PROCESS FOR PREPARING LIQUID COMPOSITIONS OF ETHERIFIED MELAMINE FORMALDEHYDE RESINS

Abstract

The present invention relates to a process for preparing liquid compositions of etherified melamine formaldehyde resins, namely melamine formaldehyde resins etherified with a primary C.sub.1-C.sub.6-alkanol, which have low formaldehyde contents. The invention also relates to such liquid compositions of etherified melamine formaldehyde resins having a content of free formaldehyde of less than 0.3% by weight. The liquid compositions of etherified melamine formaldehyde resins are useful as crosslinking agents in coating compositions.

Claims

1-21. (canceled)

22. A process for preparing a liquid composition of an etherified melamine formaldehyde resin, the process comprising: i. reacting melamine, formaldehyde and a primary C.sub.1-C.sub.6-alkanol at least temporarily under acidic conditions in the presence of an excess of the primary C.sub.1-C.sub.6-alkanol, which means that a molar amount of the primary C.sub.1-C.sub.6-alkanol employed in i. exceeds a molar amount of formaldehyde employed in i., to obtain a mixture of the etherified melamine formaldehyde resin, water, unreacted formaldehyde and unreacted primary C.sub.1-C.sub.6-alkanol; ii. distilling off at least 50% of the unreacted primary C.sub.1-C.sub.6-alkanol, unreacted formaldehyde and water comprised in the reaction mixture obtained in i., to obtain a concentrated composition of the etherified melamine formaldehyde resin; iii. diluting the concentrated composition of the etherified melamine formaldehyde resin by addition of at least one solvent; the at least one solvent being selected from the group consisting of water, a primary C.sub.1-C.sub.6-alkanol, a solvent B, and mixtures thereof, where the solvent B is selected from the group consisting of a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkanol, a secondary C.sub.3-C.sub.6-alkanol, a tertiary C.sub.4-C.sub.6-alkanol, an aliphatic monoketone having 3 to 8 carbon atoms, a cyclic monoketone having 5 to 8 carbon atoms, a C.sub.1-C.sub.6-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid, a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid and an aromatic hydrocarbon; wherein in iii. both of the following measures a) and b) are taken, where measure a) is performed first and then measure b) is taken: a) adding water or a mixture of water and at least one organic solvent, which is selected from the group consisting of water-miscible organic solvents B as defined herein and the primary C.sub.1-C.sub.6-alkanol and mixtures thereof, to the concentrated composition of the etherified melamine formaldehyde resin obtained in ii. and removing at least a major portion of the added water by evaporation under reduced pressure; b) the at least one solvent used for diluting the concentrated composition of the etherified melamine formaldehyde resin in iii. comprises at least 50% by weight, based on a total weight of solvent used, of at least one organic solvent B.

23. The process of claim 22, wherein the amount of water, which is added to the concentrated composition of the etherified melamine formaldehyde resin, is from 0.5 to 15% by weight of the concentrated composition of the etherified melamine formaldehyde resin.

24. The process of claim 22, wherein at least 80% of the water, which has been added to the concentrated composition of the etherified melamine formaldehyde resin, is removed by evaporation.

25. The process of claim 22, wherein the at least one solvent used for diluting the concentrated composition of the etherified melamine formaldehyde resin is an organic solvent comprising at least 50% by weight, based on a total weight of solvent used for dilution, of at least one organic solvent selected from the group consisting of an aliphatic monoketone having 3 to 8 carbon atoms, a cyclic monoketone having 5 to 8 carbon atoms, a C.sub.1-C.sub.6-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid, a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid and a methyl substituted benzene.

26. The process of claim 25, wherein the at least one solvent used for diluting the concentrated composition of the etherified melamine formaldehyde resin comprises at least 50% by weight, based on the total weight of solvent used for dilution, of at least one organic solvent selected from the group consisting of a C.sub.2-C.sub.6-alkyl ester of acetic acid, a methyl substituted benzene and a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkyl ester of acetic acid.

