JPH0244323B2 - MERAMINNNYOSOJUSHINOSEIZOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a melamine-urea resin for impregnated paper that releases less formalin. Impregnated paper is paper printed with woodgrain patterns or other patterns, impregnated with various resins and dried, and used as a decorative surface board for particle boards, flash boards, wood boards, etc. Melamine resins, melamine-urea resins (hereinafter simply referred to as MU resins), and urea resins are known as the above-mentioned resins, but these resins have good physical properties such as heat resistance and chemical resistance on the decorative board surface. Therefore, MU resin has been widely used. Traditionally, the manufacturing method for MU resin has been to use 0.3 to 10.0 moles of urea per 1 mole of raw material melamine.
A method has been adopted in which MU resin is produced by mixing raw materials ranging from 1.95 to 22.00 moles of formaldehyde at once, adding an alkaline substance such as sodium hydroxide, potassium hydroxide, etc., and carrying out thermal condensation. However, the resin produced by this method had a high content of released formaldehyde, and the quality of the decorative laminate obtained was somewhat lacking. The present inventors have completed the present invention by discovering that a high-quality MU resin free from the above-mentioned drawbacks can be obtained by employing a specific method. That is, the present invention makes the mixture alkaline by adding 2-dimethyl or 2-diethylaminoethanol to a mixture of 1.0 mole of melamine, 4.0 to 4.5 moles of urea, and 5.5 to 7.5 moles of formaldehyde, and
The gist of the present invention is a method for producing a melamine-urea resin, which is characterized in that the mixture is co-condensed by maintaining the mixture at reflux. The present invention will be further explained in detail. In the present invention, melamine, urea, and formaldehyde are mixed in a ratio of 1 mole of melamine (hereinafter referred to as M), 4.0 to 4.5 moles of urea (hereinafter referred to as U), and 5.5 to 7.5 moles of formaldehyde (hereinafter referred to as F). and 2-dimethylaminoethanol or 2-dimethylaminoethanol or 2-dimethylaminoethanol
- Add diethylaminoethanol to a mixed aqueous solution of M, U, and F, adjust the pH to 10.0 to 9.0, and then add M and U.
and F are co-condensed at a temperature of 75° C. to reflux. In this operation, first, the pH of formalin, which is an aqueous solution of F, is adjusted to 10.0 to 9.0 with 2-dimethylaminoethanol or 2-diethylaminoethanol, and M is added with stirring, and the temperature is raised to reflux temperature. After that, U is added, but if U is added all at once, the temperature of the reaction solution will drop to below 70°C due to endothermic dissolution of U, and the dissolved methylolmelamine will precipitate out, so U is added in two portions under reflux. Thereafter, the reaction was continued at 80°C, but as the cocondensation progressed, the pH of the reaction solution gradually decreased.
Add 2-dimethylaminoethanol or 2-diethylaminoethanol until the pH of the reaction solution is 7.5.
Keep it from falling further. As the reaction progresses, the reaction solution begins to show a cloudy point of 5 to 20℃, and as the reaction continues, the aqueous solution becomes
The solution will show a cloudiness value of 1.5 to 1.0 times, at which point the solution is cooled. The clouding point in the present invention refers to the temperature at which water becomes cloudy when one drop of a reactant is dropped into a large amount of water. In addition, the cloudiness value is the volume ratio of the reactant to water at which cloudiness occurs when the mixture obtained by adding water to 1 volume part of the reactant is heated to 20°C. The pH of the MU resin solution produced in this way is about 7.5, so the pH of the MU resin solution for impregnated paper is adjusted to 9.5 to 9.0, which has the best storage stability. - diethylaminoethanol, as well as the usual alkaline compounds,
For example, adjust with sodium carbonate, triethylamine, etc. The MU resin solution obtained by the production method of the present invention contains 4.0 to 4.5 mol of U and 5.5 mol of F per 1 mol of M.
