DD219760B5 - Process for the color stabilization of organic isocyanates - Google Patents

Description

Field of application of the invention

The invention relates to a process for the color stabilization of organic isocyanates.

Characterization of the known technical solutions

It is known that organic isocyanates tend to form undesired colored impurities during storage. This applies in particular to compounds which are prepared by phosgenation of condensation products of aromatic amines and formaldehyde.

So falls z. B. diphenylmethane-4,4'-diisocyanate in its isolation by distillation, initially white, but colors in storage in a short time, even at low temperatures and with the exclusion of light and oxygen, often yellow or brown and in certain cases even green or blue.

Other isocyanates also often discolour significantly on prolonged storage, thereby affecting the quality of the polyurethane products made from them.

Various attempts have already been made to counter these phenomena. According to the state of the art, substances with antioxidant and peroxide-decomposing properties have been added (US Pat. No. 2,885,420, US Pat. No. 2,885,426, US Pat. No. 2,957,903, US Pat. No. 3,281,446, US Pat. No. 3,555,072, US Pat -PS 3,715,381, GB-PS 990,634).

Although these measures are sufficient in certain cases, often even the presence of large amounts of stabilizers can not prevent discoloration. For this phenomenon, especially the chlorine content of the isocyanates is responsible. Therefore, a large number of proposals for reducing the chlorine content has been made (US Pat. No. 3,155,699, US Pat. No. 3,264,336, DE-OS 2,210,607, DE-OS 2,249,375), but their technological implementation is limited or requires considerable effort is charged.

Further, the addition of tertiary amines such as triethylamine (JP-PS 75.101.344) or heterocyclic amines such as imidazole (US Pat. No. 3,226,414) and oxazolines (OS PS 4,152,348) for blocking the chlorine content is recommended. When using these stabilizers is to be expected to promote polymerization reactions such as dimerization and trimerization, which is also undesirable.

Another negative characteristic of common antioxidants and blocking agents is their poor compatibility with crystalline diphenylmethane-4,4'-diisocyanate, which leads to the so-called exudation of these substances. As a result, their effectiveness is greatly reduced.

Object of the invention

The aim of the invention is to develop an easily realizable process for color stabilization of organic isocyanates.

Explanation of the essence of the invention

The invention has for its object to develop a process for the color stabilization of organic isocyanates, which does not have the deficiencies of known methods, such as polymerization reactions, poor compatibility and discoloration. According to the invention, this object is achieved in that the isocyanates to be stabilized organic compounds of the classes - Ν, Ο-acetals of the general formula R3 R2 NC R5OR3 - Ν, Ν-acetals of the general formula Ri R2 NC R5 R6 N R3 R4 and - Mannich bases of Amides, ureas, urethanes and analogously constructed heterocycles of the general formula Ri R2 NC R5 Rβ N R7 Co R3, where

Rv r2, R3, R4 - alkyl, cycloalkyl, aralkyl R5, Re. R 7 is H, alkyl, cycloalkyl, aralkyl or R 3 and R 2, R 1 and R 3, R 3 and R 4 together form a short-chain radical having 2 to 5 carbon or hetero atoms or R 3 and R 7 together form a cyclic radical of a lactame, cyclic urethane or urea or an analog

Heterocycle or R5 and R6 - together an alkylene radical having 4 to 6 carbon atoms R-i to R7 - radicals having isocyanate-reactive substituents, preferably reactive hydrogen, are added.

Suitable Ν, Ο-acetals are derived in particular from long-chain aliphatic alcohols, such as octanol, dodecanol, hexadecanol, formaldehyde and primary or secondary amines. Particularly suitable are cyclic Ν, Ο-acetals such as oxazolidines or tetrahydrooxazines. Preferably, products such as octyloxymethyl-dimethylamine, bis-butoxymethyl-methylamine, 3-cyclohexyloxazolidine, 2-isopropyl-3- (2'-hydroxyethyl) -oxazolidine, 3- (2'-hydroxypropyl) -5-methyloxazolidine, 3- (2 '-Hydroxyethyl) -oxazolidine used.

In an analogous manner suitable open-chain or cyclic Ν, Ν-acetals are constructed. Particularly noteworthy products are: - bis-morpholino-methane, - N, N'-isobutyl-hexahydropyridine, - N, N'-diethyl-imidazolidine, - N-cyclohexyl-hexahydropyrimidine.

