Process for producing polyisocyanurate plastics by means of phosphine catalysis

Abstract

The present invention relates to process for producing polyisocyanurate plastics, comprising the following steps: a) providing a polyisocyanate composition A) which comprises oligomeric polyisocyanates and is low in monomeric diisocyanates, “low in monomeric diisocyanates” meaning that the polyisocyanate composition A) has a content of monomeric diisocyanates of not more than 20% by weight, b) catalytically trimerizing the polyisocyanate composition A) using at least one tertiary organic phosphine catalyst B). The invention further relates to polyisocyanurate plastics obtainable by the process according to the invention, to coatings, films, semifinished products and mouldings comprising or consisting of the polyisocyanurate plastic according to the invention, and to the use of the polyisocyanurate plastics according to the invention for production of coatings, films, semifinished products and mouldings.

Claims

1. A process for producing a polyisocyanurate plastic, comprising the following steps: a) providing a polyisocyanate composition A) which comprises oligomeric polyisocyanates and is low in monomeric diisocyanates, “low in monomeric diisocyanates” meaning that the polyisocyanate composition A) has a content of monomeric diisocyanates of not more than 20% by weight, mixing A) with at least one tertiary organic phosphine catalyst B) of formula (I) ##STR00006## in which R1, R2 and R3 are identical or different radicals and are each an alkyl or cycloalkyl group having up to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an aryl group which has 6 to 10 carbon atoms, optionally substituted by alkyl radicals having up to 10 carbon atoms, with the proviso that not more than one of the radicals is an aryl group and at least one of the radicals is an alkyl or cycloalkyl group, or in which R1 and R2 are aliphatic and, joined to one another, together with the phosphorus atom form a heterocyclic ring having 4 to 6 ring members, where R3 is an alkyl group having up to 4 carbon atoms, forming a mixture, and b) catalytically trimerizing, at a relative air humidity of at least 20%, the polyisocyanate composition A) using the at least one tertiary organic phosphine catalyst B) and wherein the mixture does not comprise a tin compound.

2. The process according to claim 1, wherein the tertiary organic phosphine catalyst B) is selected from the group consisting of trimethylphosphine, triethylphosphine, tri-n-propylphosphine, tripropylphosphine, dibutylethylphosphine, tri-n-butylphosphine, triisobutylphosphine, tri-tert-butylphosphine, pentyldimethylphosphine, pentyldiethylphosphine, pentyldipropylphosphine, pentyldibutylphosphine, pentyldihexylphosphine, dipentylmethylphosphine, dipentylethylphosphine, dipentylpropylphosphine, dipentylbutylphosphine, dipentylhexylphosphine, dipentyloctylphosphine, tripentylphosphine, hexyldimethylphosphine, hexyldiethylphosphine, hexyldipropylphosphine, hexyldibutylphosphine, dihexylmethylphosphine, dihexylethylphosphine, dihexylpropylphosphine, dihexylbutylphosphine, trihexylphosphine, trioctylphosphine, tribenzylphosphine, benzyldimethylphosphine, dimethylphenylphosphine and butylphosphacyclopentane and mixtures of these.

3. The process according to claim 1, wherein the tertiary organic phosphine catalyst is tri-n-butylphosphine and/or trioctylphosphine.

4. The process according to claim 1, characterized in that the catalytic trimerization is conducted at least up to a conversion level at which there are only at most 20% of the isocyanate groups originally present in the polyisocyanate composition A).

5. The process according to claim 1, characterized in that the polyisocyanate composition A) consists to an extent of at least 80%, 85%, 90%, 95%, 98%, 99% or 100% by weight, based in each case on the weight of the polyisocyanate composition A), of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

6. The process according to claim 1, characterized in that the oligomeric polyisocyanates comprise one or more oligomeric polyisocyanates which are composed of or consist of 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, isophorone diisocyanate or 4,4′-diisocyanatodicyclohexylmethane or mixtures thereof.

7. The process according to claim 1, characterized in that the polyisocyanate composition A) and/or the oligomeric polyisocyanates have a mean NCO functionality of 2.0 to 5.0.

8. The process according to claim 1, characterized in that the polyisocyanate composition A) has a content of isocyanate groups of 8.0% to 28.0% by weight, based on the weight of the polyisocyanate composition A).

9. The process according to claim 1, wherein the polyisocyanate composition A) has a content of monomeric diisocyanates of not more than 15% by weight, not more than 10% by weight or not more than 5% by weight, based in each case on the weight of the polyisocyanate composition A).

Description

EXAMPLES

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

(2) The NCO contents were determined by titrimetry as per DIN EN ISO 11909.

