POLYISOCYANURATE PLASTICS HAVING HIGH THERMAL STABILITY

Abstract

The present invention relates to a polyisocyanurate plastic obtainable by catalytic trimenzation of a polyisocyanate composition A) which contains oligomeric polyisocyanates and is low in monomeric diisocyanates, where the isocyanurate structure content in the polyisocyanate composition A) is at least 50 mol %, based on the sum total of the oligomeric structures from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structure that are present in the polyisocyanate composition A). The present invention further relates to a transparent element comprising or consisting of the polyisocyanurate plastic. The invention likewise relates to a process for producing the polyisocyanurate plastics.

Claims

1.-15. (canceled)

16. A polyisocyanurate plastic obtainable by catalytic trimerization of a polyisocyanate composition A) which contains oligomeric polyisocyanates and is low in monomeric diisocyanates, wherein the isocyanurate structure content in the polyisocyanate composition A) is at least 50 mol %, based on the sum total of the oligomeric structures from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structure that are present in the polyisocyanate composition A).

17. The polyisocyanurate plastic according to claim 16, wherein the plastic has at least a degree of conversion in which only at most 20% of the isocyanate groups originally present in the polyisocyanate composition A) are present.

18. The polyisocyanurate plastic according to claim 16, wherein the degree of conversion is chosen such that the polyisocyanurate plastic contains only at most 10% or at most 5% of isocyanate groups originally present in the polyisocyanate composition A).

19. The polyisocyanurate plastic according to claim 16, wherein the polyisocyanate composition A) consists to an extent of at least 80% by weight, based on the weight of the polyisocyanate composition A), of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

20. The polyisocyanurate plastic according to claim 16, wherein the polyisocyanate composition A) consists to an extent of at least 99% by weight, based on the weight of the polyisocyanate composition A), of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

21. The polyisocyanurate plastic according to claim 16, wherein the polyisocyanate composition A) consists to an extent of 100% by weight, based on the weight of the polyisocyanate composition A), of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

22. The polyisocyanurate plastic according to claim 16, wherein the oligomeric polyisocyanates consist of one or more oligomeric polyisocyanates formed from 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, isophorone diisocyanate or 4,4-diisocyanatodicyclohexylmethane or mixtures thereof.

23. The polyisocyanurate plastic according to claim 16, wherein the polyisocyanate composition A) and/or the oligomeric polyisocyanates have/has a mean NCO functionality of 2.0 to 5.0.

24. The polyisocyanurate plastic according to claim 16, wherein 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).

25. Polyisocyanurate plastic according to claim 16, wherein said low in monomeric diisocyanates means that the polyisocyanate composition A) has a content of monomeric diisocyanates of no more than 20% by weight, based on the weight of the polyisocyanate composition A).

26. Polyisocyanurate plastic according to claim 16, wherein said low in monomeric diisocyanates means that the polyisocyanate composition A) has a content of monomeric diisocyanates of not more than 5% by weight, based on the weight of the polyisocyanate composition A).

27. The polyisocyanurate plastic according to claim 16, wherein the proportion of isocyanurate structures in the polyisocyanurate plastic obtained is at least 20% by weight, based on the weight of the polyisocyanurate plastic.

28. The polyisocyanurate plastic according to claim 16, wherein it has a delta b* value of ?20 after storage at 120? C. for 1000 h, where the b* values are determined to DIN 5033, and a transmittance loss T % of ?30% after storage at 120? C. for 1000 h, measured with a Hunter UltraScanPro 1206 at 360 nm and 400 nm.

29. The polyisocyanurate plastic according to claim 16, wherein catalytic trimerization is accomplished using sodium salts and/or potassium salts of aliphatic carboxylic acids having 2 to 20 carbon atoms in combination with complexing agents.

30. The polyisocyanurate plastic according to claim 16, wherein catalytic trimerization is accomplished using sodium salts and/or potassium salts of aliphatic carboxylic acids having 2 to 20 carbon atoms in combination with complexing agents consisting essentially of crown ethers or polyethylene glycols or polypropylene glycols or aliphatically substituted tin compounds as catalysts.

31. A transparent element comprising the polyisocyanurate plastic according to claim 16.

32. A transparent element consisting of the polyisocyanurate plastic according to claim 16.

33. The transparent element according to claim 30, wherein the element is a light diffuser or a lens.

34. A process for producing polyisocyanurate plastics, comprising the following steps: a) providing a polyisocyanate composition A) which contains oligomeric polyisocyanates and is low in monomeric diisocyanates, where the isocyanurate structure content in the polyisocyanate composition A) is at least 50 mol %, based on the sum total of the oligomeric structures from the group consisting of uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and oxadiazinetrione structure that are present in the polyisocyanate composition A); b) catalytically trimerizing the polyisocyanate composition A).