Furthermore, in the context of the invention, the specified Mannich bases are useful, in particular N-dimethylaminomethyl-formamide, N-dimethylaminomethyl-carbaminsäureethylester, N-dimethylaminomethyl-c-caprolactam, N-dimethylaminomethyl-sulfamide, N-dimethylaminomethyl-acrylamide, 1,3,5-trimethyl hexahydrotriazinone-2, 5-cyclohexyl-hexahydro-triazine-thione-2.

The incorporation of the stabilizers according to the invention requires no special measures, since these compounds are readily soluble in isocyanates. The addition to isocyanates preferably takes place in liquid form.

The color-stabilizing effectiveness is achieved with concentrations of 0.001-1%, preferably 0.01-0.2%, and depends on the proportion of active groups present. Examples of isocyanates to be stabilized according to the invention are in particular aromatic isocyanates, such as

phenyl,

chlorophenyl,

naphthalene,

toluene diisocyanate,

Diphenylmethane diisocyanate or their pre-adducts containing isocyanate groups.

A special feature of the solution according to the invention is that substances are used which are capable of reacting with isocyanates under urethane, urea or insertion product formation by their content of H-acidic groups or by insertion reactions. These properties do not lead to segregation during crystallization, the so-called exudation, and thus not to reduce the effectiveness of the substance classes of the invention. The solution according to the invention is based on the recognition that certain condensation products of amines, aldehydes, alcohols, amides, urethanes or ureas are outstandingly suitable for blocking the chlorine content of isocyanates responsible for color formation. It is essential that the substances according to the invention in the manner used to promote no polymerization of isocyanates.

It has been found that the method of color stabilization achieves optimum effect, if at the same time conventional stabilizers or combinations thereof are used. As a suitable easily accessible, effective substances of this type offer sterically hindered phenols, such as. As 2,6-di-tert-butyl-4-methylphenol, phosphites, such as. Triphenyl phosphite, tris-4-nonylphenyl phosphite, lauryl bis diphenyl phosphite, or sulfur compounds, e.g. Thio-bis-dipropionic acid dilaurate, thiourea and the like. on. A preferred combination includes the substances 2,6-di-tert-butyl-4-methylphenol and triphenyl phosphite or tris-4-nonylphenyl phosphite.

Their application concentration is 0.01-0.2%.

The joint use of compounds of the invention of the aforementioned general formula with known antioxidant stabilizers does not interfere with the mode of action according to the invention.

The color-stabilizing effect is effective over a wider temperature range (~ 20 ° C to + 100 ° C). The reactivity and the performance properties of the stabilized isocyanates are not adversely affected.

The invention will be explained in more detail below in two comparative examples and two embodiments.

Comparative Example 1 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized with: a) 0.1 g of 2,6-di-tert-butyl-4-methylphenol b) 0.1 g of triphenyl phosphite c) 0.1 g of 2 , 6-di-tert-butyl-4-methylphenol and treated with 0.04 g of benzoyl chloride.

The respective stabilizer and in Example 1 c, the benzoyl chloride are added at a temperature of 50 ° C-70 ° C the isocyanate with stirring.

The stabilized isocyanates are stored in closed glass ampoules at room temperature.

To determine the color depth, 1 g of the sample to be examined is dissolved in 9 g of a mixture of dimethylformamide and methanol (75 / 25GT) and the extinction in 2.0 cm cuvettes is determined at 400 nm using a commercially available spectrometer. The following values were found after storage for 2 months: la) E = 54 × 10 -2 lb E = 63 × 10 -2 lc) E = 73 × 10 -2 with a maximum of E = 95 × 10 -2 at 425 nm.

Comparative Example 2 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized with: a) 0.04 g of 2,6-di-tert-butyl-4-methylphenol, 0.06 g of triphenyl phosphite and 0.05 g of imidazole b) 0.04 g 2,6-di-tert-butyl-4-methylphenol, 0.06g triphenyl phosphite and 0.05g 2-ethyloxazoline.

The treatment and measurement were carried out analogously to Example 1.

After 2 months storage, the following values were found: 2a) E = 24 × 10 -2 2b) E = 19 × 10 -2

Example 1 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized analogously to Examples 1 and 2 with: a) 0.05 g of 2-hydroxyethyl-oxazolidine b) 0.04 g of 2,6-di-tert-butyl-4 methylphenol 0.06g triphenyl phosphite 0.05g 2 hydroxyethyl oxazolidine.

The color depth was measured analogously to Example 1.

After 2 months of storage, the following values were found: a) E = 23 10 "2 b) E = 16-10 * 2.