27. A process for preparing a liquid composition of an etherified melamine formaldehyde resin, the process comprising: i. reacting melamine, formaldehyde and a primary C.sub.1-C.sub.6-alkanol at least temporarily under acidic conditions in the presence of an excess of the primary C.sub.1-C.sub.6-alkanol, which means that a molar amount of the primary C.sub.1-C.sub.6-alkanol employed in i. exceeds a molar amount of formaldehyde employed in i., to obtain a mixture of the etherified melamine formaldehyde resin, water, unreacted formaldehyde and unreacted primary C.sub.1-C.sub.6-alkanol; ii. distilling off at least 50% of the unreacted primary C.sub.1-C.sub.6-alkanol, unreacted formaldehyde and water comprised in the reaction mixture obtained in i. to obtain a concentrated composition of the etherified melamine formaldehyde resin; iii. diluting the concentrated composition of the etherified melamine formaldehyde resin by addition of at least one solvent; the at least one solvent being an organic solvent comprising at least 50% by weight, based on a total weight of solvent used for dilution, of at least one organic solvent selected from the group consisting of an aliphatic monoketone having 3 to 8 carbon atoms, a cyclic monoketone having 5 to 8 carbon atoms, a C.sub.1-C.sub.6-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid, a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkyl ester of a C.sub.1-C.sub.4-alkanoic acid and a methyl substituted benzene.

28. The process of claim 27, wherein the at least one solvent used for diluting the concentrated composition of the etherified melamine formaldehyde resin comprises at least 50% by weight, based on the total weight of solvent used for dilution, of at least one organic solvent selected from the group consisting of a C.sub.2-C.sub.6-alkyl ester of acetic acid, a methyl substituted benzene and a C.sub.1-C.sub.2-alkoxy-C.sub.2-C.sub.4-alkyl ester of acetic acid.

29. The process of claim 22, where in i) formaldehyde is used in an amount of from 2.5 to 12 mol per 1 mol of melamine.

30. The process of claim 22, where in i) the C.sub.1-C.sub.6-alkanol is used in an amount of from 5.0 to 50 mol per 1 mol of melamine.

31. The process of claim 22, where i) is performed at a pH in a range of from pH 2.0 to pH 6.0.

32. The process of claim 22, where i) is performed by heating a mixture of melamine, formaldehyde and the excess of the primary C.sub.1-C.sub.6-alkanol under acidic conditions.

33. The process of claim 22, where i) comprises i.1) heating a mixture of melamine, formaldehyde and a primary C.sub.1-C.sub.6-alkanol under acidic conditions, to obtain a first reaction mixture; i.2) distilling off at least a major portion of volatiles comprised by the first reaction mixture, to obtain a concentrated reaction mixture; i.3) adding primary C.sub.1-C.sub.6-alkanol to the concentrated reaction mixture and heating the thus obtained mixture under acidic conditions, to obtain a mixture of the etherified melamine formaldehyde resin, water and primary C.sub.1-C.sub.6-alkanol.

34. The process of claim 22, where in ii. the unreacted primary C.sub.1-C.sub.6-alkanol, unreacted formaldehyde and water are distilled off until a solid content of the concentrated composition is at least 80% by weight.

35. The process of claim 22, where in iii. the concentrated composition is diluted until a solid content of the liquid composition of the etherified melamine formaldehyde resin is in a range of from 50 to 98% by weight.

36. A liquid composition, comprising an etherified melamine formaldehyde resin composition having a degree of methylolation in a range of from 3.0 to 4.5 and a degree of etherification in a range of from 50 to 95%, which is etherified with a primary C.sub.1-C.sub.6-alkanol, where a content of free formaldehyde is less than 0.1% by weight.

37. A liquid composition, which is obtainable by the process of claim 22.

38. A liquid composition, which is obtainable by the process of claim 27.

39. The liquid composition of claim 36, where an amount of bound primary C.sub.1-C.sub.6-alkanol is in a range of from 2 to 4.3 mol per 1 mol of melamine.

40. A method of producing a coating composition, the method comprising combining at least one liquid composition of an etherified melamine formaldehyde resin of claim 36 and at least one binder oligomer or polymer, which is crosslinkable.

41. A coating composition, which comprises at least one liquid composition of an etherified melamine formaldehyde resin of claim 36 and at least one binder oligomer or polymer, which is crosslinkable.