35. The process according to claim 34, wherein the oligomeric polyisocyanates consist of one or more oligomeric polyisocyanates formed from 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, isophorone diisocyanate or 4,4-diisocyanatodicyclohexylmethane or mixtures thereof and/or the polyisocyanate composition A) consists to an extent of at least 80% by weight, based on the weight of the polyisocyanate composition A), of polyisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups and/or catalytic trimerization is accomplished using sodium salts and/or potassium salts of aliphatic carboxylic acids having 2 to 20 carbon atoms in combination with complexing agents.

Description

EXAMPLES

[0113] All percentages are based on weight, unless stated otherwise.

[0114] The methods detailed hereinafter for determination of the appropriate parameters are employed for conduction and evaluation of the examples and are also the methods for determination of the parameters of relevance in accordance with the invention in general.

[0115] The NCO contents are determined by titrimetric means to DIN EN ISO 11909.

[0116] The residual monomer contents are measured to DIN EN ISO 10283 by gas chromatography with an internal standard.

[0117] All the viscosity measurements are made with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) to DIN EN ISO 3219.

[0118] The densities of the starting polyisocyanates are determined to DIN EN ISO 2811, and those of the cured polyisocyanurate plastics to DIN EN ISO 1183-1.

[0119] The contents (mol %) of the uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structures present in the starting polyisocyanates are 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.

[0120] The b* value is determined according to DIN 5033 in the L*a*b* colour space. The delta b* value is the difference between the b* value for the polyisocyanurate plastic which is determined directly after the production (b0*) and the b* value which is determined after storage in an oven at 120? C. for 1000 h (b1000*) (delta b*=b1000*?b0*). A significant increase in the b* value and hence a high delta b* value thus represents significant thermal yellowing and hence low thermal colour stability.

[0121] Discolorations were measured in accordance with DIN 5033 Part 7 on a CM-5 spectrophotometer using specimens of thickness 2 mm without gloss at a viewing angle of 8? and with diffuse illumination.

[0122] Transmittance was measured with a Byk-Gardner haze-gard plus instrument according to ASTM D1003 on specimens of thickness of 2 mm.

[0123] To determine the transmittance loss, the transmittance is determined directly after production (T0) and after storage in an oven at 120? C. for 1000 h (T1000) with a Hunter UltraScanPro 1206 over the wavelength range of 360-840 nm. The transmittance loss T % is calculated as T %=T0?T1000. The transmittance loss is calculated separately for the wavelengths of 360 nm and 400 nm.

[0124] The glass transition temperature T.sub.g was determined by means of DSC (differential scanning calorimetry) with a Mettler DSC 12E (Mettler Toledo GmbH, Giessen, Germany) in accordance with DIN EN 61006. Calibration was effected via the melt onset temperature of indium and lead. 10 mg of substance were weighed out in standard capsules. The measurement was effected by three heating runs from ?50? C. to +200? C. at a heating rate of 20 K/min with subsequent cooling at a cooling rate of 320 K/min. Cooling was effected by means of liquid nitrogen. The purge gas used was nitrogen. The values reported in the table below are each based on the evaluation of the 1st heating curve, since changes in the sample in the measurement process at high temperatures are possible in the reactive systems being examined as a result of the thermal stress in the DSC. The glass transition temperature T.sub.g determined was the temperature at half the height of a glass transition step. Shore hardnesses were measured to DIN 53505 with the aid of a Zwick 3100 Shore hardness tester (from Zwick, Germany) at 23? C. and 50% air humidity.

Process of the Invention

[0125] 100 g of the starting polyisocyanate are weighed into a polypropylene cup together with a catalyst mixture consisting of 0.177 g of potassium acetate, 0.475 g of [18]crown-6 and 3.115 g of diethylene glycol, and homogenized at 2750 rpm with the aid of a Speed-Mixer DAC 150 FVZ (from Hauschild, Germany) for 1 min. 8 g of the contents of each polypropylene cup are weighed into an aluminium dish of diameter 6.3 cm and depth 1 cm which, for better demoulding, had previously been rubbed with 1% soya lecithin W250 in ethyl acetate solution and dried. The aluminium dish thus filled is heated in a drying cabinet at 180? C. for 10 min. After cooling to room temperature, the test specimen is demoulded. Test specimens of thickness about 2 mm are obtained.