Example 2 100 g of recrystallized (from toluene) technical diphenylmethane-4,4'-diisocyanate were stabilized analogously to Example 1 and 2 with: 0.04 g of 2,6-di-tert-butyl-4-methylphenol 0.08 g of triphenyl phosphite and a) 0.01 g of dimorpholino-methane b) 0.01 g of N-dimethylaminomethyl-benzamide c) 0.01 g of N-diethylaminomethyl-e-caprolactam d) 0.01 g of 1,3,5-trimethyl-hexahydrotriazinone-2.

For comparison, an unstabilized sample c) is stored.

After 3 months, the color depth at 400 nm is determined analogously to Example 1. The following values are obtained: a) E = 12 × 10 -2 b) E = 10 × 10 -2 c) E = 5 × 10 -2 d) E = 6 × 10 -2 e) E = 26 × 10 -2 ,

Claims (5)

1. A process for the color stabilization of organic isocyanates, characterized in that the isocyanates to be stabilized organic compounds of the classes - Ν, Ο-acetals of the general formula
R ₁ R ₂ NCR ₅ R ₆ OR ₃ R ₁ N (CR ₅ R ₆ OR ₃ ) ₂ - N, N-acetals of the general formula
R ₁ R ₂ NCR ₅ R ₆ NR ₃ R ₄ Mannich bases of amides, ureas, urethanes and analogously constructed heterocycles of the general formula R ₁ R ₂ NC R ₅ R ₆ NR ₇ Co R ₃ ,
in which R _n R ₂₁ R ₃ R ₄ - alkyl, cycloalkyl, aralkyl
Rs, Re, R? - H, alkyl, cycloalkyl, aralkyl
or R ₁ and R ₂ , R ₁ and R ₃ , R ₃ and R ₄ together form a short-chain radical having 2 to 5 carbon or heteroatoms
or R ₃ and R ₇ together form a cyclic residue of a lactame, cyclic urethane or urea or an analogous heterocycle or R ₅ and R ₆ together form an alkylene radical having 4 to 6 carbon atoms R ₁ and R ₇ - radicals having isocyanate-reactive substituents, preferably reactive hydrogen and in a concentration of 0.001% to 1.0%, preferably 0.01% to 0.2%, with possibly further stabilizing additives in a concentration of 0.002% to 1.0%, preferably 0.1% up to 0.2%, can be incorporated. 2. The method according to claim 1, characterized in that as Ν, Ο-acetals preferably octyloxymethyl-dimethylamine, bis-butoxymethyl-methylamine, 3- (2'-hydroxyethyl) -oxazolidin, 3- (2'-hydroxypropyl) -5- methyloxazolidine, 3-cyclohexyloxazolidine and 2-isopropyl-3 (2'-hydroxyethyl-oxazolidine). 3. The method according to claim 1, characterized in that are preferably used as N, N-acetals bismorpholinomethane, Ν, Ν'-isobutyl-hexahydropyridine, Ν, Ν'-diethyl-imidazolidine or N-cyclohexylhexahydropyrimidine. 4. The method according to claim 1, characterized in that as Mannich bases preferably open-chain or cyclic Mannich bases of acid amides such - N-dimethylaminomethyl-formamide - N-dimethylaminomethyl-sulfamide N-dimethylaminomethyl-carbamic acid ethyl ester - N-dimethylaminomethyl-e-caprolactam - N-dimethylaminomethyl-acrylamide
1,3,5-trimethyl-2-hexahydrotriazinon
5-cyclohexyl-hexahydro-triazine thione-2
be used. 5. The method according to claim 1 to 4, characterized in that the Ν, Ο-acetals, N, N-acetals and Mannich bases in admixture with other color-stabilizing additives such as tri aryl phosphites or tris-alkyl-aryl phosphites and / or sterically hindered aromatic hydroxyl compounds be used. Field of application of the invention The invention relates to a process for the color stabilization of organic isocyanates. -2- 219 760 Characterization of known technical solutions It is known that organic isocyanates tend to form undesired colored impurities during storage. This applies in particular to compounds which are prepared by phosgenation of condensation products of aromatic amines and formaldehyde. For example, diphenylmethane-4,4'-diisocyanate initially becomes white when it is isolated by distillation, but it often turns yellow or brown upon storage in a short time, even at low temperatures and with the exclusion of light and oxygen in some cases even green or blue. Other isocyanates also often discolour significantly on prolonged storage, thereby affecting the quality of the polyurethane products made from them. Various attempts have already been made to counter these phenomena. According to the state of the art, substances with antioxidant and peroxide-decomposing properties have been added (US Pat. No. 2,885,420, US Pat. No. 2,885,426, US Pat. No. 2,957,903, US Pat. No. 3,281,446, US Pat. No. 3,555,072, US Pat -PS 3,715,381, GB-PS 990,634). Although these measures are sufficient in certain cases, often even the presence