slongation (%) 125 130 100 130 120 120 Compression hardness (KPa) with 40% deformation 3.9 5.0 5.5 4.9 6.0 4.6 Compression set after 90% deformation (%) 11 15 5 12 15 15 EXAMPLES 33 TO 37 The isocyanate component (1) is introduced at 200C into a stirrer-equipped vessel provided with an internal thermometer. The pre-mixed components (2) and (3) are then quickly added while stirring using the mixing unit described in Example 1 (50% of maximum mixing speed = 12.5 watts/cc in the region of the mixing head). The individual mixtures are then stirred for 1 hour at full speed (25 watts/cc in the region of the mixing head), the temperature being kept to around 1 050C by cooling. Finally, the mixtures are cooled to 200C and stabilised by the addition of component (4). Slightly to highly milky solutions and suspensions are obtained and may be directly used as isocyanate component in the production of polyurethane foams.

TABLE lil Example No. 33 34 35 36 37 (quantities) Component I 2,4-/2,6-diisocyanatotoluene 2000 2000 2000 2000 2000 (80:20) "T 80) Bis-(dimethylaminoethyl)-ether 0.1 0.1 0.1 0.1 0.1 Component 2 Water 30 30 30 15 30 Ethoxylated nonyl phenol 10 Ethanolamine 17.1 Ethylenediamine 15 10 Ammonia, 25% 20 Diethanolamine 17.6 Component 3 Formic acid 12.8 Acetic acid 15 20 Adipic acid 12.3 Phthalic acid 36 Component 4 Benzoyl chloride 1.0 1.0 1.0 1.0 1.0 NCO-content 39.1 40.7 38.2 39.0 41.4 EXAMPLE 38 The products of Examples 33 to 37 are each diluted with "T 80" to an NCO-content of 43%.

Foams were then produced using quantities of 51.2 parts of the samples thus diluted and 40.5 parts of unmodified "T 80". To this end, the polyisocyanate components were intensively mixed with the following polyol component and the resulting mixtures reacted in an open vessel: Polyol content: 100.00 g of a polyether (OH number 35) produced by the alkoxylation of trimethylol propane with a mixture of propylene oxide and ethylene glycol (ratio by weight 78:22), 3.00 g of water 2.00 g of diethanolamine 0.5 g of a standard commercial polysiloxane stabiliser, 0.3 g of a 33% solution of triethylene diamine in dipropylene glycol, 0.1 g of bis-(dimethylaminoethyl)-ether, 0.15 g oftindioctoate.

Open-cell, non-shrinking foams are obtained in every case where polyisocyanates modified in accordance with the invention are used. Their mechanical properties are shown in Table IV below. The foam produced using unmodified "T 80" shows a marked tendency towards shrinkage, reduced compression hardness and reduced compression set (CS).

TABLE IV Comparison Example No. 33 34 35 36 37 ("T 80") Gross density kg/m3 33 35 33 33 34 32 Tensile strength KPa 90 80 85 90 90 90 Breaking elongation % 155 1 50 1 55 160 1 55 140 Compression hardness KPa with 40% deformation 1.8 1.7 1.7 1.8 2.0 1.4 CS% after 90% deformation 3.6 6.0 5.8 6.8 6.9 11 EXAMPLE 39 The products of Examples 33 to 37 diluted to an NCO-content of 43% in the same way as in Example 38 were compared as described in the following for their suitability for the production of polyurethane foams using biuret-modified "T 80". The comparison substance is a biuret-group-containing polyisocyanate produced by reacting "T 80" with water (N CO-content 43%).

In all the tests, the polyol component consisted of 100.00 g of a polyether polyol (OH-number 28) produced by alkoxylating trimethylol propane using a mixture of ethylene oxide and propylene oxide (ratio by weight 13.4:86.6), 3.0 g of water 4.0 g of diisopropanolamine 1.5 g of triethanolamine, 0.2 g of triethylene diamine, 0.15 g of a standard commercial polysioxane stabiliser.

The polyol component is mixed with quantities of 49.7 g of the polyisocyanates mentioned and the resulting mixtures reacted in an open mould. Open-cell polyurethane foams are obtained where the products obtained by the process according to the invention are used, being distinguished from the foams produced form biuret-modified "T 80" by their particularly good compression set and their higher compression hardness.

The mechanical properties of the resulting foams are set out in Table V below.

TABLE V Comparison biuret-modif "T80" Example No. 33 34 35 36 37 NCO:43% Gross density kg/m3 36 36 35 35 35 35 Tensile strength KPa 80 85 85 95 90 85 Breaking elongation% 145 135 140 1 50 130 135 Compression hardness KPa with 40% deformation 2.3 2.2 2.2 2.0 2.2 2.0 CS% after 90% deformation 4.3 4.9 5.2 4.2 4.4 7.8

Claims (8)

1. A process for the production of a modified polyisocyanate which comprises reacting an organic polyisocyanate with a sub-stoichiometric quantity of a compound containing one or more isocyanate-reactive groups as a modifying agent, a from 10 to 80%, by weight, aqueous solution of a water-soluble isocyanate-reactive group-containing compound selected from primary and secondary alcohols, carboxylic acids, ammonium carboxylates and amides being used as modifying agents.

2. A process as claimed in claim 1 wherein a from 10 to 80%, by weight, aqueous solution of a water-soluble salt of a carboxylic acid having a molecular weight of from 46 to 200 with an amine having a molecular weight of from 31 to 200 is used as modifying agent.

3. A process as claimed in claim 1 or claim 2 wherein the reaction is carried out at a temperature of from 50 to 18O0C.

4. A process as claimed in any of claims 1 to 3 wherein the modifying agent is used in a quantity corresponding to an equivalent ratio of isocyanate groups in the polyisocyanate to be modified to isocyanate-reactive groups in the modifying agent of from 1:0.05 to 1 :0.3.

5. A process as claimed in any of claims 1 to 4 wherein the reaction is carried out in the presence of a catalyst which accelerates the isocyanate addition reaction and/or one or more homogenising aids.

6. A process as claimed in claim 1 substantially as herein described with particular reference to the Examples.

7. A process for the production of a polyurethane which comprises reacting a modified polyisocyanate produced by a process as claimed in any of claims 1 to 6 with an isocyanate-reactive component.

8. A process as claimed in claim 7 substantially as herein described with particular reference to the Examples.