[0126] The process of the invention is employed both for production of inventive and noninventive polyisocyanurate plastics.

[0127] All the polyisocyanates used are sourced from Bayer and are either commercially available or can be prepared by methods described in the patent literature on the basis of readily available monomers and catalysts.

[0128] After production, the test specimens are stored in an oven at 120? C. over a period of 1000 h. To assess the stability, a transmittance spectrum of the test specimens is recorded prior to storage and after storage for 1000 h. For this purpose, a Hunter UltraScanPro 1206 is used to determine the transmittance over the wavelength range of 360-840 nm.

Starting Compounds

Inventive Starting Polyisocyanate A

[0129] HDI polyisocyanate containing isocyanurate groups, prepared in accordance with Example 11 of EP-A 330 966, with the alteration that the catalyst solvent used was 2-ethylhexanol rather than 2-ethylhexane-1,3-diol. The reaction was stopped at an NCO content of the crude mixture of 42% 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.

NCO content: 23.0%
NCO functionality: 3.2

Monomeric HDI: 0.1%

[0130] Viscosity (23? C.): 1200 mPas
Density (20? C.): 1.17 g/cm.sup.3

[0131] Distribution of the oligomeric structure types:

Isocyanurate: 89.7 mol %

Iminooxadiazinedione: 2.5 mol %

Uretdione: 2.7 mol %

Allophanate: 5.1 mol %

Inventive Starting Polyisocyanate B

[0132] HDI polyisocyanate containing isocyanurate groups, prepared in accordance with Example 11 of EP-A 330 966, with the alteration that the catalyst solvent used was 2-ethylhexanol rather than 2-ethylhexane-1,3-diol. The reaction was stopped at an NCO content of the crude mixture of 45% 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.

NCO content: 21.8%
NCO functionality: 3.4

Monomeric HDI: 0.1%

[0133] Viscosity (23? C.): 3000 mPas
Density (20? C.): 1.17 g/cm.sup.3

[0134] Distribution of the oligomeric structure types:

Isocyanurate: 89.7 mol %

Iminooxadiazinedione: 2.5 mol %

Uretdione: 2.7 mol %

Allophanate: 5.1 mol %

Inventive Starting Polyisocyanate C

[0135] Isophorone diisocyanate (IPDI), in accordance with Example 2 of EP-A 0 003 765, was trimerized down to an NCO content of 31.1% and the excess IPDI was removed by thin-film distillation at 170? C./0.1 mbar. This gave an isocyanurate polyisocyanate as a virtually colourless solid resin having a melting range of 100 to 110? C.

NCO content: 16.4%
NCO functionality: 3.3

Monomeric IPDI: 0.2%

[0136] 70 parts by weight of the solid IPDI polyisocyanurate were coarsely comminuted and initially charged in a reaction vessel at room temperature together with 30 parts by weight of the starting polyisocyanate A under an N2 atmosphere. To dissolve the solid resin and homogenize the mixture, it was heated to 100-140? C. and stirred until a virtually clear solution was obtained. Subsequently, the mixture was cooled to 50? C. and filtered through a 200? filter.

NCO content: 21.2%
NCO functionality: 3.2

Monomeric IPDI: 0.1%

Monomeric HDI: 0.1

[0137] Distribution of the oligomeric structure types:

Isocyanurate: 92.1 mol %

Iminooxadiazinedione: 1.8 mol %

Uretdione: 1.9 mol %

Allophanate: 4.2 mol %

Inventive Starting Polyisocyanate D

[0138] The starting polyisocyanate D used was a mixture of 95% by weight of starting polyisocyanate A and 5% by weight of Isophorone diisocyanate (IPDI).

Inventive Starting Polyisocyanate E

[0139] The starting polyisocyanate A used was distilled to yield a fraction with >99% polyisocyanurate trimer of HDI according to .sup.13C NMR spectroscopy. NCO content: 24.8

NCO functionality: 3.0

Monomeric HDI: <0.1%

[0140] Viscosity (23? C.): 700 mPas
Density (20? C.): 1.17 g/cm.sup.3
Distribution of the oligomeric structure types:

Isocyanurate: 99.2 mol %

Iminooxadiazinedione+Uretdione+Allophanate: <1 mol %

Noninventive Starting Polyisocyanate F*

[0141] HDI polyisocyanate containing biuret groups, prepared in accordance with the process of EP-A 0 150 769 by reacting 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 monomeric HDI was removed together with pivalic anhydride by thin-film distillation at a temperature of 130? C. and a pressure of 0.2 mbar.