of large amounts of stabilizers can not prevent discoloration. For this phenomenon, especially the chlorine content of the isocyanates is responsible. Therefore, a large number of proposals for reducing the chlorine content has been made (US Pat. No. 3,155,699, US Pat. No. 3,264,336, DE-OS 2,210,607, DE-OS 2,249,375), but their technological implementation is limited or requires considerable effort is charged. Further, the addition of tertiary amines such as triethylamine (JP-PS 75.101.344) or heterocyclic amines such as imidazole (US Pat. No. 3,226,414) and oxazolines (OS PS 4,152,348) for blocking the chlorine content is recommended. When using these stabilizers is to be expected to promote polymerization reactions such as dimerization and trimerization, which is also undesirable. Another negative characteristic of common antioxidants and blocking agents is their poor compatibility with crystalline diphenylmethane-4,4'-diisocyanate, which leads to the so-called exudation of these substances. As a result, their effectiveness is greatly reduced. Object of the invention The aim of the invention is to develop an easily realizable process for color stabilization of organic isocyanates. Explanation of the essence of the invention The invention has for its object to develop a process for the color stabilization of organic isocyanates, which does not have the deficiencies of known methods, such as polymerization reactions, poor compatibility and discoloration. According to the invention, this object is achieved in that the isocyanates to be stabilized organic compounds of the classes - Ν, Ο-acetals of the general formula
R ₁ R ₂ NC R ₆ OR ₃ - N, N-acetals of the general formula
R ₁ R ₂ NC R ₅ R ₆ NR ₃ R ₄ and Mannich bases of amides, ureas, urethanes and analogously constructed heterocycles of the general formula R ₁ R ₂ NC R ₅ R ₆ NR ₇ Co R ₃ , where R ₁ , R ₂ , R ₃ , R ₄ - alkyl, cycloalkyl, aralkyl R5, _R6, R7 - H, alkyl, cycloalkyl, aralkyl or RI and R ₂ , Ri and R ₃ , R ₃ and R ₄ together form a short-chain radical having 2 to 5 carbon or hetero atoms or R ₃ and R ₇ together form a cyclic residue of a lactame, cyclic urethane or urea or an analogous heterocycle or R ₅ and R ₆ together form an alkylene radical having 4 to 6 carbon atoms R ₁ to R ₇ - residues with isocyanate-reactive substituents, preferably reactive hydrogen, are added. Suitable Ν, Ο-acetals are derived in particular from long-chain aliphatic alcohols, such as octanol, dodecanol, hexadecanol, formaldehyde and primary or secondary amines. Particularly suitable are cyclic Ν, Ο-acetals such as oxazolidines or tetrahydrooxazines. Preferably, products such as octyloxymethyl-dimethylamine, bis-butoxymethylmethylamine, 3-cyclohexyloxazolidine, 2-isopropyl-3- (2'-hydroxyethyl) -oxazolidine, 3- (2'-hydroxypropyl) -5-methyloxazolidine, 3- (2'-hydroxypropyl) Hydroxyethyl) oxazolidine used.
Analogously, suitable open-chain or cyclic N, N-acetals are built up. Especially to be mentioned products are: - bis-morpholino-methane, - Ν, Ν'-isobutyl-hexahydropyridine, - Ν, Ν'-diethyl-imidazolidine, - N-cyclohexyl-hexahydropyrimidine. Furthermore, in the context of the invention, the specified Mannich bases are usable, in particular N-dimethylaminomethyl-formamide, N-dimethylaminomethyl-carbarninsäureethylester, N-dimethylaminomethyl-e-caprolactam, N-dimethylaminomethyl-sulfamide, N-dimethylaminomethyl-acrylamide, 1 ^, S-trimethyl-hexahydrotriazinone ^, 5-cyclohexyl-hexahydro-triazin-thione-2. The incorporation of the stabilizers according to the invention requires no special measures, since these compounds are readily soluble in isocyanates. The addition to isocyanates preferably takes place in liquid form. The color-stabilizing effectiveness is achieved with concentrations of 0.001-1%, preferably 0.01-0.2%, and depends on the proportion of active groups present. Examples of isocyanates to be stabilized according to the invention are, in particular, aromatic isocyanates, such as phenyl isocyanate, chlorophenyl isocyanate, naphthalene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate or their prepolymers containing isocyanate groups. A special feature of the solution according to the invention is that substances are used which, by their content of H-acidic