Continuous dilution of polyisocyanates

Abstract

The invention relates to a process for producing a polyisocyanate composition comprising addition of at least one isocyanate-inert solvent to at least one polyisocyanate, characterized in that the addition of the solvent is carried out in one or more stages and at least one of these stages is performed as a continuous dilution. The invention further relates to the polyisocyanate compositions obtainable by the process, to the use of the polyisocyanate compositions, to a two-component system containing the polyisocyanate composition and to composite systems produced with the two-component system.

Claims

1. A process for producing a polyisocyanate composition comprising addition of at least one solvent to at least one polyisocyanate based on tolylene diisocyanate, wherein the addition of the solvent is carried out in one or more stages and at least one of these stages is performed as a continuous dilution and wherein the solvent is inert to isocyanate.

2. The process as claimed in claim 1, wherein the addition of the solvent is carried out in at least two stages, wherein the first stage is performed as a continuous dilution.

3. The process as claimed in claim 1, wherein a solids content of ≥30% to ≤90% by weight of the resulting composition is established in the first stage.

4. The process as claimed in claim 2, wherein a solids content of ≥10% to ≤80% by weight is established in the second stage, wherein the solids content established in the first stage is reduced by at least 15% by weight in the second stage.

5. The process as claimed in claim 1, wherein the polyisocyanate is produced by (i) reaction of tolylene diisocyanate to form a polyisocyanate and (ii) removal of the unconverted tolylene diisocyanate down to a residual content of monomeric tolylene diisocyanate of ≤0.5% by weight, based on the total weight of the polyisocyanate composed of tolylene diisocyanate.

6. The process as claimed in claim 5, wherein the removal of the unconverted tolylene diisocyanate in step (ii) is carried out by means of at least one thermal separation process.

7. The process as claimed in claim 6, wherein the at least one thermal separation process is performed at a heating medium temperature of ≥140° C. to ≤235° C.

8. The process as claimed in claim 5, wherein the polyisocyanate composed of tolylene diisocyanate is an isocyanate-containing polyisocyanurate composed of tolylene diisocyanate, wherein the reaction of tolylene diisocyanate in step (i) to form isocyanurate groups is carried out in the presence of at least one catalyst and terminated at a content of isocyanate groups of ≥30% to ≤46% by weight by addition of at least one catalyst poison.

9. The process as claimed in claim 5, wherein steps (i) and (ii) are performed in the presence of ≥0% to <1% by weight of distillation aids that are inert under distillation conditions, liquid and have a boiling point at least 50° C. higher than that of tolylene diisocyanate and/or ≥0% to <1% by weight based on the total weight of the compounds employed in step (i) and (ii) of compounds comprising one or more hydroxyl groups.

10. The process as claimed in claim 5, wherein addition of the at least one solvent to the at least one polyisocyanate is followed in a further step by addition of at least one polyisocyanate composition composed of tolylene diisocyanate which is at least one polyisocyanurate composition composed of tolylene diisocyanate and/or at least one polyurethane composition composed of tolylene diisocyanate, and optionally by addition of one or more assistant and additive substances.

11. A process for preventing cloudiness in a polyisocyanate composition, the process comprising inclusion of the process according to claim 1.

Description

EXAMPLES

(1) All reported percentages are based on weight unless otherwise stated.

(2) The NCO contents were determined by titrimetry according to DIN EN ISO 11909:2007-05.

(3) The residual monomer contents were measured according to DIN EN ISO 10283:2007-11 by gas chromatography with an internal standard.

(4) Cloudiness was determined according to DIN EN ISO 7027-1:2016.

Example 1 (Noninventive)

(5) 1500 g of a tolylene diisocyanate isomer mixture composed of about 80% 2,4-tolylene diisocyanate and 20% 2,6-tolylene diisocyanate are initially charged in a 2 L flask at 80° C. 0.52 g of a Mannich base (bisphenol/formaldehyde/dimethylamine 25% in butyl acetate/xylene 19:56) is then added over 2 hours with stirring while maintaining a temperature of 78-82° C. Once an NCO content of 40.4% is achieved 1 g of dibutyl phosphate is added to terminate the reaction. The excess diisocyanate is then continuously removed from the thus obtained crude product by distillation at temperatures of 180° C. and a pressure of 0.05 mbar. The obtained hot resin (370 g) is conveyed directly to 863 g of boiling ethyl acetate in a stirred flask fitted with a reflux cooler using a pump which corresponds to a one-stage, discontinuous dilution from 100% solids content to 30% solids content. This affords a solution having the following properties:

(6) NCO: 7.1%

(7) Monomer content: 0.08%

(8) Cloudiness: 21 NTU

Example 2 (Inventive)

(9) 1500 g of a tolylene diisocyanate isomer mixture composed of about 80% 2,4-tolylene diisocyanate and 20% 2,6-tolylene diisocyanate are initially charged in a 2 L flask at 80° C. 0.52 g of a Mannich base (bisphenol/formaldehyde/dimethylamine 25% in butyl acetate/xylene 19:56) is then added over 2 hours with stirring while maintaining a temperature of 78-82° C. Once an NCO content of 40.4% is achieved 1 g of dibutyl phosphate is added to terminate the reaction. The excess diisocyanate is then continuously removed from the thus obtained crude product by distillation at temperatures of 180° C. and a pressure of 0.05 mbar. The hot resin discharged from the distillation is conveyed directly at 105 g/h into a stirred 500 ml 4-necked flask fitted with a reflux cooler using a pump. 245 g/h of ethyl acetate are simultaneously added from a dropping funnel and the continuously diluted product is continuously transferred at 350 g/h into a cooled receiver flask via a submerged riser tube using a pump. The contents of the 4-necked flask remain constant at about 400 g and have a temperature of about 80° C. This affords a solution having a solids content of 30% and the following properties:

(10) NCO: 7.0%

(11) Monomer content: 0.03%

(12) Cloudiness: 12 NTU

Example 3 (Inventive)

(13) 1500 g of a tolylene diisocyanate isomer mixture composed of about 80% 2,4-tolylene diisocyanate and 20% 2,6-tolylene diisocyanate are initially charged in a 2 L flask at 80° C. 0.52 g of a Mannich base (bisphenol/formaldehyde/dimethylamine 25% in butyl acetate/xylene 19:56) is then added over 2 hours with stirring while maintaining a temperature of 78-82° C. Once an NCO content of 40.4% is achieved 1 g of dibutyl phosphate is added to terminate the reaction. The excess diisocyanate is then continuously removed from the thus obtained crude product by distillation at temperatures of 180° C. and a pressure of 0.05 mbar. The hot resin discharged from the distillation is conveyed directly at 105 g/h into a stirred 500 ml 4-necked flask fitted with a reflux cooler using a pump. 57 g/h of ethyl acetate are simultaneously added from a dropping funnel and the continuously diluted product is continuously transferred at 162 g/h into a cooled receiver flask via a submerged riser tube using a pump. The contents of the 4-necked flask remain constant at about 400 g and have a temperature of about 80° C.

(14) The contents of the receiver flask are subsequently diluted to 30% solids content with ethyl acetate in a discontinuous step. This affords a solution having the following properties:

(15) NCO: 7.0%

(16) Monomer content: 0.05%

(17) Cloudiness: 2 NTU

(18) Various aspects of the subject matter described herein are set out in the following numbered clauses:

(19) Clause 1. A process for producing a polyisocyanate composition comprising addition of at least one isocyanate-inert solvent to at least one polyisocyanate, characterized in that the addition of the solvent is carried out in one or more stages and at least one of these stages is performed as a continuous dilution.

(20) Clause 2. The process as in Clause 1, characterized in that the polyisocyanate is based on at least one aliphatic, cycloaliphatic, araliphatic or aromatic diisocyanate, preferably composed of an araliphatic or aromatic diisocyanate and particularly preferably composed of an aromatic diisocyanate.

(21) Clause 3. The process as in Clause 1 or 2, characterized in that the polyisocyanate is based on tolylene diisocyanate.

(22) Clause 4. The process as in any of the preceding Clauses, characterized in that the addition of the solvent is carried out in at least two stages, wherein the first stage is performed as a continuous dilution.

(23) Clause 5. The process as in any of the preceding Clauses, characterized in that a solids content of ≥30% to ≤90% by weight, preferably ≥50% to ≤85% by weight, particularly preferably ≥55% to ≤75% by weight and very particularly preferably ≥60% to ≤70% by weight is established in the first stage.