The composition has a proportion of ~7.5 moles. Analysis of the free formaldehyde content of this MU resin solution revealed that
It was 0.1-0.3% by weight. The amount of formaldehyde released from the decorative board made from paper impregnated with this MU resin solution is the same as the amount of formaldehyde released from wood boards, and does not increase further. When the number of moles of F is more than 7.5 moles, the obtained
The content of free formaldehyde in MU resin is
A decorative laminate using MU resin with such a high free formaldehyde content of 0.8% by weight or more has a release amount of formaldehyde of 2 mg/ml compared to a decorative laminate using MU resin obtained by the present invention.
or more. Also, if the number of moles of F is less than 5.5 moles, M
The quality of the decorative board produced from the resulting resin was lower than that obtained by the present invention.
This is lower than that of decorative boards using MU resin. Next, in the present invention, 2-dimethylaminoethanol or 2-diethylaminoethanol is used as a catalyst, but other alkaline catalysts such as sodium hydroxide, potassium hydroxide,
When using sodium carbonate, triethylamine, triethanolamine, guanidine carbonate, etc.
The co-condensation reaction time is within about 30 minutes. For that reason,
The free formaldehyde content in the MU resin solution is 3 to 5% by weight, and compounds with extremely small and large molecular weights are unevenly contained, making the resin so poor in storage stability that it becomes cloudy within a few hours after the completion of the reaction. A solution was obtained. On the other hand, when 2-dimethylaminoethanol or 2-diethylaminoethanol of the present invention is used, the reaction time is as long as about 100 minutes, the free formaldehyde content is 0.1-0.3% by weight, and the MU resin is large. part becomes a methylolated cocondensate, and the storage stability of the resin solution is at a temperature of 15 to
A MU resin solution that lasted for a long time at 25°C for 15-20 days was obtained. The storage stability period referred to here is the period in which the resin solution does not lose its transparency, does not become cloudy, and the viscosity of the resin solution does not increase by more than about 0.2 times the viscosity of the solution immediately after production. It means the period of time. That is, in the present invention, when a weakly alkaline 2-dimethylaminoethanol or 2-diethylaminoethanol catalyst is used in a reaction system in which the number of moles of U is larger than the number of moles of M and the amount of F is small, a uniform molecular weight distribution range can be obtained. This suggests that M, U and F are preferably co-condensed. Next, as the raw materials M and U used in the present invention, it is not necessary to particularly use purified products, and industrial standard products are sufficient. Furthermore, commercially available 37 to 50% by weight formalin can be used as F, and it is not necessary to specifically remove methanol and formic acid contained in formalin. Furthermore, water and methanol are distilled off from the MU resin solution obtained according to the present invention to a nonvolatile content of 50 to 60% by weight and a viscosity of about 40 to 50 CP/20° C., which can be easily used in the production of impregnated paper. Note that known modifiers such as ethylene glycol, ε
- caprolactam, toluenesulfonamide,
By adding thiourea, dicyandiamide, sugar, sodium sulfamate, water-soluble nylon, etc., the gloss, thermal stability, denseness, elasticity, etc. of the decorative board surface can be further improved and the quality can be enhanced. In addition, in the case of the present invention, since the number of moles of F is low relative to M and U, the amount of the modifier added is preferably in the range of 1 to 5% by weight based on the total amount of M, U, and F. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples. In addition, % in the examples is weight %.
shows. Example 1 A reactor was charged with 1520 g (18.7 mol) of 37% formalin, and 6.5 ml of 2-dimethylaminoethanol (first class reagent) was added to adjust the pH to 10.0. To this was added 400 g (3.2 mol) of melamine with stirring, and the temperature was raised to reflux temperature (96°C). 5 minutes after the start of reflux and 10
After a few minutes, 400 g (6.7 mol) of urea was added to each, and the temperature was then lowered to 80°C, and the same temperature was maintained to allow formaldehyde, melamine, and urea to react. 75 minutes after the start of reflux, the reaction solution showed a cloudy point of 15°C.