Description

EXAMPLES

[0149] The free formaldehyde content was determined in accordance with EN ISO 9020:1996 by reacting a defined probe of the composition with Na.sub.2SO.sub.3 and titration of excess sulfite with iodine.

[0150] The viscosity was determined in accordance with ISO 3219/B:1993 at 23 C. using a cone/plate viscometer at a shear rate of 41 s.sup.1.

[0151] The non-volatile fraction (NVF) was determined according to DIN EN ISO 3251:2003-07 by heating a 2 g probe of the resin composition covered with 2 ml of n-butanol in an aluminum pan for two hours at 125 C. and ambient pressure in a ventilated drying cabinet.

[0152] The compatibility with mineral spirit was determined at ambient conditions by mixing the resin composition to be tested with mineral spirit having a boiling range 155 to 185 C. and determining the amount of white spirit when the mixture becomes cloudy. For this, 5 ml of the resin composition to be tested was given in a graduated tube. To this, the mineral spirit was added in successive 1 ml portions. After each addition, the mixture was shaken vigorously and it was visually determined whether the mixture remained clear or whether the mixture has become cloudy or hazy. The compatibility is the minimum amount of mineral spirit in ml per 1 ml of the resin composition to be tested, which is required to observe haziness or cloudiness, respectively. For example, a compatibility of 6:1 means that per 1 ml of the resin composition to be tested a minimum of 6 ml of white spirit having a boiling range 155 to 185 C. is required to observe haziness or cloudiness. For the determination of the pH value of the reaction mixture pH paper type Pehanon of the company Fa. Macherey-Nagel was used (measurement accuracy +/0.1 pH).

Comparative Example

[0153] A reactor was charged with 1104 g (14.9 mol) of n-butanol and 346 g of a 40 percent by weight aqueous formaldehyde solution (corresponding to 4.61 mol of formaldehyde) were metered in at 22 C. 0.14 mL of a 25% aqueous sodium hydroxide solution and subsequently 126 g (1.00 mol) of melamine were added. The resulting mixture was heated under reflux. When the reaction mixture became clear, 0.42 mL of a 30% nitric acid were metered in. Under ambient pressure, volatile components (n-butanol, water and formaldehyde) were distilled off until the compatibility of the residue with mineral spirit was 6:1. The temperature was reduced to 95 C., and 0.76 mL of 25% aqueous sodium hydroxide solution were metered in. Further volatile components were distilled off under a reduced pressure of 100 mbar and a maximum temperature of 80 C. until the residue had a viscosity of 6200 to 8000 mPas. The temperature was then reduced to 60 C. n-Butanol was added until the NVF was 72% by weight. The free formaldehyde content of the final product was 0.8% by weight.

Example 1

[0154] A reactor was charged with 310 g of a 40% by weight aqueous solution of formaldehyde (corresponding to 4.13 mol of formaldehyde). 948 g of n-butanol (12.8 mol) were added followed by the addition of 126 g of melamine (1.00 mol). The mixture was heated at 97 C., kept at that temperature for 10 minutes and subsequently the pH was adjusted to pH 5 using nitric acid. The reaction mixture was distilled at a maximum temperature of 105 C. over a period of 4 hours to remove the volatiles. Then, distillation was continued until a temperature of 130 C. was reached. The resulting concentrated composition was cooled to 100 C. and divided into two equal portions A and B.

[0155] Portion A was divided into two equal portions A1 and A2.

[0156] Portion A1 (comparative): n-butanol was added at 95 C. until a viscosity of 6000 mPas was achieved. The free formaldehyde content was 0.30% by weight. Portion A2: n-butyl acetate was added at 95 C. until a viscosity of 6000 mPas was achieved. The concentration of free formaldehyde was 0.21% by weight.

[0157] Portion B was heated to 80 C. under reduced pressure of 100 mbar. Subsequently, 10 mL of water were slowly added while maintaining the reduced pressure. The temperature decreased. Subsequently, water was distilled off and the temperature thereby was raised to 80 C. This procedure was twice repeated. Then, portion B was divided into two equal portions B1 and B2.

[0158] Portion B1: n-butanol was added at 95 C. until a viscosity of 6000 mPas was achieved. The free formaldehyde content was 0.18% by weight.

