CS257363B1 - Process for producing urea-formaldehyde condensates with specific properties - Google Patents

Abstract

The invention relates to a method for producing urea-formaldehyde condensates with specific properties suitable as adhesives in the woodworking and furniture industries, which are prepared by adding urea and formaldehyde in a molar ratio U:F 1:1.6 to 1:2.2 at a pH of 3.5 to 8, preferably 6.5. This precondensate is further continuously processed at a temperature of 102 to 150 °C, a pressure of 0.002 to 0.5 MPa and in the second stage it is further condensed under vacuum, at a temperature of 40 to 80 °C with continuous addition of an aqueous urea solution with the addition of 0.01 to 5% calcium salt of an organic acid. The amount of urea in the second stage corresponds to the adjustment of the final molar ratio U:F 1:1.5 to 1:1.86.

Description

257363

SUMMARY OF THE INVENTION The present invention provides a method for producing urea-maldehyde condensates with specific additive-containing properties to be used as a glue in the wood and furniture industry for veneering and as an assembly adhesive having good cold adhesive properties while reducing it. ] reactivity after addition of hardener, while the effect of the additive also increases in strength.

According to the prior art processes protected by AO 209 101, urea-formaldehyde condensates suitable as adhesives are produced in the timber and furniture industry of the urea aqueous solution and formaldehyde-step polycondensation, wherein in the first stage at 102 to 150 ° C, pressures of 0.002 to 0.5 MPa in flow rate a continuous apparatus having a base molar ratio of urea feedstock to formaldehyde of 1: 1.5 to 1: 2.2, preferably 1: 1.95 in the presence of 0.001 to 0.495% by weight, preferably 0.005% by weight; . the organic or inorganic acid, preferably formic acid, is condensed. In a second stage, it is further condensed at a pressure of 2 to 20 kPa at a temperature of 30 to 90 ° C with the continuous addition of an aqueous urea solution at a concentration of 20 to 80% by weight, preferably 50% by weight. in an amount such that the resulting molar ratio of urea to formaldehyde is 1: 1.3 to 1: 1.85 and a continuous dosage of alkali metal or alkaline earth metal hydroxide solution. Other processes for the preparation of similar types of UF condensates (NSR Patent 2 287 921.2 444 856) protect the preparation processes in a very acidic environment (pH marked below 5), or NSR Pat. 2109 754 is operated continuously in stirred cascade reactors in the presence of amino acids admixing a pH of 4.2 to 8.0 under normal pressure. From the economic point of view, if the UF condensate is also a formaldehyde producer, UF condensates of formaldehyde with a low stabilizing methanol content are produced according to AO 226 922 (significant methanol savings), but the high reactivity of UF capacitors is achieved.

However, for practical use, it is important that the resulting resin, which is used as a binder in wood and furniture industry, has little ability to change - the regulation of reactivity (mainly reduction) after the addition of a solid. This requirement was created by extending the range of adhesives for small retailers in the whole of Czechoslovakia.

SUMMARY OF THE INVENTION The subject of the present invention is a process for the continuous production of urea-formaldehyde resins at a temperature of 102 to 150 ° C and pressures of 0.002 to 0.5 MPa in a continuous continuous plant, wherein the basic molar ratio of the feedstock of urea and formaldehyde is 1: 1.6 to 1: 2.2 preferably 1: 1.95. The urea-formaldehyde preconcentrate is prepared in advance with a formaldehyde apparatus, the pH of which is adjusted by the addition of alkali metal hydroxide, alkaline earth hydroxide, or sodium boronic acid, or preferably the sodium tetraborate to pH 3.5. and 8.0, preferably 4.5, and solid urea. This precondensation is fed to a pressure reactor, where the first stage of condensation takes place. In the second reaction step, further addition of the added aqueous urea solution is carried out, which contains 0.01 to 5% of the calcium salt of the organic acid, with the exception of calcium formate. The actual condensation takes place at a pressure of 2 to 20 kPa and a temperature of 30 to 80 ° C, a pH of 7 to 9, preferably 8.2. The components are fed continuously to the second stage, the pH being adjusted by the addition of alkali metal hydroxides, or alkaline earth, or sodium boronic acid, or derivatives thereof, preferably with sodium tetraborate. The total amount of urea is such that the resulting molar ratio of urea to formaldehyde is 1: 5 to 1: 1.85.

According to the invention, a simple technology provides a resin having a viscosity of 400 to 1800 mPa. s, which is suitable as a lighter for woodworking and furniture industry, which, according to the content of the retardant-calcium salt of an organic acid, has the ability to change the reactivity after addition of an amide such as ammonium chloride.

The adhesive of Example 1 can be used as a mounting adhesive (cold) or as a veneer adhesive in the furniture industry. Example 1

15 m3 of 37.1% by weight aqueous formaldehyde solution are metered into a container equipped with a stirrer for cooling, 20% of a 110% by weight aqueous tetraborate solution is added to adjust the pH, which is adjusted between 3.5 and 7 and treated with 12%. 500 kg of solid urea. After dissolving the urea-formaldehyde pre-condensate (1: 1.95 molar ratio), it is fed at a rate of 8 to 12 m 3 / h to the first reaction stage, where it is condensed at 125 ° C and 0.3 MPa pressure. reaction. The first stage product having a viscosity of 35 to 100 mPa. It is continuously withdrawn into a second reaction stage where a second stage of condensation takes place by the addition of 1.3 to 1.6 m3 / h50% urea solution containing 1.5% by weight. calcium formate and continuously adding a 10% aqueous solution of sodium tetraborate to a pH between 7.0 and 9.0 at 60 ° C and a pressure of 10.2 kPa,

The product from the second reaction stage is continuously withdrawn, cooled. It contains about 67 wt. UF resin, its viscosity is

Claims (1)

257363 5,900 mPa. s, free forxnaldehyde content 2.5% by weight, reactivity 100 min / 20 ° C with ammonium chloride as a hardener. The strength of the glued spoil on the beech plywood after the IF-20 test is 2.1 MPa. SUBSTANCE A method for producing urea-formaldehyde condensates with specific properties, characterized in that urea and formaldehyde are first introduced in the urea / formaldehyde molar ratio of 1: 1.6 to 1: 2.2 in a separate stirred and vaporized mixture at pH. 3.5 to 8, preferably 6.5, which are treated by the addition of alkali metal hydroxide, alkaline earth hydroxide, or sodium boronic acid salt, or preferably tetraborate sodium derivatives, are injected into a flow reactor, where at -10 to 150 ° C, at a pressure of 0.002 to 0.5 MPa, the polycondensation reaction will occur, and in the second step, it will be further condensed at a pressure of 2 to 20 kPa, at a temperature of 40 to 80 ° C with the continuous addition of an aqueous solution of urea of 30%. % to 80% by weight, which contains 0.01 to 5%, preferably 1.5%, by weight; calcium organic acid, preferably calcium formate, in such an amount that the resulting molar ratio of urea and formaldehyde is 1: 1.5 to 1: 1.85, wherein the alkali metal or alkaline earth hydroxide is continuously metered in and / or the sodium salt of boric acid, or derivatives thereof, to a pH of 6.5 to 9.0 preferably 8.2.