After 110 minutes, the cloudiness value reached 1.2 times, so the reaction solution was rapidly cooled while part of methanol and water was distilled off under reduced pressure. Since the pH of this resin solution was 7.5, 4 ml of a 25% aqueous sodium carbonate solution was added to adjust the pH to 9.5. The resulting resin solution had a viscosity of 40.5CP/20°C and a nonvolatile content of 55.5%. Example 2 Melamine, urea, and formaldehyde were reacted in the same manner as in Example 1. However, 40 g of ethylene glycol and 30 g of ε-caprolactam are used as modifiers.
was added before the reaction. The resulting resin solution has a viscosity of
The temperature was 45.0CP/20°C, and the nonvolatile content was 56.3%. Example 3 A reactor was charged with 1800 g (22.2 mol) of 30% formalin, and the pH was adjusted to 95 by adding 7.5 ml of 2-diethylaminoethanol (first grade reagent). To this was added 375 g (3.0 mol) of melamine with stirring, and the temperature was raised to reflux temperature. 400 g (6.7 mol) of urea was added 5 minutes and 10 minutes after the start of reflux, and the temperature was then lowered to 80° C., and the reaction was carried out while maintaining the same temperature. 2-
1.5 ml of diethylaminoethanol was added and the reaction was continued. 100 minutes after the start of reflux, the cloudiness value reached 1.3 times, so the reaction solution was rapidly cooled while methanol and part of the water were distilled off under reduced pressure. Since the pH of this resin solution was 7.7, 2 ml of triethylamine was added to adjust the pH to 9.0. The resulting resin solution had a viscosity of 48.0CP/20°C and a nonvolatile content of 60.2%. Comparative Example 1 (In the case of a large amount of F in the present invention) 1950 g (24.1 mol) of 37% formalin was charged into a reactor, and 8.2 ml of 2-dimethylaminoethanol was added to adjust the pH to 9.8. Melamine 375 under stirring
g (3.0 mol) was added thereto, and the temperature was raised to reflux temperature. 375g each after 5 minutes and 10 minutes from the start of reflux.
(6.3 mol) of urea was added, and the temperature was then lowered to 80°C.
The reaction was carried out while maintaining the same temperature. 55 minutes after the start of reflux, a white cloudiness point of 5°C was exhibited, and after 100 minutes, the white cloudiness value reached 1.2 times, so the mixture was rapidly cooled while distilling off part of methanol and water under reduced pressure. Since the pH of this resin solution was 7.5, 4 ml of a 25% aqueous sodium carbonate solution was added to adjust the pH to 9.4.
The viscosity of the obtained resin solution was 42CP/20℃,
The non-volatile content was 54.5%. Comparative Example 2 (In the case of a catalyst other than the present invention) 1520 g (18.7 mol) of 37% formalin was charged into a reactor, and 1.2 g of a 30% aqueous sodium hydroxide solution was added.
ml was added to adjust the pH to 9.5. To this was added 400 g (3.2 mol) of melamine with stirring, and the temperature was raised to reflux temperature. 5 minutes and 10 minutes after the start of reflux, respectively.
After adding 400 g (6.7 mol) of urea, the temperature was lowered to 80° C., and the reaction was carried out while maintaining the same temperature. 20 minutes after the start of reflux, it shows a cloudy point of 20℃, and after 30 minutes, it shows a cloudy value.
When the volume reached 10 times, it was rapidly cooled while distilling off part of the methanol and water under reduced pressure. Since the pH of this resin solution was 7.0, 4.5 ml of a 25% aqueous sodium carbonate solution was added to adjust the pH to 9.0. The resulting resin solution had a viscosity of 23.0CP/20°C and a nonvolatile content of 52.0%. Reference Example 1 (Conventional method) A reactor was charged with 1490 g (18.4 mol) of 37% formalin and 56 g of methanol, and 4.0 ml of a 30% aqueous sodium hydroxide solution was added to adjust the pH to 11.0.