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

(4) All the viscosity measurements were made with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (Germany) to DIN EN ISO 3219.

(5) The contents (mol %) of the uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structures present in the starting polyisocyanates were calculated from the integrals of proton-decoupled .sup.13C NMR spectra (recorded on a Bruker DPX-400 instrument) and are each based on the sum total of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structures present. In the case of HDI polyisocyanates, the individual structural elements have the following chemical shifts (in ppm): uretdione: 157.1; isocyanurate: 148.4; allophanate: 155.7 and 153.8, biuret: 155.5; iminooxadiazinedione: 147.8, 144.3 and 135.3; oxadiazinetrione: 147.8 and 143.9.

(6) The glass transition temperature Tg was determined by means of DSC (differential scanning calorimetry) with a Mettler DSC 12E (Mettler Toledo GmbH, Giessen, Germany) at a heating rate of 20° C./min.

(7) Shore hardnesses were measured to DIN 53505 with the aid of a Zwick 3100 Shore hardness tester (from Zwick, Germany).

(8) IR spectra were recorded on a Spectrum Two FT-IR spectrometer equipped with an ATR unit, from Perkin Elmer, Inc.

(9) Starting Compounds

(10) Starting Polyisocyanate A1)

(11) For use as polyisocyanate composition A), the starting polyisocyanate A1) prepared was an HDI polyisocyanate containing isocyanurate groups, prepared in accordance with Example 11 of EP-A 330 966. The reaction was stopped at an NCO content of the crude mixture of 40% by adding dibutyl phosphate. Subsequently, unconverted HDI was removed by thin-film distillation at a temperature of 130° C. and a pressu re of 0.2 mbar.

(12) NCO content: 21.8%

(13) NCO functionality: 3.4

(14) Monomeric HDI: 0.1%

(15) Viscosity (23° C.): 3000 mPas

(16) Density (20° C.): 1.17 g/cm.sup.3

(17) Distribution of the oligomeric structure types:

(18) Isocyanurate: 84.5 mol %

(19) Iminooxadiazinedione 5.4 mol %

(20) Uretdione 2.9 mol %

(21) Allophanate: 7.2 mol %

(22) Starting Polyisocyanate A2)

(23) For use as polyisocyanate composition A), the starting polyisocyanate A2) used was an HDI polyisocyanate containing biuret groups, prepared in accordance with the process of EP-A 0 150 769, by reaction of 8.2 mol of HDI with 1.0 mol of water in the presence of 0.05 mol of pivalic anhydride at a temperature of 125° C. On attainment of an NCO content of 36.6%, unconverted HDI was removed together with pivalic anhydride by thin-film distillation at a temperature of 130° C. and a pressure of 0.2 mbar.

(24) NCO content: 23.0%

(25) NCO functionality: 3.2

(26) Monomeric HDI: 0.4%

(27) Viscosity (23° C.): 2500 mPas

(28) Distribution of the oligomeric structure types:

(29) Biuret: 87.7 mol %

(30) Uretdione 12.3 mol %

(31) Starting Polyisocyanate A3)

(32) For use as polyisocyanate composition A), the starting polyisocyanate A3) prepared was an HDI polyisocyanate containing allophanate and isocyanurate groups, prepared according to Example 1 of EP-A 496 208.

(33) NCO content: 19.8%

(34) NCO functionality: 2.5

(35) Monomeric HDI: 0.3%

(36) Viscosity (23° C.): 570 mPas

(37) Distribution of the oligomeric structure types:

(38) Isocyanurate: 33.1 mol %

(39) Allophanate: 66.9 mol %

(40) Starting Polyisocyanate A4)

(41) For use as polyisocyanate composition A), the starting polyisocyanate A4) prepared was an HDI polyisocyanate containing isocyanurate and iminooxadiazinedione groups, prepared in accordance with Example 4 of EP-A 0 962 455, by trimerization of HDI using a 50% solution of tetrabutylphosphonium hydrogendifluoride in isopropanol/methanol (2:1) as catalyst. The reaction was stopped at an NCO content of the crude mixture of 43% by adding dibutyl phosphate. Subsequently, unconverted HDI was removed by thin-film distillation at a temperature of 130° C. and a pressure of 0.2 mbar.