NCO content: 23.0%
NCO functionality: 3.2

Monomeric HDI: 0.4%

[0142] Viscosity (23? C.): 2500 mPas
Density (20? C.): 1.13 g/cm.sup.3

[0143] Distribution of the oligomeric structure types:

Biuret: 87.7 mol %

Uretdione: 12.3 mol %

Noninventive Starting Polyisocyanate G*

[0144] HDI polyisocyanate containing isocyanurate and uretdione groups, prepared by tributylphosphine-catalysed oligomerization in accordance with Example 1a) of EP-A 0 377 177, with the alteration that no 2,2,4-trimethylpentane-1,3-diol was used. The reaction was stopped at an NCO content of 42%, and unconverted HDI was removed by thin-film distillation at a temperature of 130? C. and a pressure of 0.2 mbar.

NCO content: 22.7%
NCO functionality: 2.2

Monomeric HDI: 0.3%

[0145] Viscosity (23? C.): 90 mPas
Density (20? C.): 1.13 g/cm.sup.3

[0146] Distribution of the oligomeric structure types:

Isocyanurate: 15.6 mol %

Iminooxadiazinedione: 6.3 mol %

Uretdione: 78.1 mol %

Noninventive Starting Diisocyanate H*

[0147] Sourced from Bayer MaterialScience AG as Desmodur H=HDI=monomeric hexamethylene diisocyanate

Noninventive Starting Polyisocyanate 1*

[0148] Purchased from Bayer Material Science as Desmodur XP 2617. Mainly linear polyisocyanat based on a polyurethane prepolymer of HDI.

NCO-content: 12.5%

Monomeric HDI: <0.5%

[0149] Viscosity (23? C.): 4250 mPas
Density (20? C.): 1.09 g/cm.sup.3

Noninventive Starting Polyisocyanate J*

[0150] Allophanate- and isocyanurate group containing HDI-polyisocyanate, in accordance with example 1 of EP-A 496 208.

NCO-content: 19.8%

NCO-functionality: 2.5

Monomeric HDI: 0.3%

[0151] Viscosity (23? C.): 570 mPas
Density (20? C.): 1.11 g/cm.sup.3

[0152] Distribution of oligomeric structures:

Isocyanurate: 33.1 mol-%
Allophanate: 66.9 mol-%

Comparative Experiments

[0153] The experiments based on the inventive polyisocyanate starting materials show distinctly better thermal ageing and thermal discolouration characteristics of the polyisocyanurate plastics obtained after thermal stress compared to the experiments based on the noninventive polyisocyanate starting materials. This is manifested in lower starting b* values (from the L* a* b* colour measurement) after production of the polyisocyanurate plastics, and in delta b* values of <20 and transmittance losses (T %) at 360 nm and 400 nm of <30% after 1000 h at 120? C.

[0154] The polyisocyanurate plastics of the invention based on inventive polyisocyanate starting materials accordingly exhibit much better properties for use as transparent elements for applications in which very good thermal properties and thermal discolouration properties are desired, for example in optical components for light scattering and light guiding, for example in the encapsulation of high-performance LEDs.

TABLE-US-00001 Trans- mission/ Unreacted Starting % after b* isocyanate/% poly- Trans- aging b* after aging after cure for iso- mission/ 1000 h at value 1000 h at 10 min cyanate % 120? C. initial 120? C. at 180? C. A 84.7 78.0 4.8 12.3 <2 B 86.8 75.8 2.7 15.8 <2 C 86.2 57.6 3.8 12.4 <5 D 86.4 81.1 5.7 11.4 <3 E 89.5 83.3 2.9 10.3 <2 F* brown liquid >20 G* brown liquid >20 H* brown foam <10 I* 89.8 63.4 17.4 83.2 <5 J* 90.9 74.6 1.9 60.6 <5 comparative examples

[0155] Comparative examples F* and G* can not be trimerized sufficiently with the inventive method. The reaction in comparative example H* is so exothermic that the trimerization reaction concludes with the thermal decomposition reaction of the trimer and vaporization of the dimer resulting in a coloured foam.

[0156] Comparative example I* shows that typical isocyanat-terminated prepolymers containing polyether groups do not show the necessary color stability at relevant aging temperatures. Neither do products containing higher allophanate contents since allophanates seem to be instable at relevant aging temperatures for the inventive applications.