(24) Clause 6. The process as in Clause 4 or 5, characterized in that a solids content of ≥10% to ≤80% by weight, preferably ≥15% to ≤65% by weight, particularly preferably ≥20% to ≤50% by weight and very particularly preferably ≥25% to ≤35% by weight is established in the second stage, wherein the solids content established in the first stage is reduced by at least 15% by weight, preferably by at least 25% by weight, in the second stage.

(25) Clause 7. The process as in any of Clauses 3 to 6, characterized in that the polyisocyanate is produced from tolylene diisocyanate by (i) reaction of tolylene diisocyanate to form a polyisocyanate and (ii) removal of the unconverted tolylene diisocyanate down to a residual content of monomeric tolylene diisocyanate of ≤0.5% by weight, preferably ≤0.3% by weight and particularly preferably ≤0.1% by weight based on the total weight of the polyisocyanate composed of tolylene diisocyanate.

(26) Clause 8. The process as claimed in Clause 7, characterized in that the removal of the unconverted tolylene diisocyanate in step (ii) is carried out by means of at least one thermal separation process, preferably by means of at least one two-stage thermal separation process and particularly preferably by means of at least one falling film evaporator and/or at least one thin film evaporator.

(27) Clause 9. The process as in Clause 8, characterized in that the at least one thermal separation process is performed at a heating medium temperature of ≥140° C.≤ to 235° C. and preferably of ≥160° C. to ≤215° C.

(28) Clause 10. The process as in any of Clauses 7 to 9, characterized in that the polyisocyanate composed of tolylene diisocyanate is an isocyanate-containing polyisocyanurate composed of tolylene diisocyanate, wherein the reaction of tolylene diisocyanate in step (i) to form isocyanurate groups is carried out in the presence of at least one catalyst and terminated at a content of isocyanate groups of ≥30% to ≤46% by weight, preferably of ≥34% to ≤44% by weight and particularly preferably of ≥38% to ≤42% by weight by addition of at least one catalyst poison.

(29) Clause 11. The process as in any of Clauses 7 to 10, characterized in that the steps (i) and (ii) are performed in the presence of ≥0% to <1% by weight of distillation aids that are inert under distillation conditions, liquid and have a boiling point at least 50t higher than that of tolylene diisocyanate and/or ≥0% to <1% by weight based on the total weight of the compounds employed in step (i) and (ii) of compounds comprising one or more hydroxyl groups.

(30) Clause 12. The process as in any of the preceding Clauses, characterized in that addition of the at least one isocyanate-inert solvent to the at least one polyisocyanate is followed in a further step by addition of at least one polyisocyanate composition composed of tolylene diisocyanate which is distinct from the polyisocyanate of the preceding claims, preferably at least one polyisocyanurate composition composed of tolylene diisocyanate and/or at least one polyurethane composition composed of tolylene diisocyanate, and optionally by addition of one or more assistant and additive substances.

(31) Clause 13. A polyisocyanate composition produced or producible by a process of any of Clauses 1 to 12, wherein the polyisocyanate is based on 1,5-diisocyanatopentane (PDI), 2-methyl-1,5-diisocyanatopentane, 1,5-diisocyanato-2,2-dimethylpentane, 1,10-diisocyanatodecane, 2,4- and 2,6-diisocyanato-1-methylcyclohexane, 2,4′-diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4(3)isocyanatomethylcyclohexane, bis(isocyanatomethyl)norbornane, 1,3- and 1,4-bis(isocyanatomethyl)benzene (XDI), 1,3- and 1,4-bis(2-isocyanato-prop-2-yl)benzene (TMXDI), tolylene diisocyanate (TDI), 2,4′- and 4,4′-diisocyanatodiphenylmethane (MDI), 1,5-diisocyanatonaphthalene or 1,3- and 1,4-phenylene diisocyanate or any desired mixtures of these diisocyanates.

(32) Clause 14. The use of the continuous dilution in the dissolution of polyisocyanates, preferably of polyisocyanates composed of tolylene diisocyanate, for preventing cloudiness in the polyisocyanate composition.

(33) Clause 15. The use of a polyisocyanate composition as in Clause 13 as a crosslinking agent in an adhesive or in a coating material, preferably in an adhesive.

(34) Clause 16. A two-component system comprising an isocyanate component A) containing at least one polyisocyanate composition as in Clause 13 and an isocyanate-reactive component B) containing at least one isocyanate-reactive compound, preferably at least one hydroxyl-containing polyester.

(35) Clause 17. A composite system produced or producible by curing the two-component system as in Clause 16 applied to at least one substrate.