groups or by insertion reactions, are capable of reacting with isocyanates with urethane, urea or insertion product formation. These properties do not lead to segregation during crystallization, the so-called exudation, and thus not to reduce the effectiveness of the substance classes of the invention. The solution according to the invention is based on the recognition that certain condensation products of amines, aldehydes, alcohols, amides, urethanes or ureas are outstandingly suitable for blocking the chlorine content of isocyanates responsible for color formation. It is essential that the substances according to the invention in the manner used to promote no polymerization of isocyanates. It has been found that the method of color stabilization achieves optimum effect, if at the same time conventional stabilizers or combinations thereof are used. As a suitable easily accessible, effective substances of this type offer sterically hindered phenols, such as. As 2,6-di-tert-butyl-4-methylphenol, phosphites, such as. Triphenyl phosphite, tris-4-nonylphenyl phosphite, lauryl bis diphenyl phosphite, or sulfur compounds, e.g. Thiobis-dipropionsäuredilaurat. Thiourea and the like. on. A preferred combination includes the substances 2,6-di-tert-butyl-4-methylphenol and triphenyl phosphite or tris-4-nonylphenyl phosphite. Their application concentration is 0.01-0.2%. The joint use of compounds of the invention of the aforementioned general formula with known antioxidant stabilizers does not interfere with the mode of action according to the invention. The color-stabilizing effect is instead effective over a wider temperature range (-20 ° C to +100 ⁰ C). The reactivity and the performance properties of the stabilized isocyanates are not adversely affected. The invention will be explained in more detail below in two comparative examples and two embodiments. Comparative Example 1 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized with: a) 0.1 g of 2,6-di-tert-butyl-4-methylphenol b) 0.1 g of triphenyl phosphite c) 0.1 g of 2,6-di-tert-butyl-4-methylphenol and treated with 0.04 g of benzoyl chloride. The respective stabilizer and in Example 1 с the benzoyl chloride are added at a temperature of 50 ° C-70 ° C the isocyanate with stirring. The stabilized isocyanates are stored in closed glass ampoules at room temperature. To determine the color depth, 1 g of the sample to be examined is dissolved in 9 g of a mixture of dimethylformamide and methanol (75 / 25GT) and the extinction in 2.0 cm cuvettes is determined at 400 nm using a commercially available spectrometer. The following values were found after 2 months storage: 1a) E = 54 x 10 ^"2 1b) E = 63 x 10" ² 1c) E = 73 x 10 ~ ² with a maximum of E = 95 x 10 ^'2 bei425nm. Comparative Example 2 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized with: a) 0.04 g of 2,6-di-tert-butyl-4-methylphenol, 0.06 g of triphenyl phosphite and 0.05 g of imidazole b) 0.04 g of 2,6-di-tert-butyl-4-methylphenol, 0.06 g of triphenyl phosphite and 0.05 g of 2-ethyloxazoline. The treatment and measurement was based on Example After 2 months of storage, the following values were found: 2) E = 24 x 10 ^"2 2b) E = 19-10" ² Embodiment 1 100 g of unstabilized diphenylmethane-4,4'-diisocyanate are stabilized analogously to Examples 1 and 2 using: a) 0.05 g of 2 hydroxyethyl-oxazolidine b) 0.04 g of 2,6-di-tert-butyl-4-methylphenol 0.06 g of triphenyl phosphite 0.05 g 2 hydroxyethyl oxazolidine. The color depth was measured analogously to Example After 2 months of storage, the following values were found: a) E = 23-10 " ² b) E = 16- " ² . Embodiment 2 100 g of recrystallized (from toluene) technical diphenylmethane-4,4'-diisocyanate were prepared analogously to Example 1 and stabilized with: 0.04 g of 2,6-di-tert-butyl-4-methylphenol 0.08 g of triphenyl phosphite a) 0.01 g dimorpholino-methane b) 0.01 g of N-dimethylaminomethylbenzamide c) 0.01 g of N-diethylaminomethyl-e-caprolactam d) 0.01 g of 1,3,5-trimethyl-hexahydrotriazinone-2. For comparison, an unstabilized sample c) is stored. After 3 months, the color depth at 400 nm is determined analogously to Example 1. The following values are obtained: a) E = 12 x 10 ~ ² b) E = 10 - ΙΟ " ² c) E = 5-10 " ² d) E = 6-Ю " ² e) E = 26 · ΙΟ " ² .