Add to this 504 g (4 mol) of melamine and 240 urea while stirring.
g (4 mol) was added thereto, and the temperature was raised to 85°C. The reaction was carried out while maintaining the same temperature. After 2 hours and 15 minutes from 85°C, it showed a white cloudiness point of 20°C, and after 2 hours and 40 minutes, the white cloudiness value reached 2.5 times, so methanol and water were distilled off under reduced pressure, and the mixture was rapidly cooled. Since the pH of this resin solution was 7.8, 4 ml of a 25% aqueous sodium carbonate solution was added to adjust the pH to 9.2.
The viscosity of the obtained resin solution was 35.0CP/20℃,
The non-volatile content was 50.5%. The storage stability test, free formaldehyde content analysis, release formaldehyde test by producing decorative laminates, and decorative surface quality test of the MU resins obtained in Examples 1 to 3, Comparative Examples 1 to 2, and Reference Example 1 are as follows. The results are shown in Table 1. (1) Storage stability test The resin was stored at room temperature of 15 to 25°C, and the number of days until it became cloudy or the viscosity increased by 1.2 times was measured. (2) Free formaldehyde content analysis Analyzed by the ammonium chloride method of JIS K-6801. (3) Manufacturing method of decorative board 1 kg of resin is mixed with 15 to 25 g of a 25% by weight aqueous paratoluenesulfonic acid solution as a hardening agent, 0.1 g of sodium stearate (first class reagent) as a mold release agent, and polyoxyethylene nonylphenol ether as a penetrating agent. Aru Nonipole 95 (product name, manufactured by Sanyo Chemical)
2 g was added and mixed with stirring to obtain an impregnated resin solution.
This resin solution was coated with titanium white at 80g/ ^m2.
impregnated into α-cellulose white base paper and heated to a temperature of 125
The impregnated paper was obtained by drying at ℃. The impregnated paper weighed 200 g/m ² and had a volatile content of 5-6%. The volatile content is the weight loss when the impregnated paper is re-dried at 160°C for 5 minutes. This impregnated paper was incorporated into the front and back surfaces of a particle board base plate with a thickness of 15 mm, and a hot press using an aluminum plate with a pear-polished finish containing asbestos cushion as a caul plate was used at 160°C, 20 kg/cm ² for 3 minutes. A decorative board was manufactured by hot pressing. Return cooling press after hot pressing was not performed. (4) Measurement of released formaldehyde The amount of released formaldehyde was measured by the acetylacetone method of JIS A5908. The particle board base plate is manufactured using urea resin as an adhesive. (5) Quality test of decorative surface a. Appearance: The condition and gloss of the decorative surface were judged with the naked eye. b Acid resistance: The degree of action of 0.2N hydrochloric acid on the decorative surface over 24 hours was determined. c. Heat resistance: Judgment was made as to whether or not cracks occurred when heated at 70°C for 20 hours according to DIN53799. d Water resistance: Determined by water vapor test according to DIN53799. e Stainability: After applying black shoe polish, the degree of sealing was determined by wiping. The ratings a-e are on a scale of 1-6, with 1 being extremely good and 6 being completely bad.

【table】

Table 1 shows that the MU resin according to the present invention did not increase the amount of formaldehyde released from the particle board base plate. Also, as in the present invention, the U content is higher than the M content.
Surface quality evaluation of decorative board manufactured with MU resin is as follows:
Generally, scale 3 or less is considered suitable for coating the front and back surfaces, and it was confirmed that the quality of the decorative board obtained by the present invention satisfies this requirement. Furthermore, the storage stability of the MU resin solution is 15 days or more, and there is no problem in industrial implementation.

Claims (1)

[Claims] 1. 2- to a mixture of 1.0 mol of melamine, 4.0-4.5 mol of urea and 5.5-7.5 mol of formaldehyde
making the mixture alkaline by adding dimethyl or 2-diethylaminoethanol;
A method for producing a melamine-urea resin, which comprises cocondensing the mixture by maintaining the mixture at 75°C or higher under reflux.