(42) NCO content: 23.4%

(43) NCO functionality: 3.2

(44) Monomeric HDI: 0.2%

(45) Viscosity (23° C.): 700 mPas

(46) Distribution of the oligomeric structure types:

(47) Isocyanurate: 49.9 mol %

(48) Iminooxadiazinedione 45.3 mol %

(49) Uretdione 4.8 mol %

Example 1 (Inventive)

(50) 25 g of the starting polyisocyanate A1) were weighed into a polypropylene cup together with 0.25 g of tributylphosphine (1% by weight) and homogenized at 3500 rpm with the aid of a Speed-Mixer DAC 150 FVZ (from Hauschild, Germany) for 1 min. The reaction mixture was poured onto a glass plate in a layer thickness of about 2 mm and laid out for drying in the open at a temperature of about 24° C. and a relative air humidity of about 44%. After one day, the colourless transparent coating was dry to the touch. After three days, no isocyanate groups (band at 2270 cm.sup.−1) were detectable any longer by IR spectroscopy. The Shore hardness D was 75.

Example 2 (Comparative)

(51) 25 g of the starting polyisocyanate A1) were weighed into a polypropylene cup together with 0.25 g of tin(II) octoate (1% by weight) and homogenized at 3500 rpm with the aid of a Speed-Mixer DAC 150 FVZ (from Hauschild, Germany) for 1 min. The reaction mixture was poured onto a glass plate in a layer thickness of about 2 mm and laid out for drying in the open under the same conditions as in Example 1 (temperature about 24° C.; relative air humidity about 44%). After one day, the colourless coating was dry but highly foamed. By IR spectroscopy, after three days, no isocyanate groups (band at 2270 cm.sup.−1) were detectable any longer.

Example 3 (Comparative)

(52) 25 g of the starting polyisocyanate A1) were weighed into a polypropylene cup together with 0.25 g of tributylphosphine (1% by weight) and 0.25 g of dibutyltin dilaurate and homogenized at 3500 rpm with the aid of a Speed-Mixer DAC 150 FVZ (from Hauschild, Germany) for 1 min. The reaction mixture was poured onto a glass plate in a layer thickness of about 2 mm and laid out for drying in the open under the same conditions as in Example 1 (temperature about 24° C.; relative air humidity about 44%). After one day, the colourless coating was dry but cloudy, and exhibited a multitude of blisters. By IR spectroscopy, after three days, no isocyanate groups (band at 2270 cm.sup.−1) were detectable any longer.

(53) Comparison of Examples 1 to 3 shows that the process according to the invention (Example 1) with catalysis with a tertiary organic phosphine catalyst in the presence of air humidity affords an entirely transparent, blister-free polyisocyanurate plastic, whereas the use of a tin catalyst known from the prior art (Example 2), and likewise the simultaneous use of a tertiary organic phosphine catalyst and a tin catalyst, under otherwise identical trimerization conditions, leads to a polyisocyanurate material which foams because of the carbon dioxide formed in the isocyanate/water reaction, which is the reason why a multitude of blisters occur in the polyisocyanurate plastic obtained.

Examples 4 to 8 (Inventive)

(54) By the process described in Example 1, 25 g in each case of the starting polyisocyanates A1) to A4) were mixed with different amounts of different phosphine catalysts and trimerized in an open polypropylene mould to give polyisocyanurate plastics.

(55) After the test specimens had been demoulded, by IR spectroscopy, isocyanate groups (band at 2270 cm.sup.−1) were no longer detectable in any of the products obtained.

(56) The following table shows the compositions of the reaction mixtures, reaction conditions and characteristic properties of the cured products:

(57) TABLE-US-00001 Example 4 5 6 7 8 Starting polyisocyanate A1) A1) A2) A3) A4) Tributylphosphine [% by wt.] — — 1 1 1 Trioctylphosphine [% by wt.] 2 2 — — — Reaction temperature [° C.] 50 50 24 24 50 Curing conditions a) b) a) a) a) Appearance colourless, clear, blister-free Shore hardness D 82 83 74 55 79 Tg 46 108 44 38 46 a): 3 days at 50° C. b): 3 days at 50° C. + 6 hours at 120° C.

(58) In all cases, colourless, completely clear and blister-free polyisocyanurate bodies were obtained, which differ in terms of hardness and glass transition temperature depending on the starting polyisocyanate used and the curing conditions.

Example 9 (Inventive)

(59) 25 g of the starting polyisocyanate A1) were weighed into a polypropylene cup together with 0.50 g of trioctylphosphine (2% by weight) and homogenized at 3500 rpm with the aid of a Speed-Mixer DAC 150 FVZ (from Hauschild, Germany) for 1 min. The reaction mixture was poured onto a glass plate in a layer thickness of about 2 mm and then hardened in an oven at a temperature of 120° C. for 12 hours. A yellow-co loured but entirely transparent coating was obtained. By IR spectroscopy, no isocyanate groups (band at 2270 cm.sup.−1) were detectable any longer. The Shore hardness D was 79.