[0159] Portion B2: n-butyl acetate was added at 95 C. until a viscosity of 6000 mPas was achieved. The free formaldehyde content was 0.07% by weight.

Example 2

[0160] A reactor was charged with 300 g of a 40% by weight aqueous solution of formaldehyde (corresponding to 4.00 mol of formaldehyde). Subsequently, a pH value of 8.3 was adjusted using 0.23 mL of 25% aqueous sodium hydroxide solution. Then, 126 g of melamine (1.00 mol) were metered in. The resulting mixture was heated to 90 C., the temperature was maintained for 5 minutes and then the temperature was reduced to 75 C. 522 g of methanol (16.3 mol) were added followed by the addition of 5.1 mL of 30% nitric acid to adjust a pH value of 4.9. The batch was kept at 50 C. for 45 minutes. Then, the pH value was adjusted to 8.1 using 3.6 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled under reduced pressure of 150 mbar at a maximum temperature of 70 C. The resulting concentrated composition was divided into two equal portions A and B.

[0161] Portion A (comparative): Water was added at 65 C. until a viscosity of 1000 mPas was achieved. The free formaldehyde content was 0.40% by weight.

[0162] Portion B was heated to 80 C. under a reduced pressure of 100 mbar. Subsequently, 10 mL of water were slowly added under reduced pressure. The temperature decreased. Subsequently, water was distilled off and the temperature thereby was raised to 80 C. This procedure was twice repeated. Water was added at 65 C. until a viscosity of 1000 mPas was achieved. The free formaldehyde content was 0.26% by weight.

Example 3

[0163] A reactor was charged with 675 g of a 40% by weight aqueous formaldehyde solution (corresponding to 9.00 mol of formaldehyde). Subsequently, a pH value of 9.1 was adjusted using 0.9 mL of 25% aqueous sodium hydroxide solution. Then, 126 g of melamine (1.00 mol) were metered in. The mixture was heated at 70 C., held at that temperature for 20 minutes and then 480 g of methanol (15.0 mol) were metered in. 5.0 mL of 30% nitric acid were metered in to adjust a pH value of 3.8. The batch was held at 50 C. and become clear. 10 minutes after reaching the clear point, the pH value was adjusted to 9.1 using 4.0 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled at a maximum temperature of 91 C. The temperature was slightly reduced, and the reaction mixture was distilled until the residue had a viscosity of 3500 mPas. The temperature was reduced to 65 C. Further 480 g of methanol (15.0 mol) were metered in. 5.0 mL of 30% nitric acid were metered in to adjust a pH value of 3.8. The batch was held at 60 C. for 30 minutes under stirring. Then, a pH value of 8.1 was adjusted using 3.6 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled at a maximum temperature of 90 C. Temperature was slightly reduced and then the reaction mixture was distilled under a reduced pressure of 100 mbar at 100 C. The batch was divided into two equal parts, part A and part B.

[0164] Part A was also divided into two equal parts, part Al and part A2.

[0165] Part A1: isopropanol was added at 95 C. until a viscosity of 9000 mPas was achieved. The free formaldehyde content was 0.11% by weight.

[0166] Part A2: n-butyl acetate was added at 95 C. until a viscosity of 9000 mPas was achieved. The free formaldehyde content was 0.04% by weight.

[0167] Part B was heated at 100 C. under a reduced pressure of 100 mbar. Subsequently, 10 mL of water were slowly added under reduced pressure. The temperature fell. Subsequently, water was distilled off and the temperature thereby was raised to 100 C. This procedure was twice repeated. Then, part B was divided into two equal parts, part B1 and part B2.

[0168] Part B1: isopropanol was added at 95 C. until a viscosity of 9000 mPas was achieved. The free formaldehyde content was less than 0.03% by weight. Part B2: n-butyl acetate was added at 95 C. until a viscosity of 9000 mPas was achieved. The free formaldehyde content was less than 0.03% by weight.

Example 4

[0169] A reactor was charged with 390 g of a 40 percent by weight aqueous formaldehyde solution (corresponding to 5.20 mol of formaldehyde). Subsequently, the pH was adjusted to pH 6.9 using 0.3 mL of triethanolamine (purity >98%). Then, 126 g of melamine (1.00 mol) were metered in. The resulting mixture was kept at reduced pressure of 100 mbar and then heated to 60 C., the distillate being separated off. Then 384 g of methanol (12.0 mol) were added followed by the addition of 1.7 mL of 30% nitric acid to adjust the pH to pH 4.8. The resulting mixture was held at 50 C. for 60 min with stirring and became clear. The pH was adjusted to pH 8.5 using 1.8 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled at a maximum temperature of 90 C. The temperature was slightly reduced and distillation was continued at 70 C. under reduced pressure (100 mbar). The temperature was reduced to 65 C. Further 224 g of methanol (7.00 mol) were added followed by the addition of 2.6 mL of 30% nitric acid to adjust the pH value to pH 4.2. The resulting mixture was kept at 50 C. for 30 minutes with stirring. Then, a pH value of 8.5 was adjusted using 2.2 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled at a maximum temperature of 95 C. Temperature was slightly reduced and then distillation was continued under reduced pressure of 150 mbar at 100 C. The obtained concentrated composition was divided into two equal portions A and B.

[0170] Portion A was divided into three equal portions A0, A1 and portions A2.

[0171] Portion A0 (comparative): n-butanol was added at 95 C. until a viscosity of 4000 mPas was achieved. The free formaldehyde content was 0.75% by weight.

[0172] Portion A1: isobutanol was added at 95 C. until a viscosity of 4000 mPas was achieved. The free formaldehyde content was 0.60% by weight.

[0173] Portion A2: n-butyl acetate was added at 95 C. until a viscosity of 4000 mPas was achieved. The free formaldehyde content was 0.22% by weight.

[0174] Portion B was heated to 85 C. under a reduced pressure of 150 mbar. Subsequently, 10 mL of water were slowly added under reduced pressure. The temperature decreased. Subsequently, water was distilled off and the temperature thereby was raised to 85 C. This procedure was twice repeated. Then, portion B was divided into two equal portions B1 and B2.

[0175] Portion B1: isopropanol was added at 95 C. until a viscosity of 4000 mPas was achieved. The free formaldehyde content was 0.14% by weight.

[0176] Portion B2: n-butyl acetate was added at 95 C. until a viscosity of 4000 mPas was achieved. The free formaldehyde content was 0.10% by weight.

Example 5

[0177] A reactor was charged with 390 g of a 40 percent by weight aqueous formaldehyde solution (corresponding to 5.20 mol of formaldehyde). Subsequently, the pH was adjusted to pH 6.7 using 0.32 mL of triethanolamine (purity >98%). Then, 126 g of melamine (1.00 mol) were metered in. The resulting mixture was kept at reduced pressure of 150 mbar and then heated to 45 C., the distillate being separated off. Then the mixture was heated to 55 C. at reduced pressure and distillation was continued until no further distillate was observed. Then, 144 g of methanol (4.5 mol) and 614 g of n-butanol (8.3 mol) were added followed by the addition of 2.7 mL of 30% nitric acid to adjust the pH to pH 4.5. The resulting mixture was held at 70 C. for 60 min with stirring and became clear. The pH was adjusted to pH 8.1 using 3.0 mL of 25% aqueous sodium hydroxide solution. The reaction mixture was distilled at a maximum temperature of 115 C. The temperature was slightly reduced and distillation was continued at 90 C. under reduced pressure (150 mbar). Subsequently, 15 ml of water were slowly added under reduced pressure (150 mbar). Thereby the temperature decreased. Then the water was distilled off at 80 C. and 150 C. Thereafter, further 15 ml of water were slowly added under reduced pressure (150 mbar) and subsequently distilled of at 80 C. and 150 C. The addition of water and distillative removal of water was repeated again. The obtained concentrated composition was divided into two equal portions A and B.

[0178] Portion A: n-butanol was added at 80 C. until a viscosity of 7000 mPas was achieved. The free formaldehyde content was 0.31% by weight.

[0179] Portion B: n-butyl acetate was added at 80 C. until a viscosity of 7000 mPas was achieved. The free formaldehyde content was 0.08% by weight.